HELE-SHAW MODEL STUDY OF HORIZONTAL WELL PERFORMANCE IN RESERVOIR WITH GAS CAP AND BOTTOM WATER DRIVE

Abstract

The production performance of horizontal wells under simultaneous gas-cap and bottom-water drive has been investigated experimentally using a 2-dimensional Hele-Shaw model. Experiments were conducted using different well locations, relative to the gas–oil and water–oil interfaces, and different production rates at each well location with the objective of determining the optimum well location and production rate. The model, which represented a vertical section of the reservoir perpendicular to the well, consisted of two plexiglass plates 40 cm high and 120 cm long with a 0.04 cm capillary space in between. Nine wells, represented by 0.3175 cm diameter holes, were provided along the height and at the center of the model. The oil used was synthetic oil with a viscosity of 4.6 cP and a density of 0.83 g/cc, while the water was represented by a glycerol–-water solution with a viscosity of 3.26 cP and a density of 1.08 g/cc. Nitrogen was used to represent the gas phase. The model and fluids characteristics were chosen to simulate conditions for one of the major reservoirs in the Middle East. Video and still photography were used to track the movement of the water–oil and gas–oil interfaces. It was found that the well is optimally located if the ratio of the distance between the well and the water–oil interface to that between the well and the gas oil–interface is 3:5. This well location provided the highest recovery and latest breakthrough at all production rates. It was also found that better well performance (i.e., higher recovery, later water breakthrough and lower water cut) is obtained at higher than at lower production rates provided that the gas–oil and water–oil interfaces remain stable and flat as they move towards the well.