Summary The U.S. DOE Morgantown Energy Technology Center and the Pennzoil E and P Co. predicted the recovery and Pennzoil E and P Co. predicted the recovery and economic potential of a frill-field, CO2 miscible EOR flood at the Rock Creek field, Roane County, WV. Data used in this evaluation were obtained from two miscible CO2 Rock Creek field tests:a pilot test consisting of two contiguous normal five-spot patterns, each containing 10 acres [4 ha], and
a 1.55-acre [0.63-ha] normal four-spot minitest.
Core data from the eight injection wells and three observation wells were used to determine reservoir input parameters, and fluid samples were analyzed to obtain fluid properties. A predictive model was used to calculate oil recovery and project economics. The model's base-case run showed that an oil price of $39/bbl [$245/meters cubed] was required to produce a 15 percent discounted cash flow rate of return (DCF ROR). A sensitivity study was then conducted on operating parameters [i.e., pattern size, water-alternating-gas (WAG) ratio, total HCPV of WAG injected, and injection rate] and economic parameters (e.g., oil price and CO2 cost) to determine their effect on project performance and project economics.
Introduction Background. The Rock Creek CO2 field test was operated from Oct. 1976 through Jan. 1983. The field test was one of several CO2 injection projects conducted by or in cooperation with the U.S. DOE [formerly the U.S. Energy R and D Admin. (ERDA)] in Morgantown, WV. Pennzoil responded to ERDA's request for proposals by suggesting a government/industry, cost-sharing field proposals by suggesting a government/industry, cost-sharing field study of CO2 flooding.
The Rock Creek field CO2 Projects are briefly discussed before the economic analysis. More detailed information concerning the field projects can be found in Ref. 1.
Reservoir Location and Geology. The Rock Creek field is located in southeastern Roane County, WV. Fig. 1 shows the Pennzoil-operated productive acreage of the Rock Creek field, which makes Pennzoil-operated productive acreage of the Rock Creek field, which makes up a large part of the Rock Creek trend. The CO2 project site is located within this acreage.
Fig. 2 shows a general columnar section of the Rock Creek field. The sections are defined by a representative gamma ray geophysical well log. Production in the Rock Creek 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.
CO2 Tests. Two consecutive CO2 tests were conducted in the Rock Creek field. The first test, referred to as the pilot test in Fig. 3, consisted of two contiguous, normal five-spot patterns, each containing about 10 acres [4 ha]. Pilot test CO2 injection began Feb. 20, 1979, and ended June 16, 1980. The test area was surrounded by 13 back-up water-injection wells designed to confine the fluids injected into the pattern wells. The second test, referred to as the minitest in Fig. 3, consisted of a 1.55-acre [0.63-ha] normal four-spot pattern. Minitest CO2 injection began Dec. 26, 1980, and ended Jan. 13, 1982. The minitest was contained within one of the five-spot patterns of the pilot test.
During the pilot test, the gross CO2 utilization equaled injection of 13,000 scf/STB [2315 std meters cubed/stock-tank meters cubed] oil produced. This test effort recovered 13,078 STB [2079 stock-tank M3] of enhanced od [3 percent of the original oil in place (OOIP)] but was terminated after 3 years, before all oil capable of being mobilized was recovered. About 15 percent of an HCPV Of CO2 Was injected. The pilot test was replaced with the second, smaller minitest that resulted in an increase in HCPV's of CO2 injected and a greater potential for oil recovery, given the same amount of CO2 to be purchased. During the minitest, the gross CO2 utilization equaled injection of 9,000 scf/STB [1603 std meters cubed/stock-tank meters cubed] oil produced. EOR from this test was 3,821 STB [607 stock-tank meters cubed] of oil (11 percent of the OOIP). About 48 percent of an HCPV of CO2 was injected.
Core Description. All the original pilot test injection wells, Wells PI- 1 through PI-6, were diamond cored before fluid injection began. Subsequently, the injection wells for the minitest, Wells PI-7 and PI-8, and the observation wells, Wells OB-1 through OB-3, PI-7 and PI-8, and the observation wells, Wells OB-1 through OB-3, were diamond cored. Permeability, k, and porosity, averages from the core analyses are summarized in Table 1. The data shown in Table 1 include all the sample intervals with permeability greater than 6 md.
Discussion CO2 Predictive Model. The CO2 predictive model (CO2PM), developed for the U.S. DOE by Scientific Software-Intercomp, was used to evaluate the CO2 EOR flood at the Rock Creek field. CO2PM is a fast and effective way to screen oil fields technically and economically for their suitability for CO2 miscible flooding before a more in-depth analysis. CO2PM predicts oil recovery from a normal five-spot pattern. The reservoir performance predicted for the single pattern is superposed over a pattern development schedule to predict oil recovery for a given field.
The three-dimensional model assumes that the oil displaced is fully miscible with the CO2 and that the modified Koval factor adequately describes viscous fingering and gravity segregation in a heterogeneous reservoir. The method is based on the original work by Koval for linear displacements and an extension by Claridge to include areal sweep.