scholarly journals New Interface for Assessing Wellbore Stability at Critical Mud Pressures and Various Failure Criteria: Including Stress Trajectories and Deviatoric Stress Distributions

Energies ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 4019
Author(s):  
Wang ◽  
Weijermars
Keyword(s):  
Shear Failure ◽  
Axial Stress ◽  
Failure Criteria ◽  
Wellbore Stability ◽  
Tensile Failure ◽  
Wellbore Instability ◽  
Wellbore Pressure ◽  
Stress States ◽  
Deviatoric Stresses ◽  
Wellbore Failure

This study presents a new interface for wellbore stability analysis, which visualizes and quantifies the stress condition around a wellbore at shear and tensile failure. In the first part of this study, the Mohr–Coulomb, Mogi–Coulomb, modified Lade and Drucker–Prager shear failure criteria, and a tensile failure criterion, are applied to compare the differences in the critical wellbore pressure for three basin types with Andersonian stress states. Using traditional wellbore stability window plots, the Mohr–Coulomb criterion consistently gives the narrowest safe mud weight window, while the Drucker–Prager criterion yields the widest window. In the second part of this study, a new type of plot is introduced where the safe drilling window specifies the local magnitude and trajectories of the principal deviatoric stresses for the shear and tensile wellbore failure bounds, as determined by dimensionless variables, the Frac number (F) and the Bi-axial Stress scalar (χ), in combination with failure criteria. The influence of both stress and fracture cages increases with the magnitude of the F values, but reduces with depth. The extensional basin case is more prone to potential wellbore instability induced by circumferential fracture propagation, because fracture cages persists at greater depths than for the compressional and strike-slip basin cases.

scholarly journals Wellbore instability management using geomechanical modeling and wellbore stability analysis for Zubair shale formation in Southern Iraq

2021 ◽  
Vol 11 (11) ◽  
pp. 4047-4062
Author(s):  
Raed H. Allawi ◽  
Mohammed S. Al-Jawad
Keyword(s):  
Shear Failure ◽  
Gamma Ray ◽  
Failure Criteria ◽  
Wellbore Stability ◽  
Integrity Test ◽  
Direction Parallel ◽  
Wellbore Instability ◽  
Drilling Performance ◽  
Weight Window ◽  
Shale Formation

AbstractWellbore instability problems cause nonproductive time, especially during drilling operations in the shale formations. These problems include stuck pipe, caving, lost circulation, and the tight hole, requiring more time to treat and therefore additional costs. The extensive hole collapse problem is considered one of the main challenges experienced when drilling in the Zubair shale formation. In turn, it is caused by nonproductive time and increasing well drilling expenditure. In this study, geomechanical modeling was used to determine a suitable mud weight window to overpass these problems and improve drilling performance for well development. Three failure criteria, including Mohr–Coulomb, modified Lade, and Mogi–Coulomb, were used to predict a safe mud weight window. The geomechanical model was constructed using offset well log data, including formation micro-imager (FMI) logs, acoustic compressional wave, shear wave, gamma ray, bulk density, sonic porosity, and drilling events. The model was calibrated using image data interpretation, modular formation dynamics tester (MDT), leak-off test (LOT), and formation integrity test (FIT). Furthermore, a comparison between the predicted wellbore instability and the actual wellbore failure was performed to examine the model's accuracy. The results showed that the Mogi–Coulomb failure and modified Lade criterion were the most suitable for the Zubair formation. These criteria were given a good match with field observations. In contrast, the Mohr–Coulomb criterion was improper because it does not match shear failure from the caliper log. In addition, the obtained results showed that the inappropriate mud weight (10.6 ppg) was the main cause behind wellbore instability problems in this formation. The optimum mud weight window should apply in Zubair shale formation ranges from 11.5 to 14 ppg. Moreover, the inclination angle should be less than 25 degrees, and azimuth ranges from 115 to 120 degrees northwest-southeast (NE–SW) can be presented a less risk. The well azimuth of NE–SW direction, parallel to minimum horizontal stress (Shmin), will provide the best stability for drilling the Zubair shale formation. This study's findings can help understand the root causes of wellbore instability in the Zubair shale formation. Thus, the results of this research can be applied as expenditure effectiveness tools when designing for future neighboring directional wells to get high drilling performance by reducing the nonproductive time and well expenses.

Stability Analysis of Highly Deviated Boreholes to Minimize Drilling Risks and Nonproductive Time

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Ahmed K. Abbas ◽  
Ralph E. Flori ◽  
Mortadha Alsaba
Keyword(s):  
Stability Analysis ◽  
Shear Failure ◽  
Cost Effective ◽  
Failure Criteria ◽  
Horizontal Stress ◽  
Rock Failure ◽  
Wellbore Stability ◽  
Tensile Failure ◽  
Drilling Performance ◽  
Deviated Wells

The Lower Cretaceous Zubair Formation is a regionally extended gas- and oil-producing sandstone sequence in Southern Iraq. Due to the weak nature of the Zubair Formation, the lack of wellbore stability is one of the most critical challenges that continuously appears during the drilling development operations. Problems associated with lack of wellbore stability, such as the tight hole, shale caving, stuck pipe, and sidetracking, are both time-consuming and expensive. This study aimed to construct a geotechnical model based on offset well data, including rock mechanical properties, in situ stresses, and formation pore pressure, coupled with suitable rock failure criteria. Mohr–Coulomb and Mogi–Coulomb failure criteria were used to predict the potential rock failure around the wellbore. The effect of the inclination and azimuth of the deviated wells on the shear failure and tensile failure mud weights was investigated to optimize the wellbore trajectory. The results show that the best orientation to drill highly deviated wells (i.e., inclinations higher than 60 deg) is along to the minimum horizontal stress (140 deg). The recommended mud weight for this selected well trajectory ranges from 1.45 to 1.5 g/cc. This study emphasizes that a wellbore stability analysis can be applied as a cost-effective tool to guide future highly deviated boreholes for better drilling performance by reducing the nonproductive time.

Calculation and Implications of Breakdown Pressures in Directional Wellbore Stimulation

2015 ◽  
Author(s):  
Robert D. Barree ◽  
Jennifer L. Miskimins
Keyword(s):  
Shear Failure ◽  
Growth Parameters ◽  
Vertical Plane ◽  
Longitudinal Direction ◽  
In Situ Stress ◽  
Tensile Failure ◽  
Petroleum Engineering ◽  
Breakdown Pressure ◽  
Cascading Effects ◽  
Wellbore Pressure

Abstract In 1898, Kirsch published equations describing the elastic stresses around a circular hole that are still used today in wellbore pressure breakdown calculations. These equations are standard instruments used in multiple areas of petroleum engineering, however, the original equations were developed strictly for vertical well settings. In today's common directional or horizontal well situations, the equations need adjusted for both deviation from the vertical plane and orientation to the maximum and minimum horizontal in-situ stress anisotropy. This paper provides the mathematical development of these modified breakdown equations, along with examples of the implications in varying strike-slip and pore pressure settings. These examples show conditions where it is not unusual for breakdown pressure gradients to exceed 1.0 psi/ft and describes why certain stages in "porpoising" horizontal wells experience extreme breakdown issues during hydraulic fracturing treatments. The paper also discusses how, in most directional situations, the wellbore will almost always fail initially in a longitudinal direction at the borehole wall, after which the far-field stresses will take over and transverse components can be developed. Tortuosity and near wellbore friction pressure can actually add to forcing the initiation of such longitudinal fractures, which can then have cascading effects on other growth parameters such as cluster-to-cluster and stage-to-stage stress shadowing. Special considerations for highly laminated anisotropic formations, where shear failure of the wellbore may precede or preclude tensile failure, are also introduced. Such failure behaviors have significant implications on near wellbore conductivity requirements and can also greatly impact well production and recovery efforts.

scholarly journals Cracking behaviour of fine-grained soils: from laboratory testing to numerical modelling

2019 ◽  
Vol 92 ◽  
pp. 16004
Author(s):  
Pierre Gerard ◽  
Ian Murray ◽  
Alessandro Tarantino
Keyword(s):  
Effective Stress ◽  
Failure Criterion ◽  
Shear Failure ◽  
Digital Camera ◽  
Failure Criteria ◽  
Fine Grained ◽  
Fine Grained Soil ◽  
Desiccation Cracking ◽  
Stress States ◽  
Stress Dependent

Many experimental evidences suggest that desiccation cracks in clay initiate as a result of the mobilization of soil tensile strength. However this mechanical approach disregards the cohesionless and effective stress-dependent behaviour of fine-grained soil. On the other hand recent findings in the literature suggest that effective stress-dependent shear failure criteria would be appropriate to explain the mechanisms of desiccation cracking for tensile total stress states. This work aims at assessing the validity of a shear failure criterion to predict the onset of cracking in clay forms exposed to air drying. Clay forms of various geometries were experimentally subjected to non-uniform hydraulic and mechanical boundary conditions. Time and location for crack initiation are monitored using a digital camera. Cracking experiments are then modelled in a hydro-mechanical framework using an effective-stress shear failure criterion. The comparison of simulations with experimental results for both the time and the location of cracking allows assuming that cracking occurs due to failure in shearing.

scholarly journals Study on stability of filling wall under lateral large-span composite hinge fracture of hard critical block

2021 ◽  
Vol 104 (2) ◽  
pp. 003685042110216
Author(s):  
Chenghai Li ◽  
Yajie Liu ◽  
Jianbiao Bai ◽  
Qing Ge
Keyword(s):  
Field Test ◽  
Shear Failure ◽  
Lateral Displacement ◽  
Axial Stress ◽  
Tensile Failure ◽  
Shear Cracks ◽  
Large Span ◽  
The Stability ◽  
Number Of Segments ◽  
Hinge Fracture

There is still a lack of mature researches on the stability mechanism, influencing factors and control technology of the gob-side filling wall, and systematic researches on the cracking forms and characteristics of the stope roof and the stability of the filling wall are rather insufficient. This paper is aimed at investigating the deformation law of the filling wall under the large-span composite hinge fracture of the hard critical block and solving the difficulty that the large-span critical block lateral fracture poses to gob-side entry retaining. Research methods such as theoretical calculation, mechanical analysis, numerical simulation and field test were adopted comprehensively in this study. When the large-span critical block B is divided into two or three parts, its force on the immediate roof decreases with the increase in the number of segments. Meanwhile, as the number of segments grows, the displacement and axial stress of the filling wall both decrease gradually; the tensile failure weakens relatively, while the shear failure changes slightly. Moreover, both the number of shear cracks and the number of tensile cracks in the filling wall are positively correlated with the strain. When the critical block divided into four parts, the amount of lateral displacement is about 190 mm, and the axial displacement reaches the minimum (about 235 mm). The stability of the filling wall along the gob-side entry is closely related to the lateral fracture span of the stope roof. Under the lateral fracture of the hard critical block, a smaller span of the lateral fracture of the critical block corresponds to a smaller force on the filling wall and a weaker damage to the filling wall. The field test result verifies that cleaving the large-span critical block into smaller segments is conducive to reducing surrounding rock and filling wall deformation.

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

2020 ◽  
Vol 10 (2) ◽  
pp. 36-53
Author(s):  
Hussein Saeed Almalikee ◽  
Fahad M. Al-Najm
Keyword(s):  
Horizontal Wells ◽  
Wellbore Stability ◽  
Type I ◽  
Type Ii ◽  
Drilling Mud ◽  
Wellbore Instability ◽  
Type Iv ◽  
Planning And Design ◽  
Horizontal Wellbore ◽  
Wellbore Failure

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.

scholarly journals Study on the Surge-Swab Pressure considering the Effect of the Cutting Plug in Shale Drilling

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Tianyi Tan ◽  
Hui Zhang ◽  
Xusheng Ma ◽  
Yufei Chen
Keyword(s):  
Horizontal Wells ◽  
Wellbore Stability ◽  
Pressure Management ◽  
Accurate Calculation ◽  
Wellbore Instability ◽  
Wellbore Pressure ◽  
The Difference ◽  
Open Pipe ◽  
Frequent Problem

Wellbore instability is a frequent problem of shale drilling. Accurate calculation of surge-swab pressures in tripping processes is essential for wellbore pressure management to maintain wellbore stability. However, cutting plugs formed in shale horizontal wells have not been considered in previous surge-swab pressure models. In this paper, a surge-swab pressure model considering the effect of cutting plugs is established for both open pipe string and closed pipe string conditions; In this model, the osmotic pressure of a cutting plug is analyzed. The reduction of cutting plug porosity due to shale hydration expansion and dispersion is considered, ultimately resulting in an impermeable cutting plug. A case study is conducted to analyze swab pressures in a tripping out process. The results show that, in a closed pipe condition, the cutting plug significantly increases the swab pressures below it, which increase with the decrease of cutting plug porosity and the increase of cutting plug length. Under the give condition, the swab pressure at the bottom of the well increases from 3.60 MPa to 8.82 MPa due to the cutting plug, increasing by 244.9%. In an open pipe string condition, the cutting plug affects the flow rate in the pipes and the annulus, resulting in a higher swab pressure above the cutting plug compared to a no-cutting plug annulus. The difference increases with the decrease of the porosity and the increase of the length and the measured depth of the cutting plug. Consequently, the extra surge-swab pressures caused by cutting plugs could result in wellbore pressures out of safety mud density window, whereas are ignored by previous models. The model proposes a more accurate wellbore pressure prediction and guarantees the wellbore stability in shale drilling.

Mesoscopic Study of Ductile Fracture of Aluminium Alloy LY12CZ

2004 ◽  
Vol 261-263 ◽  
pp. 45-50
Author(s):  
T. Li ◽  
Qing Yuan Wang ◽  
X.M. Yuan
Keyword(s):  
Ductile Fracture ◽  
Aluminium Alloy ◽  
Shear Failure ◽  
Fracture Morphology ◽  
Tensile Failure ◽  
Fracture Parameter ◽  
Growth Ratio ◽  
Points Of View ◽  
Stress States ◽  
Critical Void

In the present paper, axisymmetric smooth and notched specimens of aluminium alloy LY12CZ were monotonic tension tested to study the ductile fracture behavior and evaluate the suitability for the critical void growth ratio, VGC of the material, from the micro and macro points of view. It's found that the material would change fracture morphology from tensile to shear failure in the various stress states; the ductile fracture parameter VGC is sensitive to the fracture morphology which is applicable for the case of tensile failure while not suitable for the case of the shear failure, i.e. the case of smooth tensile specimens.

scholarly journals The dynamic characteristics of backfill made of mining waste at one-dimensional dynamic and static loading

2021 ◽  
Vol 37 (1) ◽  
Author(s):  
X. Yang ◽  
Y. Zhang
Keyword(s):  
Shear Failure ◽  
Split Hopkinson Pressure Bar ◽  
Axial Stress ◽  
Critical Role ◽  
Tensile Failure ◽  
Hopkinson Pressure Bar ◽  
Axial Pressure ◽  
Confining Stress ◽  
Mining Operations ◽  
Shpb Test

Backfill is widely used in underground mines around the world for its effective reduction in environmental impact of mining operations by utilizing a part of mine waste as underground backfill material. The strength of backfill plays a critical role in improving stop stability and preventing surface subsidence. In this paper, a series of SHPB (Split Hopkinson Pressure Bar) tests with different strain rates and static axial pressures are conducted. The results show that: (1) The dynamic strength of the backfill specimen increases first and then decreases with the increase of static axial pressure. It reaches a maximum when the static axial pressure reaches 30% of the static compressive strength in the SHPB test. (2) The stress-strain curves of backfill specimens can be divided into three stages: elastic stage, yield stage and failure stage. The compaction stage is obscure. The backfill specimens are not sensitive at low strain rate. (3)With the increase of incident energy, the absorbed energy mounts. (4) The failure mode of the backfill specimen is tensile failure when static axial pressure is 0MPa in the SHPB test while it becomes compression shear failure when static axial pressure is higher than 0MPa. (5) The backfill specimen is very compressed when it is loaded with axial stress and confining stress simultaneously. This compression property of backfill specimen may be related to the nature of hydration products at different curing times, which requires further research in the future.

The Role of Elasto-Plasticity in Cavity Shape and Sand Production in Oil and Gas Wells

SPE Journal ◽  
2018 ◽  
Vol 24 (02) ◽  
pp. 744-756 ◽  
Author(s):  
Haotian Wang ◽  
Mukul M. Sharma
Keyword(s):  
Shear Failure ◽  
Oil And Gas ◽  
Shear Bands ◽  
Failure Criteria ◽  
Tensile Failure ◽  
Production Model ◽  
Sand Production ◽  
Plastic Properties ◽  
Cavity Shape ◽  
Failure Patterns

Summary Previous experimental observations have shown the formation of distinct failure patterns and cavity shapes under different stress and flow conditions. With isotropic stress, spiral failure patterns with localized shear bands are likely to form. On the other hand, under anisotropic stress, V-shaped cavities, dog-ear cavities, or slit-mode cavities are usually observed. However, the mechanisms for the development of these sanding cavities have not been fully articulated. In addition, to accurately predict the onset of sanding and to predict the sand-production rate, it is crucial to capture the physics of the formation of these cavities during sand production. This paper presents a fully coupled poro-elasto-plastic, 3D sand-production model for sand-production prediction around openhole and perforated wellbores in a weakly consolidated formation. Sanding criteria are based on a combination of shear failure, tensile failure, and compressive failure from the Mohr-Coulomb theory and strain-hardening/softening. After the failure criteria are met, an algorithm for the entrainment of the sand based on the calculation of hydrodynamic forces is implemented to predict sand erosion and transport. Dynamic mesh refinement has been implemented to effectively capture the strain-localization regions. The model has been validated with multiple analytical solutions. In addition, it is applied to compare with previous sand-production experiments that have explored the different cavity shapes formed under different conditions. The model is capable of not only explaining the mechanisms responsible for each type of cavity shape but also predicting the cavity shape that will be formed under a specific set of conditions. Parametric studies for these cases provide an additional insight into the important role that the post-yield, poro-elasto-plastic properties of the sand play in controlling the sanding mechanisms and cavity development. This allows us to predict, much more accurately, the onset of sanding and the sanding rate.

Sign in / Sign up

Export Citation Format

Share Document