Patent Publication Number: US-8534354-B2

Title: Completion string deployment in a subterranean well

Description:
RELATED APPLICATIONS 
     None. 
     FIELD OF THE INVENTION 
     The present invention relates generally to evaluation, completion, stimulation, and/or workovers of oil and gas wells. More particularly, the invention relates to methods for running a wellbore completion assembly into a directional and/or horizontal well. 
     BACKGROUND OF THE INVENTION 
     Drilling and completing oil and gas wells is a highly expensive undertaking since oil and gas bearing formations are generally located many thousand of feet below the surface of the earth. As is known to those of ordinary skill in the art, deviated wells are commonly utilized to improve production, reduce costs, and minimize environmental impacts. Wellbores including vertical, doglegged, and horizontal sections are now common. For example, extended reach wellbores commonly extend vertically only a few thousand feet downward from the surface but may extend many thousand feet (even tens of thousands of feet) horizontally. 
     Completing oil and/or gas wells requires deploying a completion assembly (also referred to herein as a completion string), for example, including a casing string or a sand screen in a previously drilled borehole. The completion assembly may also include a production combination string that can include many different types of downhole production or well stimulation devices (e.g. inflatable packers) and can be deployed in either a cased or open wellbore. In many completion applications, a casing string is lowered into the borehole under the influence of the Earth&#39;s gravitational field. In highly deviated, horizontal, and/or extended reach wellbores, deployment of the casing string can be problematic. For example, when the wellbore is highly deviated and of substantial length, the longitudinal frictional forces (referred to herein as drag) along the length of the casing become so great that the casing can become damaged or even stuck in the well. 
     One method that is sometimes used to deploy a casing string in a wellbore is to rotate the assembly during deployment. While rotation of the casing string tends to reduce drag, it also subjects the string to high torsional stresses. Conventional casing tends to be highly susceptible to both axial and torsional stresses. These axial and torsional stresses are known to buckle or otherwise damage completion assembly components during installation. As a result, high strength casing components (referred to in the industry as “premium joints”) are required when using rotation. This adds significant expense to a conventional casing operation and is therefore undesirable for many operations. Moreover, a completion assembly commonly includes one or more tubulars having slots, screens, or other openings (for example, heavy oil applications commonly employ a string of slotted casing). These openings tend to further reduce the strength of the casing and therefore further limit the axial and/or torsional load that can be applied to the string. 
     One disclosed method for extended reach wells is to float the casing off the bottom of the well with a dense fluid such as drilling fluid (mud). In such operations, the casing is run into the well empty with a shoe or plug deployed on the lower end. As it moves into the mud-filled well, a buoyancy force tends to float the casing string off the bottom of the well. While the buoyancy of the casing tends to reduce drag, it can also present problems. For example, floated casing has a tendency to “kick back” (up and out) of the wellbore. This kick back can be a significant safety concern and requires that the casing be firmly held at all times while it is lowered into the wellbore. 
     The aforementioned drag is often significant even when the casing is floated. Those of ordinary skill in the art will appreciate that a horizontal section of a wellbore is seldom perfectly straight and often includes various peaks, valleys, twists, and turns (especially in geosteering and well twinning applications). These borehole features can significantly increase friction. Moreover, a casing string including various openings (e.g., slots) is not readily floated since the drilling mud can quickly fill the casing as it is lowered into the wellbore. 
     Therefore, there remains a need in the oilfield services industry for improved methods for deploying a completion string in a deviated borehole. In particular, there remains a need for deployment methods that reduce drag between the casing string and the borehole wall. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above-described need for improved methods for deploying a completion string (completion assembly) in a drilled borehole. Aspects of this invention include a method in which a completion assembly is rotated at the surface while axially urging the assembly downward (deeper) into a previously drilled borehole. This rotation is preferably only partially transferred down the completion string such that a lower portion of the string typically remains rotationally stationary with respect to the borehole. In one exemplary embodiment, an applied torque may be held at a constant value (or alternatively the rotation may be stopped) when a measured parameter reaches a predetermined threshold. The completion string may then be axially reciprocated upwards and downwards from the surface so as to enable the lower portion of the completion string to rotate in the drilled borehole. The process is typically repeated numerous times during deployment of the completion string. In another exemplary embodiment, the completion assembly may be rotated back and forth, alternating between first and second rotational directions so as to maintain an applied surface torque below a predetermined threshold. For example, the completion assembly may be rotated in the first direction until the surface torque reaches the threshold. Rotation is then reversed until the torque again reaches the threshold at which point the rotation is reversed again (and so on). 
     Exemplary embodiments of the present invention advantageously provide several technical advantages. In particular, the invention has been found to reduce longitudinal frictional forces (drag) between a completion assembly (completion string) and the wall of a previously drilled borehole. Reduced drag advantageously reduces stress, and therefore reduces damage imparted to the string during deployment. The method further advantageously enables sensitive components, for example, including screens and slotted liners, to be more easily deployed. 
     Exemplary embodiments of the invention may be further advantageous in that they tend to obviate the need to use expensive, high strength components. The invention also tends to obviate the need to include additional friction reducing components in the completion string (e.g., a swivel type device between the drill pipe and completion string or low friction stabilizers for reducing drag). The invention, therefore, tends to reduce cost and save rig time in that fewer, and less expensive, completion string components are required. 
     In one aspect, the present invention includes a method for deploying a wellbore completion assembly in a previously drilled borehole. The wellbore completion assembly is deployed in the previously drilled borehole and axially urged downward into the borehole from a surface location. The completion assembly is rotated from the surface and at least one parameter is measured while rotating. An applied surface torque is held at a substantially constant value when the measured parameter reaches or exceeds a predetermined threshold (in an alternative embodiment a rotary brake may be applied). The completion string is then axially reciprocated upwards and downwards from the surface while the surface torque is held at the constant value or while the rotary brake is applied). 
     In another aspect, the present invention includes a method for deploying a wellbore completion assembly in a previously drilled borehole. The wellbore completion assembly is deployed in the previously drilled borehole and axially urged downward into the borehole from a surface location. The completion assembly is rotated in a first direction from the surface. At least a first parameter is measured while the completion string is rotated in the first direction. The completion string is rotated in a second direction from the surface when the first parameter measured reaches or exceeds a first predetermined threshold. At least a second parameter is measured while rotating the completion assembly in the second direction. The process of rotating and measuring is repeated when the second parameter reaches or exceeds a second predetermined threshold. 
     The foregoing has outlined rather broadly the features and technical advantages 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 structures for carrying out the same purposes of the present invention. It should also be realize 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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  depicts a drilling rig on which exemplary method embodiments in accordance with the present invention may be utilized. 
         FIG. 2  depicts one exemplary embodiment of a suitable system for use in deploying a completion string in a borehole 
         FIG. 3A  depicts a flow chart of one exemplary method embodiment in accordance with the present invention. 
         FIG. 3B  depicts a flow chart of another exemplary method embodiment in accordance with the present invention. 
         FIG. 4A  depicts a flow chart of still another alternative method embodiment in accordance with the present invention. 
         FIG. 4B  depicts a flow chart of yet another exemplary method embodiment in accordance with the present invention. 
         FIG. 5  depicts a flow chart of a further alternative method embodiment in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts a drilling rig  10  suitable for use with exemplary method embodiments in accordance with the present invention. In  FIG. 1 , a drilling platform is positioned in the vicinity of an oil or gas formation (not shown). The rig  10  includes a derrick and a hoisting apparatus for raising and lowering various assemblies, for example, completion assembly  30 , which, as shown, is deployed in borehole  60 . The rig typically further includes a top drive  15  (or other suitable assembly such as a rotary table) rotatably connected to the completion assembly  30 . The top drive  15  may be configured to rotate the completion assembly in either direction (clockwise or counterclockwise). It will be understood that the terms completion assembly and completion string are used interchangeably herein. 
     In  FIG. 1 , borehole  60  is a deviated borehole including vertical  62 , doglegged  64 , and horizontal  66  sections. While the invention is not limited to such deviated borehole configurations, it will be appreciated that exemplary embodiments of the invention are particularly well suited for use with highly deviated and extended reach wells including horizontal (or nearly horizontal) sections. It will also be understood by those of ordinary skill in the art that the present invention is not limited to use with a land rig  10  as illustrated in  FIG. 1 . The present invention is equally well suited for use with any kind of subterranean completions operations, either offshore or onshore. The invention is not even limited to the oilfield and may also be used, for example, in under river crossing and other similar applications. 
     With continued reference to  FIG. 1 , completion assembly  30  may be coupled to the top drive  15 , for example, via a section of conventional drill pipe  35 .  FIG. 1  further depicts one or more sensors  20  that are configured to provide measurements, for example, of the torque and axial load applied to the completion string. While these sensors  20  are depicted as being deployed in a “sub” located between drill pipe  35  and top drive  15 , it will be understood that such a depiction is for convenience of illustration only. The sensors can be located at substantially any suitable rig or top drive location. While surface sensors are preferred, it will be understood that one or more of the sensors  20  may be deployed, for example, on the drill pipe  35  or even on the completion string  30 . The sensors are further preferably, although not necessarily, electronically connected to a controller  55  which is configured to control the top drive  15  and therefore the rotation applied to the completion string  30 . 
     Completion string  30  may include a casing shoe  32  deployed at a lower end of a plurality of interconnected casing tubulars (which are not shown separately). The string  30  often further includes specialized equipment or assemblies known to those of ordinary skill in the art. For example, the completion string  30  may include one or more of the following components: axially slotted tubulars, screens, sand control screens, packers, centralizers, and the like. Slotted tubulars are commonly employed, for example, in heavy oil applications such as tar sand formations. The invention is not limited in these regards. 
       FIG. 2  depicts one exemplary embodiment of a suitable system  50  for executing method embodiments in accordance with the present invention. In the exemplary embodiment depicted, system  50  includes the aforementioned one or more sensors  20 . The system may include substantially any number of sensors  20 , for example, including a surface angle sensor  22 , a surface torque sensor  24 , and a surface axial load (hook load) sensor  26 . The system  50  may further include a downhole tool face sensor  28  (e.g., an accelerometer set and/or a magnetometer set) for measuring the tool face of a component in the completion assembly. Those of ordinary skill in the art will also understand that torque sensor  24  need not directly measure the applied torque. For example, a “torque” sensor may measure the electric current drawn by an electric motor that operates the top drive  15  or a hydraulic pressure applied to an hydraulic motor the operates the top drive  15 . The torque sensor may also be implemented as a strain gage on drill pipe  35  or on the top drive shaft. 
     At least one of the sensors is typically deployed in electronic communication with controller  55  (which may include, for example, a conventional computer or computerized system). The controller  55  may be in further communication with top drive  15  (or some other mechanism configured to rotate the completion string) and is typically configured to control the rotation of the top drive  15 . For example, in preferred embodiments of the invention, the controller may be configured to controllably rotate the top drive at low rotation rates (e.g., less than 10 rpm) while not exceeding a predetermined applied torque limit. While  FIG. 2  depicts a system suitable for automated control, it will be understood that the invention is not limited in this regard. Exemplary embodiments in accordance with the invention may likewise employ manual control schemes. 
       FIG. 3A  depicts one exemplary method embodiment  100  in accordance with the present invention. At  102  a suitable completion string is deployed in a previously drilled subterranean borehole. The completion string may include a conventional casing string (as depicted on  FIG. 1 ), for example, including a plurality of casing tubulars (commonly referred to in the industry as “joints”) connected end to end. A conventional completion string may alternatively and/or additionally include, for example, one or more slotted tubulars or screens. The completion string is typically connected to a length of drill pipe, which is in turn connected with the top drive (or other suitable rotary control mechanism). The invention is not limited in regard to the means by which the completion string is connected to the rotary control mechanism. 
     At  104  an axial force is applied to the completion string. The axial force is directed downwards into the drilled borehole and thereby urges the completion string deeper into the hole (e.g., down around a dogleg and/or further along a horizontal section). At  106  the completion string is rotated from the surface (e.g., via the top drive) in a first direction (e.g., a clockwise direction looking downward into the borehole). In one exemplary embodiment, the top drive may be accelerated to a constant rotation rate in the first direction, thereby at least partially rotating the completion string in the first direction. By partially rotating it is meant that only a portion of the completion string (typically the portion located nearer to the surface) rotates in the borehole under the influence of the applied torque. For example, rotating at the surface may be sufficient to overcome the longitudinal frictional force between the upper portion of the completion string and the borehole wall. The lower portion of the completion string may remain rotational stationary with respect to the borehole. Low rotation rates are generally preferred so as to improve the controllability of the process (e.g., to reduce the likelihood of a high torque being inadvertently applied). Preferred rotation rates are less than about 15 rpm. Most preferred rotation rates are less than about 10 rpm (e.g., about 5 rpm). 
     At  108  a first parameter is measured while rotating the completion string from the surface in the first direction in  106 . The first parameter is preferably measured “continuously”, i.e., repeatedly at some frequency, for example, at least one measurement per second (1 Hz) although lower frequencies may also be used. Such continuous measurements may be either discrete or analog and may be advantageously utilized in automated methods in accordance with the present invention. Non-continuous (or intermittent) measurements may also be utilized, for example, in manual methods. 
     The first parameter may include substantially any suitable parameter. For example, in a preferred embodiment of the invention, the first parameter is applied surface torque (the rotational force applied to the casing string at the surface). In other exemplary embodiments, the first parameter may include: (a) a length of time, (b) a surface angle, (c) an applied arc distance (a rotation angle multiplied by a radius), and (d) an applied energy (e.g., an applied torque multiplied by a surface angle). 
     The rotation in  106  is typically applied until the first parameter equals or exceeds (is greater than or equal to) a first predetermined threshold. This is depicted at  108  and  110  in which the measured first parameter is compared with the first predetermined threshold value. It will be understood by those of ordinary skill in the art that the first parameter may be readily re-defined such that the rotation in  106  is applied until the parameter is less than or equal to a threshold (e.g., by taking the inverse of the parameter). The invention is not limited in this regard. When the measured parameter is less than the threshold, the method continues to monitor the first parameter while the string is rotated at the surface (i.e., the method returns to  108  where the first parameter is measured again). When the first parameter is greater than or equal to the first predetermined threshold value, the method proceeds to  122 . For example, in a preferred embodiment of the invention, the completion string is rotated at the surface in  106  until the applied torque reaches or exceeds the predetermined value. 
     At  122 , the applied surface torque (e.g., applied via top drive  15 ) is held (or limited to) a substantially constant value. This constant value (or torque limit) may be the value of the applied surface torque at the time at which the first parameter exceeds the threshold in  110 . For example, when the measured parameter is applied surface torque, the constant value commonly equals the threshold. When some other parameter is measured (e.g., angle or time), the constant value typically equals the surface torque value applied at the time at which the parameter first exceeds the threshold. It will be understood that application of the torque limit in  122  commonly stalls the top drive (since more torque is required to continue rotating). 
     At  124 , the completion string is moved (reciprocated) upwards and downwards from the surface (e.g., between first and second longitudinally opposed positions) while the applied surface torque is held at the constant value. Such reciprocation is intended to reduce the frictional forces between the lower portion of the completion string and the borehole wall and to thereby cause the lower portion of the completion string to rotate in the drilled borehole in the same direction as the rotation in  106 . Drilling fluid may also be circulated in the drilled borehole during this step to reduce friction and promote rotation of the lower portion of the completion assembly. At some time (e.g., after a predetermined number of upward and downward movements of the completion string), method  100  typically returns to step  104  and repeats steps  104 ,  106 ,  108 ,  110 ,  122 , and  124 . This process may be continued indefinitely until the completion assembly is fully deployed in the drilled borehole. 
       FIG. 3B  depicts an alternative method embodiment  140  in accordance with the present invention. Method embodiment  140  is similar to method  100  in that it includes steps  102  through  110  as depicted on and described above with respect to  FIG. 3A . At  142 , a rotary brake is applied to the top drive. Application of the brake stops the rotation and holds the top drive at a singular angular position. At  124 , the completion string is moved (reciprocated) upwards and downwards from the surface (e.g., between first and second longitudinally opposed positions) as described above with respect to  FIG. 3A . The reciprocation is intended to cause the lower portion of the completion assembly to rotate in the drilled borehole as also described above with respect to  FIG. 3A . Drilling fluid may also be circulated in the drilled borehole during this step to reduce friction and promote rotation of the lower portion of the completion assembly. At some time (e.g., after a predetermined number of upward and downward movements of the completion string), the brake (applied at  142 ) is released and the method  140  returns to step  104  and repeats steps  104 ,  106 ,  108 ,  110 ,  142 , and  124 . This process may be continued indefinitely until the completion assembly is fully deployed in the drilled borehole. 
       FIG. 4A  depicts another alternative method embodiment  160  in accordance with the present invention. Method embodiment  160  is also similar to method  100  in that it includes steps  102  through  110  as depicted on and described above with respect to  FIG. 3A . At  162  the completion string is rotated in a second (opposite) direction when the first parameter measured in  108  is greater than or equal to the first predetermined threshold. The top drive may be rotated in the second direction, for example, by decelerating the rotation in the first direction and then accelerating rotation in the second direction to a constant rotation rate in the second direction, thereby at least partially rotating the completion string in the second direction. Low rotation rates are preferred as described above with respect to  FIG. 3A . 
     The completion string is typically rotated in  162  until a second parameter equals or exceeds a second predetermined threshold (again, this parameter may be readily redefined such that the rotation continues until the parameter is less than or equal to the threshold). This is depicted at  164  and  166  in which the second parameter is measured and compared with the second predetermined threshold value. The second parameter is also preferably (although not necessarily) measured continuously. When the second parameter is less than the corresponding threshold, the method  160  continues to monitor the second parameter while the rotational force is applied. When the second parameter is greater than or equal to the second predetermined threshold value, the method  160  returns to  106  and repeats  106 ,  108 ,  110 ,  162 ,  164 , and  166 . 
     It will be understood that in certain embodiments, the first and second parameters may be the same parameter. For example, the first and second parameter may both include an applied surface torque, such that the method includes measuring a first applied torque in  108  and a second applied torque in  164 . In such embodiments, the first and second predetermined threshold values may be equal or unequal (the invention is not limited in these regards). 
     The first and second parameters may also be different parameters. For example, in one exemplary embodiment, the first parameter may include applied surface torque and the second parameter may include another parameter such as rotation time or rotational angle. In such an embodiment, the completion string may be rotated in a first direction at  106  until a threshold torque is applied and then rotated in the opposite direction at  162  for a predetermined time or through a predetermined angle. The invention is, of course, not limited in these regards. 
     In still other embodiments of the invention, multiple parameters may be measured simultaneously at  108  and  164 . These parameters may then be used in combination at  110  and  166 . For example, applied torque and rotational angle may be simultaneously measured at  108 , with each of these parameters being compared with a corresponding threshold at  110 . In one exemplary embodiment, the method may proceed to  162  when either of the measured parameters (torque or rotational angle) is greater than or equal to corresponding threshold values. In another embodiment, the method may proceed to  162  only when both the measured parameters are greater than or equal to corresponding threshold values. In still another embodiment, the method may proceed to  162  when a combination (e.g., a product or a ratio) of the parameters is greater than a threshold value. 
     The predetermined threshold values for the first and second parameters may be set by a rig operator. For example, when the parameters include applied toque, the preselected torque value may be determined by calculating an expected friction between the completion string and the borehole wall. The predetermined torque value may be advantageously selected so that an upper portion of the completion string rotates in the borehole and a lower portion of the completion string remains rotationally stationary. Computer modeling techniques for making such calculations are known in the art. 
       FIG. 4B  depicts still another alternative method embodiment  180  in accordance with the present invention. Method embodiment  180  is also similar to method  100  in that it includes steps  102  through  110  as depicted on and described above with respect to  FIG. 3A . At  182  the rotational movement applied at the surface in  106  is ceased and the torque is released when the first parameter is greater than or equal to the first threshold in  110 . This releasing of the torque enables the completion string to rotate back in the opposite (second) direction under the influence of the elastic energy imparted to the string at  106 . Those of ordinary skill in the art will appreciate that a partial rotation of the completion string in  106  results in torsional energy being stored in the string (the string may be thought of as a torsion spring in these applications). When the torque is released in  182 , the stored energy urges the upper portion of the completion string (and the top drive) to rotate in the opposite direction. 
     The rotational force is typically released at  182  until a second parameter equals or exceeds a second predetermined threshold. This is depicted at  184  and  186  in which the second parameter is measured and compared with the second predetermined threshold value. When the measured parameter is less than the threshold, the method continues to monitor the second parameter. When the second parameter is greater than or equal to the second predetermined threshold value, the method returns to  106  and repeats  106 ,  108 ,  110 ,  182 ,  184 , and  186 . 
     As described above with respect method  160 , the first and second parameters may be the same parameter in certain embodiments of method  180 . For example, the first and second parameter may include torque. Also the first and second parameter may include rotational angle, such that the method includes measuring a first rotational angle in  108  and a second rotational angle  184 . The first and second parameters may also be different parameters. For example, in one exemplary embodiment, the first parameter may include applied torque and the second parameter may include another parameter such as release time or rotational angle. In such an embodiment, the completion string may be rotated in a first direction at  106  until a threshold torque is applied and then released at  182  for a predetermined time or until the top drive has rotated back through a predetermined angle. The invention is, of course, not limited in these regards. 
       FIG. 5  depicts a further alternative method embodiment  200  in accordance with the present invention. Method  200  may be executed as a stand alone method or in combination, for example, with methods  160  and  180  depicted on  FIGS. 4A and 4B . Method  200  is typically utilized to rotate one or more components in a completion string to a predetermined angular orientation (toolface) in the drilled borehole. The method may be advantageously utilized for substantially any number of reasons. For example, method  200  may be executed after the completion string has been deployed to its final position (or close to its final position) in the borehole to rotate the completion string to a predetermined angular orientation. Method  200  may also be executed during deployment of the completion string, for example, to enable the completion string to more easily enter a lateral or to maintain a portion of the string at a predetermined angular orientation during deployment. 
     At  202 , a downhole toolface angle may be measured, for example, using sensor  28  depicted on  FIG. 2 . The toolface measurement is intended to be indicative of the angular orientation of a particular component (or components) on the completion string (e.g., a window or slot in the casing). It will be understood that a change in tool face angle may likewise be measured (e.g., between first and second times). The invention is not limited in these regards. At  204 , the measured toolface angle is compared with a predetermined set point. When the measured toolface angle equals the set point (or is within a predetermined range of the set point), method  200  may return, for example, to step  202  or to step  106  in method  160  or method  180 . When the measured toolface angle is not equal to the set point (or is outside the predetermined range), the method proceeds to  206  at which the completion string is rotated at the surface in either the first or second direction so as to at least momentarily rotate the entire completion string. This may be accomplished, for example, by rotating at the surface to a threshold that is greater than the threshold at  110  in  FIGS. 3 and 4 . When this higher threshold is achieved, the rotation may be released at  208  and the method returns to  202  (or optionally to step  106  in method  160  or method  180 ). Method  200  may further include reciprocating the completion assembly “up and down” at the surface between first and second longitudinally spaced positions when the measured tool face angle is outside the predetermined range (or not equal to the set point). 
     As described above, method  200  may be utilized in combination with method  160  and  180 . For example, the torque applied at the surface (e.g., in step  106 ) may be momentarily increased above and beyond the predetermined threshold in  110  ( FIGS. 4A and 4B ) so as to momentarily rotate the full length of the completion string. Such full rotation may be advantageous (or even necessary) at certain times during the deployment operation. For example, a casing shoe can become stuck (or jammed) when entering a lateral section of a drilled borehole (referred to in the art as a “lateral”). Momentarily rotating the shoe to a different angular orientation often enables the shoe to smoothly enter the lateral section. 
     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.