Computer simulation of hydraulic fractures (original) (raw)
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Numerical modelling of hydraulic fracturing
Computer Methods and Recent Advances in Geomechanics, 2014
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A Review of Hydraulic Fracturing Simulation
Archives of Computational Methods in Engineering
Along with horizontal drilling techniques, multi-stage hydraulic fracturing has improved shale gas production significantly in past decades. In order to understand the mechanism of hydraulic fracturing and improve treatment designs, it is critical to conduct modelling to predict stimulated fractures. In this paper, related physical processes in hydraulic fracturing are firstly discussed and their effects on hydraulic fracturing processes are analysed. Then historical and state of the art numerical models for hydraulic fracturing are reviewed, to highlight the pros and cons of different numerical methods. Next, commercially available software for hydraulic fracturing design are discussed and key features are summarised. Finally, we draw conclusions from the previous discussions in relation to physics, method and applications and provide recommendations for further research.
SPE Hydraulic Fracturing Technology Conference, 2015
We developed a hydraulic fracturing simulator that implicitly couples fluid flow with the stresses induced by fracture deformation in large, complex, three-dimensional discrete fracture networks. The simulator can describe propagation of hydraulic fractures and opening and shear stimulation of natural fractures. Fracture elements can open or slide, depending on their stress state, fluid pressure, and mechanical properties. Fracture sliding occurs in the direction of maximum resolved shear stress. Nonlinear empirical relations are used to relate normal stress, fracture opening, and fracture sliding to fracture aperture and transmissivity. Fluid leakoff is treated with a semianalytical one-dimensional leakoff model that accounts for changing pressure in the fracture over time. Fracture propagation is treated with linear elastic fracture mechanics. Non-Darcy pressure drop in the fractures due to high flow rate is simulated using Forchheimer's equation. A crossing criterion is implemented that predicts whether propagating hydraulic fractures will cross natural fractures or terminate against them, depending on orientation and stress anisotropy. Height containment of propagating hydraulic fractures between bedding layers can be modeled with a vertically heterogeneous stress field or by explicitly imposing hydraulic fracture height containment as a model assumption. The code is efficient enough to perform field-scale simulations of hydraulic fracturing with a discrete fracture network containing thousands of fractures, using only a single compute node. Limitations of the model are that all fractures must be vertical, the mechanical calculations assume a linearly elastic and homogeneous medium, proppant transport is not included, and the locations of potentially forming hydraulic fractures must be specified in advance. Simulations were performed of a single propagating hydraulic fracture with and without leakoff to validate the code against classical analytical solutions. Field-scale simulations were performed of hydraulic fracturing in a densely naturally fractured formation. The simulations demonstrate how interaction with natural fractures in the formation can help explain the high net pressures, relatively short fracture lengths, and broad regions of microseismicity that are often observed in the field during stimulation in low permeability formations, and which are not predicted by classical hydraulic fracturing models. Depending on input parameters, our simulations predicted a variety of stimulation behaviors, from long hydraulic fractures with minimal leakoff into surrounding fractures to broad regions of dense fracturing with a branching network of many natural and newly formed fractures.
Computational Simulation of the Hydraulic Fracturing Process
necsi.edu
The hydraulic fracturing process has been used since the first half of the past century for reservoir stimulation treatments. Its bases are simple: some fluid (usually water or mud) is injected into the reservoir at a given rate. At the well's bottom, the pressure begins to increase until it ...
Simulating Fully 3D Hydraulic Fracturing
Hydraulic fracturing, the process of initiation and propagation of a crack by pumping fluid at relatively high flow rates and pressures, is one of several techniques for creating cracks in rock.
Energies
This paper describes a new modeling framework for microscopic to reservoir-scale simulations of hydraulic fracturing and production. The approach builds upon a fusion of two existing high-performance simulators for reservoir-scale behavior: the GEOS code for hydromechanical evolution during stimulation and the TOUGH+ code for multi-phase flow during production. The reservoir-scale simulations are informed by experimental and modeling studies at the laboratory scale to incorporate important micro-scale mechanical processes and chemical reactions occurring within the fractures, the shale matrix, and at the fracture-fluid interfaces. These processes include, among others, changes in stimulated fracture permeability as a result of proppant behavior rearrangement or embedment, or mineral scale precipitation within pores and microfractures, at µm to cm scales. In our new modeling framework, such micro-scale testing and modeling provides upscaled hydromechanical parameters for the reservoi...
Numerical Simulations and Experimental Test in the Development of Hydraulic Fracturing Processes
International Society for Rock Mechanics and Rock Engineering, 2015
The economic feasibility of the exploitation of unconventional oil and gas resources is enhanced when it is possible to analyze a priori, with a reasonable accuracy, the effects of different hydraulic fracturing schemes (different fracturing fluids, different proppant concentrations, etc.) and compare them with the results in terms of the predicted production, enabling therefore the selection of the optimal alternative. Two basic ingredients for these analyses are a reliable numerical technique and an adequate geomechanical characterization of the reservoir. The use of the Discontinuous Galerkin Method (DGM) to simulate fracture processes is discussed, with the perspective of implementing this technique to simulate the hydraulic fracturing of shale formations. It is important to remark that resulting models capture the proper fracture mechanical physics required to model nucleation and propagation of fractures. Two examples are discussed. First, the well-known Brazilian Test is modelled; in this case the dominant phenomenon is fracture nucleation. Second, a Brazilian Test including a slot is modelled, this is a typical fracture mechanics test used for studying fracture propagation in rocks.
Numerical simulations of a hydraulic fracturing test including pre-existing fractures
It is well known that the hydraulic fracturing is a tool commonly used for stimulating hydrocarbon reservoirs, and that the orientation and the propagation length of fractures created by hydraulic pressure are influenced in by in-situ stress field. It is, however, difficult to predict the behavior of fracture propagation from boreholes in a medium under regional stress due to a lack of numerical schemes to simulate rock failures. In order to solve this problem of hydraulic fracturing, we have developed a program to simulate fracture propagation from a borehole due to increasing fluid pressure using an extended finite difference method (X-FEM), which deals with any fractures independent from grid or mesh for the numerical simulation. Numerical simulations are conducted for a 2D elastic medium having a borehole and a fracture. We first confirmed that our program could simulate the stress distribution whose local stress field near the borehole showed some deviated orientation from the regional stress field. We then confirmed that the tendency of fracture propagations to be a function of fluid pressure to induce the extension of fracture. The orientation of the fracture propagation converges to that of the principal stress. However, the higher the fluid pressure is, the smaller the curvature of fracture trace becomes. We would like to conclude that the orientation of maximum insitu principal stress and the fluid pressure for fracturing is two major parameters to control the propagation of fractures due to increasing fluid pressure.
Impacts of natural fractures on hydraulic fracturing treatment in all asymptotic propagation regimes
Computer Methods in Applied Mechanics and Engineering, 2020
Hydraulic fracturing is a technique in which pressurized fluid is pumped into the well to induce fracture propagation in the rock formation. The treatment aims at enhancing permeability and well-reservoir connectivity. However, the presence of natural fractures can impact the hydraulic fracture propagation, increasing the complexity of the hydraulic fracturing treatment, and affect the final configuration of the fracture network. Furthermore, different propagation regimes can develop depending on field conditions, properties of the porous matrix, fractures, the injection fluid, and time. This work introduces a robust fully coupled hydro-mechanical approach to investigate the impacts of natural fractures on hydraulic fracturing in four limiting propagation regimes: toughness-storage, toughness-leak-off, viscosity-storage, and viscosity-leak-off dominated. The proposed approach is based on the finite element method and incorporates the coupling of pore pressure/stress within the permeable rock formation and fracture propagation. An innovative mesh fragmentation technique with an intrinsic pore-cohesive zone approach is implemented in the in-house multiphysics framework to simulate fracture propagation with complex crack patterns. Cohesive Zone Model (CZM) represents the initiation and propagation of hydraulic fractures while a contact model with the Mohr-Coulomb criterion is used to represent the normal closure/opening and friction/shear dilation of natural fractures. The results of the new approach are compared against analytical and numerical solutions. Moreover, the influence of parameters such as rock permeability, fluid viscosity, initial stress state, and intercepting angle on the hydraulic and natural fracture is also investigated. The robustness of the presented methodology is demonstrated by simulating crossing with an offset, branching, fracture propagation from the tip of a natural crack, and interaction of multiple cracks. These results can provide guidance for a better understanding of the complex process of hydraulic fracturing. c
International Journal for Numerical and Analytical Methods in Geomechanics, 2012
Modeling hydraulic fracturing in the presence of a natural fracture network is a challenging task, owing to the complex interactions between fluid, rock matrix, and rock interfaces, as well as the interactions between propagating fractures and existing natural interfaces. Understanding these complex interactions through numerical modeling is critical to the design of optimum stimulation strategies. In this paper, we present an explicitly integrated, fully coupled discrete-finite element approach for the simulation of hydraulic fracturing in arbitrary fracture networks. The individual physical processes involved in hydraulic fracturing are identified and addressed as separate modules: a finite element approach for geomechanics in the rock matrix, a finite volume approach for resolving hydrodynamics, a geomechanical joint model for interfacial resolution, and an adaptive remeshing module. The model is verified against the Khristianovich-Geertsma-DeKlerk closed-form solution for the propagation of a single hydraulic fracture and validated against laboratory testing results on the interaction between a propagating hydraulic fracture and an existing fracture. Preliminary results of simulating hydraulic fracturing in a natural fracture system consisting of multiple fractures are also presented. . Typical mesh arrangement around a fracture tip. A polar coordinate system is established with its origin at the tip. The reference points used in Equations and are denoted as small circles, whereas alternative reference points shown as diamonds can also be used with modified formulations as elaborated in .