Proppant Flow and Transport Modeling in Deformable Hydraulic Fracture Networks PDF Download

Author: Ruben Alberto Gonzalez Lopez
Publisher:
ISBN:
Category : Drilling muds
Languages : en
Pages : 197

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Author: Oliver Chih-Young Chang
Publisher:
ISBN:
Category :
Languages : en
Pages : 112

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Author: Christopher Allen Johnson Blyton
Publisher:
ISBN:
Category :
Languages : en
Pages : 320

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Current hydraulic fracturing practice in unconventional resource development typically involves multiple fracturing stages, each consisting of the simultaneous creation of several fractures from a horizontal well. A large mass of proppant, often millions of pounds per well, is injected with the fluid to provide post-closure conductivity. Despite the large quantity of proppant used and its critical importance to well productivity, simple models are often applied to determine its placement in fractures. Propped or effective fracture lengths indicated by modeling may be 100 to 300% larger than the lengths inferred from production data. A common assumption is that the average proppant velocity due to pressure driven flow is equal to the average carrier fluid velocity, while the settling velocity calculation uses Stokes’ law. To more accurately determine the placement of proppant in a fracture, it is necessary to rigorously account for many effects not included in the above assumptions. In this study, the motion of particles flowing with a fluid between fracture walls has been simulated using a coupled computational fluid dynamics and discrete element method (CFD-DEM) that rigorously accounts for the both aspects of the problem. These simulations determine individual particle trajectories as particle to particle and particle to wall collisions occur and include the effect of fluid flow. The results show that the proppant concentration and the ratio of proppant diameter to fracture width govern the relative velocity of proppant and fluid. Proppant settling velocity has been examined for small fracture widths to delineate the effect of several independent variables, including concentration. Simulations demonstrate that larger concentration increases the average settling velocity, in apparent contrast with much of the available literature, which indicates that increased concentration reduces settling velocity. However, this is due to the absence of displacement driven counter current fluid flow. This demonstrates that proppant settling in a hydraulic fracture is more complex than usually considered. A proppant transport model developed from the results of the direct numerical simulations and existing correlations for particle settling velocity has been incorporated into a fully three-dimensional hydraulic fracturing simulator. This simulator couples fracture geomechanics with fluid flow and proppant transport considerations to enable the fracture geometry and proppant distribution to be determined rigorously. Two engineering fracture design parameters, injection rate and proppant diameter, have been varied to show the effect on proppant placement. This allows for an understanding of the relative importance of each and optimization of the treatment to a particular application. The presence of natural fractures in unconventional reservoirs can significantly contribute to well productivity. As proppant is transported along a hydraulic fracture, the presence of a dilated natural fracture forms a fluid accepting branch and may result in proppant entry. The proportion of proppant transported into a branch at steady state has been determined using the CFD-DEM approach and is presented via a dimensionless ‘particle transport coefficient’ through normalization by the proportion of fluid flowing into the branch. Reynolds number at the inlet, branch aperture and the angle of orientation between the main slot and branch, particle size and concentration each affect the transport coefficient. A very different physical process, which controls particle transport into a branch under certain conditions, is the formation of a stable particle bridge preventing subsequent particle transport into the branch. This phenomenon was observed in several simulation cases. The complete set of equations for a three-dimensional formulation of rectangular displacement discontinuity elements has been used to determine the width distribution of a hydraulic fracture and dilated natural fracture. The widths have been determined for several combinations of stress anisotropy, net pressure, hydraulic fracture height and length. The effect of the length, height and orientation of the natural fracture and the elastic moduli of the rock have also been examined. Of the cases examined, many show that natural fracture dilation does not occur. Further, of those cases where dilation is apparent, the proppant transport efficiency corresponding to the natural fracture width is significantly less than one and in many cases zero due to size exclusion. The location and orientation of the natural fracture do not significantly affect its width, while its length and the elastic moduli of the rock substantially change the width.

Author: Endrina Rivas
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Hydraulic fracturing is a stimulation technique in which fluid is injected at high pressure into low-permeability reservoirs to create a fracture network for enhanced production of oil and gas. It is the primary purpose of hydraulic fracturing to enhance well production. The three main mechanisms during hydraulic fracturing for oil and gas production which largely impact the reservoir production are: (1) fracture propagation during initial pad fluid injection, which defines the extent of the fracture; (2) fracture propagation during injection of proppant slurry (fluid mixed with granular material), creating a propped reservoir zone; and (3) shear dilation of natural fractures surrounding the hydraulically fractured zone, creating a broader stimulated zone. The thesis has three objectives that support the simulation of mechanisms that lead to enhanced production of a hydraulically-fractured reservoir. The first objective is to develop a numerical model for the simulation of the mechanical deformation and shear dilation of naturally fractured rock masses. In this work, a two-dimensional model for the simulation of discrete fracture networks (DFN) is developed using the extended finite element method (XFEM), in which the mesh does not conform to the natural fracture network. The model incorporates contact, cohesion, and friction between blocks of rock. Shear dilation is an important mechanism impacting the overall nonlinear response of naturally fractured rock masses and is also included in the model--physics previously not simulated within an XFEM context. Here, shear dilation is modeled through a linear dilation model, capped by a dilation limiting displacement. Highly nonlinear problems involving multiple joint sets are investigated within a quasi-static context. An explicit scheme is used in conjunction with the dynamic relaxation technique to obtain equilibrium solutions in the face of the nonlinear constitutive models from contact, cohesion, friction, and dilation. The numerical implementation is verified and its convergence illustrated using a shear test and a biaxial test. The model is then applied to the practical problem of the stability of a slope of fractured rock. The second objective is to develop a numerical model for the simulation of proppant transport through planar fractures. This work presents the numerical methodology for simulation of proppant transport through a hydraulic fracture using the finite volume method. Proppant models commonly used in the hydraulic fracturing literature solve the linearized advection equation; this work presents solution methods for the nonlinear form of the proppant flux equation. The complexities of solving the nonlinear and heterogeneous hyperbolic advection equation that governs proppant transport are tackled, particularly handling shock waves that are generated due to the nonlinear flux function and the spatially-varying width and pressure gradient along the fracture. A critical time step is derived for the proppant transport problem solved using an explicit solution strategy. Additionally, a predictor-corrector algorithm is developed to constrain the proppant from exceeding the physically admissible range. The model can capture the mechanisms of proppant bridging occurring in sections of narrow fracture width, tip screen-out occurring when fractures become saturated with proppant, and flushing of proppant into new fracture segments. The results are verified by comparison with characteristic solutions and the model is used to simulate proppant transport through a KGD fracture. The final objective is to develop a numerical model for the simulation of proppant transport through propagating non-planar fractures. This work presents the first monolithic coupled numerical model for simulating proppant transport through a propagating hydraulic fracture. A fracture is propagated through a two-dimensional domain, driven by the flow of a proppant-laden slurry. Modeling of the slurry flow includes the effects of proppant bridging and the subsequent flow of fracturing fluid through the packed proppant pack. This allows for the simulation of a tip screen-out, a phenomenon in which there is a high degree of physical interaction between the rock deformation, fluid flow, and proppant transport. Tip screen-out also leads to shock wave formation in the solution. Numerical implementation of the model is verified and the model is then used to simulate a tip screen-out in both planar and non-planar fractures. An analysis of the fracture aperture, fluid pressure, and proppant concentration profiles throughout the simulation is performed for three different coupling schemes: monolithic, sequential, and loose coupling. It is demonstrated that even with time step refinement, the loosely-coupled scheme fails to converge to the same results as the monolithic and sequential schemes. The monolithic and sequential algorithms yield the same solution up to the onset of a tip screen-out, after which the sequential scheme fails to converge. The monolithic scheme is shown to be more efficient than the sequential algorithm (requiring fewer iterations) and has comparable computational cost to the loose coupling algorithm. Thus, the monolithic scheme is shown to be optimal in terms of computational efficiency, robustness, and accuracy. In addition to this finding, a robust and more efficient algorithm for injection-rate controlled hydraulic fracturing simulation based on global mass conservation is presented in the thesis.

Author: Oliver Chang
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Hydraulic fracturing is one of the most successful and widely applied techniques that ensure economic recovery from unconventional reservoirs. Oil and gas bearing formation has pre-existing natural fractures and possesses a large proportion in hydrocarbon resources. Distinct fracture propagational behavior and operational variation both affect the entire hydraulic fracturing treatment. Proppant transport and fracture network conductivity are the most significant factors determining the effectiveness of a treatment. The concept of stimulated reservoir volume (SRV) is used to characterize the efficiency of hydraulic fracturing treatment. However, the unpropped fracture will close after the well starts to produce without contributing hydrocarbon recovery. Only the propped open section of fracture contributes to the hydrocarbon recovery. Therefore, the concept of propped open stimulated reservoir volume (PSRV) is proposed to characterize the effectiveness of the treatment. Physics of proppant transport in a complex fracture network is unclear to the engineers. Most of the model simulates using simplified physics. In this work, we first identified the patterns of proppant transport and we developed equations to quantify the governing physics in each pattern, in order to capture the proppant transport process accurately. To quantify the PSRV, a dynamic 3-D, finite-difference, proppant transport model is developed and linked to a hydraulic fracture propagation model to simulate the process of proppant transport through the hydraulic fracture network. The actual propped open stimulated reservoir volume (PSRV) and fracture network conductivity can be quantified by utilizing the model. The goal of this study is to generate guidelines to maximize the effectiveness of the hydraulic fracturing treatment. Hence, a systematic parametric study was conducted to investigate the relation among engineering factors, geomechanical and reservoir properties. The effect of each parameter on PSRV, PSRV/SRV efficiency ratio, and average fracture conductivity during pressure pumping, flowback and shut-in is evaluate and quantified. Guidelines to optimize the effectiveness of hydraulic fracturing treatment for different scenarios are established based on the systematic parametric study.

Author: Yu-Shu Wu
Publisher: Gulf Professional Publishing
ISBN: 0128129999
Category : Technology & Engineering
Languages : en
Pages : 568

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Hydraulic Fracture Modeling delivers all the pertinent technology and solutions in one product to become the go-to source for petroleum and reservoir engineers. Providing tools and approaches, this multi-contributed reference presents current and upcoming developments for modeling rock fracturing including their limitations and problem-solving applications. Fractures are common in oil and gas reservoir formations, and with the ongoing increase in development of unconventional reservoirs, more petroleum engineers today need to know the latest technology surrounding hydraulic fracturing technology such as fracture rock modeling. There is tremendous research in the area but not all located in one place. Covering two types of modeling technologies, various effective fracturing approaches and model applications for fracturing, the book equips today’s petroleum engineer with an all-inclusive product to characterize and optimize today’s more complex reservoirs. Offers understanding of the details surrounding fracturing and fracture modeling technology, including theories and quantitative methods Provides academic and practical perspective from multiple contributors at the forefront of hydraulic fracturing and rock mechanics Provides today’s petroleum engineer with model validation tools backed by real-world case studies

Author: Yatin Suri
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: Yibo Song
Publisher:
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Category :
Languages : en
Pages :

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While hydraulic fracturing is recognized as the most effective stimulation technique for unconventional reservoirs, the production enhancement is influenced by several factors including proppant placement inside the fractures. The goal of this work is to understand the proppant transport and its placement process in "T" shaped fracture network through simulations. The proppant transport is studied numerically by coupling a computational fluid dynamic model for the base shear-thinning fluid and the discrete element methods for proppant particles. In the CFD model, the forces on proppants are calculated based on fluid properties, while fluid properties are updated based on the particle concentration at any point and time. In the DEM model, the motion and position of each individual proppant is calculated based on the gravity and drag forces from the CFD model, which makes it possible to reproduce some phenomena that cannot be simulated in continuum concentration-oriented models. A scaling analysis has been performed to scale down the model from field scale to lab scale by deriving relevant dimensionless variables. Different proppant size distributions and injection velocities are considered, as well as the friction and cohesion effects among particle and fracture surface. The simulation results show that in the primary fracture, the injected proppants could divide into three layers: the bottom sand bed zone, the middle surface rolling zone, and the top slurry flow zone. The total number of the proppants do not increase much after the sand dune reach an equilibrium height. A smaller size proppant would benefit the development of sand dune in the secondary fracture, whereas a larger proppant size would benefit the increase rate of the sand dune. The equilibrium height of sand dune in the minor fracture could be greater than the primary fracture, and the distribution of proppant dunes is symmetric. A lower proppant load would amplify the impact of friction as well as the erosion force, which would finally deliver a negative impact on equilibrium height. Two deposit mechanisms have also identified in the bypass fracture network.

Author: Songyang Tong
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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During hydraulic fracturing treatments, proppants - usually sand - are placed inside fractures to improve fracture conductivity. However, a large portion of the generated hydraulic fractures often remain unpropped after fracturing treatments. There are two primary reasons for this poor proppant placement. First, proppants settle quickly in common fracturing fluids (e.g., slickwater), which results in unpropped sections at the tip or top of the fracture. Second, a large number of the microfractures are too narrow to accommodate any common commercial proppant. Such unpropped fractures hold a large potential flow capacity as they exhibit a large contact area with the reservoir. However, their potential flow capacity is diminished during production due to closing of unpropped fractures because of closure stress. In this study, fractures are categorized as wider fractures, which are accessible to proppant, and narrower fractures, which are inaccessible to proppant. For wider fractures, proppant transport is important as proppant is needed for keeping them open. For narrower fractures, a chemical formulation is proposed as there is less physical restriction for fluids to flow inside across them. The chemical formulation is expected to improve fracture conductivity by generating roughness on fracture surfaces. This dissertation uses experiments and simulations to investigate proppant transport in a complex fracture network with laboratory-scale transparent fracture slots. Proppant size, injection flow rate and bypass fracture angle are varied and their effects are systematically evaluated. Based on experimental results, a straight-line relationship can be used to quantify the fraction of proppant that flows into bypass fractures with the total amount of proppant injected. A Computational Fluid Dynamics (CFD) model is developed to simulate the experiments; both qualitative and quantitative matches are achieved with this model. It is concluded that the fraction of proppant which flows into bypass fractures could be small unless a significant amount of proppant is injected, which indicates the inefficiency of slickwater in transporting proppant. An alternative fracturing fluid - foam - has been proposed to improve proppant placement because of its proppant carrying capacity. Foam is not a single-phase fluid, and it suffers liquid drainage with time due to gravity. Additionally, the existence of foam bubbles and lamellae could alter the movement of proppants. Experiments and simulations are performed to evaluate proppant placement in field-scale foam fracturing application. A liquid drainage model and a proppant settling correlation are developed and incorporated into an in-housing fracturing simulator. Results indicate that liquid drainage could negatively affect proppant placement, while dry foams could lead to negligible proppant settling and consequently uniform proppant placement. For narrower fractures, two chemical stimulation techniques are proposed to improve fracture conductivity by increasing fracture surface roughness. The first is a nanoparticle-microencapsulated acid (MEA) system for shale acidizing applications, and the second is a new technology which can generate mineral crystals on the shale surface to act as in-situ proppants. The MEA could be released as the fracture closes and the released acid could etch the surface of the rock locally, in a non-uniform way, to improve fracture conductivity (up to 40 times). Furthermore, the in-situ proppant generation technology can lead to crystal growth in both fracking water and formation brine conditions, and it also improves fracture conductivity (up to 10 times) based on core flooding experiments

Author: Wenpei Ma
Publisher:
ISBN:
Category :
Languages : en
Pages : 121

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This study investigates proppant flow and transport in intersecting fractures at angles typical for intersections of pre-existing and new hydraulic fractures. Proppant is small granular material, which is placed into hydraulic fractures during geothermal and hydrocarbon reservoir stimulation and props the fluid paths open during reservoir exploitation. This study uses plexiglas laboratory slot experiments enhanced with an advanced image analysis for identifying particle trajectories and quantifying slurry velocities. Although proppant flow and transport has been broadly studied, the effects of intersecting fracture angles have not, especially coupled with fluid viscosities, flow rates, and proppant volumetric concentration effects. This study specifically investigates the role of intermediate fracture angles, which have been identified to occur most frequently when the new hydraulic fractures intercept the existing ones. Results show that proppant flow and transport behavior after the intersection is very sensitive to carrying fluid viscosity and flow rates alteration, while differentiating proppant volumetric concentrations have a limited effect. Fracture intersection angle itself has a clear effect on proppant flow velocities and proppant settlement; furthermore, it enhances the effects from fluid viscosity, fluid flow rates, and proppant volumetric concentrations. This study also studies the proppant agglomeration phenomenon in intersecting fractures. Different shapes of agglomerations are observed and categorized.