Experiments were conducted to study the feasibility of using microorganisms in EOR, particularly for the correction of permeability varIatIOn. The use of microorganisms requires the ability to transport viable cells as well as the nutrients required for cellular growth through reservoir formations. Nutrients such as glucose. peptone-protein, and phosphate and ammonium ions were transported through brine-saturated Berea sandstone cores in amounts sufficient to support microbial growth. Viable bacterial cells were transported through sandstone cores of 170-md pemleability. Less than I % of the influent cell concentration was recovered in the effluent, indicating a high degree of cell retention inside the core. The addition of nutrients to these cores and subsequent incubation to allow for microbial growth resulted in permeability reductions of 60 to 80%. These data show that the growth of microorganisms significantly reduces the permeability of porous rock.
This paper discusses the physical parameters involved in the slow flow of high molecular weight polymer solutions in porous media. The interacting erects of polymer properties and porous media properties on flow performance are considered. Experiments were conducted with the polyethylene oxides, with molecular weights ranging from 200,000 to over 5,000,000. Frontal advance velocities ranged from 1 to 30 ft/day. The porous matrix consisted of a flow cell packed with glass beads. Polymer solutions were characterized by viscosity and normal stress measurement. Under certain condition, unexpectedly high Row resistance was observed. This behavior was observed to be a function of flow rate, pore size, polymer molecular weight and concentration. The polymer solutions exhibit "dilatant" flow behavior in porous media in contrast with the pseudo plastic behavior in simple flow systems. A theoretical explanation of such behavior is presented. Introduction The use of polymers in the injected water of a waterflood increases oil displacement efficiency by reducing the mobility (kw/uw) of the driving phase. A reduced driving phase mobility results in improvements in the areal sweep efficiency and in the vertical coverage in stratified reservoirs. This mobility reduction may be achieved by a permeability reduction, a viscosity increase or by a combination of the two. Early attempts at increasing the injected water viscosity were not successful because of the poor economics involved. The use of such materials as glycerin, sugar or glycols to increase water viscosity was not economically feasible. Attempts in using certain naturally occurring polymers were not too successful because of the high polymer losses to the rock. A high molecular weight, partially hydrolyzed polyacrylamide was introduced 3 years ago as a waterflood additive. Initial work by Pye indicated that the presence of these polymers in dilute concentrations decreases the water mobility 5 to 20 times more than would be expected from measurements of the solution viscosity. Such an effect would be of obvious economic value since only a small polymer concentration would be required to accomplish a large reduction in water mobility. This research was designed to study the basic flow mechanisms of polymer solutions in porous media. The interacting effects of polymer properties and porous media properties on flow performance are considered. This study indicates some of the conditions under which these interactions can lead to significant mobility effects. DEFINITION OF PROBLEM The Darcy equation ........................................(1) is valid only for Newtonian fluids. For polymer solutions and other non-Newtonian fluids the equation must be modified to consider that viscosity is a variable quantity. Modification of the Darcy equation to include non-Newtonian effects has been the subject of several recent investigations. The modifications generally adopt a rheological model, such as an Ellis or power law model, to porous media by defining some characteristic channel radius. Most of these studies showed the porous media flow behavior to be predictable from viscometric data. Investigations involving the flow of high molecular weight polyacrylamide solutions through cores have generally encountered the high flow resistances reported previously by Pye. This high flow resistance has generally been attributed to an in-depth permeability reduction, as evidenced by a reduced permeability to water which has displaced polymer solution from the porous media. Marshall and Metzner report high flow resistances, which they attribute to viscoelastic effects. In this paper, the effects of polymer molecular weight. pore size, flow rate and concentration are considered. The polymers used are the polyethylene oxides known as Polyox. This class of polymers was used because of its availability in a wide range of molecular weights and because of its known ability to propagate well through porous media. THEORY PHYSICAL PROPERTIES OF POLYMER SOLUTIONS The polymer molecule dissolves in water by means of hydrogen bonding, but retains some of its own structural identity while in solution. Nonionic polymers, such as polyethylene oxide, are generally considered to have a random coiling configuration. This type of molecule has the ability to "sequester" or hold a large volume of solvent within its coils in a manner similar to that of a sponge. JPT P. 1065ˆ
The object of this study was to determine if crude oii could be produced successfully by a process of crude oil vaporization using carbon dioxide repressuring. This process appears to have application to highly fractured fcwvnations where the major oil cotitent of the reservoir is contained in the non-fractured porosi~with little associated pertneability. Crude oil was introduced into the windowed cell and carbon dioxide was charged to the ceil at the desired pressure. A vapor space was formed above the oil, and the crude oil-carbon dioxide mixture was allowed to come to equilibrium. The vapor phase was retnoved and the vaporized oil collected as condensate. Samples of all produced and unprodttced fluids were analyzed. Tests were also performed to evaluate the amount of vaporized oil tilat can be produced by rocking from a high to a 10wer pressure. The carbon dioxide repressuring process was applied to a sand-filled cell to investigate the performance in a porous mediutn, A test was performed to evaluate how the condensate recovery changes as the size of the gas cap in contact with the oil changes.
A multi-well microbially enhanced oil recovery field pilot has been performed in the Southeast Vassar Vertz Sand Unit in Payne County, Oklahoma. The primary emphasis of the experiment was preferential plugging of high permeability zones for the purpose of improving waterflood sweep efficiency. Studies were performed to determine reservoir chemistry, ecology, and indigenous bacteria populations. Growth experiments were used to select a nutrient system compatible with the reservoir that encouraged growth of a group of indigenous nitrate-using bacteria and inhibit growth of sulfate-reducing bacteria. A specific field pilot area behind an active line drive waterflood was selected. Surface facilities were designed and installed. Injection protocols of i, bulk nutrient materials were prepared to facilitate uniform distribution of nutrients within the pilot area. Bythe end of December, 1991, 82.5 tons (75.0 tonnes) of nutrients had been injected in the field. A tracer test identified significant heterogeneity in the SEVVSU and made it necessary to monitor additional production wells in the field. The tracer tests and changes in production behavior indicate the additional production wells monitored during the field trial were also affected. Eighty two and one ha.lr barrels (13.1 m3) of tertiary oil have been recovered. Microbial activity has increased CO2 content as indicated by increased alkalinity. A temporary rise in sulfide concentration was experienced. These indicate an active microbial community was generated in the field by the nutrient injection. Pilot area interwell pressure interference test results showed that significant permeability reduction occurred. The interwell permeabilities in the pilot area between the injector and the three pilot production wells were made more uniform which indicates a successful preferential plugging enhanced oil recovery project.
A method for oil recovery enhancement by stimulating the growth of indigenous microbial populations in sandstones by nutrient injection was investigated. Incremental oil recovery from the cores ranged from 10–38% of the original oil in place. Volumetric and microscopic sweep efficiency was improved by the microbial selective plugging process. Biogenic gas production accompanied the oil produced from the cores. The combination of stratification correction, gas production, and pressure increase assisted in recovery of previously trapped oil.
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