Acoustic logging tool

An embodiment of the present disclosure is an acoustic logging tool for determining a characteristic of a ground formation during a drilling operation. The acoustic logging tool includes a transmitter section that houses a transmitter that is configured to emit an acoustic signal and a receiver section spaced from the transmitter section along an axial direction. The receiver section includes a receiver that is configured to receive at least a portion of the acoustic signal. The acoustic logging tool also includes an isolator section positioned between the transmitter section and the receiver section along the axial direction.

TECHNICAL FIELD

The present disclosure relates to an acoustic logging tool for measuring characteristics of an earthen formation during drilling an oil and gas well.

BACKGROUND

Drilling systems are designed to drill into the earth to target hydrocarbon sources as efficiently as possible. Typical drilling systems include a rig or derrick, a drill string supported by the rig that extends into the earth, and a drill bit disposed at the end of the drill string that drills a borehole through the earth. Sometimes, the drill string of a particular drilling system can extend several miles below the surface of the earth. As a result, during a drilling operation the drill string can extend through many different subsurface formations, each of which can require different drilling parameters to optimally drill through. Because of the significant financial investment required to reach and then extract hydrocarbons from the earth, drilling operators are under pressure to drill and reach the target as quickly as possible without compromising the safety of personal operating the drilling system or the integrity of the drilling equipment. As a result, it is advantageous for an operator of a drilling system to know the properties of the subsurface formation that the drill string is currently drilling through.

One device for detecting properties of an earthen formation is an acoustic logging tool. Typical acoustic logging tools include transmitters that produce acoustic waves that travel through the earthen formation, as well as receivers that are configured to receive at least a portion of the acoustic waves. Based upon the qualities of the acoustic waves that are received by the receivers, a controller in communication with the receivers can determine, based upon calculations and predetermined formation models, the characteristics of the earthen formation through which the drill string is passing. Based upon this determination, a drilling operator can alter the drilling operation accordingly.

However, an acoustic logging tool as described above has drawbacks. When the transmitter emits acoustic waves into the earthen formation, acoustic waves also tend to propagate along the tool body and through the acoustic logging tool toward the receivers. These acoustic waves affect the accuracy of the waves received by the receiver that pass through the earthen formation, unless they can be filtered out. Alternatively, the acoustic logging tool can be constructed such that the propagation of acoustic waves along and through the acoustic logging tool from the transmitters to the receivers is minimized.

As a result, there is a need for an acoustic logging tool with adequate features for preventing the propagation of acoustic waves along the acoustic logging tool, thus acoustically isolating the transmitters from the receivers with respect to the acoustic logging tool body.

SUMMARY

An embodiment of the present disclosure is an acoustic logging tool for determining a characteristic of an earthen formation during a drilling operation. The acoustic logging tool includes a transmitter section that includes a transmitter that is configured to emit an acoustic signal. The acoustic logging tool also includes an isolator section mounted to the transmitter section. The isolator section defines an inward surface, an outward surface spaced from the inward surface, and a curved wall that extends from the inward surface to the outward surface. The inward surface, the outward surface, and the curved wall at least partially define a recess that extends around an entirety of a circumference of the isolator section. Each recess is configured to interrupt at least a portion of the acoustic signal that travels through the isolator section. The acoustic logging tool includes an receiver section mounted to the isolator section opposite to the transmitter section. The receiver section includes a receiver that is configured to receive at least a portion of the acoustic signal.

Another embodiment of the present disclosure is an acoustic logging tool for determining a characteristic of an earthen formation during a drilling operation. The acoustic logging tool includes a transmitter section that houses a transmitter configured to emit an acoustic signal. The acoustic logging tool also includes an isolator section mounted to the transmitter section, the isolator section being elongate along an axial direction and having a first cavity, a second cavity spaced from the first cavity a first distance along the axial direction, and a third cavity spaced from the second cavity a second distance along the axial direction. The second distance is different than the first distance. Furthermore, each cavity extends around an entirety of a circumference of the isolator section. Each cavity is configured to interrupt at least a portion of the acoustic signal that travels through the isolator section. The acoustic logging tool also includes an receiver section mounted to the isolator section opposite to the transmitter section along an axial direction. The receiver section includes a receiver that is configured to receive at least a portion of the acoustic signal.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Embodiments of the present disclosure include acoustic logging tools for use in a drilling operation. The acoustic logging tool as described herein may be used to determine a characteristic of a formation during the drilling operation. As will be further explained below, the acoustic logging tool includes one or more transmitters, an isolator section with one or more isolator cavities that extend around the circumference of the logging tool, and one or more receivers. The isolator cavities are configured to isolate and/or disrupt acoustic signals traveling through the logging tool generated by the transmitter. In this manner, the acoustic logging tool is optimized to minimize the tool mode, which includes the acoustic signal generated by the transmitter. This, in turn, minimizes undo noise in the received signal so that more accurate and reliable formation velocity can be determined. This will lead to more accurate interpretations of parameters of interest, e.g. porosity, of the formation. Furthermore, the acoustic logging tool is formed using at least three distinct sections joined by weldments. By forming the acoustic logging tool in this manner, more complex internal bores, such as wire passages and other cavities can be formed into the individual sections than would otherwise be possible if similar bores and cavities where formed using conventional deep bore formation techniques. By forming three separate sections and joining them together with weldments, the intermediate or middle section, in this case the isolator section, may be formed with multiple unique features, bores, and passages.

Referring toFIG. 1, a drilling system1is depicted that includes a rig or derrick5that supports a drill string6. The drill string6includes a bottomhole assembly (BHA)12coupled to a drill bit14, and at least one acoustic logging tool100disposed along the drill string6. The drill bit14is configured to drill a borehole or well2into the earthen formation3along a vertical direction V and an offset direction O that is offset from or deviated from the vertical direction V. The drilling system1can include a surface motor (not shown) located at the surface4that applies torque to the drill string6via a rotary table or topdrive (not shown), and a downhole motor (or mud motor, not shown) disposed along the drill string6. The downhole motor is operably coupled to the drill bit14. Operation of the downhole motor causes the drill bit14to rotate along with or without rotation of the drill string6. Accordingly, both the surface motor and the downhole motor can operate during the drilling operation to define the well2. During the drilling operation, a pump17pumps drilling fluid downhole through an internal passage (not numbered) of the drill string6out of the drill bit14and back to the surface4through an annular passage13defined between the drill string6and the wellbore wall. The drilling system1can include a casing18that extends from the surface4and into the well2. The casing18can be used to stabilize the formation near the surface. One or more blowout preventers can be disposed at the surface4at or near the casing18.

Continuing withFIG. 1, the drill string6is elongate along a longitudinal central axis26that is aligned with a well axis E. The drill string6further includes an upstream end8and a downstream end10spaced from the upstream end8along the longitudinal central axis26. An internal passage extends through an entirety of the drill string6through which drilling fluid travels to the mud motor, out of the drill bit14, and back up to the surface through the annular passage13. A downhole or downstream direction D refers to a direction from the surface4toward the downstream end10of the drill string6. An uphole or upstream direction U is opposite to the downhole direction D. Thus, “downhole” and “downstream” refers to a location that is closer to the downstream end10of the drill string6than the surface4relative to a point of reference. “Uphole” and “upstream” refers to a location that is closer to the surface4than the downstream end10of the drill string6relative to a point of reference.

Continuing withFIGS. 2-7, the acoustic logging tool100is configured to be disposed along the drill string6. The acoustic logging tool100includes a transmitter section104, a receiver section102spaced uphole from the transmitter section104along an axial direction A, and an isolator section108. In operation, the axial direction A may be coincident with the central axis26. The isolator section108extends from the transmitter section104to the receiver section102. The isolator section108may be joined to the receiver section102by an upper weldment110. Further, the isolator section108is joined to the transmitter section104by a lower weldment112. The upper weldment110and the lower weldment112will be discussed further below.

Referring toFIGS. 2-7, the acoustic logging tool100includes a downhole end100b,an uphole end100aspaced from the downhole end100balong the central axis26, and a central bore115that extends from the uphole end100ato the downhole end100b.The uphole end100aof the acoustic logging tool100can be defined by the receiver section102and the downhole end100bof the acoustic logging tool100can be defined by the transmitter section104. Each section of the acoustics logging tool may include a body that defines the central bore115when the sections are mounted together as shown inFIG. 2. The central bore115can include separate segments. For example, the central bore can include a first segment115athat is defined by the receiver section102, a second segment115bdefined by the isolator section108, and a third segment115cdefined by the transmitter section104. The central bore115can be configured to allow the passage of drilling mud through the acoustic logging tool100as the drilling mud flows through the drill string6in a downhole direction D, as described above.

Continuing withFIGS. 2-4, the transmitter section104can include at least one transmitter172that is configured to emit acoustic waves into the earthen formation3surrounding the drill string6when the acoustic logging tool100is operating downhole. The transmitter172may be housed in a transmitter seat170a-170bthat extends into the transmitter section104along the radial direction R. In the depicted embodiments, the transmitter section104can include two transmitters172: a first transmitter172aand a second transmitter172b.Furthermore, the transmitter section104includes a first transmitter seat170aand a second transmitter seat170bthat houses the first transmitter172aand the second transmitter172b,respectively. It should be appreciated that more or less transmitters172can be included, though the number of transmitters172and transmitter seats170may correlate.

The transmitters172a-172bmay be configured as transducers, such as piezoelectric transducers as known in the art. The transmitters172a-172bcan be unipole, monopole, or dipole transmitters. Alternatively, the transmitters172a-172bcan be configured as transceivers or transducers.

Continuing withFIGS. 2-4, the transmitter section104will be described in further detail. The transmitter section104is positioned in the downhole direction D relative to the receiver section102and is adjacent to the isolator section108. The transmitter section104can include a stabilizer174that can be utilized to stabilize the acoustic logging tool100within the drill string6in order to avoid unintentional lateral movement of the acoustic logging tool100and reduce vibrations.

Continuing withFIGS. 2-5, the receiver section102houses at least one receiver128configured to capture the acoustic signal. As illustrated, the receiver section can preferably include multiple receivers128, such as a two or more receivers, which may be referred to collectively as a receiver array. Each receiver128is housed in a receiver seat124that extends into the receiver section102along the radial direction R. In accordance with the depicted embodiment, the receiver section102includes six receiver seats124: a first receiver seat124a,a second receiver seat124b,a third receiver seat124c,a fourth receiver seat124d,a fifth receiver seat124e,and a sixth receiver seat124f.The depicted receiver section102can therefore include six receivers128: a first receiver128a,a second receiver128b,a third receiver128c,a fourth receiver128d,a fifth receiver128e,and a sixth receiver128f.However, it is contemplated that more or less receivers128may be included. As depicted, each of the receivers are aligned and spaced apart along the axial direction A. In this case, each of the receivers can be equally spaced apart along the axial direction A. Equal spacing is preferable because in order to use the time delay between receipt of signals by each receiver, a known and equal distance apart, to determine formation characteristics. In alternative embodiments, however, each of the receivers are spaced apart with respect each other by different distances. Accordingly, the distance between adjacent receivers varies along axial direction A. However, the receivers128a-128fand receiver seats124a-124fmay be situated otherwise, as desired. In other embodiments, the receiver section102can include up to twenty-four receivers128.

The receivers128a-128fare configured to receive at least a portion of the acoustic signal transmitted by the transmitters172a-172blocated in the transmitter section104. Accordingly, the receivers128a-128feach may be configured as transducers, such as piezoelectric transducers as known in the art. Alternatively, the receivers128a-128fcan be configured as transceivers.

The receiver section102may also include an electronics bay132that is configured to contain the electrical components of the acoustic logging tool100and a hatch cover134that covers the electronics bay132. The hatch cover134protects the electrical components in the electronics bay132from external forces, such as drilling mud that flows through the drilling system1. Though labeled as a single element, there may be multiple electronics bays132located around the receiver section102. For example, the electronics bay132may include four compartments, though more or less compartments are contemplated.

The receiver section102can further include a sleeve136disposed over the electronics bay132and the hatch134, where the sleeve136further shields the electrical components in the electronics bay132from external forces. The sleeve136can be releasably coupled to the receiver section102, such that the sleeve136can be removed to provide access to the electronics bay132.

Further, the receiver section102can also include a stabilizer140and a data port138. The stabilizer140can be utilized to stabilize the acoustic logging tool100within the drill string6in order to avoid unintentional lateral movement of the acoustic logging tool100and reduce vibrations. The data port138can be in electrical communication with the electrical components contained in the electronics bay132, and can provide a drilling operator with a quick access point to extract information from or upload information to the electrical components when the acoustic logging tool100is positioned uphole.

The acoustic logging tool may include various electrical components that are used to operate and control the tool. For instance, the acoustic logging tool include a controller configured to operate the receivers128a-128fand/or the transmitters172a-172b,a storage unit configured to store information received by the receivers128a-128f,and a battery assembly configured to power the receivers128a-128fand/or transmitters172a-172b.The battery assembly may comprise a single battery, or may comprise an array of batteries arranged within the electronics bay132along the circumferential direction C. For example, the battery assembly may include eight batteries, though more or less than eight batteries is contemplated, depending on the particular electrical components contained in the electronics bay132, as well as the particular arrangement of receivers128and transmitters172. An operator at the surface4may be in communication with the electrical components of the acoustic logging tool thorough mud pulse telemetry, EM telemetry, and/or wire pipe systems as is known in the art.

Referring toFIGS. 2-7, the isolator section108includes at least one isolator cavity150configured to disrupt and/or deflect portions of the acoustic signals propagated through the isolator section108by the transmitter172. In the depicted embodiment, the isolator section108has a plurality of cavities150. Each cavity150extends from an outer surface154of the isolator section108into the isolator section108along the radial direction R. The structure of each cavity150will be described in further detail below. The isolator section108defines several cavities150spaced apart at varying distances along the axial direction A. As depicted, the isolator section108includes eleven isolator cavities150, which will be referred to as first through eleventh cavities150a-150k.However, it is contemplated that more or less cavities150are included. The isolator section108can also include at least one band152and at least one elastomeric compound that are disposed within a respective cavity150. The band152can comprise a metallic material.

Continuing withFIGS. 6 and 7, an exemplary isolator cavity150extends around an entirety of the isolator section108. Though only one isolator cavity150is described, the remaining depicted isolator cavities150are similar. The isolator cavity150includes a bottom surface188, an upper recess180a,and a lower recess180bthat is open to and faces the upper recess180a.As shown inFIGS. 6 and 7, the isolator section108defines a first inward surface184a,a first outward surface182aspaced from the first inward surface184aalong the radial direction R, and a first curved wall186athat extends from the first outward surface182ato the first inward surface184a.The first curved wall186amay have a first radius of curvature B1that is between about 0.125 inches and about 1 inch. However, the radius of curvature B1can be contingent upon the overall diameter of the acoustic logging tool100. Collectively, the first outward surface182a,the first inward surface184a,and the first curved wall186acan define an upper recess180a.Additionally, the first outward surface182a,the first inward surface184a,and the first curved wall186acan each extend substantially around an entirety of the circumference of the isolator section108. As a result, the upper recess180acan extend around an entirety of the circumference of the isolator section108.

Continuing withFIGS. 6 and 7, likewise, the isolator section108defines a second inward surface184b,a second outward surface182bspaced from the second inward surface184balong the radial direction R, and a second curved wall186bthat extends from the second outward surface182bto the second inward surface184b.The second curved wall186bmay have a second radius of curvature B2that is between about 0.125 inches and about 1 inch. However, like the first radius of curvature B1, the second radius of curvature B2can be contingent upon the overall size of the acoustic logging tool100. The second radius of curvature B2can be the same as the first radius of curvature B1. However, the first and second radii of curvature B1and B2can differ. Collectively, the second outward surface182b,the second inward surface184b,and the second curved wall186bcan define the lower recess180b.Additionally, the second outward surface182b,the second inward surface184b,and the second curved wall186bcan each extend substantially around an entirety of the circumference of the isolator section108. As a result, the lower recess180bcan extend around an entirety of the circumference of the isolator section108. As can be seen inFIGS. 6 and 7, the bottom surface188extends from the first inward surface184ato the second inward surface184balong the axial direction A.

Furthermore, each isolator cavity150(and thus each recess) is generally perpendicularly with respect to the axial direction A and central axis26of the tool. Accordingly, isolator cavity150(and/or recess) is generally parallel to the other isolator cavities.

Continuing withFIGS. 6 and 7, the isolator section108defines sets of projection pairs192that together define the respective isolator cavities150. The projection pairs192include a first projection192aand a second projection192b.The first projection192acan define the first curved wall186a,the first outward surface182a,and a first lateral surface190a.The second projection192bcan define the second curved wall186b,the second outward surface182b,and a second lateral surface190b.The first and second lateral surfaces190aand190bcan face each other to define a slot which the band152resides within.

The isolator cavity150includes multiple dimensions measured along the axial direction A. For example, the cavity150can define a first axial dimension Hi measured from the first curved wall186aof the first projection192ato the second curved wall186bof the second projection192balong the axial direction A, as well as a second axial dimension H2measured from the first lateral surface190aof the first projection192ato the second lateral surface190bof the second projection192balong the axial direction A. Due to the shape of the cavity150, the first axial dimension H1is greater than the second axial dimension H2. In this manner, the isolator section108defines the recesses as curved cutouts that extend around the entire circumference of the isolator section108.

Referring back toFIGS. 2-4, the plurality of cavities150a-150kare spaced apart from adjacent cavities150by a particular distance along the axial direction A. As depicted, the distance between adjacent cavities150varies, and generally decreases from cavity150to cavity150in the downhole direction D. Though only the distances between cavities150a-dwill be explicitly described, the general arrangement exemplified by cavities150a-dcan be representative of all of the cavities150a-150k.As shown, the first cavity150ais spaced from the second cavity150bby a first distance D1, the second cavity150bis spaced from the third cavity150cby a second distance D2, and the third cavity150cis spaced from the fourth cavity150dby a third distance D3. The first distance D1can be greater than the second and third distances D2and D3, and the first and second distances D1and D2can be greater than the third distance D3. However, in other embodiments, it is contemplated that the second and/or third distances D2and D3can be greater than the first distance D1. Also, two or more of the distances D1, D2, and D3can be equal.

The acoustic logging tool100includes one or more bores that extend through its component bodies. The bores, for example,204,208, are formed to house wires and other components of the acoustic logging tool100. The bores are also formed to be open through the various weldments that mount the tool sections together. For example, the acoustic logging tool100can define a feedthrough bore that extends from the receiver section102, through the isolator section108, and to the transmitter section104along the axial direction A. In accordance with the illustrated embodiment, the feedthrough bore can be comprised of a first feedthrough bore (not numbered) defined by the receiver section102, a second feedthrough bore208defined by the isolator section108, and a third feedthrough bore204defined by the transmitter section104. The first feedthrough bore, second feedthrough bore208, and third feedthrough bore204are each aligned along the axial direction A and but are offset with respect to the central bore115through which drilling mud flows.

The bores of the acoustic logging tool100may also include receiver bores. The receiver bores (not shown) extend from the receiver section102, through the isolator section108, and to the transmitter section104along the axial direction A. The receiver bores may include a first receiver bore defined by the receiver section102and a second receiver bore defined by the isolator section108, where the first and second receiver bores are aligned along the axial direction A.

Additionally, the bores of the acoustic logging tool100may include transmitter bores (not shown) that extend from the transmitter section104, through the isolator section108, and to the receiver section102along the axial direction A. The transmitter bores can be comprised of a first transmitter bore defined by the isolator section108and a second transmitter bore defined by the transmitter section104, where the first and second transmitter bores are aligned along the axial direction A.

The feedthrough bores, receiver bores, and transmitter bores may be spaced apart with respect to the central bore115along a radial direction R that is perpendicular to the axial direction A. The feedthrough bore, the receiver bores, and the transmitter bores may be spaced apart with respect to each other along the circumferential direction C, i.e., disposed around the central axis26.

The feedthrough, receiver, and transmitter bores may be configured to contain various components of the acoustic logging tool100, such as wires that extend between various features of the acoustic logging tool100. The bore may be configured as hydraulic passages.

Referring toFIGS. 4 and 5, a lower weldment112mounts the transmitter section104to the isolator section108. The lower weldment112defines a slot212machined into the lower weldment112that extends inwardly from an outer surface of the lower weldment112along the radial direction R. The slot212is configured to be open to first and second bores204and208. The slot212can include a slot cover214disposed within the slot212, such that the slot cover214and the lower weldment112collectively define a slot bore216that is aligned with the first bore (not shown) and the second bore208along the axial direction A. The lower weldment112can also include a sealing weld218that secures the slot cover214within the slot, such that the slot cover214is positioned between the sealing weld218and the slot bore216along the radial direction R. Though one slot is described as extending through the lower weldment112, the lower weldment112can define multiples slots as desired.

The upper weldment110is formed between the isolator section108and the receiver section102. The upper weldment110is similar in construction to the lower weldment112shown inFIG. 5. For instance, the upper weldment110includes a slot that is open to bores, a slot cover in the lower slot and a lower sealing weld that secures the lower slot cover within the lower slot. Though an upper and lower weldment110and112are specifically described, it is contemplated that the acoustic logging tool100can include more or less weldments. The upper and lower weldments attach multiple sections of the acoustic logging tool100together while allowing open communication for bores to route wires as needed.

In operation, after the acoustic logging tool100is lowered downhole into a well, the transmitters172a-172bemits acoustic waves into the earthen formation3surrounding the drill string6. These acoustic waves pass through the earthen formation3, and at least a portion of the acoustic waves are received by the receivers128a-128f.However, a portion of the acoustic waves tend to propagate through the isolator section108and toward the receiver section102. The cavities150a-150kdefined by the isolator section108, as well as the bands152that may be disposed within the cavities150a-150k,help in disrupting, attenuating, and/or dispersing the acoustic waves propagating along the isolator section108. In practice, the isolator section108, via the isolator cavities150, greatly minimizes the tool mode of the acoustic wave, which, in turn, reduces the signal noise received by the receivers128a-128f,thereby improving the signal detection capability and processing of the waveform data from the receivers128a-128f.The isolating qualities of the isolator section108can be attributed to the optimized geometry of the cavities150a-150kdescribed above, such as the curved walls186a-186b,how they extend around the entire circumference, and the variable spacing of the cavities150a-150kalong the axial direction A. Also, by varying the spacing of the cavities150a-150k,as well as by varying the geometry of the cavities150a-150kand the number of cavities150, the acoustic logging tool100can be designed to attenuate specific frequency ranges.

As discussed above, the acoustic logging tool is optimized to minimize the tool mode. “Tool mode” is a term of art that encompasses more than just the direct transmitter/receiver coupling, but also includes drilling related noise, mud flow related noise, as well as the noise contribution of surface waves along the tool body. The isolator section is configured to help manage all of these noise contributions. Furthermore, the design of the transmitters and receivers has elements, such as the structure of the seats in which they are positioned, that can help minimize direct coupling effects of the noise.

It will be appreciated by those skilled in the art that various modifications and alterations of the present disclosure can be made without departing from the broad scope of the appended claims. Some of these have been discussed above and others will be apparent to those skilled in the art. The scope of the present disclosure is limited only by the claims.