Evaluation of Microbial Systems in Porous Media for EOR
- Rebecca S. Bryant (IIT Research Inst./NIPER) | Jonell Douglas (IIT Research Inst./NIPER)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- May 1988
- Document Type
- Journal Paper
- 489 - 495
- 1988. Society of Petroleum Engineers
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- 494 since 2007
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Summary. The use of microorganisms to enhance oil recovery has become a technically feasible technology for production from stripper wells (those that produce less than 10 B/D [1.6 m/d]). As a result of microbial growth and the production Of CO and/or chemicals, oil recovery can be effectively increased in certain reservoirs with temperatures and salinities hospitable to microorganisms. Research at the Natl. Inst. for Petroleum and Energy Research has led to development of laboratory facilities for evaluating microbial systems for microbial enhanced oil recovery (MEOR) applications. Results from microbial core studies using Berea sandstone have shown that bacteria can vary greatly in their ability to recover residual oil after waterflooding, giving from 7.5 to 71 % recovery efficiency. The type of core encapsulation did not affect oil recovery. Variations in rock permeability from 134 to 1,920 md indicated that some microorganisms may exhibit a better recovery efficiency in lower-permeability cores. The results also show that gas production by microorganisms is not the only factor affecting oil recovery; some bacteria that produce surfactants but no gas could provide equally efficient additional oil recoveries. Likewise, the type of surfactant also makes a difference; two species that produce surfactants can vary in recovery efficiency. Another contributing mechanism to microbial oil mobilization may be by increasing areal sweep efficiency from microbial growth. A comparison of oil recovery efficiencies between microorganisms using a medium-to-light-gravity oil (Delaware-Childers) and two heavy oils (Wilmington, CA, and Chaffee, CA) indicates that MEOR may be effective for heavy oils as well as light oils. Correlations are presented between the recovery efficiency of a particular microbial species and its ability to mobilize crude oil in etched-glass micromodels.
The most popular technique for MEOR involves the direct injection of microorganisms into the reservoir. The in-situ MEOR processes require growth and metabolism of injected microorganisms, which provide chemicals that can aid in releasing oil from reservoir rock. Several mechanisms for microbial oil recovery have been proposed.
1. Production of gases-CO, H, N, and CH -could increase pressure in the reservoir and reduce oil viscosity. Controlled microbial activity should produce gases in pore spaces, including parts of the reservoir that would normally be bypassed in gas flooding processes.
2. Microbial acid production, primarily of low-molecular-weight fatty acids, can cause rock dissolution.
3. Biosurfactant production can cause decreases in surface and interfacial tensions.
4. Microorganisms have been shown to cause wettability alterations in glass micromodels, reservoir flow cells, and Berea sandstone.
5. Microbial growth and polymer production in high-permeability regions of the reservoir can allow additional injected fluids to bypass those regions and flow through the desired high-oil-saturation areas of the reservoir.
Oil displacement tests in Berea cores of MEOR processes were used to evaluate species of Bacillus, Clostridium, and other genera for their abilities to release crude oil from rock and survive in porous media. Such experimental parameters as core encapsulation, crude oil type, rock permeability, and microbial characteristics were varied and the effects on crude oil recovery were investigated. The results from these studies were compared with visual observations in micromodels to determine the mechanisms of oil recovery by microorganisms.
Experimental Apparatus and Procedures
Coreflood Apparatus. The experimental equipment is shown in Fig. 1. The fluid separators are piston devices used to inject microbial solutions and other fluids into the cores and were designed to prevent corrosive fluids from contacting the pumps. The frontal advance rate for the cores was 1 ft/D [0.3 m/d].
Micromodel. Glass micromodels used in this study are shown in Fig. 2. Construction of the micromodels has previously been described by Chatzis. The flow rate was adjusted to 0.01 ml/min, which corresponded to approximately 8 ft/D [2.4 m/d]. The micromodels were brine-saturated, oil-saturated with Delaware- Childers crude, and waterflooded to residual oil saturation (ROS) before microbial injection.
Core Preparation. Blocks of Berea sandstone were obtained and cut in cylindrical cores 10 in. [25 cm] in length and 1 in. [2.5 cm] in diameter. The cores were fired at 800 deg. F [427 deg. C] for 24 hours to stabilize the clays. Cores were either encapsulated in epoxy with inlet and outlet valves at the ends or were encased in rubber sleeves and placed inside stainless-steel Hassler coreholders. The cores were then evacuated and flushed with brine. Darcy's law was used to determine absolute permeability of each core. Crude oil was injected into the cores until no additional water was produced (about 24 hours; pressure drop was less than 1 psi [ less than 6.9 kPa]), then brine was flushed through the core until no more crude oil was produced. The cores thus simulated a waterflooded ROS condition designated by S.
Crude Oil. Crude oil samples were obtained from the Bartlesville sand in the Delaware-Childers field in northeastern Oklahoma or from the Wilmington or Chaffee fields in California. Delaware- Childers oil has a gravity of 31 deg. API [0. 87 g/cm ]; Wilmington, 17 deg. API [0.95 g/cm ]; and Chaffee, 14 deg. API [0.97 g/cm ].
Chemicals and Media. The molasses used in these experiments was Mr. Blackstrap 87; its composition was 5 % crude protein; 0. 5 % crude fat; 38 % total sugars; and 56.5 % fiber. It was dissolved in water to make a 4.0 wt% solution and was filtered through cheesecloth to remove the suspended fiber particles.
Microorganisms. Microorganisms N12, N17, N18, and Tu6 are Gram-negative, facultatively anaerobic rods that produce CO and acids when fermenting sucrose. Bacillus A and B, Bacillus licheniformis (Bacillus C; ATCC #27811), and Bacillus licheniformis (Bacillus D; ATCC #39307) are all facultatively anaerobic rods that produce acids and varying amounts of surfactant when fermenting sucrose. Clostridium A and B are anaerobic species that produce CO, and acids when fermenting sucrose. System PS1 is a mixture of strictly aerobic microorganisms.
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