A Study on Natural Fracture Characterization for Well Trajectory Design and Production Improvement: A Case Study from a Tight Gas Reservoir, Australia

Abstract

Multiple deformation over geologic time leads to generation of natural fractures. In naturally fractured reservoirs (NFRs), there are sets of fractures favourably oriented to fail in shear under the present-day stress field. These fractures which are critically stressed or at the threshold of being critically stressed are more likely to create good fluid conduit and to be the producing fractures in the reservoir. Conversely, non-critically stressed fractures, despite of their extensive population, do not contribute much to the reservoir permeability. Thus, identification of the critically stressed fractures, their distribution and orientations, is imperative to optimize different stages of wellbore construction ranging from wellbore trajectory planning and placement, to stimulation strategy. In this study, a tight sandstone reservoir was brought as a case study to indicate how production optimization can be achieved by a careful analysis of fractures. To do this, a comprehensive analysis was done on Formation Micro Scanner (FMS) log to identify the direction of principal stresses and natural fractures. This was followed by a thorough geomechanical model associated with coulomb failure function (CFF) to identify critically stressed natural fractures. Consequently, an optimized wellbore orientation was proposed to have the best production from the tight reservoir. In addition, the feasibility of underbalanced drilling performance due to minimizing formation damage was examined. A sensitivity analysis was also performed at the end to analyse the mud pressure reqired for hydraulic fracture propagation in order to effectively enhance reservoir permeability regarding various wellbore deviation and azimuth chosen for the wellbore.