Laboratory Measurement and Interpretation of the Changes of Physical Properties after Heat Treatment in Tight Porous Media

Abstract

Prevention of water blocking and optimization of multiscale flow channels will increase gas production of tight reservoirs. Physical properties of samples from representative tight gas reservoirs were measured before and after high temperature treatment. Results show that, with the increase of treatment temperature, mass decreases, acoustic transit time increases, and permeability and porosity increase. Permeability begins to increase dramatically if treatment temperature exceeds the threshold value of thermal fracturing, which is 600∼700 ∘ C, 500∼600 ∘ C, 300∼500 ∘ C, and 300∼400 ∘ C for shale, mudstone, tight sandstone, and tight carbonate rock, respectively. Comprehensive analyses indicate that the mechanisms of heat treatment on tight porous media include evaporation and dehydration of water, change of mineral structure, generation of microfracture, and network connectivity. Meanwhile, field implementation is reviewed and prospected. Interpretations indicate that, according to the characteristics of multiscale mass transfer in tight gas formation, combining heat treatment with conventional stimulation methods can achieve the best stimulation result.

A Fully Coupled Numerical Model for Microwave Heating Enhanced Shale Gas Recovery

“…For conventional gas reservoirs, single hydraulic fracturing mainly generates great-scale fractures from the preexisting fractures. However, the reserves for tight gas reservoirs mainly exist in micro-scale pores [8]. Therefore, maintaining high gas production for the long term mainly depends on the release of gas stored in the matrix through some special techniques [9][10][11].…”

“…In their experimental study, the shale obtained from the Shanggu basin of Shangxi, China, was burned in an air environment at a temperature of 800 • C for 45 min to oxidize the organic matter and improve the physical properties of the shale. Kang et al [1,8] investigated the change of porosity in the shale samples under a high temperature condition, up to the target temperature of 800 • C. They suggested that the application of FHT must be combined with multi-stage hydraulic fracturing in horizontal wells. The experience of Jamaluddin et al [18] had great significance as a reference.…”

“…The FHT of shale gas reservoirs mainly induces the following mechanisms. Firstly, it accelerates the desorption of methane in the matrix, especially for organic-rich rocks [8][9][10]22,23]. Secondly, it prevents water blocking evaporating blocked water and dehydrating the clay structure [1,8].…”

“…Firstly, it accelerates the desorption of methane in the matrix, especially for organic-rich rocks [8][9][10]22,23]. Secondly, it prevents water blocking evaporating blocked water and dehydrating the clay structure [1,8]. Thirdly, it enhances matrix porosity and permeability or diffusivity in the microscale uniformly [1,8,26].…”

“…Secondly, it prevents water blocking evaporating blocked water and dehydrating the clay structure [1,8]. Thirdly, it enhances matrix porosity and permeability or diffusivity in the microscale uniformly [1,8,26]. FHT is an auxiliary technique of hydraulic fracturing instead of refracturing.…”