Carbonate reservoirs have complex pore structures and serious heterogeneity, which increase the difficulty to achieve efficient oilfield development. Conventional core plugs cannot accurately depict the heterogeneity characteristics that may beyond the scale of plugs. Thus, whole core experiments are conducted to better study this issue.
The methodologies involved in this study include experimental study, outcrop observation, statistical analysis, and numerical modeling. 18 whole core sections are collected from a giant cretaceous carbonate reservoir located in the Middle East, and the OOIP of this carbonate is 4000 MM bbls. We conducted 3D CT, whole core experiments, and plug experiments for the total of 18 sections of the core. Furthermore, numerical simulation is conducted to better evaluate the impact of heterogeneity.
After integrating results from all these methodologies and technologies, 2D and 3D CT images, horizontal permeability, vertical permeability, and density of whole core, horizontal plug, and vertical plug are obtained. Then, pore structure visualization and experimental results are combined, and analysis was carefully conducted. Results show that whole core can better depict the reservoir heterogeneity, and some interesting observations were found, such as when the permeability of the core section is low, permeability of whole core is greater than that of plugs; whereas when the permeability of the core section is high, permeability of whole core is lower than that of plugs. Simulation results indicate that heterogeneity is one of the major factors determining the performance of carbonate reservoirs.
This study offers detailed evidence to support engineers and geologists for better understanding the heterogeneity and optimizing production plan on the carbonate reservoir.