Enhanced Reservoir Heterogeneity Description; Khartam Member of the Permo-Triassic Khuff Carbonate: Outcrop Reservoir Analog Approach from Central Saudi Arabia
The Permian-Triassic Khuff reservoirs in the Middle East are estimated to contain about 15–20 % of the world's gas reserves. The Perm-Triassic outcropping strata of Khuff Formation in central Saudi Arabia provide good analog to the subsurface Khuff reservoirs. The Upper Khartam composed of four depositional sequences, each of which consists of set of flow units. Generally, the flow units of the four sequences were dominated by shelly oolitic grainstone. This study proposes a practical methodology to describe carbonate reservoirs heterogeneity on high resolution scale based on an outcrop analog. The method was based on analyzing the spatial variations of critical reservoir properties such as microfacies, porosity, and permeability. The calculated reservoir quality index (RQI) was correlated throughout the reservoir using an outcrop analog sections (distance vary between 100 m to 400 m), then the correlation coefficients were used to establish the descriptive heterogeneity model. Several outcrop sections were used to describe the reservoir heterogeneity; four reservoir flow units were measured to establish the heterogeneity model. These flow units are corresponding to the four sequences of the Upper Khartam member identified and described at the outcrop reservoir analog. Based on statistical parameters analyses for the Reservoir Quality Index (RQI), from bottom to top of the outcrop sections, the units are classified from extremely heterogeneous to moderately to significantly homogeneous. The proposed model provides practical and quick methodology for describing the Khartam member of Khuff reservoir heterogeneity. This model could also be adopted to describe other subsurface carbonate reservoirs. An integrated geological and petrophysical parameters such as grain size and shape, pore size and shape, grain size and pore size distribution, packing arrangement, and pore throat and pore wall roughness could also be introduce to the model for better and more reasonable results. The results of this analog study if integrated with subsurface reservoir data might provide better understanding and prediction of Khuff reservoir quality in subsurface.
AAPG Datapages/Search and Discovery Article #90194 © 2014 International Conference & Exhibition, Istanbul, Turkey, September 14-17, 2014