Laboratory Design and Field Implementation of Microbial Profile Modification Process
- Irene Lee Gullapalli (Chevron Petroleum Technology Co.) | Jae H. Bae (Chevron Petroleum Technology Co.) | Keith Hejl (Chevron Petroleum Technology Co.) | Aimee Edwards (Chevron North America Exploration & Production Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- February 2000
- Document Type
- Journal Paper
- 42 - 49
- 2000. Society of Petroleum Engineers
- 4.4.2 SCADA, 4.3.4 Scale, 2.3.4 Real-time Optimization, 4.1.5 Processing Equipment, 5.8.7 Carbonate Reservoir, 4.1.2 Separation and Treating, 5.1 Reservoir Characterisation, 2.2.2 Perforating, 1.6.9 Coring, Fishing, 6.5.2 Water use, produced water discharge and disposal, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 5.4.1 Waterflooding
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A microbial profile modification (MPM) process consisting of sequential injection of spores and nutrient was designed and tested for the first time in a carbonate reservoir. An 80-acre, inverted five-spot pattern located in Eunice Monument South Unit in Lea County, New Mexico, was chosen for the field trial. Injection profiles taken before and after the microbial treatment showed that the thief zones were plugged by the biofilm resulting in fluid diversion. Injection profiles also indicated that the biofilm which formed in the reservoir remained stable for more than 8 months. The results of the field trial proved the viability of the MPM technology.
Field History and Geology.
The Eunice Monument field is located on the northwestern edge of the Central Basin Platform in southeastern Lea County, New Mexico, approximately 15 miles southwest of the city of Hobbs. The field was discovered on March 21, 1929 with the majority of field development occurring from 1934 through 1937. The well development in the Eunice Monument South Unit (EMSU) was on 40-acre spacing. In May 1937, primary oil production peaked. The field was produced under primary means until unitization of the field occurred in February 1985. Oil was produced primarily from dolomites of the Permian (Guadalupian) -aged Grayburg Formation. A minor amount of production was also from the overlying lower Queen (Penrose) Formation. Underlying the Grayburg is the San Andres Formation, a waterdrive reservoir. The Grayburg is at an average depth of about 3,700 ft and averages 250 ft thick with a reservoir temperature of 90°F. It is subdivided into six zones based on relatively thin, generally impermeable sandstone. Porosity ranges up to approximately 20% with a fieldwide average of 9.4%. The permeability range is approximately 0.01 to 75 md with an average of 13 md. The reservoir is very heterogeneous with the DP coefficient of about 0.85.
Waterflood pattern development of the unit was 80-acre five-spot, and the initial injection was started in November 1986 with full-scale injection underway by June 1988. The early water injection rate was limited to between 500 and 700 B/D per injector, and later the rates were increased from 500 to 2,500 B/D per well. The original oil in these formations was estimated to be 671.5 MMSTBO, and the cumulative recovery to date has been approximately 127 MMSTBO. The crude oil is light with a gravity of 32°APl, and the reservoir brine contains substantial amounts of calcium and magnesiums ions. The brine compositions are listed in Table 1.
Microbial Profile Modification Process.
In our previous papers,1,2 we presented the basic concept and some data on a microbial profile modification (MPM) process. The microbe used for this process is Salton-1, a gram-positive, rod-shaped bacterium with a width of about 0.2 to 0.3 ?m and a length of 0.5 to 1.0 ?m. It closely resembles the species Bacillus licheniformis,3 and is a facultative anaerobic mesophile. More details of this process are given elsewhere.1
In this paper, the laboratory design and implementation of the MPM process in the EMSU field are presented.
All tube and core tests were conducted at 90°F. To simulate reservoir environment, test tubes containing inoculum, were anaerobically incubated. For core tests, fired Berea cores with dimensions of 2.54 cm diam×30 were used. In some tests, reservoir plugs of 2.5 cm diam×5 to 6 cm length were used. The brine permeability of all Berea cores was about 1,000 md to mimic the thief zones. The specific values are noted in the figures. All nutrient media and spore suspensions prepared for the core and tube tests were made in injection water unless otherwise stated. We used a backpressure of 1,500 psi in the core tests to remove any spurious effect of the gas produced by the microbial activity on permeability reduction. The Berea cores had two pressure taps, equally spaced along the core. The Hassler type of core holder was used for the reservoir plugs. Generally, a 1-PV of 107 (colony forming unit per mL) of spore suspension was followed by an equal amount of nutrient solution, and the core containing inoculum was incubated or shut in for a specified period, followed by post-brineflush. The injection rate was 10 mL/h. Thereafter, some cores containing biofilm were further incubated for stability test. Any deviation from these procedures has been specified as appropriate.
The fermented medium was microscopically examined to check the viability of the microbes and also the stage of their life cycle. In addition, viable counts or enumeration were done on agar plates. The stability of biofilm was assessed by hand shaking of the tube, and the biofilm was termed stable if it did not break upon shaking.
Field water analysis was performed with an ion chromatography unit (IC). Eluants were made with de-gassed DI water and filtered through a 0.22 ?m filter. Helium gas was initially bubbled through the eluant and the eluant was kept under the helium blanket throughout the experiment. The injection and the produced water samples were passed through a cation exchange (SCX) column to remove cations prior to the chromatographic runs. Also, the guard and analytical columns were preconditioned prior to the sample runs to establish a stable baseline, and were tested with known samples for concentration and retention time.
For anion analysis, a conductivity detector with AS4A-SC analytical and guard columns, as well as an anion membrane suppressor, was used. The eluant was a mixture of 1.8 mM of Na2CO3 and 1.7 mM of NaHCO3 . The membrane suppressor solution was 50 mN of H2SO4.
Inductively coupled plasma (ICP) spectroscopy was used for the cation analysis.
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