This paper was prepared for the 44th Annual California Regional Meeting of the Society of Petroleum Engineers of AIME, to be held in San Francisco, Calif., April 4–5, 1974. 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 OF PETROLEUM TECHNOLOGY or the SOCIETY OF publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal 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

A system is presented which allows for the construction, by computer, of a numerical geological and petrophysical model of a reservoir for use, for example, in the calculation of the volume of hydrocarbons-in-place in a reservoir. Sufficient allowance is made for human intervention to direct the method of analysis used and to check the reasonability of both the intermediate and final results.

Introduction

The use of computers to perform various task in log analysis and geology has become routine in many fields. Most companies possess, or are able to lease, computer programs which analyze log data to provide values of porosity, net to gross ratio and water saturation on a foot by foot basis. The preparation of the raw log and core data for use in computer analyses and the analyses themselves have been discussed elsewhere. Additionally, techniques exist for the representation of geological structure and petrophysical trends by computer generated surfaces.

However, little effort has been directed towards relating the two processes to combine the extremely large volume of data which can be made available from wells, for example from computer precessed logs, with the accurate digital representation of geological and petrophysical data to obtain petrophysical data to obtain

  1. a numerical geological model of a reservoir

  2. an estimate of the variations in petrophysical reservoir properties, and the oil and gas in place within the reservoir, both by area and by depth.

To develop a system which performs such a task, the problems to be considered involve not only the organization of the system but also the techniques to be used in the discrete parts of the system. Further, for many portions of the system, alternative methods of analysis, each suitable under different conditions, are possible. The computer system must allow the possible. The computer system must allow the engineer to select the appropriate method and verify that it has been applied correctly.

In large reservoirs, many mechanisms for computing oil or gas volumes in place become unwieldy.

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