Acrylamide-Polymer/Chromium (III)-Carboxylate Gels for Near Wellbore Matrix Treatments
- Robert D. Sydansk (Marathon Oil Company)
- Document ID
- Society of Petroleum Engineers
- SPE Advanced Technology Series
- Publication Date
- April 1993
- Document Type
- Journal Paper
- 146 - 152
- 1993. Society of Petroleum Engineers
- 5.8.7 Carbonate Reservoir, 2.4.3 Sand/Solids Control, 1.6.9 Coring, Fishing, 5.9.2 Geothermal Resources, 5.3.4 Reduction of Residual Oil Saturation, 5.7.2 Recovery Factors, 4.1.5 Processing Equipment, 5.4.5 Conformance Improvement, 5.2.1 Phase Behavior and PVT Measurements, 5.2 Reservoir Fluid Dynamics, 4.1.2 Separation and Treating, 1.6 Drilling Operations
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Chromium (III)-crosslinked gels, which are applicable up to 260 degrees F for use in matrix reservoirs as near-wellbore total-shutoff treatments, were developed and characterized.
Acrylamide-polymer/chromium (III) - carboxylate gels have been developed for application to matrix reservoirs as near-wellbore total shutoff treatments. Laboratory development, testing, and characterization of the new chromium (III) (CrIII) aqueous gels are reported. Results of this study indicate that these gels can be applied to elevated-temperature (up to 260 degrees F) and high-salinity reservoirs. The single-fluid gels are produced by crosslinking, low-molecular-weight polyacrylamide with a Cr III - carboxylate-complex crosslinking agent. Use of low-hydrolysis polyacrylamide facilitates the application to high-temperature polyacrylamide facilitates the application to high-temperature reservoirs.
Unfractured reservoirs, with strata of differing permeability overlying one another, often suffer from vertical conformance problems. Oil-recovery drive fluids tend to channel through the problems. Oil-recovery drive fluids tend to channel through the high-permeability strata. The resulting channeling promotes poor conformance and sweep efficiency. When strata of differing permeabilities are not in vertical communication and when permeabilities are not in vertical communication and when treatment fluids are placed with use of mechanical zone isolation, near wellbore treatments which partially or totally reduce permeability in the high permeability strata can be used to permeability in the high permeability strata can be used to improve conformance.
Total shutoff gels, when placed in near-wellbore matrix rock of the target strata, function by substantially reducing the permeability, which is essentially synonymous with totally shutting off the fluidflow capacity of the treated reservoir rock volume. This, in turn, results in essentially total shutoff of liquid or gas production from, or injection into, the treated matrix rock strata. production from, or injection into, the treated matrix rock strata. Results are reported relating to the laboratory development, testing, and characterization of acrylamide-polymer/drill-carboxylate gels for use as matrix shutoff treatments. Aqueous acrylamide-polymer /CrIII carboxylate gels are formed by crosslinking water-soluble acrylamide polymers with a CrIII-carboxylate-complex crosslinking agent.
The water-soluble acrylamide polymer can be either polyacrylamide (PA), partially hydrolyzed polyacrylamide (PHPA), or terpolymers containing acrylamide. Acrylamide-polymer/CrIII-carboxylate gels discussed in this paper were formulated with low-MW PA and will hereafter be referred to as PA/CrIII-carboxylate gels. The high-temperature version of this gel technology is characterized by use of low-hydrolysis PA.
The crosslinking agent is a coordinate-covalent-bonded CrIII-carboxylate complex. The crosslinking agent is most often oligomeric in CrIII. Acetate is the preferred carboxylate anion. The chemistry of the preferred crosslinking agent in aqueous solution is discussed in Ref. 8. Intermolecular crosslinking in these gels is believed to occur through CrIII-carboxylate complexes involving coordinate-covalent bonding by the CrIII complex with two carboxylate functional groups on two different acrylamide-polymer molecules.
Production responses have previously been reported for high-molecular Production responses have previously been reported for high-molecular weight (MW) PHPA and PA CrIII-carboxylate gels used in Wyoming to treat fracture conformance problems.
A number of other permeability-reducing gel technologies, which are also applicable to matrix reservoirs, have been reported in the literature. A number of these gel technologies are commercially available. However, many of the commercially available treatments suffer from some combination of technical, economic. environmental, and operational problems. The performance of many of these gel technologies is sensitive to performance of many of these gel technologies is sensitive to oilfield environments and interferences, especially pH and H2S. None of the polymer-based gel technologies have been reported to promote persistent total shutoff (permeability reductions less promote persistent total shutoff (permeability reductions less than a factor of 10(-3) or equivalently, residual resistance factors greater than 10(3) over a broad temperature range (e.g., subambient to 260 degrees F).
Several literature references have suggested that acrylamide-polymer /CrIII gels are inherently not stable at elevated temperatures (e.g., greater than 170 degrees F). One objective of this paper is to present data which will suggest that this contention is not always the case.
Although a number of oilfield gel technologies claim to be applicable to high-temperature reservoirs, we were motivated to develop the PA/CrII - carboxylate gel technology discussed in this paper because of our inability to locate a commercial gel technology paper because of our inability to locate a commercial gel technology that met all our needs.
As previously reported, PA/CrIII-carboxylate gels are insensitive to oilfield interferences and environments and are attractive from the standpoints of operational, safety, and environmental considerations. These single-fluid gels are also attractive because they involve a rather simple and straightforward gel chemistry, usually involving only a two-component chemical system - CrIII crosslinking agent and acrylamide polymer. In addition, these gels are based on acrylamide polymers which are readily available and relatively inexpensive and which are one of the most widely applied water-soluble polymers for EOR and other oilfield uses. The base chemical of the preferred CrIII-carboxylate- complex crosslinking agent, a form of chromic acetate, is a commodity chemical which is readily available as a concentrated aqueous solution and is relatively inexpensive. Additionally, the use of CrIII to crosslink polymers has previously been somewhat widely applied and has found a degree of acceptance in the oil industry, especially for use in conformance treatment gels.
Laboratory Results and Discussion
This section, which reviews the laboratory study of PA/CrIII carboxylate gels for matrix near-wellbore shutoff applications, is divided into two major subsections: first, treatments for low- and intermediate- temperature applications and second, treatments for high-temperature applications. Chemicals and experimental details are discussed in Ref. 26. The PA polymers employed in this study possessed hydrolysis levels ranging from less than 0.1 to 2.5 mole%.
Low- and Intermediate-Temperature Treatments The study of PA/CrIII-carboxylate gels for low- to intermediate-temperature applications (subambient to 140 degrees F) involved bottle testing, viscometric measurements, and flooding experiments.
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