Laboratory testing of a recently developed chromium(III) [Cr(lll)] gel technology is reported. The gels can be used in conjunction with a number of oilfield treatments. The single-fluid acrylamide-polymer/Cr(lll)-carboxylate aqueous gels are formed by crosslinking acrylamide polymer with a Cr(lII)-carboxylate-complex crosslinking agent. Representative gel compositions and associated gel properties are discussed. IntroductionA single-fluid Cr(Ill) gel technology has been developed in which aqueous gels are formed by crosslinking acrylamide polymer with a Cr(III)-carboxylate-complex crosslinking agent. 1,2 The gel technology has been field tested and/or used for a number of oilfield ,applications, including conformance-improvement treatments (CIT's), water and gas shutoff, zone abandonment, and gel squeeze cementing. The major thrust of our effort has been to apply the gel technology for CIT's, including treating both matrix (profilemodification treatments) and fracture conformance problems. This paper focuses on CIT use of the new Cr(IlI) gel technology. Most of the gels discussed were designed to treat fracture conformance problems in naturally fractured reservoirs. Representative acrylamide-polymer/Cr(lII)-carboxylate gel compositions and associated properties are reported. The laboratory studies reviewed show the dependence of gelation rate and gel strength on (1) the concentration, molecular weight (MW), and hydrolysis level of the polymer; (2) polymer-to-Cr(III) ratio;(3) temperature; (4) polymer solution pH; and (5) salinity.The gels of this technology involve a single-fluid system and do not involve sequentially injected fluids. Gels are produced by simply adding a single aqueous crosslinking-agent solution to the aqueous polymer solution. An entire family of gels, ranging from highly flowing to rigid, rubbery gels, can be produced by varying the formulation of the same chemical set. Thus, the gel technology is applicable to a wide range of oilfield problems and uses. Highly controllable gel times, ranging from minutes to weeks, are possible and can be preselected. Gels applicable to both injection and production well treatments (e.g., CIT's) can be produced. The gels are relatively inexpensive because they typically contain 95 to 99.7 % water, with the remainder being low-cost chemicals. Field use has shown the gel technology to be attractive from operational, environmental, and safety standpoints.Almost any water-soluble carboxylate-containing polymer can be crosslinked with the Cr(lIl)-carboxylate-complex crosslinking agent. This includes carboxylate-containing acrylamide terpolymers. Only gels formulated with polyacrylamide (PA) and partially hydrolyzed polyacrylamide (PHPA) are discussed in this paper.The crosslinking agent is a mixture of oligomeric Cr(III) coordinate-covalent-bonded complex ions containing low-MW carboxylate anions. When dissolved in water, a significant portion of the carboxylate anions are bound as ligands to the hexacoordinate Cr(lll) ions. The hexacoordinate Cr(III) ions in the o...

Laboratory testing and evaluation of a new chromium(III) [criii] acrylamide-polymer gel technology for conformance-improvement-treatment (CIT) use are reported. This paper is primarily limited to discuss-; ng the ge 1 techno 1 ogy as app 1 i cab 1 e to fracture conformance problems. A H J J J J J+ Experimental: 200,000 MW, 2.7% hydrolyzed, laboratory-grade PHPA at pH 6 and crosslinked at 44:1 PHPA:Cr; all initial polymer solutions were "watery"; 72°F [22°C].

This paper describes a straightforward strategy for diagnosing and solving excess-water-production problems. The strategy advocates that the easiest problems should be attacked first and that diagnosis of water production problems should begin with the information already at hand. A listing of water-production problems is provided, along with a ranking of their relative ease of solution. Although a broad range of water-shutoff technologies is considered, the major focus of the paper is when and where gels can be effectively applied for water shutoff. Proposed StrategyOur proposed strategy for attacking excess-water-production problems advocates that the easiest problems should be attacked first and that diagnosis of water production problems should begin with information already at hand. To implement this strategy, a prioritization of water production problems is needed. Based on extensive reservoir and completion engineering studies and analyses of many field applications, the various types of water problems were prioritized and categorized from least to most difficult, as shown in Table 1. The first three listings are the easiest problems (Category

In this paper, we discuss and describe our extensive experience with the widely applied and quite successful Cr(III)-carboxylate/acrylamide-polymer (CC/AP) gel technology for use in oilfield conformance-control, sweep-improvement, and fluid-shutoff treatments, along with briefly reviewing the gel technology's development. Chromic triacetate is the oftenpreferred chemical crosslinking agent used in conjunction with this polymer-gel technology. The CC/AP gel technology, which was conceived in late 1984, is characterized as having a robust gel chemistry and as being highly insensitive to petroleum reservoir environments and interferences. This gel technology has been employed in over 1,400 conformancecontrol treatments worldwide. Highlights of illustrative field applications and results involving the CC/AP conformance-control gel technology are presented. An overview of what a decade-plus of experience in developing and applying the CC/AP gel technology has taught us is discussed. This includes discussion of: classifying and distinguishing conformance problems and treatments, attributes of good candidate wells and well patterns for gel conformance-control treatments, requirements that must be met in candidate wells and well patterns in order to achieve success, gel treatment elements that must be successfully implemented in order to achieve success, guidelines where conformance polymer-gel treatments are most successfully applied, risks and pitfalls of gel conformance treatments, and quality control issues. AbstractThis study investigates how flow profiles in injection wells are modified when zones are not isolated during placement of gelling agents. Mathematical models are used to examine the degree of gel penetration and injectivity loss in zones of different permeability. Several conclusions are drawn that apply to reservoirs in which crossflow between layers does not occur. First, zone isolation is far more likely to be needed during placement of gels in unfractured wells than in fractured wells. Productive zones in unfractured wells may be seriously damaged if zones are not isolated during gel placement. Second, gel placement without zone isolation should cause the least damage to productive zones in unfractured wells when (a) the gelling formulation exhibits a low resistance factor during placement, (b) the water-oil mobility ratio is relatively high, (c) the most-permeable layer(s) are wateredout, and (d) the waterfronts are not close to the production well in the productive zones. Third, parallel linear corefloods overestimate the degree of profile modification that can be attained in radial systems. Fourth, chemical retention, dispersion and diffusion will probably not significantly mitigate injectivity losses caused by gel penetration into low-permeability zones. Finally, a need exists to determine the permeability and velocity dependencies of gelling-agent resistance factors and of gel residual resistance factors. Sorbie, K.S., Heriot-Watt U. Seright, R.S., New Mexico Petroleum Recovery Research Center Ab...

Chromiwn(III)-crosslinked gels, which are applicable up to 260 0 P for use in . matrix reservoirs as near-wellbore total-shutofJtreatments, were developed and characterzzed.Robert D. Sydansk, Marathon Oil Company SUMMARY Acrylamide-polymer/chromium(III)-carboxylate gels have been developed for application to matrix reservoirs as near-wellbore totalshutoff treatments. Laboratory develowrent, testing, and characterization of the new chrornium(III) (Cr ) aqueous gels are reportcd. Results of this study indicate that these gels can be applied to elevated-temperature (up to 260°F) and high-salinity reservoirs. The single-fluid gels are produced by cross linking low-molecular-weight polyacrylamide with a CrIll-carboxylate-complex crosslinking agent. Use of low-hydrolysis polyacrylamide facilitates the application to high-temperature reservoirs. J J I 25 J J I 50 J J I 100 J J J-365 J J J-730 J J J- " test terminatedExperimental: Gels formulated in fresh water