An Investigation on Hydraulic Fracture Propagation in
Randomly Fractured Shale Reservoir Based on Displacement
Discontinuity
Bing Hou, Mian Chen, Wan Cheng
State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum
(Beijing), Beijing, China
Abstract: Hydraulic fracture monitoring shows that the hydraulic fracture morphology
in randomly shale reservoirs is complex, which is essentially different from traditional
sandstone reservoirs. Description about fracture propagation with a traditional way
which is successfully used in homogeneous sand stone can’t obtain enough accuracy
in this reservoir. Based on fracture characteristics observed in down-hole shale cores
and shale outcrops which are from Longmaxi formation in Sichuan basin of China, a
discrete fracture network model is proposed by Monte-Carlo simulation. Considering
the fracturing fluid pressure drop in fracture network and intersections between
hydraulic fractures and natural fractures, a two-dimensional numerical model is
developed to examine the hydraulic fracture propagation in randomly fractured shale
reservoir by using displacement discontinuity method. Numerical simulations show
that (1) hydraulic fractures’ complexity increases as natural fracture density increases
when natural fractures’ orientation is in a same distribution; (2) hydraulic fractures’
complexity increases as natural fracture length increases when natural fractures’
density is the same; (3) the influence of small natural fracture on hydraulic fracture is
regional and it can not change the overall direction of hydraulic fracture. Hydraulic
fractures can cross the natural fracture when the intersection angle between natural
fracture and minimum horizontal stress is small enough. Similarity criterion is
employed to calculate the experimental parameters for simulating the hydraulic
fracturing in Longmaxi shale formation. Hydraulic fracturing tests on fractured shale
outcrops are conducted by using truly tri-axial fracturing system. These experiments
prove the rationality of this numerical model. Microseismic monitoring on hydraulic
fracture from a test well in Longmaxi shale formation of Sichuan basin agrees very well
with this numerical model.
Keywords: hydraulic fracturing, shale gas, numerical simulation, horizontal well, multistage fracturing