BRPI0711054A2 - methods for analyzing an underground formation traversed by a wellbore and for producing a mineral hydrocarbon fluid from a geological formation, and, computer readable medium - Google Patents

Abstract

METHODS TO ANALYZE AN UNDERGROUND FORMATION THROUGH A WELL HOLE AND TO PRODUCE A MINERAL HYDROCARBON FLUID FROM A GEOLOGICAL FORMATION, AND, LEGIBLE MEDIUM BY COMPUTER Method to analyze an underground formation crossed by a well hole. The method uses a tool comprising a transmitting antenna and a receiving antenna, the underground formation comprising one or more layers of formation. The tool is suspended inside the well hole, and one or more electromagnetic fields are induced in the formation. One or more time-dependent transient response signals are detected and analyzed. Electromagnetic anisotropy of at least one of the formation layers is detectable. Geodirection indications can be derived from the time-dependent transient response signals, for continued drilling of the well until a hydrocarbon reservoir is reached. The hydrocarbon can then be produced.

Description

"METHODS FOR ANALYZING UNDERGROUND TRAINING THROUGH A WELL HOLE AND TO PRODUCE A MINERAL IROCHRON FLUID FROM A GEOLOGICAL TRAINING, AND COMPUTER READY MEANS"

Technical field

In one aspect, the present invention relates to a method for analyzing an underground formation traversed by a wellbore. In another aspect, the invention relates to a method for producing a mineral hydrocarbon fluid of a geological formation. In another aspect, the invention relates to a computer readable medium that stores computer readable instructions that analyze one or more electromagnetic response signals.

Fundamentals of the invention

In 'Record During Drilling' (LWD) geodirectional applications, it is advantageous to detect the presence of a deformation anomaly in front of or around a drill bit or bottom set. There are many cases where the ability to "anticipate" is desired in LWD logging environments. Some examples of anticipation include predicting a forward overpressurized zone, or detecting a failure ahead of the horizontal well drilling drill, or profiling a compact AL structure ahead of the drill drill.

In US Patent 5,955,884 to Payton et al., A tool and method for transient electromagnetic recording are disclosed, electrical and electromagnetic transmitters are used to apply electromagnetic energy to a formation at frequencies and selected waveforms that maximize the radial depth of penetration into the target formation. . In this transient EM method, the current applied to an anti-transmitter is usually terminated and a time change in voltage induced at a receiving antenna is monitored over time. When logging measurements are used for deposition detection, detection or anomaly identification, be critical. Such anomalies may include, for example, a fault, a diverted reservoir, a salt dome, or an adjacent layer or oil-water contact.

Published US patent applications US 2005 / 92,487,2205 / 93,546, 2006 / 38,571 describe methods for locating these anomalies in an underground geological formation employing transient electromagnetic (EM) reading. The methods particularly enable finding the direction and distance for a resistive or conductive anomaly in a formation by circling a wellbore, or in front of the wellbore, in drilling applications.

Among the above-mentioned patent application publications, US2006 / 38.571 shows that transient electromagnetic responses can be analyzed to determine conductivity values of a homogeneous (single layer) geological formation of two or three or more ground layers, as well as tool distances to the interfaces between ground layers.

In principle, the methodology as set forth in US2006 / 38.571 would work for any number of layers. However, the greater the number of layers, and particularly when the layers are thin, the more complicated the analysis. For example, a finely laminated sandstone / shale sequence would be difficult to analyze using the methodology set forth in US 2006 / 38.571.

According to one embodiment of the invention, there is provided method for analyzing an underground formation through a wellbore using a tool comprising a transmitting antenna and a receiving antenna, the underground forming comprising one or more forming layers and the method comprising: Suspending the tool inside the wellbore;

Induce one or more electromagnetic fields in the formation;

Detecting one or more time dependent transient response signals;

Analyze the one or more time-dependent transient response signals by considering the electromagnetic anisotropy of at least one of the formation layers.

The electromagnetic properties of a forming layer comprising a number of thin layers may be approximated by a forming layer comprising an electromagnetic anisotropy. This avoids taking into account each thin layer individually when reversing the responses.

Among other advantages of taking into account electromagnetic anisotropy, there is the fact that anisotropy information is useful in the precise location of reservoirs containing mineral hydrocarbon fluid, since such reservoirs are often associated with electromagnetic anisotropy of formation layers.

Said method for analyzing an underground formation may be used in a geodirectional application where a geo-directional indication may be derived from one or more time-dependent transient signals taking into account the electromagnetic anisotropy, and where a drilling operation may be continued in accordance with the indication of geodirectional derivation to precisely position a well.

In another aspect, a method is provided for producing a mineral hydrocarbon fluid of a geological formation, the method comprising the steps of:

suspending a drill string in the geological formation, the drill string comprising at least one drill bit and measuring junction comprising a transmitting antenna and an antenareceptor;

drill a well in geological formation, induce an electromagnetic field in geological formation using the transmitting antenna;

detecting a transient electromagnetic response signal from the electromagnetic field employing the receiving antenna;

derive a geodirectional indication from the electromagnetic response;

continue to drill the well according to the direction indication until a reservoir containing the hydrocarbon fluid is reached;

produce the hydrocarbon fluid.

In yet another aspect, the invention provides a computer readable medium by storing readable instructions analyzing one or more transient electromagnetic response signals that have been detected by a suspended tool inside a well bore through an underground formation after induction of one or more electromagnetic fields in the where computer readable instructions take into account the electromagnetic anisotropy of at least one layer of formation in the underground formation.

Brief Description of the Drawings

The present invention is described in more detail below by way of examples and with reference to the accompanying figures, in which:

fig. 1A is a block diagram showing an implementation system of embodiments of the invention;

Fig. 1B schematically illustrates an alternative system implementing embodiments of the invention;

fig. 2 is a flow chart illustrating a method according to a common embodiment of the invention;

fig. 3 is a graph illustrating intercoordinated directional angles of tool and anomaly;

fig. 4A is a graph showing a resistivity anomaly in a tool coordinate system;

fig. 4B is a graph showing a resistivity anomaly in an anomaly coordinate system;

fig. 5 is a graph illustrating a tool rotation within a wellbore;

fig. 6 schematically shows directional components developing electromagnetic induction tools with respect to an electromagnetic induction array;

Fig. 7 is a graph showing the voltage response of coaxial Vzz (t), coplanar Vxx (t), and cross-component Vzx (t) measurements for L = Im, for θ = 30 °, and a distance D = 10m of a layer of salt;

fig. 8 is a graph showing the voltage response of coaxial Vzz (t), coplanar Vxx (t), and cross-component Vzx (t) measurements for L = Im, for θ = 30 °, and a distance D = 100m from a layer of salt;

fig. 9 is a graph showing apparent dive (Oapp (t)) for an arrangement as in fig. 7;

fig. 10 is a graph showing apparent conductivity (aappCt)) calculated from both coaxial (Vzz (t)) and coplanar (Vxx (t)) responses for the same conditions as in fig. 9;

fig. 11 is a graph showing apparent dip 0app (t) for tool set of L = Im when the salt face is and D = 10m for various angles between the tool axis and the target;

fig. 12 is a graph similar to fig. 11, whereby the salt face is at D = 50m from the tool;

fig. 13 is a graph similar to fig. 11, whereby the salt face is s D = 100m from the tool;

fig. 14 is a schematic illustration showing a coaxial tool with its tool axis parallel to a layered interface;

fig. 15 is a graph showing transient voltage response versus t given by the coaxial tool of FIG. 14 in a two layer formation at different distances from the layer;

fig. 16 is a graph showing return response data of FIG. 15 in terms of apparent conductivity (σapp (t));

fig. 17 is similar to fig. 16, except that the resistivities of layers 1 and 2 have been interchanged;

fig. 18 shows a graph of apparent conductivity aapp (t) for the case of D = 1m and L = 1m for various resistivity ratios while the target resistivity is set at R2 = 1m;

fig. 19 shows a comparison of apparent conductivity at higher values of t, σapp (t-> infinity), for coaxial responses where D = 1m and L = 1m as a function of target layer conductivity σ2 while local conductivity O1 is fixed at 1 / S / m ;

fig. 20 graphically shows the same data as in fig. 19 plotted as the target conductivity reaction on the local decayed conductivity σ1 versus the apparent conductivity ratio σapp (t-> infinity) on the local layer conductivity σ1

fig. 21 shows a graph containing apparent conductivity (σapp (t)) versus time for various combinations of D and L;

fig. 22 graphically shows the relationship between the radius path RP and transition time tc;

fig. 23 is a schematic illustration showing a coaxial tool approaching or immediately passing a boundary boundary; 24 is a graph showing transient voltage response as a function of t as given by the coaxial tool of FIG. 23 burning distances D of the layer;

fig. 25 is a graph showing the return response data of FIG. 24 in terms of apparent conductivity (aapp (t));

fig. 26 is similar to fig. 25, except that layer 1 and 2 resistivities were interchanged;

fig. 27 presents a graph comparing the app (t) of fig. 25 efig. 26 relative to D = Im;

fig. 28 shows a linear scaled aapp (t) plot for various transmitter / receiver spacings L in the case of D = 50m;

fig. 29 graphically shows distance to tool front anomaly versus transition time (tc) as determined by the data in fig. 25;

fig. 30 schematically shows a coplanar tool approaching or immediately after a layer boundary;

fig. 31 is a graph showing transient return response data in terms of apparent conductivity (oapp (t)) as a function of t as provided by the coplanar tool of FIG. 30 at different distances D of the layer;

fig. 32 shows a comparison of apparent conductivity (oapp (t-> infinity)) for coplanar responses where D-50m and L = Im as a function of local layer G1 conductivity while target conductivity σ2 is fixed at 1 S / m;

fig. 33 graphically shows the same data as fig. 32 plotted as the target conductivity ratio σ2 over the local decayed conductivity σι versus apparent conductivity ratio (σapp (t-> infinity)) over local layer conductivity

fig. 34 graphically shows distance to tool front anomaly versus transition time (tc) as determined by the data in fig. 31;

fig. 35 schematically shows a model of a coaxial tool in a local conductive layer (1Ωm), a very resistive layer (100Ωm), and another conductive layer (1Ωm);

fig. 36 is a graph showing apparent resistance versus time response Rapp (t), for a geometer given in fig. 35 for various thicknesses Δ of the very resistive layer;

fig. 37 schematically shows a model of a coaxial tool in a local resistive layer (10Ωm), a conductive layer (1Ωm), and another resistive layer (1Ωm);

fig. 38 is a graph similar to fig. 36, showing apparent resistivity versus Rapp (X) time response for a geometry as given in nafig. 37 for various thicknesses Δ of the conductive layer;

fig. 39 schematically shows a model of a coaxial tool in a local conductive layer (1Ωm) in the vicinity of a highly resistive layer (100Ωm) with a separation layer having an intermediate resistance (10Ωm) of varying thickness between them;

fig. 40 is a graph similar to fig. 36, showing apparent resistance versus time response Rapp (t) for a geometry as given in nafig. 37 for various thicknesses Δ of the conductive layer;

fig. 40 is a graph similar to fig. 36, showing apparent resistance versus time response Rapp (t), for a geometry given in fig.39 for various thicknesses Δ of the separating layer;

fig. 41 shows coaxial transient voltage responses for a L = 1m tool in an anisotropic formation where σΗ = 0.1S / m (RH = 1Ωm) for various values of β;

fig. 42 shows apparent conductivity based on the responses

of fig. 41, fig. 43 shows apparent conductivity based on coaxial responses for a L = Im tool in a formation in which σΗ = 0,1S / m for various values of β;

fig. 44 shows apparent conductivity based on coaxial responses for a L = Im tool in a formation in which σΗ = 0.01S / m for various values of β;

fig. 45 shows a graph plotting asymptotic value of recent aapp (t-> infinity) coaxial apparent conductivity of FIG. 44, normalized by σκ, against a variable representing β;

fig. 46 shows apparent dip angle Өapp (t) as a function of time based on the calculated coaxial, coplanar, and cross-decomponent responses of a L = Im tool in a Rh = 10Ωm and Rv / Rh - 9 formation;

fig. 47 shows an electromagnetic induction tool in a forming layer comprising a package of sublayer alternate sets;

fig. 48 shows a graph of apparent resistivity in coaxial and coplanar measurement of the geometer of fig. 47;

fig. 49 schematically shows directional components of an electromagnetic induction tool relative to an anisotropic anomaly;

fig. 50 shows a plot of apparent conductivity app (z; t) at both coordinates ζ and t for various distances D;

fig. 51 shows a plot of apparent conductivity app (z; t) at both coordinates ζ and t;

fig. 52 schematically shows a model of a structure involving a highly resistive layer (100 µm) covered by a conductive local layer (1 µm) that is covered by a resistive layer (10 µm), whereby a coaxial tool is illustrated in the resistive layer;

fig. 53A shows the apparent resistivity in both coordinates z and t, whereby the inflection points are joined using small curved lines;

fig. 53B shows a picture image derived from fig. 53A;

fig. 54A schematically shows a coaxial tool approaching a highly resistive formation at a plunging angle of approximately 30 degrees;

fig. 54B shows the apparent dive response at both z and t coordinates for z-locations corresponding to those shown in fig.54A.

Detailed Description of the Invention

The present invention will now be described with respect to particular embodiments intended to be illustrative and non-restrictive in all respects. Alternative embodiments will become apparent to one skilled in the art to which the present invention belongs without departing from its scope.

It should be understood that certain characteristics and subcombinations are of utility and may be employed without reference to other features and subcombinations specifically presented. This is contemplated and within the scope of the claims.

Embodiments of the invention relate to electromagnetic induction (EM) signal analysis and a system and method for determining the distance and / or direction for an anomaly in a formation from a location within a wellbore. The analysis is sensitive to electromagnetic anomalies, in particular to electromagnetic induction anomalies.

Both frequency domain and time domain excitations were used to excite electromagnetic fields for use in anomaly detection. In frequency domain excitation, a device transmits a continuous wave of a fixed or mixed frequency and measures in the same frequency band. In time domain excitation, a device transmits a square wave signal, pulsed signal or pseudorandom binary sequence as a source and measures the broadband terrestrial response. Sudden changes in transmitter current cause transient signals to appear on a receiver caused by induction currents in the formation. Signals that appear on the receiver are called transient responses because signals on the receiver start from a first value after a sudden change in transmitter current and then decrease (or increase) over time to a new constant level at a second value. The technique disclosed herein implements the time domain excitation technique.

As shown below, embodiments of the invention propose a general method for determining a direction from a measurement joint to a resistive or conductive anomaly using transient EM responses. As will be explained in detail, the direction for the anomaly is specified by a dive angle and an azimuth angle. Embodiment modes of the invention propose to define an apparent dip (Gapp (t)) and an apparent zimuth (cpapp (t)) by combinations of transient multiaxial measurements, for example, bi-axial or triaxial. True direction, in terms of dip angles and azimuth ({θ, φ}), can be determined by analyzing the apparent direction ({cpapp (t), (papp (t)}). For example, the apparent direction ({cpapp (t), φαρρ (Χ)}) approaches the true direction ({θ, φ}) when time t) increases if the anomaly has a large thickness as seen from the tool.

Time-dependent values for apparent conductivity may be obtained from ecoplanar coaxial electromagnetic induction measurements, and may be denoted, respectively, as acoaxia (t) and COpianar (t). Both read the conductivity in the total formation present around the tool. (φapp (t) and (φapp (t) are initially read as zero when an apparent σcoaxial (t) and σcoplanar (t) apparent conductivity of the coaxial and coplanarlêem measurements, both the conductivity of the formation around the next tool. explained below and can also be used to determine the location of an anomaly in a wellbore.

Whenever the term "conductivity" is used in the present description, it has the meaning of encompassing its inverse equivalent "resistivity", and vice versa. The same applies to the terms "apparent conductivity" and "apparent resistivity".

Figs. 1A and 1B illustrate systems that can be used to implement embodiments of the method of the invention. A surface computing unit 10 may be connected to an electromagnetic measurement tool 2 disposed in a wellbore 4.

In fig. 1A, tool 2 is suspended from a cable 12. Cable 12 may be any typically known cable to transmit electrical signals between tool 2 and surface computing unit 10.

In fig. 1B, the tool is comprised of a metering junction 11 and suspended in the wellbore 4 by a drill string 15. Drill post 15 further supports a drill bit 17, and a steering system 15. The steering system may be supported. typically known, including a swivel steering system or a sliding steering system. Wellbore 4 traverses geological formation 5, and it is an objective to precisely direct drill bit 17 to a reservoir containing hydrocarbon fluid 6 to enable the production of hydrocarbon fluid via the wellbore. Such a reservoir 6 may manifest as an electromagnetic anomaly in formation 5.

Referring again to both figs. 1A and 1B, one or more transmitters 16 and one or more receivers 18 may be provided for transmitting and receiving electromagnetic signals for / from formation around the wellbore 4. A data acquisition unit 14 may be provided for transmitting data to / from them. transmitters 16 and receivers 18 for surface computing unit 10.

Each transmitter 16 and / or receiver 18 may comprise a coil wound around a support structure such as a mandrel. The support structure may comprise a nonconductive section to suppress the generation of parasitic believers. The non-conductive section may comprise one or more notches, optionally loaded with a nonconductive material, or may be formed of a nonconductive material, such as a composite plastic. Alternatively, the support structure is coated with a layer of highly magnetically permeable material to form a magnetic shield between the antenna and the support structure.

Each transmitter 16 and each receiver 18 may be bi-axial or even triaxial and thus contain components for sending and receiving signals along each of the three axes. Accordingly, each transmitter module may contain at least one single-axis or multi-axis antenna and may be a triortogonal component transmitter. Each receiver may include at least one single axis or mutiaxial electromagnetic receiver component and may be a tri-orthogonal component receiver.

A tool / wellbore coordinate system is defined as having x, y and z axes. The z axis defines the direction of transmitter T for receiver R. It will be assumed below that the axial direction of wellbore 4 coincides with the z axis, whereby the x and z axes correspond to two orthogonal directions in a plane normal to the direction of transmitter T for receiver R and wellbore 4.

The data acquisition unit 14 may include a controller for controlling the operation of tool 2. The data acquisition unit 14 preferably collects data from each transmitter 16 and receiver 18 and supplies the data to the surface computing unit 10. The unit The data acquisition 14 may comprise an analogue / digital amplifier and / or convert to simplify the responses and / or convert to a digital representation of the responses before transmitting to the surface-computing unit 10 via cable 12 and / or an optional telemetry unit 13.

Surface computing unit 10 may include computer components including a processing unit 30, an operator interface 32, and a tool interface 34. Surface computing unit 10 may also include a memory 40 including data and system transformation assumptions of relevant coordinates 42, an optional direction calculation module 44, an optional apparent directional calculation module 46, and an optional distance calculation module48. Optional direction and apparent direction calculation modules are described in more detail in US Patent Application 2005 / 92.487 and need not be described in more detail unless it is specified that these optional modules may account for forming anisotropy.

Surface computing unit 10 may include computer components including a processing unit 30, an operator interface 32 and a tool interface 34. Surface computing unit 10 may further include a memory 40 including data and system transformation assumptions. Relevant coordinates 42, a direction calculation module 44, an apparent direction calculation module 46, and a distance calculation module 48. The surface decomputing unit 10 may further include a bus 50 which couples various system components including the memory of the system 40 to processing unit 30. Computing system environment 10 is only an example of such a suitable computing environment and is not intended to displace any limitations on the scope of use or functionality of the invention. In addition, although computing system 10 is described as a surface computing unit, it can be optionally located below the surface, embedded in the tool, positioned at a remote location, or positioned at any other convenient location.

Memory 49 preferably stores one or more modules48, 44 and 46 which may be described as program modules containing computer executable instructions executable by surface-computing unit 10. each module may comprise or make use of a computer readable medium which stores computer readable instructions for analyzing one or more detected time-dependent transient electromagnetic response signals that have been detected by a tool suspended inside a wellbore through an underground formation after induction of one or more electromagnetic fields in the formation. Instructions can implement any part of the description below.

For example, program module 44 may contain computer-executable instructions for calculating a direction for an anomaly within a wellbore. Program module 48 may contain computer-executable instructions for calculating a distance to an anomaly or an anomaly thickness. Stored data 42 may include data pertaining to the tool coordinate system and anomaly coordinate system, and other data for use by program modules 44, 46 and 48. Preferably, computer readable instructions account for at least one electromagnetic anisotropy. formation layer in the underground formation.

For additional details on computer system 10, including storage media and input / output devices, please refer to US 2005 / 92,487. Accordingly, further details regarding the internal construction of computer 10 need not be disclosed for the present invention.

Fig. 2 is a flow chart illustrating the procedures involved in a method embodying the invention. Illustrative procedures can begin at S. Generally, in the "Transmit Signals" procedure (A), transmitters 16 transmit electromagnetic signals. In the "Receive Answers" procedure (B), receivers 18 receive transient responses. The procedures can then end in E and / or restart in S.

Procedure C may comprise determining a distance and / or direction for the anomaly may be determined. Procedure C may comprise creating an image of strain characteristics based on transient electromagnetic responses. Electromagnetic anisotropy of at least one of the formation layers may be taken into account.

Figs. 3-6 illustrate the technique of implementing procedure C to determine the distance and / or direction for the anomaly. Figs. 6 and 41 to 49 illustrate how electromagnetic anisotropy can be taken into account, for example, in determining the distance and / or direction for the anomaly.

Triaxial Transient EM Responses

Fig. 3 illustrates directional angles between tool and anomaly coordinates. A transmitter coil T is located in the source that is the source for each coordinate system. A receiver is placed at a distance L from the transmitter. A terrestrial coordinate system includes a Z axis in a vertical direction and an X axis and Y axis in the East and North directions, respectively. The offset hole is specified in terrestrial coordinates by an offset angle Ob and its azimuth angle cpb. A resistivity anomaly A is located at a transmitter distance D in the direction specified by a dive angle (Ga) and its azimuth (φa).

In order to practice embodiments of the method, fig. 4Samples the definition of a wellbore coordinate system having x, y and z axes. The z axis defines the direction from transmitter T to receiver R. The tool coordinates in fig. 4A are specified by the rotation of the terrestrial coordinates (Χ, Υ, Z) in fig. 3 by the azimuth angle ((φb) around the Z axis and then rotating Gb around the y axis to reach the tool coordinates (x, y, z). The anomaly direction is specified by the dive angle (υ) and the azimuth angle (φ), where:

<formula> formula see original document page 18 </formula>

<formula> formula see original document page 18 </formula>

Similarly, fig. 4B shows the definition of an anomaly decoordinate system having axes a, b c. The c axis defines the direction of the transmitter T to the center of the anomaly A. The anomaly coordinates nafig. 4B are specified by rotating the terrestrial coordinates (Χ, Υ, Z) nafig. 3 by the azimuth angle (φa) around the Z axis and subsequently rotating Ga around the b axis to arrive at the anomaly coordinates (a, b, c). In this coordinate system, the wellbore direction is specified in reverse order by the azimuth angle (φ) and the plunge angle (υ).

Transient responses in two coordinate systems

The method is further based on the relationship between transient responses in two coordinate systems. The magnetic field responders at the [X-ray, Ry, Rz] receivers that are oriented in the direction of the tool coordinate [x, y, z] axes, respectively, as referred to as: <formula> formula see original document page 19 < / formula>

Where the right hand side of the equation represents all combinations of receiver axis and transmitter axis, whereby Vy = RiTj denotes voltage response sensed by the receiver Rj (i = x, y, z) of the syntransmitted transmitter Tj ( ix, y, z). Each transmitter may comprise a magnetic dipole source ([Mx, My, Mz) in any direction.

When the resistivity anomaly is far from the tool, the formation close to the tool is seen as a homogeneous formation. For simplicity, the method may assume that isotropic formation. Only three nonzero transient responses exist in a homogeneous isotropic formation. These include the coaxial response and two coplanar responses. Coaxial response VzzCt) is the response when both the transmitter and the receiver are oriented in the common tool axis direction. Coplanar responses, VxxCt) and VyyCt), are the answers when both the transmitter T and receiver R are aligned parallel to each other, but their orientation being perpendicular to the tool axis. All cross-component responses are from a longitudinally oriented receiver with a transverse transmitter, or vice versa. The cross-component response is also zero between a mutually orthogonal transverse receiver and transmitter.

The effect of the resistivity anomaly is seen on the transient responses as time increases. In addition to ecoplanar coaxial responses, the cross-component responses Vy (t) i, j = x, y, z) return to zero. Transient magnetic field responses can also be examined in the anomaly coordinate system. The transient magnetic field responses at receivers (Ra, Rb, Rc) that are oriented in the direction of the axis [a, b, c] of anomaly coordinates can be referred to as <formula> formula see original document page 20 </formula>

where the right-hand side of the equation represents all receiver orientation and transmitter orientation combinations, so that Vij - RiTj denotes voltage response sensed by the receiver Ri (orientation i = a, b, c) of the signal transmitted by the transmitter Tj. (in orientation j = a, b, c). Each transmitter may comprise a dipolemagnetic source, [Ma. Mb, Mc], along orientation a, b or c.

When the anomaly is large and distant compared to the transmitter-receiver spacing, the effect of the spacing may be significant and the transient responses may be almost identical to those of the receivers near the transmitter. Then the method assumes that there is axial symmetry with respect to the c axis which is the direction from the transmitter to the center of the anomaly. In this axially symmetrical configuration, cross-component responses in the anomaly coordinates are identically zero time domain measurements.

β <formula> formula see original document page 20 </formula>

Transient magnetic field responses in tool coordinates are related to those in anomaly coordinates by a simple coordinate transformation.

P (d, 0) specified by the dive angle (S) and deazimuth angle (0). <formula> formula see original document page 21 </formula>

Direction Determination

The assumptions given above contribute to the determination of the target direction, which is defined as the direction of the anomaly from the origin. The tool is at the origin. When symmetriaaxial is assumed in the anomaly coordinates, the transient response measures in the tool coordinates are constrained and the two directional angles can be determined by combinations of triaxial responses.

<formula> formula see original document page 21 </formula>

In terms of each triaxial response

<formula> formula see original document page 21 </formula>

The following relationships may be noted:

<formula> formula see original document page 21 </formula> Several distinct cases may be noted. In the first of these cases, when none of the cross components is zero, neither Vxy Φ 0, nor Vyz Φ 0, nor Vzx Φ 0, then azimuth angle 0 is neither zero nor π / 2 (90 °), and can be determined. per,

<formula> formula see original document page 22 </formula>

Noting the relationship,

<formula> formula see original document page 22 </formula>

the dive angle S (deviation) is determined by,

<formula> formula see original document page 22 </formula>

In the second case, when Vxy = 0 and Vyz = 0, then $ = 0 or 0 = 0 or π (180 °) or, 0 = ± π (90 °) and ϑ = π / 2 (90 °), a since coaxial and coplanar responses must differ from each other (Vaa Φ Vcc).

If 0 = 0, then the dive angle ϑ is determined by,

<formula> formula see original document page 22 </formula>

If 0 = π (180 °), then the dive angle ϑ is determined by,

<formula> formula see original document page 22 </formula>

Likewise, in relation to the second case, if ϑ = 0, then Vxx = Vyy and Vzx = 0. If 0 = ± π / 2 (90 °) and ϑ = ± n / 2 (90 °), then Fzz - Vxx and Vzx = 0.These examples will be further discussed below in relation to the fifth case. In the third case, when <formula> formula see original document page 23 </formula>

If 0 = π / 2, then the dive angle θ is determined by,

<formula> formula see original document page 23 </formula>

If 0 = - π / 2, then the dive angle is determined by,

<formula> formula see original document page 23 </formula>

Also in relation to the third case, if S = 0, then Vxx =

Kjy and Vyz = 0. If 0 = 0 and S = ± π / 2 (90 °), F3y = Vzz and Fvz = 0. These situations will be further discussed below in relation to the fifth case.

In the fourth case, Vxz = 0 and Vyz = 0, then $ = 0 or π (180 °) or ±

<formula> formula see original document page 23 </formula>

If = $ ± π / 2, then azimuth angle 0 is determined by,

<formula> formula see original document page 23 </formula>

Also for the fourth case, if & = 0 or π (180 °), then Vxx - Vyy and Vyz - 0. This situation is also shown below in relation to the fifth case.

In the fifth case, all cross components disappear,

<formula> formula see original document page 23 </formula>

Tool rotation around tool axis / wellboreIn the above analysis, all transient responses Vij, (t) (i, j = x,

y, z) are specified by the directions of the x-, y-, and z- axes of the tool coordinates. However, the tool rotates within the drillhole and the azimuth orientation of the transmitter and receiver no longer coincides with the χ or y axis direction as shown in FIG. 5. If the measured responses are V ~ (i J = χ, γ, ζ), where the axes xq y are the directions of the fixed antennas for the turning tool, and ψ is the tool's rotation angle, then,

<formula> formula see original document page 24 </formula>

So,

<formula> formula see original document page 24 </formula> Azimuth angle 0 is measured from the triaxial responses if the tool rotation angle ψ is known. In contrast, the diving angle $ (deviation) is determined by,

<formula> formula see original document page 25 </formula>

without knowing the tool orientation ψ.

Apparent diving and azimuth angles and distance to anomaly

The dip and azimuth angles described above indicate the direction of a resistivity anomaly determined by a combination of triaxial transient responses at a time (t) when the angles deviated from a zero value. When t is small or close to zero, the effect of this anomaly is not apparent in transient responses since all cross-component responses have disappeared. To identify the anomaly and estimate not only its direction but also its distance, it is useful to define the apparent azimuth angle 0app (t) by,

<formula> formula see original document page 25 </formula>

and the effective diving angle Sapp (t) by,

<formula> formula see original document page 25 </formula>

for the time interval where neither 0app (t) 0 nor π / 2 (90 °).

For simplicity, the case examined below is one where none of the cross-component measures are zero: Vyz (t) Φ 0, and V2X (t) Φ 0.

For the time interval where 0app (t) ~ 0, Sapp (t) is defined by <formula> formula see original document page 26 </formula>

For the time interval where

<formula> formula see original document page 26 </formula>

defined by,

When t is small and transient responses do not consider the effect of a distance resistivity anomaly, the effective angles are identical to zero, 0app (t) - $ app (t) - 0. When t increases, when the transient responders consider the effect of Anomaly, 0app (t) and $ app (t) start sampling the true azimuth and dive angles. The distance to year can be indicated in time when 0app (t) and Sapp (t) start to deviate from the initial zero values. As shown in an example of modeling below, the presence of an anomaly is detected much more in time at the effective angles than in apparent conductivity (σαρρ (ί).) Even if the resistivity of the anomaly cannot be known until oapp (t) affected by the anomaly, its presence and direction can be measured by apparent angles. With time limitation, the distant anomaly may not be considered when changing oapp (t), but is visible at 0app (t) and

First example of modeling

FIG. 6 represents an example of simplified modeling where a resistivity anomaly A is described as, for example, a massive salt dome in a formation 5. The salt interface 55 may be considered as a flat interface. FIG. 6 also indicates coaxial, coplanar 62, and cross-component (64) measuring arrangements, where a transmitter coil and a receiver coil are spaced apart by a distance L. It should be understood that in a practical application , separate tools can be employed for each of these arrangements, or a multiple orthogonal tool. For further simplification, it may be assumed that the azimuth direction of the salt face, as considered from the tool, is known. Consequently, the first distance D of the tool to the salt face 55, the second distance D2 of the other side of the salt to the tool, the isotropic or anisotropic resistivity of the formation, and the approach angle (or dip angle) θ as shown in FIG. 6. The thickness Δ of the salt dome is defined as Δ = D2 - D1. In the case of resistivity in the seranisotropic anomaly, the electromagnetic properties of the anomaly may be characterized by the normal resistivity R® in the direction of the principal axis of the anisotropy (or normal conductivity σ ©), and resistivity in the R // plane (or conductivity in the σ // plane). in any direction within a plane perpendicular to the major axis. In the case of anisotropy, R // ≠ R ©.

Before discussing anisotropy in more detail, isotropic formations will first be illustrated with resistivity R (= R // = R®) (or its inverse σ = σ // = σ ©).

FIG. 7 and FIG. 8 show the calculated transient voltage (V) response from coaxial Vzz (t) (line 65), coplanar, Vxx (t) (line 66), and cross component Vzx (t) (line 67) measurements for a tooling Z = Im, for θ = 30 ° and located at a distance Dy = 10Orespectively, D} = 100m away from a salt face 55. In the calculations, D2 was assumed to be much larger than 100m, so that within the time scale calculation (up to 1s) no influence on the other side of salt A is detectable in the transient response. In addition, when the anomaly is large compared to the L-spacing of the transmitter-receiver, the effect of L-spacing may be ignored and transient responses may be approximated to those of receivers near the transmitter.

The effect of resistivity anomaly A (as depicted in FIG. 6) is considered in the transient calculated responses as time increases. In addition to the coaxial and coplanar responses (65.66), the cross-decomposing responses Vij (t) (i ≠ j; I, j = x, y, z) become nonzero. may be converted to apparent dipping and / or apparent conductivity.

The apparent dive angle θaρρ (t) as calculated by

<formula> formula see original document page 28 </formula>)

is shown in FIG. 9 for a tool assembly of L = 1m when the salt face 55 is spaced from D1 = 10m and at the approach angle of θ = 30 °.

The apparent conductivity (σapp (t)) of both coaxial (Vzz (t) of FIG. 7) and coplanar (Vxx (t)) responses of FIG. 7 are shown in FIG. 10 (lines 68, 69, respectively), where the approach angle (θ = 30 °) and salt face distance (D1 = 10 m) are the same as in FIG. 9. Details of how apparent conductivities are calculated will be provided below.

It should be noted that the true direction of the tool to the salt face (eg 30 °) is reflected in the apparent dive graph Qapp (t) of FIG. 9 at 10 "4s, when the presence of resistivity anomalies is hardly detected in the apparent conductivity graph (σapp (t)) of FIG. 10 It takes almost 10-3 s for the apparent conductivity to approach an asymptotic Oapp value ( t delayed).

FIG. 11 shows apparent dive GappOO For L ° Im tool set ° when the salt face is away from D = 10m, but at different angles between the tool axis and the target ranging from 0 to 90 ° in 15 ° increments. The approach angle (Θ) can be reflected at any angle in about 10 ~ 4s.

FIG. Ile FIGs. 12 and 13 compare the apparent diveσρρ (t) for distances other than the salt face (D = 10m; 50m; and 100m) the sharpest angles between the tool axis and the target. The distance to the salt face can also be determined by transition where 6app (t) takes an asymptotic value. Even if the salt face distance (D) is 100m it can be identified and its direction can be measured by the apparent dip 6app (t).

In summary, the method considers the decoordinated transformation of transient EM responses between fixed tool coordinates and fixed anomaly coordinates. When the anomaly is large and distant compared to the transmitter-receiver offset, one may ignore the effect of the offset and approximate EM transient responses with those near the transmitter. Then one can assume that there is axial existimetry with respect to the c axis, which defines the direction from the transmitter to the anomaly. In this axially symmetrical configuration, the cross component responses at the fixed anomaly coordinates are identical to zero. With this assumption, a general method for determining resistance to the resistivity anomaly using transient EMtriaxial responses is provided.

The method defines the apparent dip 6app (t) and the apparent azimuteate φαρρ (0 by combinations of triaxial transient measurements. The apparent direction {6aap (t), <paap (t)} reads the true direction {θ, φ) at a maistarde time. . The 0app (t) and φαρρ (0> both read zero when t is small and the effect of the anomaly is not detected on transient responses or apparent conductivity. The conductivities (ocoaxial (t) and σcopianar (t)) of coaxial and coplanar measurements indicate both the conductivity of the close formation around the tool.

Deviation from the apparent direction {{Θ app (t), φαρρ (t)}) of zero identifies the anomaly. The distance to the anomaly is measured by time when the apparent direction {{6app (t), φαρρ (0}) begins to deviate from zero or by time when the apparent direction {{θαρρ (t), φαρρ (t)}) begins to approach the true direction ({θ, φ}). Distance can also be measured from the change in apparent conductivity. However, the anomaly is identified and measured much earlier in time, in the apparent direction, than in the apparent conductivity.

As shown above, apparent conductivity can be used as an alternative technique to apparent angles to determine the location of an anomaly in a wellbore. Time-dependent apparent conductivity can be defined at each point in a time series, at each depth of record. Apparent conductivity at a z-register depth is defined as the conductivity of a homogeneous formation that would generate the same tool response measured at the selected position. In EM transient recording, transient data is collected at a recording depth, or tool location z, as a series of induced voltage times in a receiver circuit. Consequently, time-dependent apparent conductivity (σ (z, t)) can be set at each point in the time series, at each record depth, to an appropriate range of time intervals, depending on the formation conductivity and tool specifications.

The induced voltage of a coaxial tool, such as transmitter-receiver L distance, in homogeneous conductivity formation (σ) is given by,

<formula> formula see original document page 30 </formula>

where u2 = μοθ / 4 L2 / It and C is a constant.

The apparent time-varying conductivity depends on the voltage response in a coaxial tool (VzZ (t)) at each measurement time when: <formula> formula see original document page 31 </formula>

is the measured voltage response of the coaxial tool. From a single measurement type (coaxial, single offset), the larger the offset L, the longer the measurement time (t) should be to apply the concept of apparent conductivity. The oapp (t) should be constant and equal to the conductivity of the formation in a homogeneous formation: oapp (t) = oThe deviation of a constant (σ) at time (i) suggests a conductivity anomaly in the time-specified region (t). .

The induced voltage of the spacer-transmitter L-coplanar tool in the homogeneous conductivity formation (σ) is given by

<formula> formula see original document page 31 </formula>

of t, the coplanar voltage changes the polarity depending on the distance and the conductivity of the formation.

Similar to the coaxial tool response, time-varying apparent conductivity is defined as the response of the VxX (t) coplanar tool at each measurement time when,

<formula> formula see original document page 31 </formula>

voltage response measured by the coplanar tool. The longer the distance, the higher the value of t should be to apply the concept of apparent conductivity of a single type of measurement (coplanar, single spacing). The σapp (t) should be constant and equal to the conductivity of the formation in a homogeneous formation: σapp (t) = σ.

When there are two coaxial receivers, the relationship between the pair of voltage measurements is given by,

<formula> formula see original document page 32 </formula>

where L1 and L2 are two coaxial transponder transponder spacings.

Conversely, the apparent time-varying conductivity is defined for a pair of coaxial tools by,

<formula> formula see original document page 32 </formula>

at each measurement time. The σapp (t) should be constant and equal to the conductivity of the formation in a homogeneous formation: σapp (t) = σ.

Apparent conductivity is similarly defined for a pair of coplanar tools or a pair of ecoplanar coaxial tools. The σapp (t) should be constant and equal to the conductivity of the strain in a homogeneous formation: σapp (t) = σ. The deviation of the constant (cr) at time (t) suggests a conductivity anomaly in the time-specified region (t).

As will be illustrated below, apparent conductivity (σapp (t)), whether coaxial or coplanar, can reveal three parameters with respect to a two-layer formation, including:

(1) the conductivity of a first local layer in which the tool is located;

(2) the conductivity of one or more adjacent layers or strata; and

(3) the tool's distance to the layer boundaries. Coaxial transient response analysis in two-layer models

To illustrate the usefulness of the apparent conductivity concept, the transient response of a tool in a two-tier terrestrial model, as in FiG. 14, for example, can be examined.

FIG. 14 illustrates a coaxial tool 80 in which a transmitter coil (T) and a receiver coil (R) are wound around the common tool axis z and spaced from a spacing distance L. The symbols σι and 2 can represent the conductivities of two forming layers. Coaxial tool 80 is placed in a horizontal well88 across a forming layer 5 and extending parallel to the interface of layer 55.

In the present example, a horizontal well is represented such that the distance from the tool to the boundary of the layer corresponds to the distance from the horizontal wellbore to the boundary of the layer. Under a more general circumstance, the relative direction of a well and tool hole at the stratum interface is not known.

The calculated transient voltage response V (t) for the coaxial tool transmitter-receiver L-Im spacing at the various distances D between tool 80 and layer boundary 55 is shown in FIG. 15, for Rf = 1.5.10, 25, and 50m. Formation can be analyzed using these responses employing apparent conductivity as explained later in relation to FIGs. 16 and 17.

FIG. 16 shows the voltage data of FIG. 15 plotted in terms of apparent conductivity, for a geometry where σ1 = 0, lS / m (Rj = 10Ωπι) and σ2 = lS / m (R2 = 1Ωm). Similarly, FIG. 17 illustrates apparent conductivity in a two-layer model where Oj = 7 S / m (R1 = 7Ωmy) Qσ2 = 0.1S / m (R2 = 10Ωm).

The apparent conductivity plots reveal a "constant" conductivity at t small and large t, but having a valordiferent value, and a transition time tc, which marks the transition between the two "constant" conductivity values and depends on distance D.

As will be explained below, in a two-layer resistivity profile, apparent conductivity, when t approaches zero, can identify the conductivity of the σι layer around the tool, while apparent conductivity when t approaches infinity can be used to determine conductivity Q1 of the adjacent layer at a distance. The distance to the limit of stratum 55 from tool 80 can also be measured from the transition time observed in the apparent conductivity plots.

At small values of t, the tool reads the apparent conductivity σ1 of the first layer 5 around tool 80. It is assumed that the conductivity at small values of t corresponds to the local layer conductivity 5 where the tool is located. At small values of t, the signal reaches the receiver directly from the transmitter without interfering with stratum olimite. Namely, the signal is affected only by the surrounding conductivity of the tool.

At large t-values, the tool reads 0.4S / m for a two-layer model where σ1 = lS / m (R1 = 7 Qm) and σ2 = 0, lS / m (R2 = 10Ωm), or σ1 = 0, 1S / m (R1 = 10Ωm) and σ2 = 1S / m (R2 = Ωm). It is believed that the value of 0.4 corresponds to some average between the conductivities of the two layers, because at large t values, almost half of the signals come from below the tool formation, and the remaining signals come from above, if so long. the signal travels the distance between the tool and the limit of the stratum, if small.

This is further investigated in FIG. 18, which shows examples of oapp (t) graphs for D = 1mel = 1 m, but for resistivity ratios other than target layer 2, while local conductivity (σ1) is fixed at 1S / m (R1 = 1Ωm). The apparent conductivity in large values of t is determined by the conductivity of the target layer 2, as shown at line 71, in FIG. 19 when σ1 is fixed at 1S / m.

Numerically, the delayed conductivity can be approximated by the mean square root of two-layer conductivity when:

<formula> formula see original document page 35 </formula>

This is represented as line 72 in FIG. 19. Thus, the conductivity at large values of t (when t is near infinity) can be used to estimate the conductivity (σ2) of the adjacent layer, when the local conductivity (σ;) near the tool is known, for example, the from conductivity when t approaches zero, as illustrated in FIG. 20

Estimation of D. The distance to the electromagnetic anomaly

The distance D from the tool to the stratum is reflected in the time of transition tc. The transition time at which apparent conductivity (oapp (t)) begins to shift from local conductivity (σι) to conductivity at large values of t depends on D and L, as shown in FIG. 21

For convenience, the transition time (tc) may be defined as the time when aapp (tc) uses a shear conductivity (σc). In this case, the cutting conductivity is represented by the arithmetic mean between conductivity when t approaches zero and conductivity when t approaches infinity. The transition time (tc) is dictated by the radius path RP:

<formula> formula see original document page 35 </formula>

which is the shortest distance for the electromagnetic signal to travel from the transmitter to the stratum boundary to the receiver, regardless of the resistivity of the two layers. Conversely, the distance (D) to the anomaly can be estimated from the transition time (tc), as shown in FIG. 22.

Anticipating EM Transient Method Capabilities

By analyzing apparent conductivity or its inherent inverse equivalent (apparent resistivity), the present invention can identify the location of a resistivity anomaly (e.g., a conductive anomaly and a resistive anomaly). In addition, resistivity or conductivity may be determined from coaxial and / or coupling transient responses. As explained above, the direction of the anomaly can be determined if cross-component data is also available. To further illustrate the usefulness of these concepts, the foregoing analysis may also be used to detect an anomaly at an early drill bit distance.

FIG. 23 shows a coaxial tool 80, with spacer transmitter-receiver L, placed within, for example, a vertical well 88 approaching, or slightly beyond, an adjacent stratum which is a resistivity annulus. Tool 80 includes a transmitter coil T and a receiver coil R which are wound around a common tool axis and oriented in the direction of the tool axis. The symbols σι and Q1 can represent the conductivities of two deformation layers, and D the distance between the tool 80 (for example, the antenatransmitter T) and the layer boundary 55.

The calculated transient voltage response of the L - Im tooling (transceiver offset) at different distances (D = 1, 5, 10, 25, and 50m) as a function of t, in a case where O1 = 0.1 S / m (corresponding to Ri = 10Qm), εσ2 = 1S / m (corresponding to R2 = IQm) is shown in FIG. 24. Although cross-response differences are observed at different distances, it is not simple to identify the resistivity anomaly directly from these responses. The same voltage data from FIG. 24 are plotted in terms of apparent conductivity (oapp (t)) in FIG. 25. From this figure, it is clear the coaxial response can identify an adjacent stratum with a higher conductivity, at a distance. Even an L = Imp tool can detect the distant stratum 10, 25, and 50m if the low voltage response can be measured within a range of 0.1-1s.

The oapp (t) graph shows very distinctly in the drawing at least three parameters: conductivity at the beginning of time; final conductivity of time; and the transition time that moves when the distance (D) changes. In FIG. 25, it should be noted that at the beginning of time, where t is near zero, the tool reads the apparent conductivity of 0.1 S / m, which is representative of the layer immediately around the tool. The signal that reaches receiver R does not yet contain information about limit 55. At the end of the time, the tool reads close to 0.55 S / m, representing an arithmetic average between the conductivity of the two layers. At the end of time t © almost half of the signals come from the formation below the tool and the other half from the top of the tool if the time to travel the distance (D) from the stratum limit is small. The distance D is reflected in the transition time tc.

FIG. 26 illustrates the aapp (t) graph of transientecoaxial response in the two-layer model of FIG. 23, for a L = lm tool, at different distances (D), except that the local layer conductivity (σΐ) is lS / m (RI = IQm) and the target layer conductivity (σ2) is 0, lS / m (R2 = 10m). Again, the tool reads at the beginning of time the apparent conductivity of 1.0S / m which is from the layer immediately around the tool. At the end of the time, the tool reads approximately 0.55 S / m, the same as the average conductivity of FIG. . 25. The distance (D) is reflected in the time of transmission tc.

Therefore, the electromagnetic transient response method can be used as an early resistivity recording method.

FIG. 27 compares the aapp (t) graph of FIG. 25 and FIG. 26 paraL = ImeD = 5 Om. The delayed conductivity is determined solely by the conductivity of the two layers (σι and O1) alone. It is not affected by the location of the tool on both layers. However, due to the great depth of the investigation, delayed conductivity is not readily achieved even at t = 1s, as shown in FIG. 25. In practice, delayed conductivity may have to be approximated by aapp (t = Is) which slightly depends on D as illustrated in FIG. 25

Numerically, the delayed apparent conductivity may be approximated by the arithmetic mean of two-layer conductivities when: σαρρ (t -> 00; σλ, σ2) - σ1 + / 2. This is reasonable considering that, with the coaxial tool, the axial transmitter induces parasitical current to the stratum limit. At the end of time, the axial receptor receives horizontal current almost equally from both layers. As a result, delayed conductivity must consider the conductivity of both formations of almost equal weight.

FIG. 28 compares the graphs of oapp (t) to D = 50m, but with different spacing L. Oapp (t) achieves almost constant delayed apparent conductivity at later times when L increases. Delayed apparent conductivity (oapp (t ©) is almost independent of L. However, the delayed conductivity defined at t = ls is slightly dependent on distance (D).

Thus, the delayed apparent conductivity (σαρρ (1 © at t = 1s can be used to estimate the conductivity of the adjacent layer (O1) when the local conductivity near the tool (oi) is known, for example, from the apparent conductivity of the beginning). do (oapp (t © 0) = O1).

Estimated distance (D) to electromagnetic anomaly

The transition time (tc) at which conductivity appears to begin to shift from local conductivity (Oj) to delayed conductivity clearly depends on D, the distance from the tool to the limit of the layer, as shown in FIG. 25 for a dq tool L = lm.

For convenience, the transition time (7c) is defined by the time when the app (tc) uses a cutoff conductivity (oc), that is, for example, the arithmetic mean of the delayed start time conductivity: <formula> formula see original document page 39 </formula>. The transition time (tc) is dictated by the radius path RP, D minus L 2, that is, half the distance for the EM signal to travel from the transmitter to the stratum limit to the receiver, regardless of the resistivity of the two layers. Conversely, the distance (D) can be estimated from the transition time (tc), as shown in FIG. 29 when L = 1m.

Analysis of coplanar transient responses in two-layer models

Although coaxial transient data has been examined above, coplanar transient data is equally useful as a method of recording early resistivity.

FIG. 30 shows a coplanar tool 80, with transmitter-receiver gap L, placed in a well 88 and approaching (or slightly beyond) the boundary of layer 55 of an adjacent stratum which is the resistivity anomaly. In the coplanar tool, both a transmitter T and a receiver R are oriented perpendicular to the tool axis and parallel to each other. The OiQO2 symbols may represent the two-layer conductivity of the formation.

Corresponding to FIG. 25 for the axial tooling responses where L = 1m, the apparent conductivity (oapp (t)) for calculated platelet responses is plotted in FIG. 31 for different tool distances from the boundary of stratum 55. Of course, the coplanar response can also identify an adjacent stratum with a higher conductivity at a distance. Even an L = Im tool can detect the stratum at 10m, 25m, and 50m away if low voltage responses can be measured at 0.1-ls intervals. The δapp (t) graph for coplanar responses also shows three parameters, as for coaxial responses.

As is the case in coaxial geometry, it is equally true for coplanar responses that the apparent conductivity of the beginning of time. <formula> formula see original document page 40 </formula> is the conductivity of the local layer (d;) where the tool is located . Conversely, the conductivity of the layer can be easily measured by apparent conductivity at earlier times.

The delayed apparent conductivity <formula> formula see original document page 40 </formula> is an average conductivity of both layers. The conclusions derived for coaxial responses apply equally well to coplanar responses. However, the delayed conductivity value for coplanar responses is not the same as for coaxial responses. For coaxial responses, delayed conductivity is close to the arithmetic mean of two-layer conductivity in two-layer models.

FIG. 32 shows the delayed conductivity <formula> formula see original document page 40 </formula> for coplanar responses as obtained from the model calculations (line 77) where D = 50m and L = 1m, but for conductivities other than the local layer when target is set at 1S / m. Delayed conductivity is determined by the local conductivity of the layer, and is numerically near the square root mean when

<formula> formula see original document page 40 </formula> as shown by tab 78 in FIG. 32

To summarize, the delayed conductivity <formula> formula see original document page 40 </formula> can be used to estimate the conductivity of the adjacent layer (σ2) when local conductivity (σ1) near the tool is known, for example from start-time conductivity <formula> formula see original document page 40 </formula> .This is illustrated in FIG. 33, where line 79 was obtained from model calculations, and line 79a presents the average approximation. Estimate of the distance (D) to the electromagnetic anomaly

The transition time tc, when conductivity appears to begin to deviate from local conductivity (σ1) to delayed conductivity, clearly depends on the distance (D) from tool 80 (eg the transmitter T) to the boundary of stratum 55, as shown in FIG. 30

The transition time (tc) can be defined by the time when σ app (tc) uses the cutoff conductivity (σc), that is, in this example, the arithmetic mean between the start and delayed conductivities: σc = {aσpp (t

<formula> formula see original document page 41 </formula>

0) + oapp (t

<formula> formula see original document page 41 </formula>

°°)} / 2. The transition time (tc) is dictated by the pathway, D minus L / 2, that is, half the distance for the EM signal to travel from the transmitter to the boundary layer to the receiver, regardless of the resistivity of the two layers.

Conversely, the distance (D) can be estimated from the transition time (tc) as shown in FIG. 34 where Z- = Im.Electromagnetic transient response data analysis for three or more formation layers

The following model shows a nearby conductive layer, a very resistive layer, and an even more conductive layer. Geological configuration is described in FIG. 35, together with an axial tool 80, in a relatively conductive formation 82, wherein an anomaly is located in the form of a relatively resistive layer 83. As shown, the formation on the other side of layer 83 as viewed from tool 80 and identified in FIG . 35 by reference numeral 84, identical to the formation 82, on the tool side of layer 83. However, the method will also work if the formation 84 on the other side of layer 83 constitutes a layer having properties different from those of the nearby deformation 82.

In either case, the tool "sees" anomaly 83 as a first layer, at a first distance D1, spaced apart and having a thickness Δ, and "sees" the formation on the other side of anomaly 83, as a second layer 84, spaced apart. a second distance D2 = D1 + Δ and having infinite thickness.

FIG. 36 is a graph showing the calculated relative resistance resistance Rapp versus time t for a geometry as shown in FIG. 35. For the calculation of FIG. 36, it has been assumed that the anomaly is formed by a resistive salt layer having a resistivity of 100 µm, and that the formation is formed, for example, by a saturated brine formation having a resistivity of 1 µm. The tool was modeled to be oriented with its main axis parallel to the first interface 81 between saturated brine formation 82 and the distance between the main axis and the first layer 83, D1, was considered IOm. The thickness of the resistive stratum Δ was varied from a fraction to 100m.

Rapp's first rise (0 is the salt response and occurs in 10 "4s with a L = 1m tool when the salt is at D1-10m distance. If the salt is completely resolved (by infinitely thick salt beyond Dl = 10m ), apparent resistivity should read 3Ωm asymptotically.

The subsequent decline of Rapp (t) is the response to a conductive formation behind salt (resistive stratum). Rapp (retarded t) is a function of the conductive layer resistivity and salt thickness. If time measurement is limited to 10 "s, the decline of Rapp (t) may not be detected for salt over 500m thick.

Regarding the resolution of the resistive stratum, the coaxial responds to a thin stratum (1-2m thick). The time at which Rapp (t) reaches its peak or begins to decline depends on the distance to the conductive layer behind the salt.

As noted earlier, when plotted in terms of conductivity relative to opp (t), the transition time can be used to determine stratum boundary distances. As shown in FIG. 37, another three layer formation was also modeled. In this case, the intermediate layer 83 was a more conductive layer than the surrounding formation 82. This conductive layer 83 may be considered representative of, for example, a foil layer. Coaxial tool 80, having an offset L = Im, is located in a wellbore in a formation 82 having an IOQm resistivity and is located at Di = 10 m from the least resistive (most conductive) layer 83, which has a resistivity of IΩm. The third layer 84 extends beyond conductive layer 83 and has a resistivity of 10 µm as well as layer 82. Conductive layer 83 has been modeled for a range of thicknesses ranging from meter fractions to infinite thickness. The apparent resistance as calculated is shown in FIG. 38

The reduction in Rapp (t), which can be seen in FIG. 38, is attributed to the presence of the shale (conductive) layer and appears when t - »10" 5s. Shale response is completely resolved by a conductive layer of infinite thickness approaching 3Ωm. The subsequent rise in Rapp (t) is in response resistive formation 84 in addition to shale layer 83. Transition time is used to determine the distance D2 from tool 80 to interface 85 between the second and third layers (83, 84, respectively). Rapp (t delayed) is a conductivity of the conductive layer When the thickness Δ of the conductive layer increases, the time measurement must also be increased (> 10 "s) in order to measure the rise of Rapp (t) for conductive layers over 100m. of thickness.

Yet another three-layer model is shown in FIG. 39, where coaxial tool 80 is in a conductive formation 82 (IΩm), and a second highly resistive layer 84 (100Ωm) as could be found in, for example, a salt dome. . The formation 82 and the second layer 84 are separated by a first layer 83 which has an intermediate resistance (10 µm). The thickness Δ was varied in the calculations of apparent resistivity as described in FIG. 40

The response to the intermediate resistive layer is seen in 10-4s, where Rapp (t) increases. If the first layer 83 is completely resolved by an infinitely thick stratum, the apparent resistivity approaches a 2.6 μm asymptote. As noted in FIG. 40, Rapp (t) undergoes a second step of augmentation in response to the second 100 mm high resistant layer 84. Based on the transition time, the distance to the interface is determined to be 110m.

Although complex, apparent resistivity or apparent conductivity in the above examples delineate the presence of multiple layers. The observed changes in apparent conductivity (or apparent resistivity) allow the determination of distances Di and D2.

Electromagnetic transient responses involving formation anisotropy

As stated above, an electromagnetic anomaly may have anisotropic electromagnetic properties. An example is shown in FIG. 6 if R // RΦ.

Several mechanisms can give rise to a macroscopic effect of electromagnetic induction. For example, oriented fractions can generate an anisotropic response. Electromagnetic anisotropy may also occur intrinsically in certain types of formations, such as shales, or may occur as a result of relatively thin layer sequences.

As depicted in FIG. 6, the main direction of anisotropy corresponds to the approach angle Θ. This correspondence is mainly due to the simplicity of the presentation of the embodiments, and need not necessarily be the case in each situation within the scope of the invention.

In the following, it will be explained how electromagnetic anisotropy with at least one of the formation layers can be taken into consideration when analyzing time-dependent transient response signals. This may include determining one or more anisotropy parameters that characterize anisotropic electromagnetic properties. Among the anisotropy parameters are the α2 anisotropy ratio, the anisotropic factor β, conductivity along an σ® anisotropy main axis (or resistivity along the Re anisotropy main axis), conductivity on a plane perpendicular to the Q / anisotropy main axis. / (Our resistivity in a plane perpendicular to the anisotropy main axis R //), Tool axis angle to the anisotropy main axis.

Using the concepts of apparent conductivity or apparent resistance and / or apparent diving or azimuth, the distance and / or direction for an anomaly can be determined from time-dependent transient response signals, even when the anomaly, and / or a formation layer. Distant comprises (an) an electromagnetic anisotropy or, when the transmitter and / or receiver antennas are embedded in an anisotropic layer.

Using the principles set out above, the analysis taking into consideration anisotropy can be extended to multiple stratum formations, including those where only one distant formation layer, or anomaly target, gives anisotropic electromagnetic induction responses (as, for example, in FIG. 6) or, where a local deformation layer, in which the transmitter and receiver antennas are located, exhibits anisotropic behavior and one or more other isotropic or anisotropic layers are present at a distance. The distance and direction from the tool to the most distant and / or anomaly target layers can then be determined as long as anisotropy is taken into account. In the following explanation, for the sake of simplicity, it will be assumed that anisotropy has a vertically aligned main axis, so that the angle between the tool axis ζ and the main axis of anisotropy corresponds to the dip angle or offset angle θ. The term horizontal resistivity Rh may be employed, generally corresponding to the resistivity in the anisotropy plane perpendicular to the main direction of anisotropy. The term vertical resistivity Rv refers to resistivity in the principal direction of anisotropy or normal direction.

EM transient responses in a homogeneous anisotropic formation

It is considered an anisotropic formation in which a vertical resistivity Rv (or its inverse, vertical conductivity σγ) is different from horizontal resistivity Rh (or horizontal conductivity σΗ). It is assumed that the formation has symmetric azimuth in the horizontal direction. The tool axis ζ is offset from the vertical direction by the angle of dip θ (deviation) in the zx plane. The transmitting antenna is placed at the source: The receiving antenna is placed at (x = L @ sen6, y = 0, z = L @ cos9). There may be four independent combinations of receiver transmitter orientations that give nonzero responses.

In addition to a coaxial response, VZz, there are two plane responses, VXx and VYy, and a cross-component response VXz = VZx. A coplanar response, VXx, is from a transverse transmitter antenna and receiving antenna that are oriented within the zx plane. Another plane response, VYy, is of a transverse transmitter and receiver both oriented in the y-axis direction. The cross component response is from a transverse receiver antenna with the longitudinally oriented transmitting antenna, or vice versa. The transverse receiving antenna is directed within the zx plane. Any cross component that involves a transmitter or receiver oriented in the y-axis direction, that is, VYx eVxy and VYz and Vzy disappears.

The above was presented in tool coordinates. Furthermore, it is observed that any antenna sensitive to a transverse component of an induced magnetic field satisfies as a transverse antenna.

Applicants have derived the transient response in the time domain expressed in terms of horizontal conductivity σΗ, and anisotropic factor β, and are given by,

<formula> formula see original document page 47 </formula>

In these equations,

<formula> formula see original document page 47 </formula>

constant. The factor.

anisotropic β is defined as:

<formula> formula see original document page 47 </formula>

Based on these equations, the following observations can be made:

1. The coaxial response depends only on the horizontal resistivity Rh (= 1 / σH) and the anisotropic factor β which is determined by the anisotropy ratio α2 = σv / σH = R "H / R" V and the diving angle θ. Conversely, neither anisotropy nor dive angle can be determined solely from coaxial measurements.

2. Both coplanar responses depend on horizontal resistivity, anisotropic factor, and dive angle.

3. In vertical wells with θ = 0, the coaxial response depends only on horizontal resistivity, while the coplanar response is determined by both horizontal resistivity and vertical resistivity.

4. In the horizontal register with θ = π / 2, the coaxial response depends on both horizontal resistivity and vertical resistivity, but coplanar response is determined solely by horizontal resistivity.

5. Due to when t is large, the dive angle is determined by:

<formula> formula see original document page 48 </formula> where 0 (u "2) denotes a remainder in the u2 order

Delayed Responses in a Homogeneous Anisotropic Formation

Similar to the research presented above regarding layer models, the retardation limits can be derived. Quandot © «χ», u2 © O and, consequently, these limits converge. Taking anisotropy into consideration, the retardation limits of equations (41) to (44) are:

(47) '{1 + | (<r - 1) sin "0 L;

<formula> formula see original document page 48 </formula>

The dive angle (deviation) is determined by:

<formula> formula see original document page 48 </formula>

The anisotropy ratio α can be determined from:

<formula> formula see original document page 48 </formula> When the dive angle θ is known or estimated, anisotropy correlation can be alternatively determined from:

<formula> formula see original document page 49 </formula>

It is also observed that the sum of the coaxial response with coplanar response Xx is independent of the approach angle.

Apparent conductivity for coaxial and coplanar responses in a homogeneous anisotropic formation

Similar to the investigation presented above regarding layer models, apparent conductivity is also a derivative amount of formation useful in the case of an anisotropic formation layer.

Apparent conductivity is defined for both coaxial (σzz (t)) and coplanar (σΧχ (t), σYy (t)) responses. Apparent conductivity is time-varying conductivity that would give the coaxial or coplanar response measured at time t if the formation were homogeneous and isotropic.

As before, apparent time-varying conductivities depend on the voltage response in a coaxial tool (VzZ (t)) or a coplanar tool (Vxx (t)) at each measurement time as:

<formula> formula see original document page 49 </formula>

Where

<formula> formula see original document page 49 </formula>

Then, at large t, the apparent conductivity approximates the value determined by the anisotropic conductivity and the dive angle as follows:

<formula> formula see original document page 50 </formula>

In terms of apparent conductivity,

<formula> formula see original document page 50 </formula>

The anisotropy ratio α can be estimated from the

relation of equations (61) and (60), and the estimated θ as:

<formula> formula see original document page 50 </formula>

Modeling Examples

FIGs. 41 to 45 refer to transient electromagnetic induction measurements and analysis thereof, in a homogeneous anisotropic formation for several β (in order of increasing anisotropy: 1.0; 0.8; 0.6; 0.4; 0.3 ) for a coaxial tool of L = 1m.

From these figures, FIG. 41 shows the calculated coaxial feedback responses for a formation where the conductivity in the horizontal direction σΗ = lS / m (RH = IQm). The lines show the voltage response as a function of time t (ranging from lE-08s to ΙΕ + OOs in a scalalogarithmic) after sudden transmitter switching. Line 101 corresponds to a homogeneous isotropic formation (β = 1.0) and should correspond exactly to a dipole solution. Lines 102, 103, 104, and 105 represent increasing anisotropy and correspond, respectively, to β = 0.8, β2 = 0.6, β2 = 0.4, and β2 = 0.3.

FIG. 42 shows apparent conductivity that was calculated from the responses as shown in FIG. 41. Same line numbers as FIG. 4 were used.

FIG. 43 is similar to FIG. 42, but shows the apparent behavior that was derived from calculated responses for formations with σΗ = 0.1S / m (RH = 10Qm). The same general behavior was found.

FIG. 44 is similar to FIGs. 42 and 43, but show apparent conductivity that was derived from calculated responses to formations with σΗ = 0.01S / m (RH = 100Qm). Again the same general behavior was found.

In each of FIGs. 42, 43, and 44, the delayed apparent conductivity is constant for each of the anisotropic factors, indicative of a macroscopically homogeneous formation. Apparent delayed conductivity decreases with anisotropic factor, as expected, because vertical conductivity along the main anisotropy axis is lower than horizontal conductivity.

FIG. 45 plots the delayed asymptotic conductivity value of the coaxial parent oZz (t -> oo) on σΗ against <formula> formula see original document page 51 </formula>

resulting result demonstrates the linear relationship. Taking anisotropy into account, the correct value of the horizontal resistivity of the formation (or conductivity) can then be extracted from the asymptotic coaxial apparent conductivity values.

Even for highly anisotropic formations, apparent conductivity is almost indistinguishable from the apparent conductivity of a homogeneous isotropic formation with lower conductivity. Interpretation errors can then easily be made if anisotropy is not taken into consideration when analyzing.

As follows from the above, anisotropy may be taken into consideration, for example by combining coaxial responses with copoplanar responses. The precise embodiment depends on which parameters are known or estimated. The sum of the coaxial response with the coplanarXx response is independent of the approach angle. If C and σκ are known or estimated, then the anisotropy ratio α follows the delayed dasoma value Vzz + Vxx. If, on the other hand, the approximation angle θ is known, C and σκ need not be known because the anisotropy relationship α can be derived from Eq. (53). If none of the other parameters are known, aEq. (52) may be employed requiring the combination of the coaxial response with two independent coplanar responses. Apparent dip in a homogeneous anisotropic formation.

In FIG. 46, apparent dip angles 0app (t) derived using Eq. (51) from the coaxial, coplanar cross-component calculated transient responses from a L = Im tool in a Rh = IOQm and Rv / Rh = 9 formation, for various approach angles, or dive angles. Line 106 corresponds to θ = 30 °; line 107 at θ = 45 °; line 108 at θ = 60 °; and line 109 at θ = 75 °.

The dive angle is then reflected precisely by the asymptotic value of the apparent dive. The asymptotic value is reached approximately lE-06s.

Apparent resistivity for coaxial and coplanar responses in a layer formation comprising multiple sublayers

FIG. 47 shows an electromagnetic induction tool 80 in a forming layer 110 comprising a sequence or package of alternating sublayer sets 112 and 114, the set 112 having electromagnetic properties, notably conductivity, which is different from the set 114. The tool axis is shown in the sublayer plane. .

Although each sublayer in the thin layer stratification may have isotropic properties such as isotropic conductivity, the combined effect of the sublayers may be the formation layer consisting of sublayers exhibiting an anisotropic electromagnetic induction. If the layer 112, 114, in the formation layer 110, acts as an individual resistor, the macroscopic resistivity (inverse conductivity) of the formation layer in one planar direction may be a result of all parallel layer resistors, while the macroscopic resistivity in one direction. Normal (ie perpendicular to the layers) can be a result of all layer resistors in series.

In the form of the equation:

(63)

<formula> formula see original document page 53 </formula>

for vertical resistivity, or main direction, and

<formula> formula see original document page 53 </formula>

for horizontal conductivity, or noplane, direction perpendicular to the main direction. Of course, σv can be found using σv = 1 / RV, and Rh can be found using Rh = 1 / σΗ. Therefore, the resistivity in the plane is typically lower than the resistivity in the main direction. These equations are also valid for more general cases where sublayers do not have the same thickness and / or sublayers do not have equal conductivity.

FIG. 48 shows the apparent resistivity calculated for the tool in the geometry of FIG. 47, where L = 1m; the resistivity of the sublayers 112 is 10 µm; The resistivity of the sublayers 114 is 1 μm and the subsurface is 10 m thick. Line 115 corresponds to the apparent resistivity for coaxial measurement geometry while line 116 corresponds to the apparent resistivity for coplanar measurement geometry.

The apparent resistivity, represented by lines 115 and 116, reflects the 1Ωm resistivity of the near layer in short time periods after the transmitter is turned off. After a time span of approximately 2E-5s, the apparent resistivity begins to increase due to the resistivity greater than 10m in the first adjacent sublayers 112. Until then, the apparent resistivity reflects the above for formations comprising two or three isotropic forming layers.

However, for the end times, the sublayers are no longer individually solved in the responses, and in this case the apparent resistivity is believed to reflect contributions from the sublayer where the tool80 is located, the adjacent layers, and the adjacent adjacent layers, and so on. . Effectively, transient responses will show macroscopic anisotropic behavior. In the example of Fig.48, the collection of isotropic sublayers that are not individually resolved in transient responses is described by assuming an anisotropic layer with an anisotropic ratio of α = RH / Rv = 1 (aHRv) = 1 / (0.55. 5 , 5) = 0.33, which can be found using the delayed apparent resistivities as shown above for homogeneous anisotropic formation. It is better to reverse the answers by assuming a homogeneous anisotropy than to try and determine the individual sublayer structure.

The dotted lines 117 and 118 in Fig. 48 which correspond to the calculated coaxial and coplanar apparent conductivities for Rh = 1.82 (i.e., l / 0.55) Qm and Rv = 5.5 5m closely match the drawn lines 115 e116, at large t.

The combined "macroscopic" anisotropic effect of a sub-stratified anomaly, as shown in FIG. 49, can also be observed. Here, anomaly A is formed of a formation layer having a thickness Δ comprising a finely laminated sequence of a first forming material Al, and a second forming material A2. AFIG. 49 also indicates coaxial measuring arrangements 60, coplanar 62, and cross-decomposing 64, wherein a transmitter coil T and a receiver coil R are spaced apart from each other L. The distance between the coil of the nearest Tea interface transmitter 55, between the next formation line and anomaly A is indicated by D1.

Using the principles presented above, the analysis, taking into consideration anisotropy, can be extended to multi-layer formations, including those where only one distant formation layer has macroscopic electromagnetic induction responses (as, for example, in FIG. 49), or where a locally formed layer, where transmitter and receiver antennas are located, has anisotropic behavior, but where one or more other isotropic or anisotropic layers are present at a distance.

Geodirectional Applications

As stated earlier in this specification, electromagnetic anisotropy may occur intrinsically in certain types of formations, such as shales. A shale can cover a reservoir of mineral hydrocarbon fluids. It would thus be beneficial to accurately locate a shale while drilling a well and to drill between, for example, 10m and 100m below the shale to allow optimal production of reservoir hydrocarbon fluids. This can be accomplished by traversing the shale, or by directing it downward from the head into a deflected well as a horizontal section.

In other cases, the hydrocarbon-containing reservoir may have been materialized as a pile of fine sands which themselves may exhibit anisotropic electromagnetic properties. It would be beneficial to identify the presence of these sands and direct the drill bit into these sands.

In each of these cases, geodirectionalization can be performed by performing electromagnetic transient analysis while drilling, taking into account the anisotropy of the formation. This can be implemented using the system as schematically described in FIG.

More generally, geodirectional decisions can be made based on the location of any type of electromagnetic anomaly using electromagnetic transient responses. These geodirectional applications allow more precisely locating reservoirs containing hydrocarbon fluids and more accurately drill into these reservoirs, allowing the production of hydrocarbon fluids from reservoirs with a minimum of water.

In order to produce mineral hydrocarbon fluid of geological formation, a wellbore can be drilled with a method comprising the steps of:

suspending a drill string in the geological formation, the drill string comprising at least one drill bit and a metering junction comprising a transmitter antenna and a receiver antenna;

drill a wellbore in the geological formation, induce an electromagnetic field in the geological formation using the transmitting antenna;

detect an electromagnetic transient response from the electromagnetic field using the receiving antenna;

derive an indication of geodirectional electromagnetic response.

Drilling of the wellbore can then proceed according to the geodirectional indication until a reservoir containing the hydrocarbon fluid is reached.

Since the wellbore extends into the reservoir containing mineral hydrocarbon fluid, the wellbore can be terminated in any conventional manner, and the mineral hydrocarbon fluid can be produced via the wellbore.

Geodirection can be based on the location of an electromagnetic anomaly in the geological formation, analyzing the transient response according to this specification, and making a location-based drilling decision with respect to the measuring junction. Anomaly allocation may be expressed in terms of the distance and / or direction of the measurement junction to the anomaly.

To facilitate execution of the drilling decision, the drilling column may comprise a steerable drilling system 19, as shown in FIG. IA The decision to drill may comprise controlling the direction of drilling, for example, using the steering system 19, if provided, and / or establishing the remaining distance to be drilled.

Accordingly, the geodirectional indication may comprise information reflecting the distance between the target in front of the drill and the drill, and / or the direction of the drill to the target. The distance and direction of the target drill can be calculated from the distance and direction of the tool to drill as long as the drill has a known position relative to the electromagnetic measuring tool.

Transient electromagnetic induction data can be correlated to the presence of a reservoir containing mineral hydrocarbon fluid directly by establishing conductivity values for the reservoir, or indirectly by establishing quantitative information on the formation layers that typically surround a reservoir containing mineral hydrocarbon fluid.

In preferred embodiments, the electromagnetic induction transient data processed according to the above is used to decide where to drill the wellbore and / or what is its preferred path or path. For example, someone may want to remain free of failures. Instead, or, moreover, it may be desirable to deviate from the true vertical drilling and / or direct into the reservoir at the correct depth.

The distance from the measuring junction to a forming anomaly may be determined from the time at which one of the apparent conductivity and apparent resistivity begins to deviate from a corresponding conductivity and resistivity of the formation in which the measuring junction is located and / or determined the time at which it is located. one of the apparent dive, and apparent azimuth and cross component response begin to drift from zero. Distance can also be determined from when any apparent dive and apparent azimuth reaches an asymptotic value.

The electromagnetic anomaly can be localized using at least one of the time-dependent apparent conductivity, the time-dependent apparent resistivity, the time-dependent dip angle, and the time-dependent azimuth angle from the time-dependent transient response, according to with the above, elsewhere.

Any of the above time dependencies may provide a useful indication of geo-directing. Fast image formation using apparent conductivity and apparent angle

Apparent conductivity and apparent plunging can also be used to create an "image" or representation of the formation characteristics. This is accomplished by collecting apparent transient conductivity data at different positions within the deposition hole.

The apparent conductivity should be constant and equal to the conductivity of the formation in a homogeneous formation. Deviation of a constant conductivity value over time (t) suggests the presence of a conductivity year in the region specified by time (t). The data collected can be used to create an image of the tooling formation.

When apparent resistivity graphs (Rapp (z; t)) or apparent conductivity graphs ((the app (z; t)), at different tool positions, are mutually arranged to form a graph in both coordinates zet, the graph, As a whole, it can be used as an image recorder to see the geometry of the formation, even if the layer resistivity cannot be determined immediately accurately.

An example of this transient data image representation is shown in FIG. 50 for a coaxial tool of L = 1. Coordinate ζ provides the depth of the tool along the wellbore. Graph σαρρ (z; t) shows the approach of the stratum boundary as the tool moves along the wellbore.

FIG. 51 shows another example. The coordinate ζ represents depth of the tool along the wellbore with the wellbore, in this case intersecting the layer boundary. The Oapp (z, t) graph clearly helps to visualize the approach and interception of the stratum limit as the tool moves along the wellbore, for example, while drilling the wellbore. Another example is shown in FIG. 52, where a three-layer model is used together with a coaxial tool having a spacing of 1m, at two different positions in the formation. The results are plotted in FIG. 53A, where the apparent resistivity Rapp (t) is plotted at various points as coaxial tool 80 approaches the resistive layer (see FIG. 53B).

FIG. 53A may be compared to FIG. 53B to discern the characteristics of the formation. Starting at IOQm Layer 82, the drop in Rapp (t) is attributable to IQm Layer 83 and the subsequent increase in Rapp (t) is attributable to IOOQm Layer 84. Curves (91, 92, 93) can easily be adjusted to inflection points to identify responses to various strata, effectively converting the formation into an image. Line 91 corresponds to the deflection points caused by the 1 83m stratum 83, aligns 92 to salt 84, and line 93 corresponds to the 10Ωm stratum82 deflection points. In addition, the 1 Ωm curve can easily be attributed to the direct signal collected between the transmitter and receiver when the tool is located in the 1 Ωm layer.

In yet another example, the apparent dip θαρρ (ί) can be used to generate an image record. In FIG. 54Aaxial tooling is seen as approaching a highly resistive formation at a dip angle of approximately 30 degrees. The apparent dip response is shown in FIG. 54B. Arrow 94 indicates a salt response with the tool at Z = 100. As noted previously, the time at which the apparent dive response occurs is indicative of the distance to formation. When responses for different distances are plotted with each other, an indicative response curve can be drawn when the tool approaches the stratum, as shown in FIG. 54B.

In short, the underground formation through a wellbore can be converted into image using a tool comprising a transmitter for transmitting electromagnetic signals through the formation and a receiver for detecting response signals in a procedure comprising steps where

- the tool is brought to a first position within the wellbore;

- the transmitter is energized to propagate an electromagnetic signal within the formation;

- a response signal that has propagated through deformation is detected;

- a derived amount is calculated for the formation based on the response signal detected for the formation;

- The amount derived for the formation is plotted against time.

The tool is then moved to at least one other position within the wellbore, where after that, the above steps are repeated. Optionally this can be done again. Then an image of the formation within the underground formation is created based on the derived quantity graphs.

Optionally, the tool is then moved back to at least one to several positions within the wellbore, and the entire procedure can be repeated.

Imaging the features of the formation may include identifying one or more inflection points in each derived quantity plotted and fitting a curve to one or more inflection points.

Thus, an image of the formation can be created using apparent conductivity / resistivity and the apparent dive angle, without the additional processing required for inversion and information extraction. This information is able to provide indications of geodirectionality as well as the ability to profile underground formations.

Claims (15)

1. Method for analyzing an underground formation through a wellbore, characterized by the use of a tool comprising a transmitting antenna and a receiving antenna, the underground forming comprising one or more forming layers, and the method comprising: suspending the tool inside the hole. induce one or more electromagnetic fields in the formation, detect one or more time-dependent transient response signals, analyze the one or more time-dependent transient response signals taking into account electromagnetic anisotropy of at least one of the formation layers. Method according to claim 1, characterized in that the pellet of at least one forming layer comprises three or more sublayers. A method according to claim 2, characterized in that one of the three or more sublayers has a first resistivity or conductivity different from a second resistivity or conductivity of another of the three or more sublayers. Method according to either of claims 2 or 3, characterized in that the sublayers which are not individually resolved in the transient response signals together are approximated as an anisotropic forming layer. Method according to any one of claims 1 to 4, characterized in that the analysis of one or more time-dependent transient response signals, taking into consideration the electromagnetic anisotropy, includes deriving an anisotropy parameter from at least one formation layer of the one or more more time-dependent transient response signals detected. Method according to claim 5, characterized in that the anisotropy parameter phage comprises at least one of a group of parameters comprising anisotropy index, anisotropic factor, conductivity along a major anisotropy axis, long resistivity of the main anisotropy axis, conductivity in a planoperpendicular to the main anisotropy axis; resistivity in a planoperpendicular to the main anisotropy axis; tooling axis angle relative to the main anisotropy axis. Method according to any one of claims 1 to 6, characterized in that the analysis of one or more transient response signals comprises the combination of multiaxial transient measurements, deference, biaxial or triaxial transient measurements, to derive an anisotropy parameter. A method according to any one of claims 1 to 7, characterized in that the analysis of one or more time-dependent transient response signals, taking into account the electromagnetic anisotropy, comprises deriving at least one time-dependent apparent conductivity, time-dependent apparent resistivity. , time dependent dip angle, and time dependent azimuth angle time dependent on the transient response signals. A method according to any one of claims 1 to 8, characterized in that one of the forming layers comprises an anomaly, and that analysis of one or more time-dependent transient response signals comprises determining at least one of distance and direction. between the tool and the anomaly of one or more time-dependent transient response signals. Method according to any one of claims 1 to 4, characterized in that the induction of one or more electromagnetic fields in the formation comprises generating a transmission and terminating the transmission, and detecting one or more time-dependent transient response signals comprising the measurement of a receiver response as a function of time following completion of transmission. Method for producing a geological formation mineral hydrocarbon fluid, comprising the steps of: suspending a drill string in the geological formation, the drill string comprising at least one drill bit and a measuring junction comprising a transmitting antenna and a receiving antenna; drill a wellbore in the geological formation; induce an electromagnetic field in the geological formation employing the transmitting antenna; detect one or more time-dependent electromagnetic response signals employing the receiving antenna; derive an indication of geo-direction of the electromagnetic response; continue drilling the wellbore according to the geodirectional indication until a reservoir containing the hydrocarbon fluid is reached, produce the hydrocarbon fluid, where the geodirectional indication derivation comprises analyzing or m or more time dependent transient response signals taking into account the electromagnetic anisotropy of at least one of the formation layers. Method according to claim 11, characterized in that the well drilling comprises operating a steerable drilling system in the geological formation. Method according to claim 11 or 12, characterized in that the geodirectional indication derivation comprises locating an electromagnetic anomaly in the geological formation based on one or more of the time-dependent transient response signals. A method according to claim 13, characterized in that the location of the electromagnetic anomaly comprises determining at least one distance from the measuring junction to the anomaly and the direction of the measuring junction to the anomaly. 15. Computer readable medium, characterized in that it contains computer readable instructions analyzing one or more time-dependent transient electromagnetic response signals that have been detected by a tool suspended inside a wellbore passing through an underground formation after induction of one or more electromagnetic fields in the formation, where computer readable instructions take into account the electromagnetic anisotropy of at least one layer of formation in the underground formation.