--> A New Approach for Production Forecasting in a Sub-Andean Over-pressured Gas Reservoir Using Rate Transient Analysis: A Field Case Study

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A New Approach for Production Forecasting in a Sub-Andean Over-pressured Gas Reservoir Using Rate Transient Analysis: A Field Case Study

Abstract

The Bolivian Sub-Andean region is well known for exhibiting various complex fold-and-thrust belt structural reservoir systems. Because of such geological features, pressure and temperature settings are usually favorable for the occurrence of gas reservoirs, and even some of them exhibiting over-pressured reservoir conditions. Information provided by 2D and 3D seismic studies usually is limited and insufficient for a robust structural modeling which derives in estimations of reservoir rock volume and Original Gas In-Place (OGIP) with high level of uncertainty. Thus, the preparation of a production forecast in the early stages of field development becomes a challenging task. Additional conventional methods to determine the OGIP are material balance and numerical reservoir simulation. However, the volume of production and pressure history data required for application of any of them is considerable. Moreover, for the case of over-pressured gas reservoirs where the depletion mechanism is affected by both water and rock compressibility effects, knowledge of the effective rock compressibility is essential if any reliable estimation of OGIP is desired. Nevertheless, if continuous reservoir monitoring is conducted then it is possible to access to valuable information that, if combined with Rate Transient Analysis (RTA) techniques, can overcome some of the aforementioned limitations and yield a useful estimation for the Original Gas In-place. The use of Rate Transient Analysis (RTA) techniques has increased in the last decade though its application to over-pressured gas reservoirs has not been studied in depth. This work aims to perform a production forecast for an over-pressured gas reservoir based on the analysis of daily production data by application of Rate Transient Analysis. The relation between pseudo-material balance time and the normalized pseudo-pressure drop present a change in slope similar to the observed in conventional material balance plots. A case study for application of the proposed methodology is presented.