Whole-Core Analysis Methods and Interpretation of Data from Carbonate Reservoirs
- R.S. Bynum Jr. (Core Laboratories Inc.) | E.H. Koepf (Core Laboratories Inc.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- November 1957
- Document Type
- Journal Paper
- 11 - 15
- 1957. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
- 1.10 Drilling Equipment, 1.11 Drilling Fluids and Materials, 5.8.7 Carbonate Reservoir, 5.2.1 Phase Behavior and PVT Measurements, 1.5 Drill Bits, 5.5.2 Core Analysis, 5.6.2 Core Analysis, 4.6 Natural Gas, 1.6.9 Coring, Fishing, 2.2.2 Perforating, 5.3.4 Reduction of Residual Oil Saturation
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During recent years reservoirs where the hydrocarbon storage capacity and the permeability characteristics are due chiefly to fractures and vugs, and tight formations with non-homogeneous porosity development, have become of major importance in West Texas oil production. Diamond coring equipment and methods were devised which permitted excellent recovery of cores from these formations. Examination of these cores with erratic porosity development frequently indicated individual fracture or vug volume greater than the "perm-plug" sample normally used in conventional analysis. It is evident that actual reservoir properties are more closely approached in the sample as the sample size is increased and that the entire core from this type of formation should be analyzed.
Although the literature on general whole-core analysis procedures has been rather limited many innovations have been introduced, both in methods of analysis and in the interpretation and application of the data. The experienced core analyst has determined a set of optimum conditions which permit a confident approach to his specialized work. These optimum conditions include a completely cored interval, beginning several feet above the pay zone, cut with large diameter coring equipment at maximum speed in a properly selected drilling fluid, pulled to the derrick floor in minimum time, described and logged by an experienced man, properly preserved by quick-freezing in dry ice or by sealing in plastic or other suitable means, and delivered immediately to a well-equipped laboratory where the tests are made on maximum-sized samples. Current coring equipment and practices permit a close approach to these optimum conditions.
Coring and Sampling of Core
Although the successful application of the diamond bit was a great step forward in the coring of dense carbonate reservoirs, there still is no means available to recover a sample of the reservoir in an undisturbed condition. Normally, the drilling mud filtrate flushes the core to an irreducible oil saturation. As the core is brought to the surface, the gas in solution in this residual oil is evolved, expands and expels oil and water until liquid saturations are reduced to the point where only gas will flow. The core, as recovered at the surface, then, contains residual oil after water flushing and solution gas drive, some original water and some mud filtrate, and solution gas from the oil. There appears to be a relationship between the formation volume factor of the oil and the efficiency of liquid expulsion by the gas as it expands with pressure reduction.
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