Roy M. Knapp

In Situ Biosurfactant Production by Bacillus Strains Injected into a Limestone Petroleum Reservoir

ABSTRACT Biosurfactant-mediated oil recovery may be an economic approach for recovery of significant amounts of oil entrapped in reservoirs, but evidence that biosurfactants can be produced in situ at concentrations needed to mobilize oil is lacking. We tested whether two Bacillus strains that produce lipopeptide biosurfactants can metabolize and produce their biosurfactants in an oil reservoir. Five wells that produce from the same Viola limestone formation were used. Two wells received an inoculum (a mixture of Bacillus strain RS-1 and Bacillus subtilis subsp. spizizenii NRRL B-23049) and nutrients (glucose, sodium nitrate, and trace metals), two wells received just nutrients, and one well received only formation water. Results showed in situ metabolism and biosurfactant production. The average concentration of lipopeptide biosurfactant in the produced fluids of the inoculated wells was about 90 mg/liter. This concentration is approximately nine times the minimum concentration required to mobilize entrapped oil from sandstone cores. Carbon dioxide, acetate, lactate, ethanol, and 2,3-butanediol were detected in the produced fluids of the inoculated wells. Only CO2 and ethanol were detected in the produced fluids of the nutrient-only-treated wells. Microbiological and molecular data showed that the microorganisms injected into the formation were retrieved in the produced fluids of the inoculated wells. We provide essential data for modeling microbial oil recovery processes in situ, including growth rates (0.06 ± 0.01 h−1), carbon balances (107% ± 34%), biosurfactant production rates (0.02 ± 0.001 h−1), and biosurfactant yields (0.015 ± 0.001 mol biosurfactant/mol glucose). The data demonstrate the technical feasibility of microbial processes for oil recovery.

Experimental Studies of In-Situ Microbial Enhanced Oil Recovery

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 permeability. Less than 1% 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.

Microbial selective plugging and enhanced oil recovery

SummaryThe ability of indigenous populations of microorganisms in Berea sandstone to improve the volumetric sweep efficiency and increase oil recovery by in situ growth and metabolism following the injection of nutrients was studied. Cores of differing permeabilities connected in parallel without crossflow and slabs of sandstone with differing permeabilities in capillary contact to allow crossflow were used. The addition of a sucrosenitrate mineral salts medium stimulated the growth and metabolism of microorganisms in the sandstone systems. This resulted in a preferential decrease in permeability in the core or slab with the higher initial permeability, diverted flow into the lower-permeability core or slab and improved the volumetric sweep efficiency. Injectivity into the slab with the lower initial permeability in the crossflow system increased during subsequent nutrient injections. Thus, microbial selective plugging does occur in laboratory systems that have the complex flow patterns observed in petroleum reservoirs without losing the ability to inject fluids into the formation. In situ microbial growth and metabolism increased oil recovery 10 to 38% of the original oil in place. Biogenic gas production accompanied oil production, and much of the gas was entrained within the produced oil suggesting that gas production was an important factor leading to increased oil recovery. Quantitation of the amount of phospholipid in the core confirmed that microbial growth preferentially occurred throughout the core with the higher initial permeability. These data showed that in situ microbial growth in the high-permeability regions improved not only the volumetric sweep efficiency but also the microscopic oil displacement efficiency.

Selectivity and depth of microbial plugging in Berea sandstone cores

SummaryThe depth of plugging by the in situ growth of either injected or indigenous microorganisms was investigated using Berea sandstone cores with pressure taps located along the length of the core. The continuous injection of aerobically prepared sucrose-mineral salts medium with 5% NaCl and 0.1% NaNO3 resulted in large permeability reductions (70–98%). The plugging was localized at the inlet and outlet faces of the cores, and was attributed to microbial biomass production at the inlet face and biogas accumulation at the outlet face. Batch addition of aerobic medium resulted in more uniform permeability reduction along the cores length, but the magnitude of the permeability reduction was not as large (about 65%). The semi-continuous injection of oxygen-free medium resulted in a slower but a more uniform permeability reduction throughout the core compared to cores which received aerobically prepared medium. The selectivity of the process was investigated in a dual core system where two cores of 240 and 760 mdarcy permeability were connected parallel to each other without crossflow. Initially, about 85% of the total fluid flow passed through the high permeability core. After the addition ofBacillus species and medium, the flow pattern changed and about 85% of the total fluid passed through the low permeability core. These results show that the in situ growth of microorganisms can selectively plug high permeability zones and that control of the process may be achieved by alterations in the method of nutrient injection.

Pretest studies for a microbially enhanced oil recovery field pilot in a hypersaline oil reservoir

Abstract The ecological and physiological factors governing microbial activity in the Southeast Vassar Vertz Sand Unit (SEWSU), Payne County, OK, an oil reservoir selected for a microbially enhanced oil recovery field pilot, were studied. Analysis of the brines from the reservoir showed that the SEWSU reservoir is a hypersaline environment rich in calcium and magnesium cations, and contains most of the inorganic nutrients required for microbial growth. Substantial amounts of sulfate and sulfide were detected in the brines, indicating a potential for sulfate reduction activity. Of the various carbohydrate‐based nutrients tested, a molasses‐ammonium nitrate nutrient mixture best stimulated the metabolism and growth of the microbial communities in the brines. Sulfide was not detected in any brine samples that received high levels of nitrate, even when additional carbon sources such as molasses were added. The addition of nitrate also resulted in shorter lag times, higher maximum turbidities, and larger press...

Microbially enhanced oil recovery from carbonate reservoirs

Abstract About half of the worlds oil production is from carbonate formations. However, most of the research in microbially enhanced oil recovery (MEOR), a potentially important tertiary recovery technology, has focused on sandstone reservoirs because, in general, they are geologically simpler than carbonate reservoirs and easier to model in the laboratory. Carbonate formations have a wide range of pore geometries and distributions, resulting in complex flow dynamics. The low matrix permeabilities and the dual porosity characteristics of most carbonate formations, coupled with the chemistry of carbonates, have slowed implementation of enhanced oil recovery methods. A review of the data on carbonate reservoirs in Dwights Energydata TOTL System indicated that 40% of the oil‐producing carbonate reservoirs surveyed in the United States have environmental, geological, and petrophysical conditions that would make them candidates for MEOR. A review of a number of MEOR field trials showed that rates of oil prod...

Effect of microbial growth on pore entrance size distribution in sandstone cores

SummaryThe in situ growth of microorganisms in Berea sandstone cores preferentially plugged the larger pore entrances. The largest pore entrance sizes after microbial plugging ranged from 20 to 38 μm, compared with 59 to 69 μm before plugging. The pore entrance size distribution of plugged cores was shifted to smaller sizes. A mathematical model based on Poiseuilles equation was found to adequately predict permeability reductions (greater than 90%) caused by microbial growth in the large pore entries.

Alteration of permeability by fine particle processes

Permeability reduction and skin effect caused by water sensitivity of clay particles in petroleum reservoirs is a primary source of decreasing well performance. Therefore, it is of paramount interest to the petroleum industry to understand the fundamental mechanisms leading to skin development and to find ways to alleviate this problem. Numerous studies have been reported in the literature addressing some aspect of permeability reduction phenomena. The applicability of these studies is limited to particular cases considered. What is needed is a fundamental approach to describe the particulate processes which will allow for later extension and modification as more data become available and our understanding of various processes advances. In this respect, Civan and Knapp (1987) took the approach of phenomenological modeling, in which all governing phenomena were described based on fundamental conservation laws and principles. They considered the combined effects of formation swelling and migration and retention of fine particles in porous media during flow for prediction of the permeability reduction. Specifically, their study was limited to the case of injection of a suspension of fine particles to porous media. This model was tested and confirmed using the data of Hart et al. (1960), who studied the effect of injecting brine containing dead bacteria into Berea cores. In this study, the model of Civan and Knapp (1987) is extended to include the swelling and capture of clay particles from the pore surface by fluid shear. The extended model considers two distinct sources of particles: those directly generated within the porous media and others previously deposited in porous media from the flowing suspension of particles as shown in Fig. 1. Addition of this feature enables the model to simulate a wide variety of realistic cases involving particulate processes in petroleum reservoirs. This model is verified using the data of Hart et al. (1960), Gruesbeck and Collins (1982), and Khilar and Fogler (1983). In each case, however, some of the information required for simulation is missing. Therefore, the missing data are approximated based on the description of the experimental system and common knowledge available in the literature. Various model parameters are determined using the statistical parameter identification method described by Kerig and Watson (1986). It is shown that the model can reproduce the fundamental characteristics of the experimental measurements within the uncertainties of the experimental data.

Ch. R-7 Isolation and Characterization of Novel Halophilic Anaerobic Bacteria from Oil Field Brines

Abstract The development of a succesful microbially enhanced oil recovery process requires a thorough understanding of the factors affecting microbial activity in the oil reservoir. A study has, therefore been initiated to evaluate the ecological and physiological factors governing the microbial activity in the oil field brines collected from the South East Vassar Vertz Sand Unit, Payne County, Oklahoma. The brines were highliy saline containing 11 to 19% NaCl and 1 to 2% of calcium and magnesiumions. Diverse populations of anaerobic heterotrophic bacteria were present at densities of 2.4 × 10 3 to 4.6 × 10 3 MPN/ml. Of the several strains isolated, five strictly anaerobic and obligately halophilic strains were selected for further characterization. None of the isolates grew at salt concentrations less than 3% (w/v). All strains grew in a mineral salts medium containing glucose, yeast extract and casamino acids in the presence of NaCl concentrations of up to 20% (w/v), but the optimum concentration for growth was around 12%. The doubling time of the isolates ranged between 7 and 11 hours. Addition of nitrate to the growth medium did not stimulate growth of any of the isolates. However the addition of sulfite as the external electron acceptor stimulated the growth yield of the strain TTL-30. All of the isolates metabolized a variety of carbohydrate substrates but not several of the tested aromatic compounds and amino acids. Acetate, butanol and propanol were detected as the fermentative products on glucose. The change of gas phase from N 2 /CO 2 to H 2 /CO 2 stimulated the growth of strains TA and SA, but completely inhibited the growth of the strain TTL-30. Methane was never produced by any of the five strains showing that these strains are not methanogens. The ability to use a fermentable carbohydrate make these strains suitable candidates for microbial selective plugging process in hypersaline environments.

Microbially enhanced oil recovery from unconsolidated limestone cores

Abstract The enhanced recovery of residual oil from unconsolidated carbonate cores using microorganisms was examined in model cores packed with chips of Viola limestone. Vibrio aspartigenicus strain GSP‐1, an acid producer, and Bacillus licheniformis strain JF‐2, a surfactant producer, were used as the test microorganisms. The primary hypothesis tested was that microbial treatment of a packed core system would result in the recovery of residual oil from the carbonate test system. After three treatments, 39–44% of the residual oil‐in‐place was recovered from packed core systems after treatment with strain GSP‐1. Two treatments with strain JF‐2 resulted in a 27% recovery of the residual oil‐in‐place. Modification of the core matrix was indicated by the presence of calcium in the core effluents and significant amounts of carbonate fines found in the dissected cores, presumably caused by dissolution of the carbonate matrix by microbial acid end products of metabolism (microbial matrix acidizing). These result...