Numerical modelling of hydraulic fracturing (original) (raw)
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A simplified model for hydraulic fracturing and its role in seismicity
Applications in Engineering Science
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Hydraulic fracturing and its peculiarities
Asia Pacific Journal on Computational Engineering, 2014
Background: Simulation of pressure-induced fracture in two-dimensional (2D) and three-dimensional (3D) fully saturated porous media is presented together with some peculiar features. Methods: A cohesive fracture model is adopted together with a discrete crack and without predetermined fracture path. The fracture is filled with interface elements which in the 2D case are quadrangular and triangular elements and in the 3D case are either tetrahedral or wedge elements. The Rankine criterion is used for fracture nucleation and advancement. In a 2D setting the fracture follows directly the direction normal to the maximum principal stress while in the 3D case the fracture follows the face of the element around the fracture tip closest to the normal direction of the maximum principal stress at the tip. The procedure requires continuous updating of the mesh around the crack tip to take into account the evolving geometry. The updated mesh is obtained by means of an efficient mesh generator based on Delaunay tessellation. The governing equations are written in the framework of porous media mechanics and are solved numerically in a fully coupled manner. Results: Numerical examples dealing with well injection (constant inflow) in a geological setting and hydraulic fracture in 2D and 3D concrete dams (increasing pressure) conclude the paper. A counterexample involving thermomecanically driven fracture, also a coupled problem, is included as well. Conclusions: The examples highlight some peculiar features of hydraulic fracture propagation. In particular the adopted method is able to capture the hints of Self-Organized Criticality featured by hydraulic fracturing.
Environmental Earth Sciences, 2015
In this paper, numerical and semi-analytical investigations were conducted to understand the hydraulic fracturing operation in the tight gas reservoir only identified by the code A7 in the North German Basin. Two simulators, FLAC3D plus (numerical, full 3D model) and MFrac (semi-analytical, modified model based on the conventional pseudo-3D model), were used to model the fracturing operations including fracture propagation, proppant transport and settling. A comparison of the two simulators was carried out through simulations. Meanwhile, the function of the geological barrier integrity in A7 was also studied and confirmed. The simulations were based on the history matching of the in situ measured well head pressure. At the end of the simulation, a long fracture (length ) height) was modeled by both simulators. Although the results express some differences in the modeled fracture length and width (average), their results for fracture pressure, fluid leak off and proppant distribution are comparable. That means they would provide similar productivity in the later production. Investigation of the geological barrier integrity confirms that the cap rock, formed from rock salt and anhydrite, normally has higher minimum horizontal stress and lower permeability providing enough resistance to prevent the fracture from propagating in the vertical direction of the cap rocks. The case study reveals that, even when the injection volume was increased 10 times the initial volume, the integrity of the cap rocks could not be broken. Despite the presence of interbedded shale formations, in the reservoir as those of the cap rock an impediment function, if their thicknesses are too small to prevent their breakage and the injection volume too large for them to resist fracturing.
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.
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.
Computer simulation of hydraulic fractures
International Journal of Rock Mechanics and Mining Sciences, 2007
We provide a brief historical background of the development of hydraulic fracturing models for use in the petroleum and other industries. We discuss scaling laws and the propagation regimes that control the growth of hydraulic fractures from the laboratory to the field scale. We introduce the mathematical equations and boundary conditions that govern the hydraulic fracturing process, and discuss numerical implementation issues including: tracking of the fracture footprint, the control of the growth of the hydraulic fracture as a function of time, coupling of the equations, and time-stepping schemes. We demonstrate the complexity of hydraulic fracturing by means of an application example based on real data. Finally, we highlight some key areas of research that need to be addressed in order to improve current models. r
Recent Developments in Multiscale and Multiphase Modelling of the Hydraulic Fracturing Process
Mathematical Problems in Engineering, 2015
Recently hydraulic fracturing of rocks has received much attention not only for its economic importance but also for its potential environmental impact. The hydraulically fracturing technique has been widely used in the oil (EOR) and gas (EGR) industries, especially in the USA, to extract more oil/gas through the deep rock formations. Also there have been increasing interests in utilising the hydraulic fracturing technique in geological storage of CO2in recent years. In all cases, the design and implementation of the hydraulic fracturing process play a central role, highlighting the significance of research and development of this technique. However, the uncertainty behind the fracking mechanism has triggered public debates regarding the possible effect of this technique on human health and the environment. This has presented new challenges in the study of the hydraulic fracturing process. This paper describes the hydraulic fracturing mechanism and provides an overview of past and r...
Hydraulic fracturing: a review of theory and field experience
2015
This report summarises the current state-of-the-art knowledge of the hydraulic fracturing process used by the shale gas/oil industry using open peer-reviewed literature and from government commissioned research reports. This report has been written to make statements on our knowledge of the following questions: • How do hydrofractures form? • How far do hydrofractures extend during stimulation? • What dictates where hydrofractures propagate? • How do hydrofractures interact with the existing fracture network? • Can the size and distribution of hydrofractures be controlled? Gaps in our knowledge have been highlighted, with the largest of these resulting from differences between North American and European shale rocks.
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 ...
D.H.: Numerical modeling of hydraulic fracturing in oil sands
2008
Hydraulic fracturing is a widely used and ecient technique for enhancing oil extraction from heavy oil sands deposits. Application of this technique has been extended from cemented rocks to uncemented materials, such as oil sands. Models, which have originally been developed for analyzing hydraulic fracturing in rocks, are in general not satisfactory for oil sands. This is due to a high leak-o in oil sands, which causes the mechanism of hydraulic fracturing to be dierent from that for rocks. A thermal hydro-mechanical fracture nite element model is developed, which is able to simulate hydraulic fracturing under isothermal and non-isothermal conditions. Plane strain or axisymmetric hydraulic fracture problems can be simulated by this model and various boundary conditions, such as specied pore pressure / uid ux, specied temperature/heat ux, and specied loads/traction, can be modeled. The developed model has been veried by comparing its results to existing analytical and numerical solu...