The Effects and Modelling of Stress in Hydraulically Fractured Tight Reservoirs

摘要

Rock stress changes strongly impact well drilling schedules, well placement, fracture design and fluid production in unconventional reservoirs. The objectives of this work are to understand and quantify the effects of stress changes caused by production and fracture stimulation in tight reservoir (shale oil/gas) plays. The implications of stress changes on well drilling (timing), interference between wells due to stresses (well placement) and fracture design (number, placement and timing) are investigated in this work. Numerical simulation models that integrate several physical effects have been used to achieve these objectives. This integration includes the modelling of fluid flow for reservoir pressure and temperature calculations, full field geomechanical stress, fracture initiation and propagation, rock failure, along with detailed wellbore models. The work shows that the creation of a single fracture on a well strongly affects the formation of a nearby fracture on the same well. The entire process of multistage hydraulic fracturing can be simulated by integrating the above-mentioned physics in a single model. The results can be used for fracture placement and surface pump duty estimates. The fracture creation model can also be used to estimate the extent of stimulated rock volumes in the reservoir. Stress interference effects between wells can also be investigated using full field modelling. Furthermore, the closure of natural fractures within stimulated volumes in the reservoir, which reduces permeability affecting future production, can be estimated using full field geomechanics modelling. The far field effects of stress in unconventional plays show that, although the wells are in pressure isolation, there are strong stress interference effects between wells. The models can be used to generate guidelines on well drilling schedules, well placement, and fracture design and location in such systems. Several papers exist in the literature on different physical effects studied in isolation within the context of geomechanics in unconventional reservoirs. Importantly, this work integrates the different physical effects in a single model. The work introduces novel considerations on the importance of drilling schedules, well placement and fracture design in unconventional plays.