What Is the Real Measure of Gas-Well Deliverability Potential?

Abstract

Summary This paper probes the usefulness of establishing the traditional time-variant, absolute-open-flow potential (AOFP) on a given well. Our contention is that a well's AOFP is not a measure of its future potential in a volumetric system owing to ever-declining reservoir pressure. To circumvent this reality, we suggest a two-step approach. First, conduct a multirate test to establish reservoir parameters, such as permeability, mechanical and non-Darcy skin, and average pressure. Second, with these known parameters, use an analytic tool to describe the deliverability potential for a well or a group of wells, including reservoir uncertainty and/or operational constraints. This paper presents a simple methodology for establishing reservoir parameters and predicting a well's future deliverability potential. Field examples show that computing reservoir parameters from buildup and drawdown data and establishing the deliverability relation instills confidence in analysis. We also show that the traditional log-log graphing of the backpressure equation is no longer required because we avoid the notion of a stabilized deliverability concept. An analytic reservoir simulator was developed to handle well location in various drainage shapes using the pressure-transient analog for rate computation. Material-balance calculations form the backbone when depletion sets in. This simulator is also capable of handling the uncertainty of various input variables and performs full-factorial design calculations for a three-level design (that is, P10, P50, and P90). This feature facilitates capturing uncertainty of drainage area and/or any other variables while predicting future rates.