Not applicable.
During the drilling and completion of oil and gas wells, it may be necessary to engage in ancillary operations, such as monitoring the operability of equipment used during the drilling process or evaluating the production capabilities of formations intersected by the wellbore. For example, after a well or well interval has been drilled, zones of interest are often tested to determine various formation properties such as permeability, fluid type, fluid quality, formation temperature, formation pressure, bubblepoint and formation pressure gradient. These tests are performed in order to determine whether commercial exploitation of the intersected formations is viable and how to optimize production.
Wireline formation testers (WFT) and drill stem testing (DST) have been commonly used to perform these tests. The basic DST test tool consists of a packer or packers, valves or ports that may be opened and closed from the surface, and two or more pressure-recording devices. The tool is lowered on a work string to the zone to be tested. The packer or packers are set, and drilling fluid is evacuated to isolate the zone from the drilling fluid column. The valves or ports are then opened to allow flow from the formation to the tool for testing while the recorders chart static pressures. A sampling chamber traps clean formation fluids at the end of the test. WFTs generally employ the same testing techniques but use a wireline to lower the test tool into the well bore after the drill string has been retrieved from the well bore, although WFT technology is sometimes deployed on a pipe string. The wireline tool typically uses one or more packers also, although the packer/packers are placed closer together, compared to drill pipe conveyed testers, for more efficient formation testing. In some cases, packers are not used. In those instances, the testing tool is brought into contact with the intersected formation and testing is done without zonal isolation.
WFTs may also include a probe assembly for engaging the borehole wall and acquiring formation fluid samples. The probe assembly may include an isolation pad to engage the borehole wall. The isolation pad seals against the formation and around a hollow probe, which places an internal cavity in fluid communication with the formation. This creates a fluid pathway that allows formation fluid to flow between the formation and the formation tester while isolated from the borehole fluid.
Another testing apparatus is a measurement while drilling (MWD) or logging while drilling (LWD) tester. Typical LWD/MWD formation testing equipment is suitable for integration with a drill string during drilling operations. Various devices or systems are provided for isolating a formation from the remainder of the wellbore, drawing fluid from the formation, and measuring physical properties of the fluid and the formation. With LWD/MWD testers, the testing equipment is subject to harsh conditions in the wellbore during the drilling process that can damage and degrade the formation testing equipment before and during the testing process. These harsh conditions include vibration and torque from the drill bit, exposure to drilling mud, drilled cuttings, and formation fluids, hydraulic forces of the circulating drilling mud, and scraping of the formation testing equipment against the sides of the wellbore. Sensitive electronics and sensors must be robust enough to withstand the pressures and temperatures, and especially the extreme vibration and shock conditions of the drilling environment, yet maintain accuracy, repeatability, and reliability.
In order to acquire a useful sample, the probe must stay isolated from the relative high pressure of the borehole fluid. Therefore, the integrity of the seal that is formed by the seal pad is important to the performance of the tool. If the borehole fluid is allowed to leak into the collected formation fluids, a non-representative sample will be obtained and the test will have to be repeated. The reliability and ability for seal pads or isolation probes to seal and isolate becomes increasingly more difficult when the borehole temperature rises due to the materials used in the seal pad to form or maintain a seal between the pad and formation or borehole.
What is needed is a seal pad designed for the hostile conditions that is able to maintain a seal or isolation in these conditions, and that provides reliable sealing performance with an increased durability and resistance to damage.
For a more detailed description of preferred embodiments of the present invention, reference will now be made to the accompanying drawings, wherein:
In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the present invention. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.
Certain terms are used throughout the following description and claims to refer to particular system components. This document does not intend to distinguish between components that differ in name but not function.
In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ”. Also, the terms “couple,” “couples”, and “coupled” used to describe any mechanical or electrical connections are each intended to mean and refer to either an indirect or a direct mechanical or electrical connection. Thus, for example, if a first device “couples” or is “coupled” to a second device, that interconnection may be through an electrical conductor directly interconnecting the two devices, or through an indirect electrical connection via other devices, conductors and connections. Further, reference to “up” or “down” are made for purposes of ease of description with “up” meaning towards the surface of the borehole and “down” meaning towards the bottom or distal end of the borehole. In addition, in the discussion and claims that follow, it may be sometimes stated that certain components or elements are in fluid communication. By this it is meant that the components are constructed and interrelated such that a fluid could be communicated between them, as via a passageway, tube, or conduit. Also, the designation “MWD” or “LWD” are used to mean all generic measurement while drilling or logging while drilling apparatus and systems.
In the drawings and description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. The present invention is susceptible to embodiments of different forms. Specific embodiments are described in detail and are shown in the drawings, with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results. The various characteristics mentioned above, as well as other features and characteristics described in more detail below, will be readily apparent to those skilled in the art upon reading the following detailed description of the embodiments, and by referring to the accompanying drawings.
The downhole tool 113 includes, in various embodiments, one or a number of different downhole sensors, which monitor different downhole parameters and generate data that is stored within one or more different storage mediums within the downhole tool 113. The downhole tool 113 can include a power source, such as a battery or generator. A generator could be powered either hydraulically or by the rotary power of the drill string. The generator could also be on the surface and the power supplied through conductor or conductors in a wireline or drillpipe.
The downhole tool 113 includes a downhole sampling device such as a formation tester tool 10, which can be powered by the power source. In one embodiment, the formation tester tool 10 may be mounted on a drill collar or wireline deployed. Thus, even though formation tester 10 is shown as part of drill string 105, the embodiments of the invention described below may be conveyed down borehole 8 via any drill string or wireline technology, as is partially described above and is well known to one skilled in the art.
Formation tester tool 10 has a substantially cylindrical body that is typical of tools used in downhole environments. Formation tester tool 10 includes hydraulic conduits and sample conduits therethrough. For example, a sample conduit can be in fluid communication with a drawdown chamber whose volume can be varied by actuating one or more draw-down pistons, such as are known in the art.
Formation probe assembly 50 generally includes stem a 92, a piston chamber 94, a piston 96 adapted to reciprocate within piston chamber 94, a snorkel 98 adapted for reciprocal movement within piston 96, and a seal pad 180 located at an end of piston 96. Snorkel 98 includes a central passageway 127. Formation probe assembly 50 is configured such that piston 96 extends and retracts through aperture 52 of the formation tester tool 10. Stem 92 includes a tubular extension 107 having central passageway 108. Central passageway 108 is in fluid connection with fluid passageways leading to other portions of tester tool 10, including a drawn down assembly, for example. Thus, a fluid passageway is formed from the formation through snorkel passageway 127 and central passageway 108 to the other parts of the tool.
Formation probe assembly 50 is assembled such that piston 96 includes shoulders 97 to allow hydraulic pressure to be used to extend and retract the piston. In use, snorkel 98 further extends into the formation wall to communicate with the formation fluid. Probe assembly 50 is extended by applying fluid pressure through hydraulic conduits so that hydraulic pressure is applied to shoulder 97. The pressure advances piston 96 and seal pad 180 toward the wall of the wellbore.
Seal pad 180 seals and prevents drilling fluid or other contaminants from entering the probe assembly 50 during formation testing. Typically, the pressure of the formation fluid is less than the pressure of the drilling fluids that are injected into the borehole. A layer of residue from the drilling fluid forms mud cake 24 on the borehole wall and separates the two pressure areas. Pad 180, when extended, contacts the borehole wall and, together with the mud cake, forms a seal.
In order to acquire a useful sample, probe assembly 50 should stay isolated from the relative high pressure of wellbore fluid. Therefore, the integrity of the seal that is formed by seal pad 180 is important to the performance of the tool. If wellbore fluid is allowed to leak into the collected formation fluids, a non-representative sample will be obtained and the test will have to be repeated.
The elements 234 and 236 may include but are not limited to rubber products, HNBR, Teflon, peak, metal, alloys and/or combination thereof. The elements 234 and 236 may be supported and/or energized by additional materials behind the elements so to enable them to adjust the shape of the borehole and/or retract into the pad 230 depending on the force applied. In most cases mud cake 24 is present and the mud cake 24 and/or borehole fluid may be captured and trapped in the slot or space 235 as the pad is deployed from tool 10 and the mud cake is fully or partially sealed in place by elements 234 and 236 so to form a compressed liquid barrier between elements 234 and 236. The compression and compaction of the trapped mud cake 24 and borehole fluid in the slot or space 235 will depend on the thickness and compressibility of the mud cake between the pad and the formation wall 112 and the size and shape of the elements 234 and 236.
After being set, formation fluid can be drawn into one or more flowlines 164 (
As the plate 253 is deployed and compressed into the formation wall 112 (
When extended, the metallic pad 242 pushes into the mudcake 24 and/or formation wall 112 it may form a primary seal and it may also trap the mud cake 24 between the sealing elements 241 for a secondary sealing system.
The raised rings 241 of material on the surface of the metal pad 242 may also be embedded into the formation wall 112 forming a seal or isolation. With the primary and secondary seals energized, a fluid sample can be collected from the formation wall 112; formation fluid may now be drawn into the flowline 164 through port 240 which may contain a probe or snorkel.
In one embodiment, the metallic pad 242 includes a smooth surface. The pad 242 in the outer edge 254 may be flexible and of a radius greater than the borehole so to promote the outer edge 254 of pad 242 to come into contact first when the plate 233 is deployed from assembly 50 (
In one embodiment the metallic pad 242 has a coated surface, and the coating may consist but not limited to rubber products, HNBR, Teflon, peak, metal, alloys or and combination and be bonded, glued or attached in any manner to allow for the metallic pad to flex. The pad 242 in the outer edge may be flexible and of a radius greater than the borehole so to promote the outer edge of pad 242 to come into contact first when the plate 233 is deployed from assembly 50 (
The pad 260 is set against the formation wall 112 (
Pad edge 262 and/or 263 may be coated with materials and/or shaped to promote a seal between the formation wall 112 and the borehole fluid. Pad edges 262 and/or 263 may employ other embodiments discussed in this disclosure to form a seal.
Formation fluid may now be drawn into the flowline through port 240 which may contain a probe or snorkel. During the flow of formation fluid into the tool flowline through port 240, a drawdown of the pressure may take place. During the drawdown there may be a pressure differential between the borehole fluid representing the fluid behind plate 263 and inlet port 240 which may be maintained by the seal formed by pad edges 263 and/or 262.
There may be a differential pressure across piston 267 if there is any fluid communication between flow path port 240 and the slot or space 265 containing sealing element 264 between pad edge 262 and 263. This differential pressure may cause the piston 267 to move forward due to the pressure isolation provided by seal 269 which may exert force equal to the differential pressure across the area of piston 267 between the sealing element 264 and formation wall 112 and/or the mud cake 24. The greater the differential pressure across piston 267 the greater the force is applied to sealing element 264 improving the seal between the borehole and the desired flow of fluid into the flowline 164 through flowpath 240. The inner edge of surface of edge 263 adjacent to sealing element 264 may be shaped to support the sealing element 264 to reduce extrusion damage.
In one embodiment, the seal pad 178 further includes an elastomer o-ring 186 encircling the first inner metallic ring 182. The elastomer o-ring 186 can be mounted by mounting a metal retaining member 188 over the o-ring 186 and attaching retaining member 188 using fasteners 190, such as screws. In one embodiment, o-ring 186 can be configured so as to extend slightly beyond the outer surface of inner metallic ring 182. O-ring 186 helps provide sealing against the well bore wall. In this example, the metallic outer surfaces of first metallic ring 182 and second metallic ring 184 limit the compression of o-ring 186 when the seal pad 178 is pressed against a well bore wall. This allows for more used of the seal pad 178 without having to replace o-ring 186 since compression of an elastomer o-ring at high temperatures breaks down the elastomer o-ring.
The outer surface of seal pad 178 is generally congruent to the inner surface of a cylindrical wall 112 (
Referring to
Upon an appropriate command to formation probe assembly 50, a force is applied to the base portion of piston 96, preferably by using hydraulic fluid. Piston 96 rises relative to the other portions of probe assembly 50. The seal pad 178 is advanced until its outer surfaces contact the mud cake 24. Mud cake 24 then enters the space 195 and helps form a seal, along with first inner metallic ring 182, second outer metallic ring 184, and o-ring 186. The highly viscous mud cake 24 is trapped between the two metallic rings 182, 184 and forms a liquid o-ring to become an effective seal against the well bore. After the seal pad 178 is set, the formation draw down procedure, or other downhole procedure, is started. Continued force from hydraulic fluid causes snorkel assembly 98 to extend such that the outer end of the snorkel extends beyond the seal pad 178 surface through seal pad aperture 186.
To retract probe assembly 50, forces, or pressure differentials, may be applied to snorkel 98 and piston 96 in opposite directions relative to the extending forces. Simultaneously, the extending forces may be reduced or ceased to aid in probe retraction.
In one embodiment, the probe assembly 50 can be a telescoping probe including a second inner piston to further extend the probe assembly. In other embodiments, formation tester tool 10 can further include fins or hydraulic stabilizers or a heave compensator located proximate formation probe assembly 50 so as to anchor the tool and dampen motion of the tool in the bore hole.
Although the discussed embodiments describe several methods that improve the ability to seal a formation for the borehole for the purpose of formation testing in hostile environments, the embodiments may be suitable to both hostile and non hostile borehole conditions.
Moreover, although the above discussion relates generally to formation tester pads used to form a seal from the borehole to the formation for pressure testing, fluid sampling and fluid analysis, the seal pads may also be used for other applications of downhole measuring where isolations mechanical, electrically or pressure is required.
The disclosures above assume a borehole with drilling fluids and mud cake. However, the disclosures are not limited to fluid filled boreholes but air-filled holes will not be discussed in the disclosures.
The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. While the preferred embodiment of the invention and its method of use have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described herein are exemplary only, and are not limiting. Many variations and modifications of the invention and apparatus and methods disclosed herein are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims.
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Number | Date | Country | |
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20080295588 A1 | Dec 2008 | US |