Production Management of Solution Gas Drive Partially Naturally Fractured Reservoirs

-

Flow behavior of naturally fractured reservoirs is quite different from that of conventional reservoirs. Most of the techniques used to interpret the recovery performance of naturally fractured reservoirs (NFR) utilize analytical models based on simplified assumptions. One of such assumptions is uniform distribution of fractures in the reservoir which never holds true for most of the NFR. Naturally fractured reservoirs always have fracture flow networks which are more or less irregular, discontinuous or clustered. A naturally fractured reservoir with such spatially non-uniform distribution of fractures can be called partially naturally fractured reservoir (PNFR). Interconnectivity, length of penetration and intensity of fractures are the important attributes which determine their contributions in the overall fluid flow. Fracture intensity, identified as the key factor in characterizing the PNFR, is believed to be directly related to the reservoir productivity. Important mechanisms that affect the recovery efficiency of PNFR are expansion of fluids and rock, gas-oil gravity drainage, molecular diffusion and re-infiltration of drained oil at the down structure matrix blocks. In PNFR, the fractures may not be all open to vertical flow, thus providing a partial capillary continuity only. Therefore, shape and the effect of secondary gascap formed in the PNFR may be quite different than that in the conventional reservoirs. In view of all this, PNFR provide considerable challenge in studying their recovery performance by natural depletion or gas injection. The first objective of this proposed research is to improve the understanding in the area of PNFR. The second objective is to study the recovery performance of PNFR under solution gas drive and gas injection for the purpose of pressure maintenance. Specifically, in case of solution gas drive (primary depletion) the effect of fracture intensity and liquid withdrawal rate on the recovery performance will be investigated. Whereas, in the case of gas injection (pressure maintenance) the effect of fracture intensity and gas injection rate on the recovery performance will be investigated. The proposed research is very important for Kuwait and other Gulf countries because most of the giant oil/gas reservoirs are partially fractured. This study is expected to set forth and describe conditions that would help in better management and exploitation of these hydrocarbon resources