Detailed study of hydraulic fracturing of Kashiro-Verey rocks by electron microscopy

Abstract

The fracturing of carbonate rocks of the Kashiro-Verey formation in the Volga-Urals region is studied using X-ray tomography and electron microscopy methods. The lithological and structural features of the formation consisting of four lithotypes are described. The lithotypes differ markedly in the degree of clay material, the nature of the void space, and reservoir properties. Two lithotypes are weakly permeable. Experimental modeling of the effect of proppant hydraulic fracturing technology on core samples is applied.It is established that loading affects the interlayers differently depending on their structure and material composition, and the presence of clay and the nature of porosity have the greatest influence. The microcracks of hydraulic fracturing under loading of samples develop to the maximum extent in the densest rocks, in which extended cracks with an opening of about 100 µm or more are formed. In turn, in the permeable part of the lithotypes, extended, usually narrow (thickness less than 20 µm) rectilinear cracks are also formed, oriented in one direction and connecting neighboring microcaverns and pores. Their strict orientation in space reflects the direction of the load on the samples, but may also be partly due to the hidden microlayering of the rocks.The conclusion is made about the possibility of forming through oil migration channels in the reservoir. The results of the experimental study will lead to increasing of the using efficiency of the hydraulic fracturing technology in the operation of the Kashiro-Vereya productive reservoirs.