The economic viability of shale gas development hinges on uniform proppant distribution and sustaining sufficient fracture conductivity in hydraulic fractures over the lifetime of a well; however, it is very challenging to simultaneously maintain uniform proppant distribution and such conductivity due to proppant settlement, proppant embedment and proppant crushing in shale reservoirs, especially in soft shale formations. It has been reported that the proppant concentration is heavily weighted toward the end clusters, while the initial clusters receiving much less proppant in the same stage. In addition, proppant will settle rapidly in slickwater fracture treatments, forming a proppant bank at the bottom of the fracture, which results in uneven proppant distribution along the fracture height. The effects of the above proppant distribution along with stress-dependent fracture conductivity on ultimate gas recovery are not clearly understood and systematically studied, and have been largely neglected by most fracture modeling work in the literature. Therefore, it is absolutely critical to develop a reservoir-modeling approach that properly examines the relationships between proppant distribution, stress-dependent fracture conductivity and well performance for shale gas reservoirs.
In this paper, numerical reservoir simulation techniques, validated by field production data from Marcellus Shale, are employed to model the proppant distribution and geomechanics effect. A series of reservoir simulations was performed to quantify the impact of uneven proppant distribution between different clusters in the same stage on well performance. The fracture conductivity ratio of 1:1.5:2.5:4 for four clusters within one stage was investigated in this study. The simulations evaluate a range of reservoir permeability from 0.00001 to 0.0001 md. Gas desorption effect is also taken into account. This work enables operators to develop an early understanding of the effects of proppant distribution and geomechanics on shale gas well productivity, and provides insights into fracture conductivity requirements in shale gas reservoirs that can be used to improve hydraulic fracturing treatment design through improved proppant distribution.