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Simulation Study of Geomechanics Effect for Hydraulically Fractured Reservoirs

Abstract

Unconventional resources such as shale gas and tight oil play an increasingly important role in energy supply worldwide. Production from these resources requires horizontal drilling with multi-stage hydraulic fracturing. Uniform proppant distribution and sufficient fracture conductivity are important for the long-term economic development of shale reservoirs; however, it is very challenging to achieve them in the field due to proppant settlement, proppant embedment and proppant crushing, especially in the soft shale reservoirs. The effects of the above proppant distribution along with stress-dependent fracture conductivity on gas and oil recovery are not clearly understood and systematically studied. Accordingly, it is essential to develop a numerical simulation approach to investigate the relationships between proppant distribution, stress-dependent fracture conductivity and well performance for shale gas and tight oil reservoirs. In this work, we use the numerical reservoir simulation approach, validated by field production data from Marcellus Shale and Bakken Formation, to model proppant distribution and stress-dependent fracture conductivity, including hydraulic fractures and natural fractures. For shale gas reservoirs, gas desorption effect is considered. Based on the laboratory measurements of stress-dependent fracture conductivity due to proppant embedment in shale samples from stiff to soft shale, we obtain the relationship between fracture conductivity and closure stress for different shale samples. Effects of the different scenarios of stress-dependent fracture conductivity on well performance in shale gas and tight oil reservoirs are investigated systematically. Also, we perform a series of reservoir simulations to quantify significant parameters controlling the impact of geomechanics in shale gas and tight oil reservoirs. This work can provide critical insights into the relationship between proppant distribution, stress-dependent fracture conductivity and well performance in shale reservoirs. In addition, it can contribute to providing guidance for engineers to optimize fracture design prior to the actual fracture treatments.