BACKGROUND OF THE INVENTION

Field of the Invention

[0001] In many oil production operations, enhanced oil recovery techniques are employed to facilitate oil production. Many enhanced oil recovery projects use thermal recovery methods in which steam is injected to enable recovery of heavy oil. Production from heavy oil reserves is expanding worldwide.

[0002] During enhanced oil recovery operations, formation properties are monitored at different locations within a reservoir. The monitored formation properties may include fluid saturation, interfacial fronts, wettability, pressure, temperature, and other properties as a function of time. Monitoring the various formation properties enables an operator to identify problems or the potential for problems that can interfere with oil production.

Description of Related Art

[0003] In some applications, monitoring wells are drilled at select strategic locations to enable use of logging tools and/or permanent sensors. If logging tools are used to detect and measure formation properties, the logging techniques are carried out in an open hole completion because standard casings interfere with the logging measurements. Attempts have been made to utilize casings that do not interfere with operation of the logging tools, however such attempts have met with limited success often due to the extremely harsh wellbore environment.

BRIEF SUMMARY OF THE INVENTION

[0004] In general, the present invention provides a system and methodology for facilitating the detection and measurement of formation properties with various measurement devices, such as logging tools. The technique comprises locating a standard tubular, e.g. casing, in a well proximate a zone of interest to be logged. A tubing that is transparent to signals associated with logging tools, e.g. non-metallic and non-magnetic casing or liner, is attached to the standard tubing so as to extend along the zone of interest. Additionally, a protective material is directed to the region adjacent the transparent tubing to protect the transparent tubing from detrimental contact with deleterious well fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and:

[0006] Figure 1 is a schematic view of a well system utilizing a transparent tubing to facilitate a logging operation, according to an embodiment of the present invention;

[0007] Figure 2 is a schematic view of a well system in which an observation well is positioned between a water injection well and a production well, according to an embodiment of the present invention;

[0008] Figure 3 is a view of one example of a transparent tubing employing sensors, according to an embodiment of the present invention;

[0009] Figure 4 is a view of a well system having a transparent tubular and a fluid injection system, according to an embodiment of the present invention;

[0010] Figure 5 is a view of a well system having a transparent tubing and an internal fluid removal pumping system, according to an embodiment of the present invention;

[0011] Figure 6 is a view of a well system having a transparent tubing and a fluid recirculation system, according to an embodiment of the present invention; [0012] Figure 7 is a view of a well system with a casing having a perforated zone which is to be removed to facilitate a logging operation, according to an embodiment of the present invention; and

[0013] Figure 8 is a view of the well system illustrated in Figure 7 in which a transparent casing has been deployed to replace the removed section of casing, according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0014] In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these details, and that numerous variations or modifications from the described embodiments may be possible.

[0015] The present invention relates to a system and method for completing a well. For example, the system and method can be used for drilling and completing observation wells used in enhanced oil recovery applications. Generally, standard metal tubing is used in combination with one or more sections of transparent tubing, which may be non-metallic, non-magnetic tubing that is transparent with respect to signals associated with measurements made by logging tools. The standard tubing and the transparent tubing may comprise a variety of casings, including liners, used in observation wells or other suitable wells. Additionally, a material, such as a protective fluid, is disposed adjacent the transparent tubing to protect the tubing from deleterious well fluid.

[0016] In one specific example, an observation well is drilled slightly overbalanced using oil-based mud. The resulting wellbore is lined with a standard casing to a specific well zone of interest for logging. A transparent casing is then installed at the zone of interest and removably attached to the standard casing by an attachment mechanism, such as a liner hanger. The oil-based mud is subsequently isobarically displaced down through the casing and up through an annulus between the casing and the open hole with a specially formulated protective fluid, such as a non-aqueous fluid. The protective fluid may be designed to augment some aspect of logging by, for example, matching the acoustic impedance of the casing, e.g. liner.

[0017] The non-aqueous fluid is generally benign to epoxy and high-temperature thermoset resins. Consequently, the injection of non-aqueous fluids isobarically into and around the transparent casing helps prevent harsh, detrimental, aqueous reservoir fluids from coming into contact with the transparent casing. The transparent casing may be formed of, for example, a polymer material, a thermoset-based composite, or another material that could otherwise undergo severe degradation and/or hydrolyses.

[0018] In this specific example, the pressure differential across the wall of the transparent casing is relatively low which allows the casing to be designed with a relatively thin wall thickness. The use of a thin wall can be helpful for logging tools with short effective depths of investigation, such as nuclear magnetic resonance tools. In some applications, the protective fluid placed in the annulus between the transparent casing and the open hole may be designed to set if and when necessary. Furthermore, the removable attachment mechanism enables the transparent casing to be retrieved for inspection, repair, and/or replacement. The material of the transparent casing also is drillable which allows it to be drilled through if necessary. In some applications, the transparent casing is fitted with one or more of a variety of sensors or other tools that enable continued enhanced oil recovery monitoring.

[0019] Referring generally to Figure 1 , one embodiment of a well system 20 is illustrated for use in a wellbore 22. The well system 20 comprises a standard tubing 24, e.g. a well casing 26, deployed along wellbore 22 into proximity with a zone of interest 28. The zone of interest 28 may comprise a zone that is to be logged to collect data on a surrounding formation 30. It should be noted that well casing 26 may comprise a variety of standard casings, including liners, which are typically formed from a metal material. [0020] Well system 20 further comprises a transparent tubing 32 deployed adjacent the zone of interest 28 in, for example, an open hole section 34 of wellbore 22. In the example illustrated, transparent tubing 32 is deployed at least partially through the zone of interest 28 between a lower casing shoe 36 and an upper casing shoe 38. The transparent tubing 32 may comprise a transparent casing and may be attached to standard tubing 24 by an attachment mechanism 40. By way of example, attachment mechanism 40 comprises a liner hanger. In some embodiments, the attachment mechanism/liner hanger 40 comprises a packer sealing liner hanger to provide isolation with respect to an upper formation layer. The liner hanger 40 or other type of attachment mechanism also may provide a releasable attachment to enable retrieval of transparent tubing 32.

[0021] The transparent tubing 32 comprises a non-metallic, non-magnetic tubing that is transparent with respect to the operation of logging tools or other related tools that are used to obtain information on surrounding formation 30 in the zone of interest 28. In other words, the transparent tubing 32 does not interfere with logging measurements. One embodiment of transparent tubing 32 is formed from a polymer-based material, such as fiber reinforced plastic, but such materials can be susceptible to aqueous fluids (e.g. brine or water) and other corrosive fluids in the well environment. A protective fluid 42, such as a liquid, foam, slurry, gel (which can be triggered to set and become solid), or gas, is deployed adjacent transparent tubing 32 to isolate and protect the transparent tubing 32 from deleterious fluids, such as aqueous fluids (e.g. brine or water) or other problematic fluids found in the well environment. The protective fluid 42 can be located in an annulus 44 between transparent tubing 32 and a surrounding wellbore wall 46 in open hole section 34. The protective fluid 42 may also be located inside the transparent tubing 32.

[0022] As illustrated in Figure 1, the use of transparent tubing 32 facilitates a variety of logging and other data collection procedures. For example, a logging tool 48 can be lowered through wellbore 22 into the zone of interest 28 by a conveyance 50, e.g. a wireline or coiled tubing. A logging truck 52 may be used in cooperation with surface equipment 54 to deploy, retrieve, and operate logging tool 48 during a logging operation. The logging tool 48 may comprise a variety of tools, including resistivity tools, nuclear magnetic resonance tools, gamma ray tools, neutron tools, sonic tools, and other logging related tools. In one example, the logging tool 48 is designed to measure the chemical composition of a sample using spectroscopy or another appropriate technique for such measurement. The measurements can be performed at desired time intervals based on the expected efficiency of the enhanced oil recovery operation or on the sweep efficiency of an injected fluid. The measurements may be used to calculate the change in formation fluid content by providing the saturation of different fluids. In some applications, chemical reactions may change the nature of the fluids in the zone of interest. In other cases, a sweeping fluid may come into the zone of interest and bring new fluids with it. The logging tool or tools 48 can be used to measure the nature, saturation, and/or spatial distribution of such different fluids within the given zone. In some embodiments, the nature of injected fluids may be such that the wettability of the formation changes. Techniques such as nuclear magnetic resonance may be used to provide information on the wettability of the formation.

[0023] In one operational example, the wellbore 22 is initially drilled in an overbalanced condition using oil-based mud. The wellbore 22 is then cased with standard casing 26 to a depth just above the zone of interest 28. The standard casing 26 may be cemented into place to achieve total zonal isolation, to meet regulatory requirements, and/or to ensure good mechanical strength. It should be noted that in some applications, multiple casing strings above the liner hanger 40 are possible. The transparent tubing 32, e.g. casing, is subsequently attached to the standard casing 26 in a manner that is removable and serviceable. For example, the transparent tubing 32 may be removably attached to the standard casing 26 by liner hanger 40.

[0024] The transparent tubing 32 is placed into the wellbore 22 in a manner designed to minimize interference with reservoir measurements taken from inside the transparent tubing 32. In at least some well environments, the reservoir, the fluid in the reservoir, the formation properties, the temperature, and other environmental parameters may have a detrimental effect on the transparent tubing 32. However, the protective fluid 42 can be used to protect the transparent tubing 32. Additionally, the retrievability of the transparent tubing 32 enables repair or replacement of the transparent tubing. Consequently, the risk of losing the entire wellbore is much lower.

[0025] In at least some operations, the casing string is not cemented in place.

Instead, the connection mechanism comprises the liner hanger 40 combined with a sealing packer 56 to provide zonal isolation with respect to the upper formation layer. In any event, the transparent tubing 32 need not be cemented into place unless desired, which opens up many service and retrieval options.

[0026] Liner hanger 40 enables retrieval of the transparent tubing 32. This can be accomplished by killing the well so that a retrieval tool can be run downhole to retrieve liner hanger 40 and transparent tubing 32 as many times as desired over the life of the reservoir. However, if solids block the transparent tubing 32 (or a portion of the transparent tubing) at a downhole location, the well operator may not be able to retrieve the entire transparent tubing. In such event, the lower zone may be redrilled to remove the buried transparent casing and the solid fill.

[0027] Following the initial overbalanced drilling, but prior to original installation of the tubing string with the transparent tubing 32, a complete displacement of the oil- based mud may be performed with a non-aqueous fluid. The use of the non-aqueous fluid provides time and positive hydrostatic pressure to displace reservoir fluids in the near wellbore formations. As a result, the barrier provided by the protective fluid 42 extends beyond the wellbore and into the permeable formation to provide an additional degree of isolation from deleterious reservoir fluids, e.g. water, that would otherwise contact the transparent tubing 32. In some embodiments, before this step, the inner wall of the open hole section 34 may be sealed with a layer of polymer or resin to minimize leakage of protective fluid 42 into the formation 30 and, in turn, help maintain an overbalanced condition in the open hole section 34. [0028] The actual running of the completion assembly is relatively straightforward. In the example illustrated and described, the overall string comprises lower casing shoe 36 designed to seal desired components to the bottom of the string, e.g. to the bottom of the transparent tubing 32. In some embodiments, a ported sub can be positioned at the bottom of the string, e.g. at the bottom of the transparent tubing 32, to facilitate fluid communication and/or sampling. The ported sub may be generally shaped like a bullet to enable easier running into the wellbore 22. Alternatively, circulation can be achieved along the length of the transparent tubing 32.

[0029] In an alternate arrangement, attachment mechanism 40 comprises a solid connection, such as a threaded connection between the standard casing 26 and transparent tubing 32. The transparent tubing 32 may also comprise a connection end formed of the same transparent material and fused for a seamless connection. The transparent tubing 32 is then connected to the top of liner hanger 40 with, for example, an integrated sealing packer assembly to form the liner hanger with sealing packer 56.

[0030] According to one embodiment, the tubing string components are initially assembled, e.g. preassembled, and run into the wellbore 22. The liner hanger 40 is set to "space out" the landing such that there is sufficient overlap of the liner hanger and the previously set and cemented standard casing string 26. The weight of the transparent tubing 32 is supported by the standard casing 26. Prior to setting the liner hanger 40 and releasing, a fluid is circulated in the casing 26 and transparent tubing 32. The fluid is selected to function as a protective fluid 42 and may vary depending on the type of material used to form transparent tubing 32. For example, if the transparent tubing 32 is more likely to be attacked by aqueous fluid, the circulating protective fluid 42 may be an oil or other non-aqueous fluid.

[0031] The protective fluid 42 may be circulated down the entire length of a running string, through the liner hanger 40, down the transparent tubing 32, up through annulus 44 in open hole section 34, and inside the outer cemented standard well casing 26 such that the entire running assembly is surrounded by protective fluid 42, e.g. non- aqueous fluid. The protective fluid minimizes, and potentially eliminates, contact between harsh reservoir fluids, e.g. water, and the entire transparent tubing 32.

[0032] In some applications, the protective fluid 42 is selected with characteristics that enable triggering of the fluid to set if and when necessary. For example, certain non-aqueous organic fluids may be displaced into the annulus 44 and activated/triggered to set when desired. Examples of such protective fluids include organic sealants such as those used in zonal isolation applications.

[0033] Once the transparent tubing 32 is properly located and completely bathed in protective fluid 42, a liner hanger setting tool is activated to allow the liner hanger 40 to engage the standard casing 26 and to transfer the weight of the transparent tubing 32 from a running string to the cemented standard casing 26. Once the liner hanger 40 is supporting the transparent tubing 32, the liner hanger setting tool can again be activated to allow setting of the sealing packer 56 to provide the required seal and consequent isolation of the reservoir.

[0034] Upon setting the sealing packer 56, the annulus region between the cemented standard casing 26 and the running string is pressure tested to ensure a positive seal. After completing the pressure test, the running string and liner hanger setting tool are disengaged from the liner hanger 40 to allow forward circulation above the sealing packer 56. At this stage, protective fluid 42, e.g. oil or other non-aqueous fluids, can again be circulated down the running string to ensure the entire wellbore is filled with this protective fluid barrier at a slightly overbalanced condition for added protection. In this example, the pressure differential across the transparent tubing 32 is relatively low if not insignificant. Consequently, the transparent tubing may be designed with a relatively thin wall thickness which facilitates the use of logging tools with short effective depths of investigation, such as nuclear magnetic resonance tools.

[0035] Once a positive indication is received that uncontaminated protective fluid

42, e.g. oil or other non-aqueous fluid, has completely filled the wellbore with "clean" surface returns, the running string can be removed from the wellbore leaving only the sealing packer 56/liner hanger 40 and the monitoring string, e.g. transparent tubing 32, below the liner hanger 40 in wellbore 22. At this stage, installation of the transparent tubing 32 is achieved, and further completion of the well can be conducted according to normal completion routines. For example, wellhead assemblies and other surface equipment can be installed. Environmental barriers for the surface and reservoir monitoring equipment can be run into the wellbore 22 and placed inside the transparent tubing string 32. This allows reservoir measurements to be taken without the interference that would otherwise occur with traditional casing installations of steel and cement.

[0036] Referring again to Figure 1 , an illustration is provided of a completed installation which allows various logging operations to be conducted in the zone of interest 28. The logging tool 48 is operated within transparent tubing 32 which, as described above, is formed from a non-metallic, non-magnetic material to facilitate the detection and measurement of desired parameters during the logging operation.

[0037] Although the transparent tubing 32 can be used in cooperation with standard tubing 24 in a variety of well-related applications, the technique is useful in a monitoring well 58 positioned between a water injection well 59 and a production well 60 of an enhanced oil recovery operation, as illustrated in Figure 2. A variety of logging tools 48 and or sensors 62 can be used in cooperation with transparent tubing 32 to detect well- related, environmental parameters. For example, monitoring well 58 can be used to detect a moving water front 64. Data is provided to a control system 66 to enable appropriate corrective or remedial action, i.e. adjustment of water injection rate and/or volume. In some applications, control system 66 may be part of logging truck 52.

[0038] In Figure 3, one embodiment of transparent tubing 32 is illustrated as a casing suspended from standard casing 26 by liner hanger 40. In this embodiment, permanent sensors are combined with transparent tubing 32 and may comprise one or more internal sensors 68 and/or one or more external sensors 70. The sensors 68 and/or 70 may be mounted to or embedded in transparent tubing 32. Additionally, the sensors are designed to communicate data to the surface via communication lines 72 which may be permanently installed wires, fiber optics, or wireless communication lines. Depending on the type of sensor and the environment in which the sensors are used, power may be provided to the sensors 68, 70 from the surface, or by battery packs located downhole. The sensors 68, 70 may be employed to provide continuous information on physical properties and their time dependence may be used to decide when to perform a complete logging operation. The sensors may include pressure sensors, temperature sensors, resistivity sensors, and other sensors designed to detect and/or measure desired well- related parameters.

[0039] In some applications, protective fluid 42 is maintained in the annulus 44 between transparent tubing 32 and the surrounding wellbore wall. As illustrated in Figure 4, a protective fluid injection system 74 can be used to deliver protective fluid downhole through an injection tubing 76. In this example, shoe 36 is a ported shoe, and flow control equipment 78 is used to control flow down through injection tubing 76 to ported casing shoe 36. Injection system 74 can be used to maintain the pressure of protective fluid 42 within a desired, relatively narrow range. By keeping the protective fluid pressure substantially equal to the formation pressure, the protective fluid is prevented from invading the surrounding formation while simultaneously preventing formation fluid from contacting transparent tubing 32. The protective fluid 42 may be chosen so as to be immiscible with and of similar viscosity to the formation fluid to help maintain pressure balance and to prevent fingering of the sweep front.

[0040] As illustrated in Figure 5, deleterious fluids, such as water, can also be removed using a submersible pump 80 and/or injection system 74. If a deleterious fluid invades the zone of interest 28 surrounding transparent tubing 32, the fluid can be removed by pump 80 via outflow tubing 82 and appropriate flow control mechanisms 84. Additionally, protective fluid 42 can be injected via injection system 74 to ensure the transparent tubing 32 is protected. The pumping and/or injection operations can be performed either intermittently or continuously on a regular basis to maintain protection of transparent tubing 32. Further, the formation fluid having seeped out into the protective fluid and been pumped to the surface may be sent to a laboratory for chemical analysis.

[0041] Another embodiment is illustrated in Figure 6 and includes a recirculation system 86. In this embodiment, recirculation system 86 can be used to change the fluid or the nature of the protective fluid 42 filling the annulus 44 between transparent tubing 32 and the surrounding wellbore wall 46. A tubing 88 is deployed down through transparent tubing 32 and sealed with respect to an interior of the transparent tubing via a packer 90. The tubing 88 may extend through a lower ported sub. The recirculation system 86 may be used to circulate protective fluid down through tubing 88, into the annulus 44 surrounding transparent tubing 32, and up through circulation ports 92 of liner hanger 40. Alternatively, the protective fluid may be delivered down through an annulus surrounding the standard casing 26, through circulation ports 92 of liner hanger 40, through annulus 44 surrounding transparent tubing 32, and then up through tubing 88. The recirculation of fluid also may be used to remove undesirable, invading fluids.

[0042] Referring generally to Figures 7 and 8, transparent tubing 32 may be used along standard tubing 24 at locations other than a location below the bottom of the standard tubing. In some applications, the transparent tubing is placed at an intermediate location along the length of, for example, permanent standard casing 26. In one example, a perforated section 94 of an existing well casing (see Figure 7) is removed and substituted with the transparent tubing 32 (see Figure 8). Once the old section of standard casing is replaced with transparent tubing 32, logging measurements can be conducted without interference.

[0043] Replacement of casing sections with transparent tubing 32 can be applied to specific wells selected from multiple wells used in multiple zone production. Later in the life of the wells, some or all of the multiple zones may require an enhanced oil recovery operation that can be improved by converting some of the wells in the well field to monitoring wells. In such cases, sections of standard casing can be, for example, machined and removed from the well or dropped to a rat hole at the bottom of the well. The transparent tubing 32, e.g. casing, is then lowered into the well and hung at the desired depth at a bottom position or an intermediate position along the standard casing. Figure 8 illustrates a transparent tubing 32 that is sealed at the top to standard tubing 24. However, the invention is not limited to this arrangement, and the transparent tubing 32 may be sealed on both ends to the top and bottom sections of casing 26.

[0044] Transparent tubing 32 may be used in cooperation with standard tubing to facilitate logging operations in a variety of wells, such as enhanced oil recovery monitoring wells. The size, shape, and structure of the transparent tubing may vary depending on the specific logging operation and environment. Additionally, the material from which transparent tubing 32 is constructed may vary according to environmental factors, protective fluid, potential deleterious fluids, logging equipment, and other operational parameters. Furthermore, the overall system may utilize a variety of protective materials, such as protective fluids that are delivered downhole by suitable delivery systems. Similarly, many types of attachment mechanisms can be used to attach the transparent tubing 32 to the standard tubing 24. In some embodiments, the attachment mechanisms enable easy removal and/or replacement of the transparent tubing.

[0045] Accordingly, although only a few embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Such modifications are intended to be included within the scope of this invention as defined in the claims.