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This paper was selected for presentation ty en SPE Program CommKfee Iolbwmg review of udormation contained In an absfracf aubmmed by the author(s). Contents of the paper, as presented, have not been reviewed by Iha Scmefy QI Petrofeum Engumerz and are subject to mrr-tbn by the aulh+). Tim mafenal, as pmsenfad, does not _sanfy rdlsct any gmsihon of the SOctoty of Petrol-sum Engineers, ifs dtiwrs, w members. Papem presented at SPE meetings ere subject to puMcation revbw by Edtorial Committee of the .%ciafy of Petroleum Engineers. Permission to cow IS restrm fed to an ab$fracl of not more than 300 words. Illustrations may nol ba COPM. The abstracl should contain ccmspIcuous acknow'bdgment of wtfere and b whom the eper m presented. Write Libfarian, SPE, P.O. Sox S33S%, R!chaJdson, XL? TX 750S3-6, U.S.A. dOX, 1K?245 SPEUT, AbstractWater handling is a major expense involved in producing mature oil fields, Reservoir heterogeneities and variations in permeability can aggravate the problem of water production and significantly reduce the efficiency of oil production. Several methods for improving reservoir sweep through conformance control have been used. Methods such as crosslinked polymer technology have alleviated problems associated with reservoir heterogeneity.Other alternatives such as microbial-and surfactant-based methods have been proposed. This paper presents the results of research conducted on polymer-producing bacteria that were isolated and tested at various temperatures and salinities. Coreflooding experiments were conducted to show the effectiveness of microbial treatments, Reduction in effective permeabilities by as much as 90% were achieved due to in situ polymer production. Noninvasive imaging techniques such as magnetic resonance imaging (MRI) and computer-aided tomography (CT) were employed to visualize changes in fluid distribution in porous media. High permeability areas were blocked by biopolymer production, resulting in brine diversion into lower permeability areas.

Four experiments investigated taste potentiation in weanling rats. In Experiment 1, the animals that drank a conditioning compound of denatonium and saccharin consumed significantly less on the test than controls that drank only saccharin during conditioning. This enhanced saccharin aversion was decremented by postconditioning extinction to denatonium in Experiment 2, and no generalization of saccharin aversions to the denatonium was observed in Experiment 3. Extinction of either saccharin or denatonium aversions after compound conditioning was shown in Experiment 4 to result in substantial decrements in aversions to the compound. The relationship of these outcomes to a multiple-association account of potentiation and to the role of discrimination processes in ingestional learning is discussed.

The field history and performance of microbial culture products for the oil field is examined. For over 15 years, microbial culture products have been used for paraffin control, production enhancement, well bore treatments as well as for scale and corrosion problems. The wide-ranging capacity of microbes to effect positive changes in oil and water properties is described. The broad spectrum of oil types and formations that have been treated successfully is reported along with treatment protocols. Mechanistic considerations for modes of action are analyzed. Traditionally, these considerations involve the continuous production of biosurfactants, solvents and other oil mobilizing agents. Continuous advancement of microbial technology has led to more recent development of new applications that use unique metabolic capabilities of microorganisms to address specific well problems. Examples of applying these products to problems in oil field production systems are shown. The outlook for development of new technologies and the future application of these products to the oil field is discussed. Introduction Microbial culture products occupy an increasingly important and growing segments in oil field production operations. They are a truly environmentally benign treatment technology that can be used to replace and augment many conventional technologies, including many oil field chemicals. The extraordinary diversity of microorganisms with the concomitant likelihood for many more such products in the future suggests that their role in oil field operations will continue to expand and will supplant many conventional technologies in the next 100 years. It is therefore important to review the prior and current uses of this technology. Historical Applications of Microbial Culture Products Paraffin Control. Microbial culture products (MCPs) were first used in 1986 in the Austin Chalk formation in Texas to control paraffin deposition. The theory behind these products was that microorganisms can be isolated and combined in novel mixtures which will produce biochemicals that will mimic the action of classic oil field chemicals such as pour point depressants, crystal modifiers and wax dispersants. The advantage of using such biological products is the fact that the microorganisms will 1) produce these biochemicals continuously and 2) attach to surfaces where paraffin deposition is occurring and act directly at the site of deposition. The first successful application of these products began a pattern of expansion that continued throughout the 80s and 90s. Paraffin deposition results in a variety of problems for oil field operators, ranging from plugging of tubulars to occult formation deposition that reduces formation permeability. A continual increase in the number of products available to the industry allowed the expansion of the microbial technology for paraffin control into a variety of different oil types and formations. Conventional technologies to control paraffin deposition are thermal and chemical treatments. Both of these technologies have limitations that restrict their long-term effectiveness. In particular, hot oil or water treatments may lead to increased formation damage by forcing deposited high molecular weight paraffins into the formation where they can contribute to pore throat plugging and lead to production loss. Development of MCPs represents a successful alternative technology to remove paraffin deposits without causing lasting formation damage. Long term use of MCPs showed no damage to the oil field production system and their use increased throughout the mid continent region in the early 1990s. Examples of the successful application of this technology in the oil field have been previously documented in SPE papers.1,2,3

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Gelled polymer systems are widely used in petroleum production to modify permeability of reservoir rock. These gel systems are injectable as low-viscosity gelants and then triggered in situ to form a gel. The use of biocatalysts to trigger the delayed gelling reaction of a biopolymer gelant was evaluated in this study. The gelant was a pH-sensitive glucan biopolymer. Two bacterial strains were isolated from lake sediment and used to trigger the gelling reaction. Both strains grew anaerobically, and were mesophilic, halotolerant, and obligately alkaliphilic. Using the biocatalysts to trigger gel formation, gelation delay time was inversely proportional to initial biocatalyst concentration and gelation could be delayed up to 12 days after mixing. Each of the bacterial strains had distinct effects on the rate of the gelling reaction and permanence of the formed gel. Data indicate that these strain-specific characteristics can be exploited to design gelled polymer systems with controlled performance properties. The new polymer system was injected into sand-packed columns, glass bead-packed columns, and Berea sandstone cores, and then triggered in situ by the biocatalyst to form gel. Analysis of core effluent indicated that the in situ gelling reaction was complete. Brine permeability of cores was decreased by two to four orders of magnitude after treatment with the new gel system. In parallel core floods, the bio catalyzed gel blocked flow through high permeability zones and diverted flow into low permeability zones. Permeability modification with the polymer system improved sweep efficiency and increased oil recovery over water flooding alone. Introduction Permeability variations in the reservoir matrix can cause excess water production and poor oil recovery efficiency. Gelled polymer systems are widely used in petroleum reservoirs to modify permeability of reservoir formations and reduce the flow of water through permeable zones. Many of the popular gel systems use high molecular weight polymers mixed with complexing metal ions and/or reactive compounds. These gelants have a low viscosity immediately after mixing and can be injected into the reservoir formation. After mixing and injection, crosslinking by the metal ions initiates gel formation. Because the gelation is delayed, these gel systems have the advantage of deep penetration by a low viscosity gelant and effective blockage after gelation.1 For successful applications of gelled polymer systems, the rate of the triggering gelation reaction must be controllable to allow injection and placement in the reservoir before formation of the gel. This rate is commonly dependent on several variables including critical concentrations of polymer and crosslinking ions, additional reactants, pH, temperature, salinity, and/or other competing chemical species and reactions. Also, many of the popular gelled polymer systems are plagued with problems related to chemical toxicity and public health concerns. Simpler gel systems which are directly controllable and more environmentally sound are desirable.

Permeability modification is a useful technology for extending the productive life of watered-out oil fields. Polymers are widely used to decrease permeability of high permeability zones or water channels that form in heterogeneous petroleum reservoirs. Decreasing permeability of these previously swept zones diverts injected fluids into unswept regions of the reservoir, increasing the sweep efficiency and extending the production life of marginal fields. Many of the gelled polymers that have been developed for this purpose rely on toxic reagents and are environmentally unfavorable. Microbial polymer systems offer low cost, environmentally safe methods to produce polymer gels in situ. Several microbially controlled polymer systems are being developed to provide in depth permeability modification in heterogeneous reservoirs. One system uses polymer-producing bacteria to produce polymer biomass in situ. Another microbial method under development is a novel gelled polymer system that uses microorganisms to cause delayed gelation of an ex-situ produced biopolymer. This paper presents laboratory results from the microbial systems. Introduction Applying permeability modification treatments can significantly extend the productive lives of active oil recovery projects, curtailing the prospect of premature abandonment. Effective modification of reservoir sweep can improve the economics of an oil recovery process. The National Energy Strategy-Advanced Oil Recovery Program has identified permeability modification as an improved oil recovery (IOR) method having significant potential to arrest the current high rate of well abandonment. Efforts to develop methods for permeability modification stem from the need to improve the efficiency of applied recovery methods such as waterflooding. Inherent reservoir characteristics can significantly impact field production. Current state-of-the-art technology in this area uses crosslinked polymer technology to alleviate problems associated with reservoir heterogeneity. Treatments in both injection and production wells have been applied. Limitations of technology are being addressed by continued research efforts in the area, but many of the current applications still rely on the use of crosslinking agents that may pose an environmental hazard. This paper addresses the development of alternative methods using biotechnology for permeability modification. One of the microbial technologies under development uses microbial metabolism to trigger gelation of an ex-situ produced biopolymer. Curdlan biopolymer exhibits a pH-dependent reversible solubility, being soluble in alkaline solutions (pH >10) and insoluble in neutral or acidic solutions. A similar polymer has been tested for permeability reduction using a layered process of alternating injections of alkaline-soluble polymer and neutralizing acid. The curdlan microbial gelation process described here places the polymer gelation process under the control of acid-producing bacteria. Another microbial process for permeability reduction uses bacteria to produce polymer in situ. The bacteria are injected into porous media and then stimulated to produce permeability-modifying biopolymer. Experimental studies were conducted to evaluate the effectiveness of these methods for permeability modification. P. 649