Rate-transient analysis of liquid-rich tight/shale reservoirs using the dynamic drainage area concept: Examples from North American reservoirs

Abstract

The early-time performance of multi-fractured horizontal wells is mainly controlled by fracture geometry, total effective area of the fractures, and conductivity of the primary fracture system. Inverse modeling using rate-transient analysis (RTA) methods has historically been used to characterize MFHWs at different stages of well life, including the early-time performance. In particular, linear flow analysis is used to estimate the total effective fracture area from online production data, provided that reservoir and fluid properties are known. However, a primary complication in analytical linear flow analysis is the incorporation of nonlinearities such as multi-phase flow and pressure-dependent rock/fluid properties into the calculations.A new linear flow analysis technique is presented in the current study, which can be applied to tight/shale systems with multi-phase flow and pressure-dependent rock/fluid properties. The method combines three important reservoir engineering concepts for linear flow analysis: dynamic drainage area (DDA), material balance, and decoupling of saturation and pressure (which is analogous to the decoupling of geomechanics and fluid flow). The DDA approach has been used previously by the authors for history-matching and forecasting using a semi-analytical model, but not for inverse modeling (RTA). The DDA concept, which uses a time-dependent well productivity index equation for the transient flow period, facilitates the incorporation of any sort of nonlinearity (including decoupled saturation functions) and operational constraints in modeling and RTA of linear flow in MFHWs.The method is validated against numerical simulation and applied to various sets of field production data from tight/shale gas and oil wells with different levels of condensate- (oil-) gas ratio. For all the field cases, total effective fracture area obtained from the new analytical RTA method is in reasonable agreement with numerical modeling results.Regarding accuracy and practicality, the new method represents an improvement in RTA of liquid-rich tight/shale reservoirs, particularly for cases with multi-phase flow and pressure-dependent rock/fluid properties. Further, the concepts used in the new model development are easy to understand and implement.