[PDF] Experimental And Modeling Evaluation Of Proppant Transport In Complex Fractures eBook

Author : Songyang Tong
Publisher :
Page : 0 pages
File Size : 24,1 MB
Release : 2019
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ISBN :

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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 : Christopher Allen Johnson Blyton
Publisher :
Page : 320 pages
File Size : 33,11 MB
Release : 2016
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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 : Raimbay Aigerim
Publisher :
Page : 111 pages
File Size : 10,38 MB
Release : 2015
Category : Hydraulic fracturing
ISBN :

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Since the introduction of hydraulic fracturing technique, industry has been attempted to enhance production of hydrocarbon from tight reservoirs by selecting optimum design of hydraulic fracturing treatment. One of the essential parameters in hydraulic fracturing design is the proper selection and injection of proppants. They not only provide fracture permeability but also prevent "healing" of fractures. Hence, the quantification of proppant transport characteristics is highly critical in a sustainable production from hydraulically fractured wells. Previous studies in this regard were limited to smooth (parallel) fracture surfaces to a great extent ignoring the effect of roughness of fractures, which may have significant impact in controlling the permeability of hydraulic fractures in the presences of proppants. In this thesis, effect of surface roughness to fluid flow and transportation/distribution of propping agents were investigated through experimental work. Water and polymer solutions representing typical rheological properties of hydraulic fracturing fluids were injected through transparent models of the fractures of different origin rocks (granite, marble, and limestone) with and without propping agents. The permeability changes due to proppant distribution caused by the roughness of fracture surfaces were quantified and correlated to different fractal characteristics of surface roughness. Qualitative and quantitative analyses were supported by visualization of experiments.

Author : Yu-Shu Wu
Publisher : Gulf Professional Publishing
Page : 568 pages
File Size : 32,5 MB
Release : 2017-11-30
Category : Technology & Engineering
ISBN : 0128129999

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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 : Oliver Chang
Publisher :
Page : pages
File Size : 42,26 MB
Release : 2016
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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 : Yanan Ding
Publisher :
Page : 0 pages
File Size : 48,94 MB
Release : 2021
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In addition to conventional enhanced oil recovery (EOR) technologies, extensive efforts have been made to explore new approaches to sustain the increasing global oil and gas consumption while lowering the operational costs. In recent decades, nanoparticles (NPs) have seen their promising potentials in recovering hydrocarbons from numerous laboratory experiments and field pilots. Also, hydraulic fracturing techniques have unlocked a significant quantity of hydrocarbon resources from unconventional reservoirs. Solid particle transport including NP transport, dispersion, and distribution in hydrocarbon reservoirs, proppant placement within hydraulic fractures, and sand production is critical to the efficient and effective hydrocarbon exploitation. Considering the petrophysical complexity as well as the intricate interactions among particles, fluids, and rock matrix, it is, therefore, an extremely challenging task to accurately predict the associated transport and placement behaviour of solid particles in a hydrocarbon reservoir. Theoretically, a robust and pragmatic method has been developed and validated to analytically determine the dynamic dispersion coefficients for particles flowing in a parallel-plate fracture with instantaneous point source as well as uniform and volumetric line sourcess, in which particle gravity settling effect has been considered. It is found that the point source and the uniform line source are respectively the most and least sensitive to the gravity effect. An increase of particle size larger than its critical value decreases the asymptotical dispersion coefficient for all the source conditions, while gravity settling promotes the dispersion phenomenon during the early-stage of point source condition. Particle-tracking simulations have been performed and validated on polydisperse dense particle transport in a randomly-orientated fracture with spatially variable apertures. The simulated results indicate that the mass breakthrough efficiency of particles and particle plume distribution in a randomly-orientated rough fracture are significantly influenced by different factors when particle gravity settling occurs. In addition, particle attachment consisting of reversible and irreversible adsorptions on an aperture surface is quantified applying the Derjaguin-Landau-Verwey-Overbeek (DLVO) kinetics. With sensitivity analysis performed, the impacts of different factors on particle attachment are found to vary with each other through non-unique patterns. By integrating the Perkins-Kern-Nordgren-Carter (PKN-C) fracture propagation model and the particle tracking algorithm, a novel Eulerian-Lagrangian (E-L) model has been developed and validated to simulate field-scale proppant transport during hydraulic fracturing operations. Such an E-L model incorporates pertinent empirical correlations determined from regressing experimental measurements regarding the proppant settling velocity and the drag/lift forces, which is applicable to both the Newtonian and non- Newtonian fluid conditions. The non-Newtonian fluid is usually found to yield a less "heel-biased" pattern of proppant distribution in a hydraulic fracture, e.g., a larger slurry coverage together with a longer proppant dune, while distinct patterns of the dominant factors are observed and evaluated.