Estimation of critical rate is required for maximizing oil production from horizontal well before water breakthrough. Post-breakthrough recovery is dependent on parameters viz: Horizontal length (L), withdrawal rate (Q) and offset from WOC (h). Critical rate has been determined using various analytical methods whereas EUR from horizontal well has been calculated for forty-eight cases (L-4 no's, Q-3 no's, h-4 no's) using commercial black oil simulator. Result of the study shows that maximum impact on cumulative oil production is given by offset from WOC followed by withdrawal rate and lastly on horizontal well length.

In most reservoirs with oil rims, as the production begins, the gas-oil and oil-water fluid interfaces start deforming because of the imbalance between viscous and gravitational forces, leading to coning or cusping. This can be overcome using proper withdrawal rate, offset from water-oil contact and horizontal length. Further smart horizontal wells require optimization of nozzle size and compartment length also. To see the effect of these parameters on recovery, a three-dimensional geological model of a clastic reservoir from Upper Assam Basin has been used. This model was history matched for a period of 16 years on 46 wells. After successful validation of model on field scale and well level, performance prediction was carried out to see the effect of withdrawal rate, offset from water-oil contact, horizontal length, compartment length and nozzle size using vertical/horizontal and ICD completion. From the analysis, it is evident that application of advanced well completion, ICD, is suitable for such reservoir. Depending on the scenario, maximum cumulative oil production was obtained from ICD wells with 1.08 MMm 3 compared to vertical well with cum oil production of 0.63 MMm 3 . Economic analysis has been carried out for the examined scenarios.

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