Application of deconvolution and decline-curve analysis methods for transient pressure analysis

Traditionally well testing is completed by analysing transient pressure due to constant production rate. However, in the oil industry practice, engineer often has to deal with the transient pressure resulted from variable flowing rate history. This is particularly true in the case, when transient pressure data is from a PDG over a relatively long period of production time. Another well testing method is to analyse transient flowing rate as a result of the constant well bottom hole flowing pressure. The method is so-called decline curve analysis. However in reality, because of production constraints or changes in operating procedures, the down-hole flowing pressure seldom remains at a constant level over a long period of time. Deconvolution is a technique, which can be used to convert measured transient pressure due to variable sand-face rate into the transient pressure response as a result of equivalent constant flowing rate. This technique can also be used to derive the transient flowing rate due to equivalent constant- pressure of a reservoir system from measured variable pressure. Once having these tasks completed, the traditional well test analysis methods including decline-curve analysis can be applied to analyse the field data. This paper presents study results based on synthetic cases and numerical well testing. Deconvolution codes were developed for the study. It was proved that deconvolution algorithm works well in the case with single phase oil, but breaks down when dealing with cases having multi-phase flow and well interference effects in the data. These aspects need to be addressed in the future investigations. Copyright 2008, Society of Petroleum Engineers.