Daniel A. Deboer
Mud logging has long been a part of the complete formation evaluation picture in most oil and gas producing provinces of the United States. In Kansas, however, mud logging has often been omitted from this picture.
Typically, a well in central and western Kansas is drill-stem tested and then logged. Although this technique is often successful, there are also times when drill-stem tests and logs conflict with one another. Mud-logging techniques, especially hydrocarbon ratio analysis, could provide this necessary third aspect of formation evaluation to be integrated with drill-stem tests and wireline logs.
Generally, the most important characteristics of a reservoir are porosity, permeability, and petroleum saturation. All three styles of formation evaluation (mud logs, wireline logs, and drill-stem tests) can determine most of these characteristics either qualitatively or quantitatively. The mud log, through hydrocarbon ratio analysis in conjunction with the drilling time log, can contribute at least ballpark estimates on porosity, permeability, and type of reservoir fluid. Wireline logs and drill-stem tests provide the more direct or quantitative measure of these formation characteristics.
The central/western Kansas wells chosen for this study show that no single formation evaluation method is more important than the others. Each method must be weighed or calibrated to each specific study area as to its particular track record in that area. The difficulty in answering the question, "Should I set pipe?" therefore can be minimized by integrating the mud log, the wireline log, and drill-stem test information.
AAPG Search and Discovery Article #91025©1989 AAPG Midcontinent, Sept. 24-26, 1989, Oklahoma City, Oklahoma.