Application of Heat Treatment to Prevent Fracturing Fluid-Induced Formation Damage and Enhance Matrix Permeability in Shale Gas Reservoirs

Abstract

The low flowback efficiency of fracturing fluid would severely increase water saturation in a near-fracture formation and limit gas transport capacity in the matrix of a shale gas reservoir. Formation heat treatment (FHT) is a state-of-the-art technology to prevent water blocking induced by fracturing fluid retention and accelerate gas desorption and diffusion in the matrix. A comprehensive understanding of its formation damage removal mechanisms and determination of production improvement is conducive to enhancing shale gas recovery. In this research, the FHT simulation experiment was launched to investigate the effect of FHT on gas transport capacity, the multi-field coupling model was established to determine the effective depth of FHT, and the numerical simulation model of the shale reservoir was established to analyze the feasibility of FHT. Experimental results show that the shale permeability and porosity were rising overall during the FHT, the L-1 permeability increased by 30- 40 times, the L-2 permeability increased by more than 100 times. The Langmuir pressure increased by 1.68 times and the Langmuir volume decreased by 26%, which means the methane desorption efficiency increased. Results of the simulation demonstrate that the FHT process can practically improve the effect of hydraulic fracturing and significantly increase the well production capacity. The stimulation mechanisms of the FHT include thermal stress cracking, organic matter structure changing, and aqueous phase removal. Furthermore, the special characteristics of the supercritical water such as the strong oxidation, can not be ignored, due to the FHT can assist the retained hydraulic fracturing fluid to reach the critical temperature and pressure of water and transform to the supercritical state. The FHT can not only alleviate the formation damage induced by the fracturing fluid, but also make good use of the retained fracturing fluid to enhance the permeability of a shale gas reservoir, which is an innovative method to dramatically enhance gas transport capacity in shale matrix.

Heating-Induced Enhancement of Shale Gas Transport and Its Application for Improving Hydraulic Fracturing Performance

“…Heat treatment can be applied as a follow-up method of hydraulic fracturing to generate new gas transport pathways on a smaller scale and shorten the gas transport path length in the shale matrix near the hydraulic fracture wall surface. The major heating methods currently investigated by scholars include electric heating, microwave heating, high-energy laser, and chemical heating. ,, In all these heating methods, the desirable or economic production of heating wells remains controversial as the energy required for heating comes from artificial transport from the ground. The in situ combustion in formation can be a feasible method considering the proven application in the extraction of heavy oil, oil shale, and shale oil. − The shale matrix can be heated by in situ combustion of part of the free shale gas within hydraulic fractures after the fracturing fluid flowback process.…”

“…The major heating methods currently investigated by scholars include electric heating, microwave heating, high-energy laser, and chemical heating. 35,79,80 In all these heating methods, the desirable or economic production of heating wells remains controversial as the energy required for heating comes from artificial transport from the ground. The in situ combustion in formation can be a feasible method considering the proven application in the extraction of heavy oil, oil shale, and shale oil.…”

“…Heat treatment is another possible method to address the water-related damage in shale formation. , Jamaluddin et al first proposed heat treatment to eliminate the water block and clay swelling in the near-wellbore zone of water-sensitive sandstone formation. Experimental results showed that the bound and blocked water in sandstone core samples with 8–15% clay minerals can be removed after the heat treatment in a high-temperature oven, leading to permeability improvements of 51 and 764–988% in cores exposed to 600 and 800 °C, respectively.…”