Efficient evaluation of gas recovery enhancement by hydraulic fracturing in unconventional reservoirs

- Capability for fast evaluating EGR effect by hydraulic fracturing.
- A hybrid of DFM and DP model is used to describe the multi-scale fractures in the stimulated region.
- A flow-based upscaling technique is developed to provide more precise transmissibilities of upscaled grid blocks.
- No synthetic parameters like shape factors are needed in the framework.
- Suitable for evaluating numerous recovery plans and for uncertainty analysis.

Hydraulic fracturing is an important approach to improve production rate in unconventional gas reservoirs. A proper evaluation of the effectiveness of fracturing process is essential for designing and optimizing future stimulation operations. The recent advances in diagnostic techniques and mineback observations provide evidences of the existence of complex fracture networks. Decline curve analysis also highlights the impact of pre-existing fractures on production. In this paper, we propose a hybrid model which is capable of simulating the multi-scale complex fracture network in a very efficient way.A uniformly global upscaling technique is used to get reliable calculation of transmissibilities between sim-grids of different media without introducing artificial parameters such as shape factors. In the upscaling framework, a high-resolution discrete fracture model of the complex fracture network is firstly built as the reference model. Then a coarse unstructured grid conforming to primary fractures is generated based on this fine scale model and serves as the simulation grid. In the coarse model, large scale fractures are treated explicit like conventional discrete fracture models, while relatively small-scale fractures are upscaled into dual porosity grids by global upscaling procedures.A synthetic case and a field scale problem are designed and implemented to validate and illustrate the capability of the proposed method. The results show that our model can save considerable computation time while preserve the accuracy of simulation. This model can serve as a reliable tool to fast evaluate different plans for enhanced gas recovery, especially in the case when multiple realizations are required for uncertainty analysis.