Abstract

Core damage is a permanent alteration of rock properties as a result of drill-out and retrieval of the core from the in situ environment to the surface. For reservoir rocks, stress release during coring is thought to be a major core damage mechanism. In this paper, we present a systematic approach to correcting core compaction data for effects of such damage. Our core damage quantification strategy has the following 3 steps:

  • A synthetic rock, analogous to the reservoir rock with respect to rock mechanical and petrophysical properties, plus texture, is created under stress. Comparative tests are performed to simulate virgin compaction behavior, and the behavior of an unloaded and reloaded simulated core.

  • Based on these experiments, a simple elastoplastic model has been developed, describing both the core and virgin compaction behavior of the synthetic analogues. The model is currently in a preliminary stage, but we present it here as an important element in our strategy.

  • Tests with natural reservoir rocks are performed. Obtained parameters are fed to the mathematical model above, permitting a prediction of the expected compaction of the same rock sample placed in the reservoir.

A field example illustrating the use of this approach is presented. The results, based on measurements on synthetic and real cores, indicate that core damage corrections may be substantial, reducing the expected compaction by 25 - 50 % during reservoir depletion.

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