Alternative Interpretations of Shale Gas/Oil Rate Behavior Using a Triple Porosity Model

Abstract

Abstract In this work, the fully transient triple porosity model proposed by Al-Ahmadi and Wattenbarger (2011) is selected to model the existence of natural fractures in shale reservoirs. This triple porosity describes three linear flow systems: from the matrix into natural fractures, from natural fractures into hydraulic fractures, and from hydraulic fractures into the wellbore. To completely identify this mathematical model, properties and dimensions of three mediums (matrix, natural fractures, and hydraulic fractures) must be known. This may be too complicated to be a practical interpretation tool. To use the triple porosity model in a practical way, the original model is simplified. Assuming an infinite conductivity of hydraulic fractures, the triple porosity model is reduced to a dual porosity model. This Simplified Model considers only the natural fracture and matrix systems and treats the hydraulic fractures as a constant pressure boundary. The analysis equations and guidelines for this Simplified Model are presented for interpreting production data. Interpretation guidelines are proposed corresponding to five production scenarios which are combinations of bilinear flow, linear flow, and boundary dominated flow (BDF) periods. With the interpretation guidelines, various analysis equations for different flow periods or different physical conditions are used to interpret production data. Field examples are presented with the calculation procedures of interpretation guidelines. The possible errors in general interpretation are also presented. Furthermore, this work also compares the results from the Simplified Model with those from a model with no natural fracture.