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The first microbial-enhanced waterflood field project sponsored by the U.S. Department of Energy (DOE), Microbial Systems Corp. (MSC), and INJECTECH, Inc., and being conducted in cooperation with the National Institute for Petroleum and Energy Research (NIPER) was initiated in October of 1986. One of the major goals of this project was to develop a technology that could be implemented by independent oil producers; thus, the field site chosen for the pilot test was representative of a mid-continent waterflood operation with stripper wells. The methodology for designing and optimizing MEOR field technology has yet to be established; however, literature information and experience with MEOR processes indicate that there are certain necessary procedures to implement for a microbial waterflooding process. The site selected for the project is in the Mink Unit of Delaware-Childers field in Nowata County, Oklahoma. This field is typical of mid-continent reservoirs in the United States. The pilot area consisted of four adjacent inverted five-spot patterns drilled on 5-acre spacing. There are 21 injection and 15 production wells on this pilot. Four of the 21 injection wells were treated with NIPER's microbial formulation. Laboratory screening criteria were developed to evaluate microorganisms for this project. Several different microbial formulations were tested in Berea sandstone cores with reservoir fluids to determine oil recovery efficiency. Baseline monitoring of oil production was conducted to establish pre-pilot conditions, and fluid samples were collected on a weekly basis from producing wells. Injectivity and microbial field survivability tests were conducted during the baseline period on two off-pattern wells, and a chemical tracer, fluorescein, was injected into the four injection wells during the baseline period. Tracer was observed in production wells about 1.6 years after injection, which corresponded reasonably well with the predicted tracer breakthrough from simulation studies. Methodologies for field applications of microorganisms in ongoing waterfloods were developed as a result of this project. Results from the field pilot showed that microorganisms could be injected into an ongoing waterftood operation without causing any problems in injectivity. Microorganisms were injected only at the onset of the project, while molasses was injected daily for 2.5 years. Routine injection well backflushing continued to show that the injected microorganisms are thriving in the reservoir. Some of the injected microorganisms were detected at producing wells 32 weeks after injection, which was probably a result of microbial transport through low-volume, high-permeability stringers in the formation. Microbial treatment did improve oil production rate, and water/oil ratios for producing wells nearest the microbially treated injection wells continue to be more favorable than baseline values. The results from this test are encouraging that microbial-enhanced waterflooding can be applied by independent producers. |
