Productivity Prediction From Well Logs In Variable Grain Size Reservoirs Cretaceous Qishn Formation, Republic Of Yemen

The Upper Qishn Clastics of Cretaceous age are the primary producing reservoirs in the Masila Block Development area. The underpressured, low gas-oil ratio reserves require artificial lift from initial completion. Electric submersible pumps are used to produce these reservoirs; consequently, knowledge of initial reservoir productivity is essential to the well completion designs and pump sizing. Conventional core and log evaluation methods used to predict reservoir productivity have not been reliable because of variation in reservoir quality and facies changes between pools. A simple and cost effective prediction technique using commonly available open-hole log data has been developed. The method uses log-derived normalized resistivity ratios that characterize reservoir fluid mobility, and predict well productivity indices (PIS). The correlation was developed using well test data from 20 oil bearing zones in 9 wells, and is routinely applied to predict initial PIS in new development wells. The method has been proven effective over four years of field development and production in the Masila Block. The R, technique is a natural extension of the conventional moved-oil plot method in log analysis that is used to infer zones of maximum permeability and movable hydrocarbon. The model is simple and appears to be grain size independent. Further, the technique does not require complex petrophysical and geological analysis; it utilizes data sets (i.e., dual laterolog with microspherically focused resistivity devices) that are consistent between wells.