Wellbore Stability Analysis Research Articles

Optimization of Deviated and Horizontal Wells Trajectories and Profiles in Rumaila Oilfield

Directional and horizontal wellbore profiles and optimization of trajectory to minimizeborehole problems are considered the most important part in well planning and design. Thisstudy introduces four types of directional and horizontal wells trajectory plans for Rumailaoilfield by selecting the suitable kick off point (KOP), build section, drop section andhorizontal profile. In addition to the optimized inclination and orientation which wasselected based on Rumaila oilfield geomechanics and wellbore stability analysis so that theoptimum trajectory could be drilled with minimum wellbore instability problems. The fourrecommended types of deviated wellbore trajectories include: Type I (also called Build andHold Trajectory or L shape) which target shallow to medium reservoirs with lowinclination (20o) and less than 500m step out, Type II (S shape) that can be used topenetrate far off reservoir vertically, Type III (also called Deep Kick off wells or J shape)these wells are similar to the L shape profile except the kickoff point is at a deeper depth,and design to reach far-off targets (>500m step out) with more than 30o inclination, andfinally Type IV (horizontal) that penetrates the reservoir horizontally at 90o. The study alsorecommended the suitable drilling mud density that can control wellbore failure for the fourtypes of wellbore trajectory.

Parametric sensitivity study of wellbore stability in transversely isotropic medium based on polyaxial strength criteria

Borehole instability in laminar formations often occurs during drilling operations without a clear explanation. Two dominant factors, rock lithology and stress concentration effects on borehole instability, are investigated in this study. The microstructure and mineral composition are evaluated to determine the possible reactions of the drilling fluid and shale interaction. A borehole stability model in a transversely isotropic medium is established using three different types of polyaxial strength criteria to study the effect of the degree of elastic anisotropy and intermediate principal stress on the lower boundary of the safe drilling window. Research has indicated that Poisson's ratio anisotropy does not markedly change the collapse pressure at low anisotropy. However, the effect of the elastic modulus anisotropy is notable, and the collapse pressure predicted by polyaxial criteria is more sensitive to elastic anisotropy. The collapse pressure calculated by the Mohr–Coulomb criterion is the upper limit; the results predicted by the Modified Lade and Modified Wiebols–Cook criterion are similar, corresponding to the wellbore orientations. This study explores the failure mechanisms of wells drilled in layered shales, which can help determine critical mud pressure and well orientation design. The outcomes of this investigation indicate the implications of fully accounting for the degree of elastic anisotropy and the influence of intermediate stress in conducting wellbore stability analysis.

Anisotropic Wellbore Stability Analysis: Impact on Failure Prediction

Shale formations are the main source of borehole stability problems during drilling operations. Suboptimal predictions of borehole failure may partly be caused by neglecting the anisotropic nature of shales: Conventional wellbore stability analysis is based on borehole stresses computed from isotropic linear elasticity (Kirsch solution) with the assumption of no induced pore pressure. This is very convenient for a practical implementation but does not always work for shales. Here, anisotropic wellbore stability analysis was performed targeting an offshore gas field to investigate in particular the impact of elastic anisotropy on borehole failure predictions. Stress concentration around a circular borehole in anisotropic shale was calculated by the Amadei solutions, and induced pore pressure was obtained from the Skempton parameters based on anisotropic poroelasticity. Borehole failure regions and modes were then predicted using the effective stresses and those are apparently consistent with observations. A comparison with the conventional approach suggests the importance of accounting for elastic anisotropy: Predicted failure regions, modes, and also the associated mud weight limits can be completely different. This observation may have significant implications for other fields since shale often show strong elastic anisotropy.

Integrated mechanical earth model and quantitative risk assessment to successful drilling

Use of vital geomechanical parameters for determination of safe mud pressure window is generally associated with high level of uncertainty primarily because of absence of sufficient calibration data including laboratory and field test information. The traditional deterministic wellbore stability analysis methodologies usually overlooked the uncertainty of these key parameters. This paper exhibits implementing a quantitative risk assessment technique on the basis of Monte-Carlo modeling to consider uncertainty from input data so as to make it possible to survey not just the likelihood of accomplishing a desired level of wellbore stability at a particular mud weight, but also the impacts of the uncertainty in each single parameter on the wellbore stability. This methodology was implemented to a case study. The most important parameters have been recognized using a sensitivity analysis approach in which the outcome of this QRA procedure suggests the mud weight window with likelihood of well drilling success which can elude the wellbore collapse and lost circulation events. This sort of stochastic approach to deal with anticipated safe mud weight window can guarantee stable wellbore with considerable cost viability associated with drilling success. The technique built up in this paper can give the scientific foundation for assessment of wellbore stability under complicated geological circumstances. It was likewise noted that based on sensitivity analysis, uniaxial compressive strength and maximum horizontal stress are the most effective parameter in estimation of mud weight window. This accentuates the significance of trustworthy determinations of these two parameters for safe drilling of the future wells in the field.

Relationship between wellbore instability and rock mechanics when drilling in the fault area of Shunbei Formation

The Tarim Basin is one of the most important oil formations in China, and it is prospected to exceed 110 billion barrels. Recently, some fault areas were drilled to achieve high potential oil reservoirs in the Tarim Basin. However, during drilling, wellbore stability is difficult to ensure in the fault areas. Wellbore collapse and lost circulation may unexpectedly occur. Therefore, analysis of wellbore stability according to the formation characteristics of the fault zone is necessary. On the basis of the formation mechanism of the fault zone, the stratigraphic characteristics corresponding to the internal structure of different fault zones were analyzed in this work. As a result of the formation characteristics, the corresponding logging identification methods of the induced fracture zone and sliding crushing zone formed, and the differences in wellbore instability in different internal structures were compared. The formation characteristics and mechanical properties of the sliding crushing zone were characterized by XRD, SEM, linear expansion rate test, rolling recovery test, and other physical experiments. Logging calculations were also conducted to assess the phenomenon of collapse that often occurs in the sliding crushing zone, and the collapse mechanism was analyzed accordingly. In view of the leakage phenomenon in the induced fracture zone, the complex mechanism of the leakage was analyzed, and the traditional minimum principal stress model was modified to obtain the leakage pressure calculation model suitable for the fault zone. Finally, taking the F1 fault zone in Shunbei area as an example, the internal structure of the fault zone was divided by using the summarized logging identification method. The wellbore instability of the different internal structures was compared, and the newly established loss pressure model was applied in the SHBX1 well, thereby proving that the model has a good application effect. The study in this paper provided some mechanisms of wellbore instability based on formation property and rock mechanics in the fault area. In addition, a loss pressure model based on the special formation characteristics was proposed to guide drilling in the fault zone.

Wellbore stability analysis for arbitrary inclined well in anisotropic formations

Wellbore instability is a classic rock mechanics problem encountered during drilling and completing. The traditional model for wellbore stability analysis assumes that formation rocks are homogenous, continuous, and isotropic. However, most of the deep formation rocks are naturally anisotropic. Therefore, this study proposes an anisotropic wellbore stability model for an arbitrary inclined well, considering the anisotropic elastic properties, shear strength, and in-situ stress. This model was compared to the traditional model. The equivalent mud weight of collapse pressure (EMWCP) was predicted for three types of typical in-situ stress states, such as normal faulting (NF), strike-slip faulting (SSF), and reverse faulting (RF). The results show that rock anisotropy significantly influenced EMWCP compared to the traditional model. The anisotropy of in-situ stress and shear strength increase the EMWCP, whereas the anisotropy of rock elastic properties decreases the EMWCP. The optimal well path is in the ranges of the attack angle (the angle between the borehole axis and the normal of weak planes) lower than 45°. In other words, the anisotropy shear strength is harmful to keeping wellbore stability, whereas the anisotropy of rock elastic properties is conducive. Thus, the influence of anisotropic shear strength cannot be ignored for wellbore stability analysis, whereas the influence of anisotropic elasticity can be ignored. This model provides theoretical guidance for drilling mud density optimization, well trajectory optimization, and well drilling and completion safety.

Shear strength parameter determination for the single plane of weakness criterion: Implications for wellbore stability

Wellbore stability is a classic rock mechanics problem encountered during drilling and completion, which costs the drilling industry more than $100 million per year worldwide. The failure criterion is a very important aspect of the wellbore stability analysis. Accordingly, for shale rich in bedding, fissures, joints, and cuts, we often use the single plane of weakness criterion to describe the compressive shear strength. The anisotropic strength of a rock depends on the strength of the rock matrix and the weak plane (i.e., cohesive strength of the matrix, friction angle in the matrix, cohesion of the weak plane, and friction angle in the weak plane). However, directly and accurately determining the compressive shear strength parameters of the rock matrix and the weak plane using the conventional least square and molar stress circle methods is difficult because of the difference between the rock matrix and the weak plane. This study uses the grid search algorithm to quickly match the optimal matrix cohesion, matrix internal friction angle, weak plane cohesion, and weak plane internal friction angle through the published triaxial test data of two sets of anisotropic rocks. The four parameters of the compressive shear strength materials obtained by the grid search algorithm are used to predict the results, which are very consistent with the experimental results. The correlation coefficient (R 2) above 0.98 is enough to meet the engineering requirements. Taking a shale gas well in the Sichuan Basin as an example, a collapse pressure prediction model is finally established by combining the grid search method to determine the material parameters of the compressive shear strength, shear wellbore instability model, and SWP criterion. Consequently, the model results are found to be in good match with the engineering practice.

Material constituents and mechanical properties and macro-micro-failure modes of tight gas reservoirs

In this work, a series of intensive laboratory tests are conducted to measure the material constituents, mechanical properties, and to examine macro-micro-failure modes of various types of rocks from tight gas reservoirs in the Da Qing oilfield in China. A set of key parameters are experimentally determined, including porosity, mineralogical compositions, microstructure, Young’s modulus, Poisson’s ratio, triaxial compressive strength, as well as macro- and micro-morphology failure modes. The relationships of these parameters are systematically analyzed, and the effects of the material constituents and microstructure characteristics such as cementation type, porosity, and mineral composition on rock mechanical properties are revealed as well as the patterns of micro- and macro-failures in types of rocks are investigated. The result shows that the micro-failure mainly exhibits features of transgranular and intergranular porous polymer fracture, and the macro-failure modes are mainly three types: shear-dominated, mixed shear–tensile and mixed tensile–shear. The mixed tensile–shear failure has mainly tensile fractures with branch fractures crossing each other, which forms a complex system fracture network. These findings are of importance for “sweet pot” evaluations, wellbore stability analysis, and hydraulic fracturing design for oil and gas production in tight gas reservoirs.

Infill well wellbore stability analysis by considering plasticity, stress arching, lateral deformation and inhomogeneous depletion of the reservoir

The traditional way of analyzing wellbore stability of infill wells relies on the analytical solution of the stress path, which assumes uniaxial strain, homogenous depletion, constant overburden stress, and linear elastic condition. The objective of this study is to re-evaluate all the above four assumptions and analyze the plasticity, stress arching, lateral deformation and inhomogeneous depletion of the reservoir. Coupled geomechanics and fluid flow analysis is conducted to get the time and location dependent stress field and pressure field, which serve as inputs for wellbore stability analysis for infill wells. Considering four cases, the ranking according to the width of the safe drilling mud weight windows is 1) plasticity, 2) elasticity, 3) plasticity with stress arching, and 4) elasticity with stress arching. This coupled geomechanics and fluid flow can provide dynamic information concerning where to drill, when to drill, and how to drill for infill wells.

Experimental investigation of thermal expansion of organic-rich shales

Experimental data on thermal expansion of rocks are necessary for many applications involving wellbore stability analysis, designing radioactive waste repositories, etc. Such information is especially actual for organic-rich shales that exhibits significant thermal anisotropy and heterogeneity and were not studied comprehensively previously. The coefficient of linear thermal expansion (CLTE) of 23 shale samples from three wells of three oilfields of the Bazhenov and Abalak formations (West Siberia, Russia) was studied with a quartz dilatometer specially adapted for the measurements on standard core plugs. Differential CLTE of shales was determined within temperature range 25–300 °C through every 25 °C for directions parallel and perpendicular to rock bedding. Strong correlations between the CLTE, thermal conductivity, and total organic carbon were established. Detailed profiles of CLTE along studied wells were obtained due to application of the optical scanning technique. These profiles fit well with total organic carbon obtained with pyrolysis. CLTE anisotropy was assessed for organic-rich shale samples together with thermal conductivity anisotropy. The thermal conductivity measurements before and after heating allowed estimation of structural changes in rock samples during heating.

Impact of geomechanics in coal bed methane development and production, Barakar coals in central India

Geomechanics plays a critical role in the different stages of coal bed methane (CBM) operations, starting from its development through production to its abandonment as in Sohagpur field of central India. In general, higher gas production has been observed from the coal seams in low-stress regimes compared to high-stress regimes; however, during the CBM development planning, stress information has been overlooked. The need for inclined and horizontal wellbores in coal seams has increased due to their many-fold rise in production when compared to vertical wells with a minimum surface footprint. However, these non-vertical wells have wellbore instability issues leading to high nonproductive time (NPT) during drilling and completion operations. Prolong challenges exist in achieving the desired half-length from hydraulic fracturing (HF) stimulation due to the limited understanding of the stress contrast between target coal and bounding lithology. The permeability of the coal reservoir varies greatly during depletion due to the combined effects of effective stress and matrix shrinkage. These effects directly impact productivity and hence, require a detailed understanding of how permeability varies during production life. In many instances, production from coal seams is complicated and unpredictable because of the influence of stress induced natural fractures. A geomechanical earth model is focused on understanding and mitigating the aforementioned challenges. In addition to coal thickness and gas content, stress-permeability maps are prepared to assist in the development program to prioritize wells in lower and moderate stress areas. Wellbore stability analysis has been carried out using calibrated stress and strength profiles along with other rock mechanical inputs to successfully drill high angle wells. This analysis indicates that with a slightly higher mud weight, high angle and horizontal wells can be drilled successfully. Hydraulic fracturing design incorporating the available stress contrast can help in achieving the desired fracture parameters without height growth. The coal permeability model suggests that during depletion, coal permeability is expected to increase by about 1.2–3.5 times with a positive impact on productivity. Critically stressed fracture analysis has been carried out on mapped fractures, which suggest that about 48% of the natural fractures are in a stressed state. Presence of these natural fractures has a positive (faster dewatering) as well as a negative (external water) impact on productivity at different places in the study area.

The Analytical Model for Horizontal Wellbore Stability in Anisotropic Shale Reservoir

Wellbore collapse is a frequent problem during drilling in shale gas reservoir, restricting efficient exploration of shale gas. Due to the presence of bedding plane, conventional homogeneity model is inappropriate to conduct wellbore stability analysis in shale reservoir. Therefore, in this study, under the influence of bedding plane, stress distributions including in situ stress components, pore pressure, seepage stress have been calculated. Meanwhile, shale strength is expressed using the Jaeger's criterion, which assumes shale is isotropic body with one group of weak planes. In combination with stress distribution and shale strength, an analytical model has been developed to investigate wellbore failure region. By using this model, influence factors of wellbore stability have been fully analyzed. Results demonstrate that the difference between bedding plane and rock matrix will modify in situ stress components, transport equations and rock mechanical properties around wellbore. As a result, there are heterogeneous distributions of shale strength and stress state. When the shear failure along bedding plane happens, shale strength has clearly reduction and breakout region has increment, changed from two-lobed failure to four-lobed failure shape. The different intersections between bedding plane and wellbore make variable anisotropy in wellbore plane, modifying the pore pressure propagation and seepage stress distribution. When the bedding plane angle in wellbore plane is low or high value, shear failure along bedding plane doesn’t happen and wellbore stability is depended on rock matrix strength. For middle bedding plane angle, failure region clearly increases and shear failure along bedding plane occurs, aggravating the instability. Furthermore, drilling fluid reduces shale strength, thus increasing region area and changing failure mode. This drilling fluid impact is strong in initial stage and becomes stable after 96 h. By having comprehensive investigation on bedding plane influence, findings in this study are advantageous for drilling operations in shale reservoir.

Analysis of the Collapse Gradient of Deep Water Horizontal Wellbore and the Effects of Mud Chemical Activity and Variation in Water Depth

Abstract Wellbore collapse is an instability-event that occurs at low mud density and leads to unfavorable economic project, reaching billions of US dollars. Thus, it is important to accurately determine its value, especially in deepwater horizontal wellbores. The main reasons for nontrivial problems with such wellbores are evident: the shale encountered are anisotropic in nature and possess planes of weakness; they react with water-based mud, generate osmotic stresses, swell, and fall unto the wellbore bottom, thereby increasing the non-productive time. To this end, salts are added to reduce the collapse tendency, but it is not currently known what amount of salt addition maintains stability, and does not lead to wellbore fracture; in deepwater, the current trend in global warming means there is a future concern to the industry. As the climate temperature increases, more ice melts from the polar region, the seawater expands and the sea level rises. How to incorporate the corresponding effect on collapse gradient is scarcely known. This study captures the major concerns stated above into wellbore stability analysis. Following the classical approach for geomechanical analysis, Mogi-Coulomb criterion was combined with a constitutive stress equation comprising contributions from mechanical and osmotic potentials of mud and shale. A sophisticated industry model was used to consider the deepwater effect. The results show significant reduction in collapse gradient as the water depth increases, also, larger difference between the mud and shale chemical activities represents higher complexities in the wellbore. In addition, the reduction in the chemical activities of mud limited to 37.5% of the initial value can be practically safe.

Wellbore stability and failure regions analysis of shale formation accounting for weak bedding planes in ordos basin

Borehole instability problem is one of the key problems in drilling engineering, especially the shale formation with bedding planes and natural fractures, the failure of shale rock could be divided into two parts, shear failure across intact rock matrix and slippage failure in shale bedding, resulting in more serious borehole instability problem during drilling process. In this study, combining with rock strength anisotropy, a method of failure region around wellbore is developed for layered rocks on the basis of isotropic borehole stability model. The effect of shale bedding occurrence on failure region around wellbore, what was hardly conducted by former researchers, is examined systematically. The results show that, polar plot of critical lower mud weight with rock strength anisotropy considered reflects the actual situation of a shale formation; the shale bedding strength, pore pressure and intrinsic cohesion are the three most impact parameters on wellbore stability. Moreover, the maximum failure depth is no longer in the minimum principal stress, but locates in four corners at top and bottom of wellbore, which is induced by slippage failure in laminated formations; the collapse of wellbore will be aggravated due to the overlapping of failure in rock matrix and bedding. This proposed model not only can provide guiding suggestions for well constructions and cementations, but also can be used as an effective complement to provide richer ground stress inversion data.

An Assessment of the Causes of Wellbore Instability and Stuck Pipe Occurrences in an Offshore Field, Niger Delta, Nigeria

Wellbore instability and consequential stuck pipe issues are a common challenge associated with offshore drilling. Usually, the effect of wellbore instability is an increase in nonproductive time, possible loss of tools and costly drilling operations. Hence, there is a need for wellbore stability analyses before and during drilling operations. In “Agaza Field”, offshore Niger Delta, wellbore instability problems were encountered at various depths between 3,696-4,270 ft.; 5,000-5,425 ft. and 7,600-8000 ft. intervals. Sixty-five ditch-cutting samples and composite log plots obtained from both wells were and analyzed to determine the clay swelling potential and the cationic exchange between the formation and the drilling fluid as well as causes of formation instability. Agaza-1 well showed evidence of tight hole at intervals between 4,200 and 7,600 ft. In Agaza-2, there were indications of wellbore stresses from 1,908 ft. to 2,030 ft. However, deeper than 4,225ft depth, high fluctuation of pore pressure coincided with wellbore instability between 4,810 ft. and 5,200 ft. The principal clay minerals present within the formations are Illite, Smectite and Smectite/Illite interlayered types. Result of the cation exchange analysis showed that high concentration of calcium and sodium in the shale is responsible for high dissociation of the constituent minerals hence making the shales unstable. Analysis has shown that samples at some intervals from both wells are associated with high swelling potential while average cation exchange value is 40 meq/100g. Therefore, the primary cause of wellbore instability and stuck pipe within the studied intervals are attributed to high swelling and reactivity over time due to fluidformation interaction. Keywords: Clay cationic exchange, Clay swelling potential, Offshore drilling challenges, Reactive shales. African

Uncertainty assessment of wellbore stability analysis in horizontal sections

Over the last years, horizontal wells have found applications in many different geological and technical situations to enhance the production rate from the oil and gas reservoirs. However, well instability problems are often reported during construction of these types of wells. To mitigate instability problems, which are usually difficult and costly to solve, well stability analysis are conducted before the construction process begins. Different geomechanical and mathematical models that are used in the well stability studies, do not include the uncertainty assessments of the models. As majority of input parameters into the geomechanical models are subjected to some extent of errors and uncertainties, therefore, it is essential to quantify the uncertainty associated with the output of the geomechanical models. In this work, a Monte Carlo simulation technique is applied to quantify the uncertainty in the output of a poroelastic model to make more reliable decisions in the well construction process.

Wellbore stability analysis using integrated geomechanical modeling: a case study from the Sarvak reservoir in one of the SW Iranian oil fields

In this study, an integrated geomechanical analysis was carried out for the Sarvak carbonate reservoir in three wells of one of the oil fields in Abadan Plain, SW Iran. The static Young’s modulus (ES), unconfined compressive strength (UCS), cohesion (C), and angle of internal friction (Φ) were determined directly, using rock mechanics tests. Subsequently, some correlations were introduced based on tests-to-logs relationships. The 1D geomechanical models were constructed for three wells in the north, center, and south of the studied field. The results show that the stress state is not uniform for the studied wells, as it is strike-slip normal in northern well, strike-slip in central well, and strike-slip reverse in southern well. Likewise, the stability of the wells was evaluated using Mohr-Coulomb and Mogi-Coulomb criteria, and it was observed that the Mogi-Coulomb criterion could more accurately estimate the breakout pressure. According to the recognized borehole breakouts in image logs, the SHmax direction is to NE-SW in all three wells. Based on the wellbore stability analysis, it was concluded that the more stable directions for drilling are NW-SE in the northern part, E-W and N-S in the central part, and NE-SW in the southern part of the studied oil field.

Determining the domain of in situ stress around Marun Oil Field\u2019s failed wells, SW Iran

Accurate determination of the in situ stress domain in oil fields is of paramount importance in drilling, completion, and maintenance of wells and in petroleum geomechanics. Determination of the magnitude and direction of stresses induced by drilling around the wellbores is the first step in geomechanical studies and wellbore stability analyses. Regarding the importance of casing collapse problems in Marun Oil Field, as the first step of this investigation, geomechanical studies were conducted to determine the in situ stress domain in the failed wellbores. Using density measurements, the vertical stress (SV) was estimated to be within the range of 85–90 MPa for all wellbores. To estimate maximum-horizontal-stress (SHmax) domain, Anderson’s faulting theory and stress polygon were employed, and a value close to SV was achieved. Also, minimum horizontal stress (Shmin) was estimated using different approaches and was found to have the minimum in situ stress. Finally, the faulting regime of the areas was found to be normal/strike slip, where the stress values are close to each other due to salt lithology and high pore pressures in the Gachsaran Formation and thereby could be assumed as hydrostatic stresses.

Wellbore stability analysis based on geomechanical modeling using finite element method

The analysis and prediction of the wellbore stability is considered as one of the sensitive and critical factors in oil wells’ drilling operations. Parameters affecting well stability include region’s in situ stresses, pores’ water pressure, rock strength, drilling fluid pressure and drilling direction, respectively. In general, in situ stresses and rock resistance are some of the uncontrollable parameters affecting the wellbore and will become possible only by adjusting controllable parameters such as fluid pressure and drilling direction to avoid well instability problem occurrence. This paper has tried to investigate well instability problem in one of the Asmari Reservoir wells in one of the southwestern Iran fields in different ways and present the necessary approaches and suggestions for better promotion of drilling operations in the aforesaid field. To achieve induced stresses around the wellbore, numerical method and Phase 2 software have been used. Rock mechanical parameters including modulus of elasticity, Poisson's ratio, cohesive bond, friction angle, over-burden floor stress amount, minimum and maximum horizontal stresses along the well depth have been investigated and their variations have been shown and then, to simulate the wellbore stability, these data were entered at a cross-section (2380 m) into the Phase 2 software and the output of this software including stresses, displacements around the wellbore has been analyzed finally after solving with finite element method.

Numerical modeling of plastic deformation and failure around a wellbore in compaction and dilation modes

SummaryIn many wellbore stability analyses, the ability to forecast both the occurrence and extent of plastic deformation and failure hinges upon a fundamental understanding of deformation mode and failure mechanism in the reservoir rock. This study focuses on analyzing plastic zones, localized deformations, and failures around a borehole drilled overbalanced or underbalanced through a highly porous rock formation. Based on several laboratory experiments, porous rocks are prone to deform under both shear‐induced dilation and shear‐enhanced compaction mechanisms depending on the stress state. The shapes of the deformation and failure patterns around the borehole are shown, depending on the initial stress state and the local stress paths. The inquiry of the local stress paths in the near‐wellbore zone facilitates the understanding of the reasons for different types of failure mechanisms, including the mixed‐mode and the plastic deformation structures. The modification of the 2D plane strain condition by imitating third stress in the numerical scheme helps us bring the stress paths closer to the real state of loading conditions. Our modeling reveals that the transition from isotropic to anisotropic stress state is accompanied by an increase in the deviatoric part of effective shear tensor that leads to the development of inelastic deformation, degradation, and subsequent rock failure. Particular interest is devoted to the modeling of strain localization especially in compaction mode around a wellbore and computing the amount of stress concentration at the tips of dog‐eared breakouts. Stress concentration can result in a change in irreversible deformation mode from dilatancy to compaction, elucidating the formation of the shear‐enhanced compaction phenomenon at the failure tips in the direction of the minimum horizontal stress.