US20140003190A1 - Method for Gas Zone Detection Using Sonic Wave Attributes - Google Patents
Method for Gas Zone Detection Using Sonic Wave Attributes Download PDFInfo
- Publication number
- US20140003190A1 US20140003190A1 US14/016,134 US201314016134A US2014003190A1 US 20140003190 A1 US20140003190 A1 US 20140003190A1 US 201314016134 A US201314016134 A US 201314016134A US 2014003190 A1 US2014003190 A1 US 2014003190A1
- Authority
- US
- United States
- Prior art keywords
- stoneley
- determining
- formation
- borehole
- kick
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/40—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/40—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging
- G01V1/44—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging using generators and receivers in the same well
- G01V1/48—Processing data
Definitions
- This invention relates to wireline and logging-while-drilling measurement of sonic wave component attributes and use of that information for determining gas zones within a formation and/or kick detection. More specifically, this invention is directed to determining traditional compressional slowness (DTc), shear slowness (DTs) and Stoneley slowness (DTst) and in addition determining attributes of coherent energy (CE) and attenuation (ATT) for use in detecting the real time presence of gas in a formation and/or kick detection.
- DTc compressional slowness
- DTs shear slowness
- DTst Stoneley slowness
- CE coherent energy
- ATT attenuation
- acoustic tools are used to provide operationally significant information about borehole and formation attributes adjacent the tools such as compressional, shear and Stoneley slowness. These attributes are analyzed for determining, inter alia, the rate of flow of a hydrocarbon (gas or oil) out of a producing borehole in the hydrocarbon production industry. This critical information fundamentally depends on permeability of the formation, viscosity of the hydrocarbon and the existence of fractures. Collecting and recording this information on a delayed or real time basis is known as well logging.
- MWD measurements-while-drilling
- LWD logging-while-drilling
- acoustic well logging techniques that involve placing an acoustic tool within a well bore to make measurements indicative of formation attributes such as compressional slowness (DTc), shear slowness (DTs) and Stoneley slowness (DTst).
- Sonic logs can be used as direct indications of subsurface properties and in combination with other logs and knowledge of subsurface properties can be used to determine subsurface parameters, such as those related to borehole structure stability, that can not be measured directly.
- Rosenbaum Synthetic Microseismograms: Logging in Porous Formations”, Geophysics, Vol. 39, No. 1, (February 1974) the disclosure of which is incorporated by reference as though set forth at length.
- Acoustic logging tools typically include a transmitter and an array of axially spaced acoustic detectors or receivers. These tools are operable to detect, as examples, formation compressional waves (P), formation shear waves (S) and Stoneley waves. These measurements can be performed following drilling or intermediate drill string trips by wireline logging operations.
- sonic monopole tools can be used to measure compression waves (P) and shear waves (S) in fast formations.
- techniques have been developed where piezoelectric transmitters and hydrophone receivers are imbedded within the walls of drill string segments so that sonic LWD operations can be performed.
- Sonic wireline tools such as a Dipole Shear Sonic Imager (DSI—trademark of Schlumberger) and Schlumberger's Sonic Scanner generally have a multi-pole source.
- a multi-pole source may include monopole, dipole and quadrupole modes of excitation.
- the monopole mode of excitation is used traditionally to generate compressional and shear head waves in logging operations such that formation compressional and shear slowness logs can be obtained by processing the head wave components.
- the head wave components are non-dispersive and are generally processed by slowness-time-coherence (STC) methods as discussed in the Schlumberger Kimball et al. '691 patent and Vol. 49 Geophysics article noted above.
- STC slowness-time-coherence
- the slowness-time-coherence (STC) method is employed to process the monopole wireline or LWD sonic waveform signals for coherent arrivals, including the formation compressional, shear and borehole Stoneley waves.
- This method systematically computes the coherence (C) of the signals in time windows which start at a given time (T) and have a given window move-out slowness (S) across the array.
- the 2D plane C(S,T) is called the slowness-time-plane (STP). All the coherent arrivals in the waveform will show up in the STP as prominent coherent peaks.
- the compressional, shear and Stoneley slowness (DTc, DTs, and DTst) will be derived from the attributes of these coherent peaks.
- the attributes associated with the wave components found in the STP are the slowness, time and the peak coherence values. These three attributes are used in a labeling algorithm, discussed below, to determine the compressional, shear and Stoneley slowness from all of the STP peak candidates. These attributes can also be used for quality control purposes.
- the methods of the subject invention includes the slowness, time, coherence attributes and in addition the attributes of coherent energy and attenuation.
- the combination of these attributes can be advantageously used for detecting with well logging and logging while drilling operations formation gas zones and kick detection on a real time basis.
- FIG. 1 is a schematic of a typical derrick and a logging-while-drilling (LWD) system where a drill string is positioned within a borehole and a well logging segment near a drill bit is shown within a borehole;
- LWD logging-while-drilling
- FIG. 2 a is an enlarged diagram of a logging tool within a borehole taken at a location above a drill bit within a borehole of FIG. 1 ;
- FIG. 2 b is a schematic cross-sectional view of a quadrupole sonic transmitter taken from the LWD segment shown in FIG. 2 a.
- FIG. 2 c is a schematic cross-sectional view of a quadrupole receiver from a stack of receivers of the LWD tool shown in FIG. 2 a;
- FIG. 3 is a schematic diagram disclosing traditional sonic wave technology including a representative transmitter, receiver and compressional waves, shear waves and Stoneley sonic waves;
- FIG. 4 is a synthetic waveform illustrating waveform attribute computation
- FIG. 5 a is a graph depicting a combination of an increase in compressional slowness (DTc) along with a decline in compressional to shear velocity (Vp/Vs) indicative of the presence of gas;
- FIG. 5 b is a graph depicting the pattern of compressional and shear attenuation (ATTc and ATTs) when a gas zone is encountered;
- FIG. 5 c is a graph showing a pattern of shear and compressional energy (CEs and CEc) indicative of when a driller is about entering into a gas bearing formation;
- FIG. 6 a is a graph illustrating the effect on Stoneley slowness (DTst) of the influx of gas in a well bore;
- FIG. 6 b is a graphic illustration of the effect on a ratio of Stoneley slowness (DTst) to shear slowness (DTs) due to an influx of gas within a borehole;
- FIG. 6 c is a graph showing a baseline Stoneley coherent energy (CEst) and a baseline Stoneley attenuation (ATTst) and the effect due to an influx of gas useful for kick detection;
- FIG. 7 is an illustrative flow diagram for gas zone detection in accordance with one embodiment of the subject invention.
- FIG. 8 is an illustration of Gas Response Indicator (GRI) and Gas Flag (GF) as a function of Depth or Time for gas zone detection;
- FIG. 9 is a flow diagram for sonic attributes kick detection within a bore hole in accordance with another embodiment of the invention.
- FIG. 10 is an illustration of Gas Response Indicator (GRI) and Kick Flag (KF) as a function of depth or time to provide warning of an imminent gas kick event.
- GPI Gas Response Indicator
- KF Kick Flag
- the subject invention is directed to the concept of sonic measurements and systematically determining formation attributes of compressional, shear, and Stoneley slowness (DT) coherent energy (CE) and attenuation (ATT) and using the information on a real time basis to detect the presence of a gas zone or kick within a borehole.
- DT compressional, shear, and Stoneley slowness
- CE coherent energy
- ATT attenuation
- FIG. 1 discloses a drilling derrick 100 positioned over a well hole 102 being drilled into an earth formation 104 .
- the drilling derrick has the usual accompaniment of drilling equipment including a processor 106 and recorder 108 of the type used for measurements-while-drilling (MWD) or logging-while-drilling (LWD) operations.
- MWD measurements-while-drilling
- LWD logging-while-drilling
- the borehole is formed by a drill string 110 carrying a drill bit 112 at its distal end.
- the drill bit crushes its way through earth formations as the drill string is rotated by drilling equipment within the drilling derrick.
- the depth of a well will vary but may be as much at 25,000 feet or more in depth.
- FIGS. 2 a - 2 c a quadrupole acoustic shear wave LWD tool segment 114 is shown in a degree of schematic detail. A more detailed discussion of a LWD tool of this type can be seen in Hsu et al. Publication No. US 2003/0058739 of common assignment with the subject application. The disclosure of this entire publication is incorporated by reference here. Briefly, however, the quadrupole LWD tool segment 114 includes at least one transmitter ring 200 and an array of receivers 212 .
- FIG. 2 b illustrates a transmitter 200 divided into four quadrants 202 , 204 , 206 and 208 .
- Each quadrant contains a quarter-circle array of piezoelectric transducer elements 210 .
- FIG. 2B shows six piezoelectric transducer elements in each quadrant although in some embodiments nine elements may be preferred uniformly spaced around the azimuth.
- each receiver 214 of receiver array 212 has a quarter circle of piezoelectric transducer elements in each of quadrants 216 , 218 , 220 and 222 as shown in FIG. 2 c .
- Each ring transducer is capable of detecting a quadrupole shear wave refracted through a formation as discussed more fully in the above referenced Hsu et al publication US 2003/0058739.
- FIGS. 1-2 schematically disclose a LWD system where sonic transmitters and receivers are embedded within the side walls of a drill string near the drilling bit
- FIG. 3 discloses a wireline tool or sonde 300 which is lowered down a borehole suspended by a wireline 302 following a drill string tripping operation or subsequent logging following drilling operations.
- the sonde carries a transmitter 304 and an array of receivers 306 similar to the LWD tool discussed in connection with FIGS. 1 and 2 .
- the transmitting component 304 sends sonic waves 308 into the surrounding earth formation 310 and compressional or “P” waves 312 , shear or “S” waves 314 and Stoneley or tube waves 316 (that are propagated along the interface between a formation and the borehole fluid) are received by an array of the receiver components 306 as illustrated in FIGS. 2A-2C above.
- the subject invention expands the wave component attributes to include coherent energy (CE) and attenuation (ATT) which are useful in detecting the presence of formation gas and kick detection.
- CE coherent energy
- ATT attenuation
- FIG. 4 depicts a set of synthetic waveforms, as a function of time, as they appear to an array of receivers placed at equal intervals, 400 (RR), along the tool.
- the abscissa in FIG. 4 is the arrival time of sonic waves in micro seconds and the ordinate represents sonic receivers 1-12. (Equal spacing of receivers (RR) is not a requirement, although this assumption is made here to simplify calculations.)
- the compressional 402 , shear 404 , and borehole (or Stoneley) 406 wave components generally appear at different times and, because the components differ in “slowness” (S), move out across the array at different rates.
- a waveform arriving at time (T) at the first receiver will arrive at the nth receiver at time (T)+(n ⁇ 1) ⁇ (receiver spacing) ⁇ (S).
- the slowness-time-coherence (STC) method discussed in Kimball et al. Geophysics, above, is used to process the monopole wireline or LWD sonic waveform signals for coherent arrivals. This method systematically computes the coherence (C) of signals that start at the first receiver at time (T) and move out across the array at a rate corresponding to slowness (S). All of the coherent arrivals appear in the slowness-time plane (STP) as prominent coherent peaks.
- STP slowness-time plane
- Estimates of compressional, shear, and Stoneley slowness (DTc, DTs, and DTst) are derived from the attributes of these coherent peaks.
- the slowness (S) and arrival time at the first receiver (T) are used to construct a time window over the array.
- One such time window is shown in FIG. 4 .
- the time window is of the same length for each receiver, but, to account for the slowness (S) a time window that begins at time (T) for the first receiver will begin at time (T)+(n ⁇ 1) ⁇ (receiver spacing) ⁇ (S) for the nth receiver.
- the length of the window is the same as the (STC) computation window and consists of the number equally spaced points within a time window (nptw) at which the waveform is computed.
- hw(j,k) be the (discrete) Hilbert transform of w(j,k) in the time domain.
- the proposed invention uses the framework described above of defining several attributes of the wave components found in the slowness-time plane (STP).
- STP slowness-time plane
- the subject invention demonstrates the utility of coherent energy and attenuation attributes to oil and gas drilling and production operations.
- the wave component coherent energy attribute (CE) is computed for a given (S) and (T) in the (STP) by stacking the analytic signals across the array for a given time index “j”, multiplying the result by its conjugate to get the square of the magnitude for each “j”, and finally averaging over the time index “j”.
- the wave component attenuation attribute (ATT) is computed for a given (S) and (T) in the (STP) by using a linear least square fit algorithm to determine how TE(k), the total energy within the time window for receiver “k”, attenuates as a function of TR(k), the distance from the transmitter to the kth receiver.
- TE(k) is in a log scale with unit of dB referenced to 1 Pascal.
- ⁇ k 1 nrec ⁇ ( P ⁇ ( TR ⁇ ( k ) ) - TE ⁇ ( k ) ) 2
- the negative value of the coefficient “a 1 ” (which is normally negative) will be defined as the attenuation (ATT).
- the coefficient matrix (A) for the polynomial can be obtained from the data pairs by means of the matrix formula:
- A ( X T ⁇ X ) - 1 ⁇ X T ⁇ Y ⁇ ⁇
- A [ a 0 a 1 ... ... a n ]
- X [ 1 x 1 x 1 2 ... ... x 1 n 1 x 2 x 2 2 ... ... x 2 n ... ... ... ... ... ... ... ... ... ... ... ... ... 1 x N x N 2 ... ... x N n ]
- Y [ y 1 y 2 ... ... y N ]
- N nrec
- x i TR(i)
- y i TE(i)
- Gas even in trace amounts, affects certain wave components such as compressional waves and Stoneley waves. Accordingly, the attributes of the sonic wave components discussed above can be used to detect the presence of gas in the formation in real time.
- the sonic tool which may be 50 to 100 feet behind the drill bit, can provide the data needed to determine the attributes of the sonic wave components and can, therefore, provide a driller with near real-time detection of gas zones. This information will, for example, help the driller choose an appropriate mud weight so that the formation gas does not continually seep into the borehole. Alternatively, if the mud weight has to be lower for other drilling reasons, the driller could set pipe to protect the borehole from a gas zone.
- Stoneley (ST) waves Since gas will travel with the circulating mud uphole immediately, Stoneley (ST) waves, as detected by the sonic tool, will be affected by the presence of gas in the borehole well before the sonic tool reaches the gas zone.
- the attributes of the Stoneley waves may be the first indicators of gas in the formation. Gas, even a trace amount, is known to slow down and attenuate tremendously the Stoneley wave in the borehole over the sonic logging frequency range.
- the slowness (DT), coherent energy (CE), and the attenuation (ATT) attributes of the Stoneley wave components can be monitored as a function of depth to provide early detection of the presence of gas in a borehole.
- compressional (C) and shear (S) waves can also be used to detect the presence of gas.
- compressional waves are known to slow down and attenuate tremendously in the presence of a small amount of gas.
- the slowness and attenuation of the shear wave changes relatively little in the presence of gas.
- FIG. 5 illustrates how compressional and shear waveform attributes can be used to detect a gas zone.
- the three graphs in FIGS. 5 a , 5 b and 5 c show how the different attributes (slowness, attenuation, and coherent energy) are affected by the presence of gas.
- the three patterns of variation can be used to corroborate each other in identifying the presence of gas.
- DTc 500 increases rapidly, while the change in DTs 502 is relatively minor ( FIG. 5 a ). This results in a significant increase in the ratio DTc/DTs (or as shown in FIG. 5 a a significant decrease in its reciprocal (Vp/Vs 504 ) decrease in the compressional to shear velocity as the tool moves down the hole. If DTc increases due to lithology changes, as opposed to the presence of gas, Dts will also increase and the velocity ratio Vp/Vs is also likely to increase.
- the attenuation associated with shear waves, (ATTs) 506 is slightly higher than the attenuation associated with compressional waves, (ATTc) 508 ( FIG. 5 b ).
- Gas causes ATTc to increase more rapidly than ATTs, resulting in a crossover of the two curves—note point 510 in FIG. 5 b and the ratio ATTc/ATTs will increase.
- the coherent energy attribute of compressional waves, (CEc) 512 will also show a much greater rate of decrease than the coherent energy attribute of shear waves, (CEs) 514 (see FIG. 5 c ) in the presence of gas. Thus the ration CEC/CES will decrease.
- an alert could be triggered when the baseline Vp/Vs ratio decreases below a certain value.
- Increases in (DTc) and behavior of DTc/DT s , ATTc, ATTs, ATTc/ATTs, CEc, CEs and CEc/CEs, consistent with FIGS. 5 a - 5 c could be used to substantiate the presence of gas.
- Stoneley wave attributes are particularly sensitive indicators for the presence of gas in the well bore. Accordingly they can be used on a real time basis as incipient kick indicators to provide a driller with valuable reaction time for safe drilling of a well.
- the added reaction time provided by the Stoneley wave attributes, as opposed to compressional and shear wave attributes, may significantly increase drilling safety.
- the Stoneley slowness (DTst), attenuation (ATTst), and amplitude (CEst) are functions of the mud and formation properties.
- DTst Stoneley slowness
- ATTst attenuation
- CEst amplitude
- FIGS. 6 a - 6 c illustrate how Stoneley wave attributes can be used to construct a kick warning flag.
- the lithology of the zone of interest is shown to be essentially uniform, as verified by sonic delta-t logs (DTc 600 and DTs 602 ) and (GR 604 ) logs. These logs are controlled primarily by properties of the formation, while the Stoneley wave slowness, (DTst), is also sensitive to the borehole and mud properties.
- a sudden change in (DTst) in the uniform formation zone of FIG. 6 a usually implies significant influx of gas or formation fluid. An influx of gas will cause (DTst) to increase drastically (note 606 in FIG. 6 a ) while an influx of connate water will usually cause (DTst) to decrease somewhat (note 608 in FIG. 6 a ).
- FIG. 6 b depicts an increase of the ratio (DTst/DTs) 610 as compared with its baseline ratio, which is due to an influx gas.
- FIG. 6 b also depicts a decrease of the ratio (DTst/DTs) 612 as compared with its baseline, which is due an influx in formation fluid. It suggests that a trigger level for this ratio would be typically a certain fractional increase or decrease relative to the baseline of the (DTst/DTs) ratio.
- FIG. 6 c shows that an influx of gas will result in a significant increase in (ATTst) 614 , while (CEst) 616 will experience a rapid decrease.
- An influx of fluid will usually cause (ATTst) to decrease slightly (note 618 ), while (CEst) may increase somewhat (note 620 ).
- (ATTst) and (CEst) can, therefore, provide corroboration to a warning triggered by changes in the (DTst/DTs) ratio.
- Change detection logic can be used to set change flags (CFs) based on a given type of input that is continually generated as a tool proceeds down the borehole.
- FIGS. 7 and 9 are illustrative diagrams, based on the change detection logic described here, for gas zone detection and kick detection, respectively. Input used in the illustrative charts include:
- Attenuation ratio for compressional and shear waves (R ATT )
- the inputs involving compressional and shear waves are primarily useful in formation gas zone detection while the inputs involving Stoneley waves are primarily useful in kick detection.
- Gamma ray measurements could be used in both gas zone and kick detection, but are most useful in gas zone detection, since the Stoneley waves reacts almost immediately to a small amount of gas released to the borehole fluid at the bit.
- the gamma ray input will be particularly helpful for kick detection if the gamma ray sonde is very near or inside the bit.
- a Change Flag for a given type of input can take on the values 1, ⁇ 1, or 0, corresponding, respectively, to the input exhibiting a large increment, a large decrement, or no change, relative to previous measurements.
- a driller needs to determine how much past data is stored for comparison and how large an increment or decrement over earlier data is required to assign the flag a value of 1 or ⁇ 1.
- (N) represents the (user-chosen) amount of previous input data that is maintained for comparison.
- the most recent (N) inputs are placed in a buffer that maintains a running average (M)—the most recent (N) inputs are added and the result is divided by (N) to determine (M) at any given time.
- (M) will be the average over the inputs that have been recorded.
- a driller chosen number (D) represents the number that will be used to determine if a significant change has occurred.
- the most recent input (X) is compared with (M), the running average in the buffer. If (X ⁇ M>D), (CF) is set to 1 indicating a large increment in the particular input data. If (X ⁇ M ⁇ D), (CF) is set to ⁇ 1 indicating a large decrement in the particular input data. If
- the (N) and (D) will likely be different for the different kinds of input and thus are subscripted as (N in ) and (D in ) for generic index in.
- gas zone detection flags are used to detect gas-containing formations in the vicinity ( ⁇ 100 feet behind the bit) of the sonic tool.
- the gas in the formation may or may not seep out into the well bore depending on the mud weight and the bottom hole pressure.
- Stoneley or borehole waves may not provide instantaneous detection at the tool.
- this flow diagram exploits the changes—particular the relative changes—in coherent energy (CE), attenuation (ATT) and slowness (DT) of the compressional and shear waves to the presence of gas in the formation.
- Each of the four types of input has its own selected (N) (number of retained data points or the size of the data buffer) and (D) (the difference between the buffer average (M) and the most recent input data that will trigger a change flag for the type of input).
- the change flags (CFs) for the four types of input (each with value 1, ⁇ 1, or 0) 710 , 712 , 714 and 716 are used to compute the value of the Gas Zone Flag 718 , which may then trigger a response by the driller to suspected gas in the formation. The computation of this value may also involve driller-supplied weights.
- the weights assigned to the flags for the slowness and attenuation ratios (R DT and R ATT ) will be positive, and the weight assigned to the flag for the coherent energy ratio (R CE ) will be negative.
- the flag associated with gamma ray measurement may be incorporated as a separate term or a factor of the form: [1 ⁇ abs (CF GR )] in order to help eliminate setting a gas flag when changes are due to lithology.
- the Gas zone Flag (GF) in FIG. 7 behaves like a switch on state change indicator. If the attributes respond to the onset of gas, GF would be expected to increase from zero to a positive value depending on the weighting factors and the number of corresponding indicators. If the attributes remain unchanged, there will be no change in GF, whether gas is present or not present. If the sonic tool moves away from a gas zone, GF would take on a negative value signifying the disappearance of gas.
- the Gas Flag should be used in conjunction with a gas response indicator (GRI) which may be a combination of the basic attributes.
- GRI gas response indicator
- Wdt and Wce are nonnegative weighting coefficients.
- FIG. 8 illustrates the relationship between the Gas Flag 800 (GF) which is a state change indicator and Gas Response Indicator (GRI) 802 which takes on larger values when gas is present than when it is absent.
- GF Gas Flag
- GRI Gas Response Indicator
- kick detection flags are used to detect a small amount of gas released to the borehole fluid from the formation at the bit and, therefore, provide early warning time to a driller.
- Stoneley or borehole waves which exhibit predictable changes in coherent energy, attenuation and slowness in this situation, provide the primary method of detection.
- Change detection as described in the “Change Detection Logic” above, uses the following input data:
- GR Gamma Ray measurement
- Each of the four types of input has its own selected (N) (number of retained data points or the size of the data buffer) and (D) (the difference between the buffer average (M) and the most recent input data that will trigger a change flag for the type of input).
- the change flags (CFs) for the four types of input (each with value 1, ⁇ 1, or 0) 904 , 906 , 908 and 910 are used to compute the value of a Kick Detection Flag 912 , which may then trigger a response by the driller to suspected gas at the drill bit. The computation of this value will probably involve driller-supplied weights.
- a flag associated with gamma ray measurement may be incorporated as a separate term or a factor of the form: [1 ⁇ abs (CF GR )] if the gamma ray sonde is very near the drill bit.
- the Kick detection Flag (KF) in FIG. 9 behaves like a switch or state change indicator. As with the Gas zone Flag (GF) in FIG. 7 , this flag should be used in conjunction with a Gas Response Indicator (GRI). In this case, some examples of a GRI based on the attributes of Stoneley or borehole waves are:
- Wdt and Wce are nonnegative weighting coefficients.
- FIG. 10 illustrates the relationship between the Kick detection Flag (KF) 1000 and the Gas Response Indicator) GRI) 1002 , which takes on larger values when kick is imminent.
- the two indicators are used in combination to inform a driller of the possibility of a kick event.
Landscapes
- Physics & Mathematics (AREA)
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Acoustics & Sound (AREA)
- Environmental & Geological Engineering (AREA)
- Geology (AREA)
- Remote Sensing (AREA)
- General Life Sciences & Earth Sciences (AREA)
- General Physics & Mathematics (AREA)
- Geophysics (AREA)
- Geophysics And Detection Of Objects (AREA)
- Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
Abstract
A method for determining on a real time logging while drilling (LWD) basis gas within earth formations traversed by a borehole. Continuous LWD acoustic measurements are recorded and processed including coherent energy and attenuation attributes to detect downhole gas zones and kick during drilling operations.
Description
- This application is a continuation application of U.S. patent application Ser. No. 11/964,731, filed Dec. 27, 2007.
- This invention relates to wireline and logging-while-drilling measurement of sonic wave component attributes and use of that information for determining gas zones within a formation and/or kick detection. More specifically, this invention is directed to determining traditional compressional slowness (DTc), shear slowness (DTs) and Stoneley slowness (DTst) and in addition determining attributes of coherent energy (CE) and attenuation (ATT) for use in detecting the real time presence of gas in a formation and/or kick detection.
- In the oil and gas industry acoustic tools are used to provide operationally significant information about borehole and formation attributes adjacent the tools such as compressional, shear and Stoneley slowness. These attributes are analyzed for determining, inter alia, the rate of flow of a hydrocarbon (gas or oil) out of a producing borehole in the hydrocarbon production industry. This critical information fundamentally depends on permeability of the formation, viscosity of the hydrocarbon and the existence of fractures. Collecting and recording this information on a delayed or real time basis is known as well logging.
- Evaluation of physical properties such as pressure, temperature and wellbore trajectory in three-dimensional space and other borehole characteristics while extending a wellbore is known as measurements-while-drilling (MWD) and is standard practice in many drilling operations. MWD tools that measure formation parameters such as resistivity, porosity, sonic velocity, gamma ray, etc. of a formation are known as logging-while-drilling (LWD) tools. An essential formation parameter for determination in a drilling operation is the existence of gas deposits or zones in a formation, on a real time basis. Similarly, early detection of kick is essential information for conducting safe and efficient drilling operations.
- For the above and other reasons, the oil industry has developed acoustic well logging techniques that involve placing an acoustic tool within a well bore to make measurements indicative of formation attributes such as compressional slowness (DTc), shear slowness (DTs) and Stoneley slowness (DTst). Sonic logs can be used as direct indications of subsurface properties and in combination with other logs and knowledge of subsurface properties can be used to determine subsurface parameters, such as those related to borehole structure stability, that can not be measured directly. Early efforts in this connection were reported by Rosenbaum in “Synthetic Microseismograms: Logging in Porous Formations”, Geophysics, Vol. 39, No. 1, (February 1974) the disclosure of which is incorporated by reference as though set forth at length.
- Acoustic logging tools typically include a transmitter and an array of axially spaced acoustic detectors or receivers. These tools are operable to detect, as examples, formation compressional waves (P), formation shear waves (S) and Stoneley waves. These measurements can be performed following drilling or intermediate drill string trips by wireline logging operations. In wireline logging, sonic monopole tools can be used to measure compression waves (P) and shear waves (S) in fast formations. In addition to wireline logging, techniques have been developed where piezoelectric transmitters and hydrophone receivers are imbedded within the walls of drill string segments so that sonic LWD operations can be performed.
- Early wireline and LWD and sonic data processing techniques developed by the Schlumberger Technology Corporation such as a slowness-time-coherence (STC) method is disclosed in U.S. Pat. No. 4,594,691 to Kimball et al. entitled “Sonic Well Logging” as well as in Kimball et al. “Semblance Processing of Borehole Acoustic Array Data,” Geophysics, Vol. 49, No. 3 (March 1984). This method is most useful for non-dispersive waveforms (e.g. monopole compressional and shear head waves). For processing dispersive waveforms a dispersive slowness-time-coherence (DSTC) is preferred. This process is disclosed in U.S. Pat. No. 5,278,805 to Kimball entitled “Sonic Well Logging Methods and Apparatus Utilizing Dispersive Wave Processing.” The disclosures of these patents, of common assignment with the subject application, as well as the noted Geophysics publication authored by an employee of Schlumberger are hereby also incorporated by reference.
- Sonic wireline tools, such as a Dipole Shear Sonic Imager (DSI—trademark of Schlumberger) and Schlumberger's Sonic Scanner generally have a multi-pole source. A multi-pole source may include monopole, dipole and quadrupole modes of excitation. The monopole mode of excitation is used traditionally to generate compressional and shear head waves in logging operations such that formation compressional and shear slowness logs can be obtained by processing the head wave components. The head wave components are non-dispersive and are generally processed by slowness-time-coherence (STC) methods as discussed in the Schlumberger Kimball et al. '691 patent and Vol. 49 Geophysics article noted above.
- The slowness-time-coherence (STC) method is employed to process the monopole wireline or LWD sonic waveform signals for coherent arrivals, including the formation compressional, shear and borehole Stoneley waves. This method systematically computes the coherence (C) of the signals in time windows which start at a given time (T) and have a given window move-out slowness (S) across the array. The 2D plane C(S,T) is called the slowness-time-plane (STP). All the coherent arrivals in the waveform will show up in the STP as prominent coherent peaks. The compressional, shear and Stoneley slowness (DTc, DTs, and DTst) will be derived from the attributes of these coherent peaks.
- Traditionally, the attributes associated with the wave components found in the STP are the slowness, time and the peak coherence values. These three attributes are used in a labeling algorithm, discussed below, to determine the compressional, shear and Stoneley slowness from all of the STP peak candidates. These attributes can also be used for quality control purposes.
- Although determining traditional attributes has been highly effective in the past a need exists for enhancing information that can be determined from traditional wave form attributes and determining additional attributes such as coherent energy and attenuation that can be used to determine the existence of a gas zone and/or kick detection, on a real time basis, during LWD operations.
- The methods of the subject invention includes the slowness, time, coherence attributes and in addition the attributes of coherent energy and attenuation. The combination of these attributes can be advantageously used for detecting with well logging and logging while drilling operations formation gas zones and kick detection on a real time basis.
- Other aspects of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.
-
FIG. 1 is a schematic of a typical derrick and a logging-while-drilling (LWD) system where a drill string is positioned within a borehole and a well logging segment near a drill bit is shown within a borehole; -
FIG. 2 a is an enlarged diagram of a logging tool within a borehole taken at a location above a drill bit within a borehole ofFIG. 1 ; -
FIG. 2 b is a schematic cross-sectional view of a quadrupole sonic transmitter taken from the LWD segment shown inFIG. 2 a. -
FIG. 2 c is a schematic cross-sectional view of a quadrupole receiver from a stack of receivers of the LWD tool shown inFIG. 2 a; -
FIG. 3 is a schematic diagram disclosing traditional sonic wave technology including a representative transmitter, receiver and compressional waves, shear waves and Stoneley sonic waves; -
FIG. 4 is a synthetic waveform illustrating waveform attribute computation; -
FIG. 5 a is a graph depicting a combination of an increase in compressional slowness (DTc) along with a decline in compressional to shear velocity (Vp/Vs) indicative of the presence of gas; -
FIG. 5 b is a graph depicting the pattern of compressional and shear attenuation (ATTc and ATTs) when a gas zone is encountered; -
FIG. 5 c is a graph showing a pattern of shear and compressional energy (CEs and CEc) indicative of when a driller is about entering into a gas bearing formation; -
FIG. 6 a is a graph illustrating the effect on Stoneley slowness (DTst) of the influx of gas in a well bore; -
FIG. 6 b is a graphic illustration of the effect on a ratio of Stoneley slowness (DTst) to shear slowness (DTs) due to an influx of gas within a borehole; -
FIG. 6 c is a graph showing a baseline Stoneley coherent energy (CEst) and a baseline Stoneley attenuation (ATTst) and the effect due to an influx of gas useful for kick detection; -
FIG. 7 is an illustrative flow diagram for gas zone detection in accordance with one embodiment of the subject invention; -
FIG. 8 is an illustration of Gas Response Indicator (GRI) and Gas Flag (GF) as a function of Depth or Time for gas zone detection; -
FIG. 9 is a flow diagram for sonic attributes kick detection within a bore hole in accordance with another embodiment of the invention; and -
FIG. 10 is an illustration of Gas Response Indicator (GRI) and Kick Flag (KF) as a function of depth or time to provide warning of an imminent gas kick event. - Turning now to the drawings, the subject invention is directed to the concept of sonic measurements and systematically determining formation attributes of compressional, shear, and Stoneley slowness (DT) coherent energy (CE) and attenuation (ATT) and using the information on a real time basis to detect the presence of a gas zone or kick within a borehole.
-
FIG. 1 discloses adrilling derrick 100 positioned over awell hole 102 being drilled into anearth formation 104. The drilling derrick has the usual accompaniment of drilling equipment including aprocessor 106 andrecorder 108 of the type used for measurements-while-drilling (MWD) or logging-while-drilling (LWD) operations. A more detailed disclosure of conventional drilling equipment of the type envisioned here is described in Schlumberger's Wu et al published application No. 2006/0120217 the disclosure of which is incorporated by reference as though set forth at length. - The borehole is formed by a
drill string 110 carrying adrill bit 112 at its distal end. The drill bit crushes its way through earth formations as the drill string is rotated by drilling equipment within the drilling derrick. The depth of a well will vary but may be as much at 25,000 feet or more in depth. - Turning to
FIGS. 2 a-2 c a quadrupole acoustic shear waveLWD tool segment 114 is shown in a degree of schematic detail. A more detailed discussion of a LWD tool of this type can be seen in Hsu et al. Publication No. US 2003/0058739 of common assignment with the subject application. The disclosure of this entire publication is incorporated by reference here. Briefly, however, the quadrupoleLWD tool segment 114 includes at least onetransmitter ring 200 and an array ofreceivers 212. -
FIG. 2 b illustrates atransmitter 200 divided into fourquadrants piezoelectric transducer elements 210.FIG. 2B shows six piezoelectric transducer elements in each quadrant although in some embodiments nine elements may be preferred uniformly spaced around the azimuth. - As noted above an array of
quadrupole receivers 212 is shown inFIG. 2 a embedded within the side wall ofdrill pipe segment 114. These receivers are equally spaced vertically and may be ten to fifty or more in a vertical array. The receivers are similar to the transmitter in that eachreceiver 214 ofreceiver array 212 has a quarter circle of piezoelectric transducer elements in each ofquadrants FIG. 2 c. Each ring transducer is capable of detecting a quadrupole shear wave refracted through a formation as discussed more fully in the above referenced Hsu et al publication US 2003/0058739. - While
FIGS. 1-2 schematically disclose a LWD system where sonic transmitters and receivers are embedded within the side walls of a drill string near the drilling bit,FIG. 3 discloses a wireline tool orsonde 300 which is lowered down a borehole suspended by a wireline 302 following a drill string tripping operation or subsequent logging following drilling operations. The sonde carries atransmitter 304 and an array ofreceivers 306 similar to the LWD tool discussed in connection withFIGS. 1 and 2 . In this, the transmittingcomponent 304 sendssonic waves 308 into the surroundingearth formation 310 and compressional or “P” waves 312, shear or “S” waves 314 and Stoneley or tube waves 316 (that are propagated along the interface between a formation and the borehole fluid) are received by an array of thereceiver components 306 as illustrated inFIGS. 2A-2C above. - Measurement of arrivals of these waveforms will show up in a slowness-time plane (STP) as prominent coherent peaks. The compressional, shear and Stoneley slowness (DTc, DTs and DTst) will be derived from the attributes of these coherent peaks. The subject invention expands the wave component attributes to include coherent energy (CE) and attenuation (ATT) which are useful in detecting the presence of formation gas and kick detection.
-
FIG. 4 depicts a set of synthetic waveforms, as a function of time, as they appear to an array of receivers placed at equal intervals, 400 (RR), along the tool. The abscissa inFIG. 4 is the arrival time of sonic waves in micro seconds and the ordinate represents sonic receivers 1-12. (Equal spacing of receivers (RR) is not a requirement, although this assumption is made here to simplify calculations.) AsFIG. 4 illustrates, the compressional 402,shear 404, and borehole (or Stoneley) 406 wave components generally appear at different times and, because the components differ in “slowness” (S), move out across the array at different rates. - A waveform arriving at time (T) at the first receiver will arrive at the nth receiver at time (T)+(n−1)·(receiver spacing)·(S). The slowness-time-coherence (STC) method discussed in Kimball et al. Geophysics, above, is used to process the monopole wireline or LWD sonic waveform signals for coherent arrivals. This method systematically computes the coherence (C) of signals that start at the first receiver at time (T) and move out across the array at a rate corresponding to slowness (S). All of the coherent arrivals appear in the slowness-time plane (STP) as prominent coherent peaks. Estimates of compressional, shear, and Stoneley slowness (DTc, DTs, and DTst) are derived from the attributes of these coherent peaks.
- For each coherent peak in the S/T plane, the slowness (S) and arrival time at the first receiver (T) are used to construct a time window over the array. One such time window is shown in
FIG. 4 . The time window is of the same length for each receiver, but, to account for the slowness (S) a time window that begins at time (T) for the first receiver will begin at time (T)+(n−1)·(receiver spacing)·(S) for the nth receiver. The length of the window is the same as the (STC) computation window and consists of the number equally spaced points within a time window (nptw) at which the waveform is computed. - Let TR(k), k=1, 2, . . . , number of receivers (nrec) be the transmitter-to-receiver distance for the k-th receiver. Under the assumption of equal spacing, (RR), between adjacent receivers, TR(k+1)−TR(k)=RR, k=1, 2, . . . , nrec−1.
- Let w(j,k), j=1, 2, . . . , (nptw), k=1, 2, . . . , (nrec) be the sampled waveform (at the “j”th sampling point and at the “k”th receiver) within the selected time window—“j” represents the time index, and “k” represents the receiver index.
- Let hw(j,k) be the (discrete) Hilbert transform of w(j,k) in the time domain. The analytic representation of the signal, wa (j,k), is a complex signal defined in terms of w(j,k) and hw(j,k): wa (j,k)=w(j,k)+(i)·(hw(j,k)).
- The proposed invention uses the framework described above of defining several attributes of the wave components found in the slowness-time plane (STP). In addition to slowness, time, and coherence, however, the subject invention demonstrates the utility of coherent energy and attenuation attributes to oil and gas drilling and production operations.
- The wave component coherent energy attribute (CE) is computed for a given (S) and (T) in the (STP) by stacking the analytic signals across the array for a given time index “j”, multiplying the result by its conjugate to get the square of the magnitude for each “j”, and finally averaging over the time index “j”. Specifically:
-
- The wave component attenuation attribute (ATT) is computed for a given (S) and (T) in the (STP) by using a linear least square fit algorithm to determine how TE(k), the total energy within the time window for receiver “k”, attenuates as a function of TR(k), the distance from the transmitter to the kth receiver.
- The total energy within the time window for receiver “k”, TE(k), is computed using the formula:
-
- Here, TE(k) is in a log scale with unit of dB referenced to 1 Pascal.
- For the set of real data pairs (TR(k), TE(k)), k=1, nrec, an nth order least squares fit polynomial Pn(x)=a0+a1x+ . . . +anxn can be constructed for n≦nrec−1. This polynomial will minimize:
-
- over all polynomials (P) of degree≦n.
- The linear least square fit polynomial, P1(x)=a0+a1x, is used here to determine the attenuation attribute. In particular, the negative value of the coefficient “a1” (which is normally negative) will be defined as the attenuation (ATT).
- In the general case of the nth order least square fit polynomial for the data set {(xi, yi), i=1, 2, . . . , N} where N≧n−1, the coefficient matrix (A) for the polynomial can be obtained from the data pairs by means of the matrix formula:
-
- For the linear least square fit polynomial where n=1, this formula for the coefficients reduces to:
-
- For the particular application involving attenuation, as described above, N=nrec; xi=TR(i), the distance between the transmitter and the “i”th receiver; and yi=TE(i), the total energy at the “i”th receiver.
- Where: (ATT), the attenuation, =−a1
- Gas, even in trace amounts, affects certain wave components such as compressional waves and Stoneley waves. Accordingly, the attributes of the sonic wave components discussed above can be used to detect the presence of gas in the formation in real time.
- When a drill bit penetrates a gas-bearing formation with unexpected high pressure (higher than the mud pressure), gas may seep into the well bore. The sonic tool, which may be 50 to 100 feet behind the drill bit, can provide the data needed to determine the attributes of the sonic wave components and can, therefore, provide a driller with near real-time detection of gas zones. This information will, for example, help the driller choose an appropriate mud weight so that the formation gas does not continually seep into the borehole. Alternatively, if the mud weight has to be lower for other drilling reasons, the driller could set pipe to protect the borehole from a gas zone.
- Since gas will travel with the circulating mud uphole immediately, Stoneley (ST) waves, as detected by the sonic tool, will be affected by the presence of gas in the borehole well before the sonic tool reaches the gas zone. Thus, the attributes of the Stoneley waves may be the first indicators of gas in the formation. Gas, even a trace amount, is known to slow down and attenuate tremendously the Stoneley wave in the borehole over the sonic logging frequency range. The slowness (DT), coherent energy (CE), and the attenuation (ATT) attributes of the Stoneley wave components can be monitored as a function of depth to provide early detection of the presence of gas in a borehole.
- The attributes of compressional (C) and shear (S) waves can also be used to detect the presence of gas. Like the Stoneley waves, compressional waves are known to slow down and attenuate tremendously in the presence of a small amount of gas. On the other hand, the slowness and attenuation of the shear wave changes relatively little in the presence of gas.
-
FIG. 5 illustrates how compressional and shear waveform attributes can be used to detect a gas zone. The three graphs inFIGS. 5 a, 5 b and 5 c show how the different attributes (slowness, attenuation, and coherent energy) are affected by the presence of gas. The three patterns of variation can be used to corroborate each other in identifying the presence of gas. - In the gas zone,
DTc 500 increases rapidly, while the change inDTs 502 is relatively minor (FIG. 5 a). This results in a significant increase in the ratio DTc/DTs (or as shown inFIG. 5 a a significant decrease in its reciprocal (Vp/Vs 504) decrease in the compressional to shear velocity as the tool moves down the hole. If DTc increases due to lithology changes, as opposed to the presence of gas, Dts will also increase and the velocity ratio Vp/Vs is also likely to increase. - Normally, in formations without gas, the attenuation associated with shear waves, (ATTs) 506, is slightly higher than the attenuation associated with compressional waves, (ATTc) 508 (
FIG. 5 b). Gas causes ATTc to increase more rapidly than ATTs, resulting in a crossover of the two curves—note point 510 inFIG. 5 b and the ratio ATTc/ATTs will increase. - The coherent energy attribute of compressional waves, (CEc) 512, will also show a much greater rate of decrease than the coherent energy attribute of shear waves, (CEs) 514 (see
FIG. 5 c) in the presence of gas. Thus the ration CEC/CES will decrease. - Data from the compressional and shear wave attributes as a function of depth or time, as depicted in
FIGS. 5 a-5 c, can be used to set a trigger level or gas zone flag that is sent uphole to warn the driller of entry into a gas bearing formation. As an example, an alert could be triggered when the baseline Vp/Vs ratio decreases below a certain value. Increases in (DTc) and behavior of DTc/DTs, ATTc, ATTs, ATTc/ATTs, CEc, CEs and CEc/CEs, consistent withFIGS. 5 a-5 c, could be used to substantiate the presence of gas. - A sudden infusion of fluid or gas within a borehole is known as kick. Stoneley wave attributes (DTst, ATTst, and CEst) are particularly sensitive indicators for the presence of gas in the well bore. Accordingly they can be used on a real time basis as incipient kick indicators to provide a driller with valuable reaction time for safe drilling of a well. The added reaction time provided by the Stoneley wave attributes, as opposed to compressional and shear wave attributes, may significantly increase drilling safety.
- The Stoneley slowness (DTst), attenuation (ATTst), and amplitude (CEst) are functions of the mud and formation properties. When drilling through formations of the same lithology, the variation in these Stoneley wave attributes are sensitive indicators of kick of gas or formation fluid. Normally, these attributes will be very slowly changing variables within a given zone of the same lithology. Their baseline values, as a function of time or well depth, can be established by other LWD measurement techniques such as gamma ray (GR), sonic delta-t, resistivity and nuclear tools. Any abrupt changes in the attributes may signify the possible influx of gas or formation fluids and will, therefore, trigger a warning flag.
-
FIGS. 6 a-6 c illustrate how Stoneley wave attributes can be used to construct a kick warning flag. InFIG. 6 a, the lithology of the zone of interest is shown to be essentially uniform, as verified by sonic delta-t logs (DTc 600 and DTs 602) and (GR 604) logs. These logs are controlled primarily by properties of the formation, while the Stoneley wave slowness, (DTst), is also sensitive to the borehole and mud properties. A sudden change in (DTst) in the uniform formation zone ofFIG. 6 a usually implies significant influx of gas or formation fluid. An influx of gas will cause (DTst) to increase drastically (note 606 inFIG. 6 a) while an influx of connate water will usually cause (DTst) to decrease somewhat (note 608 inFIG. 6 a). - In order to detect a sudden change in Stoneley slowness due to an influx of gas or fluid, it may be advantageous to monitor the ratio (DTst/DTs), which can normalize some variation in (DTst) due to changes in the properties of the formation.
FIG. 6 b depicts an increase of the ratio (DTst/DTs) 610 as compared with its baseline ratio, which is due to an influx gas.FIG. 6 b also depicts a decrease of the ratio (DTst/DTs) 612 as compared with its baseline, which is due an influx in formation fluid. It suggests that a trigger level for this ratio would be typically a certain fractional increase or decrease relative to the baseline of the (DTst/DTs) ratio. -
FIG. 6 c shows that an influx of gas will result in a significant increase in (ATTst) 614, while (CEst) 616 will experience a rapid decrease. An influx of fluid will usually cause (ATTst) to decrease slightly (note 618), while (CEst) may increase somewhat (note 620). (ATTst) and (CEst) can, therefore, provide corroboration to a warning triggered by changes in the (DTst/DTs) ratio. - Change detection logic can be used to set change flags (CFs) based on a given type of input that is continually generated as a tool proceeds down the borehole.
FIGS. 7 and 9 are illustrative diagrams, based on the change detection logic described here, for gas zone detection and kick detection, respectively. Input used in the illustrative charts include: - Gamma Ray measurement (GR)
- Coherent Energy ratio for compressional and shear waves (RCE)
- Attenuation ratio for compressional and shear waves (RATT)
- Slowness ratio for compressional and shear waves (RDT)
- Coherent Energy for Stoneley waves (CEST)
- Attenuation for Stoneley waves (ATTST)
- Slowness for Stoneley Waves (DTST)
- The inputs involving compressional and shear waves are primarily useful in formation gas zone detection while the inputs involving Stoneley waves are primarily useful in kick detection. Gamma ray measurements could be used in both gas zone and kick detection, but are most useful in gas zone detection, since the Stoneley waves reacts almost immediately to a small amount of gas released to the borehole fluid at the bit. The gamma ray input will be particularly helpful for kick detection if the gamma ray sonde is very near or inside the bit.
- A Change Flag for a given type of input can take on the
values 1, −1, or 0, corresponding, respectively, to the input exhibiting a large increment, a large decrement, or no change, relative to previous measurements. A driller needs to determine how much past data is stored for comparison and how large an increment or decrement over earlier data is required to assign the flag a value of 1 or −1. - If (N) represents the (user-chosen) amount of previous input data that is maintained for comparison. The most recent (N) inputs are placed in a buffer that maintains a running average (M)—the most recent (N) inputs are added and the result is divided by (N) to determine (M) at any given time. In the start-up period when the buffer is not full, (M) will be the average over the inputs that have been recorded.
- A driller chosen number (D) represents the number that will be used to determine if a significant change has occurred. The most recent input (X) is compared with (M), the running average in the buffer. If (X−M>D), (CF) is set to 1 indicating a large increment in the particular input data. If (X−M<−D), (CF) is set to −1 indicating a large decrement in the particular input data. If |X−M|≦(D), (CF) is set to 0 indicating no significant change in the input data.
- The (N) and (D) will likely be different for the different kinds of input and thus are subscripted as (Nin) and (Din) for generic index in.
- In
FIG. 7 gas zone detection flags are used to detect gas-containing formations in the vicinity (˜100 feet behind the bit) of the sonic tool. The gas in the formation may or may not seep out into the well bore depending on the mud weight and the bottom hole pressure. Thus, Stoneley or borehole waves may not provide instantaneous detection at the tool. Thus, this flow diagram exploits the changes—particular the relative changes—in coherent energy (CE), attenuation (ATT) and slowness (DT) of the compressional and shear waves to the presence of gas in the formation. - Unfortunately, the responses of the compressional and shear waves also vary with lithology or rock type. Lithology change is reflected independently using gamma ray measurement and this measurement is used to minimize false alarms triggered by changes in the compressional and shear waves due to lithology.
- Change detection, as described in the “Change Detection Logic” discussed above, relies on the following input data and derived ratios:
-
- Gamma Ray measurement (GR)—
box 702; - Coherent Energy ratio for compressional and shear waves (RCE=CEc/CEs)—
boxes - Attenuation ratio for compressional and shear waves (RATT=ATTc/ATTs)
boxes - Slowness ratio for compressional and shear waves (RDT=DTc/DTs)
boxes
- Gamma Ray measurement (GR)—
- Each of the four types of input has its own selected (N) (number of retained data points or the size of the data buffer) and (D) (the difference between the buffer average (M) and the most recent input data that will trigger a change flag for the type of input). The change flags (CFs) for the four types of input (each with
value 1, −1, or 0) 710, 712, 714 and 716 are used to compute the value of theGas Zone Flag 718, which may then trigger a response by the driller to suspected gas in the formation. The computation of this value may also involve driller-supplied weights. To get a correct result, the weights assigned to the flags for the slowness and attenuation ratios (RDT and RATT) will be positive, and the weight assigned to the flag for the coherent energy ratio (RCE) will be negative. The flag associated with gamma ray measurement may be incorporated as a separate term or a factor of the form: [1−abs (CFGR)] in order to help eliminate setting a gas flag when changes are due to lithology. - The Gas zone Flag (GF) in
FIG. 7 behaves like a switch on state change indicator. If the attributes respond to the onset of gas, GF would be expected to increase from zero to a positive value depending on the weighting factors and the number of corresponding indicators. If the attributes remain unchanged, there will be no change in GF, whether gas is present or not present. If the sonic tool moves away from a gas zone, GF would take on a negative value signifying the disappearance of gas. - The Gas Flag (GF) should be used in conjunction with a gas response indicator (GRI) which may be a combination of the basic attributes. The following are some examples of GRI that will have higher values in a gas zone.
-
GRI=ATTc/ATTs*DTc/DTs*CEs/CEc -
GRI=(DTc*ATTc)/CEc -
GRI=Att*ATTc/ATTs+Wdt*DTc/DTs+Wce*CEs/CEc - where Watt, Wdt and Wce are nonnegative weighting coefficients.
-
FIG. 8 illustrates the relationship between the Gas Flag 800 (GF) which is a state change indicator and Gas Response Indicator (GRI) 802 which takes on larger values when gas is present than when it is absent. The two indicators would be used in combination to inform the decision maker of the presence of a gas zone. - In
FIG. 9 kick detection flags are used to detect a small amount of gas released to the borehole fluid from the formation at the bit and, therefore, provide early warning time to a driller. Stoneley or borehole waves, which exhibit predictable changes in coherent energy, attenuation and slowness in this situation, provide the primary method of detection. - Change detection, as described in the “Change Detection Logic” above, uses the following input data:
- Gamma Ray measurement (GR)—
box 900; - Coherent Energy for Stoneley waves (CEST)—
box 902; - Attenuation for Stoneley waves (ATTST)—
box 902; and - Slowness for Stoneley Waves (DTST)—
box 902. - Each of the four types of input has its own selected (N) (number of retained data points or the size of the data buffer) and (D) (the difference between the buffer average (M) and the most recent input data that will trigger a change flag for the type of input). The change flags (CFs) for the four types of input (each with
value 1, −1, or 0) 904, 906, 908 and 910 are used to compute the value of aKick Detection Flag 912, which may then trigger a response by the driller to suspected gas at the drill bit. The computation of this value will probably involve driller-supplied weights. To get the correct result, the weights assigned to the flags for Stoneley slowness and attenuation (DTst and ATTst) will be positive, and the weight assigned to the flag for the coherent energy (CEst) will be negative. A flag associated with gamma ray measurement may be incorporated as a separate term or a factor of the form: [1−abs (CFGR)] if the gamma ray sonde is very near the drill bit. - The Kick detection Flag (KF) in
FIG. 9 behaves like a switch or state change indicator. As with the Gas zone Flag (GF) inFIG. 7 , this flag should be used in conjunction with a Gas Response Indicator (GRI). In this case, some examples of a GRI based on the attributes of Stoneley or borehole waves are: -
GRI=(ATTst*DTst)/CEst -
GRI=Watt*ATTst+Wdt*DTst+Wce/CEst - where Watt, Wdt and Wce are nonnegative weighting coefficients.
-
FIG. 10 illustrates the relationship between the Kick detection Flag (KF) 1000 and the Gas Response Indicator) GRI) 1002, which takes on larger values when kick is imminent. The two indicators are used in combination to inform a driller of the possibility of a kick event. - The various aspects of the invention were chosen and described in order to best explain principles of the invention and its practical applications. The preceding description is intended to enable those of skill in the art to best utilize the invention in various embodiments and aspects and with modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims.
Claims (10)
1. A method for determining the presence of a formation gas kick on a real time basis by a logging while drilling process comprising:
emitting periodic sonic wave energy toward a borehole formation by a logging while drilling tool;
receiving Stoneley waveform signals transmitted within the borehole;
determining the lithology of formations as drilling progresses;
determining the Stoneley wave slowness (DTst) within the well bore; and
for an essentially uniform formation lithology determining the presence of gas kick within the borehole by a sudden change at different depths in Stoneley slowness (DTst) over formations with essentially similar lithology.
2. A method for determining the presence of a formation gas kick on a real time basis by a logging while drilling process as defined in claim 1 and further comprising:
determining the Stoneley wave attenuation (ATTst) within the well bore; and
for an essentially uniform formation lithology confirming the presence of a gas kick within the borehole by a sudden increase in Stoneley attenuation (ATTst).
3. A method for determining the presence of formation gas kick on a real time basis by a logging while drilling process as defined in claim 1 and further setting as gas kick flag comprising:
detecting a change in the Stoneley slowness (DTst); and
setting a kick flag to warn a driller of the drilling operation encountering a formation gas kick in the event the detected change in (DTst) exceeds a set value.
4. A method for determining the presence of a formation gas kick on a real time basis by a logging while drilling process as defined in claim 1 and further comprising:
determining the Stoneley wave coherent energy (CEst) within the well bore; and
for an essentially uniform formation lithology confirming the presence of a gas kick within the borehole by a sudden decrease in Stoneley coherent energy (CEst).
5. A method for determining the presence of a formation gas kick on a real time basis by a logging while drilling process as defined in claim 4 and further comprising:
detecting a change in one or more Stoneley attributes of (DTst, ATTst and CEst) and prior to setting a kick detection flag assigning a weighting factor to one or more of the Stoneley attributes (DTst, ATTst and CEst).
6. A method for determining the presence of a formation gas kick on a real time basis by a logging while drilling process comprising:
emitting periodic sonic wave energy toward a borehole formation by a logging while drilling tool;
receiving Stoneley waveform signals transmitted within the borehole;
determining the lithology of formations as drilling progresses;
determining the Stoneley wave attenuation (ATTst) within the well bore from the attributes of received coherent Stoneley waveform signal peaks; and
for an essentially uniform formation lithology determining the presence of gas kick within the borehole by a sudden change at different depths in Stoneley wave attenuation (ATTst) over formations with essentially similar lithology.
7. A method for determining the presence of a formation gas kick on a real time basis by a logging while drilling process as defined in claim 6 and further comprising:
determining the Stoneley wave coherent energy (CEst) within the well bore; and
for an essentially uniform formation lithology confirming the presence of a gas kick within the borehole by a sudden decrease in Stoneley coherent energy (CEst).
8. A method for determining the presence of formation gas kick on a real time basis by a logging while drilling process as defined in claim 6 and further setting as gas kick flag comprising:
detecting a change in the Stoneley attenuation (ATTst); and
setting a kick flag to warn a driller of the drilling operation encountering a formation gas kick in the event the detected change in (ATTst) exceeds a set value.
9. A method for determining the presence of a formation gas kick on a real time basis by a logging while drilling process comprising:
emitting periodic sonic wave energy toward a borehole formation by a logging while drilling tool;
receiving Stoneley waveform signals transmitted within the borehole;
determining the lithology of formations as drilling progresses;
determining the Stoneley wave coherent energy (CEst) within the well bore; and
for an essentially uniform formation lithology determining the presence of gas kick within the borehole by a sudden change in Stoneley coherent energy (CEst) over formations with essentially similar lithology.
10. A method for determining the presence of formation gas kick on a real time basis by a logging while drilling process as defined in claim 9 and further setting as gas kick flag comprising:
detecting a change in the Stoneley coherent energy (CEst); and
setting a kick flag to warn a driller of the drilling operation encountering a formation gas kick in the event the detected change in (CEst) exceeds a set value.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US14/016,134 US20140003190A1 (en) | 2007-12-27 | 2013-09-02 | Method for Gas Zone Detection Using Sonic Wave Attributes |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US11/964,731 US8547789B2 (en) | 2007-12-27 | 2007-12-27 | Method for gas zone detection using sonic wave attributes |
US14/016,134 US20140003190A1 (en) | 2007-12-27 | 2013-09-02 | Method for Gas Zone Detection Using Sonic Wave Attributes |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/964,731 Continuation US8547789B2 (en) | 2007-12-27 | 2007-12-27 | Method for gas zone detection using sonic wave attributes |
Publications (1)
Publication Number | Publication Date |
---|---|
US20140003190A1 true US20140003190A1 (en) | 2014-01-02 |
Family
ID=40551990
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/964,731 Expired - Fee Related US8547789B2 (en) | 2007-12-27 | 2007-12-27 | Method for gas zone detection using sonic wave attributes |
US14/016,134 Abandoned US20140003190A1 (en) | 2007-12-27 | 2013-09-02 | Method for Gas Zone Detection Using Sonic Wave Attributes |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/964,731 Expired - Fee Related US8547789B2 (en) | 2007-12-27 | 2007-12-27 | Method for gas zone detection using sonic wave attributes |
Country Status (2)
Country | Link |
---|---|
US (2) | US8547789B2 (en) |
WO (1) | WO2009090463A2 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2017205075A1 (en) * | 2016-05-25 | 2017-11-30 | Halliburton Energy Services, Inc. | An improved stoneley wave slowness and dispersion curve logging method |
Families Citing this family (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CA2829764A1 (en) * | 2011-03-15 | 2012-09-20 | Halliburton Energy Services, Inc. | Acoustic signal processing using model-based adaptive filtering |
US10253620B1 (en) | 2014-09-23 | 2019-04-09 | Kelly K. Rose | System for kick detection during a drilling operation |
US10415369B2 (en) | 2014-12-18 | 2019-09-17 | Halliburton Energy Services, Inc. | Blowout rate correction methods and systems |
EP3227531A4 (en) * | 2015-01-30 | 2018-08-15 | Halliburton Energy Services, Inc. | Peak tracking and rejection in acoustic logs |
CN107045142B (en) * | 2017-07-04 | 2019-04-30 | 吉林大学 | Compressed sensing based wavelet field seismic data Real Time Compression and High precision reconstruction method |
US11649717B2 (en) | 2018-09-17 | 2023-05-16 | Saudi Arabian Oil Company | Systems and methods for sensing downhole cement sheath parameters |
WO2021046380A1 (en) * | 2019-09-04 | 2021-03-11 | Schlumberger Technology Corporation | Monitoring a well barrier |
US20220243575A1 (en) * | 2019-09-04 | 2022-08-04 | Schlumberger Technology Corporation | Autonomous operations in oil and gas fields |
GB2615844B (en) * | 2020-01-20 | 2024-01-31 | Schlumberger Technology Bv | A multi-resolution based method for automated acoustic log depth tracking |
Citations (13)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4232378A (en) * | 1978-09-20 | 1980-11-04 | Standard Oil Company (Indiana) | Formation absorption seismic method |
US4561074A (en) * | 1982-12-29 | 1985-12-24 | Amoco Corporation | Computationally efficient weighting and vertical stacking methods and apparatus for improving signal-to-noise ratio of seismic data |
US4964101A (en) * | 1989-03-23 | 1990-10-16 | Schlumberger Technology Corp. | Method for determining fluid mobility characteristics of earth formations |
US20040068376A1 (en) * | 2002-10-04 | 2004-04-08 | Baker Hughes Incorporated | Walkaway tomographic monitoring |
US20040145968A1 (en) * | 2003-01-29 | 2004-07-29 | John Brittan | Method for processing dual sensor seismic data to attenuate noise |
US20040162676A1 (en) * | 2000-10-10 | 2004-08-19 | Exxonmobil Upstream Research Company | Method for borehole measurement of formation properties |
US20060016592A1 (en) * | 2004-07-21 | 2006-01-26 | Schlumberger Technology Corporation | Kick warning system using high frequency fluid mode in a borehole |
US20060198242A1 (en) * | 2005-02-22 | 2006-09-07 | Halliburton Energy Services, Inc. | Acoustic logging-while-drilling tools having a hexapole source configuration and associated logging methods |
US20060235617A1 (en) * | 2005-03-31 | 2006-10-19 | Schlumberger Technology Corporation | System and method for detection of near-wellbore alteration using acoustic data |
US20070076525A1 (en) * | 2005-10-04 | 2007-04-05 | Craft Kenneth L | Coherent wave energy removal from seismic data |
US20070203673A1 (en) * | 2005-11-04 | 2007-08-30 | Sherrill Francis G | 3d pre-stack full waveform inversion |
US20080143330A1 (en) * | 2006-12-18 | 2008-06-19 | Schlumberger Technology Corporation | Devices, systems and methods for assessing porous media properties |
US20080221801A1 (en) * | 2007-03-09 | 2008-09-11 | Craft Kenneth L | Geophone noise attenuation and wavefield separation using a multi-dimensional decomposition technique |
Family Cites Families (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4449208A (en) * | 1981-11-23 | 1984-05-15 | Mobil Oil Corporation | Lithologic studies utilizing acoustic wave attenuation |
US4594691A (en) | 1981-12-30 | 1986-06-10 | Schlumberger Technology Corporation | Sonic well logging |
US4858200A (en) * | 1987-04-24 | 1989-08-15 | Mobil Oil Corporation | Method for determining the presence of hydrocarbons in subsurface geological formations by comparative assessment of compressional and shear wave reflection data |
US5278805A (en) | 1992-10-26 | 1994-01-11 | Schlumberger Technology Corporation | Sonic well logging methods and apparatus utilizing dispersive wave processing |
US5594706A (en) | 1993-12-20 | 1997-01-14 | Schlumberger Technology Corporation | Downhole processing of sonic waveform information |
US6631327B2 (en) | 2001-09-21 | 2003-10-07 | Schlumberger Technology Corporation | Quadrupole acoustic shear wave logging while drilling |
WO2004095077A1 (en) | 2003-04-23 | 2004-11-04 | Commonwealth Scientific And Industrial Research Organisation | Method for predicting pore pressure |
WO2005052639A1 (en) | 2003-10-28 | 2005-06-09 | Western Geco, Llc | A method for estimating porosity and saturation in a subsurface reservoir |
US6957572B1 (en) | 2004-06-21 | 2005-10-25 | Schlumberger Technology Corporation | Apparatus and methods for measuring mud slowness in a borehole |
US8238194B2 (en) | 2004-09-23 | 2012-08-07 | Schlumberger Technology Corporation | Methods and systems for compressing sonic log data |
US20060062081A1 (en) | 2004-09-23 | 2006-03-23 | Schlumberger Technology Corporation | Methods and systems for compressing sonic log data |
US7764572B2 (en) | 2004-12-08 | 2010-07-27 | Schlumberger Technology Corporation | Methods and systems for acoustic waveform processing |
-
2007
- 2007-12-27 US US11/964,731 patent/US8547789B2/en not_active Expired - Fee Related
-
2008
- 2008-12-11 WO PCT/IB2008/003410 patent/WO2009090463A2/en active Application Filing
-
2013
- 2013-09-02 US US14/016,134 patent/US20140003190A1/en not_active Abandoned
Patent Citations (13)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4232378A (en) * | 1978-09-20 | 1980-11-04 | Standard Oil Company (Indiana) | Formation absorption seismic method |
US4561074A (en) * | 1982-12-29 | 1985-12-24 | Amoco Corporation | Computationally efficient weighting and vertical stacking methods and apparatus for improving signal-to-noise ratio of seismic data |
US4964101A (en) * | 1989-03-23 | 1990-10-16 | Schlumberger Technology Corp. | Method for determining fluid mobility characteristics of earth formations |
US20040162676A1 (en) * | 2000-10-10 | 2004-08-19 | Exxonmobil Upstream Research Company | Method for borehole measurement of formation properties |
US20040068376A1 (en) * | 2002-10-04 | 2004-04-08 | Baker Hughes Incorporated | Walkaway tomographic monitoring |
US20040145968A1 (en) * | 2003-01-29 | 2004-07-29 | John Brittan | Method for processing dual sensor seismic data to attenuate noise |
US20060016592A1 (en) * | 2004-07-21 | 2006-01-26 | Schlumberger Technology Corporation | Kick warning system using high frequency fluid mode in a borehole |
US20060198242A1 (en) * | 2005-02-22 | 2006-09-07 | Halliburton Energy Services, Inc. | Acoustic logging-while-drilling tools having a hexapole source configuration and associated logging methods |
US20060235617A1 (en) * | 2005-03-31 | 2006-10-19 | Schlumberger Technology Corporation | System and method for detection of near-wellbore alteration using acoustic data |
US20070076525A1 (en) * | 2005-10-04 | 2007-04-05 | Craft Kenneth L | Coherent wave energy removal from seismic data |
US20070203673A1 (en) * | 2005-11-04 | 2007-08-30 | Sherrill Francis G | 3d pre-stack full waveform inversion |
US20080143330A1 (en) * | 2006-12-18 | 2008-06-19 | Schlumberger Technology Corporation | Devices, systems and methods for assessing porous media properties |
US20080221801A1 (en) * | 2007-03-09 | 2008-09-11 | Craft Kenneth L | Geophone noise attenuation and wavefield separation using a multi-dimensional decomposition technique |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2017205075A1 (en) * | 2016-05-25 | 2017-11-30 | Halliburton Energy Services, Inc. | An improved stoneley wave slowness and dispersion curve logging method |
Also Published As
Publication number | Publication date |
---|---|
WO2009090463A2 (en) | 2009-07-23 |
US20090168595A1 (en) | 2009-07-02 |
WO2009090463A3 (en) | 2009-09-03 |
US8547789B2 (en) | 2013-10-01 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US8547789B2 (en) | Method for gas zone detection using sonic wave attributes | |
US7639563B2 (en) | Method for sonic indication of voids in casing cement | |
US7516015B2 (en) | System and method for detection of near-wellbore alteration using acoustic data | |
CA2511280C (en) | Kick warning system using high frequency fluid mode in a borehole | |
US7289909B2 (en) | Method for borehole measurement of formation properties | |
US4831600A (en) | Borehole logging method for fracture detection and evaluation | |
US6614716B2 (en) | Sonic well logging for characterizing earth formations | |
CA1210492A (en) | Indirect shearwave determination | |
AU2006262684B2 (en) | Method for determining reservoir permeability from borehole Stoneley-wave attenuation using Biot's poroelastic theory | |
US8553493B2 (en) | Method for permeable zone detection | |
US5616840A (en) | Method for estimating the hydraulic conductivity of a borehole sidewall fracture | |
EP0568643B1 (en) | Method for predicting formation pore-pressure while drilling | |
CN101553742A (en) | Discriminating natural fracture- and stress-induced sonic anisotropy using a combination of image and sonic logs | |
US8681582B2 (en) | Method for sonic indication of formation porosity and lithology | |
US6526354B2 (en) | Sonic well logging for alteration detection | |
Williams et al. | The long spaced acoustic logging tool | |
US4575828A (en) | Method for distinguishing between total formation permeability and fracture permeability | |
US4852067A (en) | Low frequency sonic logging | |
US4797859A (en) | Method for determining formation permeability by comparing measured tube waves with formation and borehole parameters | |
GB2313667A (en) | Acoustic velocity well logging using dispersion characteristics of the formations | |
US4008608A (en) | Method of predicting geothermal gradients in wells |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION |