Slowing Production Decline and Extending the Economic Life of an Oil Field: New MEOR Technology

Summary This project demonstrated the effectiveness of a microbial permeability profile modification (MPPM) technology for enhancing oil recovery by adding nitrogenous and phosphorus-containing nutrients to the injection water of a conventional waterflooding operation. The MPPM technology extended the economic life of the field by 60 to 137 months, with an expected recovery of 63 600 to 95 400 m3 (400,000 to 600,000 bbl) of additional oil. Chemical changes in the composition of the produced fluids proved the presence of oil from unswept areas of the reservoir. Proof of microbial involvement was shown by increased numbers of microbes in cores of wells drilled within the field 22 months after nutrient injection began. Introduction The target for enhanced oil recovery processes is the tremendous quantity of unrecoverable oil in known deposits. Roughly two thirds [approximately 55.6×109 m3 (350 billion bbl)] of all of the oil discovered in the U.S. is economically unrecoverable with current technology. Because the microbial enhanced oil recovery (MEOR) technology in this report differs in several ways from other MEOR technologies, it is important that these differences be delineated clearly. In the first place, the present project is designed to enhance oil recovery from an entire oil reservoir, rather than treat single wells. Even more important is the fact that this technology relies on the action of the in-situ microflora, not microorganisms injected into the reservoir. It is important to note that MPPM technology does not interfere with the normal waterflood operation and is environmentally friendly in that neither microorganisms nor hazardous chemicals are introduced into the environment. Description of the Oil Reservoir. The North Blowhorn Creek Oil Unit (NBCU) is located in Lamar County, Alabama, approximately 75 miles west of Birmingham. This field is in what is known geologically as the Black Warrior basin. The producing formation is the Carter sandstone of Mississippian Age at a depth of approximately 700 m (2,300 ft). The Carter reservoir is a northwest/ southeast trending deltaic sand body, approximately 5 km (3 miles) long and 1 to 1.7 km (1/2 to 1 mile) wide. Sand thickness varies from only 1 m up to approximately 12 m (40 ft). The sand is relatively clean (greater than 90% quartz), with no swelling clays. The field was discovered in 1979 and initially developed on 80-acre spacing. Waterflooding of the reservoir began in 1983. The initial oil in place in the reservoir was approximately 2.54×106 m3 (16 million bbl), of which 874 430 m3 (5.5 million bbl) had been recovered by the end of 1995. To date, North Blowhorn Creek is the largest oil field discovered in the Black Warrior basin. Oil production peaked at almost 475 m3/d (3,000 BOPD) in 1985 and has since declined steadily. Currently, there are 20 injection wells and 32 producing wells. Oil production at the outset of the field demonstration was approximately 46 m3/d oil (290 BOPD), 1700 m3/d gas (60 MCFD), and 493 m3/d water (3,100 BWPD), with a water-injection rate of approximately 660 m3/d (4,150 BWPD). Projections at the beginning of the project were that approximately 1.59×106 m3 oil (10 million bbl of oil) would be left unrecovered if some new method of enhanced recovery were not effective. Prefield Trial Studies The concepts of the technology described in this paper had been proven to be effective in laboratory coreflood experiments.1,2 However, it seemed advisable to conduct coreflood experiments with cores from the reservoir being used in the field demonstration. Toward this end, two wells were drilled, and cores were obtained from one for the laboratory coreflood experiments to determine the schedule and amounts of nutrients to be employed in the field trial.3