Role of Geological Core Evaluation in an Integrated Petroleum Engineering Environment

Stephen J. James, W. J. Evert Van De Graaff

Geological core evaluation calibrated with wireline logs aims at describing reservoirs in terms of rock units which are characterized by distinct wireline log and petrophysical properties. The core/log calibration combined with depositional interpretation of the cores improves evaluation of uncored wells, such as identification of discrete reservoir units with different drainage/flooding characteristics. Such reservoir subdivisions also form an essential framework for the selection of representative samples for special analyses required for detailed petroleum engineering reservoir studies. Two case studies are presented which illustrate the impact of core evaluation on improved reserve estimations and development planning.

A Tertiary clastic reservoir in the Far East, considered for a water-injection project, consists of cyclic regressive/transgressive coastal deposits. The transgressive events deposited 0.25-2.00-m thick, relatively coarse-grained transgressive lags which act as thief zones. Sedimentologic characterization of such high injectivity/productivity layers is vital for prediction of reservoir and/or well performance. For such predictions, grouping of petrophysical core analysis results per sedimentological facies and identification of these facies from log characteristics and/or log correlations are essential.

A Cretaceous rudist complex carbonate reservoir in the Middle East was evaluated to be oil bearing over an interval of 30 ft in three wells, but production could only be obtained from the upper 13 ft of one well. Core evaluation showed a distinct contrast in lithological and capillary properties between the productive and nonproductive layers and indicated that STOIIP would have been overestimated if petrophysical parameters (m, n) had been selected without reference to the lithological framework derived from a detailed core evaluation.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.