Experimental study on thermally enhanced permeability of rock with chemical agents

Abstract

Previous researches focused on dry sample thermal treatment to enhance rock permeability indicate that thermal treatment can be a novel stimulation technique for geothermal and hydrocarbon reservoirs development. The mechanicm of thermal permeability enhancement depends on the generation of microcracks by thermal cracking. In this study, chemical solutions were introduced on sandstone rock samples and observed that they can be used to control thermal permeability enhancement. Sandstone specimens with the same order of permeability were saturated with different salt solutions and heated to different temperatures. The results quantify permeabilities and porosities of specimens saturated with electrolyts over them without chemical treatment but heated to the same temperature. The KCl solution had the largest effect on permeability enhancement for the tested rock and showed a tenfold increase in permeability, and followed by NaCl and K2CO3 solutions. However, CaCl2 solution and distilled water had negative effects. Laboratory results also revealed a positive correlation between some chemical concentration with the permeability increment of rock. The effects of electrolyte type and concentration on thermally permeability enhancement of the tested rocks were determined and a statistical model was fitted. The results show that the permeability increment follows an exponential growth with temperature when the rock was heated over the threshold temperature of thermal cracking. Introducing specific chemical species into a low-permeability formation and heating the formation beyond the threshold temperature of rock thermal cracking will be a promising way to further enhance formation permeability.