Simulation of the Effect of Non-Uniform Proppant Distribution on Well Productivity in Shale Gas Reservoirs

摘要

Uniform proppant distribution in multiple perforation clusters plays a crucial role on sufficiently propping fractures conductivity in hydraulic fracturing. These propped fractures and their effectiveness is critically influenced by the in situ stress in the formation. As great uncertainty exists in uneven propped fracture, this paper examines the impact of proppant distribution and fracture conductivity variation on the gas productivity for shale gas reservoirs, by developing a reservoir simulation model. In this paper, numerical reservoir simulation, which involves application of a constantly decreasing permeability to the propped fracture, are used to model the uneven proppant distribution and geomechanics effect. The decrease of permeability, along from the wellbore toward the tip, is simulated using an exponential approach, as well as a linear approach. Moreover, Effects of gas desorption and stress-dependent fracture conductivity are taken into account in this model. Sensitivity analysis is carried out on critical parameters to quantify the key parameters affecting gas productivity between uniform and nonuniform proppant distribution. The degree of non-uniform proppant distribution is also investigated and divided into four types of proppant distribution scenarios. The following conclusions can be obtained based on the simulation results. A big difference on well performance between the case of linear and exponential permeability degradation is observed. The pressure distribution comparison shows higher pressure drops in the exponentially decreasing permeability case, which results in a lower gas production. Reservoir permeability plays a critical role in cumulative gas production, no matter in case of permeability exponentially degrading or linear degrading, followed by fracture half-length, primary fracture conductivity, Fracture complexity, permeability anisotropy. Furthermore, the effect of uneven proppant distribution between different clusters can significantly reduce the gas recovery, especially in low proppant concentration and small fracture conductivity. The model presented in this paper takes the uneven proppant distribution and geomechanics effect into consideration and shows good agreement with real field production. This paper can demonstrate its own merits on the optimization of hydraulic fracturing treatments, and provide a better understanding of the effect of proppant distribution on well performance.