scholarly journals A Stability Analysis of Directional Drilling on the Shales with Weak Bedding Planes

2013 ◽  
Vol 50 (3) ◽  
pp. 329-338 ◽  
Author(s):  
Jae Pil Yoon ◽  
Hyun Tae Kim ◽  
Hee Won Park
Keyword(s):  
Stability Analysis ◽  
Directional Drilling ◽  
Bedding Planes

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.

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.

scholarly journals Slope Stability Analysis of Haibat Sultan Road Cut, Kurdistan Region, Iraq Using a Field Method

2021 ◽  
Vol 54 (1F) ◽  
pp. 98-109
Author(s):  
Varoujan K. Sissakian
Keyword(s):  
Stability Analysis ◽  
Slope Stability ◽  
Satellite Images ◽  
Field Method ◽  
Slope Stability Analysis ◽  
The Road ◽  
Clastic Rocks ◽  
Bedding Planes ◽  
Almost All ◽  
Very High

The road that crosses the Haibat Sultan Mountain in the northern part of Iraq; is one of the dangerous roads in this region. To perform a slope stability analysis for the dangerous parts of the road, we have used Bejerman’s Method. We have reviewed satellite images of the road and all those potential areas were checked in the field; accordingly, eleven stations were recognized. Landslide Possibility Index was determined at the studied stations following Bejerman’s field method. The road climbs the southern face (dip slope) of the mountain through very hard carbonate rocks of the Pila Spi Formation, where the bedding planes daylight in the slope face near the road cuts. This produced many large landslides. Along the northern face of the mountain, the road runs through soft clastic rocks where joint planes in the rock mass intersect and daylight in the slope face near the road cut. In order to prevent future wedge failures, a 30 m offset was created from the toe of the slope to the road. In almost all cases, the Landslide Possibility Index indicated a moderate to very high likelihood for failure along all road cuts.

Wellbore-Stability Analysis Considering the Weak Bedding Planes Effect: A Case Study

2018 ◽  
Vol 33 (04) ◽  
pp. 377-384 ◽  
Author(s):  
Amin Mehrabian ◽  
Arturo Diaz Pérez ◽  
Claudia Santana
Keyword(s):  
Stability Analysis ◽  
Wellbore Stability ◽  
Bedding Planes

Coupled Thermal-Hydro-Mechanical-Chemical Modeling for Time-Dependent Anisotropic Wellbore Stability Analysis

2021 ◽  
Author(s):  
Jingyou Xue ◽  
Kenji Furui
Keyword(s):  
Stability Analysis ◽  
Chemical Potential ◽  
Bedding Plane ◽  
Wellbore Stability ◽  
Time Dependent ◽  
Drilling Fluids ◽  
Shale Formations ◽  
Wellbore Instability ◽  
Bedding Planes ◽  
Stress Changes

<p>Wellbore instability is one of the most serious drilling problems increasing well cost in well construction processes. It is widely known that many wellbore instability problems are reported in shale formations where water sensitive clay mineral exist. The problems become further complicated when the shale exhibits variation in strength properties along and across bedding planes. In this study, a coupled thermal-hydro-mechanical-chemical (THMC) model was developed for time-dependent anisotropic wellbore stability analysis considering chemical interactions between swelling shale and drilling fluids, thermal effects, and poro-elastoplastic stress-strain behaviors.</p><p>The THMC simulator developed in this work assumes that the shale formation behaves as an ion exchange membrane where swelling depends on chemical potential of drilling fluids invading from the wellbore to the pore spaces. The time-dependent chemical potential changes of water within the shale are evaluated using an analytical diffusion equation resulting in the evolution of swelling strain around the wellbore. On the other hand, the thermal and pressure diffusion equations are evaluated numerically by finite differences. The stress changes associated with thermal, hydro, and chemical effects are coupled to the 3D poroelastoplastic finite element model. The effects of bedding planes are also taken into account in the FEM model through the crack tensor method in which the normal and tangential stiffnesses of the bedding planes have stress dependency. The failure of the formation rock is judged based on the critical plastic strain limit.</p><p>The numerical analysis results indicate that the rock strength anisotropy induced by the existence of bedding planes is the most important factor influencing the stability of the wellbore among various THMC process parameters investigated in this work. The numerical results also reveal that an established theory to orient the wellbore in the direction of the minimum principal stress is not always a favorable option when the effect of the anisotropy of in-situ stresses and the distribution angle of bedding planes cancel out each other. Depending on both the distribution angle of bedding plane and ratio of the vertical to the horizontal stress, the trend of minimum mud pressure showed a great variation as predicted by the yield and failure criterion implemented in the model. Furthermore, the analysis results reveal that the distribution and evolution of plastic strains caused by the THMC processes have the time dependency, which can be controlled by the temperature and salinity of the drilling fluids.</p><p>The numerical wellbore stability analysis model considering shale swelling and bedding plane effects provides an effective tool for designing optimum well trajectories and determining safe mud weight windows for drilling complex shale formations. The time-dependent margins of safe mud weight window of drilling can be fine-tuned when the interaction among various parameters is fully considered as the THMC processes.</p>

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