A Microbial Enhanced Oil Recovery (MEOR) process was successfully applied to a mature waterflood in Southern California, using indigenous microbes that normally remain dormant during the producing life. Certain indigenous microbial species can be activated in waterflood reservoirs by introducing the correct blend of nutrients. Once activated, the microbes multiply when the nutrients deplete, then migrate to immobile oil in search of a food source. The microbes break up this residual oil saturation into smaller micro-droplets that can flow through pore throats and be swept to producers, yielding an increase in oil recovery. The application on a producing well led to an increase in well tests from 20 to over 80 BOPD. Following this encouraging test, the nutrients were applied in three batch treatments on each of the waterflood injectors. At peak response a thirty percent oil rate increase was seen in the offset producers. Because this process uses indigenous microbes, there are no compatibility issues with reservoir fluids or concerns about survival in a foreign environment. The results from this field application demonstrate that managing a reservoir's indigenous microbes can yield significant incremental oil production in a mature waterflood with a minimal investment.
The Beverly Hills field has two major producing horizons, the Hauser and the Ogden. The Hauser has been waterflooded since the mid-1980's, although producers in the field are commingled in both the Hauser and the Ogden formations. All water injection is into down-dip Hauser completions on the northeastern flank of the reservoir in the proximity of the original oil water contact. Oil gravity averages 22.5° and ranges from 22 to 26° API. The field has fourteen active producers and three active injectors with well spacing of approximately 10 acres. Field production is currently about 400 BOPD, 2,000 BWPD and 300 MCFD (Figure 1). All produced water is reinjected into Hauser (Figure 2).
The results reported in this paper are based on well tests. Allocation of metered oil from the lease by well test is usually within 10% of the well tests. As in many fields, water cut data is limited as there is no provision for continuous sampling during well tests. Water cuts are based on wellhead samples taken by hand while the wells are being tested.
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