WO2012012098A1

WO2012012098A1 - Method for in situ fluid assessment and optimization during wellbore displacement operations

Info

Publication number: WO2012012098A1
Application number: PCT/US2011/041824
Authority: WO
Inventors: Earl J. Coludrovich Iii; H. Mitchell Cornette; Thomas G. Corbett; John Cameron
Original assignee: Chevron U.S.A. Inc.
Priority date: 2010-06-30
Filing date: 2011-06-24
Publication date: 2012-01-26
Also published as: EP2588716A1; CN103038439A; WO2012012098A8; US20120000658A1; CA2804053A1

Abstract

The present invention is, in some embodiments directed to methods for optimizing wellbore displacement operations via in situ fluid property assessment/monitoring. By monitoring fluid properties in situ (i.e., downhole), fluid property assessment is direct instead of being inferred. Additionally, wherein such assessment/monitoring is carried out in real time, changes to the displacement fluid can be made "on-the-fly," thereby contributing to an enhancement of the overall efficiency of the method.

Description

METHOD FOR IN SITU FLUID ASSESSMENT AND OPTIMIZATION DURING WELLBORE DISPLACEMENT OPERATIONS

FIELD OF THE INVENTION

[0001] This invention relates generally to wellbore completion operations, and specifically to methods for assessing and/or optimizing wellbore fluid displacement operations.

BACKGROUND

[0002] Numerous situations and/or scenarios exist in which wells are extended to subterranean locations in the earth's crust. For example, wells are drilled into subterranean/geo logic formations in order to provide for the production of a variety of fluids, such as water, gas and/or oil; or for the injection of fluids, such as is employed in the secondary and tertiary recovery of oil (e.g., enhanced oil recovery). In many such situations and/or scenarios, in order to properly support the wall of the well, and possibly to exclude fluids from undesirably traversing the boundaries of at least some portions of the well, the well is cased with one or more strings of pipe, i.e., casing strings.

[0003] In order to complete the well, the casing must be bonded to the formation using a cementing procedure. Cementing procedures typically involve a drilling fluid displacement step, followed by a step of pumping a cement formulation (e.g., as a slurry) through the casing to the bottom of the well and then upwardly through the annular space between the outer surface of the casing and the surrounding wall structure, i.e., the formation. After the cement formulation is in place, it is allowed to set, thereby forming an impermeable sheath which, assuming that good bonding is established between the cement and the formation, and the cement and the casing, such bonding prevents the migration of fluids through the annulus surrounding the casing. The cement bonds further enhance the overall integrity of the well. For an example of a well cementing procedure, see, e.g., Parker, U.S. Patent No. 3,799,874, issued Mar. 26, 1974.

[0004] After cementing the casing in a well, one or more cleanout operations or procedures are typically employed to clean out the well in preparation for production. Such procedures can vary considerably, but often involve running a workstring down the well with one or more cleaning tools and/or devices attached to it. Such cleaning tools can include brushes, scrapers, drill bits (e.g., for drilling out cement plugs, etc.), and means for delivering (and circulating) fluids and/or chemicals to the wellbore for the purpose of cleaning out the cased wellbore (including cleaning of the drilling fluid contained therein) and/or the interior surfaces of the associated casing prior to drilling fluid displacement, perforation and subsequent production. See, e.g., Reynolds et al, U.S. Patent No. 5,570,742, issued Nov. 5, 1996; Reynolds et al, U.S. Patent No. 5,419,397, issued May 30, 1995; Reynolds, U.S. Patent No. 6,758,276, issued Jul. 6, 2004; and Carmichael et al, U.S. Patent No. 6,401,813, issued June 11, 2002.

[0005] After such above-described cleanup operations, the drilling fluid present in the wellbore must be displaced by completion fluid, i.e., a displacement operation or procedure. However, because completion fluids are typically incompatible (for a variety of reasons) with drilling fluids, the completion fluid can be preceded by a spacer fluid during a displacement operation. In some such instances, the spacer fluid may comprise a series of fluids having a graduated progression in value of one or more property, so as to provide for a gradual transition from one end of a fluid property range to the other— for at least one such fluid property. For background and examples of such spacer fluids and their use, see, e.g., Oliver et al, U.S. Patent No. 4,474,240, issued Oct. 2, 1984; Thomas, U.S. Patent No. 4,423,781, issued Jan. 3, 1984; and Ray et al, U.S. Patent No. 6,196,320, issued Mar. 6, 2001.

[0006] In view of the foregoing, new methods for monitoring displacement fluids in situ would be extremely useful— particularly wherein such a method and/or system provides greater efficiency with respect to completions operations. Furthermore, while the discussion which follows focuses primarily on oil and gas wells, those of skill in the art will appreciate that at least some of the method and system embodiments discussed herein can be extended to a variety of displacement operations in one or more situations/scenarios mentioned above.

BRIEF DESCRIPTION OF THE INVENTION

[0007] The present invention is generally directed to methods for optimizing wellbore displacement operations via in situ fluid property assessment/monitoring, thereby providing direct assessment of one or more properties of one or more fluids under the environmental conditions to which that fluid(s) experience in the well. In some embodiments, such in situ fluid property assessment/monitoring is performed in real time. By monitoring fluid properties in situ (i.e., downhole), fluid property assessment can be direct, as opposed to being inferred (as in the prior art). Additionally, changes to the displacement fluid can be made "on-the-fly," thereby contributing to an enhancement of the overall efficiency in terms of time savings and reduced fluid waste.

[0008] In some embodiments, the present invention is directed to one or more methods for optimizing wellbore displacement operations, such methods comprising the steps of: (a) introducing a quantity of spacer fluid into a well via a workstring, said well initially occupied by a solids-laden working fluid, the spacer fluid establishing a first interface between it and the solids-laden working fluid; (b) following the spacer fluid introduction with a completion fluid, a second interface being established between the completion fluid and the spacer fluid; (c) monitoring, in situ, at least one fluid selected from the group consisting of working fluid, spacer fluid, and completion fluid, as said fluid is displaced up the annular region of the well; wherein such monitoring provides an in situ fluid property assessment of at least one fluid property (e.g., turbidity, density, solids concentration, capacitance, viscosity, resistivity, temperature, pressure, radioactivity, salinity, basic sediment and water (BS&W), and the like); and (d) communicating the in situ fluid property assessment uphole for purposes of optimizing wellbore displacement operations. In some such method embodiments, there may further comprise a step (e) of facilitating optimization of wellbore displacement operations via the real time assessment of fluid properties communicated in step (d). [0009] In some or other embodiments, the present invention is directed to one or more methods for in situ downhole monitoring of fluids in a well during fluid displacement operations, said well being operable for producing hydrocarbons, and said method comprising the steps of: (a') introducing a quantity of spacer fluid into a well via a workstring, said well initially occupied by a solids-laden working fluid, the spacer fluid establishing a first interface between it and the solids-laden working fluid, wherein the solids laden working fluid is selected from the group consisting of drilling fluids, workover fluids, brine systems, and combinations thereof; (b') following the spacer fluid introduction with a completion fluid, a second interface being established between the completion fluid and the spacer fluid; (c') monitoring, in situ, at least one fluid selected from the group consisting of working fluid, spacer fluid, and completion fluid, as said fluid is displaced up the annular region of the well; wherein such monitoring provides an in situ fluid property assessment of at least one fluid property selected from the group consisting of turbidity, density, solids concentration, capacitance, viscosity, resistivity, temperature, pressure, radioactivity, salinity, basic sediment and water (BS&W), and combinations thereof); (d') wirelessly-communicating the in situ fluid property assessment uphole, wherein such wireless communication is of a form selected from the group consisting of pressure pulses, acoustic transmissions, electromagnetic transmissions, and combinations thereof; and (e') facilitating optimization of wellbore displacement operations, wherein optimization is afforded by real time assessment of fluid properties in situ.

[0010] The foregoing has outlined rather broadly the features of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings, in which: [0012] FIG. 1 illustrates, in stepwise fashion, one or more methods for optimizing wellbore displacement operations via in situ fluid property assessment/monitoring, in accordance with one or more embodiments of the present invention; and

[0013] FIG. 2 illustrates an exemplary variational system embodiment for implementing one or more method embodiments described herein.

DETAILED DESCRIPTION OF THE INVENTION

1. Introduction

[0014] As mentioned above, the present invention is generally directed to methods (and in some instances, systems) for optimizing wellbore displacement operations via in situ fluid property assessment/monitoring of one or more of the fluids present in the wellbore during the displacement operations. In some such embodiments, such fluid property assessment/monitoring is carried out and communicated to the surface in real time. In contrast to existing methods (vide supra) of monitoring fluids at the surface, by monitoring fluid properties in situ (i.e., downhole), fluid property assessment is direct instead of by inference. Additionally, at least to the extent that such fluid property assessment/monitoring is performed in real time, changes to the displacement fluid (or one or more other aspects of the displacement operations) can be made ex tempore, thereby contributing to an enhancement of the overall efficiency.

2. Definitions

[0015] Certain terms are defined throughout this description as they are first used, while certain other terms used in this description are defined below:

[0016] The term "well," as defined herein, refers to a wellbore disposed in a geological volume, most typically for the direct or indirect production of one or more fluids from the surrounding geological reservoir(s).

[0017] The term "cased wellbore," as defined herein, refers to a wellbore into which one or more casing strings have been run and cemented into place. This definition is extended to include one or more liner strings (in place of casing strings), wherein such liner strings are suspended at various depths via one or more liner hangers.

[0018] The term "displacement operations," as defined herein, refers to the displacement of one fluid in the wellbore by another. An exemplary such operation involves removing drilling fluid from the well after cleanup operations and replacing it with completion fluid.

[0019] The term "workstring," as defined herein, refers to a string of tubulars deployed in a subterranean wellbore for the purpose of performing tasks during the course of drilling and/or completion operations.

[0020] The term "drilling fluid," as defined herein, refers to any of a number of liquid and gaseous fluids and mixtures of fluids and solids (as solid suspensions, mixtures and emulsions of liquids, gases and solids) used in operations to drill boreholes into the earth. Unless specifically stated otherwise, the terms "drilling fluid" and "drilling mud" are used interchangeably herein.

[0021] The term "completion fluid," as defined herein, refers to a substantially solids- free liquid used to "complete" an oil or gas well. This fluid is generally placed in the well to facilitate final operations prior to initiation of production, such as setting screens production liners, packers, downhole valves or shooting perforations into the producing zone. The fluid is meant to control a well should downhole hardware fail, without damaging the producing formation or completion components. The fluid should be chemically-compatible with the reservoir formation and fluids, and is typically filtered to a high degree to avoid introducing solids to the near-wellbore area.

[0022] The term "spacer fluid," as defined herein, refers to any liquid used to physically separate one working fluid (vide infra) and/or completion fluid from another, wherein the spacer fluid is compatible with both of the fluids it is being used to separate.

[0023] The term "working fluid," as defined herein, broadly categorizes any fluid used in well operations other than completion fluids (and any spacer fluids used prior to the introduction of such completion fluids). Examples of such working fluids include, but are not limited to, drilling fluids, brine systems, workover fluids, etc. 3. Methods

[0024] As mentioned previously herein (vide supra), methods of the present invention provide for optimization of wellbore displacement operations via in situ fluid property assessment/monitoring of one or more of the fluids present in the wellbore during the displacement operations. Additionally, where such fluid property assessment/monitoring is carried out and communicated to the surface in real time, changes to the displacement fluid (or one or more other aspects of the overall operation) can be made ex tempore, thereby permitting enhancement of the overall displacement operation process efficiency.

[0025] With reference to FIG. 1, in some embodiments the present invention is directed to one or more methods for in situ downhole monitoring of fluids in a well during fluid displacement operations, said method comprising the steps of: (Step 101) introducing a quantity of spacer fluid into a well via a workstring, said well initially occupied by a solids-laden working fluid, the spacer fluid establishing a first interface between it and the solids-laden working fluid; (Step 102) following the spacer fluid introduction with a completion fluid, a second interface being established between the completion fluid and the spacer fluid; (Step 103) monitoring, in situ, at least one fluid selected from the group consisting of working fluid, spacer fluid, and completion fluid, as said fluid is displaced up the annular region of the well; wherein such monitoring provides an in situ fluid property assessment of at least one fluid property (e.g., turbidity, density, solids concentration, capacitance, viscosity, resistivity, temperature, pressure, radioactivity, salinity, basic sediment and water (BS&W), and the like); and (Step 104) communicating the in situ fluid property assessment uphole for purposes of facilitating wellbore displacement operations. In some such method embodiments, there may further comprise a (Step 105) of facilitating optimization of wellbore displacement operations via the real time assessment of fluid properties communicated in (Step 104).

[0026] Regarding such above-described method embodiments, the type of well to which it is applied is not particularly limited. Accordingly, such wells can be vertical, deviated, or horizontal, or combinations thereof. Such wells can be capable of producing oil, gas, and/or other fluids (vide supra). Such wells are also contemplated to include, for example, injection wells operable for stimulating production (e.g., steam injection). Similarly, the wells can be onshore or offshore, and in the latter case, they can be in either shallow or deepwater. Furthermore, the wells can vary considerably over a wide range of depths and/or lengths, and the methods can typically be tailored so as accommodate the particular procedures unique to any or all of such wells (e.g., unique to oil wells).

[0027] In some such above-described method embodiments, the solids-laden working fluid is selected from the group consisting of drilling fluids, workover fluids, brine systems, and combinations thereof. Solids present in the working fluid can be from a variety of sources (e.g., from the cleanout operations done previously, and native components of the fluid composition), of a variety of dimensions, and of a variety of compositions. Depending upon the embodiment, the solids-laden working fluids can be aqueous-based, non-aqueous-based (e.g., oil-based), or emulsion-based (e.g., an oil/water emulsion). By "-based" attention is directed to the base or primary fluid of which the working fluid is comprised. Typically, this base fluid would be that component present in the working fluid composition in greatest amount (e.g., by volume), and/or that component from which the properties of the resulting composition are largely derived. For a variety of reasons, largely relating to formation incompatibility and/or productivity impairment, the composition of such fluids typically precludes their use as completion fluids.

[0028] By way of example and not limitation, suitable such above-mentioned drilling fluids can include, but are not limited to, mixtures of bentonite clay with water and/or oil, as well as one or more additives such as weighting agents (e.g., barite), viscosifiers, and/or deflocculants. In some instances, drilling fluids can be foams. For background and examples of these and similarly-suitable such drilling fluids, see, e.g., Patel et al, U.S. Patent No. 7,250,390, issued Jul. 31, 2007; Rayborn et al, U.S. Patent No. 5,843,872, issued Dec. 1, 1998; and Peacock, U.S. Patent No. 3,215,628, issued Nov. 2, 1965. [0029] In some such above-described embodiments wherein the working fluid is or comprises a workover fluid, exemplary such workover fluids include, but are not limited to, those well intervention fluids used to control a well during one or more workover operations. The workover fluids must generally be compatible with the formation and are typically brine or brine-based. For the purposes of this description, some kill fluids, i.e., those fluids used for stopping flow of production fluids out of a well, can be considered workover fluids— at least to the extent that they are utilized to kill the well in advance of a workover. Background and examples on workover fluids can be found in Sydansk, U.S. Patent No. 5,682,951, issued Nov. 4, 1997; Shell, U.S. Patent No. 4,559,149, issued Dec. 17, 1985; and Gruesbeck et al, U.S. Patent No. 4,046,197, issued Sep. 6, 1977.

[0030] In some such above-described embodiments wherein the working fluid is or comprises a brine system, exemplary such brine systems include, but are not limited to, brine-based fluids, typically comprising one or more of a variety of additive species. Background and examples on such brine systems can be found in, e.g., Murphey, United States Patent No. 6,124,244, issued Sep. 26, 2000.

[0031] Spacer fluids are generally described in Ray et al, United States Patent No. 6,196,320, issued Mar. 2001; and Thomas, United States Patent No. 4,423,781, issued Jan. 3, 1984. In some such above-described method embodiments, the spacer fluid can be viewed a spacer system comprising a plurality of components and/or a progression of components/properties as it is introduced into the well. In some such embodiments, such spacer fluids enhance compatibility and/or promotes or inhibits mixing of fluids at one or both of the first and second fluid interfaces.

[0032] In some such above-described method embodiments, the spacer fluid is introduced as a pill, wherein such a pill can be either substantially homogenous or inhomogeneous (in terms of composition and/or physiochemical properties) along the length of its introduction and/or its cross-section, wherein such inhomogeneity can be slight, moderate, or substantial in character. In some such method embodiments, the spacer fluid is introduced as a series of pills exhibiting a variation in at least one property between adjacent pills. [0033] In some such above-described method embodiments, the spacer fluid is compatible with both the solids-laden working fluid and the completion fluid. By "compatible," it is meant that the spacer fluid does not cause degradation or alteration of the physical and/or chemical properties of the other fluid(s) with which it shares an interface.

[0034] In some such above-described method embodiments, the spacer fluid permits mixing at the interface. In some or other embodiments, the spacer fluid serves to inhibit or at least curtail mixing of fluids at a fluid interface in the well. In some such embodiments, such above-mentioned fluid compatibility neither effects nor precludes such interfacial mixing {vide supra).

[0035] In some such above-described method embodiments, the spacer fluid (or spacer fluid system) is preceded by a scrubber spacer and/or followed by a chase spacer. Such scrubber and chase spacers can be viewed either as components of a single (e.g., inhomogeneous) spacer fluid pill, or as a series of spacer fluid pills collectively representing a spacer train. Such spacer systems are known in the art and are described in, for example, Thomas, United States Patent No. 4,423,781, issued Jan. 3, 1984.

[0036] Completion fluids generally used in at least some of the above-described method embodiments are not particularly limited. Those of skill in the art will recognize that a wide variety of compositions can be used for such fluids, but that they are generally free of large solids. Background on completion fluids and exemplary such compositions can be found in, e.g., Walker et al, United States Patent No. 4,444,668, issued Apr. 24, 1984; Loftin et al, United States Patent No. 4,440,649, issued Apr. 3, 1984; Fischer et al, United States Patent No. 3,882,029, issued May 6, 1975; Peterson, United States Patent No. 4,780,220, issued Oct. 25, 1988; McLaughlin, United States Patent No. 4,462,718, Jul. 31, 1984.

[0037] In some such above-described method embodiments, monitoring, in situ, the working fluid, the spacer fluid, and/or the completion fluid, as such a fluid is displaced up the annular region of the well, typically involves one or more fluid property analyzers operable for fluid property assessment of at least one fluid property. Exemplary such fluid properties include, but are not limited to, (e.g., turbidity, density, solids concentration, capacitance, viscosity, resistivity, temperature, pressure, radioactivity, salinity, basic sediment and water (BS&W), and combinations thereof— under conditions found in the wellbore, i.e., in situ. Depending on the embodiment and the property under investigation, such fluid properties can be monitored directly or indirectly by inference from a directly measurable property. While ex situ fluid property analyzers/monitors are known in the art, they are designed for use at the surface of the well, not under temperatures and pressures found inside the well. See the following for background and examples of turbidity analyzers/monitors: Sweeney, United States Patent No. 3,215,272, issued Nov. 2, 1965; Abrams et al, United States Patent No. 4,436,635, issued Mar. 13, 1984; Malbrel et al, United States Patent No. 5,439,058, issued Aug. 8, 1995; and Sollee et al., "Field Application of Clean Fluids," SPE Annual Technical Conference and Exhibition, Las Vegas, NV, Sep. 22-26, 1985, Paper No. 14318. See the following for background and examples of density analyzers/monitors: Fischer et al., United States Patent No. 3,882,029, issued May 6, 1975; Betancourt et al, "Exploration Applications of Downhole Measurement of Crude Oil Composition," SPE Asia Pacific Conference on Integrated Modelling for Asset Management, Kuala Lumpur, Malaysia, Mar. 29-30, 2004, Paper No. 87011; and Ryan et al, "Mud Clean-Up in Horizontal Wells: A Major Joint Industry Study," SPE Annual Technical Conference and Exhibition, Dallas, TX, Oct. 22-25, 1995, Paper No. 30528. See the following for background and examples of viscometers (i.e., instruments for assessing viscosity): Watson, United States Patent No. 4,141,843, issued Feb. 27, 1979; Kennedy et al., United States Patent No. 2,957,338, issued Oct. 25, 1960; and Saasen et al, "Well Cleaning Performance," IADC/SPE Drilling Conference, Dallas, TX, Mar. 2-4, 2004, Paper No. 87204. See the following for background and examples of solids concentration analyzers/monitors: Jones et al., United States Patent No. 5,360,738, issued Nov. 1, 1994.

[0038] In some such above-described method embodiments, at least one of the one or more fluid property analyzers (assessment tools) is affixed to an interior surface of the workstring. In some such embodiments, there may be a recessed portion of the workstring pipe (possibly a "sub") in which the at least one such fluid property analyzer resides, and/or there may be one or more coverings and/or other devices to protect any or all of said fluid property analyzers. In some or other embodiments, at least one of the one or more fluid property analyzers is affixed to an exterior of the workstring. In such latter instances, the one or more analyzers can be affixed directly to the workstring 's exterior pipe and/or in a recessed portion thereof. Where affixation is in a recessed portion of said workstring pipe, the one or more analyzers can still be allowed to protrude out beyond the workstring pipe outer diameter (OD).

[0039] In some such above-described method embodiments, said step of monitoring is carried out in a manner selected from the group consisting of continuous monitoring, discrete monitoring, and combinations thereof. For the purposes of this invention, continuous monitoring is contemplated to include discrete monitoring with timescales of 1 analysis per second or faster. The monitoring is deemed discontinuous or discrete at timescales slower than 1 analysis per second.

[0040] In some such above-described method embodiments, the step of monitoring requires a plurality of fluid property analyzers are positioned in said well to monitor the at least one fluid. Wherein a plurality of such analyzers are employed, any or all of them can be used for continuous and/or discrete monitoring of any or all of the fluid properties under assessment. In some such embodiments, at least some of the plurality of fluid property analyzers provide fluid assessment of different fluid properties. In some or other such embodiments, the plurality of fluid property analyzers are positioned at different locations in the well, so as to monitor fluids at different points along the annular region of the well.

[0041] Depending on the embodiment, and by way of example and not limitation, the fluid property analyzers employed in at least some of the embodiments of the present invention can be powered via batteries and/or other electrical means (e.g., wireline or wet connect), or they can be powered wirelessly via, e.g., one or more resonant capacitive and/or inductive circuits. Depending on the embodiment, it is contemplated that a plurality of power delivery means could be used to power a plurality of different types of fluid property analyzers at multiple locations— in the same well.

[0042] Similar to the above-described power conveyance, in some such above- described method embodiments, the step of communicating can involve either or both of cabled and wireless communication of fluid property analyzer data. In some such above- described method embodiments, wireless communication (i.e., transmission) of data up (and/or down) a well is of a form selected from the group consisting of pressure pulses, acoustic transmissions, electromagnetic transmissions, and combinations thereof.

[0043] In some embodiments, where wireless transmission of data is relied upon, such wireless transmission of data can be at least partially provided by mud-based telemetry methods and/or acoustic transmissions. Such techniques are known in the art and will not be described here in further detail. For examples of such mud-based telemetry methods, see, e.g., Kotlyar, U.S. Patent No. 4,771,408, issued Sept. 13, 1988; and Beattie et al, U.S. Patent No. 6,421,298, issued Jul. 16, 2002. For examples of wireless transmission of data (and power) up and/or down a well using acoustic transmissions, see, e.g., Klatt, U.S. Patent No. 4,215,426, issued Jul. 29, 1980; and Drumbeller, U.S. Patent No. 5,222,049, issued Jun. 22, 1993.

[0044] In some embodiments, electromagnetic (EM) transmissions of a type described in, for example, Briles et al, U.S. Patent No. 6,766,141, issued Jul. 20, 2004, are used to transmit data and/or power into and out of the cased wellbore. The downhole resonant circuits used in such methods and systems can be integrated directly or indirectly with the one or fluid property analyzers, so as to convey information into, and out of, the well. See also, e.g., Coates et al, U.S. Patent No. 7,636,052, issued Dec. 22, 2009; Thompson et al, U.S. Patent No. 7,530,737, issued May 12, 2009; Coates et al, U.S. Patent Appl. Pub. No. 20090031796, published Feb. 5, 2009; and Coates et al, U.S. Patent Appl. Pub. No. 20080061789, published Mar. 13, 2008, wherein such "infinite communication" systems and methods are additionally referred to as "INFICOMM."

[0045] In some such above-described method embodiments, such methods may further comprise a step of optimizing wellbore displacement operations, wherein optimization is afforded by real time assessment of fluid properties. By "real time," it is typically contemplated that this term refer to timescales for communicating fluid analysis data out of the well, as well as any subsequent interpretation of said data, wherein such timescales are substantially instantaneous or at least less than about 1 second.

[0046] In some such above-mentioned method embodiments, data (from the fluid property analyzer(s)) is collected and stored in memory. Such memory storage of data is not particularly limited (hard drives, flash drives, optical drives, etc.), but must generally be able to withstand the environmental conditions present downhole. In some cases, storage containers can be configured to afford such memory drives protection from adverse downhole environments. Additionally or alternatively, in some embodiments the memory storage device is positioned uphole from the sensors, and data transmission between the sensor and the storage device occurs via cabled and/or wireless means. In some embodiments, the memory storage is at the surface. It goes without saying, however, that an exclusive reliance on downhole storage of data, wherein the step of communicating said data merely involves physically transporting the storage device to the surface, may generally preclude any real time fluid property assessment and any impromptu optimization opportunities that might otherwise be realized through real time assessment.

5. Variations

[0047] While the aforementioned embodiments are generally directed to methods for optimizing wellbore displacement operations via in situ fluid property assessment/monitoring, some variational embodiments are directed to corresponding system embodiments that describe, in largely functional terms, the infrastructure required to implement one or more method embodiments of the present invention.

[0048] As a non-limiting example, attention is now directed to FIG. 2 depicting an exemplary such system for optimizing displacement operations via real time, in situ monitoring of fluids. Shown in FIG. 2 , in accordance with one or more embodiments of the present invention is exemplary system 20, wherein wellbore 22 is established in geological formation 24, and wherein wellbore 22 has disposed within it workstring 29. In addition to having bottom hole assembly (BHA) 39 attached at its end, workstring 29 has attached to it a first fluid analyzer 35 and a second fluid analyzer 33— both of which have integral wireless communication means for communicating data through wellbore 22 to surface 26. Solids-laden working fluid 60, having previously been pumped downhole (in the form of drilling fluid), is displaced from the well by completion fluid 58 using spacer fluid 59 in juxtaposition between them. [0049] As the fluids emanate from BHA 39 and migrate up the annular region of wellbore 22, they are analyzed by fluid analyzers 35 and 33 so that, for example, the cleanliness (e.g., in terms of turbidity) of completion fluid 58 can be ascertained by fluid analyzer 35 before drilling fluid 60 has been completely eliminated from wellbore 22. Furthermore, turbidity (and/or another property) data can be wirelessly communicated from fluid analyzer 35 and/or fluid analyzer 33 to data processing unit 41 via wireless communication receiver 43, whereby data processing unit 41 provides quantitative real time assessment of fluid turbidity (processed data) at the position of fluid analyzers 35 and 33. This processed data is then fed to control unit 46, whose job it is to control valves in pump/manifold 47 such that the flow of any one of fluids 58-60 through conduit 49 can be controlled during displacement operations. Integration of data processing unit 41 with pump/manifold 47 via control unit 46 affords those fielding such a system the ability to make changes in the displacement operations extemporaneously.

[0050] Other variations on the above-described method embodiments, involve inclusion of one or more tracer and/or taggant species to one or more of the fluids to yield one or more "traceable fluids" and/or "tagged fluids," and monitoring the said one or more traceable or tagged fluids for said one or more tracer and/or taggant species. Exemplary such tracers/taggants include, but are not limited to, chemical tracers (e.g., having unique molecular and/or isotopic signatures), radioactive tracers, and/or electrical tracers (e.g., radio-frequency identification (RFID) tags).

6. Summary

[0051] As described throughout, the present invention is directed to methods for optimizing wellbore displacement operations via in situ fluid property assessment/monitoring, wherein in some such method embodiments, said assessment/monitoring is carried out (and processed) in real time. By monitoring fluid properties in situ (i.e., downhole), fluid property assessment is direct instead of being inferred. Additionally, changes to the displacement fluid can be made "on-the-fly," i.e., extemporaneously, thereby contributing to an enhancement of the overall efficiency. To an extent not inconsistent with the method embodiments described herein, the present invention is further directed to variational system embodiments— generally for implementing one or more methods of the present invention.

[0052] All patents and publications referenced herein are hereby incorporated by reference to an extent not inconsistent herewith. It will be understood that certain of the above-described structures, functions, and operations of the above-described embodiments are not necessary to practice the present invention and are included in the description simply for completeness of an exemplary embodiment or embodiments. In addition, it will be understood that specific structures, functions, and operations set forth in the above-described referenced patents and publications can be practiced in conjunction with the present invention, but they are not essential to its practice. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without actually departing from the spirit and scope of the present invention as defined by the appended claims.

Claims

WHAT IS CLAIMED:

1. A method for in situ downhole monitoring of fluids in a well during fluid displacement operations, said method comprising the steps of:

a) introducing a quantity of spacer fluid into a well via a workstring, said well initially occupied by a solids-laden working fluid, the spacer fluid establishing a first interface between it and the solids-laden working fluid;

b) following the spacer fluid introduction with a completion fluid, a second interface being established between the completion fluid and the spacer fluid; c) monitoring, in situ, at least one fluid selected from the group consisting of working fluid, spacer fluid, and completion fluid, as said fluid is displaced up the annular region of the well; wherein such monitoring provides an in situ fluid property assessment of at least one fluid property; and

d) communicating the in situ fluid property assessment uphole for purposes of facilitating wellbore displacement operations.

2. The method of Claim 1, wherein the well is operable for producing hydrocarbons, wherein said hydrocarbons are selected from the group consisting of oil, gas, and combinations thereof, and wherein the well is selected from the group consisting of a land-based well and an offshore well.

3. The method of Claim 1, wherein the at least one fluid property is selected from the group consisting of turbidity, density, solids concentration, capacitance, viscosity, resistivity, temperature, pressure, radioactivity, salinity, basic sediment and water, and combinations thereof.

4. The method of Claim 1, wherein the solids laden working fluid is selected from the group consisting of drilling fluids, workover fluids, brine systems, and combinations thereof.

5. The method of Claim 1, wherein the spacer fluid is introduced as a pill.

6. The method of Claim 5, wherein the spacer fluid is introduced as a series of pills exhibiting a progressive variation in at least one property across the series.

7. The method of Claim 5, wherein the spacer fluid is compatible with both the solids-laden working fluid and the completion fluid.

8. The method of Claim 1, wherein said step of monitoring is carried out in a manner selected from the group consisting of continuous monitoring, discrete monitoring, and combinations thereof.

9. The method of Claim 1, wherein the step of monitoring requires a plurality of fluid property analyzers positioned in said well to monitor the at least one fluid.

10. The method of Claim 9, wherein at least some of the plurality of fluid property analyzers provide fluid assessment of different fluid properties.

11. The method of Claim 9, wherein the plurality of fluid property analyzers are positioned at different locations in the well, so as to monitor fluids at different points along the annular region of the well.

12. The method of Claim 1, wherein the step of communicating involves cabled communication of fluid property analyzer data.

13. The method of Claim 1, wherein the step of communicating involves wireless communication of fluid property analyzer data.

14. The method of Claim 13, wherein wireless communication is of a form selected from the group consisting of pressure pulses, acoustic transmissions, electromagnetic transmissions, and combinations thereof.

15. The method of Claim 1, further comprising a step of facilitating optimization of wellbore displacement operations, wherein optimization is afforded by real time assessment of fluid properties.

16. A method for in situ downhole monitoring of fluids in a well during fluid displacement operations, said well being operable for producing hydrocarbons, and said method comprising the steps of:

a) introducing a quantity of spacer fluid into a well via a workstring, said well initially occupied by a solids-laden working fluid, the spacer fluid establishing a first interface between it and the solids-laden working fluid, wherein the solids laden working fluid is selected from the group consisting of drilling fluids, workover fluids, brine systems, and combinations thereof;

b) following the spacer fluid introduction with a completion fluid, a second interface being established between the completion fluid and the spacer fluid; c) monitoring, in situ, at least one fluid selected from the group consisting of working fluid, spacer fluid, and completion fluid, as said fluid is displaced up the annular region of the well; wherein such monitoring provides an in situ fluid property assessment of at least one fluid property selected from the group consisting of turbidity, density, solids concentration, capacitance, viscosity, resistivity, temperature, pressure, radioactivity, salinity, basic sediment and water (BS&W), and the like, and combinations thereof;

d) wirelessly-communicating the in situ fluid property assessment uphole, wherein such wireless communication is of a form selected from the group consisting of pressure pulses, acoustic transmissions, electromagnetic transmissions, and combinations thereof; and

e) facilitating optimization of wellbore displacement operations, wherein optimization is afforded by real time assessment of fluid properties in situ.

17. The method of Claim 16, wherein the spacer fluid is introduced as a pill.

18. The method of Claim 17, wherein the spacer fluid is introduced as a series of pills exhibiting a progressive variation in at least one property across the series.

19. The method of Claim 16, wherein the step of monitoring requires a plurality of fluid property analyzers are positioned in said well to monitor the at least one fluid, and wherein at least some of the plurality of fluid property analyzers provide fluid assessment of different fluid properties.

20. The method of Claim 19, wherein the plurality of fluid property analyzers are positioned at different locations in the well, so as to monitor fluids at different points along the annular region of the well.