Esperson Dome Oxygen Combustion Pilot Test: Postburn Coring Results
- S.P. Choquette (Mobil R and D Corp.) | Sampath Krishnaswamy (Mobil R and D Corp.) | P.S. Northrop (Mobil R and D Corp.) | J.T. Edwards (Mobil R and D Corp.) | Laall Hooman (Mobil R and D Corp.) | Rowland Bret (Mobil E and P Services Inc.) | D. Morrow (Mobil E and P U.S.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- May 1993
- Document Type
- Journal Paper
- 85 - 93
- 1993. Society of Petroleum Engineers
- 5.4.6 Thermal Methods, 4.1.2 Separation and Treating, 1.6.9 Coring, Fishing, 4.6 Natural Gas, 5.2.1 Phase Behavior and PVT Measurements, 4.1.5 Processing Equipment, 5.1.2 Faults and Fracture Characterisation, 5.1.1 Exploration, Development, Structural Geology, 1.2.3 Rock properties, 2.4.3 Sand/Solids Control, 5.8.8 Gas-condensate reservoirs, 1.6 Drilling Operations, 5.3.4 Reduction of Residual Oil Saturation, 2.2.2 Perforating, 5.1 Reservoir Characterisation, 5.5.2 Core Analysis, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 5.6.5 Tracers, 5.7.2 Recovery Factors, 5.8.5 Oil Sand, Oil Shale, Bitumen, 4.6.2 Liquified Natural Gas (LNG)
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Postburn corehole data from an O2 combustion pilot test in Esperson Dome field, Liberty County, TX, show that the combustion temperature was 930 to 1,020°F. Final oil saturation was 0% in the burned zone and 11% to 34% in the sand adjacent to the burned zone. Roughly 49,000 bbl of incremental oil was produced at an injected O2/produced-oil ratio of 4.1 Mscf/bbl.
Our first O2 combustion pilot test was conducted at the Esperson Dome field.1 The pilot was in the Northwest fault block, in Miocene I sand, at a 2,670-ft depth. The pilot test demonstrated that the O2 combustion process could be applied safely to recover incremental oil from a watered-out, medium-gravity (21°API) oil reservoir. A total of 200 MMscf O2 and 55 MMscf N2 was injected between April 1984 and Aug. 1987 at O2 concentrations up to 100%.
Operational changes, including failure of three older wells and drilling of three new or replacement wells, complicated project evaluation. Geological uncertainty about the extent of tight streaks encountered during the drilling of new wells raised questions about stratification effects on sweep efficiency.
A two-well postburn coring program was conducted to address these questions. The program was devised to obtain information about the nature of the combustion process, to identify thermal effects on reservoir minerals and oil, and to develop estimates of incremental recovery.
Reservoir Description and Corehole Locations
The field is a highly faulted piercement-type salt dome. Stratigraphic and structural traps, folds, faults, and pinchouts isolate many discrete sands. The pilot area, which is a part of the Miocene I sand body, is bounded on the east by a major fault. The reservoir dips about 4° west and is bounded by an oil/water contact at 2,717 ft. The Miocene I sand in this area is 50 to 80 ft thick and has a porosity of about 31 % and a permeability ranging from 200 to > 6,000 md. The reservoir is underlain by an active aquifer entering from the northwest, which maintains reservoir pressure at about 1,190 psi. At the beginning of pilot operations, water cut was about 98 %. Table 1 summarizes reservoir and fluid properties.
An earlier geologic study identified the Miocene I sand as a meandering-river point-bar deposit, with coarse-grained, poorly sorted sand at the base and a fining-upward trend. The new cores, correlation with core from Well X-219, and logs from other wells indicate that the reservoir in the pilot area transgresses a beach environment. The z injection well is in a shallow marine depositional area. The updip producing wells are in the onshore beach environment.
The two postburn coreholes were drilled on-line between the O2 injection well, Well D-77, and the main pilot producer, Well X-219. Coreholes D-81 and X-221 were roughly 130 and 470 ft from the injector, respectively. Fig. 1 shows corehole locations. Clean burned sand was found only near the top of the reservoir in both coreholes. Tight streaks, not present in the oxygen injector, separate the Miocene I sand into upper and lower zones in the coreholes and in Well X-219.
Corehole D-81, near the injector, encountered 13 ft of sand above the first tight streak. Sidewall-core samples showed that the sand between 2,678 and 2,683 ft had been burned. Whole core was not recovered from this interval. Fig. 2 shows sidewall-core samples of overlying shale, 6 ft of clean burned sand with 0% residual oil saturation, and transition to unburned sand with oil saturation below the burned zone. A thin (1-ft) hard streak was noted at 2,689 ft.
Corehole X-221 encountered about 15 ft of sand above the first tight streak. The top of the Miocene I sand is at 2,666 ft at this location. Whole core showed about 3 ft of clean burned sand between 2,669.6 and 2,672.2 ft. Fig. 3 shows the burned interval; also visible are portions of adjacent overlying and underlying unburned shaly sands with oil indication under ultraviolet light. Whole-core analyses indicated oil saturations ranging from 11 % to 34 % in the thin stringers.
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