--> Fracture-Matrix Interaction, Fluid Flow and Chemical Movement in Shale

AAPG Southwest Section Annual Convention

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Fracture-Matrix Interaction, Fluid Flow and Chemical Movement in Shale

Abstract

Even after hydraulic fracturing, the issues of steep initial decline and low overall recovery of hydrocarbons (oil and gas) from fine-grained reservoirs affect the economic sustainability of shale resource development. In low-permeability unsaturated fractured shale, fluid flows predominantly through the interconnected fracture network, with some fluid imbibing into the neighboring shale matrix. Imbibition (driven by capillary pressure gradient) advectively transports chemicals from fracture into matrix. Diffusion (driven by concentration gradient) can diffusively transport chemicals into/from the matrix. Once in the matrix, sorbing chemicals can sorb onto matrix rock. All these interacting processes (imbibition, sorption, and diffusion) control fluid flow and chemical transport in fractured shale. Microscopic characteristics of porous matrix – pore shape, pore-size distribution, pore connectivity – influence macroscopic behavior of fluid flow and chemical transport, and can therefore affect the fate of injected fracturing fluids, flowback and produced fluids, as well as the exploration of hydrocarbons in hydraulically-fractured shales. Using an innovative and complementary laboratory approaches, such as imbibition & diffusion tests employing nano-sized tracer recipe followed with microscale mapping of tracers, our work indicates the limited fracture–matrix interactions in fractured shale, with low pore connectivity of nm-sized shale matrix pores and the consequent limited (sub-mm near the fracture face) accessible porosity and anomalous diffusion to the stimulated fracture network and producing wellbore.