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Yuxuan Liu - One of the best experts on this subject based on the ideXlab platform.
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opening of natural fracture and its effect on Leakoff behavior in fractured gas reservoirs
Journal of Natural Gas Science and Engineering, 2014Co-Authors: Jianchun Guo, Yuxuan LiuAbstract:Abstract Fluid Leakoff is one of the most important issues frequently encountered in hydraulic fracturing, especially in naturally fractured gas reservoirs. Opening of natural fractures will bring about excessive Fluid loss and restrain the propagation of major hydraulic fractures. A mathematical model of natural fracture dominant Leakoff in fractured gas reservoirs has been developed in this paper. Besides, the opening mechanism of natural fractures has been discussed and a new criterion is proposed. Simulation results indicate that open natural fractures have a dominant effect on fracturing Fluid Leakoff. The wider the opening of the natural fractures, the larger the Leakoff of fracturing Fluid. The opening of natural fractures depends not only on stress but also the hydrodynamic size of polymer molecules. Due to the formation of filter-cake, the solid phase in fracturing Fluid, consisting of polymer residues, formation fines and Fluid loss additives plays an important role in the Fluid Leakoff behavior, which could be divided into two regions, solid dominant region and reservoir dominant region. Moreover, the Leakoff behaviors between slick water and cross-linked Fluid are compared for shale gas reservoirs, demonstrating that it is easier for slick water to seep into natural fractures and produce a fracture network.
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A comprehensive model for simulating fracturing Fluid Leakoff in natural fractures
Journal of Natural Gas Science and Engineering, 2014Co-Authors: Jianchun Guo, Yuxuan LiuAbstract:Abstract Fluid Leakoff in natural fractures determines hydraulic fracture geometry, especially in unconventional reservoirs. A mathematical model of fracturing Fluid Leakoff in natural fractures was developed in this study. The model considers more realistic conditions, including fracture fractal features, matrix filtration, stress sensitivity, and temperature. Simulation results indicate that fracture geometry, solid deposition, pressure conditions, and temperature have a significant effect on fracturing Fluid Leakoff. The Leakoff velocity is significantly higher under high fractal dimension. However, Leakoff velocity decreases with time owing to the formation of filter-cake. Pressure also influences Leakoff velocity: with increasing pressure, the Leakoff velocity increases significantly. In addition, the temperature in the natural fracture is almost equal to the formation temperature, which increases Leakoff velocity significantly.
Jianchun Guo - One of the best experts on this subject based on the ideXlab platform.
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opening of natural fracture and its effect on Leakoff behavior in fractured gas reservoirs
Journal of Natural Gas Science and Engineering, 2014Co-Authors: Jianchun Guo, Yuxuan LiuAbstract:Abstract Fluid Leakoff is one of the most important issues frequently encountered in hydraulic fracturing, especially in naturally fractured gas reservoirs. Opening of natural fractures will bring about excessive Fluid loss and restrain the propagation of major hydraulic fractures. A mathematical model of natural fracture dominant Leakoff in fractured gas reservoirs has been developed in this paper. Besides, the opening mechanism of natural fractures has been discussed and a new criterion is proposed. Simulation results indicate that open natural fractures have a dominant effect on fracturing Fluid Leakoff. The wider the opening of the natural fractures, the larger the Leakoff of fracturing Fluid. The opening of natural fractures depends not only on stress but also the hydrodynamic size of polymer molecules. Due to the formation of filter-cake, the solid phase in fracturing Fluid, consisting of polymer residues, formation fines and Fluid loss additives plays an important role in the Fluid Leakoff behavior, which could be divided into two regions, solid dominant region and reservoir dominant region. Moreover, the Leakoff behaviors between slick water and cross-linked Fluid are compared for shale gas reservoirs, demonstrating that it is easier for slick water to seep into natural fractures and produce a fracture network.
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A comprehensive model for simulating fracturing Fluid Leakoff in natural fractures
Journal of Natural Gas Science and Engineering, 2014Co-Authors: Jianchun Guo, Yuxuan LiuAbstract:Abstract Fluid Leakoff in natural fractures determines hydraulic fracture geometry, especially in unconventional reservoirs. A mathematical model of fracturing Fluid Leakoff in natural fractures was developed in this study. The model considers more realistic conditions, including fracture fractal features, matrix filtration, stress sensitivity, and temperature. Simulation results indicate that fracture geometry, solid deposition, pressure conditions, and temperature have a significant effect on fracturing Fluid Leakoff. The Leakoff velocity is significantly higher under high fractal dimension. However, Leakoff velocity decreases with time owing to the formation of filter-cake. Pressure also influences Leakoff velocity: with increasing pressure, the Leakoff velocity increases significantly. In addition, the temperature in the natural fracture is almost equal to the formation temperature, which increases Leakoff velocity significantly.
Michael J. Economides - One of the best experts on this subject based on the ideXlab platform.
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Fluid Leakoff determines hydraulic fracture dimensions: Approximate solution for non-Newtonian fracturing Fluid
International Journal of Engineering Science, 2011Co-Authors: Dmitry N. Mikhailov, Michael J. Economides, Victor N. NikolaevskiyAbstract:Abstract The Leakoff of fracturing Fluid is the main factor that determines the crack useful dimensions (length and width). This idea was introduced into the fracture design by Biot in 1988 and was further expounded upon by Economides and coauthors in a comprehensive design approach in 2002. Here the analytical solution is developed for a real Fluid rheology generalizing the earlier approach of the authors (2007) assuming then a simple Newtonian Fluid used for hydro-fracturing of the formation. The analytical full solution becomes possible if one introduces the special boundary condition for pore pressure spreading in the formation that is modeling the thin growing crack. While the hydraulic fracture is propagating, Fluid flow and associated pressure drops must be accounted for both along the fracture path and perpendicularly, into the formation that is fractured.
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On the problem of Fluid Leakoff during hydraulic fracturing
Transport in Porous Media, 2007Co-Authors: Michael J. Economides, Dmitry N. Mikhailov, Victor N. NikolaevskiyAbstract:While a hydraulic fracture is propagating, Fluid flow and associated pressure drops must be accounted for both along the fracture path and perpendicularly, into the formation that is fractured, because of Fluid Leakoff. The accounting for the Leakoff shows that it is the main factor that determines the crack length. The solved problem is useful for the technology of hydraulic fracturing and a good example of mass transport in a porous medium. To find an effective approach for the solution, the thin crack is represented here as the boundary condition for pore pressure spreading in the formation. Earlier such model was used for heat conduction into a rock massif from a seam under injection of hot water. Of course, the equations have other physical sense and mathematically they are somewhat different. The new plane solution is developed for a linearized form that permits the application of the integral transform. The linearization itself is analogous to the linearization of the natural gas equation using the real gas pseudo-pressure function and where the flux rates are held constant and approximations are introduced only into the time derivatives. The resulting analytical solution includes some integrals that can be calculated numerically. This provides rigorous tracking of the created fracture volume, Leakoff volume and increasing fracture width. The solutions are an advance over existing discreet formulations and allow ready calculations of the resulting fracture dimensions during the injection of the fracturing Fluid.
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Fluid-Leakoff Delineation in High-Permeability Fracturing
Spe Production & Facilities, 1999Co-Authors: Peter P. Valko, Michael J. EconomidesAbstract:Starting from the original concept proposed by Carter, Howard and Fast, this paper reviews the description of fracturing Fluid Leakoff in view of modeling flow in porous media. It is shown how various linear Leakoff models have been developed and why a new, radial Leakoff concept is necessary for high-permeability fracturing, where the injection time is commensurable to the response time of the reservoir. Using Laplace space methods, the new radial Leakoff law is calculated and compared to linear Leakoff. For comparison purposes a calibration test executed in high-permeability formation is interpreted using several approaches, namely: linear Leakoff1bulk Leakoff coefficient; filtercake resistance1linear flow in the formation and finally, filtercake resistance1radial flow in the formation.
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Methodology of Fluid Leakoff Analysis in High-Permeability Fracturing
All Days, 1998Co-Authors: I.n. Ispas, L.k. Britt, Peter P. Valko, D. Tiab, Michael J. EconomidesAbstract:Abstract Hydraulic fracturing in medium and high-permeability reservoirs differs significantly from conventional fracturing, since the optimal placement of proppant requires shorter and wider fractures. The optimal fracture dimensions are achieved by executing a tip screenout design technique. Successful application of this technique assumes realistic description of the Fluid Leakoff process. Fracture calibration treatments (minifracs) have been used to identify Leakoff characteristics. In addition to the application of data obtained from such tests (i.e. incorporation into the fracture job design) an increasingly important use is to obtain reservoir engineering parameters, such as formation permeability. This paper is based on two methods, used for the determination of the Leakoff parameters from the pressure fall-off stage of a calibration treatment. The first method is the well known technology, which we have called the Nolte-Shlyapobersky method to determine an overall Leakoff coefficient. The second method is a modified form of the Mayerhofer et al technique, which attempts to de-couple the two main elements of the Leakoff process: the filtercake resistance and the transient flow in the formation. For other methods concentrating more on the pressure fall-off after the fracture closes see References 3 and 5. Field examples will be used to demonstrate the basic steps of the presented methodology. Emphasis is on limitations and possible pitfalls with suggested remedies. A detailed sensitivity analysis is presented which underlines the data quality required to determine reservoir and treatment parameters with any accuracy. P. 493
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Fluid Leakoff Delineation in High-Permeability Fracturing
All Days, 1997Co-Authors: Peter P. Valko, Michael J. EconomidesAbstract:Abstract Starting from the original concept proposed by Carter, Howard and Fast, this paper reviews the description of fracturing Fluid Leakoff in view of modeling flow in porous media. It is shown how various linear Leakoff models have been developed and why a new, radial Leakoff concept is necessary for high-permeability fracturing, where the injection time is commensurable to the response time of the reservoir. Using Laplace space methods the radial Leakoff law is calculated and compared to linear Leakoff. For comparison purposes a calibration test executed in high-permeability formation is interpreted using several approaches, namely: linear Leakoff + bulk Leakoff coefficient; filtercake resistance + linear flow in the formation and finally, filtercake resistance + radial flow in the formation. Introduction The polymer content of the fracturing Fluid is partly intended to impede the loss of Fluid. The phenomenon is envisioned as a continuous build-up of a thin layer (the filtercake) which manifests a resistance to flow through the fracture face. For one of the latest reviews see McGowen and Vitthal. During fracturing, the actual Leakoff is determined by a coupled system, of which the filtercake is only one element. The other two important elements are the region invaded by the polymer and/or filtrate and the bulk reservoir itself, containing the original (slightly compressible) reservoir Fluid. This work concentrates on the aspect of Fluid Leakoff which is connected with the bulk reservoir. The methods used are borrowed from the literature on flow in porous media. As usual, we assume that the two wings of a vertical fracture are identical. For modeling purposes we will deal only with one wing. All our variables, including injection rate, i, injected volume, Vi, fracture volume, V refer to one wing. (If we want to refer to total injection rate, we write 2i.) By the fracture surface, A we mean the area of one face of one wing. All these variables may refer to a given time, t during the treatment. It is important to make a clear distinction between the values of the above variables at any time, t, and at the end of pumping, i.e, at time te. We will use the subscript e if we wish to emphasize that a given value corresponds to the end of pumping. Figure 1 shows the basic notation on an example of radial fracture. Fluid efficiency, is defined as the fraction of the Fluid remaining in the fracture: = V/Vi. As any other state variable it might vary with time. The average width, w, is defined by the relation V = Aw. The difference of injected and contained volume is the lost volume. The Leakoff rate, qL defined here as the volume leaving one wing in unit time and can be calculated from an appropriate Leakoff model. Often we assume that the fracture is contained in the permeable layer. Then the whole fracture surface takes part in the Leakoff process. If we know the height of the permeable layer, hp, we can be more rigorous in taking into account only the actual Leakoff surface. Figure 2 shows how we calculate the ratio of the Leakoff surface to the total surface for radial geometry. The ratio, rp, is unity for a fracture contained perfectly in the permeable layer and is less than unity if the fracture grows out from the permeable layer. In the case of rectangular fracture shape rp is the ratio of the "net" height to the "gross" height. The factor is easily incorporated into the derivations, but in the following we do not show rp to increase the readability of the equations. Previous work Carter Leakoff Model A fruitful approximation dating back to Carter, Howard and Fast considers the combined effect of the different phenomena as a material property. According to this concept, the Leakoff velocity, uL, is given by the Carter equation: (1) P. 135^
Victor N. Nikolaevskiy - One of the best experts on this subject based on the ideXlab platform.
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Fluid Leakoff determines hydraulic fracture dimensions: Approximate solution for non-Newtonian fracturing Fluid
International Journal of Engineering Science, 2011Co-Authors: Dmitry N. Mikhailov, Michael J. Economides, Victor N. NikolaevskiyAbstract:Abstract The Leakoff of fracturing Fluid is the main factor that determines the crack useful dimensions (length and width). This idea was introduced into the fracture design by Biot in 1988 and was further expounded upon by Economides and coauthors in a comprehensive design approach in 2002. Here the analytical solution is developed for a real Fluid rheology generalizing the earlier approach of the authors (2007) assuming then a simple Newtonian Fluid used for hydro-fracturing of the formation. The analytical full solution becomes possible if one introduces the special boundary condition for pore pressure spreading in the formation that is modeling the thin growing crack. While the hydraulic fracture is propagating, Fluid flow and associated pressure drops must be accounted for both along the fracture path and perpendicularly, into the formation that is fractured.
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On the problem of Fluid Leakoff during hydraulic fracturing
Transport in Porous Media, 2007Co-Authors: Michael J. Economides, Dmitry N. Mikhailov, Victor N. NikolaevskiyAbstract:While a hydraulic fracture is propagating, Fluid flow and associated pressure drops must be accounted for both along the fracture path and perpendicularly, into the formation that is fractured, because of Fluid Leakoff. The accounting for the Leakoff shows that it is the main factor that determines the crack length. The solved problem is useful for the technology of hydraulic fracturing and a good example of mass transport in a porous medium. To find an effective approach for the solution, the thin crack is represented here as the boundary condition for pore pressure spreading in the formation. Earlier such model was used for heat conduction into a rock massif from a seam under injection of hot water. Of course, the equations have other physical sense and mathematically they are somewhat different. The new plane solution is developed for a linearized form that permits the application of the integral transform. The linearization itself is analogous to the linearization of the natural gas equation using the real gas pseudo-pressure function and where the flux rates are held constant and approximations are introduced only into the time derivatives. The resulting analytical solution includes some integrals that can be calculated numerically. This provides rigorous tracking of the created fracture volume, Leakoff volume and increasing fracture width. The solutions are an advance over existing discreet formulations and allow ready calculations of the resulting fracture dimensions during the injection of the fracturing Fluid.
M.t. Satyagraha - One of the best experts on this subject based on the ideXlab platform.
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Frac/Pack Modeling for High-Permeability Viscous Oil Reservoirs of the Duri Field, Indonesia
SPE Production & Facilities, 2001Co-Authors: Y. Fan, D.e. White, A. Aimar, M.t. SatyagrahaAbstract:Summary This paper documents frac/pack completions conducted in the Duri field for the shallow, highly permeable, and unconsolidated formations containing heavy viscous crude. A treatment design model with a pressure-dependent Leakoff option is presented to investigate effects of fracturing Fluids, reservoir mobility, and Young's modulus on the Fluid Leakoff, net pressure, and fracture propagation. Field treatment data are analyzed with the provided model, and several factors that have significant influence on treatment results are discussed. Introduction Duri field is located in the eastern coastal plain of central Sumatra, approximately 70 miles northwest of the city of Pekanbaru. Oil is produced from a structurally trapped Miocene sandstone at depths between 200 and 900 ft. Duri field encompasses 30,000 acres and holds an estimated 5.4 billion bbl of original oil in place. It is the second largest oil field in Indonesia in terms of original oil in place. Rindu and Pertama/Kedua sands are two major producing intervals in the Duri reservoir where the combined pay thickness averages 250 ft and is located at depths between 250 and 700 ft. The formation has initial oil saturation of about 55%, average porosity of 34%, and air permeability in the pay formation ranging from 200 to 5,000 md. Currently, reservoir pore pressure is between 85 and 180 psi. The initial reservoir temperature is 92°F. The crude gravity is about 21°API (400 to 900 cp at the initial reservoir conditions). More information on typical reservoir properties is given in Table 1. In Duri, frac/pack became an attractive completion option owing to potential problems of formation damage and sand production. The first frac/pack pilot for the Duri field was conducted in 1996 for the Rindu Vertical Expansion Project.1 Some 500 wells of the Duri field were treated with cased-hole frac/pack techniques in 1999. Frac/pack techniques were widely implemented as a simultaneous solution for both sand control and production problems in highly permeable and unconsolidated formations.2–6 However, field experience indicates that some treatments do not perform as designed because of failure to achieve either tip screenout (TSO) or uncontrollable pressure growth. One of the challenges in treatment design and implementation is to accurately predict Fluid Leakoff in order to terminate fracture propagation at the desirable fracture length.7,8 However, prediction of the Fluid Leakoff is difficult because viscous Fluids invade the formation and subsequently influence formation rock and Fluid properties.9 Recent experiments also showed that spurt loss is a dominant Leakoff phenomenon when the formation permeability is over 400 md.10,11 Therefore, the traditional model that does not account for spurt loss and fracture pressure is inadequate for modeling frac/pack applications in high-permeability formations.12–14 Recently, Fan and Economides introduced a Leakoff model that predicts the transient flow of polymer solution displacing a reservoir Fluid with a moving interface.15 The Leakoff is pressure-dependent, with consideration of the pressure profile from the fracture face to the reservoir. In this paper, a frac/pack model with a pressure-dependent Leakoff option is presented to study the interactions among the Fluid Leakoff, net pressure, and fracture dimensions for the Duri reservoir. The effects of Fluid viscosity, reservoir mobility, and elastic modulus on the Fluid efficiency and fracture net pressure are discussed. Field data are analyzed to demonstrate the model and its applications. Several aspects of treatment designs concerning selection of fracturing Fluids, proppants, and treatment size are also discussed in this paper. Well-Completion Procedure in the Duri Field The bottomhole assembly for frac/pack treatment used in the Duri field is presented in Fig. 1. The completion event sequence is as follows.Rig-up and perforate intervals, with 180 phasing, 6 shots/ft, and 1.08-in.-diameter perforations.Wash perforations with KCl water between isolation cups.Run in hole with 6 5/8-in. wire wrap screen liner.Set modified fracture crossover with stinger.Perform minifracture on target intervals.Pump the frac/pack treatment per design.Pull fracture assembly out of hole.Set lead seal and place on production.
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Fluid Leakoff and Net Pressure Behavior of Frac&Pack in High-Permeability Viscous Oil Reservoirs of the Duri Field, Indonesia
All Days, 2000Co-Authors: Y. Fan, D.e. White, A. Aimar, M.t. SatyagrahaAbstract:Frac&pack has become a preferred completion method for the Duri field in Indonesia, where the reservoir is shallow, highly permeable and unconsolidated containing heavy viscous crude. This paper presents simulation of Fluid Leakoff and net pressure behavior for the frac&pack treatments in the Duri field. Several issues concerning selection of fracturing Fluids and proppant, fracture dimensions and treatment designs are also discussed in the paper. A pressure-dependent Leakoff model that is based on a transient flow of a polymer solution displacing a reservoir Fluid is presented and coupled with a fracture mechanics model to investigate the interactions among the Leakoff, net pressure and created fracture dimensions during different stages of frac&pack treatments. The results indicate that the Leakoff is controlled by reservoir Fluid viscosity and is dependent upon the rock-mechanics properties and the mobility ratio between the invaded solution and the reservoir Fluid. In the absence of filtercake, the traditional Leakoff notion using the concept of a constant Leakoff coefficient fails to capture the transient behavior of polymer invasion and reservoir Fluid compression. Because of high sensitivity to Leakoff and the rock-mechanics properties, the net pressure behavior is also quite different from the one anticipated. For the typical formation with an elastic modulus of 50,000 to 100,000 psi in the Duri field, the net pressure is in a range of 20-40 psi during fracture propagation, The simulation also indicates thit the net pressure over 200 psi would result in desirable fracture widths for Duri field applications.
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Fluid Leakoff and net pressure behavior of frac pack in high permeability viscous oil reservoirs of the duri field indonesia
SPE International Symposium on Formation Damage Control, 2000Co-Authors: Y. Fan, D.e. White, A. Aimar, M.t. SatyagrahaAbstract:Frac&pack has become a preferred completion method for the Duri field in Indonesia, where the reservoir is shallow, highly permeable and unconsolidated containing heavy viscous crude. This paper presents simulation of Fluid Leakoff and net pressure behavior for the frac&pack treatments in the Duri field. Several issues concerning selection of fracturing Fluids and proppant, fracture dimensions and treatment designs are also discussed in the paper. A pressure-dependent Leakoff model that is based on a transient flow of a polymer solution displacing a reservoir Fluid is presented and coupled with a fracture mechanics model to investigate the interactions among the Leakoff, net pressure and created fracture dimensions during different stages of frac&pack treatments. The results indicate that the Leakoff is controlled by reservoir Fluid viscosity and is dependent upon the rock-mechanics properties and the mobility ratio between the invaded solution and the reservoir Fluid. In the absence of filtercake, the traditional Leakoff notion using the concept of a constant Leakoff coefficient fails to capture the transient behavior of polymer invasion and reservoir Fluid compression. Because of high sensitivity to Leakoff and the rock-mechanics properties, the net pressure behavior is also quite different from the one anticipated. For the typical formation with an elastic modulus of 50,000 to 100,000 psi in the Duri field, the net pressure is in a range of 20-40 psi during fracture propagation, The simulation also indicates thit the net pressure over 200 psi would result in desirable fracture widths for Duri field applications.