Digital core construction of fractured carbonate rocks and pore-scale analysis of acoustic properties

Abstract

Fractures in carbonate rocks make the reservoir and its elastic properties complex, which creates challenges in the geophysical exploration of oil and gas resources. To study the elastic properties of fractured carbonate rocks, pore-scale numerical simulations and microscopic analyses are necessary for theoretically comprehensive analysis. First, a digital core of carbonate rock was established from X-ray CT scan using medium filtering and threshold segmentation method technologies. Then, some carbonate rock digital cores with different types of fractures were constructed by inserting fractures into scanning slices. Based on the theory of elastic mechanics, the elastic properties of carbonate rock cores with fractures were calculated using the finite-element method, and the effects of the microscopic factors on the rock elastic properties were studied in detail. The calculated stiffness-matrix elements of the digital core are consistent with the Gassmann fluid-substitution theory in isotropic rock. For the digital cores with coin-shaped and penetrating fractures, the influence of fracture density, fracture opening, and fracture length on the stiffness-matrix elements and the wave velocity were studied in detail through pore-scale simulations. This work provides a new perspective for carbonate rock physics and lays a foundation for multi-scale analysis of acoustic properties in carbonate rock reservoirs.