Critically-Stressed-Fracture Analysis in Naturally Fractured Carbonate Reservoir–A Case Study in West Kuwait

Abstract

Abstract This paper presents the methodology to identify critically stressed fractures, CSF, in naturally fractured reservoirs. A natural fracture is considered to be critically stressed if the ratio of shear and normal stresses acting on the fracture surface exceeds the frictional strength of the reservoir rock. The main objective is to identify the critically stressed fracture trends in the reservoirs in order to design wellbore trajectories that efficiently intersect theses fracture trends. In addition, geomechanical analysis for drilling scenarios under depleting reservoir conditions addressing well-bore stability is attempted to formulate drilling and completion strategy. Critically stressed fracture identification has several important implications on fluid flow behavior through naturally fractured porous media. It has been shown that fluid flow in fractured rocks is largely controlled by critically stressed fractures; therefore, critically stressed fracture analysis may enable to systematically identify producing fractures in the reservoirs that mainly produce through natural fractures. The CSF analysis includes the mechanical property characterization of the formations and the in-situ stress tensor description acting on the reservoirs. The fracture orientations from core description & borehole image log interpretation were used for the CSF analysis because fracture dip and strike are needed for the stress calculation on fracture planes. This analysis is particularly useful where several fracture trends are identified in a reservoir, with some trends more likely to be open and productive due to horizontal stress anisotropy. The case history illustrates application of CSF Analysis in conjunction with geomechanical wellbore stability analysis in selection of optimal well trajectory and formulation of drilling and completion strategy for producing a naturally fractured carbonate reservoir.