Investigation of water blocking mitigation in a normal-pressure shale gas reservoir by high-temperature treatment: Insights from heat transfer range

Abstract

A normal-pressure shale gas reservoir generally exhibits a low formation pressure coefficient, making fracturing fluid flow-back difficult and leading to severe water blocking. Formation heat treatment (FHT) can effectively remove water and induce new fractures to prevent such formation damage and increase shale permeability. However, the range of the heat treatment in shale gas reservoir remains unclear, as does its effectiveness in mitigating water blocking. Laboratory experiments and numerical simulation are conducted in this paper. The experimental results indicate that shale permeability is significantly improved by FHT. A mathematical model coupling heat transfer and shale permeability is established, considering the initial reservoir permeability and heat treatment time. The heat transfer range around a shale gas well after injection of 800℃ gas at a pressure difference of 5 MPa is simulated. The results indicate that (1) the heat transfer range can extend over 1.0 m within a heat treatment time longer than 48 h for a shale formation with the permeability more than 0.1mD after hydraulic fracturing; (2) a one order of magnitude increase in permeability enhances the heat transfer range by 40 %-100 %; (3) with each 24 h increase in heat treatment time, the heat transfer range expands by 27 %- 40 %; (4) the primary factors controlling the heat transfer range are initial reservoir permeability and heat treatment time; (5) an autocatalytic effect in actual FHT suggests the treatment range may exceed simulation estimates. This study illuminates the stimulation effect of FHT technology, which is beneficial for further understanding the increase of productivity of a normal-pressure shale gas well.