Impact of Complex Fracture Networks on Well Productivity: A Case Study of the Hydraulic Fracturing Test Site #2

Abstract

Abstract For simplicity, planar fractures are usually used for simulating well performance. This is clearly an oversimplification for naturally fractured formations. Core data from both HFTS 1 and 2 show that a much more complex fracture network is created. In this work, a novel three-dimensional fracturing-reservoir simulator is applied to the Hydraulic Fracturing Test Site (HFTS2) data to provide a thorough assessment of the impact of the fracture network on well performance. A methodology is also presented to effectively represent realistic complex fracture networks generated by hydraulic fracturing when simulating well productivity. Data that characterizes the natural fractures at HFTS 2 are used to create a realistic representation of the reservoir. A fracturing simulator which fully couples fluid flow, fracture mechanics and a black oil reservoir simulator is used to first create the fracture network and then simulate flowback and production. The complex fracture networks, generated by fracture propagation is compared with the core data collected at the site. The production flowback results are also compared with the field and are found to agree well with actual production data. We demonstrate a workflow to create a realistic natural fracture network based on core data. A comparison of our simulation results with core data shows good agreement with the characteristics of the NF network based on the post-frac core analysis. The characteristics of this fracture network control the well productivity. While it is possible to use planar fractures to history match production, the results provide unrealistic fracture dimensions and reservoir drainage volumes. This directly impacts design and operational decisions related to well spacing and fracture sizing demonstrating the importance of incorporating realistic complex fracture networks into reservoir simulators for production evaluation and forecasting as well as fracture design and selecting well spacing. In this paper the rich dataset provided by HFTS-2 is used to demonstrate a methodology to generate a realistic natural fracture network and to create hydraulic fractures that create a fracture network that can be used to simulate well productivity and reservoir drainage. The results show that it is possible to simulate the creation of complex fracture networks that provide much more realistic estimates of well productivity and reservoir drainage area. This is essential for fracture sizing and estimating the optimum well spacing.