Abstract
Although tight sandstone gas formations are abundant in China, their single-well productivities and exploitation efficiencies are restricted by water blocking from drilling and completion. At present, shut-in, chemical additive application, and hydraulic fracturing are the common approaches applied to handle this problem. However, these approaches are also characterized by low efficiencies or even cause secondary damage. In this study, the impact of high temperatures (of up to 800 °C) on the microstructure of a tight sandstone, including water blocking and gas permeability, are investigated through the electric heating of a simulated wellbore. The results show that the threshold temperature for fracturing of the tight sandstone is approximately 450 to 600 °C. Many secondary microcracks emerged near the wellbore beyond this temperature, improving the gas permeability, with some microcracks visible even after cooling. The gas permeability of the formation after heating to 800 °C increased by 456% and 3992% compared with the initial gas permeability and the water-blocking impacted gas permeability, respectively. This study demonstrates that electric heating is a potential method for improving the permeability of tight gas formations.
Highlights
IntroductionTight sandstone gas is an unconventional energy resource hosted in a reservoir characterized by very low porosity and permeability [1]
Zeng et al, and Wang et al indicate that the gas permeability of tight sandstones decreases by 70% to 95% due to water blocking, which is consistent with the results of this study [25,26,27]
The gas permeabilities of samples E, F, and G increased by 491%, 426%, and 451%, respectively, relative to the initial gas permeability, with an average increase of 456%
Summary
Tight sandstone gas is an unconventional energy resource hosted in a reservoir characterized by very low porosity and permeability [1]. According to Zhao et al, tight sandstone gas reservoirs are prone to water blocking and stress variations [3]. The superimposed effect of water blocking and stress aggravate the damage of such reservoirs during water-based underbalanced drilling. Dong et al and Shao et al reported that drilling-fluid invasion decreases the permeability of the formation, thereby reducing gas production [4,5]. Lei et al studied the B block, a typical tight sandstone gas reservoir in the Tarim Basin of the Xinjiang Uygur Autonomous Region, China, and reported that the main factors responsible for damage were solid-phase invasion of fractures, wettability alteration, oil-phase trapping, and emulsion plugging [6]
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