Inflow performance relationships for damaged or improved wells producing under solution-gas drive

Abstract

Inflow performance of 21 theoretical solution-gas-drive reservoirs was simulated with the Weller method. These reservoirs contained a wide range of rock and fluid properties, relative permeability characteristics, and skin effects. Two types of inflow performance relationships (IPR's) were developed from about 19,500 generated data points. The first type, using traditional IPR nomenclature, represents dimensionless pressure vs. the oil flow rate normalized to its actual, maximum flow rate. The second relates dimensionless pressure with the ratio of flow rate to the maximum theoretical, undamaged flow rate. Results show that Type 1 IPR's are strongly dependent on bubblepoint pressure and reservoir depletion effects. Skin characteristics and reservoir extent have serious effects only on the unnormalized, Type 2 curves. Nonlinear regression techniques then were used to develop empirical equations that fit normalized, dimensionless flow rate as a function of dimensionless pressure, depletion, and bubblepoint pressure. Type 2 equations were developed that included the effects of skin, depletion, bubblepoint pressure, and the ratio of reservoir extent to wellbore radius. The resulting equations proved to be statistically sound and generally are significantly more accurate than traditional IPR approaches.