Well Test Analysis & Simulation of Gas Condensate Reservoir

Abstract

Gas condensate reservoirs are actually gas reservoirs but as pressure declines with depletion, reservoir pressure may go below dew point. Conventional analysis of transient testing which include Horner approximation, type curve analysis and Derivative type curves used for the estimation of permeability do not give accurate results for gas condensate reservoirs below dew point. Problem in this case is that as liquid starts to build-up two phase flow of gas and condensate begins and there is no more absolute permeability. Because of change in composition of reservoir fluids at each point, it requires many pressure transient tests to find permeability or it requires relative permeability curves which need laboratory experiments on cores, making it an expensive procedure. The solution of the problem with relatively newer techniques is presented here. Methodology is based on two techniques; one involving calculation (Fevang’s) from relative permeability data acquired from core analysis conducted in laboratory. Special emphasis have been given to second technique (Jokhio’s) which includes the calculation of effective permeability as a function of pressure by using pressure transient test data only one time with the help of two phase pseudo pressure. This effective permeability of any phase can be used to predict production of second phase. Also the requirement of relative permeability as function of saturation pressure is eliminated. A field example is solved to show step by step procedure of this method. A Well test interpretation of DST (Drill Stem Test) data using Transient testing with log-log plots, radial flow plots and type curve plots is also demonstrated using PAN SYSTEM (Software). In last two chapters reserve estimation methods with introduction to Agarwal-Gardner Flowing Material Balance and Reservoir Simulation is done respectively.