Gas Reserve Estimation and Performance Prediction of a Fracture-Dominated Unconventional Reservoir Using Weibull Model

Abstract Gas-in-place estimation and fractured gas-well performance prediction are crucial for determining the effectiveness of hydraulic fracture treatment and making technical and economic decisions. Existing empirical models have been used to analyze both oil and gas wells regardless of whether they are exponential decline-based or stretched exponential decline-based. Furthermore, estimation of the parameters of Weibull model is currently carried out on a trial-and-error basis. In this paper, the Weibull model is used to analyze and predict the performance of a fractured gas well depleting an unconventional reservoir. We demonstrate that the Weibull model can be linearized, with cumulative production as the independent variable and thus allowing the determination of estimated ultimate recovery. Furthermore, probabilistic estimates (P10, P50, and P90) of Barnett shale gas wells are presented. The proposed analysis method uses performance data (rate-cumulative-time data) and circumvents any iteration schemes. Numerical and field data have been used to validate and demonstrate the applicability of the analysis method. Transient-decline exponent is related to the shape parameter of the Weibull model; consequently, the shape parameter can be estimated during the transient state. However, the scale parameter cannot be estimated until boundary-dominated flow is reached. Although the scale parameter gives an indication of the time at which 63.2% of the gas-in-place has been recovered, it does not suggest the onset of boundary-dominated flow. The Weibull model is suitable for analyzing a fractured gas-well performance, but not oil-well performance. While oil-well performance is amenable to an exponential decline, not all gas-well performances exhibit an exponential decline. This paper contributes to the existing techniques for estimating gas reserve and predicting the performance of a fracture-dominated unconventional gas reservoir.