Development of Generalized Well Semi-Analytical Coning Models

Abstract

Oil deposits are often found in association with a communicating gas or water zone. The production of the oil often leads to the coning of water or gas. This dynamic interaction can be captured by a properly detailed reservoir simulation, which unfortunately may not always be practical. To brigde the gap, researchers over the years have developed both analytical and empirical methods of modelling gas and water coning in oil reservoir.

The fundamental questions have always been: what is the critical rate of oil production; what is the breakthrough time if the critical rate is exceeded; and what is the post-breakthrough behaviour? Using analytically derived line source vertical and horizontal well breakthrough time expressions, a method has been developed to estimate oil critical rate, breakthrough time and post-breakthrough trend for inclined wells. The Post-breakthrough prediction scheme was extended to vertical and horizontal wells. Simplified correlations have also been generated for the easy application of the method without the need of analyzing complex mathematical functions. Within the accuracy of the numerical simulation results, the breakthrough times for the inclined well were consistently and correctly predicted. Literature correlations and numerical simulation comparisons showed that the post-breakthrough production predictions tended to underpredict oil production, but the trends were much more consistent with simulation results than other correlations studied. To the best of the knowledge of the author, this is the first semi-analytical coning model of an inclined well, as well as, the first semi-analytical post-breakthrough trend prediction for vertical and horizontal wells.