A Correlating Device for Predicting Reservoir Performance

Abstract

Abstract The paper develops a means for predicting the relative permeability of gas to oil for a reservoir on the basis of early production data. The method is based on the observation that a log-log plot of the cumulative gas versus the cumulative oil production frequently results in a straight line, particularly in the case of solution-gas drive reservoirs, or reservoirs with a partial or delayed water drive. The method of calculating the relative permeability of gas to oil from this relationship is discussed, together with the specific application to the actual behavior of the Schuler Jones sand pool, Union County, Ark. Introduction Ultimately, the determination of accurate relative permeability values may be solved, partially or completely, in the laboratory. At present the difficulty in obtaining representative core samples, the proper weighting of relative permeability values and the inadequacies existing in reservoir equations make it desirable to find some way for the determination of the ratio kg/ko which, when substituted in existing equations, will permit the prediction of future reservoir performance. The experimental values of relative permeability as determined in the laboratory do not coincide closely with values calculated from field production data. This difference, probably, is a reflection of the original fluid distribution as well as that resulting from dynamic conditions of flow, which result in non-uniform saturation-permeability relationships from one portion of the reservoir to another. The calculated relative permeability for the field is a weighted average value, representing all the instantaneous variations in permeability alone flow lines into the well-bore due to differences in absolute permeability, saturation, pressure and pressure gradient. At present, it is virtually impossible to simulate these conditions in the laboratory. This paper was written in an attempt to determine the relative permeability of the gas to oil phases from the relationship between oil and gas cumulative production. A prior method for determining field relative permeability by means of the "conformance factor" has been described by Patton.