Method to generate microfractures by chemical reaction in low carbonate mineral content shale reservoirs

Abstract

Method to generate microfractures by chemical reaction in low carbonate mineral content shale reservoirs in which sulfate acid or persulfate compound (such as ammonium persulfate ((NH4)2S2O8) at a relatively high content) injected into conventional fracturing fluid can react with shale carbonate components resulting in the precipitation reaction of gypsum crystal (CaSO4.2H2O) to occur because an insoluble calcium sulfate (CaSO4) solid is formed. It has been found that expansion stress generated by rapid crystallization in the shale nanoscale pore space can intensively crack shale rocks without additional energy input. Not only does this lead to the formation of much denser secondary microfracture networks, it also can increase SRV by the micrometer-scale gypsum crystals prohibiting these secondary microfracture networks from closure under a normal stress, thereby, improve the efficiency of hydraulic fracturing and hydrocarbon production.

Dependencies are inferred from the claim text.