DE2033721A1 - Method of keeping records in a cased borehole - Google Patents

Description

K, SPARING WNIiBMANNSrTKASSB Sl

TEtBIOTI 67 22 46

Description for patent also

the pirma

Soei & tl de Prospection Electrique Schlumberger 42, lue Saint-Dominique,
P aris

concerning

"Learned to keep records in one

cased borehole *

In a wellbore construction, the casing string or pipe is placed in a wellbore and cement is placed in the king space between the casing and the borehole, primarily to release oil and gas Layers of each other and of water-bearing layers to separate. It follows, therefore, that if the cementation is insufficient to separate one zone from the other, then pressurized fluid escapes from one zone and a nearby, otherwise productive, one

Q09884 / poss

033721

Zone can contaminate you churn, especially from Water, creates an undesirable separation »an | iroductive one Zone through water and can potentially make a borehole uneconomical

^{is difficult to} get an accurate picture of the conditions behind a casing, which is related to the difficulty of sending signals through the metal casing wall of the casing KU have not been entirely successful in clearly determining the effective presence of cement in the annulus between the casing and the formation. Furthermore, it has not been possible to reliably measure the quality of the cement bond between the casing and the cement and the quality of the cement bond between the cement and the formation using methods as heretofore suggested.

The mere presence or absence of cement in the bing space between the casing and the formation is valuable information, but it does did not create a complete picture of the cement ratios. While cement is in the bing room in front of * may exist, but canals or inadequate seals can still be a fluid connection between allow neighboring formations.

The use of the term "binding" in context with the relationship of the cement to the casing or the formation is somewhat vague as there is adhesion along the entire interface between the casing and the cement or not necessary between the cement and the formation is to prevent fluid communication between adjacent porous zones. Everything for a bond

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What is needed is that the relationships are an escape prevent all fluids. The following is a note to "bond" mean a separation of zones sufficient cement to prevent fluid from migrating from one zone to another.

Various Prior Art Methods and Apparatus to Provide a Measure of the Quality of the Cement Bond in Relation to the Piping to obtain are in the TJS patents 3,291,247, 3,291,248 and 3,292,246 are disclosed. The concerned Patents are all assigned to the assignee of the present invention. These systems generally use acoustic methods in which an acoustic signal is transmitted from a transmitter to a receiver. The amplitude of the initial reception signal (this initial reception is the piping signal, since the acoustic pulses generally move faster in the casing than in the surrounding cement or in the formation) at the receiver is measured and used for determination the quality and bonding of the cement to the casing “If there is a good bond, then it is to be expected that the casing signal is attenuated as energy is drawn from the Casing migrates into the cement or into the surrounding formation. If, on the other hand, there is no bond or a bad one If there is a binding, the piping signal is relatively undamped. This procedure is then successful enough when there is good contact between the cement and the casing. But if only a small space or annulus (sometimes called a micro-annulus) between the pipework and the cement is present, such a measurement may indicate poor cementation even if the Cementation is fully sufficient. The word sufficient here means that the micro-annulus, even if it is present, it does not allow the fluid to communicate between adjacent porous formations. In addition, such false indications of moderate attachment can easily occur by the way how the cementation was done.

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With a direct cementing process, cement becomes pressed the annulus upward around the housing, with a relatively high pressure exerted on the inside of the Piping is exercised. This pressure tends to expand the piping. The pressure is in the piping maintained while the cement sets, and when the cement has set then the pressure is relieved * When the pressure is relieved, the tubing can contract to form a micro-annulus between the set cement and the casing.

A more sophisticated technique for determining the quality of the cement in the annulus between the casing and the formations is disclosed in U.S. Patent 3,401,773 under the heading "Method and Apparatus for Cement Inspection in Cased Boreholes", and also the patent in question is assigned to the assignee of the present patent application. In this procedure, the amplitude of a reflected initial casing signal upon arrival recorded and in addition the total energy of a selected one later part of the acoustic signal obtained by integration, providing a second clue for the quality of the cement bond is obtained. Even in the absence of a weak piping start signal, the additional step of evaluating the entire energy received by integrating a later part of the signal, is used to determine the presence of cement in the annulus between the casing and the formation will. Details of the procedures involved can be found here can also be taken from the ÜS patent pen No. 3 401 772, which is entitled "Procedure of your investigation of cased boreholes ".

While the procedures and facilities described above «was bu very useful information guide,

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so it is desirable to examine more closely the quality of the cement bond. For example, the energy content the acoustic examination signals that arrive at the receiver also depend on factors other than the cement bond with the casing or the integrity of the cement column (sometimes called cement grade). Factors which can influence the acoustic energy are: the iOrmationshhartj the eccentricity of the acoustic Under Booking Toolf the properties of the material, from which the Son% for acoustic examination is made; the type of piping and the diameter of the Borehole and casing, as well as the design the piping.

Recognizing these difficulties and some analogous results of the various previously published Have suggestions for the development of the process and the Device of the present invention performed with the help which is a direct record with precise clues becomes possible through the effectiveness of the cement layer in the area of a borehole. The results are through use obtained a quantitative theoretical model of the cement problem, combined with the analysis of the theoretical Results and comparing these results with acoustic investigations carried out by drilling in the concerned Branch have been preserved.

Accordingly, the invention provides a method and apparatus for determining the effectiveness of cement in a cased borehole.

Another object of the invention is a method and a device for cement evaluation in one cased borehole in which the effectiveness of the cement derived by evaluating the reflection coefficients that with radial processes or resonances in the system Probe-borehole-casing-annulus-poriBation

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Another object of the present invention is the method and devices for evaluating cement, which gives improved results by studying reflection coefficients in which radiant energy transfer of acoustic energy from a cased Bohrlooh into the formation surrounding the borehole, and by checking these reflection coefficients in a plurality of relatively broad frequency bands across the spectrum of acoustic energy, which has been used to excite the system.

Briefly, in accordance with the objectives of the present invention is a method and apparatus for underbooking cased boreholes provided, in which a direct recording of the cement quality takes place. In accordance with the present invention, the transmission of acoustic energy in the probe-borehole-casing-annulus-formation system is achieved used to determine the cement quality in the annulus between the casing and the formation to investigate. This is made possible by using a novel examination device and a method including the use of a plurality of relatively wide band pass filters through which that part of the acoustic energy happens in broad frequency bands which is of particular value for the determination the nature of the cement. The individual becomes a special one Parameter, the reflection coefficient associated with the radial transfer of energy into the formation is associated with three relatively broad frequency bands below. Among a variety of Bohrlooh textures is that Height of the reflection coefficient in at least two of the three frequency bands a sign of the quality of the cement in the annulus between the tubing and the formation. A facility is provided for the relative reflection coefficients in each of the three selected Examine frequency bands and make comparisons

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between the reflection coefficients in these bands, to evaluate the cement consistency.

Embodiments of the invention are shown in the drawings and are described in more detail below.

Show it:

Fig.l is a schematic three-dimensional view the cylindrical configuration of a probe-borehole-casing system;

Fig.2 is a schematic cross-sectional view showing

represents the individual layers of this system;

Pig.3 a typical reflection coefficient spectrum;

4 shows a reflection coefficient spectrum, from which the changes in the reflection coefficient result depending on whether cement or no cement is present in the annulus is;

Fig. 5 Multiple reflection coefficient spectra for larger annular spaces than those according to Figure 4;

6 shows an exemplary embodiment of an examination

systems, which covers the basics of the present Invention used, in the form of a blook diagram;

7 shows a block diagram of the cement evaluation computer according to the present invention;

flg.8 the FreoLueni dependence of a typical acoustic search transducer;

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Pig. 9 is a block diagram of the cement evaluation

fuel consumption of the cement evaluation computer of the present invention;

Fig. 10 is a block diagram showing a system "which uses a general purpose digital computer to perform the method of the present To carry out the invention;

Fig. 11 is a flow chart showing a subroutine of a digital computer for performing the Shows logistics of the cement inspection.

The method and the device for direct ' drawing of the cement evaluation according to the present invention is based on the concept of the investigation of certain Parameters related to the characteristic frequencies or radial methods or resonances of a well-casing-annulus-formation system accompanied. The method and apparatus of the present invention are directed to To determine the properties of the Cement® in a Bohrlooh, and ewar through the direct recording of what is called the reflection coefficient curves of Systems, namely ^ M of a plurality of Frequency regions of relatively wide bandwidth selected in the acoustic energy spectrum, which is used to excite the system "

When using the cylinder coordinate system, which is shown in Fig.l with the cylinder coordinates r " θ and ζ, the displacement of particles from different substances in the system, if it is by" acoustic! " Energy is excited-is represented by the functions U _r , U _@ and XJ. If the case of cylindrical symmetry is taken into account, in which the motion is the same in all Θ and the z ** dependence is neglected

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(this is valid in the vicinity of the characteristic frequencies or modes of the system) and only the motion dependent on r needs to be considered. This type of motion can be written in the manner of a scalar potential function ψ defined by

The wave equation for the r dependent motion is then

. ' .ΙΑ

where G is then the velocity of the pressure waves in the system. This equation is derived from well known physical principles and can be found, for example, in the Elastic Waves in Layered Media, by Ewing, Jardetsky and Press, published by McGraw Hill Company of New York, 1957 edition.

The scalar potential function φ is naturally time-dependent as well as dependent on r, ie φ = φ (r, t). However, the time dependency can be assumed as that of a traveling wave, (ie φ (r, t) «P (r) e) where CJ = 2 TTt represents the angular frequency of the wave movement from the frequency f. Using this relationship, equation (1) can be put into the form

Cu ² " F. _ ? ' F ■ ■ <■ ^ F _(ο λ

Equation (2) is detected equation ale a form of Beseel'sohen having a general solution that can be in the form gea ore! Just *

F (r) - A nj ¹ ^ (kr) + B xj ² ) (kr)

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Here k = Q) / C is the wave number of the r waves. Hq '' (kr) and H ₀ * ' (kr) are called Henkel ¹ rope punctures of the first and second kind of the zeroth order. The coefficients A and B can be respectively the complex amplitudes of incoming. outgoing waves, where the Α-coefficients are the amplitudes of the incoming waves and the B-coefficients are the amplitudes of the outgoing waves.

If you look at the definition of displacement TJ. under the conditions of the potential function 0 (the time-dependent exponential function can be omitted, since it is only a phase factor that has no influence on the amplitude of the r-waves), the shift can be written as follows:

U _r - | # - »- IcAH ₁ C ¹ ) (kr) - kBH ^^ ikr) (3)

where H ₁ "(kr) and H ₁ " (kr) are Hankel functions of the first and second kind and of the first order, where again k »ui / σ represents the wave number.

The radial tension (which is equal to the pressure in the Medium is if the medium is a fluid) can also be written in the solution conditions of equation (1). The tension is defined as

_r,. u ^> ££. ♦ 4 ff (4)

where Ji and ^ die Lame »see are constants which determine the elastic properties of an isotopic body. These are related to the pressure and Soher C, wave tightness in the internal body

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where ^ is the density of the material. Taking advantage this relationship can be written as the tension

^A L ⁽ l ² / < ^H i ^{(1) (kr)} - ^

H ₀ ⁽²⁾ (kr)] (7)

The general solution (equation 2) above is in each of the different layers are valid. This solution must now be adapted to the case of a particular problem of interest like the cement evaluation problem. The · is done by considering the boundary or interface conditions of the problem is used to determine the complex coefficients A and B.

As Figure 2 shows, the five layers 1-5 play a role in the cement evaluation problem. While the general solution is valid for each layer, the coefficients A and B are different in each layer, which is expressed below by A _n and B for the respective layers. In general, if "n" represents the number of layers, then two η coefficients must be determined using the interface conditions. Two boundary conditions that can be used are ι

(1) the shift U _r takes place continuously at the interfaces between the layers, ie u " _pl « U ^, ^ü _r 2 " ^Bti r3 ^uew · *

(2) the normal stress tT _r is continuous at the interfaces between each of the layers, ie tT _rl "Έ"

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Since there are n-1 interfaces between η-layers of material, these two interface conditions yield 2 (n-1) = 2n-2 equations in the 2n unknown coefficients A _n and B. Since two more interface conditions have to be introduced into the system in order to find a complete solution, they are introduced in the following way.

In the outer layer (the formation) there is no further outer boundary surface to reflect waves. Therefore the coefficient A- must be the same for the outer layer Be zero (i.e. since the Α-coefficients may be thought of as the amplitudes of the incoming waves). Furthermore it is within the probe (position 5) impossible to distinguish incoming from outgoing waves at the origin of the coordinate system, because when the waves go through the starting point, they are converted from incoming waves to outgoing waves i.e. that A, - must be equal to Bc. These two extra interface conditions provide the necessary 2n equations for determining the 2n unknown complex coefficients A and B are required.

In order to finally complete the solution of the 2n equations for the coefficients A and B, a calculation must be made the acoustic energy source that dee to excite If the fluid is used, this is indicated by the acoustic signal emitted by the A probe comes and can have a frequency dependency, comparable to that of the typical acoustic vision ζ a clueless converter. This source function can © ine Yer » Be sliding function, which ssu the (Ireiizflächenbedixigung must be set up for displacement in the probe base can (i.e. position 4-5 of Fig. 2), Eb results in a Function of form

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\ -2 «χ ( OLy ₁ - 6 U?)

s () = -τ— τ —--> TTh ^Υ1000

in which & _Ί and oil «are adjustable constants. If 0 ^ ₁ = VlQ / jf and 3 ^ ₂ * 120, the result is a source function whose peak is> 9 19KC with half the width of about 13 KC, which is typical for acoustic transducers used today.

With these boundary conditions, 2n can be simultaneous Equations for coefficients A and B solved and many properties of the system which may be of interest can be observed. For example it was found that for one size the ratio A, / B, as of particular interest for evaluating the quality of the cement is in the annulus between the housing and the formation. This quantity represents the ratio of the amplitudes from incoming to outgoing waves in the mud within the casing. Such a magnitude is the Measurement accessible and can be thought of as a reflection coefficient, which indicates how much acoustic energy escapes in the radial direction from the system into the formation.

3 shows a representative reflection coefficient curve. The reflection coefficient Q is plotted as a function of the frequency for values given in Table I. A coefficient of reflection value close to 1 is an indication that very little energy is escaping radially into the formation. Low values indicate that more energy is escaping into the formation at a particular frequency. The first minimum 131 in FIG. 3 is a consequence of a transmission resonance in the piping-annulus system at approximately 9 kHz. The second " minimum" 132 is a "consequence" in the transmission resonance of the annulus itself at about 27 khe. This frequency

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corresponds to a wavelength that is equal to twice that is the annulus width.

Table I.

Outside piping diameter 194 mm (7 5/8 inches) piping diameter 8 mm (»32 inches)

Borehole diameter 254 'mm (10 inches)

Formation pressure run time 334 ^ 8βο / ΐπ (100yu SEC / FT) uncemented (fluid-filled) annulus

Other minima, such as that marked with 133, appear at harmonics of the last-mentioned frequencies for the wavelength Z £ / η η s 1, 2, 3, etc., where £ represents the annulus width. An approximate expression for these frequencies is

■ p nc "no

ι = η β JL, £, ——

where C is the velocity of the sound (under pressure) in the annulus. It follows, therefore, that if that Annular material is changed (e.g. cement or no cement) the frequencies of the reflection coefficient mlnima be changed accordingly.

The diagram of Figure 4 clearly shows this point. The diagrams stand for hole diameters according to Table II for uncemented annulus and cemented annulus, limited by both hard and soft Formations.

Table II

Outer piping diameter 152.4 mm (6 inches)

Piping 6.35 mm («25 inohea)

Bohrloohdurohmeaaer 203 mm (θ inohea)

Format! Onsdruoklaufmeit (wtioh) 334y «a« o / a (100 / i S & O / Jf)

Foraationadruoklauf "old (hard) 167 ju-aeo / m (50 u SBO / FT)

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The diagrams of FIG. 4 show that the reflection coefficient curves have large differences between cemented and non-cemented casing, namely especially in the frequency range just above the first minimum of the curves. It was found that this Differences regardless of the distance between the acoustic Transmitters and receivers appear on the probe over a wide range of small annulus (micro-annulus) Sizes between the casing and the cement. A quantitative measurement of these differences can be and provides an accurate indication of the quality of the cement in the hanging space. It is intends to use the method and equipment just discussed for such measurement.

If the whole frequency range above the first minimum in the reflection coefficient curve is used is used to check the reflection coefficient minima, however, the results are not reliable. this is a consequence of the additional effect shown in Fig.5 is pictured. The diagram of Fig. 5 corresponds to that in ! Table 3 given parameters.

Table III

6 inohes outer tubing diameter

Piping Thickness 6.35mm (.25 inches)

Hole diameter 229 mm (9 inches)

Formation pressure run time (hard) 167ytcsec / m ('5Op.SEC / FT)

"(soft) 334yusec / m (100 p. SEC / FT)

These diagrams illustrate the effect of larger annulus sizes on the reflectance coefficient curves for cemented ones and uncemented conditions. As eioh from these

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Curves, "becomes the second for larger annulus widths Minimum for the uncemented casing shifted down in frequency (i.e. minimum 151 and 152 of Pig. 5), and in general this would lead to the production of abnormal results in the frequency range of 20-25 khz, i.e. the observation of the size of the reflection coefficient minima in this area would lead to results that im Are contrary to the general trend. The absence of cement leads to lower reflection coefficients than the presence of cement. For even larger annulus sizes than those of tubing such as those in 5, third and higher minima can be introduced into the low frequency range and continue to do so interfere with the results expected from graphs such as that of Figure 4. Since the annulus widths are not exactly known for all casings of conventional boreholes (in general, the annulus width is on not known to a point unless a caliber is introduced before the casing is placed, and by yourself then the cementing process can change the borehole diameter due to washouts or the like) some means may be provided to measure the cement in the annulus, which is independent of the annulus width.

Such means are provided according to the invention by Use of three relatively wide bandpass filters chosen to cover the frequency range above of the first minimum. The filter passbands are chosen so that under a given set of conditions only one of the filter bands is seriously disturbed by the anomaly described above. So there are at least two of the three filters provide a correct record of the general cementing trend. With 125 mm piping For example, such filters can be selected in such a way that their center frequencies are 12.5 kHz, 20 kHz, 35 kHz

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and that the pass band widths 5 kHz, 10 kHz respectively. 20 kHz. The pass bandwidth is defined by the frequency interval between two symmetrical half-amplitude points on either side of the central maximum in the filter curve. The exact shape of the filter curve is not of great importance.

If the center frequency and the bandwidth of the three filters are chosen accordingly, then each set would from conditions outside the piping the outputs from two of the three filters in the combination have a relatively low level Assume value if there would be a good cementation there, while at least one filter output is relative would be low if there was poor cementation there.

It has been found that the center frequencies of Such a set of three optimally placed filters will vary with different tubing sizes. By doing The embodiment shown in Figure 6 is a 152 mm Piping used with the center frequencies of the filters, as previously stated. In general, the larger the tubing diameter, the lower the filter media frequencies be. An empirically found relation between the lowest center frequency and the casing outside diameter arises to

f (kH _B ) = 50 χ + 4.5 (9)

diameter

This sets the lowest center frequency, and the others Filter mean frequencies and bandwidths can then be determined accordingly.

When examining boreholes with acoustic Submission devices of usual training is ei Unfortunately, it is not possible to use the reflection coefficient directly to meeeen. However, this can be done with the help of a

. _{18 m} ÖÖ9Ö84 / 162Q

Investigation tool, which for this purpose was developed directly. However, it has been found that the methods of the present invention under Utilization of acoustic logging tools of conventional design find application in the following manner can.

The area under the reflection coefficient curve within a filter bandwidth is approximately proportional to the acoustic pressure level which would be measured in the filter band. Referring to equation (7), this B result follows since the radial tension function UT, (pressure) as a function of the reflection coefficient Q can be written as

\ cQ + d

where a, b, e, and d represent complex expressions involving the Hankel functions. In equation (10), the term cQ is practically much less in height than the complex function d. If so, the function * C can be said to be roughly a linear function of Q (i.e. ^ is direct proportional Q in the approximation carried out here). Therefore, the radial stress (pressure) integrated across the bandpass filter of a filter is equivalent to a good approximation equivalent to the area under the reflection coefficient curve in the filter area. This enables a useful direct recording of the cement occupancy using the three-fold method using conventional recording devices, since the pressure impinging on the surface of an acoustic receiving transducer is converted into an electrical signal proportional to it. It follows, of course, for those skilled in the art that a direct reward for the yeast function coefficient can be carried out with the aid of an investigation, if it would lead to a poor result without the need for an mathematical approximation.

In Pig.6 the present invention is related shown with an acoustic well logging tool of the usual type, such as an acoustic one Runtime recording tool that compensates for the borehole effect. Details of the operation of the acoustic The recording tool shown in Figure 6 can be found in the previously cited U.S. Patent No. 3,304,537. This tool has a plurality of acoustic transmitters and spaced receivers and can be used for acoustic runtime recording over an area of the borehole application where the borehole effects are compensated for by taking a plurality of measurements of the acoustic transit time between each transmitter and a plurality of receivers is performed and Then these acoustic transit time measurements are combined to averages the solution over a fixed interval To get borehole.

Although the derivation of the principles of the present invention is based on the assumption of only radial expansion Based on acoustic energy, it has been found that the present invention can be carried out with tools can, which are shown in Pig.6, as a result of The fact that considerable acoustic energy propagates axially along the borehole. Furthermore, this energy is which emanates from a receiver at an axial distance of a few cm from the acoustic transmitter or microphone, equal proportional to the radial reflection coefficient, as described above. The real relation corresponds roughly to equation (10), but is of of considerably greater complexity and includes integrals over the wave numbers of conical waves that are in to widen the borehole. As a result of the extreme mathematical difficulty of a more detailed analysis of these Problems will not be pursued further on this point.

OMINAL

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Experimental results have the accuracy of assumption an approximate proportionality between the reflection coefficient and the acoustic pressure of a receiver Confirmed at a moderate distance from the transmitter. Hence, although in the idealized case the energy is only radially spreads, in practice such a spread of energy is given axially along the borehole, whereby the principles of the present invention are to be applied with tools such as those illustrated in FIG are. It will, of course, be apparent "to those skilled in the art that other common acoustic exploration tools include the are based on a different principle than that of borehole compensation can be used to practice the present invention. For the sake of brevity this will be discloses the practice of the methods of the present invention with a well effect compensating tool; but it should be understood that the present invention is not limited by the use of such a tool.

The overall arrangement of a well logging system using the principles of the present invention is shown in block form in Fig. 6. A long one Survey tool 20 is suspended in a cased borehole and is provided with the usual centering equipment near its top and bottom, thereby centering the tool as effectively as possible is held in the borehole 22. The borehole 22 is filled with the usual drilling mud or fluid 24.

The tool 20 hangs in the borehole by means of the armored cable 26 "which extends from the upper. end of Tool extends to the surface of the earth * The cable is wound onto a winch 28, which is shown schematically. The winch is of well-known design, and the operation the same is used to raise and lower the Werkseuges through the borehole. The cable 26 may contain a plurality of lines to swipe paths for electrical signals

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the surface facility and those downhole To manufacture equipment and also to obtain electrical energy from an energy source on the earth's surface to send to the facility down the hole.

The tool 20 itself is divided into two parts. Of the upper part 20A houses the electrical equipment carried by the tool, while the lower part 2OB for holding the acoustic transmitter and receiver serves. Although not shown in the drawing, it will be understood by those skilled in the art that portion 20B of the Housing can be designed so that a direct transmission of acoustic energy there through from the Transmitting to the receivers is either suppressed to a negligible value or shifted in with respect to the transit time through the formations, so that the measurements are not disturbed by it. Different types of housing constructions, such as the open-work construction, are state of the art for this purpose.

The surface facility of the system is generally in block diagram form shown above the dashed lines in Figure 6. the Main reference frequency for the overall operation of the examination system comes from a 60 hz power source, which is from a normal supply network or from a special one Generator can be generated. Preferably the energy from their source on the surface to the Oberfiäoheneinrichtung and passed through suitable conduits in the cable 26 to downhole installation. For reasons of presentation are three separate 60hz input lines 30a, 30b and 30c shown in Fig. 6. As can be seen from the description below results, the 60 hz power source supplies the operating energy for the electronic device as well as a Reference frequency.

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Main tent control pulses for synchronizing the various components of the system are made with the help of a Pulse train circuit 32 generated. This circle creates a train of sharp pulses whose frequency is an integral Is a sub-multiple of the 60 Hz reference frequency. Therefore, for example, the repetition frequency of the timing pulses, generated by the circuit 32 can be varied from 1/9 to 1/2 of the 60 Hz reference frequency. Naturally other frequencies or ratios can be generated if desired. Between every pair of successive pulses passed through the pulse train circuit 32 can be generated, an individual measurement, e.g. a transmitter-to-receiver transit time measurement or a cement thaw evaluation recording measurement can be made. The pulse frequency chosen will therefore depend on the particular type of formations expected. One Timing pulse frequency, which has been found suitable for a wide range of applications, is 20 pulses each Second at which an interval of 50 milliseconds is provided between successive control pulses.

The timing pulses that are generated in the pulse train circuit 32 are via a line 33 directly a control signal generator 34 is supplied. The control pulses also serve to synchronize a selection program planner 36, the output of which is connected to the control signal generator 34.

The selection program planner 36 may be provided with means such as a manually operated switch arm, which enables the selection of any one of a plurality of measurement sequences for acoustic signal propagation time measurements and optionally the selection of cement evaluation recording measurements is allowed. The cement evaluation examinations can can be carried out at the same time as the acoustic runtime measurements. Of course, it is piped in a Borehole the transit time measurement generally only the

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Show arrival transit time in the piping when the piping is practically tighter than for acoustic propagation the surrounding formation. This is useful information because piping collar on the running time recording (the running time) and in addition the casing arrival amplitude can be used as before for the display of the cement bond. Between each successive pair of control pulses from the pulse train circuit 32, the control signal generator generates a control signal on line 38 to the downhole equipment.

Electrical signals corresponding to acoustic measurements made in the facility in the borehole are transmitted to the surface via conduit 40 into cable 26. These signals become one Rectifier circuit 42 supplied, which has an output signal generated that is related to the runtime measurement and that is suitable as an input to the runtime computer 44. In addition, the rectifier circuit 42 can input signals to the Feed cement evaluation computer 70, which is operated in a manner to be described below. The rectifier circuit 42 is a function of electrical signals which are received from the device below in the Borehole are transmitted via control pulses, starting from the pulse train circuit 32 via a fixed delay means 46. The delay means 46 is synchronized with the 60 hz reference frequency source 30B and ensures that the rectifier circuit is inoperative before the expected arrival signal from inside the Borehole is coming. This reduces the possibility of errors resulting from the interference signals.

The computers 44 and 70 can be operated directly from the program planner 36, and computer 44 also becomes conditioned by the output of the AND circle 50, which of the simultaneous arrival of signals from that

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Delay means 46 and the program planner 36 is dependent. These instruction signals, which are fed to the computer 44, dictate the particular arithmetic sequence, which is produced for acoustic runtime recording. Computers 44 and 70 are provided with reset Information on preparing for the next calculation cycle.

The output signals of the computers 44 and 70 have the form of electrical signals, which display means », such as to the recorders 52 and 71. As shown by the dashed line, the registration feed means for the registration devices is mechanical connected to the shaft 28 so that it moves therewith, creating a curve of the acoustic travel time record and the cement consistency survey is obtained with respect to the depth of the well.

Control signal pulses from the control signal generator 23 are fed via a conduit 38 to a cable 26 for operating the device in the borehole, as shown in FIG. 6 below the dashed lines, which in the upper part 20a of the examination tool 20 is arranged. This device has a selection and control means 54 which evaluates the received control signal pulses and selects a specific transmitter-receiver combination, so that it is put into operation during each measuring cycle. You actual selection is made by a broadcaster and Receiver selection means 56 accomplished, which responds to transmitter control means and places the usual transmitter-receivers rp aar in the circuit.

You control signal pulse · from the control signal generator 34 on the surface also become an end channel in the downhole facility. The 8 * n4 * rchannel 58 is synchronized with a 60 Hz reference frequency 300 and fulfills the tint 4r · double · function, lunäohst is amf d «a Stndtrkanal 58« in Ausganfslaufiapult vorg · - •• h «m, among other things to activate 4 · η tender, d» r duroa 4a · corrugating agent

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56 has been selected. This creates the acoustic energy for the evaluation of the cement composition and for the implementation the runtime measurements.

The transmitter channel 58 also carries a blocking signal, to deactivate part of the receiver channel 60. Of the Receiver channel 60 has a multi-stage amplifier with masking means to prevent an input signal the first stage reaches its initial stage. The output of the transmitter channel 53 supplies a blocking signal su the receiver channel 60, which just prior to the generation of the Transmitter output pulse begins and up to a time instant which is just before the earliest possible arrival of a signal from the selected receiver. Through this can cause interference or cross talk during this period not through the receiver channel 60 to the surface facility be transmitted. The input stage of the receiver channel 60 is coupled to the isolating receiver via the isolating means 56.

The transmitter channel 58 also carries a transmitter ignition signal at the instant in which the transmitter receives pulses will. This signal is a tight impulse that comes in the instant the transmitter is healed. The ignition signal pulse is coupled to the unblocked output stage of the transmitter channel 60 and is immediately used Surface transmitted via line 40, thereby indicating becomes that the transmitter has been healed at this moment in time is.

After the input stage of the receiver channel 60 has been opened, electrical signals resulting from the application of acoustic energy are scanned and amplified by the selected receiver and each measurement transmitted to the surface via the cable 40 is then the surface direction, yes, a marking -iapuli supplied, the tine display · ifüf ^ the time of the ignition _; . of the transmitter and an electrical signal, which »

BADORlGtNAL _. ₂ 6 - 009 * 8 84/1 6 20

the application of acoustic energy to the associated receiver corresponds to «Be of course, that the selected receiver in the recording tool converts the impinging acoustic energy into electrical signals which have a waveform representative of such acoustic energy in the usual manner.

Sa the details of the operation of the device for performing acoustic time of flight measurements of the above mentioned patent can be found, this will be not detailed below. Attention is drawn to the operation of the cement evaluation computer 70, which can be found in more detail in Pig. 8 and " 10 results.

As Fig.7 shows, the acoustic signal is 1 / el before s originating from the tool at the depth of the wellbore, reinforced and fed to the input side of the timing gate 80 of the cement evaluation computer placed. As previously described, the timing gate 80 is arranged to be used by the selection program planner can be operated and a signal selects a cement texture record if so desired perform. From the timing gate 80 the signal is the input of three bandpass filters 81, 82 and 83 supplied. The band pass filters 81, ^, 82. and 83 can be conventional L-C filter circuits that are compatible with the desired Medium frequency and bandwidth can be designed as described above for a specific piping size, For example, for 152 mm tubing, the band pass filter Mr. 1 be a ten to 15 khz Piltor while that Bandpass filter no. 2 can have a bandwidth of 15 to 25 khz and bandpass filter 3 a solone of 25 - 45 khs.

The output signals of the bandpass filters 1, 2 and 3 become Reinforced in regulators 84, 85 and 86. This· Amplifiers amplify the signal · their corresponding Bandpass filters in different gradations, including each one

0 0 9 8 8 4/1620

- 27 - jtyn- . ■ ·, ■ tr.-t · - ¹

Vtreerrang for the relevant signal as a result of the acoustic frequency dependence of the lower Bohrlooh receiving transmitter is present to compensate. The * concept is even clearer with reference to Pig.8, which shows the output frequency as a function of a typical acoustic recording transducer for a constant input signal level that is transverse to its frequency spectrum with the frequency-dependent bandwidths from the three filters 81, 82 and 85, which are superimposed on this curve. It follows from FIG. 8 that such a reception transducer in the frequency range of the BandpaJfilters Mr. 2 is considerably more sensitive and that Has less sensitivity in the frequency range Ton Bandpass Filter No. 1 and 3. If it is desired the absolute level of the output signal of the converter measure as it is desired to measure the acoustic pressure for the cement scoring record, then one must such bias as introduced by the frequency dependence of the transducer can be removed. This bias is removed by control amplifiers 84, 85 and 86, which are set to amplify the outputs of their respective filters in proportion to the frequency used by the Smpfangswandlern depends in the tool in the borehole. This is easy to do because of the frequency used by the acoustic transducer is well known, and if the frequency range of band pass filters 81, 82 and 83 is set, the gain of amplifiers 84, 85 and 86 can be adjusted accordingly. This one This process can be referred to as normalizing the output of the bandpass filters.

After the output signals of the band filter in this Normalized sin *, the signals are given by the int grators 87, ββ respectively. 89 integrated. Dl · · occurs as before described, for & · ■ purpose, dsj «in electrical ·· signal

- 28 -

009884/1620

is generated, which is approximately proportional to the reflection coefficient is in the frequency range of the band pass filters 81, 82 and 83. The integrators 87, 88 and 89 can be common R-O integrators in which the charge that is stored on a capacitor during the integration interval, proportional to the area under the curve of the signals, in the bandwidths of the filters 81, 82 and 83.

The output signals of the integrators 87 »88 and 89 can be recorded directly, or the signals can optionally be further processed by the circuit 90 and recorded in a single track, which gives an indication of the cement ratios or the percentage ' set of cement in the annulus. The operation of the cement scoring circuit 90 can be seen in greater detail in FIG Fig. 9 can be taken.

As Fig. 9 shows, this circuit comprises three differential comparators 101, 102 and 103, a multiple-nor gate 104 and three signal gates 105, 106 and 107 and an averaging circuit 108. The output signals from the averaging circuit 108 xm ± are smoothed and are fed to the recorder by the smoothing circuit 91 of FIG. The overall function of the circuit according to FIG. 10 is to select and balance those output signals from the two integrators which have the lowest output signal levels. With reference to the integrator inputs of the integrators 87, 88 and 89 corresponding to A, B and C, the operation of the circuit will be described as follows.

Differential comparators 101, 102 and 103 each receive all three of the input signals A, B and C. These differential comparators each compare the relative magnitude of one of the input signals with each of the other two Input signals. Each comparator has two outputs. It

0 0 G b ü A / T 6 2 0

- 29 -

an output signal is generated from the differential comparator for example on the line that is marked A > B, if the height of the signal A is greater than that of the Signal B and also an output pulse on the line, which is marked A> C if A is greater than C. The differential comparators compare in a similar manner 102 the signal B with the "two other signals and the differential comparator 103 compares the signal C with the other two signals, each time output pulses recorded on the lines to the result to display these comparisons. When the condition recorded on the output line is unsatisfactory then there would be no output pulse on this line generated by the differential comparator, i.e. if A were not greater than B, it would be on the line A> B no output pulse generated by the differential comparator 101 arise.

The output lines of the differential comparators are used as inputs to the multiple nor gate circuit. This circuit acts to select the two filter output signals which are lower than the third. Each individual NOR gate in multiple NOR gate circuit 104 has two input lines. An output pulse is only generated if an input voltage is present on both of its input lines at the same time. Therefore, if, for example, the input lines to the one individual NOR gate of the multiple NOR gate circuit are the lines marked A> B and A> 0 and there is a pulse on both of these lines , then a pulse will appear the Mehrfaoh-NQR-Stromkreisausgangsleitung produces » which B + 0 <A is marked . Similarly, all possible combinations of signals in the Mehrfaoh-HOR - Ga introduced toward tter and the Auewahl of. two signals of the lowest value takes place. It should be noted that

009684/1620

only one of three output lines on the multiple NOR gate circuit 104 results in an output pulse at a given time, since only one of the output combinations is possible, i.e. one signal must be smaller than the other two by a finite amount. The output of the multiple NOR gate circuit is used to condition the three signal gates 105, 106 and 107.

Signal gates 105, 106 and 107 are used to control the passage of input signals A, B and C ± n through averaging circuit 108. Unless there is a signal on one of the secondary inputs 109, 110 and 111 of gates 105, 106 and 107, the gates will not allow their primary input signals A, B and C to pass into the thermosetting circuit. Thus, for example, if the multiple NOR gate output B + C> A has an output pulse on it, then signal gates 106 and 107 are conditioned to pass signals B and C to the averaging circuit 108. Similarly, the other multiple NOR gate outputs activate other pairs of signal gates and allow other signal combinations to reach the averaging circuit 108. The averaging circuit 108 then averages the two lowest signals appearing at its input and this average, which is indicative of the cement quality in the annulus, is fed to the record smoothing circuit 91 of FIG.

It will be apparent to those skilled in the art that the outputs of integrators 87, 88 and 89 of Figure 7 can be recorded on magnetic tape for later data processing by an all-purpose digital computer, or if a small general-purpose digital computer is available downhole, then he can use it

"009884/1620

to process the signals immediately. One such Digital processing scheme has been considered for the present invention, and a schematic diagram, which discloses part of such a system is shown in FIG.

Fig.11 shows how the output signals of the integrators 87, 88 and 89 in analog-to-digital converters 115, 116 and 117 enter. These output signals just discussed can be taken directly from the integrators or from magnetic tape. Optionally, the raw acoustic Waveform blows to the tool in the borehole a magnetic tape can be recorded and played back into a system, as Pig.7 represents, which is connected to a remote location, for which purpose the integrator outputs are provided. Optionally, the raw acoustic Waveform converted in an analog to digital converter and are fed to a general purpose digital computer and broken down into their frequency components by Fourrier analysis and digitally filtered to obtain the equivalent of the outputs of integrators 87, 88 and 89. In any case The integrator outputs may be converted into digital (binary) form and processed in a general purpose computer 118 will. Analog-to-digital converters 115, 116 and 117 can be of any prior art design. Similarly, general purpose computers 118 can be of any well known type that can process such input data.

11 shows a flow diagram of a subroutine for processing the integrator output data, which is converted into digital Shape have been transformed. The sub-program can be part of a processing system of the computer 118 and is called to perform or comes on a periodic basis whenever such data is available for processing are present. The subroutine basically accomplishes the same bills generated by the cement evaluation stream

\ 52 JJ0988A / 16 20

circle of Fig.9 can be carried out. When the subroutine starts, then the digital values of the integrator outputs A, B and O are available in a database 121 of a general purpose computer 118. The input signal A is first checked against the input signal B in block 122. If A is greater than B, then A is tested along with C in block 123. If A is greater than both B and C, then the output variable (called AVG) is equal to (B + C) / 2. If A is greater than B but less than C, then AVG is equal to (A + B) / 2. On the other hand, if A is less than B then B is compared to C in block 124, and if B is greater than A and 0 then AVG is equal (A + C) / 2. On the other hand, C is the largest input variable and AVG is (A + B) / 2. The variable AVG then becomes the exit for a recorder 119 or other computer display device 120 such as an oscilloscope or a Digital printer by other suitable computer subroutines known in the art in a general purpose computer 118.,

In either case of analog or digital processing of the data, the final result is an output display, the Has relation to the cement effectiveness as a function of the depth of the borehole. Such a display can, for example, take the form a record of the percentage of cement in the annulus as a function of depth. Like previously described, can have the acoustic run-time record alongside this record along with a cement bond record be shown, based on a measurement of the amplitude of the first audio input signal β, if desired. It is evident that such a combination of records reveals a great deal more information about the cement conditions in the annulus of the borehole operator delivers than was previously possible.

While a particular embodiment of the present With the invention shown and described, it is apparent that changes and modifications

_ 33 .009884 / 1620

can be carried out without being affected by this invention in to deviate from a broader aspect, and hence it is that The aim of the following claims is to claim all such changes and modifications which appear in the real Mind and fall into the goal of the invention.

In connection with the principles of the present invention, methods and devices for evaluation the effectiveness of the cement provided in cased boreholes. Acoustic energy is used to do that System of vibrating well-casing-annulus-formation, and the radial passage of energy into the Formation is established by examining the reflection coefficients of the system in a plurality of relatively broad frequency bands These are determined to span the spectrum of acoustic energy used to excite the system will. Me spectrum analysis is performed by adding electrical signals responsible for the reflected acoustic energy are representative are passed through a plurality of relatively wide band pass filters whose center frequencies are selected according to the design of the piping to be evaluated. A relatively low level of the Reflection coefficient in a majority of these filters is an indication of the presence of good cement quality.

34 -

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Claims (3)

Claims 1. Method of keeping records in a cased borehole to determine the effectiveness of the cement determine which is located in an adjoining space between the casing and the formation, wherein a Component of acoustic energy radially outward from the borehole into the casing and the surrounding area Formations is transmitted and a reflected portion of the transmitted energy is received and a representative one electrical signal is generated, characterized by the process steps of separating the representative signal of the received energy in components of the acoustic frequency spectrum Selecting at least three of the components of the frequency spectrum that have relatively wide bandwidths and by generating signals functionally related to the acoustic reflection coefficient are in the part or parts of the acoustic frequency spectrum of the selected components. 2. The method according to claim 1, characterized in that a dependent on the effectiveness of the cement Signal is generated indicating a functional relationship to the signal of the acoustic reflection coefficient. 3. The method according to claim 2, characterized in that / vÜJn the effectiveness of the cement dependent signal is generated by generating a representative signal from the consistency of two signals of the reflection coefficient, which have the smallest height. 009884/1620 Blank page