Geologic Description of East Velma West Block, Sims Sand Unit, for an Enhanced Oil Recovery Project
- R.C. Boyer (Arco Oil and Gas Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- August 1985
- Document Type
- Journal Paper
- 1,420 - 1,428
- 1985. Society of Petroleum Engineers
- 2 Well Completion, 5.1 Reservoir Characterisation, 4.3.4 Scale, 5.4.2 Gas Injection Methods, 5.6.1 Open hole/cased hole log analysis, 6.5.2 Water use, produced water discharge and disposal, 4.1.5 Processing Equipment, 5.6.5 Tracers, 1.14 Casing and Cementing, 1.6.9 Coring, Fishing, 2.4.3 Sand/Solids Control, 1.6 Drilling Operations, 4.1.2 Separation and Treating, 5.4 Enhanced Recovery, 1.2.3 Rock properties, 5.1.5 Geologic Modeling
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East Velma West Block, Sims Sand Unit (EVWBSSU), located in Stephens County, OK, is currently being flooded with CO2. A detailed, quantitative, reservoir description was constructed for a simulation model that will aid in the evaluation and operation of the CO2 flood. The Sims sandstone member of the Upper-Mississippian/ Lower Pennsylvanian Springer formation was deposited in a deltaic environment. Four deltaic facies are present: the delta plain, proximal and distal delta-front, present: the delta plain, proximal and distal delta-front, and abandonment phase. The delta-plain facies forms a shale barrier to vertical fluid flow between the abandonment and proximal delta-front sandstones. The proximal delta-front facies forms the bulk of the reservoir. Porosity (16%) and permeability (70 md) in this facies are high Porosity (16%) and permeability (70 md) in this facies are high because of minor clay and cement content. The proximal delta-front facies grades laterally downstructure into the distal delta-front facies. Authigenic clays and carbonate and silica cement have reduce porosity (14%) and permeability (30 md) in the distal delta-front sandstones. permeability (30 md) in the distal delta-front sandstones. A reservoir description was built from the geologic analysis for a four-component, three-dimensional (3D) full-field model. Reservoir zonation was based on the arrangement of deltaic facies. Porosity from gamma-ray/density logs was calibrated to core porosity to determine porosity in uncored wells. A linear correlation between core porosity in uncored wells. A linear correlation between core porosity and permeability was established for each facies. porosity and permeability was established for each facies. Permeability and gamma ray cutoffs were statistically Permeability and gamma ray cutoffs were statistically determined to define net pay. Vertical-to-horizontal permeability ratios were determined from measurements on permeability ratios were determined from measurements on oriented core plugs. Computer isopach maps of gross pay, net pay, porosity, and horizontal and vertical permeability were generated for individual reservoir zones and permeability were generated for individual reservoir zones and then entered into the reservoir model.
ARCO Oil and Gas Co. is conducting an enhanced-oil-recovery program on EVWBSSU in Stephens County, program on EVWBSSU in Stephens County, OK. Continuous injection Of CO2 into the updip portion of the reservoir began in Sept. 1983. EVWBSSU was discovered in 1949 with an estimated 220 x 10 STB [34 958 x 10 m3] of original oil in place (OOIP). Primary depletion was by gravity drainage. Crestal gas Primary depletion was by gravity drainage. Crestal gas injection for pressure maintenance began in 1962 and water injection began in 1972. Approximately 32% of OOIP was recovered by these methods of production. Success Of CO2 flood depends on distribution of reservoir lithology, porosity, and permeability. Distribution and continuity Of sandstone reservoirs are controlled by depositional environments. Clay and cement content determine the subsurface distribution of porosity and permeability. Thus the purpose of this study was to analyze permeability. Thus the purpose of this study was to analyze mineral composition and to determine the depositional setting of Sims sandstone. On the basis of this geologic analysis, a reservoir description was constructed for a simulation model.
The Upper-Mississippian/Lower-Pennsylvanian Springer formation consists of approximately 2,500 ft [7670 m] of alternating sandstone and shale. The Goddard formation conformably underlies the Springer formation, which is unconformably overlain by Morrowan-Age rocks.
Four subsurface Springer sandstone members-in descending order, the Markham, Aldridge, Humphreys, and Sims-have been defined by drilling in the western Ardmore basin. The Sims sandstone member, ranging in apparent gross thickness from 300 to 600 ft [91.4 to 182.9 m], is the major oil-producing horizon within the Velma reservoir. It consists of three sandstone units: in descending order, C1, C2, and C3. Sandstones are white to buff, fine-grained, and subrounded to subangular. They grade basinward into clay-rich sandstones and finally into shales. Approximately 250 ft [77.1 m] of shale overlies the Sims sandstone member.
The Sims member of the Springer formation was deposited on moderately subsiding shelves in the Anadarko-Ardmore basin, which is bounded by the Arbuckle uplift to the north, by the Wichita-Criner uplift to the south, and by the Ouachita foldbelt to the east (Fig. 1).
The EVWBSSU is part of the Velma reservoir, located in the northwestern part of the Ardmore basin. The EVWBSSU is approximately 3.5 miles [5.6 km] long and 0.75 miles [1.2 kin] wide (Fig. 2). This reservoir strikes in a southeast-northwest direction. It dips steeply (30 to 60* [0.52 to 1.04 rad]) to the northeast. To the south, the EVWBSSU is bounded by an erosional unconformity and, to the north, by poor reservoir quality and a water/oil contact (WOC).
Folding and faulting of the Velma reservoir, which occurred in Early Pennsylvanian times during collision of North American, South American, and African continental masses, is postdepositional.
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