Simultaneous initiation and growth of multiple radial hy- draulic fractures from a horizontal wellbore (original) (raw)
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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
SPE Annual Technical Conference and Exhibition, 2015
Multi-stage hydraulic fracturing together with horizontal drilling plays an important role in the economic development of unconventional reservoirs. However, according to field analysis of stimulation effectiveness, only a small percentage of perforation clusters contribute to most of the well production. One reason for this low effectiveness is that multiple fractures do not take the same amount of fluid and proppant due to fracture interaction (i.e., stress shadow effects). Unfortunately, how best to minimize the negative effects of stress shadowing is still poorly understood in the petroleum industry. In this paper, we analyzed this problem in order to promote more uniform fracture growth using our complex hydraulic fracture development model. We employed our fracture propagation model that couples rock deformation and fluid flow in the fracture and horizontal wellbore. Partitioning of flow rate between multiple fractures was calculated by analogizing to the electric circuit netw...
Time-Delayed Fracturing: A New Strategy in Multi-Stage, Multi-Well Pad Fracturing
SPE Annual Technical Conference and Exhibition, 2013
The creation of a hydraulic fracture changes the stress distribution in the vicinity of the fracture. This stress shadow can influence the growth of subsequent fractures. Immediately after a hydraulic fracture treatment is pumped, the width of the propped fracture and the associated induced unpropped (IU) fracture network is at its maximum. The hydraulic fracture and the induced unpropped fractures close as a result of fluid leak-off over time. This implies that the stress shadow in their vicinity also decreases over time. Complete closure of induced, unpropped fractures can significantly reduce the stress shadow and make subsequent fracture stages less susceptible to fracture interference and more efficient by avoiding wastage of fluid / proppant into preexisiting fractures. This suggests that increasing the time between successive fractures in a wellbore will lead to improved fracture performance. Using geomechanical computations we show that waiting for longer times between successive stages of a horizontal well allows for a reduction in the stress shadow and less fracture interference leading to a more efficient fracture network by successive fractures in a horizontal well. We, therefore, propose the idea of establishing a minimum time between successive fracture stages in a well. The time required for the induced un-propped fractures to close can be calculated from our models and varies based on the reservoir and fluid properties but is of the order of hours. This controlled time-delay in fracturing can be achieved in several ways, without wasting valuable rig time in the field. We suggest several alternate innovative strategies to achieve this on the field. For example, two-well or multi-well zipper fracs can be pumped, hence increasing the time between fractures in a given well substantially (by several hours). Alternatively, in the Texas Two Step method it would be better to pump the fractures in the sequence 1, 3, 5, 2, 4 than the sequence 1, 3, 2, 5, 4 where the numbers represent the sequence of the fractures along a well starting at the toe. We propose several other fracturing sequences for multi-well pad fracturing applications and suggest how the impact of a multi-stage, multi-well pad fracturing treatment can be enhanced while conserving the time and resources used.
Interaction of Multiple Hydraulic Fractures in Horizontal Wells
All Days, 2013
The use of multi-fracced horizontal well technology in unconventional gas and liquid rich reservoirs is one of the key reasons for the recent success in the exploitation of Unconventional Resources. These multiple fractures are placed in many stages along the horizontal well using diverse completion technologies. Yet, the understanding of fracture growth mechanics and the optimum fracture placement design methodology are still preliminary. Recent advances in computational mechanics and the development of appropriate stimulation modeling technology will further nurture innovation and press forward much needed optimization of the Completion and Stimulation technology in multi-fracced horizontal wells. This paper contains two key components. Firstly, an analytical model is used to highlight some of the salient features of multiple hydraulic fractures interaction. The advantage of an analytical model is that it provides immediate insights into the controlling parameters and steer furthe...
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.
Shale Energy Engineering 2014, 2014
The technique of multistage hydraulic fracturing from horizontal wells is universally credited with enabling the economical production of hydrocarbon resources from shale formations. The method almost always entails the injection of fluid through the wellbore with the potential to create hydraulic fractures from multiple reservoir entry points, typically clusters of wellbore perforations, that are spaced out along the wellbore within a section that is colloquially referred to as a "stage". Arguably the most basic question about this situation is how many perforation clusters within a given fracturing stage can be expected to produce growing hydraulic fractures. This paper presents a numerical investigation of this issue that employs a newly-developed, fully coupled parallel planar 3D hydraulic fracturing simulator that features: implicit time stepping, an implicit level set scheme to locate the propagating hydraulic fracture fronts that respond to their regimes of propagation and enables highly accurate simulations using a very coarse mesh, and the capability to dynamically partition the fluid among multiple, simultaneously growing hydraulic fractures in parallel, overlapping planes. Our results demonstrate the dependence of the energetically preferred number of growing hydraulic fractures on the length of the isolated zone, the height of the reservoir, and the relative importance of the fluid viscosity. In particular, we show that reservoirs with effective height containment and injection strategies that ensure substantial viscous dissipation will promote growth of multiple simultaneous hydraulic fractures rather than localization to just one or two dominant fractures.
Influence of pre-existing discontinuities and bedding planes on hydraulic fracturing initiation
European Journal of Environmental and Civil Engineering, 2013
Pressure-driven fracturing, also known as hydraulic fracturing, is a process widely used for developing geothermal resources, extracting hydrocarbons from unconventional reservoirs such as tight sandstone and shale formations, as well as for preconditioning the rock-mass during deep mining operations. While the overall process of pressure-driven fracturing is well understood, a quantitative description of the process is difficult due to both geologic and mechanistic uncertainties. Among them, the simulation of fractures growing in a complex heterogeneous medium is associated with computational difficulties. Experimental evidence based on micro-seismic monitoring clearly demonstrates the important influence of rock mass fabric on hydraulic fracture development, and the interaction between fluid-driven fractures and pre-existing discontinuities. However, these components are not well accounted for by standard numerical approaches. Thus, the design of hydraulic fracturing operations continues to be based on simplified models whereby the rock mass is treated as a homogeneous continuum. The purpose of this paper is to present the preliminary results obtained using the combined finite-discrete element technology to study the interaction between fluid driven fractures and natural rock mass discontinuities.
Processes
The multifracture competitive growth from a horizontal well is an essential issue in multi-cluster fracturing design. In recent years, extremely limited entry (ELE) fracturing has been implemented to promote uniform multifracture growth. However, the mechanism of multifracture growth and ELE design remain unclear. Based on the planar three-dimensional multifracture propagation model, a multi-cluster horizontal well fracturing model that considers ELE design has been developed. The model considers flow in the wellbore and fluid filtration loss in the fracture. The simulator enables the simulation and analysis of non-uniform in situ stress, filtration loss, and fracture properties. Using this program, we simulated the propagation process of multiple clusters of fractures in ELE fracturing of horizontal wells. The results show the following: The perforation friction in the ELE fracturing can counteract the difference in fluid allocation caused by stress interference, allowing all clust...
Journal of Petroleum Science and Engineering, 2006
Hydraulic fracturing from vertical wells subject to reverse faulting stress regimes is found to be problematic due to turning and twisting of propagating fractures, and eventually resulting in ineffective treatments to increase production. The primary motivation of this paper is to investigate whether effective hydraulic fracturing can be achieved in these reservoirs in a number of stages with production intervals. The basic mechanism that is envisaged to achieve a long, planar productive fracture in such a manner is the production-induced change of stress state around the current fracture tip to be suitable for further planar propagation of the fracture in the next treatment stage. The time-dependent production-induced stress state can be formulated by coupled fluid flow and deformation principles. This concept has been applied to a model-scale reservoir to produce some insightful results. Based on results from the model study, the paper has demonstrated the wide implications of the concept for successful hydraulic fracturing in the mentioned reservoir conditions, and highlighted further research directions with full-scale reservoirs.
SPE Western North American and Rocky Mountain Joint Meeting, 2014
The revolution of the multistage horizontal completions has made low-permeability laminated reservoirs a cost-effective business. The key to success relies on maximizing the surface area contacted, a process that requires an adequate stage isolation technique. From traditional "plug and perf" to efficient sliding sleeves, the application of a particular system is related to the number of fractures that can be propagated during a single treatment injection. This condition varies according to rock and reservoir properties, principal stresses, zonal isolation and stimulation design. This study introduces a methodology to build predictive, repeatable models that integrate reservoir characteristics (mineralogy, pore pressure, thickness) along with geomechanics (anisotropic Poisson's Ratio, Young's Modulus, and horizontal stresses) and fracture pressure diagnostics (pressure history match, near-wellbore pressure analysis) to predict the likelihood of propagating multiple...