Optimized Isochronal Flow Tests

Abstract

An Optimized Isochronal Test (OIT) is presented to evaluate the deliverability of a reservoir eliminating the need of shut-in periods during a multirate well test, which represents an operational constraint for classical isochronal tests and in some instances for modified isochronal tests. The proposed technique is based on the effect of several consecutive and different production rates over the well-reservoir model during both transient flow and pseudo-steady state flow; thus, it is possible to estimate the reservoir pressure at different radius of investigation, and the ratio between production volume and pressure drop. This method does not require stabilization of static reservoir pressure after a flowing period since it is calculated using a mathematical procedure based on the transient pressure equation. A reservoir simulation model with known petrophysical parameters, fluid properties, pressure and temperature, is used as a reference to evaluate the accuracy of the proposed methodology. Two types of fluids are tested, a low compressible black oil and a high compressible gas condensate, with the objective to demonstrate the optimized isochronal test applicability with pressure, pressure squared P^2, and pseudo-pressure Ψ(P) equations. The production deliverability is evaluated applying four different analysis: flow after flow test, isochronal flow test, modified isochronal flow test and the proposed optimized isochronal flow test; the results are compared and analyzed using the percentage of error found for every method. The optimized isochronal analysis provides the option to avoid shut-in periods during a multipoint well test and provide reliable production deliverability curves. OIT has a direct impact in reduction of costs and deferred production for companies involved in oil and gas operations.