Karst Heterogeneities: Static Modeling and Impact on Field Flow Behavior

Abstract

Karstic features are common heterogeneities in carbonate fields worldwide, having either a positive impact (drains enhancing well productivity) or negative (drive injection fluid faster than anticipated into producing well). Once identified, it is a key heterogeneity to be preserved in the geomodel, whom objective is to get a 3D distribution of these conduits within the reservoir model, consistent with the geological description. Even advanced geostatistical methods have difficulties to adequately represent the conduits network: a specific tool that mimics karst development was developed to represent several kinds of karsts (island karst, epigenic and hypogenic), multiple karstic phases and to handle uncertainties on the geometry, conduit density and diameters. Conduit density and diameter distribution can be evaluated using core and imagery data, but conduit network geometry remains unknown. Therefore, this tool offers the possibility to generate multiple patterns. It also provides a calculation of karst impact on petrophysical properties at reservoir model resolution, either with equivalent properties or dual medium property. Sensitivities were done on synthetic model to compare dynamic behavior in both cases and also to analyze the impact of karst geometry (nature of the maze pattern), conduit density and diameters on the field flow behavior. This tool was used on several fields in history match studies using multi-scenarios and multi-realizations, offering different conduit patterns and multiple images. Each pattern was generated, then simulated. Various tools (including connectivity tools) are used to analyze the resulting static realizations, especially karstic features, allowing dynamic match (well scale) . The goal is to converge faster toward history match. Results on an operational case are presented.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019