UTILIZING CONCEPTUAL MODELING IN THE STUDY OF ONE OF THE IRANIAN FRACTURED CARBONATE RESERVOIRS

A typical Iranian carbonate matrix block surrounded by an open fracture was modeled in order to understand the fracture-matrix interaction and realize how to model the interaction best. The modeling was carried out by using a fine-scaled Eclipse model in the single porosity mode (the fractures were explicitly modeled). The model was extended to a stack of 6 matrix blocks to understand block-to-block interaction under both water and gas injection scenarios. The results and conclusions obtained from the single porosity single block and 6-block model were used in order to optimize the full field model. The simulation results showed that gas injection worked as a major recovery mechanism for medium and good rock types at all block heights and for poor rock type with block heights of more than 2 meters. The oil recovery results were in the same range for the single and six-stack block model, but the delay of oil recovery by gas gravity drainage is clearly seen in the six-stack block results indicating a period of at least 8-10 years required for reaching ultimate oil recovery for typical block heights. The water injection simulations showed that water imbibes drained the matrix block in a short time dependent on water front advancement in the fracture system surrounding the block. From the simulation results, it was concluded that the water imbibition process was a fast recovery mechanism for all block heights dependent on injection rate and fracture volume which had to be flooded to achieve full recovery of the block. The expected recovery factor of drained oil to initial oil in place after water injection was in the range of 15-35 % for poor to good rock types and different block sizes in the range of 1-5 meters. The results were highly influenced by wettability conditions in the reservoir