scholarly journals 3D mechanical earth model for optimized wellbore stability, a case study from South of Iraq

2021 ◽  
Author(s):  
Abdulaziz M. Abdulaziz ◽  
Hayder L. Abdulridha ◽  
Abdel Sattar A. Dahab ◽  
Shaban Alhussainy ◽  
Ahmed K. Abbas
Keyword(s):  
Three Dimensional ◽  
Friction Angle ◽  
Failure Criteria ◽  
Wellbore Stability ◽  
Rock Properties ◽  
Earth Model ◽  
The North ◽  
Geomechanical Analysis ◽  
Mechanical Earth Model ◽  
South Of Iraq

AbstractWellbore instability issues represent the most critical problems in Iraq Southern fields. These problems, such as hole collapse, tight hole and stuck pipe result in tremendous increasing in the nonproductive time (NPT) and well costs. The present study introduced a calibrated three-dimensional mechanical earth model (3DMEM) for the X-field in the South of Iraq. This post-drill model can be used to conduct a comprehensive geomechanical analysis of the trouble zones from Sadi Formation to Zubair Reservoir. A one-dimensional mechanical earth model (1DMEM) was constructed using Well logs, mechanical core tests, pressure measurements, drilling reports, and mud logs. Mohr–Coulomb and Mogi–Coulomb failure criteria determined the possibility of wellbore deformation. Then, the 1DMEMs were interpolated to construct a three-dimensional mechanical earth model (3DMEM). 3DMEM indicated relative heterogeneity in rock properties and field stresses between the southern and northern of the studied field. The shale intervals revealed prone to failure more than others, with a relatively high Poisson's ratio, low Young's modulus, low friction angle, and low rock strength. The best orientation for directional Wells is 140° clockwise from the North. Vertical and slightly inclined Wells (less than 40°) are more stable than the high angle directional Wells. This integration between 1 and 3DMEM enables anticipating the subsurface conditions for the proactive design and drilling of new Wells. However, the geomechanics investigations still have uncertainty due to unavailability of enough calibrating data, especially which related with maximum horizontal stresses magnitudes.

Geomechanics Insights for Successful Well Delivery in Complex Kutch - Saurashtra Offshore Region

2021 ◽  
Author(s):  
Rahul Talreja ◽  
Somessh Bahuguna ◽  
Rajeev Kumar ◽  
Joseph Zacharia ◽  
Ashani Kundan ◽  
...  
Keyword(s):  
Deccan Trap ◽  
Shear Failure ◽  
Wellbore Stability ◽  
Earth Model ◽  
Plane Failure ◽  
Gun Barrel ◽  
Geomechanical Analysis ◽  
Fracture Sealing ◽  
Mechanical Earth Model ◽  
Weak Plane

Abstract Subsurface lithofacies sequences encountered in the Kutch & Saurashtra Basin has its own set of challenges brought about due to its complex geological settings. These challenges are related to drilling, logging and completion and demand rigorous planning for the upcoming wells with detailed analysis of hazards associated with the overburden and reservoir rocks. In the study, these challenges are found to be linked with three prime geological sequences. Detailed integrated geomechanical analysis with inputs from drilling parameters, real-time formation experience, geophysical and geological are conducted for the improvement in borehole condition and improvising the effective drilling rate. A customized geomechanical workflow has been adopted to construct Mechanical Earth Model (MEM, Plumb et al., 2000) for strategic wells across the basin. Wellbore stability events related to geomechanics were reproduced and analyzed. The cause of the events was established and mitigatory methods were proposed. In addition, stress orientation along the wellbore trajectory and across the basin was estimated using breakouts identified on images and multi-arm calipers. Fast shear azimuth from Dipole Shear Sonic anisotropy analysis was also integrated to provide more robust and accurate estimates. Wells in the region are characterized by slow ROP, high torque and drag, wellbore instabilities (severe held ups, cavings, stuck pipes, string stalling etc.) and challenges while logging and running casing. The study has characterized these challenges and identified required solutions linked to the three geological sequences - weak Tertiary, Late Cretaceous Deccan Trap and Early Cretaceous to Jurassic clastic formations. The Tertiary formations are relatively weak (UCS∼300 to 1500psi) and prone to sanding and cavings due to breakouts. MEM based mud weight window estimation predicts that shear/failure hole collapse can be prevented using 10ppg to 11ppg mud weight. The formations below the Deccan Trap are locally categorized under Mesozoic sequence. The Deccan Trap and Mesozoic formations are extremely hard, tight, extremely stressed, heavily fractured and in some areas are also of HPHT nature. Rock strength shows a wide variation (UCS ∼5,000psi to 25,000psi) making bit selection a difficult task. Borehole failure is complex and cuttings analysis shows the signature of both shear and weak plane failure. Fractures on the image logs, rotation of breakouts, and fast shear azimuth support this theory. Mixing fracture sealing agents along with the use of optimal mud weights is found to be the most likely drilling solution. The understanding developed in the region and implementation of recommended steps assisted in successful drilling of two recent wells wherein gun-barrel shape borehole condition in both Tertiary and the Mesozoic sequence was achieved. The non-productive time was reduced by nearly 40 days increasing the effective ROP by 40%. In addition, smooth borehole prevented any major issues while carrying out casing and cementing operations.

Application of Computational Intelligence in Generating Synthetic Reservoir Rock Mechanical Parameters for Building Geo-Models.

2015 ◽  
Author(s):  
L. C. Akubue ◽  
A.. Dosunmu ◽  
F. T. Beka
Keyword(s):  
Neural Network ◽  
Statistical Analysis ◽  
Numerical Models ◽  
Petroleum Industry ◽  
Oil Field ◽  
Wellbore Stability ◽  
Reservoir Rock ◽  
Rock Properties ◽  
Earth Model ◽  
Sonic Log

Abstract Oil field Operations such as wellbore stability Management and variety of other activities in the upstream petroleum industry require geo-mechanical models for their analysis. Sometimes, the required subsurface measurements used to estimate rock parameters for building such models are unavailable. On this premise, past studies have offered variety of methods and investigative techniques such as empirical correlations, statistical analysis and numerical models to generate these data from available information. However, the complexity of the relationships that exists between the natural occurring variables make the aforementioned techniques limited. This work involves the application of Artificial Neural Networks (ANNs) to generating rock properties. A three-layer back-propagation neural network model was applied predicting pseudo-sonic data using conventional wireline log data as input. Four well data from a Niger-Delta field were used in this study, one for training, one for validating and the two others for generating and testing results. The network was trained with different sets of initial random weights and biases using various learning algorithms. Root mean square error (RMSE) and correlation coefficient (CC) were used as key performance indicators. This Neural-Network-Generated-Sonic-log was compared with those generated with existing correlations and statistical analysis. The results showed that the most influential input vectors with various configurations for predicting sonic log were Depth-Resistivity-Gamma ray-Density (with correlating coefficient between 0.7 and 0.9). The generated sonic was subsequently used to compute for other elastic properties needed to build mechanical earth model for evaluating the strength properties of drilled formations, hence optimise drilling performance. The models are useful in Minimizing well cost, as well as reducing Non Productive Time (NPT) caused by wellbore instability. This technique is particularly useful for mature fields, especially in situations where obtaining this well logs are usually not practicable.

Uncertainty Evaluation of Wellbore Stability Using Comparative Rock Strength Criterions

2020 ◽  
Author(s):  
Rasool Khosravanian ◽  
Bernt Sigve Aadnøy
Keyword(s):  
Sensitivity Analysis ◽  
Wellbore Stability ◽  
Tensile Failure ◽  
Rock Properties ◽  
Uncertainty Evaluation ◽  
Fluid Loss ◽  
Real Problem ◽  
Wellbore Integrity ◽  
Drilling Operation ◽  
Geomechanical Analysis

Abstract The requirement of uncertainty analysis has shifted the transformation of sensitivity analysis from the deterministic area to the stochastic area.Geomechanical wellbore integrity problems during drilling operation can occur due to wellbore shear failure or tensile failure. To guarantee wellbore integrity, breakout and fracture geomechanical analysis is essential to estimate the Safe Mud Weight Window (SMWW). Wellbore stability problems causes many challenges in a drilling operation, such as pipe sticking, wellbore collapse, fluid loss and poor cement jobs. A drilling engineer must minimize the risk of these problems, however, there is a considerable uncertainty of different parameters such as geomechanical rock properties of drilled formation, and, data and parameters gathering are often incomplete. This uncertainty of main parameters have impact on the resulting SMWW.This paper perform an uncertainty evaluation of wellbore stability and its effect on the optimum interval of SMWW. The SMWW Uncertainty Evaluation of Wellbore Stability assessment for two failure criteria are compared, Mohr-Coulomb and Modified Lade criterion. We apply Monte Carlo simulations to investigate the uncertainty of the models and we do a sensitivity analysis and confidence level analysis. The paper will show the advantage of including uncertainty evaluation when determining the optimum SMWW window, as opposed to classical deterministic analysis. A case study is presented to draw a perfect understanding of the foundation of the MCS approach with practical and good results. It confirmed the capability of the proposed approach in solving such a strong-nonlinear, complex real problem.

scholarly journals VARIATION OF THE INTRINSIC ROCK PROPERTIES ON HOEK-BROWN FAILURE CRITERION PARAMETERS

2021 ◽  
Vol 36 (4) ◽  
pp. 73-84
Author(s):  
Sina Salajegheh ◽  
Kourosh Shahriar ◽  
Hossein Jalalifar ◽  
Kaveh Ahangari
Keyword(s):  
Inverse Relationship ◽  
Rock Strength ◽  
Contact Stiffness ◽  
Friction Angle ◽  
Failure Criteria ◽  
Rock Properties ◽  
Fundamental Parameter ◽  
Constant Parameter ◽  
Rock Failure Criteria ◽  
Triaxial Compressive Strength

The Hoek-Brown (H-B) criterion is one of the most commonly used rock failure criteria in recent years. This criterion includes a constant parameter called mi which is a fundamental parameter for estimating rock strength. Due to the importance of the mi parameter in the H-B criterion, it is necessary to conduct comprehensive studies on various aspects of the effect of this parameter on the behavior of rocks. Therefore, in this study, using numerical simulation of the Triaxial Compressive Strength (TCS) tests in PFC-2D code, the effects of microscopic properties of different rocks on the H-B parameter mi have been studied. Based on the results of this study, it was found that the effects of micro-parameters on the H-B parameter mi can be different depending on the type of rock, however this parameter has an inverse relationship to the micro-parameters of bond tensile strength and bond fraction of the rocks. Also, the mi parameter increases with an increase in the micro-parameters of the friction coefficient, the friction angle, the particle contact modulus, and the contact stiffness ratio of rocks.

scholarly journals A Simple Three-Dimensional Failure Criterion for Jointed Rock Masses under True Triaxial Compression

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Yaohui Gao ◽  
Chunsheng Zhang ◽  
Zhaofeng Wang ◽  
Jun Chen
Keyword(s):  
Failure Criterion ◽  
Triaxial Compression ◽  
Three Dimensional ◽  
Friction Angle ◽  
Failure Criteria ◽  
Jointed Rock ◽  
Rock Masses ◽  
True Triaxial ◽  
Jointed Rock Masses ◽  
Triaxial Strength

The joint configuration and the intermediate principal stress have a significant influence on the strength of rock masses in underground engineering. A simple three-dimensional failure criterion is developed in this study to predict the true triaxial strength of jointed rock masses. The proposed failure criterion in the deviatoric and meridian planes adopts the elliptic and hyperbolic forms to approximate the Willam–Warnke and Mohr–Coulomb failure criterion, respectively. The four parameters in the proposed failure criterion have close relationships with the cohesion and the internal friction angle and can be linked with the joint inclination angle using a cosine function. Two suits of true triaxial strength data are collected to validate the correctness of the proposed failure criterion. Compared with other failure criteria, the proposed failure criterion is more reasonable and acceptable to describe the strength of jointed rock masses.

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