Impact of water and nitrogen fracturing fluids on fracturing initiation pressure and flow pattern in anisotropic shale reservoirs

Hydraulic fracturing with oriented perforations is an effective technology for reservoir stimulation for gas development in shale reservoirs. However, fracture reorientation during fracturing operation can affect the fracture conductivity and hinder the effective production of shale gas. In the present work, a numerical simulation model for investigating fracture reorientation during fracturing with oriented perforations was established, and it was verified to be suitable for all investigations in this paper. Based on this, factors (such as injection rate and fluid viscosity) affecting both of initiation and reorientation of the hydraulically induced fractures were investigated. The investigation results show that the fluid viscosity has little effect on initiation pressure of hydraulically induced fracture during fracturing operation, and the initiation pressure is mainly affected by perforation azimuth, injection rate and the stress difference. Moreover, the investigation results also show that perforation azimuth and difference between two horizontal principle stresses are the two most important factors affecting fracture reorientation. Based on the investigation results, the optimization of fracturing design can be achieved by adjusting some controllable factors. However, the regret is that the research object herein is a single fracture, and the interaction between fractures during fracturing operation needs to be further explored.

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Design and Development of CaCO3 Nanoparticles Enhanced Fracturing Fluids for Effective Control of Leak-off During Hydraulic Fracturing of Shale Reservoirs

Nanotechnology ◽

10.1088/1361-6528/ac074f ◽

2021 ◽

Author(s):

Ying Zhong ◽

Hao Zhang ◽

Jiang Zhang

Keyword(s):

Hydraulic Fracturing ◽

Effective Control ◽

Design And Development ◽

Caco3 Nanoparticles ◽

Fracturing Fluids ◽

Shale Reservoirs

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The Influence of Bedding Planes and Permeability Coefficient on Fracture Propagation of Horizontal Wells in Stratification Shale Reservoirs

Geofluids ◽

10.1155/2020/1642142 ◽

2020 ◽

Vol 2020 ◽

pp. 1-19

Author(s):

Yuepeng Wang ◽

Xiangjun Liu ◽

Lixi Liang ◽

Jian Xiong

Keyword(s):

Permeability Coefficient ◽

In Situ Stress ◽

Stress Difference ◽

Strength Parameters ◽

Breakdown Pressure ◽

Permeability Coefficients ◽

Bedding Planes ◽

Initiation Pressure ◽

Shale Reservoirs

The complexity of hydraulic fractures (HF) significantly affects the success of reservoir reconstruction. The existence of a bedding plane (BP) in shale impacts the extension of a fracture. For shale reservoirs, in order to investigate the interaction mechanisms of HF and BPs under the action of coupled stress-flow, we simulate the processes of hydraulic fracturing under different conditions, such as the stress difference, permeability coefficients, BP angles, BP spacing, and BP mechanical properties using the rock failure process analysis code (RFPA2D-Flow). Simulation results showed that HF spread outward around the borehole, while the permeability coefficient is uniformly distributed at the model without a BP or stress difference. The HF of the formation without a BP presented a pinnate distribution pattern, and the main direction of the extension is affected by both the ground stress and the permeability coefficient. When there is no stress difference in the model, the fracture extends along the direction of the larger permeability coefficient. In this study, the in situ stress has a greater influence on the extension direction of the main fracture when using the model with stress differences of 6 MPa. As the BP angle increases, the propagation of fractures gradually deviates from the BP direction. The initiation pressure and total breakdown pressure of the models at low permeability coefficients are higher than those under high permeability coefficients. In addition, the initiation pressure and total breakdown pressure of the models are also different. The larger the BP spacing, the higher the compressive strength of the BP, and a larger reduction ratio (the ratio of the strength parameters of the BP to the strength parameters of the matrix) leads to a smaller impact of the BP on fracture initiation and propagation. The elastic modulus has no effect on the failure mode of the model. When HF make contact with the BP, they tend to extend along the BP. Under the same in situ stress condition, the presence of a BP makes the morphology of HF more complex during the process of propagation, which makes it easier to achieve the purpose of stimulated reservoir volume (SRV) fracturing and increased production.

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Laboratory Investigation of Fracture Initiation Pressure and Orientation

Society of Petroleum Engineers Journal ◽

10.2118/6087-pa ◽

1979 ◽

Vol 19 (02) ◽

pp. 129-144 ◽

Cited By ~ 25

Author(s):

W.L. Medlin ◽

L. Masse

Keyword(s):

Hydraulic Fracture ◽

Field Data ◽

Laboratory Experiments ◽

Fracture Initiation ◽

Stress Conditions ◽

Elastic Behavior ◽

Fracturing Fluids ◽

Initiation Pressure ◽

Cylindrical Cavities ◽

Griffith Theory

Abstract The mechanics of hydraulic fracture initiation have been investigated by comparing laboratory experiments with theoretical predictions based on poro-elastic behavior. Experiments were conducted poro-elastic behavior. Experiments were conducted with 4-in. (10-cm) diameter cores containing spherical and cylindrical cavities and loaded in a triaxial cell under variable confining pressure, end load, and pore pressure. Experimental results agreed with theory for nonpenetrating fracturing fluid for limited ranges of hydrostatic confining stresses for four kinds of limestone rock. With penetrating fracturing fluids, the theory was penetrating fracturing fluids, the theory was confirmed only partially. Under nonhydrostatic stress conditions, reproducibility of measurements was too poor to evaluate the theory. Fracture orientation was controlled predominantly by stress conditions and cavity geometry. Notching of cylindrical cavities failed through notch extension only if the notch depth exceeded the value predicted approximately by a simple Griffith theory predicted approximately by a simple Griffith theory equation. Field applications of all results are discussed. Introduction This paper describes a combined theoretical/ experimental investigation of the mechanics of hydraulic fracture initiation. We considered fracture initiation pressure, fracture orientation, and mode of failure for various stress conditions and wellbore geometries. Our intention has been to consider theory applicable for both field and laboratory conditions, to test this theory with laboratory experiments, and to apply the results to interpretation of field data. The laboratory experiments were designed not to duplicate field conditions so much as to provide a critical test of the theory. Some field data are examined, but it is impractical to learn much about fracture initiation from field experiments because of the limited number of quantities that can be measured. The theory presented here is more a generalization of earlier work than a development of new theory. It provides a completely general treatment of fracture initiation in spherical and cylindrical cavities for poro-elastic materials. An extension of this theory poro-elastic materials. An extension of this theory to porous materials with nonelastic behavior already has been developed by Biot and will be referred to later. We begin by presenting theory for fracture initiation in spherical and cylindrical cavities. The theoretical results are followed by descriptions of laboratory experiments that test the equations for failure pressure in these geometries under various stress conditions, using penetrating and nonpentrating fracturing fluids. The effects of notching in cylindrical cavities then are considered, and a simple model based on Griffith crack theory is developed to explain experimental results. Field applications of all results then are discussed in detail. THEORY OF FRACTURE INITIATION The theory of hydraulic fracture initiation in rock materials has been treated in successive degrees of refinement. Cases of interest are hollow sphere and long hollow cylinder geometry with penetrating and nonpenetrating fracturing fluids. penetrating and nonpenetrating fracturing fluids. Refs. 1 through 7 cover various parts of the overall picture; Rice and Cleary give the most complete picture; Rice and Cleary give the most complete analysis. We present here an independent analysis based on Biot's theory for fluid saturated porous solids. Our analysis adds little that is new to the basic literature of fracture initiation theory. It is presented mainly to provide a way to analyze presented mainly to provide a way to analyze scaling effects between field results and our laboratory experiments. We start with Biot's stress-strain relations for a fluid saturated porous solid: (1) SPEJ P. 129

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The Calculation of Apparent Permeability for Shale Gas Considering Adsorption and Flow Patterns

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1073-1076.2305 ◽

2014 ◽

Vol 1073-1076 ◽

pp. 2305-2309

Author(s):

Wen Xu She ◽

Jun Bin Chen ◽

Jie Zhang ◽

Bo Wei ◽

Han Qing Wang ◽

...

Keyword(s):

Pore Size ◽

Flow Pattern ◽

Shale Gas ◽

Knudsen Diffusion ◽

Slip Flow ◽

Great Influence ◽

Flow Patterns ◽

Apparent Permeability ◽

Longmaxi Formation ◽

Shale Reservoirs

The flow pattern is unique in a certain range of pore size divided by the Knudsen number. In order to characterize permeability of nanopore in shale gas reservoir more accurately, the formulas of nanopore permeability are put forward considering the influence of adsorption gas and flow patterns. After the calculated results were compared and analyzed, the conclusions are obtained as follows: (1) Pore size is the main factor to determine the flow pattern; (2) There are three main flow pattern in the nanopore of Longmaxi formation shale reservoirs, slip flow, Fick diffusion and transition diffusion, meanwhile Darcy percolation and Knudsen diffusion do not exist; (3) Flow pattern has great influence on apparent permeability and adsorption has a greater impact in a high pressure condition (greater than 20MPa).

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Discrete Element Analysis for Hydraulic Fracture Propagations in Laminated Reservoirs with Complex Initial Joint Properties

Geofluids ◽

10.1155/2019/3958583 ◽

2019 ◽

Vol 2019 ◽

pp. 1-23 ◽

Cited By ~ 4

Author(s):

Fakai Dou ◽

J. G. Wang ◽

Huimin Wang ◽

Bowen Hu ◽

Chengxuan Li

Keyword(s):

Mechanical Properties ◽

Hydraulic Fracture ◽

Fracture Morphology ◽

Fracture Network ◽

In Situ Stress ◽

Element Analysis ◽

Approach Angle ◽

Bedding Planes ◽

Fracturing Fluids ◽

Shale Reservoirs

Previous studies on hydraulic fracturing mainly focus on the effects of the in-situ stress state, permeability, fracturing fluids, and approach angle in homogeneous rocks, but the impacts of joint mechanical properties in laminated shale reservoirs on the propagation and formation of the fracture network are still unclear. In this study, a coupled fluid-mechanical model was developed to investigate the impacts of joint mechanical properties on hydraulic fracture propagation. Then, this model was validated with Blanton’s criterion and some experimental observations on fracture morphology. Finally, a series of numerical simulations were conducted to comparatively analyze the impacts of joint mechanical properties on the total crack number, the percentage and distribution of each fracture type, the process of crack propagation, and the final fracture morphology. Numerical results show that the cracking behaviors induced by joint mechanical properties vary with the approach angle. Joint strength has a significant influence on the generation of matrix tensile cracks. The tensile-to-shear strength ratio plays an even more important role in the shear slips of bedding planes and is conducive to the formation of complex fracture morphology.

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Stimuli-responsive/rheoreversible hydraulic fracturing fluids as a greener alternative to support geothermal and fossil energy production

Green Chemistry ◽

10.1039/c4gc01917b ◽

2015 ◽

Vol 17 (5) ◽

pp. 2799-2812 ◽

Cited By ~ 30

Author(s):

H. B. Jung ◽

K. C. Carroll ◽

S. Kabilan ◽

D. J. Heldebrant ◽

D. Hoyt ◽

...

Keyword(s):

Hydraulic Fracturing ◽

Igneous Rock ◽

Volume Expansion ◽

Energy Production ◽

Fracture Initiation ◽

Stimuli Responsive ◽

Fossil Energy ◽

Fracturing Fluids ◽

Initiation Pressure

A reversible CO2-triggered volume expansion significantly lowers the fracture initiation pressure in highly impermeable igneous rock as compared to conventional fracturing fluids.

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Morphology and development of flow-pattern defect with extended nonagitated Secco etching

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100172073 ◽

1994 ◽

Vol 52 ◽

pp. 868-869

Author(s):

Y. Pan

Keyword(s):

Flow Pattern ◽

Silicon Crystal ◽

Gate Oxide ◽

Crystal Growth Rate ◽

Etch Depth ◽

Force Microscopy ◽

Etch Pit ◽

Float Zone ◽

Atomic Force ◽

Multiple Step

The D defect, which causes the degradation of gate oxide integrities (GOI), can be revealed by Secco etching as flow pattern defect (FPD) in both float zone (FZ) and Czochralski (Cz) silicon crystal or as crystal originated particles (COP) by a multiple-step SC-1 cleaning process. By decreasing the crystal growth rate or high temperature annealing, the FPD density can be reduced, while the D defectsize increased. During the etching, the FPD surface density and etch pit size (FPD #1) increased withthe etch depth, while the wedge shaped contours do not change their positions and curvatures (FIG.l).In this paper, with atomic force microscopy (AFM), a simple model for FPD morphology by non-crystallographic preferential etching, such as Secco etching, was established.One sample wafer (FPD #2) was Secco etched with surface removed by 4 μm (FIG.2). The cross section view shows the FPD has a circular saucer pit and the wedge contours are actually the side surfaces of a terrace structure with very small slopes. Note that the scale in z direction is purposely enhanced in the AFM images. The pit dimensions are listed in TABLE 1.

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