Gas-Well Production Decline in Multiwell Reservoirs

Summary

This paper introduces a pseudosteady-state constant pseudosteady-stateconstant pressure solution for gas wells. The pressure solution for gas wells.The solution was used to develop a type-curve-based method to history match andpredict multiwell gas reservoir production. Good agreements production. Goodagreements between the predicted and actual gas-well production rates wereobtained.

Introduction

The determination of future production rates and recoverable gas reservesare the primary requirements for the evaluation of natural gas reservoirs. Theconventional method of predicting long-term gas reservoir predicting long-termgas reservoir performance uses the deliverability and performance uses thedeliverability and materialbalance equations. To use these equations, thereservoir parameters included in them, such as gas in place and formationcharacteristics, must be determined. Often, however, the only available dataare from the production history (production rate vs. production history(production rate vs. time). Also, using numerical reservoir models (simulators)to analyze the production history is impractical when the production history isimpractical when the formation and pressure data are unavailable.

In the absence of complete reservoir data, production-decline type curvescan be used production-decline type curves can be used to predict the futureperformance and reserves. Generally, production-decline type curves are thelong-term, constant-pressure solutions. The type curves usually are plotted inthe form of dimensionless flow rate plotted in the form of dimensionless flowrate vs. dimensionless time on log-log paper. The production-decline history ismatched graphically with the production-decline type curves, and the futureproduction rates and reserves are evaluated.

The idea of using the log-log type curves to analyze the production declinehistory was originally introduced by Fetkovich. A number of production-declinetype curves for gas reservoirs have since been published. These type curveswere published. These type curves were generated from analytical and/ornumerical solutions. These solutions, however, often ignored one or more of thefactors that affect the long-term production performance of gas wells, such asthe pressure dependency of natural gas viscosity and compressibility, thepressure loss owing to non-Darcy flow, and the existence of other producingwells in the same reservoir.

The objective of this study has been to derive a representativeproduction-decline type curve solution that accounts for all theabove-mentioned factors. This solution provides a better understanding of howthese provides a better understanding of how these factors influence the typecurves. The resulting type curves can then be used to analyze theproduction-decline history. The results of the history match will provide therequired parameters for predicting the future performance and reserves. Thisapproach performance and reserves. This approach also allows prediction ofproduction rates when reservoir parameters are altered by infill drilling,compressor installation, or stimulation.

Performance in Performance in Muitiwell Reservoirs

Gas-well performance and interference in multiwell reservoirs were firststudied by Muskat, who used Darcy's law to derive the steady-state pressuredistribution in multiwell oil reservoirs. The results of his study indicatedthat the interference is significant only when the distance between the wellsis less than the drainage radii of the wells. Muskat concluded that theinterference in a multiwell reservoir is controlled by the distance between thewells, number of producing wells, and well pattern (four-spot, producing wells,and well pattern (four-spot, five-spot, etc.).

The factors that control interference determine the shape and relativelocation of the drainage boundary for each well in a multiwell reservoir.Consequently, the well performance in a multiwell reservoir can be performancein a multiwell reservoir can be determined by including the shape factor in theflow equation for a single-well reservoir.