Fracture Properties and Their Impacts on Performance in Carbonate Reservoir, Central Block B on the Right Bank of Amu Darya

Abstract

Abstract The Callovian-Oxfordian carbonate reservoir in central Block B on the right bank of Amu Darya is composed of different mechanical and petrophysical layers, where the tectonic fractures have major influences on both the performance and production of the low-permeability reservoir. The development of the tectonic fractures is mainly controlled by the mechanical properties of rocks (e.g., lithology, rock texture, porosity, and shale volume), and the differences in the development of tectonic fractures leading to the high production intervals are restricted preferentially due to fractured mechanical layers. Our study results show that the three main tectonic fracture systems are developed in the Callovian-Oxfordian Stage, including the fracture systems caused by extension movement, compression movement, and fold deformation. Specifically, high-angle extensional fractures and conjugate shear fractures are generally caused by extension movement, which are of small apertures and are mostly fully mineralized and have little impact on fluid flow. Medium- and low-angle extensional fractures as well as conjugate shear fractures are generally caused by compression movement where the strike is nearly parallel to the present-day maximum horizontal stress. These fractures have large aperture and good connectivity with strong flow conductivity of the fluid. However, fewer tectonic fractures are caused by fold deformation. The main properties of natural fractures, such as fracture length, fracture density, fracture aperture, fracture porosity, and stress sensitivity as well as their impacts on the Callovian-Oxfordian reservoir performances, are described herein. We conclude that the tectonic fractures have slight impacts on porosity albeit significant impacts on permeability. Hence, the well placement and well type are optimized under the guidance of the study results.