Effect of Wellbore Storage on the Analysis of Multiphase-Flow-Pressure Data

Summary This paper investigates the effect of wellbore storage on the analysis of pressure drawdown data obtained at a well producing a solution-gas-drive reservoir. Wellbore storage effects are incorporated by specifying a sandface oil flow rate that increases exponentially from zero to the specified constant value of the oil flow rate at the surface. Use of new computational equations derived here shows that effective oil permeability as a pointwise function of pressure can be computed directly from the measured values of the flowing wellbore pressure, provided the sandface oil flow rate is measured and incorporated into the analysis. If the sandface flow rate is unknown, effective permeability can be computed only after wellbore storage effects become negligible. In all cases, a semilog plot of wellbore pressure squared vs. time is shown to be a viable method for estimating effective oil permeability at initial conditions, effective oil permeability at the final flowing wellbore pressure value, and mechanical skin factor.