Abstract
Hydraulic fracturing technology is usually used to stimulate tight gas reservoirs for increasing gas production. The stimulated volume depends in part on the pre-existing natural fractures in a reservoir. The mechanisms influencing the interaction between hydraulic fractures and natural fractures have to be well understood in order to achieve a successful application of hydraulic fracturing. In this paper, hydraulic fracturing simulations were performed based on a two-dimensional Particle Flow Code with an embedded Smooth Joint Model to investigate the interactions between hydraulic fractures and natural fractures and compare these against laboratory experimental results and analytical models. Firstly, the ability of the Smooth Joint Model to mimic the natural rock joints was validated. Secondly, the interactions between generated hydraulic fractures and natural fractures were simulated. Lastly, the influence of angle of approach, in situ differential stress, and the permeability of natural fractures was studied. It is found that the model is capable of simulating the variety of interactions between hydraulic fractures and natural fractures such as Crossed type, Arrested type and Dilated type, and the modeling examples agree well with the experimental results. Under high approach angles and high differential stresses, the hydraulic fractures tend to cross pre-existing natural fractures. Under contrary conditions, a hydraulic fracture is more likely to propagate along the natural fracture and re-initiate at a weak point or the tip of the natural fracture. Moreover, these numerical results are in good agreement compared with Blanton’s criterion. The variety of permeability of natural fractures has a great effect on their interactions, which should not be overlooked in hydraulic fracturing studies.
Highlights
Since shale gas reservoirs often have very low permeability [1], the technique of hydraulic fracturing is commonly used to enhance shale gas production
PFC2D is based on the discontinuum method, with the help
It can be found that the natural fracture is more favorable for opening and diverting fracturing fluid under low approach angles and low differential stresses, which results in the propagation of a hydraulic fracture along the natural fracture and its re-initiation at a weak point or the tip of the natural fracture
Summary
Since shale gas reservoirs often have very low permeability [1], the technique of hydraulic fracturing is commonly used to enhance shale gas production. The successful application of hydraulic fracturing in low permeability reservoirs has resulted in a rapid increase of natural gas production in recent years. The sealed narrow fractures cannot contribute to the reservoir storage, they act as weakness planes and reactivate during hydraulic fracturing treatments, which can produce additional flow paths from formation to borehole to enhance the Energies 2017, 10, 1001; doi:10.3390/en10071001 www.mdpi.com/journal/energies. It is essential to understand more details about the hydraulic fracturing processes, including the interaction between hydraulic fractures and natural fractures, and fracture patterns to achieve a complex fracture network
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