Multiphase flowback rate-transient analysis of shale gas reservoirs

Abstract

Multi-fractured horizontal well (MFHW) is commonly used in the development of unconventional reservoirs. Flowback data after hydraulic fracturing is of critical importance in the characterization of hydraulic fracture, stimulation evaluation, and reservoir simulation. This study presents a two-phase diagnostic plot and a semi-analytical flowback model for the early-time flowback period when fluid influx from matrix remains insignificant and production is mainly from the fracture network. The developed model considers the changes of water saturation in hydraulic fracture (HF) under fracture depletion mechanism and pressure-dependent permeability and porosity, and is able to predict HF attributes, such as fracture half-length, initial fracture permeability, and initial pore volume of fracture network. A new method of calculating average pressure in the fracture is developed based on the solution of water-phase diffusivity equation and is compared with the traditional material balance approach based on the tank model. Three iterative workflows are proposed using the successive substitution method to calculate fracture attributes under different production conditions. Validation of the developed flowback model, average pressure calculation method, and the analysis workflow, as well as their application in an MFHW drilled in Horn River Shale show the applicability of this study to interpret flowback data quickly and estimate HF properties accurately.