Transient shale gas flow model

This paper develops a new transient shale gas flow (TSGF) model specifically tuned for typical hydraulically-fractured horizontal gas wells and addresses the role of fracture-network conductivity in the evaluation of unconventional reservoir performance. This flow model includes the desorption effect and is analytically developed to derive the dimensionless pressure response to the primary depletion phase in shale gas reservoirs. The TSGF model captures the linear flow in the hydraulic fracture and the stimulated reservoir volume under the effects of well geometry, multiple reservoir and hydraulic-fracture properties, and well operating conditions. The unique feature of the unconventional shale gas wells is the simultaneous decline of average reservoir pressure, production rate, and bottomhole flowing pressure with an ultimate bottomhole pressure constraint. This important feature is analytically investigated with the TSGF model. Other pressure-dependent reservoir characteristics such as gas compressibility, viscosity, formation volume factor, and adsorbed gas density are included in the TSGF model. The TSGF model is validated through the history-matching and predictions of Haynesville and Marcellus monthly flowrate data for about 20 wells. The model yields appropriate estimations of well and reservoir properties and predicts the estimated ultimate recovery (EUR) in the multiple hydraulically-fractured horizontal wells. Compared to the empirical stretched exponential production decline (SEPD) and power-law exponential (PLE) models, the TSGF model shows similar flowrate predictions at late-production times. The results also show that given a minimum 12 months of production data, the TSGF model robustly predicts the well performance and the EUR for typical shale gas reservoirs.