Borehole stability analysis accounting for anisotropies in drilling to weak bedding planes

2013 ◽  
Vol 60 ◽  
pp. 160-170 ◽  
Author(s):  
Jincai Zhang
Keyword(s):  
Stability Analysis ◽  
Borehole Stability ◽  
Bedding Planes

Borehole-Stability Analysis for the Design of the First Horizontal Well Drilled in the U.K. Southern V Fields

1991 ◽  
Vol 6 (03) ◽  
pp. 169-176 ◽  
Author(s):  
G.F. Fuh ◽  
E.G. Dew ◽  
C.A. Ramsey ◽  
Keith Collins
Keyword(s):  
Stability Analysis ◽  
Horizontal Well ◽  
Borehole Stability

Effect of confining pressure unloading on strength reduction of soft coal in borehole stability analysis

2017 ◽  
Vol 76 (4) ◽  
Author(s):  
Qingquan Liu ◽  
Yuanping Cheng ◽  
Kan Jin ◽  
Qingyi Tu ◽  
Wei Zhao ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Confining Pressure ◽  
Strength Reduction ◽  
Borehole Stability ◽  
Soft Coal

Wellbore Stability in Layered Rocks: A Comparative Study of Strength Criteria

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Xiangchao Shi ◽  
Xiao Zhuo ◽  
Yue Xiao ◽  
Boyun Guo ◽  
Cheng Zhu ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Good Choice ◽  
Wellbore Stability ◽  
Gas Field ◽  
Well Drilling ◽  
Shale Formations ◽  
Single Plane ◽  
Collapse Pressure ◽  
Bedding Planes ◽  
Laminated Structures

Abstract Wellbore instability is a critical issue restricting efficient well drilling and successful development of oil and gas field. Most instability problems originate from shale formations because of their distinct laminated structures that cause significant anisotropy and moderate to high clay contents that are prone to shrinkage and swelling. To account for these influences on the mechanical responses of shales, this study aims to identify an appropriate strength criterion for stability analyses. Two anisotropic criteria including single plane of weakness and the modified Hoek–Brown criteria were compared to evaluate their suitability in characterizing the anisotropic strength of layered rocks including shale, schist, and slate under different confining pressures. Comparative case studies indicated that the single plane of weakness criterion overestimates the strength of layered rocks at some orientation angles. The modified Hoek–Brown criterion can fit well with the experimental data of layered rocks. Moreover, wellbore stability analysis models for shale gas wells were built, respectively, for each criterion and applied to in situ scenarios. The single plane of weakness and modified Hoek–Brown criteria provide similar results of collapse pressure, and the shale failure is mainly determined by the bedding plane. This further validates that the modified Hoek–Brown criterion is a good choice for wellbore stability analysis in shale formations with bedding planes. This study shows the potential of using the modified Hoek–Brown criterion to enhance the safety and efficiency of well drilling and operation in shale formations.

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.

Mechanical Earth Model (MEM): An Effective Tool for Borehole Stability Analysis and Managed Pressure Drilling (Case Study)

2009 ◽  
Author(s):  
Meisam Afsari ◽  
Mohammadreza Ghafoori ◽  
Mohammad Roostaeian ◽  
Ashkan Haghshenas ◽  
Abdolrahim Ataei ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Earth Model ◽  
Borehole Stability ◽  
Managed Pressure Drilling ◽  
Mechanical Earth Model

The Evolution Mechanism of the Slope Toppling Deformation for Early-Warning Analysis

2021 ◽  
Author(s):  
Jian-qiao Mu ◽  
Tian-tao Li ◽  
Xiang-jun Pei ◽  
Run-qiu Huang ◽  
Fu-an Lan ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Early Warning ◽  
Structural Damage ◽  
Optimal Path ◽  
Instability Criterion ◽  
Fracture Plane ◽  
Evolution Mechanism ◽  
Bedding Planes ◽  
Deformation Stability ◽  
Toppling Deformation

Abstract With massive engineering projects performed in high and steep mountain areas, the evidence of toppling deformation, which has been an important engineering geological problem in construction, has been exposed and observed in quantities. Three key issues in the early warning of toppling slopes are the boundary condition, evolution mechanism, and deformation stability analysis. This paper investigates an evolution mechanism for timely predicting the occurrence of toppling induced slope failure in rock masses, relates boundary formation and progressive development about toppling fracture planes. By describing an instantaneous toppling velocity field and identifying two possible fracture plane geometries (linear and parabolic), the optimal path of toppling fracture plane is searched via critical toppling heights (i.e., minimum loads) calculation using the upper bound theory of limit analysis. It is interesting to find that no matter what the slope structures and mechanical parameters are, the optimal path of toppling fracture plane is straight and most likely oriented perpendicular to the bedding planes. Hereby, considering structural damage will enable progressive toppling deformation instead of systemic failure, the toppling deformation evolution is probably taking place of a loop following the formation of the first fracture plane due to exceeding slope critical height. In the loop, deformation and column inclination updates due to fracture plane formation and fracture plane inclination increase to adjust the changed inclination of columns, as it may take degrees perpendicular to columns. And this progressive formation of ever more inclined fractures plane is what lead to sliding collapse. Altogether we divide the toppling evolution into 5 stages, and define the instability criterion for toppling deformation transform into sliding collapse as the fracture plane inclination being equal to its friction angle. In addition, a PFC2D simulation of the entire slope toppling process is performed to verify this speculative evolution mechanism, and a satisfactory result is acquired. Finally, a deformation calculation model of toppling slopes is proposed for stability analysis in accordance with the instability criterion, which is further applied in a typical toppling case. The findings of this study could lay a foundation for the deformation, stability and early-warning analysis of toppling slopes.

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