Exploration and Production Technologies

Improved Oil Recovery from Upper Jurassic Smackover Carbonates (Class II Reservoir) Through the Application of Advanced Technologies at Womack Hill Oil Field, Choctaw and Clarke Counties, Alabama, Eastern Gulf Coastal Plain

DE-FC26-00BC15129

Project Goal
The goal of the project is to adress technologies to extend the economic life of Womack Hill field's Smackover reservoir through improved understanding of the reservoir, recovery processes and producibility constraints and to transfer this technology to domestic operators with analogous reservoirs or similar production problems.

Performers

University of Alabama
Tuscaloosa, AL

Pruet Production Co.
Jackson, MS 

Mississippi State University
Starkville, MS 

University of Mississippi
Oxford, MS 

Wayne Stafford and Associates
Jackson, MS 

Texas A&M University
College Station, TX

Project Results
These reservoirs occur in vertically stacked, heterogeneous depositional and porosity cycles. The cycles consist of lime mudstone/wackestone at the base and ooid grainstone at the top. Porosity has been enhanced through dissolution and dolomitization. Porosity is chiefly interparticle, solution-enlarged interparticle, grain moldic, intercrystalline dolomite and vuggy pores. Reservoir performance analysis and simulation indicate that the unitized western area has less than 1 MMSTB of oil remaining to be recovered, and that the eastern area has 2 to 3 MMSTB of oil to be recovered. A field-scale reservoir management strategy that includes the drilling of infill wells in the eastern area of the field and perforating existing wells in stratigraphically higher porosity zones in the unitized western area is recommended for sustaining production from the Womack Hill field.

The drilling and testing of the 13-10 well showed that the eastern part of the field continues to have a strong water drive; and therefore, there is no need to implement a pressure maintenance program in the eastern part of the field at this time, and the drilling of this well did not provide information that would be useful in modifying the existing water flood project in the western part of the field or in initiating an advanced oil technology application. Pruet decided not to drill a second infill well in the Womack Hill Field; therefore, an evaluation of the feasibility to use lateral/multilateral well completion technology was not undertaken.

Benefits
Because of the highly complex nature of carbonate reservoirs, cost-effective development of these reservoirs requires the implementation of an integrated reservoir management strategy. The Smackover reservoir characterization and modeling at Womack Hill field can be used to assess the current field-scale reservoir management practices in this field.

The unit operator is integrating the information from the reservoir characterization, 3-D geologic modeling, reservoir performance analysis, and reservoir simulation into a field-scale reservoir management strategy to improve operations in the Womack Hill field Unit. The project identified the field areas with the highest potential for oil recovery in both the western and eastern portions of Womack Hill field. The reservoir performance, multiwell productivity analysis, and reservoir simulation studies indicate that water injection continues to provide stable support to maintain production from wells in the unitized western area and that the strong water drive present in the eastern area of the field presently is adequate to sustain production in this part of the Womack Hill field.

Background
Womack Hill field, producing from the Jurrasic Smackover in southwest Alabama, was discovered in 1970. The petroleum trap was originally interpreted as a salt pillow anticline. With increasing oil production rates, the reservoir pressure declined rapidly on the west end of the field. Because of this decline in reservoir pressure in the western area of the reservoir, this portion of the field was unitized in 1975, and a fresh and salt water injection program for pressure maintenance was initiated. Ultimate oil recovery was estimated to be 17.1 MMSTB from the unitized western area. 

Ultimate primary oil recovery from the entire Womack Hill field was estimated at 25.2 MMSTB or 29% of the original oil in place (87 MMSTB). The estimated oil recovery from secondary operations was 40% or 34.8 MMSTB of oil from the field. As a result of the modeling, it was concluded that a fluid-flow barrier was present.

Thirty-seven (37) wells have been drilled within the field area. Overall, the Womack Hill Field has produced 31.2 MMSTB of oil, 15.4 BSCF of gas, and 51.7 MMSTB of water from the Upper Jurassic Smackover Formation from 27 wells. The unitized western area of Womack Hill field has produced 17.0 MMSTB of oil and 9.3 BSCF of gas.

The principal problem at the field is productivity and profitability. With time, there has been a decrease in oil production, while operating costs continue to increase. The major producibility problems are related to cost-effective, field-scale reservoir management; reservoir connectivity due to carbonate rock architecture and heterogeneity; pressure communication due to carbonate petrophysical and engineering properties.

Project Summary
Geologic reservoir characterization has shown that the upper part of the Smackover Formation in Womack Hill field is productive from carbonate shoal reservoirs that occur in vertically stacked, heterogeneous depositional and porosity cycles. The cycles typically consist of lime mudstone/wackestone at the base and ooid grainstone at the top. The lime mudstone/wackestone lithofacies has been interpreted as restricted bay and lagoon sediment, and the grainstone lithofacies has been described as beach shoreface and shoal deposits. Dolomitizied cycles occur across the field, but they are laterally heterogeneous in depositional texture and diagenetic fabric. Porosity consists chiefly of depositional interparticle, solution-enlarged interparticle, grain moldic, dolomite intercrystalline and vuggy pores. Dolostone pore systems and flow units dominated by intercrystalline and vuggy pores have the highest reservoir potential.

Engineering characterization and analysis has shown that the reservoir fluid in Womack Hill field is conventional black oil. Pressure transient test data support the interpretations that the Womack Hill field reservoir is compartmentalized and that a fault bounds the field reservoir to the south. Reservoir performance analysis indicates good volumetric correlation for high producing wells, and that low producing wells correlate with lower reservoir continuity. Reservoir performance studies have shown that 10% of the recoverable 34.6 MMSTB of oil remains to be produced from the field. The undrained oil is concentrated in structural highs associated with footwall uplifts in the unitized western area, and along an elongated west-east anticline in the eastern part of the field. Water injection in the field should be continued and conducted downdip and focused towards areas of the field that are structurally low.

A 3-D geologic model has been constructed for the Womack Hill field structure and reservoir. It shows that the petroleum trap is more complex than originally interpreted. The trapping mechanisms include a fault trap (footwall uplift with closure to the south against a major west-southeast trending, high-angle normal fault) in the western area, a footwall uplift trap associated with a possible southwest-northeast trending, high-angle normal fault in the south-central area, and a salt-cored anticline with four-way dip closure in the eastern area. The pressure difference between wells in the unitized western area of the field and wells in the eastern area of the field may be attributed to a flow barrier due to the presence of a possible southwest-northeast trending fault and a change in porosity and/or permeability in Smackover facies. Reservoir characterization and geologic modeling have shown that four areas in the Womack Hill field have potential for the recovery of undrained oil.

Current Status (May 2006)
The project is on schedule and will be concluded on May 29, 2006. Pruet will continue to monitor and report the production of oil, gas and water from the infill well without DOE funding support. Anticipated DOE Contribution: $2,875,122 Performer Contribution: $4,324,480 (60% of total)

Project Start: May 1, 2000
Project End: May 29, 2006

Anticipated DOE Contribution: $2,875,122
Performer Contribution: $4,324,480 (60% of total)

Contact Information
NETL - Chandra Nautiyal (chandra.nautiyal@netl.doe.gov or 918-699-2021)
U. of Alabama - Ernest Mancini (emancini@wgs.geo.ua.edu or 205-348-4319)

Publications
Hopkins, T.L., 2002, Integrated petrographic and petrophysical study of the Smackover Formation, Womack Hill Field, Clarke and Choctaw Counties, Alabama, M.S. thesis, Texas A&M University, 96 p

Mancini, E.A., Blasingame, T.A., Archer, R., Panetta, B.J., Llinas, J.C., Haynes, C.D., and Benson, D.J., 2004, Improving recovery from mature oil fields producing from carbonate reservoirs: Upper Jurassic Smackover Formation, Womack Hill Field (eastern Gulf Coast U.S.A): American Association of Petroleum Geologists Bulletin, v.88, p. 1639 – 1651.

Mancini, E.A., et al., 2004, Improved oil recovery from Upper Jurassic Smackover carbonates through the application of advanced technologies at Womack Hill Oil Field, Choctaw and Clarke Counties, Alabama, eastern Gulf Coast Plain, Phase I Final Report, DE-FC26-00BC15129, U.S. Department of Energy, 300 p.

Tedesco, W.A., 2002, Dolomitization and reservoir development of the Upper Jurassic Smackover Formation, Womack Hill Field, eastern Gulf Coastal Plain, Ph.D. dissertation, University of Mississippi, 251 p.

Tedesco, W.A., and Major, R.P., 2002, Stratigraphic and diagenetic controls on production from Smackover Formation reservoirs, Womack Hill Field, eastern Gulf Coastal Plain, Am. Assoc. Petroleum Geologists 2002 Abstract Volume, p. A174.

3-D geologic model of Womack Hill field.

 
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