Twelve Years of Gas Injection in a Frio Sand
- B.T. Millikin Jr. (Continental Oil Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- June 1954
- Document Type
- Journal Paper
- 11 - 15
- 1954. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
- 5.2.1 Phase Behavior and PVT Measurements, 5.4.2 Gas Injection Methods, 4.1.5 Processing Equipment, 5.1.1 Exploration, Development, Structural Geology, 3.1.6 Gas Lift, 4.6 Natural Gas, 2.2.2 Perforating, 1.2.3 Rock properties, 5.2 Reservoir Fluid Dynamics, 4.1.2 Separation and Treating, 2.4.3 Sand/Solids Control, 5.1.2 Faults and Fracture Characterisation, 5.6.4 Drillstem/Well Testing
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The purpose of this paper is to contribute to the existing knowledge of the economic recovery of oil by methods other than normal depletion. A case history is presented of a gas injection project in one zone of the multiple producing zone Frio sands of south Texas. Approximately 75 per cent of the produced gas has been returned to the formation for 12 of the 13 years of producing life. The study is an example of the performance which has been experienced by return of a large portion of the produced gas to the gas cap of a thin non-homogeneous sand.
The producing zone is the Frio sand of lower Oligocene age. The oil and gas accumulation is a combination of a structural and stratigraphic trap. The structure consists of a large asymmetrical nose plunging gently to the northeast. The reservoir is limited on the west flank by an oil-water contact, on the north and south by the sand lens grading into shale, and on the east by a steep fold or fault parallel to the axis of the structure. The dip of the west flank or oil producing flank is approximately 130 ft per mile, or only 1.5 degrees.
There are 11 separate Frio producing zones in the field but this paper is limited to only one of the zones. The sand lenses are separated vertically by 25 to 75 ft of shale and were correlated across the field by means of markers picked from the electric logs. A portion of a typical cross section is shown on Fig. 1 and the section is located with reference to the area on Fig. 2. The D-5 reservoir is the large sand lens which appears in the D zone on the cross sections. It covers an area of approximately 2,100 acres. The structural map of the D zone (Fig. 2) was contoured on the subsea correlation points on the top of the D zone.
The reservoir rock is predominately firm, medium to fine-grained gray, argillaceous sandstone but lenses of soft, loosely consolidated sandstone occur throughout the producing zone. An x-ray diffraction indicates the clay content to be chiefly of the montmorillonite group and solubility tests indicate a low carbonate content. The porosity ranges from 8 to 28 per cent with a weighted average of 23 per cent. The majority of the horizontal permeability ranges from 100 to 500 md and averages 194 md. The vertical permeability is approximately one-half of the horizontal permeability.
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