This paper was prepared for the 47th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in San, Antonio, Tex., Oct. 8–11, 1972 Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers Office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract

In a wildcat well or early in the life of a reservoir, drill stem test data is quite often the only means available to estimate reservoir values of transmissibility, effective permeability, well bore damage, well bore permeability, well bore damage, well bore stimulation and productivity.

The Horner pressure buildup method is generally accepted as the best means of determining reservoir data from short time tests such as a drill stem test.

The Horner method requires that the steady state or straight line portion of the buildup curve be reached. For various reasons, approximately 25% of all drill stem tests run do not meet this requirement. This group of wells are the ones with the highest economic risk involved in making a decision on whether to abandon or complete.

A 1971 paper published by Mr. McKinley, "Transmissibility from Afterflow Dominated Pressure Buildup Data", gives a means to Pressure Buildup Data", gives a means to calculate reservoir values when pressure buildup curves are still under the influence of afterflow.

A research program was recently completed using drill stern test data to calculate transmissibility and effective permeability by the McKinley method and to compare the results obtained against the Horner method.

Fifty drill stem tests were chosen for analysis that had an appreciable afterflow period and steady state period on the same buildup curve. The comparison of results was very close as long as the basic assumptions were not deviated from too far. Most drill stem tests, where it is necessary to use the afterflow buildup method, do deviate considerably from these basic assumptions.

Therefore, it is necessary to use a correction factor in interpreting the afterflow method.

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