Early Analysis of Fractured Reservoirs Compared To Later Performance
Authors: Groves D.L. , Abernathy B.F. 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
This paper was prepared for the 43rd Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Houston, Tex., Sept. 29-Oct. 2, 1968. 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 request 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 discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract
Early in the life of the fields studied, it was realized that conventional pore volume methods for estimating original oil-in-place and reserves were not applicable for reservoirs where a large portion of the oil is contained in a natural fracture system. Therefore, a study was undertaken to develop methods to detect and analyze this type of reservoir. It was necessary to await partial depletion before the validity of the methods could be tested. Based on the reservoirs studied, these fractured reservoirs can be detected early by a thorough analysis of generally available data used in conjunction with a special core analysis. Early reserve estimates using a combination of techniques discussed in this paper have been substantiated by performance paper have been substantiated by performance data for the three fields discussed in this study. Thus, for future fields such as these, development alternatives can be selected which will make the plays much more attractive economically.
Early analysis of the Dean-Wolfcamp in West Texas and of the San Andres in New Mexico in the Chaveroo and Cato Fields indicated these fields were producing from reservoirs wherein the flow channels and the storage volume in these reservoirs was contained either totally or in part in fractures. The detection of reservoirs of this type consists of comparing core permeabilities run in two directions, comparing well capacity as determined by core analysis with capacity determined from bottom hole pressure build-up and running special mercury injection tests on core samples.
After detecting a reservoir where fractures are affecting performance, early reserve estimates must be made to ascertain the proper development alternative. These early reserve estimates are made from the following:
effective pore volume based on mercury injection tests, material balance, and "equivalent producing time scale" -capacity test curve.
In the three fields studied in this paper these early reserve estimates have now paper these early reserve estimates have now been verified by performance data.
The ability to drain areas considerably larger than current well density has been proved in the three fields studied by proved in the three fields studied by production and pressure data. In the Chaveroo Field production and pressure data. In the Chaveroo Field drainage of greater than 80 acres was proved with pressure data. An interference test in the Cato Field indicated drainage of 640 acres per well. per well.