Simulation Of Hydraulic Fracturing Process Research Articles

Modeling the Hydraulic Fracturing Processes in Shale Formations Using a Meshless Method

Complex bedding properties and in situ stress conditions of shale formation lead to complex hydraulic fracturing morphologies. However, due to the limitations of traditional numerical methods, the simulation of hydraulic fracturing in shale formation still needs further development. Based on this, the liquid–solid interaction modes and the SPH governing equations considering liquid–solid interaction force have been introduced. The smoothing kernel function in the traditional SPH method is improved by introducing the fracture mark ξ, which can realize the simulation of rock hydraulic fracturing processes. The stress boundary of the SPH method is applied by stress mapping of “stress particles”, and the feasibility and correctness of the method are verified by two numerical examples. Then, the simulation of hydraulic fracturing processes of bedding shale formations are carried out. With the increase of horizontal stress ratio, the total number of damaged particles decreases, but the initiation and extension pressure increase gradually. The initiation stress of small bedding dip angles (θ < 45°) is larger than that of big bedding dip angles (θ > 45°). The hydraulic fracture propagation range at low horizontal stress ratio is wider and the fracture is along the direction of maximum principal stress, while the hydraulic fracture propagation range at high horizontal stress ratio is limited to the perforation. The hydraulic fracture will propagate through the bedding with small dip angles. However, when the bedding dip angle is larger, the hydraulic fracture will propagate along the bedding direction.

Numerical simulation of hydraulic fracturing process with consideration of fluid–solid interaction in shale rock

As a critical technology for the efficient exploitation of shale gas, hydraulic fracturing is a two-way fluid-solid coupling interaction process of water-rock. The accurate water pressure calculation in single shale rock fracture during hydraulic fracturing is critical to the fluid-solid coupling analysis. This paper selected the fractured shale rock from the shale reservoir for analysis based on the Saint-Venant principle. Moreover, the water pressure in a single shale rock fracture was calculated by solving the Navier-Stokes equations. Meanwhile, a fluid-solid coupling model of fractured shale rock during hydraulic fracturing was established and evaluated the changing process of hydraulic fracturing. Our results show that in the hydraulic fracturing process, the changing process of water pressure in a single shale fracture with or without fluid-solid coupling is similar, and both have a water hammer effect. Single shale rock fracture opened instantly in an elliptical shape. The maximum instantaneous water pressure at the fracture tip considering fluid-solid coupling was 3.01 times the initial water pressure. The Mises stress at the fracture tip caused by the maximum instantaneous water pressure was 2.97 times the Mises stress at the fracture tip caused by the water pressure in the fracture after stable water pressure change. Mode Ⅰ fracture occurred in the fractured shale rock when high-pressure water rapidly invaded 2/3 of the length of the fracture. The findings in this study may help to understand the hydraulic fracturing mechanism in shale rock.

A parallel staggered hydraulic fracture simulator incorporating fluid lag

In this work we present a computational framework for the parallel simulation of hydraulic fracturing processes. The simulation algorithm is built upon the staggered coupling of a fluid model that describes the viscous flow in the fractured domain and a model of the solid deformation and fracture response, driven by the pressure field induced by the fluid injection. The use of standard finite elements for the fluid model and a DG formulation for the solid tied together in a staggered fashion, allowing us to focus on the optimal solution strategy for each individual system, furnish the simulator with the robustness and parallel scalability properties needed to handle the strongly nonlinear processes associated with this physical phenomenon as well as the highly demanding computational requirements that come with large-scale field simulations. Importantly, the fluid is allowed to lag behind the crack front thus giving place to a lag region, which has recently been recognized as important in some hydraulic fracture applications, and further broadens the range of applicability of the simulator. We verify the proposed computational framework against known analytical results and we demonstrate its capabilities in complex scenarios such as the interaction with natural cracks and the propagation of simultaneous and sequential fractures, as well as its parallel scalability properties.

Study on Breakdown Pressure in Hydraulic Fracturing Process of Hard Rock Based on Numerical Simulation

Pre-conditioning by hydraulic fracturing is a vital work in block caving mining of hard-rock metal mine, and breakdown pressure is one of the important parameters in rock hydraulic fracturing process, which determines the equipment selection and job-parameter control. Based on numerical simulation method, a pre-holed cylindrical hard rock sample was built for simulation of hydraulic fracturing process to investigate the effect of stress condition, rock properties and water injection rate on breakdown pressure. The results show that the breakdown pressure is increased with the confining stress, and the breakdown pressure is 2.28 times confining stress based on rock tension strength. The variation of rock tension strength affects the breakdown pressure and a positive linear relation exists. Pre-formed notch could obviously reduce the breakdown pressure and control the orientation of hydraulic fracture. And the borehole diameter has a reverse influence on rock breakdown pressure.

An NMM-based fluid-solid coupling model for simulating rock hydraulic fracturing process

Simulation of hydraulic fracturing process based on numerical manifold method (NMM) is a valuable research direction considering its advantages in dealing with continuous-discontinuous deformation problems. In this paper, an NMM-based fluid-solid coupling model is proposed, including numerical solution of unsteady fracture flow, hydraulic pressure-load conversion algorithm, rectification of hydraulic aperture and programming realization of arbitrary crack growth increment etc. In terms of the fluid phase, the fracture flow network is constructed based on the closed loops formed by cutting the mathematical mesh with fractures; in order to eliminate the sensitivity of explicit algorithm to time-step size, an unconditionally stable numerical solution scheme for unsteady flow is established. In terms of the solid phase, for the sake of realizing coupling process of hydraulic pressure to solid deformation, hydraulic pressure is converted into load vector by hydraulic pressure-load conversion algorithm to calculate the deformation of fractured surrounding rock; and Delaunay triangulation algorithm is introduced to subdivide manifold elements with multiple kinks, which effectively solves the problem that the crack tip cannot stop or kink in the same manifold element in the subsequent growth steps, realizes arbitrary crack growth increment. Several benchmark examples are utilized to demonstrate the accuracy of the proposed hydraulic fracturing model in simulating fracture fluid flow and solid deformation. Finally, the developed fluid-solid coupling model is used to simulate rock hydraulic fracturing processes under different conditions. The ability and reliability of the proposed model to describe the hydraulic fracture propagation laws are verified by comparing with previous experimental and numerical results.

Phase-field simulation of hydraulic fracturing with a revised fluid model and hybrid solver

With an intrinsic advantage in describing complex fracture networks, the phase field method has demonstrated promising potential for the simulation of hydraulic fracturing processes in recent literatures. We critically examine the existing phase-field hydraulic fracturing models, and propose a hybrid solution scheme with a revised fluid model. Specifically, the formation deformation and phase field are solved using the finite element method (FEM), while the fluid flows are solved using the finite volume method (FVM). The proposed hybrid scheme is validated with the analytical solution for the toughness-dominated fracture propagation and is tested on the complex hydraulic fracturing process in a naturally fractured formation. Demonstrated by numerical examples, the proposed hybrid phase-field framework has several advantages: (1) it captures the effect of fluid pressure inside the fracture and reservoir more accurately than existing models; (2) it provides a sharper capture of formation fractures; (3) it avoids the nonphysical oscillation of fluid pressure when using a pure FEM solver; and (4) it has a superior performance in mesh and time step convergence.

A super-convergent staggered algorithm for the simulation of hydraulic fracturing treatments

In this paper, a super-convergent algorithm is presented for the simulation of hydraulic fracturing process in impervious domains using the extended finite element framework. The hydro-fracture inflow is modeled based on the Darcy law, in which the fracture permeability is incorporated by taking advantages from the well-known cubic law. The hydro-mechanical coupling between the fracturing fluid flow and the surrounding bulk is carried out by employing a sequential iterative procedure known as the staggered Newton algorithm. The convergence rate of the existing staggered solutions in the literature is examined, and an alternative super-convergent approach is proposed. Finally, through several numerical simulations the sanity of the developed framework is demonstrated.

Approximations for fluid pressure and flux of hydraulic flow in three-dimensional fractures

In this paper, we implement a finite volume method for approximating the pressure of fluid flowing within three dimensional fractures and formulate a scheme for computation of the fluid velocity and flux in the fractures. These are needed to couple with an existing fracture propagation code based on a displacement discontinuity method for simulation of hydraulic fracturing processes. Both of the methods discretise the fracture only, not its two surfaces. The pressure and velocity computed with the proposed numerical schemes are shown to qualitatively agree with analytic solutions for several cases of flow in planar annular fractures.

Simulation of hydraulic fracturing processes in rocks by coupling the lattice Boltzmann model and the Park-Paulino-Roesler potential-based cohesive zone model

This paper contributes a scheme for two-dimensional (2D) numerical simulation of hydraulic fracturing processes in geological materials, which consists of a numerical coupling between the finite element method (FEM) and the lattice Boltzmann (LB) model. The Park-Paulino-Roesler potential-based cohesive zone model (PPR) is used to simulate the fracture propagation by means of interface finite elements, such that cohesive forces act on the fracture surface, capturing the softening process. The PPR model is used because it is a generalized fracture model that can represent the fracture process for mode I, mode II and mixed mode I-II, and can be applied to various materials, including heterogeneous materials, such as rock. The FEM and LB are coupled in an iterative process. The paper describes implementation details including procedures for coupling both methods. Examples of hydraulic fracturing process, modeled with the proposed FEM-LB coupling demonstrate the potential of this numerical procedure to model hydraulic fracturing processes in geomaterials of complex geometries.

Numerical Simulation of Hydraulic Frac-turing Process for an Iranian Gas Field in the Persian Gulf

Most of the Iranian oil and gas wells in the Persian Gulf region are producing through their natural productivity and, in the near future, the use of stimulation methods will be undoubtedly necessary. Hydraulic fracturing as a popular technique can be a stimulation candidate. Due to the absence of adequate research in this field, numerical simulation can be an appropriate method to investigate the effectiveness of hydraulic fracturing. In the current study, the hydraulic fracturing process is simulated for a wellbore in the Persian Gulf region with Abaqus software. The main parameters that are necessary for the simulation are collected through wellbore logs and core tests. Fracturing process is studied with more emphasis on the pressure of fracturing fluid and fracture opening. Finally, several 3D fluid-solid coupling finite element models are generated and the main obtained results are compared.

Numerical Simulation of Hydraulic Fracturing Process in an Enhanced Geothermal Reservoir Using a Continuum Homogenized Approach

The current study presents a numerical modeling approach for three-dimensional simulation of hydro-shearing in jointed rocks for the generation of a man-made, multi-fracture heat exchanger in Hot Dry Rock (HDR) Geothermal reservoir. Various literatures have suggested the presence of in-situ fractured rock mass even in massive granite formations. Thereby, 3D numerical modelling is essential, since the prediction of fracture growth in 3D is key to investigation of different fracture designs and furthermore various operational parameters in order to optimize the heat exchanger design and the resulting energy production. The numerical approach incorporates the Dynardo's approach of homogenized continuum method to simulate the hydro-shearing process in jointed rocks unlike vast majority of commercial and scientific approaches which use the discrete modelling technique. The main motivation of the continuum approach is the numerical efficiency of the 3D coupled hydraulic-mechanical simulations of hydraulic fracturing process in comparison to other alternatives. The input parameters of the numerical model from the best available well log and reservoir data are calibrated from diagnostics measurements such as Micro-seismic events, Bottom Hole Pressure, etc to assign the correct level of forecast quality to the important mechanisms of hydraulic fracturing. The numerical procedure is applied to a prospective Granite reservoir in Thüringen, Germany within the purview of a German joint research project – optiRiss. The integrated approach involves ANSYS as a pre-processor and solver, Dynardo's fracturing simulator on top of ANSYS, Tamino – a post-processing tool and optiSLang – an environment for optimization and uncertainty quantification.

Evaluation of developing an enhanced geothermal heating system in northeast China: Field hydraulic stimulation and heat production forecast

In this work, the feasibility of using enhanced geothermal system correlation techniques (hydraulic fracturing and heat extraction) to develop medium–low temperature geothermal resources for heating purposes in northeast China is investigated. A detailed experiment on field hydraulic fracturing stimulation is conducted. Combining with numerical simulation approaches, heat production potential of this system is forecasted. Field hydraulic stimulation results indicate that the matrix acidizing treatment significantly limits near wellbore friction loss. For network fracturing treatment, however, the formation of branching fractures and its enhancing effects on reservoir flow conductivity needs to be verified by production tests in the future. The geometric dimension and flow conductivity of the induced fracture are determined by numerical simulation of hydraulic fracturing process. The accuracy of the numerical model is verified through matching well head pressure curve. Parameters including production flow rate, flow impedance, production temperature, heat extraction rate and energy efficiency are determined through the simulation results of heat production forecast. The results indicate that thermal energy production from the stimulated reservoir is satisfactory for heating purpose. However, water flow impedance maintains at a relative high level during production period.

A finite element model for three dimensional hydraulic fracturing

This paper is devoted to the development of a model for the numerical simulation of hydraulic fracturing processes with 3d fracture propagation. It takes into account the efects of fluid flow inside the fracture, fluid leak-off through fracture walls and elastic response of the surrounding porous media. Finite element techniques are adopted for the discretization of the conservation law of fluid flow and the singular integral equation relating the traction and the fracture opening. The discrete model for the singular integral equation is implemented using a stencil matrix structure allowing an efficient implementation of the fluid–structure interaction problem. Newton’s method combined with GMRES linear solver are used to solve the resulting nonlinear set of equations. An algorithm for fracture propagation is proposed which is based on the balance of the amount of fluid transported to a certain point with the amount of fluid that could be lost by leak-off. To illustrate the feasibility of the model, we present simulation results for typical operational parameters.