Permeability Modification by In-Situ Gelation With a Newly Discovered Biopolymer
- Shapour Vossoughi (U. of Kansas) | C.S. Buller (U. of Kansas)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- November 1991
- Document Type
- Journal Paper
- 485 - 489
- 1991. Society of Petroleum Engineers
- 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 5.4.10 Microbial Methods, 5.3.2 Multiphase Flow, 4.1.5 Processing Equipment, 1.6.9 Coring, Fishing, 4.1.2 Separation and Treating, 4.3.4 Scale, 4.2 Pipelines, Flowlines and Risers, 5.4.1 Waterflooding
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In a typical gelled polymer process, a polymer reacts with a metal ion toyield a 3D crosslinked system. The success of the process depends on monitoringa large number of variables, including the concentrations of the metal ions,polymer, and reducing agent. Controlling these variables in field-scale testsis extremely difficult, if not impossible. Devising a process with fewervariables is therefore desirable. The in-situ gelation process with fewervariables is therefore desirable. The in-situ gelation process in this paperuses a newly discovered biopolymer produced by process in this paper uses anewly discovered biopolymer produced by Cellulomonas flavigena Strain KU. Thebacteria produce the biopolymer when cultured in a simple salts mediumcontaining any one of a variety of hexoses, pentoses, disaccharides, or suchinexpensive substrates as starch or molasses as the carbon and energy sourcesfor growth. The polymer produced remains associated with the producer bacteria,causing them to produced remains associated with the producer bacteria, causingthem to aggregate and to settle out from the growth medium. The polymer isextracted from the bacteria easily by suspension in dilute alkali. Uponneutralization of such extracts, the polymer precipitates as a hydrogel. Thegelation process is reversible, and the hydrogels are stable at hightemperatures. A linear coreflood was performed to reveal the feasibility ofusing the microbial polymer for the in-situ gelation process. The coreinitially was waterflooded and then flushed with acid. The subsequent injectionof an alkaline solution of the polymer resulted in in-situ formation ofhydrogels.
State of the Art
Early polymer treatment procedures involved simply the injection of polymersolutions and was called polymer flooding or polymer-augmented waterflooding.The technique works to some extent, but many reservoirs do not benefit frompolymer flooding. Some factors responsible for these failures are polymerdegradation caused by mechanical shear, high injected or resident watersalinity, and the tendency of polymer retained by adsorption or mechanicalentrapment to be washed from the porous rock over a period of time. Thus, inmany reservoirs, the amount of intact polymer retained is insufficient tomaintain permeability reduction for the desired period. More recent processesused in attempts to produce large permeability reductions in porous mediainvolved crosslinking permeability reductions in porous media involvedcrosslinking and in-situ gelation of polymers. A polymer-gelation processtypically involves reaction of the polymer with metal ions to yield a 3Dcross-linked system. Gelation times are influenced by concentrations of thecomponents, temperature, pH, and/or other chemical and physical factors and canbe pH, and/or other chemical and physical factors and can be controlled to someextent. Although the technique may produce satisfactory results inlaboratory-scale tests, it fails in most field applications. Additionally,while some success in modifying the permeability of the subterranean strata canbe achieved in sites near the wellbore, little success is experienced in sitesfarther removed from the wellbore, which require greater gelling-agentpenetration into the porous strata. The failures are mostly a result of thecomplexity of the process, which requires the control of a large number ofvariables, including the concentrations of ions, polymer, and reducing agent. Aprocess in which the gelation step is independent of the time that individualcomponents are added and in which the gelation process is reversible isdesirable. A newly discovered biopolymer that meets these requirements, andtherefore has potential for use in in-situ gelation, is described here. Thepotential for use in in-situ gelation, is described here. The polymer is anexopolysaccharide produced by Cellulomonas flavigena polymer is anexopolysaccharide produced by Cellulomonas flavigena Strain KU. Gas, liquid,and thin-layer chromatography of the polymer's acid hydrolyzates anddetermination of the total polymer's acid hydrolyzates and determination of thetotal reducing sugar content of the polysaccharide indicate that it is aglucose homopolymer. The type of glycosidic bonds in the polyglucan was notdetermined. Because it is not hydrolyzed by polyglucan was not determined.Because it is not hydrolyzed by either amylases or cellulases, we concludedthat the polymer is neither a starch nor cellulose. The U. of Kansas has beengranted two patents: one on the process of polymer production and the productof that process and another on the use of the polymer in product of thatprocess and another on the use of the polymer in subterranean permeabilitymodification.
Materials and Methods
Bacteria. The bacterium that produces the polysaccharide polymer used inmost of the experiments described here was isolated from leaf litter on thebasis of its ability to hydrolyze cellulose. It has been characterized as a newstrain of Cellulomonas flavigena. All other species of Cellulomonas andAlkaligenes faecalis were obtained from the American Type Culture Collection(ATCC) in Rockville, MD.
Polymer Synthesis and Purification, Cellulomonas flavigena was PolymerSynthesis and Purification, Cellulomonas flavigena was grown in a minimal-salts(CM9) medium containing an excess of glucose, and polymer was extracted andpurified as described in Ref. 9. In brief, alter a 72-hour incubation of thecultures, polymer was extracted by resuspending the culture in 1 N NaOH.polymer was extracted by resuspending the culture in 1 N NaOH. Aftercentrifugation to remove cell debris, the alkaline supernatants wereneutralized, resulting in precipitation of the polymer in gel form. Thecultivation of Alkaligenes faecalis subspecies myxogenes (ATCC #28180) in aminimal medium containing glucose and purification of the polyglucan producedwas performed as described by Harada et al. The polymer used in the corefloodtest described below was a cell-free crude extract purified by many cycles ofwater washes. The extracts were made by centrifuging batch cultures of C.flavigena, prepared as described in Table 1, and extracting the sedimentedprepared as described in Table 1, and extracting the sedimented cells with 1 NNaOH by use of 8 mL alkali/g (wet weight) cells. After brief stirring at roomtemperature, the cell residue was removed by centrifugation and the alkalinesupernatant, containing the dissolved polymer, was used for the corefloodexperiments. Such alkaline extracts typically contained 1.5 to 2 mgpolysaccharide/mL.
Viscometric Measurements. The Weissenberg rheogoniometer Model R19, equippedwith cone and plate, was used to measure the viscosities of polymer solutionsand gels. The instrument is capable of operating in either a steady rotationalmode or a sinusoidal oscillatory mode. The oscillatory testing mode was used todetermine the dynamic viscosity and the storage modulus, which characterizedthe elastic behavior of the gel. All measurements on the polymer solutions wereperformed under steady shear. Rheological measurements were performed at aconstant temperature of 77 degrees F (+0.4 degrees F). To maintain thistemperature, a constant-temperature circulator bath and a set of flexiblesilicon rubber heaters attached to the lower platen were used. Data acquisitionfrom the Weissenberg rheogoniometer was achieved by an IBM personal computer XTattached to the ISAAC control system.
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