Explicit Modeling of Hydraulic Fracture Propagation in Fractured Shales

Abstract

Recently a combined application of two technologies, horizontal drilling and multi-stage massive hydraulic fracturing (HF) has made vast resources of shale gas commercially viable. The HF is a well-established reservoir stimulation technique, which has been developed over the last half century. There are reliable tools for designing HF in conventional reservoirs, in which a planar HF is assumed.On the contrary, in shale gas fracturing, micro-seismic observations have illuminated a complex internal structure resulting from the interaction of the induced hydraulic fractures with natural fractures. It is widely speculated that the stimulated natural fractures make a significant contribution to the gas production.The mechanics of the interaction between multiple fractures during a HF treatment is very complicated. In this paper we present the results of state-of-the-art modeling of an explicit interaction between a propagating hydraulic fracture and a statistically generated discrete fracture network. A sensitivity study reveals a number of interesting observations including importance of initial fracture conductivity for growth of the fracture system, effect of the dilation angle on the generated conductivity and net pressure and uneven distribution of fracture aperture that is critical for proppant placement.This work strongly links the production technology and geomechanics and suggests an approach for modeling and designing HF treatments in unconventional shale gas plays.

Fracture propagation in a naturally fractured formation

“…The condition given in Eq. (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26) ensures that Eq. (7-60) has a solution for 0 < f L0 < 1.…”

“…However, since a very complex fracture network is created, a solution from the 2D transient proppant transport equation (Eq. (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)) would be very computationally intensive. In this model, a fracture network whose length is much greater than its height is assumed, and a one-dimensional transport model is used as an approximation.…”

“…Repeating the process from Eqs. (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) to (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21), a series of pressure updates are obtained. If dp converges to zero, p k is the sought-after solution of the nonlinear system of equations.…”

“…(7)(8)(9)(10)(11)(12)(13)(14) and (7)(8)(9)(10)(11)(12)(13)(14)(15) and applying boundary and junction conditions (Eq. 7-16) and (Eq.…”

“…In recent years, many HF models [8][9][10][11][12][13][14][15][16] for simulating the propagation of a fracture network have been developed. The creation and propagation of a HF network is a very complicated phenomenon that includes the interaction between HF and NF, fluid flow and proppant transport in fracture network, stress concentration at the fracture tip, fracture height growth, and rock properties.…”