This innovative project seeks to link an established enhanced oil recovery (EOR) procedure: carbon dioxide (CO2) water-after-gas (WAG) flood, with a new technology: microbial permeability profile modification (MPPM), developed at Mississippi State University (MSU) under prior DOE contract.
Mississippi State University, Starkville, MS
Denbury Resources, Inc., Plano, TX
A major challenge to improving oil recovery by CO2 flooding is reducing the amount of oil bypassed due to poor sweep efficiency. As much as two-thirds of the oil discovered in the United States (350 billion barrels) is economically unrecoverable with current EOR technology. CO2 flooding, widely used in the United States, was responsible for more than 200,000 barrels of incremental oil per day in 2004. Even so, the recovery efficiency for CO2 flooding in oil reservoirs is low. The project’s industrial partner (Denbury Resources) found that in the study area, about 20 percent of original-oil-in-place (OOIP) is produced initially, another 20 percent can be produced with waterflooding, and a further 20 percent can be produced with CO2 flooding. This leaves at least 40 percent of the OOIP in the reservoir. A potential solution to this problem is to combine CO2 flooding—specifically the CO2WAG procedure—with the MPPM procedure.
MPPM technology utilizes environmentally friendly nitrogen- and phosphorus- containing solutions (essentially diluted fertilizer) to stimulate the growth of naturally occurring in situ microbes in the most permeable zones of the reservoir. Because the nutrient solution promotes some growth of microbes in the most porous layers of the reservoir, the CO2 is diverted to less permeable previously unswept zones, thus improving production. MPPM combined with CO2 flooding improved residual oil recovery by 10–80% over conventional CO2 flooding alone.
The technology tested here can be applied to any field undergoing CO2 enhanced oil recovery (EOR). Potential contributions of the combined procedure include significantly improved sweep efficiency and oil production, and longer economic life of fields. Additionally, the nitrate and nitrate-reducing microorganisms in the MPPM technology reduce or eliminate hydrogen sulfide production.
High-resolution, 3-D computed tomography (CT) imagery has been completed and is currently being used by the High Performance Computing Collaboratory at Mississippi State. Testing of the microbial permeability profile modification (MPPM) procedure in the Little Creek Field was carried out between December 2008 and October 2010. After approximately nine months, a significant increase in production occurred in two of the five production test wells; furthermore, the decline curve in each of the production wells became noticeably less steep. The test was terminated in October 2010, due to operational issues unrelated to nutrient injection. The field test of the MPPM procedure in association with carbon dioxide flood was successful and the MPPM procedure has the potential to increase production if implemented in other fields. Mississippi State University is using the data as one of the favorite data sets in their walk-in virtual reality demonstration lab. Testing of microbial permeability profile modification to carbon dioxide sweep was shifted from the Eucutta field to the Little Creek field. It took approximately nine months to see a response to the MPPM procedure in this field. Over the remaining ten months of the test, production from the test wells increased 20–80% and in each well the decline curve became noticeably less steep.
Microorganisms were found to be present in samples from two fields. Laboratory tests on live cores obtained from a newly drilled well in the Heidelberg oil field have shown that the cores contain microorganisms that grow at 66ºC. Laboratory tests on oil and water samples from the Little Creek field show that indigenous microorganisms can be grown in culture at 115ºC using a specialized high temperature/pressure culture vessel. In the Heidelberg field, the Eutaw Formation occurs as relatively thin, laminated sandstone interbedded with clay-rich sandstone and shale. Microscopic analysis reveals quartz, calcite, and siderite. Quartz and calcite cements are more abundant in sandstones without oil than those with oil, suggesting that oil emplacement affected diagenesis. Live core samples of Eutaw Formation from the Heidelberg field were treated with nutrients and held in an anaerobic chamber. This resulted in the growth of biofilm used to prepare samples for SEM. Quantitative analysis of SEM photomicrographs shows that permeability modification occurs in pore and throat spaces of 10–20 microns in diameter.
The Eucutta field produces from the Eutaw Formation, which is composed of heterogeneous, well laminated sandstone interbedded with clay-rich sandstone and shale. The Upper Cretaceous Eutaw Formation is among the most prolific hydrocarbon reservoirs in Mississippi. Analysis of 200 ft of core from the nearby Heidelberg field reveals that oil is found almost exclusively in sandstone layers thicker than 3 or 4 ft. in the sand-rich upper portion of the core. In the finer-grained, lower section of the core, oil is found in sandstone just a few inches/centimeters thick. Diagenesis of the sandstone includes the growth of siderite, quartz, and calcite cements, as well as the dissolution of feldspars and deformation of glauconite. The absence of oil in sandstone with abundant calcite implies that reservoir charging significantly affected diagenesis (and consequently the reservoir quality) of the rocks.
The project is completed. The final project report is listed below under "Additional Information".
$600,000 (44 percent of total)
Final Project Report [PDF-1.80MB]