--> Chemical-Mechanical Interactions in Natural Fracture Growth
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Chemical-Mechanical Interactions in Natural Fracture Growth

Abstract

The formation of natural fractures in oil and gas reservoirs is traditionally viewed as a process of mechanical brittle failure that involves fracture nucleation, propagation, and coalescence. Field and core observations have demonstrated that natural fracture formation under reservoir conditions is frequently accompanied by mineral cement precipitation that is concurrent or synkinematic with fracture opening and growth. Textural and fluid inclusion studies of synkinematic fracture cement provide insight into fracture opening rates and opening kinematics indicative of fracture growth concurrent with solution-precipitation reactions in the host rock. Solution-precipitation creep is inferred to allow fracture opening displacements beyond small elastic strains. These observations suggest that natural fracture formation under reservoir conditions involves coupled chemical and mechanical processes. Double-torsion fracture mechanics experiments quantify effects of chemically assisted subcritical fracture processes in a wide range of lithologies relevant to unconventional reservoirs, top and fault seals, CO2 sequestration, and geothermal systems. This work is integrated with numerical simulations of chemically assisted single fracture growth and of fracture network evolution associated with fracture cement growth. Results of numerical simulations demonstrate the effects of coupled chemical and mechanical fracture processes on fracture geometry, aperture and length distribution, spatial organization, connectivity, and flow properties. Upscaled models are intended to guide reservoir development and well completion decisions that reduce development cost and improve hydrocarbon recovery.