A method is presented for automatic decline-curve analysis (DCA) of wells in gas reservoirs. It is based on the production behavior of a vertical well in a finite, plane reservoir containing dry gas. The method accounts for pressure-dependent gas properties, covers both transient and boundary-dominated flow, and can accommodate varying wellbore pressures. The physical parameters that govern the production behavior are estimated by nonlinear regression of observed-rate data. Interpretation of the transient flow period yields flow capacity (kh) and skin factor; the boundary-dominated flow period provides well index (WI) and gas initially in place (GIIP). Future production rates can be estimated for operating conditions other than those that prevailed during the historical production period. These estimates also may include upper and lower bounds for a given confidence level. The method is illustrated by a synthetic and a real-life example of a declining production well.

Keywords:
type curve, semisteady-state period, upstream oil & gas, drillstem testing, coefficient, flow capacity, confidence interval, fetkovich, viscosity, reservoir
Subjects:
Drillstem/well testing, Estimates of resource in place, Flow in porous media, Formation Evaluation & Management, Pressure transient analysis, Production forecasting, Reserves Evaluation, Reservoir Fluid Dynamics, Well & Reservoir Surveillance and Monitoring
Copyright 2003, Society of Petroleum Engineers
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