scholarly journals Elastic-Plastic-Damaged Zones around a Deep Circular Wellbore under Non-Uniform Loading

Symmetry ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 323 ◽  
Author(s):  
Xiaoji Shang ◽  
Zhizhen Zhang
Keyword(s):  
Stress Field ◽  
In Situ Stress ◽  
Surrounding Rock ◽  
Wellbore Stability ◽  
Boundary Line ◽  
Uniform Stress ◽  
Elastic Plastic ◽  
Special Cases ◽  
Uniform Stress Field

Wellbores are largely constructed during coal mining, shale gas production, and geothermal exploration. Studying the shape and size of the disturbed zone in surrounding rock is of great significance for wellbore stability control. In this paper, a theoretical model for elastic-plastic-damage analysis around a deep circular wellbore under non-uniform compression is proposed. Based on the elastoplastic softening constitutive model and Mohr-Coulomb strength criterion, the analytical expressions of stresses in the elastic, plastic and damaged zones around a circle wellbore are derived. Further, the boundary line equations among the three zones are obtained according to the conditions of stress continuity. Then, the influence rules of non-uniform in-situ stress and mechanical parameters on the stress distribution and plastic zone size in surrounding rock mass are analyzed. The plastic and the damaged zones are both approximately elliptical in shape. When the lateral stress coefficient of the in-situ stress field takes the value 1, the model degenerates into the Yuan Wenbo’s Solution. If the brittleness coefficient of the surrounding rock is 0, the model degenerates into the Kastner’s Equation. Finally, the results are compared with those under two special cases (in the elastoplastic softening rock under a uniform stress field, in the ideal elastoplastic rock under a non-uniform stress field) and a common approximation method (the perturbation method).

scholarly journals Study on In Situ Stress Measurement and Surrounding Rock Control Technology in Deep Mine

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Zhongcheng Qin ◽  
Bin Cao ◽  
Yongle Liu ◽  
Tan Li
Keyword(s):  
Stress Field ◽  
Principal Stress ◽  
Coal Mine ◽  
Maximum Principal Stress ◽  
In Situ Stress ◽  
Measured Data ◽  
Surrounding Rock ◽  
In Situ Stress Measurement ◽  
Surrounding Rock Control

In situ stress is the direct cause of roadway deformation and failure in the process of deep mining activities. The measured data of in situ stress in the Shuanghe coal mine show that the maximum principal stress is 44.94~50.61 MPa, and the maximum principal stress direction is near horizontal direction, which belongs to tectonic stress field. The maximum horizontal principal stress is 1.66~1.86 of the vertical stress. The horizontal principal stress controls the deep stress field. According to the measured data of in situ stress, the high-strength prestress bolt and cable collaborative support form is designed in the Shuanghe coal mine. Based on the stress field research of bolt and cable, the optimal prestress ratio of bolt and cable is proposed as 3. When the prestress ratio of bolt and cable is constant, the smaller the length ratio of bolt and cable is, the better the effect of prestressed field formed by cooperative support is. The results are applied to the support design of the mining roadway in the Shuanghe coal mine. Through the field monitoring test results, it is found that the maximum roof subsidence is 86 mm, the maximum floor deformation is 52 mm, and the maximum deformation of two sides is 125 mm. The surrounding rock control effect of the roadway is good, and the surrounding rock deformation conforms to the engineering technology standard requirements. The research results of this paper can provide some reference for the surrounding rock support of high ground stress mining roadway under similar conditions.

scholarly journals A Workflow to Predict the Present-day in-situ Stress Field in Tectonically Stable Regions

2019 ◽  
Vol 1 (2) ◽  
Author(s):  
Wei Ju ◽  
Ke Xu ◽  
Jian Shen ◽  
Chao Li ◽  
Guozhang Li ◽  
...  
Keyword(s):  
Stress Distribution ◽  
Stress Field ◽  
Ordos Basin ◽  
Simulation Method ◽  
In Situ Stress ◽  
Wellbore Stability ◽  
Central China ◽  
Geometric Framework ◽  
In Situ Stress Field

Knowledge of the present-day in-situ stress distribution is greatly important for better understanding of conventional and unconventional hydrocarbon reservoirs in many aspects, e.g., reservoir management, wellbore stability assessment, etc. In tectonically stable regions, the present-day in-situ stress field in terms of stress distribution is largely controlled by lithological changes, which can be predicted through a numerical simulation method incorporating specific mechanical properties of the subsurface reservoir. In this study, a workflow was presented to predict the present-day in-situ stress field based on the finite element method (FEM). Sequentially, it consists of: i) building a three-dimensional (3D) geometric framework, ii) creating a 3D petrophysical parameter field, iii) integrating the geometric framework with petrophysical parameters, iv) setting up a 3D heterogeneous geomechanical model, and finally, v) calculating the present-day in-situ stress distribution and calibrating the prediction with measured stress data, e.g., results from the extended leak-off tests (XLOTs). The approach was successfully applied to the Block W in Ordos Basin of central China. The results indicated that the workflow and models presented in this study could be used as an effective tool to provide insights into stress perturbations in subsurface reservoirs and geological references for subsequent analysis.

CHARACTERISING THE FULL STRESS TENSOR BASED ON OBSERVATIONS OF DRILLING-INDUCED WELLBORE FAILURES IN VERTICAL AND INCLINED BOREHOLES LEADING TO IMPROVED WELLBORE STABILITY AND PERMEABILITY PREDICTION

1998 ◽  
Vol 38 (1) ◽  
pp. 466 ◽  
Author(s):  
C.A. Barton ◽  
D.A. Castillo ◽  
D. Moos ◽  
P. Peska ◽  
M.D. Zoback
Keyword(s):  
Stress Field ◽  
Stress Tensor ◽  
Image Data ◽  
In Situ Stress ◽  
Wellbore Stability ◽  
Efficient Production ◽  
Sand Production ◽  
Inclined Boreholes ◽  
In Situ Stress Field

To minimise wellbore failures in unstable environments, knowledge of the complete stress tensor is crucial to designing optimally-stable borehole trajectories, selecting suitable mud weights, and determining appropriate casing points. Understanding how the in situ stress field interacts with the drilling and production of a well enables one to design for maximum stability and to facilitate intersecting the greatest population of hydraulically-conductive fractures for efficient production. Knowledge of the in situ stress field is also important to reduce uncertainties in sand production prediction to allow more aggressive completion designs and production schedules.A new interactive software system, Stress and Failure of Inclined Boreholes (SFIB) (Peska and Zoback, 1995a) is used to demonstrate how observations of drilling-induced compressive and tensile wellbore failures from acoustic and electrical images in vertical and inclined boreholes can be integrated with routinely-collected drilling data (leak-off and drill stem tests) to construct a well-constrained stress tensor. These techniques can also exploit wellbore image data to constrain in situ rock strength in vertical and inclined wells. This paper illustrates how to apply this knowledge to limit wellbore instability, design optimally stable wellbores, develop constraints that help mitigate problems associated with sand production, and optimise productivity of fractured reservoirs.In addition to mapping drilling-induced wellbore features, image data can also be used to determine the distribution, orientation, and apparent aperture of natural fractures and fault systems. With knowledge of the orientations and magnitudes of the in situ stresses it is possible to identify the subset of fractures that are likely to be hydraulically conductive.Examples of recent applications in the North Sea, Gulf of Mexico, California, and Puerto Rico illustrating how this integrated approach can be used in a variety of tectonic settings.

The Stress Distribution and Calculation of the Different Zone of Wellbore Surrounding Rock Based on the Damaged Theory

2012 ◽  
Vol 170-173 ◽  
pp. 1052-1055
Author(s):  
Wan Chun Zhao ◽  
Chen Yan Sun ◽  
Ting Ting Wang ◽  
Yu Liu ◽  
Cai Ping Yang
Keyword(s):  
Stress Distribution ◽  
Stress Field ◽  
In Situ Stress ◽  
Surrounding Rock ◽  
Oil Well ◽  
Damage Area ◽  
Stress Direction ◽  
The Stability ◽  
Adjacent Rock

In order to describe the stability of borehole face and the theory of hydraulic fracture fissure stretch in real, the stress field of adjacent rock in the hole should be constituted exactly .The article is based on the damnification dynamics theory, meanwhile, considered the rock is fracture-pore dual medium and the damnification characteristic of the rock in hole .Adjacent formation is sectioned three areas: damage-area, damnification-area, elasticity-area. And we have calculated the ambient stress distribution of one oil-well .The results show that the destructive radius of the minimum in-situ stress direction is 1.247m, the damage radius is 8.082m, the destructive radius of the maximum in-situ stress direction is 0.998m, and the damage radius is 6.5865m.

A Novel Method to Determine the Drilling Fluid Density for Gypsum-Salt Layer

2021 ◽  
Author(s):  
Jitong Liu ◽  
Wanjun Li ◽  
Haiqiu Zhou ◽  
Yixin Gu ◽  
Fuhua Jiang ◽  
...  
Keyword(s):  
Drilling Fluid ◽  
In Situ Stress ◽  
Wellbore Stability ◽  
Shrinkage Rate ◽  
Fluid Density ◽  
Salt Layer ◽  
Rock Creep ◽  
Key Factor ◽  
Well Abandonment

Abstract The reservoir underneath the salt bed usually has high formation pressure and large production rate. However, downhole complexities such as wellbore shrinkage, stuck pipe, casing deformation and brine crystallization prone to occur in the drilling and completion of the salt bed. The drilling safety is affected and may lead to the failure of drilling to the target reservoir. The drilling fluid density is the key factor to maintain the salt bed’s wellbore stability. The in-situ stress of the composite salt bed (gypsum-salt -gypsum-salt-gypsum) is usually uneven distributed. Creep deformation and wellbore shrinkage affect each other within layers. The wellbore stability is difficult to maintain. Limited theorical reference existed for drilling fluid density selection to mitigate the borehole shrinkage in the composite gypsum-salt layers. This paper established a composite gypsum-salt model based on the rock mechanism and experiments, and a safe-drilling density selection layout is formed to solve the borehole shrinkage problem. This study provides fundamental basis for drilling fluid density selection for gypsum-salt layers. The experiment results show that, with the same drilling fluid density, the borehole shrinkage rate of the minimum horizontal in-situ stress azimuth is higher than that of the maximum horizontal in-situ stress azimuth. However, the borehole shrinkage rate of the gypsum layer is higher than salt layer. The hydration expansion of the gypsum is the dominant reason for the shrinkage of the composite salt-gypsum layer. In order to mitigate the borehole diameter reduction, the drilling fluid density is determined that can lower the creep rate less than 0.001, as a result, the borehole shrinkage of salt-gypsum layer is slowed. At the same time, it is necessary to improve the salinity, filter loss and plugging ability of the drilling fluid to inhibit the creep of the soft shale formation. The research results provide technical support for the safe drilling of composite salt-gypsum layers. This achievement has been applied to 135 wells in the Amu Darya, which completely solved the of wellbore shrinkage problem caused by salt rock creep. Complexities such as stuck string and well abandonment due to high-pressure brine crystallization are eliminated. The drilling cycle is shortened by 21% and the drilling costs is reduced by 15%.

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