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

Geofluids ◽  
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.

Optimization of In-Stage Diversion To Promote Uniform Planar Multifracture Propagation: A Numerical Study

SPE Journal ◽  
2020 ◽  
Vol 25 (06) ◽  
pp. 3091-3110
Author(s):  
Ming Chen ◽  
Shicheng Zhang ◽  
Tong Zhou ◽  
Xinfang Ma ◽  
Yushi Zou
Keyword(s):  
Numerical Study ◽  
High Stress ◽  
In Situ Stress ◽  
Stress Difference ◽  
Multiple Fractures ◽  
Stress Shadow ◽  
Limited Entry ◽  
Fully Coupled ◽  
Flux Redistribution

Summary Creating uniform multiple fractures is a challenging task due to reservoir heterogeneity and stress shadow. Limited-entry perforation and in-stage diversion are commonly used to improve multifracture treatments. Many studies have investigated the mechanism of limited-entry perforation for multifracture treatments, but relatively few have focused on the in-stage diversion process. The design of in-stage diversion is usually through trial and error because of the lack of a simulator. In this study, we present a fully coupled planar 2D multifracture model for simulating the in-stage diversion process. The objective is to evaluate flux redistribution after diversion and optimize the dosage of diverters and diversion timing under different in-stage in-situ stress difference. Our model considers ball sealer allocation and solves flux redistribution after diversion through a fully coupled multifracture model. A supertimestepping explicit algorithm is adopted to solve the solid/fluid coupling equations efficiently. Multifracture fronts are captured by using tip asymptotes and an adaptive time-marching approach. The modeling results are validated against analytical solutions for a plane-strain Khristianovic-Geertsma de Klerk (KGD) model. A series of numerical simulations are conducted to investigate the multifracture growth under different in-stage diversion operations. Parametric studies reveal that the in-stage in-situ stress difference is a critical parameter for diversion designs. When the in-situ stress difference is larger than 2 MPa, the fracture in the high-stress zone can hardly be initiated before diversion for a general fracturing design. More ball sealers are required for the formations with higher in-stage in-situ stress difference. The diverting time should be earlier for formations with high in-stage stress differences as well. Adding more perforation holes in the zone with higher in-situ stress is recommended to achieve even flux distribution. The results of this study can help understand the multifracture growth mechanism during in-stage diversion and optimize the diversion design timely.

scholarly journals Numerical Investigation of the Impacts of Borehole Breakouts on Breakdown Pressure

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 888 ◽  
Author(s):  
Hua Zhang ◽  
Shunde Yin ◽  
Bernt Aadnoy
Keyword(s):  
Hydraulic Fracturing ◽  
Shear Failure ◽  
In Situ Stress ◽  
Test Results ◽  
Breakdown Pressure ◽  
Borehole Breakout ◽  
Borehole Breakouts ◽  
The Difference ◽  
Mud Pressure

Borehole breakouts appear in drilling and production operations when rock subjected to in situ stress experiences shear failure. However, if a borehole breakout occurs, the boundary of the borehole is no longer circular and the stress distribution around it is different. So, the interpretation of the hydraulic fracturing test results based on the Kirsch solution may not be valid. Therefore, it is important to investigate the factors that may affect the correct interpretation of the breakdown pressure in a hydraulic fracturing test for a borehole that had breakouts. In this paper, two steps are taken to implement this investigation. First, sets of finite element modeling provide sets of data on borehole breakout measures. Second, for a given measure of borehole breakouts, according to the linear relation between the mud pressure and the stress on the borehole wall, the breakdown pressure considering the borehole breakouts is acquired by applying different mud pressure in the model. Results show the difference between the breakdown pressure of a circular borehole and that of borehole that had breakouts could be as large as 82% in some situations.

scholarly journals Numerical Investigation of Injection-Induced Fracture Propagation in Brittle Rocks with Two Injection Wells by a Modified Fluid-Mechanical Coupling Model

Energies ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4718
Author(s):  
Song Wang ◽  
Jian Zhou ◽  
Luqing Zhang ◽  
Zhenhua Han
Keyword(s):  
Fracture Propagation ◽  
In Situ Stress ◽  
Hydraulic Fractures ◽  
Fracture Networks ◽  
Breakdown Pressure ◽  
Injection Wells ◽  
Mechanical Coupling ◽  
Stress Shadow ◽  
Well Spacing

Hydraulic fracturing is a key technical means for stimulating tight and low permeability reservoirs to improve the production, which is widely employed in the development of unconventional energy resources, including shale gas, shale oil, gas hydrate, and dry hot rock. Although significant progress has been made in the simulation of fracturing a single well using two-dimensional Particle Flow Code (PFC2D), the understanding of the multi-well hydraulic fracturing characteristics is still limited. Exploring the mechanisms of fluid-driven fracture initiation, propagation and interaction under multi-well fracturing conditions is of great theoretical significance for creating complex fracture networks in the reservoir. In this study, a series of two-well fracturing simulations by a modified fluid-mechanical coupling algorithm were conducted to systematically investigate the effects of injection sequence and well spacing on breakdown pressure, fracture propagation and stress shadow. The results show that both injection sequence and well spacing make little difference on breakdown pressure but have huge impacts on fracture propagation pressure. Especially under hydrostatic pressure conditions, simultaneous injection and small well spacing increase the pore pressure between two injection wells and reduce the effective stress of rock to achieve lower fracture propagation pressure. The injection sequence can change the propagation direction of hydraulic fractures. When the in-situ stress is hydrostatic pressure, simultaneous injection compels the fractures to deflect and tend to propagate horizontally, which promotes the formation of complex fracture networks between two injection wells. When the maximum in-situ stress is in the horizontal direction, asynchronous injection is more conducive to the parallel propagation of multiple hydraulic fractures. Nevertheless, excessively small or large well spacing reduces the number of fracture branches in fracture networks. In addition, the stress shadow effect is found to be sensitive to both injection sequence and well spacing.

Methodology for predicting reservoir breakdown pressure and fracture opening pressure in low-permeability reservoirs based on an in situ stress simulation

2018 ◽  
Vol 246 ◽  
pp. 222-232 ◽  
Author(s):  
Jingshou Liu ◽  
Wenlong Ding ◽  
Yang Gu ◽  
Zikang Xiao ◽  
Junsheng Dai ◽  
...  
Keyword(s):  
In Situ Stress ◽  
Low Permeability ◽  
Opening Pressure ◽  
Breakdown Pressure ◽  
Fracture Opening ◽  
Low Permeability Reservoirs ◽  
Stress Simulation

Design and performance evaluation of vertical shafts: rational shaft design method and verification of design method

1988 ◽  
Vol 25 (2) ◽  
pp. 320-337 ◽  
Author(s):  
R. C. K. Wong ◽  
P. K. Kaiser
Keyword(s):  
Design Method ◽  
Three Dimensional ◽  
Earth Pressure ◽  
In Situ Stress ◽  
Cohesive Soils ◽  
Strength Parameters ◽  
Yield Zone ◽  
Ground Deformations ◽  
And Performance

Ground deformations around axisymmetric shafts cannot be determined with the design approaches currently available, which are mostly based on plasticity methods. The convergence–confinement method (usually applied to tunnels), with consideration of gravitational effects and the three-dimensional conditions near a shaft, is proposed as a tool to predict formation pressure on a shaft and radial ground displacements. It is shown that the behaviour of a shaft is governed by (1) the mode of yield initiation dominated by the in situ stress state and the soil strength parameters and (2) the extent of the yield zone that develops if wall displacements are allowed to occur during construction.Closed-form solutions are presented to approximate the pressure–displacement relationship for cohesionless and cohesive soils. Results from this approach compare well with those obtained by finite element analyses. The conventional design methods that provide the minimum support pressures required to maintain stability are not conservative. These pressures are generally less than those actually encountered if ground movements during construction are restricted with good ground control. Key words: shaft, design method, support, interaction, yielding, stress, displacement, earth pressure, arching.

Micromechanical Model for Simulating Hydraulic Fractures of Rock

2005 ◽  
Vol 9 ◽  
pp. 127-136 ◽  
Author(s):  
Tian Hong Yang ◽  
Leslie George Tham ◽  
S.Y. Wang ◽  
Wan Cheng Zhu ◽  
Lian Chong Li ◽  
...  
Keyword(s):  
Numerical Model ◽  
Stress Ratio ◽  
Failure Process ◽  
Micromechanical Model ◽  
In Situ Stress ◽  
Hydraulic Fractures ◽  
Breakdown Pressure ◽  
Heterogeneous Rocks ◽  
Material Homogeneity

A numerical model is developed to study hydraulic fracturing in permeable and heterogeneous rocks, coupling with the flow and failure process. The effects of flow and in-situ stress ratio on fracture, material homogeneity and breakdown pressure are specifically studied.

Comprehensive Analysis of Borehole Stability with Temperature, Swelling, and Pore Pressure Change for Layered and Orthotropic Formations

2021 ◽  
Author(s):  
Takuma Kaneshima ◽  
Fuqiao Bai ◽  
Nobuo Morita
Keyword(s):  
Pore Pressure ◽  
Numerical Models ◽  
Pressure Change ◽  
In Situ Stress ◽  
Borehole Stability ◽  
Bedding Planes ◽  
Layered Formation ◽  
Side Track ◽  
Failure Theories

Abstract Borehole stability depends on various parameters such as rock strength, rock deformations, in-situ stress, borehole trajectory, shale swelling, pore pressure change due to osmosis, overbalance mud weight and temperature. The objective of this work is to construct analytical and numerical equations to predict borehole failure including all these parameters, and to comprehensively propose a methodology to improve the borehole stability. Analytical solutions are developed for inclined wells with respect to in-situ stress, shale swelling, pore pressure change due to osmosis, overbalance mud weight and temperature. A numerical model is developed for 3D inclined wells with orthotropic formation and layered formation. Using the analytical and the numerical models, stress state around inclined wells are evaluated. The breakout angle is predicted based on Mohr-Coulomb, Mogi, Lade and Drucker-Prager failure theories. Polar diagrams of mud weights are compared to judge the effect of each parameter and the magnitude predicted by the different failure theories. Shale swelling and pore pressure change due to osmosis are the most difficult to estimate among above-mentioned parameters. The laboratory measured swelling of cores obtained from various formations showed that the magnitude to induce breakouts caused by swelling was the largest comparing with other parameters. Therefore, when shale stability problems occur, we need to estimate the magnitude of shale swelling and osmosis due to water potential difference. Then, to overcome the shale stability problem, we evaluated the sensitivity of human controllable parameters on borehole stability. The parameters which can be controlled by drilling engineers are overbalance, type of mud, borehole temperature and borehole trajectory. If the shale swelling is small, the borehole stability is improved by the mud weight. However, from the swelling tests from the cores of Nankai-Trough, we estimated unless we used a swelling inhibitor to reduce the swelling less than 0.1%, the well was not possible to drill through. Actually, the well was abandoned due to instability after trying side track several times. Unlike previous works, this paper uses all important parameters (swelling, temperature, pore pressure, orthotropic formation, layered formation) to estimate the stresses around inclined wells with the same formation conditions for quantitative analysis. Failure analysis include Mohr, Mogi, Lade and Drucker-Prager. Finally, the polar diagrams of critical mud weight are used to judge whether we can choose well trajectory, orientation with respect to bedding planes, mud weight, shale inhibitor, and temperature to stabilize the borehole.

scholarly journals Mathematical Modelling of Fault Reactivation Induced by Water Injection

Minerals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 282 ◽  
Author(s):  
Thanh Son Nguyen ◽  
Yves Guglielmi ◽  
Bastian Graupner ◽  
Jonny Rutqvist
Keyword(s):  
Induced Seismicity ◽  
Water Injection ◽  
In Situ Stress ◽  
Fault Reactivation ◽  
Shear Strength Parameters ◽  
Radionuclide Migration ◽  
Strength Parameters ◽  
Mont Terri ◽  
Underground Research Laboratory

Faults in the host rock that might exist in the vicinity of deep geological repositories for radioactive waste, constitute potential enhanced pathways for radionuclide migration. Several processes might trigger pore pressure increases in the faults leading to fault failure and induced seismicity, and increase the faults’ permeability. In this research, we developed a mathematical model to simulate fault activation during an experiment of controlled water injection in a fault at the Mont-Terri Underground Research Laboratory in Switzerland. The effects of in-situ stress, fault shear strength parameters and heterogeneity are assessed. It was shown that the above factors are critical and need to be adequately characterized in order to predict the faults’ hydro-mechanical behaviour.

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