ABSTRACT:

A powerful method to explore the degrees of connectivity of the complex spatial distributions of natural fractures on the well performance is important to evaluate the potential productivity of the shale reservoir and thus economic performance. In this study, we present a robust EDFM (Embedded Discrete Fracture Model) numerical method along with a collision detection algorithm to conduct a sensitivity study of complicated natural fracture connectivity on the well performance, which is rarely investigated by any other researchers. Through this coupled method, complex natural fracture network can be simulated non-intrusively to be supported by any reservoir simulator. Based on the available geology model of a shale gas well, along with a geologist-characterized natural fracture network in Sichuan Basin in China, we performed natural fracture connectivity analysis. In addition, through keeping the natural fracture's center locations fixed, we generated three more models with no natural fractures, 1.5 times, and 1.8 times the height/length of original natural fractures. 20-year production forecasting is then studied and the pressure visualizations for drainage area/volumes for both matrix and fractures are completed. We found out that by enlarging natural fractures' geometry by 1.5 times and 1.8 times, the 20-year EUR (estimated ultimate recovery) could be improved by 83% and 150%, respectively. The workflow proposed in this study is easily applicable to other shale reservoirs, and it could provide crucial understandings of the in-situ natural fractures and invaluable suggestions regarding the recovery optimizations.

1. Introduction

The presence of natural fracture connectivity in shale reservoirs plays an important role in creating fracture complexity during the hydraulic fracturing process and affecting well productivity (Wu and Olson, 2015; Raterman et al., 2017; Gale et al., 2018; Yu and Sepehrnoori, 2018). In general, natural fracture size including length and height is the key property to control the natural fracture connectivity. Larger fracture size is easier to generate stronger fracture connectivity under the condition of the same fracture number. Actually, it is extremely challenging to accurately characterize the natural fracture size. Although there are many studies to investigate the effect of complex natural fractures on well performance of unconventional reservoirs, the impact of natural fracture connectivity on well performance based on real field data is not examined. Hence, an effective method to analyze and modify the natural fracture connectivity is needed. Furthermore, an efficient method to model well production with complex hydraulic and natural fracture network is also required.

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