Shield assembly for logging tool sensors

A shield assembly for logging tool sensors includes a single piece cylindrical shield and first and second cylindrical end clamps deployed about opposing axial ends of the cylindrical shield. The cylindrical shield is deployed about a logging sensor disposed on a logging tool collar. At least one of the first and second end clamps includes one or more keys for engaging a corresponding slot in the shield and a corresponding pocket in an outer surface of the tool collar. Engagement of the key with the corresponding slot and the corresponding pocket is operative to prevent relative rotational and relative axial motion between the cylindrical shield, the first and second end clamps, and the tool collar.

FIELD OF THE INVENTION

Disclosed embodiments relate generally to logging tools and more particularly to a shield assembly for protecting sensors deployed on logging tools such as electromagnetic logging tools.

BACKGROUND

The use of electromagnetic measurements in prior art downhole applications, such as logging while drilling (LWD) and wireline logging applications is well known. Such techniques may be utilized to determine a subterranean formation resistivity, which, along with formation porosity measurements, may be used to indicate the presence of hydrocarbons in the formation. Moreover, azimuthally sensitive directional resistivity measurements are employed to map subterranean reservoirs or to provide information upon which steering decisions may be made in pay-zone steering applications.

In such electromagnetic logging tools, shields may be used to protect the antennas and sensors that are integrated on the outer surface of the tool collar. The shields are intended to prevent the antennas from being damaged during downhole drilling, wellsite rigging up and rigging down, and shipping and handling. A reliable and effective shield and shield-mounting design can improve measurement and performance of LWD and wireline tools. There remains a need in the art for improved shields and shield mounting configurations.

SUMMARY

A shield assembly for logging tool sensors is disclosed. In disclosed embodiments the antenna shield includes a single piece cylindrical shield and first and second cylindrical end clamps deployed about opposing axial ends of the cylindrical shield. In certain embodiments, the cylindrical shield may optionally include a plurality of slits formed therethrough and may be sized and shaped for deployment about at least one electromagnetic antenna disposed about a logging tool collar. At least one of the first and second end clamps includes one or more keys sized and shaped for engaging a corresponding slot in the shield and a corresponding pocket in an outer surface of the tool collar. Engagement of the key with the corresponding slot and the corresponding pocket is operative to prevent relative rotational and relative axial motion between the cylindrical shield, the first and second end clamps, and the tool collar.

DETAILED DESCRIPTION

A shield assembly for logging tool sensors is disclosed. In one example embodiment, the shield assembly includes a single piece cylindrical shield secured to a logging tool collar by first and second axially opposed end clamps. Engagement of at least one key with a corresponding pocket is operative to prevent relative rotational and relative axial motion between the cylindrical shield, the first and second end clamps, and the logging tool collar.

The disclosed embodiments may provide various technical advantages and improvements to prior art shield assemblies employed in electromagnetic logging tools. For example, disclosed shield assembly embodiments tend to exhibit significantly improved structural integrity, particularly for shield embodiments having a length to diameter ratio greater than about 1 (e.g., 1.5 or more or 2 or more). The disclosed shield assembly tends to improve resistance to bending, bidirectional torsion loads, impacting, wearing, and tearing during drilling and further tends to be more resistant to the ingress of drilling fluid since there are no seams that can open and close during tool bending or rotation. Such resistance also tends to provide a more stable electromagnetic window (as defined by the slits) and therefore tends to improve the quality and reliability of the transmitted or received electromagnetic signal during various drilling conditions. Moreover, the use of end clamps having integral keys that engage corresponding embedded pockets in the collar enables the clamps to be load bearing and withstand large bidirectional torsional loads from lateral impacts and frictional interaction with the borehole wall during drilling.

FIG. 1depicts a drilling rig10suitable for using various logging tools employing the shield assembly embodiments disclosed herein. A semisubmersible drilling platform12is positioned over an oil or gas formation disposed below the sea floor16. A subsea conduit18extends from deck20of platform12to a wellhead installation22. The platform may include a derrick and a hoisting apparatus for raising and lowering a drill string30, which, as shown, extends into wellbore40and includes a drill bit32and an electromagnetic logging tool50upon which the disclosed shield assembly may be deployed (e.g., about a directional resistivity antenna). Drill string30may optionally further include any number of other downhole tools, for example, including a rotary steerable drilling tool, a downhole drilling motor, a downhole telemetry system, a wellbore reaming tool, and one or more additional measurement while drilling (MWD) or LWD tools including various sensors for sensing downhole characteristics of the wellbore and the surrounding formations. The disclosed embodiments are not limited in these regards.

It will be understood by those of ordinary skill in the art that the deployment illustrated onFIG. 1is merely an example. It will be further understood that disclosed embodiments are not limited to use with a semisubmersible platform12as illustrated onFIG. 1. The disclosed embodiments are equally well suited for use with any kind of subterranean drilling operation, either offshore or onshore. Moreover, disclosed embodiments are not limited to logging while drilling embodiments as illustrated onFIG. 1. The disclosed embodiments are equally well suited for use with any logging tool, including wireline logging tools and logging while drilling tools.

FIG. 2Adepicts one prior art shield assembly60that includes a slide-on shield64. Rings66are threadably connected to the logging tool collar62and thereby secure the shield64to the collar62. During tool makeup, the slide-on shield64is deployed about the antenna, rotated to an appropriate orientation, and secured in place at opposing axial ends by the threaded rings66. Tightening of the threaded rings66axially compresses the shield64and is intended to thereby secure the shield in place. Shield assembly60is commercially available in various PeriScope® and GeoSphere® logging tools available from Schlumberger Technology Corporation (Sugar Land, Tex.). The threaded rings66, having an outer diameter greater than that of the shield64and the collar62, can be prone to borehole contact and loosening during a drilling operation. Loosening of the threaded rings66allows the shield to move/vibrate about the collar62and may ruin the electromagnetic measurements (especially when the shield62is deployed about a directional antenna). In severe cases, loosening of the threaded rings66can be accompanied by the loss of tool parts downhole which may compromise the overall drilling objective.

FIG. 2Bdepicts another prior art shield assembly70that includes a split shield74including first and second semi-cylindrical shield components74A and74B mounted on the logging tool collar72. During tool make-up, the shield components74A and74B are deployed about the antenna, rotated to an appropriate orientation, and secured in place on the collar72and to one another with screws at each corner quadrant (as depicted). Shield assembly70is commercially available in various arcVISION®, EcoScope®, and MicroScope® logging tools available from Schlumberger Technology Corporation (Sugar Land, Tex.). One advantage of shield assembly70is the low profile of the shield74in which the outer diameter of the shield74can be essentially flush with the outer diameter of the collar. However, the use of the split shield configuration tends to result in a loss of structural integrity in the vicinity of the seams76located between the two shield components74A and74B. This loss of structural integrity can lead to warping or bending of the shield or opening of the seam which may create another slit and may therefore contaminate the electromagnetic measurements. The loss of structural integrity may further result in damage to the antenna itself. This can be particularly acute in shield assemblies configured for use in directional antennas or triaxial antennas in which the axial length of the shield is greater than the diameter of the tool collar.

Turning now toFIG. 3, one example embodiment of logging tool50is depicted including at least one of the disclosed shield assemblies100deployed about a logging tool collar110. It will be understood that the logging tool50may include substantially any suitable number of the shield assemblies100deployed about corresponding sensors (which may be the same or different). The sensors may be configured as electromagnetic transmitters and/or electromagnetic receivers. Moreover, the shield assembly(ies)100may be deployed about a single antenna or a plurality of collocated antennas (e.g., biaxial or triaxial antennas). The disclosed embodiments are not limited in any of these regards.

The disclosed shield assembly100may be particularly useful when deployed about a directional antenna or a tilted antenna. For example, the shield assembly100may be deployed about a triaxial antenna arrangement such as an arrangement including three tilted antennas or an arrangement including an axial antenna and two transverse antennas. It will be understood that an axial antenna is one whose moment is substantially parallel with the longitudinal axis of the tool while a transverse antenna is one whose moment is substantially perpendicular to the longitudinal axis of the tool. A tilted antenna is one whose moment is neither parallel nor perpendicular with the axis of the tool. Such antennas are well known.

It will be understood that directional antennas, tilted antennas, and bi- and triaxial antenna arrangements may have having a length to width ratio greater than one (i.e., such that the axial dimension of the antenna along the collar is greater than the diameter of the collar). In such embodiments, the length to diameter ratio of the shield assembly may exceed 1 (or about 1.5 or even about 2 or more). Such high ratio antenna configurations can result in severe loads being imparted to the shield assembly during service, for example, via bending or twisting of the shield. Suitable shield assemblies advantageously account for and are configured to withstand this loading.

While the disclosed embodiments are described in detail with respect to shielding transmitting and receiving antennas employed electromagnetic logging tools, it will be understood that the disclosed embodiments are not so limited. The disclosed shield assembly may be used to protect substantially any suitable logging sensor, for example, including piezoelectric transducers used in sonic or ultrasonic logging tools and radio frequency antennas used in nuclear magnetic resonance logging tools.

FIGS. 4A-4C and 5A-5Bdepict side (4A) and cross sectional views (4B-4C and5A-5B) of one example embodiment of antenna assembly100. As depicted, the antenna assembly100includes a single-piece, cylindrical shield120deployed about the tool collar110and covering the electromagnetic antenna55. The cylindrical shield may be made from a high strength, erosion and corrosion resistant, non-magnetic material. While non-magnetic metals may be used, the disclosed embodiments are not limited to metal shields. When a metallic (electrically conductive) shield is employed, a plurality of slits122may be formed therethrough (i.e., such that they extend through the thickness of the cylinder wall). For example, the slits122may be machined (cut) into the cylindrical shield120. Such slits122allow a portion of the electromagnetic wave (e.g., emanating from a transmitting antenna or passing from the formation to receiving antenna) to pass through the cylindrical shield120. The slits122may be filled with a non-conductive, electromagnetically transparent material such as epoxy, fiberglass, or plastic so as to allow passage of the electromagnetic wave while inhibiting fluid communication therethrough.

The disclosed embodiments may include substantially any suitable slit configuration, for example, including axial slits, circumferential slits, sloped or tilted slits, curved slits, or combinations thereof. It will be understood that the preferred slit configuration largely depends on the antenna configuration protected by the shield and that the slits may be selected to promote transparency of certain preferred electromagnetic waves. The disclosed embodiments are not limited to any particular slit configuration.

Shield assembly150further includes first and second cylindrical end clamps130deployed about opposing axial ends of the cylindrical shield120. In the depicted embodiment, the end clamps130each include first and second semi-cylindrical split clamps130A,130B (FIG. 6B). While the disclosed embodiments are not limited in this regard, these split clamps may be screwed132to one another during tool assembly thereby securing the cylindrical shield120in place about the tool collar110and the electromagnetic antenna55. In alternative embodiments, the single piece shield and/or the end clamps may be screwed directly to the collar. In another alternative embodiment the split clamps may be connected to another via other (non-screw) connectors.

The end clamps130further include at least one key135, for example, integral with an inner diameter thereof. The key135is sized and shaped to engage a corresponding slot142(FIG. 6A) in the cylindrical shield and a corresponding pocket112located on an outer surface of the collar110. In the depicted embodiment, each of the split clamps130A,130B in each of the end clamps130includes a corresponding key135(for a total of 4 keys), such that the made up end clamp130includes first and second diametrically opposed keys135that are configured to engage corresponding diametrically opposed pockets112in the tool collar110.

While the embodiments disclosed onFIGS. 4A-4C, 5A-5B, and 6A-6B, employ four keys, it will be understood that some embodiments may employ only a single key. For example, the disclosed embodiments may make use of a one or two keys located on one of the end clamps130(e.g. on either the uphole or the downhole end clamp). In such an embodiment, the axially opposing end clamp is allowed to “float” in the sense that it is not rotationally or axially fixed to the collar110. Such floating may optionally be restricted to rotation only or translation only.

In the depicted embodiments, the keys135and pockets112are integral with and embedded in the inner diameter of the end clamp130and the outer diameter of the tool collar110, respectively. In addition to providing proper alignment between the shield assembly components, such a configuration enables these components to be load bearing. For example, the above described configuration may advantageously withstand bidirectional torsional loads from lateral impacts and frictional interaction with the borehole wall during drilling.

While the use of an integral key (or integral keys) may be advantageous as described above, the disclosed embodiments are expressly not limited in this regard. For example, the key (or keys) may be a distinct component that is configured to engage a corresponding pocket, slot, or window in each of the collar, cylindrical shield, and end clamps. Such a distinct key may be deployed before or after securing the end clamp to the collar.

With reference now toFIGS. 5A, 5B, 6A, and 6B, the cylindrical shield120may include a cylindrical body portion121(through which the slits122penetrate) and a plurality of tabs140extending axially from the body portion121. These tabs140define axial slots142,144. Upon deployment of the end clamps130, the tabs140are radially interposed between the tool collar110and corresponding ones of the end clamps130(e.g., corresponding ones of the split clamps130A,130B in the depicted embodiment). Slots142engage keys135as described above. Slots144accommodate screws132used to secure the split clamps130A,130B to one another. The disclosed embodiments are not limited to the use tabs that result in open ended slots142as depicted. In some embodiments, the slots may be closed, for example, cut out of the cylindrical shield.

The cylindrical body portion121may further include at least one stepped down outer diameter surface125located on either one or both axial ends thereof. One or both of the end clamps130may further include corresponding stepped out inner surfaces136configured to engage the stepped down outer diameter surfaces125of the cylindrical shield120during makeup of the shield assembly. While not limited in this regard, in the depicted embodiment, the stepped down outer diameter surfaces125include a circumferential protrusion127that is sized and shaped to engage a corresponding circumferential channel138in the stepped out inner surfaces136of the end clamps130. The protrusion127and corresponding channel138are intended to further secure the end clamps130to the cylindrical shield120.

In the depicted embodiments, the end clamps130and the cylindrical shield120have substantially equal outer diameters (e.g., as depicted onFIG. 4A). Such a configuration advantageously reduces the chance of a direct strike of the clamps130on the borehole wall and further tends to reduce erosion and wear of the clamps130during service. The low-profile clamp configuration also enables the clamps130to be more easily protected by sacrificial components on the collar (such as wear rings).

During makeup of the disclosed shield assembly, the cylindrical shield120slides over the outer surface of the collar110until it covers the antenna55. The cylindrical shield120is rotated into the proper orientation, for example, such that the slits122are properly aligned with the underlying antenna coils. The split clamps135A,135B are then installed about the axial ends of the cylindrical shield120such that the keys135engage corresponding pockets112and slots142. Such engagement controls the alignment/orientation of the cylindrical shield and further prevents relative rotational and relative axial motion between the cylindrical shield120, the first and second end clamps130, and the tool collar110. As stated above, the split clamps135A,135B may be secured to one another via screws132. Torqueing the screws132generates clamp pressure which is applied to the external surfaces of the shield120and secures the assembly to the mandrel110. With a proper amount of preload in the screws132, significant clamping force and elastic deformation among the components can be generated to secure the shield120to the collar so as to withstand downhole pressure, bending, shock, and vibration.

Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. For example, any element described in relation to an embodiment herein may be combinable with any element of any other embodiment described herein.