Geomechanical and Reservoir Integrated Hydraulic Fracturing Optimisation for a Tight Oil Reservoir: A Case Study from Offshore Vietnam

Abstract

Abstract Producing tight oil reservoirs by hydraulic fracturing is especially challenging due to relatively low oil mobility. At the planning stage, an integrated approach is essential to optimise fracture parameters using a reliable geomechanical model and reliable reservoir simulations to predict the post-fracture productivity and the net present value (NPV). This paper presents such an integrated case study. The reservoir contained relatively clean sandstones interlaying only a few thin shale layers. A relatively low recovery was expected to yield a good positive NPV because production was planned using a nearby existing production facility. A geomechanical model was built using core, well log and drilling data characterizing the in situ stress, pore pressure and rock mechanical properties in the field. The reservoir properties were characterized from core-log calibration and PVT data from analogue reservoirs. The initial reservoir pressure was very close to the bubble point pressure. Thus, multiphase reservoir simulations were essential to predicting post-fracture production profiles. The study integrated geomechanical modeling, hydraulic fracturing design, reservoir simulations and economic assessments to investigate various well completion scenarios. Various scenarios included a single vertical fracture in a deviated well, an un-fractured 1,000 m horizontal openhole well and a 1,000 m horizontal well with multiple transverse fractures. The un-fractured horizontal openhole scenario required a life cycle wellbore stability assessment. The fractured horizontal well scenario required the optimisation of transverse fractures and their spacing. The production constraints included a 600 psi tubing head pressure, a maximum oil flow rate of 5,000 bbl/d and a maximum 5-year production period with preference for more accelerated recovery. The results from this integrated scheme enabled understanding of the impact of various well completion scenarios on decision-making based on technical and economic issues. The lessons learned in the study can be a guide for optimal development of the target field and other similar fields.