None.
The present invention relates generally to downhole tools, for example, including directional drilling tools such as three-dimensional rotary steerable tools (3DRS). More particularly, embodiments of this invention relate to rotary steerable tools having formation evaluation sensors deployed in an outer housing thereof. The invention further relates to geosteering methods.
Logging while drilling (LWD) techniques for determining numerous borehole and formation characteristics are well known in oil drilling and production applications. Such logging techniques include, for example, natural gamma ray, spectral density, neutron density, inductive and galvanic resistivity, micro-resistivity, acoustic velocity, acoustic caliper, physical caliper, downhole pressure, and the like. Formations having recoverable hydrocarbons typically include certain well-known physical properties, for example, resistivity, porosity (density), and acoustic velocity values in a certain range. Such LWD measurements (also referred to herein as formation evaluation measurements) may be used, for example, in making steering decisions for subsequent drilling of the borehole.
LWD sensors (also referred to herein as formation evaluation or FE sensors) are commonly used to measure physical properties of the formations through which a borehole traverses. Such sensors are typically deployed in a rotating section of the bottom hole assembly (BHA) whose rotational speed is substantially the same as the rotational speed of the drill string. LWD imaging and geo-steering applications commonly make use of focused FE sensors and the rotation (turning) of the BHA (and therefore the FE sensors) during drilling of the borehole. For example, in a common geo-steering application, a section of a borehole may be routed through a thin oil bearing layer (sometimes referred to in the art as a payzone). Due to the dips and faults that may occur in the various layers that make up the strata, the drill bit may sporadically exit the oil-bearing layer and enter nonproductive zones during drilling. In attempting to steer the drill bit back into the oil-bearing layer (or to prevent the drill bit from exiting the oil-bearing layer), an operator typically needs to know in which direction to turn the drill bit (e.g., up or down). Such information may be obtained, for example, from azimuthally sensitive measurements of the formation properties.
One drawback associated with the above described configuration (in which the FE sensors are rotationally coupled to the drill string) is that the vibration and shock sensitive FE sensors are subject to high lateral, axial, and torsional vibrations during normal drilling operations. Conventional FE sensor deployments are known to be susceptible to vibration and shock related errors and failures. Another drawback associated with the above-described conventional FE sensor deployments is that azimuthal logging techniques require a substantially uniform drill string rotation rate during drilling in order to suitably reduce statistical errors in the azimuthally focused logging data. While the above-mentioned conventional deployments are serviceable, and have been commercially utilized, an improved apparatus and method for acquiring near-bit formation evaluation sensor measurements is needed. In particular, there is a need for an apparatus that is less susceptible to shock and vibration related errors and failures and that is capable of providing both azimuthally focused and non-azimuthally focused formation evaluation sensor measurements.
The present invention addresses the need for improved formation evaluation sensor deployments and improved geosteering methods. Aspects of this invention include rotary steerable deployments including at least one (and preferably a plurality of) formation evaluation sensor(s) deployed in the steering tool housing. In one preferred embodiment, the steering tool housing includes at least first and second circumferentially opposed gamma ray sensors. In a second preferred embodiment, the steering tool includes at least first, second, and third neutron density sensors, each of which is radially offset and circumferentially aligned with a corresponding one of the steering tool blades. The invention further includes methods for geosteering in which a rotation rate of the steering tool housing in the borehole (and therefore the rotation rate of the formation evaluation sensors) is controlled via controlling blade force. The rotation rate may be controlled, for example, so as to promote formation evaluation measurements at or near predetermined tool face angles. The rotation rate may also be controlled so as to enable borehole imaging. Steering decisions may then be made utilizing the formation evaluation measurements and/or derived borehole images.
Exemplary embodiments of the present invention may advantageously provide several technical advantages. For example, deployment of the formation evaluation sensors in the steering tool housing has been found to reduce both shock and vibration exposure and therefore tends to minimize shock and/or vibration related errors and/or failures. Exemplary steering tool embodiments of the invention also advantageously provide for both azimuthal (focused) and non-azimuthal (non-focused) formation evaluation measurements. Exemplary steering tool embodiments of the invention may also provide for simultaneous formation evaluation and physical standoff measurements. Such physical standoff measurements tend to be more reliable than conventional ultrasonic standoff measurements and may be utilized to interpret the formation evaluation measurements (e.g., neutron density measurements).
The invention further provides near-bit, azimuthally resolved formation evaluation measurements which may be utilized, for example, in geosteering applications. The use of azimuthally resolved formation evaluation measurements in geosteering tends to advantageously optimize wellbore placement and reduce dependence on pre-well geological models. Such models are known to be limited by the resolution of seismic data and commonly fail to include faults and other complex geological features (even when correlated with nearby offset wells). Thus, the invention may also provide for improved wellbore placement in geosteering applications.
The invention also advantageously provides a method for controlling the rotation rate of the steering tool housing in the borehole during drilling (e.g., in the range of from about 0.1 to about 30 revolutions per hour). Since the formation evaluation sensor(s) are deployed in the steering tool housing, the invention also advantageously enables the rate at which these sensors rotate in the borehole to be controlled. Controlling the rotation rate of the housing advantageously enables the sensors to be maintained at a desired orientation (e.g., in high side or low side quadrants) for longer periods of time than an undesirable orientation (e.g., in left side or right side quadrants). Such control tends to be advantageous in geosteering applications.
Moreover, controlling the rotation rate of the steering tool housing advantageously enables borehole images (images based on formation evaluation measurements) to be acquired. Such borehole images may also be advantageously utilized in geosteering applications.
In one aspect the present invention includes a downhole steering tool configured to operate in a borehole. The steering tool includes a shaft deployed substantially coaxially in a housing, the shaft and the housing being free to rotate relative to one another about a longitudinal axis of the steering tool. A plurality of blades are deployed on the housing. The blades are disposed to extend radially outward from the housing and engage a wall of the borehole, said engagement of the blades with the borehole wall operative to eccenter the housing in the borehole. A plurality of circumferentially spaced formation evaluation sensors are deployed in the housing, each of the formation evaluation sensors being configured to individually provide a corresponding azimuthally focused sensor response. The plurality of formation evaluation sensors are further configured to collectively provide a non-azimuthally focused sensor response. A controller is configured to acquire sensor data from the formation evaluation sensors and to compute both azimuthally focused and non-azimuthally focused formation evaluation measurements.
In another aspect this invention includes a downhole steering tool configured to operate in a borehole. The steering tool includes a shaft deployed substantially coaxially in a housing, the shaft and the housing being free to rotate relative to one another about a longitudinal axis of the steering tool. At least first, second, and third blades are deployed on the housing. The blades are disposed to extend radially outward from the housing and engage a wall of the borehole, said engagement of the blades with the borehole wall operative to eccenter the housing in the borehole. At least first, second, and third circumferentially spaced formation evaluation sensors are deployed in the housing. Each of the first, second, and third formation evaluation sensors is axially spaced from and circumferentially aligned with a corresponding one of the first, second, and third blades. A controller is configured to compute a standoff distance at each of the formation evaluation sensors based on a radial position of the corresponding blades.
In another aspect the present invention includes a method for geosteering. The method includes deploying a steering tool in a subterranean borehole. The steering tool includes a housing deployed about a shaft, the housing and the shaft free to rotate relative to one another about a longitudinal axis of the steering tool. A plurality of blades are deployed on the housing, the blades disposed to extend radially outward from the housing and engage a wall of the borehole, said engagement of the blades with the borehole wall operative to eccenter the housing in the borehole. The steering tool housing further includes at least one formation evaluation sensor and a tool face sensor deployed therein; The method further includes causing the tool face sensor to measure a tool face angle of the formation evaluation sensor; processing the measured tool face angle to determine a target rotation rate of the housing in the borehole, and causing the housing to rotate in the borehole at about the target rotation rate.
In still another aspect the present invention includes a method for geosteering. The method includes deploying a steering tool in a subterranean borehole. The steering tool includes a housing deployed about a shaft, the housing and the shaft free to rotate relative to one another about a longitudinal axis of the steering tool. A plurality of hydraulically actuated blades are deployed on the housing, the blades disposed to extend radially outward from the housing and engage a wall of the borehole, said engagement of the blades with the borehole wall operative to eccenter the housing in the borehole. The steering tool housing further includes a hydraulic pressure sensor, at least one formation evaluation sensor, and a tool face sensor deployed therein. The method further includes causing the tool face sensor to measure a tool face angle of the formation evaluation sensor, processing the measured tool face angle to acquire a target hydraulic pressure, causing the hydraulic pressure sensor to measure a hydraulic pressure in the housing, comparing the target hydraulic pressure with the measured hydraulic pressure, opening at least one valve when the measured hydraulic pressure is greater than the target hydraulic pressure.
In a further aspect the present invention includes a method of geosteering. The method includes deploying a steering tool in a subterranean borehole, the steering tool including a housing deployed about a shaft, the housing and the shaft free to rotate relative to one another about a longitudinal axis of the steering tool. A plurality of blades are deployed on the housing, the blades disposed to extend radially outward from the housing and engage a wall of the borehole, said engagement of the blades with the borehole wall operative to eccenter the housing in the borehole. The steering tool housing further includes at least one formation evaluation sensor and a tool face sensor deployed therein. The method further includes causing the housing to rotate in the borehole at substantially a predetermined rotation rate, causing the at least one formation evaluation sensor and the tool face sensor to acquire a plurality of data pairs, each data pair comprising at least one formation evaluation measurement and a corresponding tool face angle and processing the acquired data pairs to construct a borehole image. The method still further includes processing the borehole image to acquire at least one image parameter and evaluating the at least one image parameter to control a direction of drilling, the direction of drilling being controlled via controlling extension and retraction of the blades.
The foregoing has outlined rather broadly the features of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other methods, structures, and encoding schemes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
Referring first to
It will be understood by those of ordinary skill in the art that methods and apparatuses in accordance with this invention are not limited to use with a semisubmersible platform 12 as illustrated in
Turning now to
Steering tool 100 may be used in directional drilling operations (including geosteering applications) to steer drill bit 32 along a predetermined drilling path. To steer (i.e., change the direction of drilling), one or more of blades 150 are extended and exert a force against the borehole wall. The steering tool 100 is moved away from the center of the borehole by this operation, altering the drilling path. It will be appreciated that the tool 100 may also be moved back towards the borehole axis if it is already eccentered. In general, increasing the offset (i.e., increasing the distance between the tool axis and the borehole axis) tends to increase the curvature (dogleg severity) of the borehole upon subsequent drilling. In the exemplary embodiment shown, steering tool 100 is configured for “push-the-bit” steering in which the direction (tool face) of subsequent drilling tends to be the same (or nearly the same; depending, for example, upon local formation characteristics) as the offset between the tool axis and the borehole axis. The invention is not limited to a push-the-bit configuration. It is equally well suited for “point-the-bit” steering in which a near-bit stabilizer is utilized and the direction of subsequent drilling tends to be opposite the offset between the tool axis and borehole axis.
As described above, shaft 115 and housing 110 are configured to rotate substantially freely with respect to one another. To facilitate controlled steering, the housing 110 preferably is substantially non-rotating or slowly rotating with respect to the borehole. By keeping the blades 150 in a substantially fixed position with respect to the circumference of the borehole (i.e., by limiting rotation of the housing 110), it is possible to steer the tool without constantly extending and retracting the blades 150. During a typical drilling operation, housing 110 typically rotates slowly in the borehole (e.g., at a rate in the range from about 0.1 to about 30 revolutions per hour). In order to accommodate the slow rotation of housing 110 and maintain a predetermined drilling direction, adjustments are typically made to the blade positions during drilling.
With reference now to
Hydraulic module 130 further includes a piston pump 240 operatively coupled with drive shaft 115. In the exemplary embodiment shown, pump 240 is mechanically actuated by a cam 118 formed on an outer surface of drive shaft 115, although the invention is not limited in this regard. Pump 240 may be equivalently actuated, for example, by a swash plate mounted to the outer surface of the shaft 115 or an eccentric profile formed in the outer surface of the shaft 115. In the exemplary embodiment shown, rotation of the drive shaft 115 causes cam 118 to actuate piston 242, thereby pumping pressurized hydraulic fluid to high pressure reservoir 236. Piston pump 240 receives low pressure hydraulic fluid from the low pressure reservoir 226 through inlet check valve 246 on the down-stroke of piston 242 (i.e., as cam 118 disengages piston 242). On the upstroke (i.e., when cam 118 engages piston 242), piston 242 pumps pressurized hydraulic fluid through outlet check valve 248 to the high pressure reservoir 236. It will be understood that the invention is not limited to any particular pumping mechanism. In other embodiments, an electric powered pump may be utilized, for example, powered via electrical power generated by a mud turbine or from batteries such as lithium batteries.
Hydraulic fluid chamber 220 further includes a pressurizing spring 234 (e.g., a Belleville spring) deployed between an internal shoulder 221 of the chamber housing and a high pressure piston 232. As the high pressure reservoir 236 is filled by pump 240, high pressure piston 232 compresses spring 234, which maintains the pressure in the high pressure reservoir 236 at some predetermined pressure above wellbore pressure. Hydraulic module 130 typically (although not necessarily) further includes a pressure relief valve 235 deployed between high pressure and low pressure fluid lines. In one exemplary embodiment, a spring loaded pressure relief valve 235 opens at a predetermined differential pressure (e.g., about 750 psi), thereby limiting the pressure of the high pressure reservoir 236 a predetermined amount above wellbore pressure. However, the invention is not limited in this regard.
With continued reference to
In order to extend blade 150A (radially outward from the tool body), valve 254A is opened and valve 256A is closed, allowing high pressure hydraulic fluid to enter chamber 244A. As chamber 244A is filled with pressurized hydraulic fluid, piston 252A is urged radially outward from the tool, which in turn urges blade 150A outward (e.g., into contact with the borehole wall). When blade 150A has been extended to a desired (predetermined) position, valve 254A may be closed, thereby “locking” the blade 150A in position (at the desired extension from the tool body).
In order to retract the blade (radially inward towards the tool body), valve 256A is open (while valve 254A remains closed). Opening valve 256A allows pressurized hydraulic fluid in chamber 244A to return to the low pressure reservoir 226. Blade 150A may be urged inward (towards the tool body), for example, via spring bias and/or contact with the borehole wall. In the exemplary embodiment shown, the blade 150A is not drawn inward under the influence of a hydraulic force, although the invention is not limited in this regard.
Hydraulic module 130 may also advantageously include one or more sensors, for example, for measuring the pressure and volume of the high pressure hydraulic fluid. In the exemplary embodiment shown on
In the exemplary embodiments shown and described with respect to
Referring now to
With further reference to
In the preferred embodiment depicted in
With reference now to
As is known to those of ordinary skill in the art, nuclear logging measurements are particularly degraded with increasing standoff distance (the distance between the FE sensor and the borehole wall) due to neutron scattering in the borehole fluids in the annulus between the sensor and formation. Therefore, a measurement of the standoff distance between the sensor and borehole wall is important in order to properly weight the acquired sensor data. Prior art neutron density logging tools often utilize simultaneous ultrasonic standoff measurements as the tool is rotating in the borehole. Alignment of the standoff sensor with the neutron sensors provides a determination of the standoff distance between the neutron sensors in the formation. While such prior art techniques are commercially serviceable, there are drawbacks. For example ultrasonic standoff tools are known to provide inaccurate or unreliable standoff measurements in certain borehole environments and drilling fluids. Ultrasonic caliper tools also tend to be expensive and prone to shock and vibration related failure during operation in harsh borehole environments. They also have difficulty measuring a reliable standoff when there are gas bubbles in the drilling fluid.
The preferred embodiment depicted in
The steering tool 100 described above with respect
During a typical directional drilling application (e.g., a geosteering application), a steering command may be received at steering tool 100, for example, via drill string rotation encoding. Exemplary drill string rotation encoding schemes are disclosed, for example, in commonly assigned U.S. Pat. Nos. 7,222,681 and 7,245,229. Upon receiving the steering command (which may be, for example, in the form of transmitted offset and tool face values), new blade positions are typically calculated and each of the blades 150A, 150B, and 150C is independently extended and/or retracted to its appropriate position (as measured by displacement sensors 274A, 274B, and 274C). Two of the blades (e.g., blades 150B and 150C) are preferably locked into position as described above (valves 254B, 254C, 256B, and 256C are closed) with respect to
It has been found that the rotation rate of the housing 110 with respect to the borehole is approximately inversely related to the force of the floating blade (e.g., blade 150A) against the borehole wall. In other words, the rotation rate of the housing 110 tends to increase with decreasing floating blade force and decrease with increasing floating blade force. Therefore, in order to increase the rotation rate of the housing 110, the force applied to the floating blade may be decreased. Alternatively, in order to decrease the rotation rate of the housing 110, the force applied to the floating blade may be increased. It will be appreciated that it is typically necessary to maintain some minimum applied force to the floating blade so as not to degrade the steerability of the tool 100 (the blade force of the floating blade has also been found to effect the steerability of the tool 100 as is described in more detail in commonly assigned, U.S. application Ser. No. 11/595,054 now U.S. Pat. No. 7,464,770).
In one exemplary embodiment of the invention, the blade force of the floating blade may be controlled by controlling the system pressure of the hydraulic fluid used to extend the blades 150. For clarity of exposition, control of the hydraulic fluid pressure will be described for a tool configuration in which blade 150A is floating and blades 150B and 150C are locked in their predetermined positions (as described above). The invention is, of course, not limited in this regard. As described above with respect to
An exemplary geosteering operation is now described in more detail with respect to
It will be appreciated that the housing 110 rotates significantly slower than the drill string. Therefore accelerometers may be advantageously utilized to measure the sensor tool face. The use of gravity-based sensors tend to be advantageous in steering tool 100 embodiments (as opposed to magnetometers) since the housing is often fabricated from at least some Ferro-magnetic materials. The invention is not limited in this regard, however, since magneto-sensitive devices (e.g. magnetometers) and/or gyroscopic sensors (e.g. mechanical gyro) can be used to obtain tool face angle.
It will be appreciated that the rotation rate of the housing 110 in the borehole may be controlled by controlling the extendable blades deployed in the housing. For example, in one exemplary embodiment, the housing may be made to rotate at the first rotation rate by causing at least one of the blades to engage the borehole wall at a first radial force and at the second rotation rate by causing the blade(s) to engage the borehole wall at a second radial force (with the first radial force being less than the second radial force). As described above, the rotation rate of the housing 110 typically decreases with increasing blade force. It will be understood that the blade force applied to the borehole wall may be controlled using either type of directional control mechanism described above in the Background Section of commonly assigned, co-pending U.S. Patent Application Publication 2008/0110674.
In a preferred embodiment of the method depicted in
As stated above,
After a predetermined time (e.g., 1 second), the blade pressure is measured again and is compared with the target pressure (at 814 and 816). If the pressure measured at 814 is less than or equal to the target pressure acquired at 808, the valve is closed at 818 and the controller returns to step 804 at which the hydraulic pressure is again measured after some predetermined time. If the measured pressure remains greater than the target pressure, the valve is left open and the controller waits for a predetermined time before repeating steps 814 and 816.
The target system pressure may be acquired at step 808 using substantially any suitable protocol. For example, the controller may be preprogrammed to include first and second, upper and lower target system pressures. When the measured tool face of a preselected one of the sensors 120 is in either of the high side or low side quadrants 601 or 603 (
It will further be appreciated that the system pressure may also be controlled via implementing a controllable system valve (e.g., a solenoid valve) in place of (or in parallel with) pressure relieve valve 235 (
It will be understood that the closed loop geosteering methods depicted in
Steering tool embodiments in accordance with the present invention may also be utilized to acquire formation evaluation images, which may be further utilized in geosteering applications. For example, the radial force on at least one of the blades 150 may be controlled such that housing 110 rotates at an approximately constant rate in the borehole. In general, a relatively fast, approximately constant rotation rate is desirable for acquiring images. A rotation rate in the range from about 5 to about 30 revolutions per hour has been found to be suitable for such formation evaluation imaging applications. Rotation rates less than about five revolutions per hour tend to be too slow for imaging applications at most serviceable rates of penetration. Rotation rates greater than about 30 revolutions per hour may adversely affect the steerability of the steering tool (since very low blade forces tend to be required). Rotation rates greater than about 30 revolutions per hour also tend to require a large hydraulic fluid pumping capacity in order to continually adjust the position of the blades.
In such imaging applications, formation evaluation measurements may be acquired and correlated with corresponding tool face measurements while the housing 110 rotates in the borehole. The formation evaluation measurements and corresponding tool face measurements may be used to construct a borehole image using substantially any know methodologies, for example, conventional binning, windowing, or probability distribution algorithms. U.S. Pat. No. 5,473,158 discloses a conventional binning algorithm for constructing a borehole image. Commonly assigned U.S. Pat. No. 7,027,926 discloses a technique for constructing a borehole image in which sensor data is convolved with a one-dimensional window function. Commonly assigned, U.S. patent application Ser. No. 11/881,043 (now U.S. Pat. No. 7,558,675) describes an image constructing technique in which sensor data is probabilistically distributed in either one or two dimensions. It will be appreciated by those of ordinary skill in the art that a borehole image is essentially a two-dimensional representation of a measured formation (or borehole) parameter as a function of sensor tool face and measured depth of the borehole.
The constructed borehole images may be evaluated uphole and/or downhole using techniques known to those of ordinary skill in the art. The evaluated borehole images may then be used as the basis for steering decisions (i.e., blade adjustment decisions). For example, the ratio of high side gamma ray counts to low side gamma ray counts may be obtained from the constructed borehole image and may be used to control the direction of drilling in the manner described above. Moreover, evaluation of the borehole image may advantageously enable a formation dip angle to be determined. The dip angle is known to those of ordinary skill in the art to be the tilt angle of the subterranean formation relative to the surface of the earth. The dip angle acquired from the borehole image may also be used as a basis for steering decisions.
With reference again to
In the exemplary embodiments shown above, modules 130 and 140 are in electronic communication with pressure sensors 262, 272A, 272B, 272C and displacement sensors 264, 274A, 274B, 274C. Modules 130 and 140 are further in electronic communication with valves 235, 254A-C, and 256A-C. The control modules 130 and 140 may further include instructions to receive rotation and/or flow rate encoded commands from the surface and to cause the steering tool 100 to execute such commands upon receipt. Module 140 typically further includes at least one tri-axial arrangement of accelerometers as well as instructions for computing gravity tool face and borehole inclination (as is known to those of ordinary skill in the art). Such computations may be made using either software or hardware mechanisms (using analog or digital circuits). Electronic module 140 may also further include one or more sensors for measuring the rotation rate of the drill string (such as accelerometer deployments and/or Hall-Effect sensors) as well as instructions executing rotation rate computations. Exemplary sensor deployments and measurement methods are disclosed, for example, in commonly assigned, U.S. Patent Publications 2007/0107937 and 2007/0289373.
Electronic module 140 typically includes other electronic components, such as a timer and electronic memory (e.g., volatile or non-volatile memory). The timer may include, for example, an incrementing counter, a decrementing time-out counter, or a real-time clock. Module 140 may further include a data storage device, various other sensors, other controllable components, a power supply, and the like. Electronic module 140 is typically (although not necessarily) disposed to communicate with other instruments in the drill string, such as telemetry systems that communicate with the surface and an LWD tool including various other formation sensors. Electronic communication with one or more LWD tools may be advantageous, for example, in geo-steering applications. One of ordinary skill in the art will readily recognize that the multiple functions performed by the electronic module 140 may be distributed among a number of devices.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alternations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
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