Patent Grant
9045970
Various embodiments described herein relate to the field of the acquisition of seismic data from one or more sensing devices located in a borehole, and devices, systems and methods associated therewith.
It is common in the oil and gas industry to collect data about the properties of the geologic layers within oil and gas wells by lowering sensing instruments down the well and taking measurements. Using various sensors, many different attributes of the subsurface may be measured and recorded, including electrical resistivity, conductivity, natural radioactivity, density, gravity, and temperature. Acoustic properties may be measured, and various types of seismic data collected, including VSP (Vertical Seismic Profile) data and microseismic data. It is also common when collecting seismic or microseismic data to place one or more geophones in boreholes drilled specifically for the purpose.
Some downhole sensors require that the sensor or some portion thereof be in physical contact with the sidewall of a borehole to increase coupling between the sensor and the borehole. In many cases, coupling may be achieved by pressing or clamping the sensor into firm contact with the sidewall of the borehole. Downhole sensors typically include transducers capable of sensing seismic signals such as geophones and accelerometers, which typically require good acoustic coupling to the borehole so that they may reliably and accurately receive and measure sound waves passing through adjoining geologic formations. Good acoustic coupling can sometimes be achieved by pressing the geophone into the sidewall of the borehole. This approach, however, introduces a directional variation in acoustic coupling, and therefore may not work well.
Another approach is to position an acoustic sensor centrally within a borehole while maintaining good acoustic coupling. In such an approach, for example, cement is poured into the borehole and fills the annular space between the sensor and the sidewall so that the sensor is firmly cemented in place. This provides efficient acoustic coupling between the sensor and the subsurface, and also maintains the sensor in a fixed orientation, which may be important for certain sensors.
Pouring cement into a borehole until the sensor is covered works well when a single sensor is located at the bottom of a borehole. This approach may not work so well when sensors are spaced at multiple points in a borehole, or are relatively close to the surface within a deep borehole. Conventional techniques can involve cementing sensors at such locations to achieve the desired acoustic coupling by filling almost the entire borehole with cement. There are some drawbacks to this approach, however. It is expensive, and requires more cement than would be needed just to ensure that the sensors are coupled to the sidewalls of the borehole. Moreover, for seismic or microseismic data being recorded with downhole geophones, there is a problem with noise being transmitted down the cement plug and the adjoining taut mechanical and electrical connections between adjoining downhole sensors, which together act as very efficient transducers, and pick up surface noise from well operations, roads, machinery, and the like, and broadcasting such noise deep into the subsurface. Such noise can also be reflected back to the geophones, and may overwhelm signals from desired seismic sources, especially in microseismic recording applications where the sources are relatively weak signals originating from naturally occurring faults and fracturing operations.
What is required are systems and methods of coupling downhole sensors to boreholes that overcome the problems associated with noise generation and propagation described above.
In one embodiment, there is provided a plurality of downhole geophysical sensors configured in a string, at least one of the geophysical sensors in the string being configured for securing or coupling to the sidewall of a borehole, the at least one geophysical sensor comprising at least one geophysical transducer; and an expandable member configured to be deployed into an open or expanded position when the at least one geophysical sensor is located at a desired depth in a borehole having sidewalls, at least portions of the expandable member being configured to engage at least portions of the sidewalls and prevent the passage of a securing or coupling material therearound or therethrough when the securing or coupling material is poured around or atop at least portions of the at least one geophysical sensor when the expandable member is in the open or expanded position.
In another embodiment, there is provided a method of securing or coupling at least one geophysical sensor in a string of geophysical sensors to a borehole, the at least one geophysical sensor comprising at least one geophysical transducer and an expandable member configured to be deployed into an open or expanded position when the at least one geophysical sensor is located at a desired depth in the borehole, the borehole having sidewalls, at least portions of the expandable member being configured to engage at least portions of the sidewalls to prevent the passage of a securing or coupling material therearound or therethrough when the securing or coupling material is poured around or atop at least portions of the at least one geophysical sensor when the expandable member is in the open or expanded position, comprising: lowering the string into the borehole to a desired depth; expanding the expandable member into the open position such that the expandable member engages the at least portions of the sidewall; pouring the securing or coupling material into the borehole around or atop at the at least portions of the at least one geophysical sensor, and permitting the securing or coupling material to substantially to cure or solidify in place around the at least one sensor;
Further embodiments are disclosed herein or will become apparent to those skilled in the art after having read and understood the specification and drawings hereof.
Different aspects of the various embodiments of the invention will become apparent from the following specification, drawings and claims in which:
a) and 1(b) illustrate prior art methods and devices for coupling seismic sensors to a borehole;
a) through 3 (c) show some embodiments of a geophysical sensor configured for coupling to a borehole;
a) through 5(d) show some embodiments of geophysical sensors 200(a) and 200(b) and illustrate a method of securing or coupling same to a borehole.
The drawings are not necessarily to scale. Like numbers refer to like parts or steps throughout the drawings.
In the following description, specific details are provided to impart a thorough understanding of the various embodiments of the invention. Upon having read and understood the specification, claims and drawings hereof, however, those skilled in the art will understand that some embodiments of the invention may be practiced without hewing to some of the specific details set forth herein. Moreover, to avoid obscuring the invention, some well known methods, processes and devices and systems finding application in the various embodiments described herein are not disclosed in detail.
In the drawings, some, but not all, possible embodiments are illustrated, and further may not be shown to scale.
In the following descriptions, the term “well bore” is used generally to describe a production and/or injection well. The term “borehole” is used generally to describe a shallower hole drilled for the purpose of placing seismic sensors in the subsurface. This distinction is made because a borehole drilled for seismic sensors requires cementing to improve acoustic coupling, whereas a well bore drilled for purposes of producing hydrocarbons, injecting fracturing fluids, or the disposal of waste fluids usually is cemented to avoid contamination of the subsurface. Note that the terms “well bore” and “borehole” are interchangeable, however.
Some of the embodiments shown below may be used to secure geophones or accelerometers in a borehole to record microseismic data. Such embodiments are provided as examples, and the methods and techniques described herein may be applied to the cementing of any downhole instrumentation in a well bore or borehole.
Some downhole sensors require that the sensor or some portion thereof be in physical contact with the sidewall of borehole to ensure that the properties being measured are those of the adjoining geologic formation, as well as to ensure proper physical coupling therewith. Sensors such as geophones and accelerometers require good acoustic coupling to the well bore, or to a borehole drilled specifically for the sensors, so that sound waves passing through the adjoining geologic formations may be sensed and measured reliably and accurately. In some cases physical coupling may be achieved by pressing or clamping the sensor into firm contact with the sidewall of the borehole. Often, good acoustic coupling can be achieved by some means of pressing the geophone against the sidewall of the borehole. This approach, however, introduces a directional variation in acoustic coupling, and may not work very well.
As described above, another approach is to position a sensor centrally within a borehole while maintaining good acoustic coupling by pouring cement into the borehole, filling the annular space between the sensor and the sidewall, and surrounding the sensor with cement so that the sensor is firmly secured in place. This provides efficient acoustic coupling between the sensor and the subsurface, and also maintains the sensor in a fixed orientation, which may be important for certain sensors. For example, multi-component borehole geophones capable of measuring all three components of a seismic wave (the compressional wave and both polarizations of shear waves) are frequently used in downhole applications. Knowing their orientation is important when analyzing the data recorded with such geophones. Further, the foregoing method does not introduce any directionality into the data acquired by the sensor.
Cementing instruments in boreholes and wells is common and goes back many years. Many wells are cemented for most of their extent. This may be required for hydrocarbon production wells, and wells for injecting waste fluids into the subsurface for disposal. It is also sometimes done just for the purpose of cementing instruments, in particular seismic sensors such as geophones or accelerometers, into boreholes drilled for the purpose of placing the acoustic sensors in the subsurface.
As described above, pouring cement into a borehole until a seismic sensor is covered works well when there is a single sensor at or near the bottom of the borehole. Just enough cement may be poured into the borehole to cover the measuring sensor and ensure good coupling. This approach may not work well, however, when individual sensors are spaced at multiple points in a borehole, or are relatively close to the surface within a deep borehole. Conventional techniques may involve cementing sensors at such locations to achieve the desired acoustic coupling by filling almost the entire borehole with cement. There are some drawbacks to this approach, however. It is expensive, and requires more cement than would be needed just to ensure that the sensors are coupled to the sidewalls of the borehole.
With the recent growth of microseismic data recording the industry has become more aware of how the cementing process may introduce powerful and unwanted sources of noise into the subsurface. The cement column and the mechanical and electrical couplings and cables between adjoining sensors may act as very efficient transducers, sending noise from surface sources such as pumps, drilling platforms and generators into the subsurface, although some of this noise can reach seismic sensors directly through the subsurface. Further, the cement column may transfer such noise into the geologic layers of the subsurface, whence it may be reflected back from the interfaces between the geologic layers to the seismic sensors. Such noise can overwhelm signals from the desired seismic sources, especially in microseismic recording applications where the microseismic signal sources are relatively weak and originate from naturally occurring faults and hydraulic fracturing operations.
Some early patents describe drilling wells to dispose of waste fluids by injecting such fluids into geologic formations. For this purpose, the well must be fully cemented to avoid the possibility of contamination of the geologic layers the fluid penetrates before reaching the target geologic formation. Placing sensors in the annulus between the well bore and the pipe through which the fluids are injected, and then performing the cementing operation, ensures good coupling between the sensors and the adjacent geologic formations, but at the cost of increased noise levels.
U.S. Pat. No. 5,265,680 to Withers entitled “A method of installing instruments in wells” (“the '680 patent”) describes cementing geophones in wells, but only at or near the bottom of the well. This method is adequate for one sensor housing but is not applicable when a series or string of sensor housings is positioned in the well bore. While such a method may meet the needs of the engineers who need to place an instrument permanently at the bottom of a well bore, it is generally not suitable for recording microseismic data with a string of sensors at multiple points in a borehole or well bore.
U.S. Pat. No. 5,503,225 to Withers entitled “System and method for monitoring the locations of fractures in earth formations” (“the '225 patent”) shows in FIG. 1 thereof a “packer” 18 that “isolates the injection zone from the well annulus.” The '225 patent describes placing sensors in an injection well in the annulus between a pipe and the walls of the well bore. One function of packer 18 is to prevent injected fracturing fluid from flowing back up the well annulus. Packer 18 also allows the cementing of sensors in the well annulus without the risk of cement flowing into the injection zone, which is hopefully part of the path through which recovered hydrocarbons will flow after the fracturing has been completed. Even if sensors are placed some distance above packer 18, cement is poured from the packer 18 all the way up past the sensors because injection wells are generally cemented to prevent high pressure fracturing fluids from leaking into other geologic layers.
U.S. Pat. No. 5,524,709 to Withers entitled “A method of coupling geophones in a borehole” (“the '709 patent”) also shows “packer” 19 in FIG. 1 thereof, where packer 19 serves the same function as in the '225 patent. The '709 patent shows two “listening” boreholes drilled for the purpose of placing geophones below the surface of the earth. Such boreholes do not use a packer, and cement is shown extending uninterrupted from the bottom of the borehole to above the level of the uppermost geophone. The resulting cement plug is likely to cause unwanted noise transmission as described above.
Cementing sensors in place reduces the load on support or transmission cables interconnecting sensors, thereby reducing the risk of failure. U.S. Pat. No. 5,607,015 to Withers entitled “Method and Apparatus for installing acoustic sensors in a well bore” (“the '015 patent”) does not disclose cementing sensors in a well bore or borehole, but instead shows a method of using a load-bearing cable such that sensors are not supported only by a transmission cable used to transmit signals from adjoining sensors to a recording unit. The '015 patent also shows in FIG. 1 thereof “packer” 19, which again is described as being for the purpose of isolating the injection chamber from the well annulus. In the '015 patent, packer 19 performs such a function and is not used to prevent cement from flowing into the injection chamber.
Some patents in the field of microseismic data acquisition describe cementing the entire borehole. This is often unavoidable when the only available location for downhole geophones is the injection well itself. U.S. Pat. No. 5,771,170 to Withers entitled “System and program for locating seismic events during earth fracture propagation” (“the '170 patent”) shows an injection well and two listening boreholes. The '170 patent describes geophone units being cemented in boreholes to enhance acoustic coupling. Such cementing is shown in FIG. 1 of the '170 patent extending from the bottom of the listening boreholes to above the highest geophone units. In the injection well, a “packer” is shown but not mentioned or numbered. While it may be impossible to avoid cementing an injection well, cement plugs in listening boreholes are potential sources of noise, and are not required for production or environmental reasons.
a) and 1(b) illustrate some of the problems in the prior art described above. For purposes of illustration, note that in
In
b) shows a conventional method for improving sensor coupling to sidewalls 26, where sensors 200 are cemented into borehole 20 by cement 28 to produce good acoustic coupling. As described above, one problem created by cementing substantially the entirety of borehole 20 is that the resulting cement plug may act as a noise antenna to propagate and transmit surface noise into the subsurface and thus to sensors 200. Cementing substantially the entirety of borehole 20 also requires considerable time, increased costs and the use of large amounts of cement. Further, cement 28 remains in place after data collection has been completed, and will thereafter continue to broadcast surface noise that may interfere with future data collection and that may also interfere with monitoring instruments in other wells (including production wells).
Referring now to
As further shown in
Still referring to
Data acquisition and processing configurations other than that shown in
Continuing to refer to
In other embodiments, signals generated by surface sensors 12 and/or downhole string of sensors 22 are transmitted by wireless transmitters to a receiver operably connected to data acquisition and recording system 10. In still other embodiments, the electrical, magnetic and/or optical signals generated by surface sensors 12 and/or downhole string of sensors 22 are stored as data in solid state or other memory or recording devices associated with one or more surface sensors 12 and/or downhole string of sensors 22. The electronic memories or recording media associated with the recording devices may be periodically collected or polled, and the data stored therein uploaded to data acquisition and recording system 10.
Other embodiments include, but are not limited to, the recording of seismic waves created by the energy released by explosive charges during the perforation of wellbore 30. When wellbore 30 is cased with a metal pipe or casing, the casing must be perforated so that oil or gas may flow into pipe 34 and thence to the surface of the earth at wellhead 38. Small explosive charges are used to perforate the casing and create perforations 36 through which oil or gas may then flow. Yet further embodiments include, but are not limited to, the recording of seismic waves created by the energy released by explosive charges placed at the very bottom or “toe” of a well, or by a “string shot” (generated by a cord-like length of explosive material placed within the well), both of which techniques are typically carried out for the purpose of developing a seismic velocity depth profile of the well.
Still other configurations and embodiments may be employed to locate, measure and analyze faults in the subsurface of the earth by microseismic detection and processing means, such as, for example, sensing, recording and analyzing seismic energy originating from naturally occurring events, such as slippage along faults, settling or tilting of the subsurface, earthquakes, and other naturally-occurring events.
Data recorded by data acquisition and recording system 10 is typically, although not necessarily, in the form of digitally sampled time series referred to as seismic traces, with one time series or seismic trace for each surface sensor 12 or each sensor contained within downhole string of sensors 22. Each value in the time series is recorded at a known time and represents the value of the seismic energy sensed by surface sensors 12 and downhole string of sensors 22 at that time. The data are recorded over a period of time referred to as the data acquisition time period. The data acquisition time period varies depending on the objective of the seismic survey. When the objective of the survey is to monitor a fracturing operation, for example, the data acquisition time period may be in hours or even days. When the objective of the survey is to acquire data associated with perforating a well, the data acquisition time period is much shorter and may be measured, by way of example, in seconds or minutes.
The rate at which data are recorded for each of the channels corresponding to each of the surface sensors 12 and the sensors contained within downhole string of sensors 22 may also be varied in accordance with the objectives of the survey, and the frequencies characteristic of the seismic energy generated at point of fracture 42, and seismic wavefront 44 as it propagates through subsurface 15 and to surface 8. For example, if frequencies less than or equal to 125 Hz are expected to be sensed or measured in acoustic wavefront 44, data may be sampled at a rate of 2.0 milliseconds (“ms”) per channel to ensure aliasing does not occur. Other sample rates are also possible such as 0.25 ms, 0.5 ms, 1 ms, 4 ms, 8 ms, 16 ms, and so on.
Once the seismic data have been recorded, they must be processed and converted to produce a useful display of information. The types of data processing and the algorithms used varies depending on the type of data collected, and are familiar to those skilled in the art. The objective of processing conventional seismic data is to produce a display of the geologic formations 1, 3, 5 and 7 and corresponding interfaces 2, 4 and 6. The objective of processing microseismic data is to image and monitor the fractures produced by the hydraulic fracturing process. A substantial component of data processing typically concerns noise reduction. Methods or techniques may be implemented during the collection of the data to enhance the recorded signal or reduce the recorded noise and thereby result in a better image of the geologic formations 1, 3, 5 and 7, or better imaging of the fractures. Such techniques and methods are well known in the art and need not be elaborated on further herein.
Referring now to
As described above, a typical string of downhole sensors 22 comprises a plurality of sensors 200 located at different depths along string 22. In one embodiment, sensor housings 208 and 212 are associated with each sensor 200, and one or more of such sensors 200 include expandable members 220 that are configured to expand radially outwardly and deploy from housings 208 and/or 212 into open positions thereby to engage sidewalls 26 of borehole 20. In one embodiment, expandable members 220 are deployed into open and/or closed positions through the control of a user operating control panel 11. Note that sensors 200 may include upper housing 208 and lower housing 212 operably connected to one another, where upper housing 208 has geophysical transducer 210 disposed therewithin, and where lower housing 212 is configured to have expandable member 220 be deployed radially outwardly therefrom. Lower housing 212 may further have solenoid 224 and source of compressed air 216 disposed therewithin or operably attached thereto. Housings 208 and 212 may be integrated into a single housing, or may include yet additional housings.
As shown in
According to other embodiments, not all sensors 200 are fitted with expandable members 220, and cement is blocked from flowing past only selected sensors 200 of string 22. For example, according to one embodiment only the lowermost of sensors 200 is fitted with an expandable member 220 and cement is emplaced from the lowest sensor 200 to the highest sensor 200 or a higher sensor 200 in a continuous column. In another embodiment, cement is emplaced only around and above selected sensors 200 and corresponding expandable members 220
Referring now to
Still referring to
According to one embodiment, and as shown in
Continuing to refer to
Continuing to refer to
Referring to
Referring to
Note further that geophysical transducer 210 in any of sensors 200 in string 22 may be configured not only to sense selected geophysical parameters, but also to act as sources. By way of example, geophysical transducer 210 may be a piezoelectric source transducer that is configured to emit seismic source signals therefrom, which then propagate through housing 208 and cement 26 into the adjoining geologic formation(s) through which borehole 20 has been drilled. Moreover, selected sensors in string 22 may be configured to sense such source signals emitted by other sensors 200 in string 22 so as to, for example, develop a seismic velocity model in the vicinity of borehole 20. In another embodiment, geophysical sensors 210 in sensors 200 may be electrical, magnetic or capacitive electrodes that are electrically, magnetically or capactively coupled through cement 26 (or another suitable securing or coupling material, more about which is said shortly) into the adjoining geologic formation. To that end, cement 26 or other suitable securing or coupling material may be configured to provide the requisite amount of electrical conductivity, magnetic susceptibility or permeability, capacitive dielectric properties or other geophysical parameters to permit accurate measurement of electrical fields, magnetic fields, capacitance, self-potential, or other geophysical parameter, as the case may be. Note further that sensors 200 in string 22 may be configured to measure electrical resistivity or other geophysical parameters between one or more sensors 200.
For clarity, various components of sensors 200 with expandable members 220 are not shown in the Figures, including certain details of downhole string of sensors 22, certain connections to data acquisition and recording system 10, certain connections to and details concerning control panel 11, support cables, pumps, equipment associated with mixing, preparing and delivering cement 26, and other components and devices that those skilled in the art will understand are required to position and cement sensors 200 in borehole 20 and acquire data from same.
Referring now to
Further steps may be included in method 300 described above. In one embodiment, the lowest sensor 200 of string 22 is cemented in place and cement 28 is allowed to set. Cable 24 is then lowered by a small distance of (e.g., several inches) to remove some tension in cable 24 before cementing occurs at the next highest sensor 200. This further reduces noise transmission from the surface of the earth down and through cable 24. In another embodiment, once all sensors 200 have been cemented in place, the orientations of three-component geophones within sensor housings 208 may be determined using techniques well known in the art, including, but not limited to, the recording of seismic signals generated by a small explosive charge, or the impact of a heavy hammer on a plate placed on the surface of the earth. Because one or more sensors 200 are cemented in place, once the orientations of the three-component geophones have been determined they remain substantially constant. In another embodiment, where the lowest sensor 200 in string 22 is proximate the bottom of borehole 20, the lowest sensor 200 may be cemented in borehole 20 without the use of a device to block the annulus of the borehole. Sensors 200 further up string 22 are then cemented in place as described above.
Note that compressed air working in conjunction with expandable or inflatable bladders or reservoirs does not constitute the only means of providing expandable members 220 in sensors 200. For example, electric motors in sensors 200 may be employed in conjunction with worm or other types of gears to open and close expandable arms or sleeves that are configured to engage sidewalls 26 and couple sensors 200 thereto. Expandable foam that hardens once expelled from a suitable container disposed within sensors 200 may also be employed to couple sensors 200 to sidewalls 26; expandable lattices or other structures may be provided in each of sensors 200 that are projected outwardly from the sensors before the expandable foam is ejected from the containers, where the lattices or other structures are configured to hold the foam in place adjacent the sidewalls until the foam hardens.
Note further that expandable members 220 need not “completely” seal the annulus of borehole 20, and instead need only provide only a degree of sealing sufficient to hold cement 28 in place until the cement—or at least most of the cement—sets. In addition, liquids which harden and set in place in borehole 20 other than cement are contemplated, such as the expandable foam described above.
Referring now to
In some embodiments, and as shown in
Referring to
Note that according to some embodiments, cement 28 is pumped down borehole 20 through a hose or tube having an upper end connected to a cement pump at surface 8 of the earth and a lower end positioned just above the top of lowest sensor 200 in string 22. In one embodiment, sufficient cement is poured to completely cover the lowest sensor 200. The hose is then withdrawn to a position above the next lowest sensor 200 in string 22 and the expandable member 220 corresponding thereto is deployed to ensure coupling of such sensor 200 to borehole 20. These steps are repeated until all or selected sensors 200 have been cemented to borehole 20, and the hose is then withdrawn from borehole 20.
The embodiments described herein avoid the problems of previously used approaches by cementing only the extent of borehole 20 proximate sensors 200, while leaving most of borehole 20 open to water and other fluids that do not transmit noise as effectively. This achieves a high degree of acoustic coupling of sensors 200 to borehole sidewalls 26 and adjoining geologic formations 1, 3, 5 and 7 through which borehole 20 has been drilled, but only where such acoustic coupling is desired. As shown in
Various other embodiments of expandable members 220 are contemplated, such as: (a) expandable members operably connected to CO2 cartridges instead of compressed air; (b) comprising sets of overlapping blades configured around housings 212 that are configured to expand radially and that are operably connected to micro-motors controllable from the surface, where the overlapping blades are radially expanded and contracted by activating the micro-motors; (c) sets of overlapping, radially-expanding, spring-loaded blades that are actuated into open positions through control or operation from the surface; (d) deformable or flexible collars formed of materials such as plastic or other deformable and pliant material such as rubber and disposed around sensor housings 212, where the diameters of the collars are slightly greater than that of borehole 20; collars of varying sizes may be provided to allow seismic survey crews to adapt sensors 200 to different sizes or diameters of borehole 20.
Although the above description includes many specific examples, they should not be construed as limiting the scope of the invention, but rather as merely providing illustrations of some of the many possible embodiments of this method. The scope of the invention should be determined by the appended claims and their legal equivalents, and not by the examples given.
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