Numerical Simulation of Simultaneous Hydraulic Fracture Growth Within a Rock Layer: Implications for Stimulation of Low‐Permeability Reservoirs

Abstract

Multistage multicluster hydraulic fracturing is currently the most effective method to stimulate low‐permeability hydrocarbon reservoirs. The desired result of this stimulation technique is highly uniform growth of multiple closely spaced hydraulic fractures. In order to deepen our understanding on the competitive growth of these fractures, we have investigated the growth behaviors of multiple hydraulic fractures under different conditions. A fully coupled model with a 3‐D influence coefficient is presented for fracture growth in a rock layer, based on a combination of boundary element method and finite volume method. It is validated against classic solutions and lab experiments. The parametric analyses of dimensionless arguments to quantify the uniformity of fracture growth are performed, with varying fracture geometries and geotechnical conditions including preexisting natural fractures. The results demonstrate that fracture competition is controlled by the dimensionless toughness, the initial fracture geometric settings, and the ratio of fracture spacing to height. A higher fluid viscosity, a smaller initial length offset, and a larger spacing benefit simultaneous fracture growth for conventional bi‐wing hydraulic fractures. By contrast, single wing ones exhibit a remarkably better performance in long‐time simultaneous fracture growth at a small separation, especially at low dimensionless toughness. Under certain conditions, the closely spaced single‐wing fractures are prone to grow simultaneously and uniformly in less energy consumption. The simultaneous growth is found to be insensitive to the interference from small‐scale natural fractures. The uniform single‐wing fracture growth from the perspective of geomechanics will provide a new insight for both reservoir stimulation and formation of vein and dike swarms.

An enhancedJ‐integral for hydraulic fracture mechanics

“…Such a result is achieved by using existing and novel asymptotic solutions to express the $$J_{HFM}$$‐integral in semi‐analytical form, and solving for the distance to the fracture tip. The procedure provides a novel energy‐based alternative to the aperture‐based approaches of state‐of‐the‐art HFM simulators 18–20,24–26,31,34,78 . Such a technique is implemented within a $$J_{HFM}$$‐algorithm that converges on the fracture front via iteratively calculating the $$J^A_{HFM}$$‐integral, inverting the result to predict the location of the fracture tip, and modifying the time step.…”

“…The procedure provides a novel energy-based alternative to the aperture-based approaches of state-of-the-art HFM simulators. [18][19][20][24][25][26]31,34,78 Such a technique is implemented within a 𝐽 𝐻𝐹𝑀 -algorithm that converges on the fracture front via iteratively calculating the 𝐽 𝐴 𝐻𝐹𝑀 -integral, inverting the result to predict the location of the fracture tip, and modifying the time step. The 𝐽 𝐻𝐹𝑀 -algorithm is shown to accurately and quickly converge on the location of the fracture front throughout the toughness and viscous propagation regimes, with small but modest errors in the toughness regime, and promising results with coarse resolutions of the fracture (ℎ∕𝓁 ∼ 0.2).…”

“…18 Among the possible solutions to this problem, [19][20][21][22] the aperture asymptote of Dontsov and Peirce 23 constitutes the latest approach in predicting propagation throughout the toughness-viscous-leak-off regimes, 24 providing a general solution adopted by subsequent studies. [25][26][27][28][29][30][31][32] A salient result that has emerged from HFM is that the tip asymptotes incorporate information on the propagation velocity of the fracture. 17,33 This is a consequence of the conservation of mass of a viscous fluid, which limits the propagation of the fracture to the fluid's capacity to fill the additional space.…”

“…As it became well‐established that such solutions depend on the propagation regime of the fracture, 12–14,17 one of the key challenges for numerical simulations in HFM was to derive a propagation strategy that can equally well be applied to the viscous and toughness regime and the transition between them 18 . Among the possible solutions to this problem, 19–22 the aperture asymptote of Dontsov and Peirce 23 constitutes the latest approach in predicting propagation throughout the toughness‐viscous‐leak‐off regimes, 24 providing a general solution adopted by subsequent studies 25–32 …”

Factors Controlling the Hydraulic Fracture Trajectory in Unconventional Reservoirs

“…By 2020, fossil fuel consumption accounts for 90% of the world primary energy consumption (24.7% natural gas and 31.2% oil) [4]. Currently, unconventional oil and gas reserves are abundant, but due to its low flow capacity [5][6][7][8], hydraulic fracturing technology is an important way to enhance oil and gas recovery on unconventional reservoir [9][10][11][12].…”