Development and Application of Subsurface-pressure Data in Kettleman Hills

The decision of the California Oil Umpire's office to accept well potentialsestablished from subsurface-pressure data has brought to the attention of manyoperators for the first time the application of such data to productionproblems. This paper reviews the development and application ofsubsurface-pressure data in Kettleman Hills, where these data have been used inproduction work since 1932. The Kettleman Hills field was discovered in October 1928. The firstsubsurface-pressure surveys were made early in 1932 and by the middle of 1933the two major operators in the field were making routine pressure runs in theirrespective wells. Shortly thereafter, these companies agreed to exchangepressure data, and later a third company entered into the agreement. This madeit possible to analyze the effects upon the reservoir pressure of pastproduction practices, which are discussed in the latter part of thereport. It is interesting that many of the applications of subsurface-pressure datadiscussed herein were anticipated by C. L. Clarkt and C. B. Kimberlint in areport2 dated March 1933. Productivity Index In the majority of individual well problems involving the use ofsubsurface- pressure data, it is necessary to use a factor known as the" productivityindex," which indicates the ability of a well to produce and represents thenumber of barrels of oil or oil and water per day that will enter the well borefor each pound per square inch pressure drop made opposite the producinginterval of the well. The productivity index may be determined from pressureand production data for one or more rates of flow and a static or shut-inpressure surveyor from production and pressure data for two or more rates offlow. Productivity indices may be based upon either net oil or total fluidproduction. All indices referred to in this report are based upon netoil. The value of the productivity index for Kettleman Hills wells decreasesgenerally with time and it is not uncommon for the index to vary in value atany specific time for various rates of flow. The decline of the productivityindex may be attributed partly to the loss of reservoir pressure. As thereservoir pressure decreases, gas originally in solution is released from theoil, congesting the flow of fluids through the formation and increasing theviscosity and surface tension of the oil; thus the flow resistance of thefluids through the formation is increased, resulting in a decrease of theproductivity index. T.P. 1303