Rock Creek Oil Field CO2, Pilot Tests, Roane County, West Virginia
Authors: Brummert A.C. , Watts R.J. , Boone D.A. , Wasson J.A. 
Published: December 2007

Summary
This paper reports on the design and operation of two CO2 EOR tests conducted in the Rock Creek field in Roane County, WV. The history, fluid properties, and geology of the Rock Creek field are presented first. The test area is then addressed more specifically with an evaluation of the cores and the geophysical logs of the injection, production, and observation wells. Finally, the injection history and the production response are documented.
The first test was conducted in two 10-acre [4-ha], normal five-spot patterns, with 13,000 scf CO2/STB oil [2315 std M3/ stock-tank m3) injected. This test effort recovered 13,078 STB [2079 stock-tank m3] of oil [3% of the original oil in place (OOIP) but was terminated after 3 years before all oil capable of being mobilized was recovered. About 15 of an HCPV was injected. The first test was followed by a second, smaller test that, given the same amount of CO, to be purchased, would result in a increase in HCPVs of CO2 injected and a greater potential for oil recovery. The second test-was conducted in a 1.55-acre [0.63-ha], normal four-spot pattern contained within the original test pattern. This test lasted 2 years, with 9,000 SCf CO2/STB oil [1603 std M3/stock-tank M3] injected. Recovery from this test was 3,821 STB [607 stock-tank M3] Of oil (11 % of the OOIP). About 48 % of an HCPV was injected. It appears that CO2 miscible flooding is technically successful in Appalachian reservoirs.

Introduction
Background. The U.S. DOE Morgantown Energy Technology Center has studied eastern U.S. oil reservoirs for many years. The purpose of these studies has been to improve oil-recovery efficiency through the application of secondary and EOR methods. The Rock Creek Field Test, operated from October 1976 through Jan. 1983, was one of several CO2 injection projects conducted by or in cooperation with the U.S. DOE [formerly the U.S. Energy Research and Development Admin. (ERDA)].
The Rock Creek oil field was selected for this study because very large volumes of oil remained in place and secondary recovery by waterflooding had proved to be ineffective. Pennzoil E&P Co., which owns and operates the leases, responded to' ERDA's request for proposals by suggesting a government/industry, cost-sharing field test of CO2 flooding.
The objectives of this study were to determine the efficiency of CO2 flooding in a shallow, low-temperature, Appalachian basin reservoir and to gain first-hand field experience with the CO2 EOR process. Evaluation of the information and experience obtained could determine the future of CO2 flooding in similar reservoirs throughout the region. Data for this paper were taken from reports by SanFilippo, Guckert and SanFilippo, and King.

Reservoir History.
The Rock Creek oil field is located in southeastern Roane County, WV. Fig. 1 shows the Pennzoil-operated productive acreage of the Rock Creek field, which makes up the larger part of the Rock Creek trend. The CO2 project site is located in the southeast portion of the Rock Creek field.
Fig. 2 shows a general columnar section of the Rock Creek field with a representative gamma-ray geophysical well log used to define the section tops and bottoms. Production in the Rock Creek oil field is from the Pocono "Big Injun" sandstone, a formation that occurs in the upper Pocono group of lower Mississippian Age. Overlying the Big Injun is the Greenbrier "Big Lime" limestone. The Big Lime is separated from the Big Injun by an unconformity. Underlying the Big Injun is the Pocono "Squaw" siltstone, which is separated from the Big Injun by a sporadic shale.
Although an updip gas cap was present, primary production from the Big Injun was principally by solution-gas drive. Based on incomplete early production records, it is estimated that the average primary oil recovery was 2,900 bbl/acre [1139 m3 /ha], or about 10% of the OOIP. The low primary recovery was probably a result of excessive gas production from the gas cap; this production caused oil migration into the gas zone and accelerated the loss of reservoir pressure.
Low-pressure gas recycling, begun in 1935, is still being used in part of the reservoir. The relative success of recycling in this reservoir results from a relatively uniform permeability profile and a high total liquid saturation. Oil remaining in place at the end of recycling operations, however, will be about 80% of the OOIP.
Although three separate pilot waterfloods were attempted during the 1950's and 1960's, increases in oil production were insufficient to justify expansion of the projects. Oil banks were very thin because of high interstitial water saturations and high permeability to water. One pilot steamflood was attempted, but excessive heat losses resulting from low injectivity prevented effective mobilization of the oil.
Reservoir Fluid Properties. The crude oil in the Rock Creek field is a paraffin-based, Pennsylvania-grade oil. The minimum miscibility pressure (MMP) of the crude oil was determined from three recombined samples of Rock Creek oil field hydrocarbon fluids used in slim-tube tests. The MMP was found to be 1,000 psia [6.89 MPa] at the reservoir temperature of 73deg.F [23deg.C]. A summary of reservoir fluid properties can be found in Table 1.

Reservoir Lithology.
Lithologically, the Big Injun is a very-fine-to medium-grain, subangular, moderately well-sorted, argillaceous, slightly feldspathic sandstone. Grain size increases upward. In the upper part of the Big Injun, occasional thin lenses with very coarse grains and well-rounded pebbles occur. These lenses, as well as the slight calcareous and/or dolomitic cementation, account for the variability exhibited in permeability profiles.
The matrix clay material consists of kaolinite and illite. The kaolinite may have been derived from weathered feldspar, which is evident as white specks in the matrix material, during disaggregation of the rock. Matrix material and framework constituents are slightly to moderately cemented, in part, by carbonates and secondary quartz.
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