Effect of uneven distribution of proppant in fracture network on exploitation dynamic characteristics

Proppant injection during hydraulic fracturing is to prevent the closure of hydraulic fractures. As a result, the distribution of proppant in the fracture impact the productivity to a great extent. In order to study the rule of proppant transportation and distribution in complex fracture network, and the influence of uneven proppant distribution on the exploitation dynamic characteristics, a full-coupled 3D finite element method calculation model for tight oil reservoir considering sand injection during hydraulic fracturing was established, based on several mathematical models proposed by the author in the past. In the model, a mixture model was utilized, which had advantages to deal with two-phase flow containing solid particles in dispersed phase, to simulate the proppant transportation process in fracture networks. Then, a tight oil reservoir model was established to evaluate the effect of the proppant distribution on the reservoir performance. The calculation results show that in the fracture network, proppant particles will accumulate at the fracture intersection, and the proppant concentration is higher than other parts of the fracture network. The height of proppant settlement dune in the secondary fracture is 25%–50% lower than that in the main fracture, and the communication of secondary fractures has enhanced the proppant settlement degree. Moreover, factors like injection velocity, proppant materials and proppant size are proved to have a strong relation to the average conductivity of fracture network, which could impact the fracture design considerably. Furthermore, the uneven distribution of proppant in fracture network has a great influence on the simulation results. When the reservoir permeability reaches 0.05 mD, the calculation results show that the height, without considering the uneven distribution, of proppant settlement is 41.7% higher than the actual value. Therefore, the uneven distribution of proppant cannot be ignored in the simulation of low permeability reservoir. However, when the matrix permeability is 5 mD, the difference between the actual and simulated result will be within 5%. Thus, it is reasonable to neglect the uneven distribution of proppant in estimations.