Design and Evaluation of Hydraulic Fracture Stimulation of Gas and Coalbed Methane Reservoirs Under Complex Geology and Stress Conditions

摘要

As exploitation of unconventional resources such as coalbed methane (CBM) reservoirs becomes increasingly essential, there is a growing need to develop hydraulic fracture treatment design for these reservoirs with complex geology and stress conditions. Conventional methodologies have failed to address the difficulties involved in the design and execution of fracture treatments in these complex conditions. These include unrestricted height growth breaking through the roof and floor of the coal seam, massive fluid loss as a consequence of the high leak-off formation and poroelastic effects. This paper presents an integrated approach to optimise hydraulic fracture treatments and addresses the associated problems encountered during the hydraulic fracturing process. A 3D poroelastic, finite element based numerical design tool has been developed to describe the fracture geometry for given reservoir and operating conditions. This is coupled with a production model appropriately quantifying the post-frac productivity of a CBM reservoir. Finally, cost analysis carried out to optimise design parameters against different production scenarios using a hybrid genetic-evolutionary optimisation tool. Our study has shown a significant improvement understanding the fracture containment mechanisms and impact of poroelastic effects in stimulating CBM reservoirs. Furthermore, results of this study demonstrate that use of an integrated approach in the design of hydraulic fracture treatments results in a higher yield and cost-effective exploitation of CBM prospects.