Wellbore Stability Beyond Mud Weight

2021 ◽  
Author(s):  
Khaqan Khan ◽  
Mohammad Altwaijri ◽  
Sajjad Ahmed
Keyword(s):  
Oil And Gas ◽  
Rock Strength ◽  
Tectonic Stress ◽  
Strength Properties ◽  
Wellbore Stability ◽  
Drilling Mud ◽  
Stress Regime ◽  
Drilling Parameters ◽  
Well Trajectory ◽  
Formation Pore Pressure

Abstract Drilling oil and gas wells with stable and good quality wellbores is essential to minimize drilling difficulties, acquire reliable openhole logs data, run completions and ensure well integrity during stimulation. Stress-induced compressive rock failure leading to enlarged wellbore is a common form of wellbore instability especially in tectonic stress regime. For a particular well trajectory, wellbore stability is generally considered a result of an interplay between drilling mud density (i.e., mud weight) and subsurface geomechanical parameters including in-situ earth stresses, formation pore pressure and rock strength properties. While role of mud system and chemistry can also be important for water sensitive formations, mud weight is always a fundamental component of wellbore stability analysis. Hence, when a wellbore is unstable (over-gauge), it is believed that effective mud support was insufficient to counter stress concentration around wellbore wall. Therefore, increasing mud weight based on model validation and calibration using offset wells data is a common approach to keep wellbore stable. However, a limited number of research articles show that wellbore stability is a more complex phenomenon affected not only by geomechanics but also strongly influenced by downhole forces exerted by drillstring vibrations and high mud flow rates. Authors of this paper also observed that some wells drilled with higher mud weight exhibit more unstable wellbore in comparison with offset wells which contradicts the conventional approach of linking wellbore stability to stresses and rock strength properties alone. Therefore, the objective of this paper is to analyze wellbore stability considering both geomechanical and drilling parameters to explain observed anomalous wellbore enlargements in two vertical wells drilled in the same field and reservoir. The analysis showed that the well drilled with 18% higher mud weight compared with its offset well and yet showing more unstable wellbore was, in fact, drilled with more aggressive drilling parameters. The aggressive drilling parameters induce additional mechanical disturbance to the wellbore wall causing more severe wellbore enlargements. We devised a new approach of wellbore stability management using two-pronged strategy. It focuses on designing an optimum weight design using geomechanics to address stress-induced wellbore failure together with specifying safe limits of drilling parameters to minimize wellbore damage due to excessive downhole drillstring vibrations. The findings helped achieve more stable wellbore in subsequent wells with hole condition meeting logging and completion requirements as well as avoiding drilling problems.

APPLICATION OF GUIDELINE CHARTS IN DECISIONMAKING ON WELL TRAJECTORY AND MUD WEIGHT PROGRAM

2001 ◽  
Vol 41 (1) ◽  
pp. 609
Author(s):  
X. Chen ◽  
C.P. Tan ◽  
C.M. Haberfield
Keyword(s):  
Stability Analysis ◽  
Case Studies ◽  
In Situ Stress ◽  
Wellbore Stability ◽  
Material Strength ◽  
Stress Regime ◽  
Wellbore Instability ◽  
Well Trajectory

To prevent or minimise wellbore instability problems, it is critical to determine the optimum wellbore profile and to design an appropriate mud weight program based on wellbore stability analysis. It is a complex and iterative decisionmaking procedure since various factors, such as in-situ stress regime, material strength and poroelastic properties, strength and poroelastic anisotropies, initial and induced pore pressures, must be considered in the assessment and determination.This paper describes the methodology and procedure for determination of optimum wellbore profile and mud weight program based on rock mechanics consideration. The methodology is presented in the form of guideline charts and the procedure of applying the methodology is described. The application of the methodology and procedure is demonstrated through two field case studies with different in-situ stress regimes in Australia and Indonesia.

The Effects of Filter-Cake Buildup and Time-Dependent Properties on the Stability of Inclined Wellbores

SPE Journal ◽  
2011 ◽  
Vol 16 (04) ◽  
pp. 1010-1028 ◽  
Author(s):  
Minh H. Tran ◽  
Younane N. Abousleiman ◽  
Vinh X. Nguyen
Keyword(s):  
Pore Pressure ◽  
Filter Cake ◽  
Wellbore Stability ◽  
Time Dependent ◽  
Transient Effects ◽  
Drilling Mud ◽  
Property Variation ◽  
Lost Circulation ◽  
Wellbore Strengthening ◽  
Formation Pore Pressure

Summary The effects of filter-cake buildup and/or filter-cake-property variation with time on wellbore stability have been plaguing the industry. The increasing use of lost-circulation materials (LCMs) in recent years for wellbore strengthening in weak and/or depleted formations necessitates models that can predict these effects. However, the complexities of effective-stress and pore-pressure evolution around the borehole while drilling, coupled with the transient variation of mud-filtration properties, have delayed such modeling efforts. In this paper, the analytical solutions for the time-dependent effects of mudcake buildup and mudcake properties on the wellbore stresses and formation pore pressure, and thus the safe-drilling-mud-weight window, are derived. The transient effects of mudcake buildup and mudcake buildup coupled with its permeability reduction during filtration on the safe-drilling-mudweight window are illustrated through numerical examples. The results showed that the safe-mudweight windows were greatly affected by the buildup of filter cake and its permeability variation. For example, the analysis for filter-cake buildup with cake permeability of 10–2 md showed that the safe-mudweight window was widened by 0.5 g/cc after 2.5 hours post-excavation when compared to the case of a wellbore without mudcake. On the other hand, a lower mudcake permeability of 10–3 md widened the mudweight window by as much as 1 g/cc. Last but not least, the analyses revealed that even for mudcake permeability as low as 10–3 md, neglecting the permeable nature of the mudcake can result in overestimation of the safe-drilling-mudweight window.

A Comprehensive Wellbore Stability Model Considering Poroelastic and Thermal Effects for Inclined Wellbores in Deepwater Drilling

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Xuyue Chen ◽  
Deli Gao ◽  
Jin Yang ◽  
Ming Luo ◽  
Yongcun Feng ◽  
...  
Keyword(s):  
Thermal Effects ◽  
Oil And Gas ◽  
Oil And Gas Industry ◽  
Wellbore Stability ◽  
Pressure Gradients ◽  
Stress Regime ◽  
Collapse Pressure ◽  
Wellbore Instability ◽  
Deepwater Drilling ◽  
Stability Model

Exploring and developing oil and gas in deepwater field is an important trend of the oil and gas industry. Development of deepwater oil and gas fields from a platform always requires a number of directional wells or extended reach wells targeting to different depth of water in various azimuth. Drilling of these wells is mostly associated with a series of wellbore instability problems that are not encountered in onshore or shallow water drilling. In the past decades, a number of studies on wellbore stability have been conducted. However, few of the models are specific for wellbore stability of the inclined deepwater wellbores. In this work, a comprehensive wellbore stability model considering poroelastic and thermal effects for inclined wellbores in deepwater drilling is developed. The numerical method of the model is also presented. The study shows that for a strike-slip stress regime, the wellbore with a low inclination poses more risk of wellbore instability than the wellbore with a high inclination. It also shows that cooling the wellbore will stabilize the wellbore while excessive cooling could cause wellbore fracturing, and the poroelastic effect could narrow the safe mud weight window. The highest wellbore collapse pressure gradients at all of the analyzed directions are obtained when poroelastic effect is taken into account meanwhile the lowest wellbore fracture pressure gradients at all of the analyzed directions are obtained when both of poroelastic effect and thermal effect are taken into account. For safe drilling in deepwater, both of thermal and poroelastic effects are preferably considered to estimate wellbore stability. The model provides a practical tool to predict the stability of inclined wellbores in deepwater drilling.

Efficient Wellbore Optimization Through Rock Property Analysis and Evaluation

2021 ◽  
Author(s):  
Joshua Oluwayomi Ogunrinde
Keyword(s):  
Poisson’S Ratio ◽  
Rock Strength ◽  
Wellbore Stability ◽  
Poisson's Ratio ◽  
Drilling Mud ◽  
Rock Property ◽  
Analysis And Evaluation ◽  
Property Analysis ◽  
Sonic Log ◽  
Well Data

Abstract There are numerous problems encountered during drilling such as wellbore instability, drilling mud weight estimation, as well as selecting good casing and bit for the drilling operations. It is therefore important to understand and accurately determine the strength of the rock in order to avoid these common drilling problems which are mostly encountered during well operations. It is of paramount importance to determine uniaxial compressive strength (UCS) from core and sonic log data so as to accurately predict rock strength for better well planning. In this work, we were able to obtain a correlation to determine UCS from data obtained from ten (10) wells in different locations in onshore Niger Delta using the regression analysis method. The correlation of UCS versus Poisson's ratio gave R2 value of 90.0%. The R2- value tending towards one (1) indicates that this model can be reliably used to predict ND-UCS and the p<0.05 shows that there is significant relationship between ND-UCS and Poisson's ratio. The model was validated with an entirely different well data and it predicted over 89% rock UCS data when compared to the actual rock UCS data. This study also provides an understanding of the variation in UCS and Poisson's ratio with depth for effective rock property analysis and evaluation. These correlations will help well engineers to make informed decisions on rock strength predictions during well planning and operations as well as manage wellbore stability optimally.

Wellbore-Stability Analysis by Integrating a Modified Hoek-Brown Failure Criterion With Dual-Porochemoelectroelastic Theory (includes associated erratum)

SPE Journal ◽  
2019 ◽  
Vol 24 (05) ◽  
pp. 1957-1981 ◽  
Author(s):  
Chao Liu ◽  
Yanhui Han ◽  
Hui–Hai Liu ◽  
Younane N. Abousleiman
Keyword(s):  
Stability Analysis ◽  
Pore Pressure ◽  
Failure Criterion ◽  
Rock Strength ◽  
Chemical Potential ◽  
Wellbore Stability ◽  
Natural Fracture ◽  
Analysis Tool ◽  
Drilling Mud

Summary When drilling through naturally fractured formations, the existence of natural fractures affects the fluid diffusion and stress distribution around the wellbore and induces degradation of rock strength. For chemically active formations, such as shale, the chemical–potential difference between the drilling mud and the shale–clay matrix further complicates the nonmonotonic coupled pore–pressure processes in and around the wellbore. In this work, we apply a recently formulated theory of dual–porosity/permeability porochemoelectroelasticity to predict the time evolution of mud–weight windows, while calculating stresses and pore pressure around an inclined wellbore drilled in a fractured shale formation. The effects of natural–fracture geometric and spatial distributions coupled with the chemical activity are considered in the wellbore–stability analysis. To account for the degrading effect of the fractured shale matrix on the bulk rock strength, a modified Hoek–Brown (MHB) criterion is developed to more closely describe the in–situ state of stress effects on the compressive shearing strength at great depth. Compared with the original Hoek–Brown (HB) failure criterion, the MHB criterion considers the influence of the intermediate principal stress and thus shows better agreement with true–triaxial data for various rocks at varying stress levels. The MHB criterion converges to the original HB criterion when the confining in–situ stresses are equal. Two field case studies indicate that this novel integrative methodology is capable of predicting the operational drilling–mud–weight windows used in these two cases. Another advantage of this newly developed technique is that it can be used as a back–analysis tool to estimate the fracture–matrix permeability from field operational data.

Anisotropy signatures in the Cooper Basin of Australia: Stress versus fractures

2016 ◽  
Vol 4 (2) ◽  
pp. SE51-SE61 ◽  
Author(s):  
Stephanie Tyiasning ◽  
Dennis Cooke
Keyword(s):  
Seismic Data ◽  
Oil And Gas ◽  
Seismic Anisotropy ◽  
Transverse Isotropy ◽  
Ground Truth ◽  
Tectonic Stress ◽  
Reverse Fault ◽  
Stress Regime ◽  
Velocity Anisotropy ◽  
Cooper Basin

Theoretically, vertical fractures and stress can create horizontal transverse isotropy (HTI) anisotropy on 3D seismic data. Determining if seismic HTI anisotropy is caused by stress or fractures can be important for mapping and understanding reservoir quality, especially in unconventional reservoirs. Our study area was the Cooper Basin of Australia. The Cooper Basin is Australia’s largest onshore oil and gas producing basin that consists of shale gas, basin-centered tight gas, and deep coal play. The Cooper Basin has unusually high tectonic stress, with most reservoirs in a strike-slip stress regime, but the deepest reservoirs are interpreted to be currently in a reverse-fault stress regime. The seismic data from the Cooper Basin exhibit HTI anisotropy. Our main objective was to determine if the HTI anisotropy was stress induced or fracture induced. We have compared migration velocity anisotropy and amplitude variation with offset anisotropy extracted from a high-quality 3D survey with a “ground truth” of dipole sonic logs, borehole breakout, and fractures interpreted from image logs. We came to the conclusion that the HTI seismic anisotropy in our study area is likely stress induced.

STEP Change in Preventing Stuck Pipe and Tight Hole Events Using Machine Learning

2021 ◽  
Author(s):  
Salah Bahlany ◽  
Mohammed Maharbi ◽  
Saud Zakwani ◽  
Faisal Busaidi ◽  
Ferrante Benvenuti
Keyword(s):  
Oil And Gas ◽  
Wellbore Stability ◽  
Sensor Data ◽  
Pilot Phase ◽  
Stability Problems ◽  
Engineering Data ◽  
Execution Phase ◽  
Drilling Parameters ◽  
Drilling Operations ◽  
Productive Time

Abstract Wellbore stability problems, such as stuck pipe and tight spots, are one of the most critical risks that impact drilling operations. Over several years, Oil and Gas Operator in Middle East has been facing problems associated with stuck pipe and tight spot events, which have a major impact on drilling efficiency, well cost, and the carbon footprint of drilling operations. On average, the operator loses 200 days a year (Non-Productive Time) on stuck pipe and associated fishing operations. Wellbore stability problems are hard to predict due to the varying conditions of drilling operations: different lithology, drilling parameters, pressures, equipment, shifting crews, and multiple well designs. All these factors make the occurrence of a stuck pipe quite hard to mitigate only through human intervention. For this reason, The operator decided to develop an artificial intelligence tool that leverages the whole breadth and depth of operator data (reports, sensor data, well engineering data, lithology data, etc.) in order to predict and prevent wellbore stability problems. The tool informs well engineers and rig crews about possible risks both during the well planning and well execution phase, suggesting possible mitigation actions to avoid getting stuck. Since the alarms are given ahead of the bit, several hours before the possible occurrence of the event, the well engineers and rig crews have ample time to react to the alarms and prevent its occurrence. So far, the tool has been deployed in a pilot phase on 38 wells giving 44 true alarms with a recall of 94%. Since mid-2021 operator has been rolling out the tool scaling to the whole drilling operations (over 40 rigs).

Nanoparticles As Promising Additives to Improve the Drilling of Egyptian Oil and Gas Fields

2020 ◽  
Author(s):  
Ahmed Mady ◽  
Omar Mahmoud ◽  
Abdel Sattar Dahab
Keyword(s):  
Oil And Gas ◽  
Nile Delta ◽  
Drilling Fluid ◽  
High Surface ◽  
Wellbore Stability ◽  
Western Desert ◽  
Drilling Process ◽  
Drilling Mud ◽  
Gas Field ◽  
The Impact

Abstract Egypt is both one of the major oil-producing non-OPEC countries and one of the oldest energy producers in the Middle East. Recently, the Egyptian government have signed several agreements for the exploration of oil and gas in several provinces/regions including; the Mediterranean, the Western Desert, the Nile Delta, and the Gulf of Suez. Petroleum companies have given great attention to Egypt’s new discoveries such as Zohr Gas Field and Nour exploration prospect. Successful drilling operations to reach the oil and gas targets depends strongly on the effectiveness of the drilling fluid (mud). It can be considered as the heart of the drilling process, where they are used to fulfil several valuable functions. Drilling fluid technology is one of the most targeted and developed technologies worldwide. Several studies have examined the use of various types of nanoparticles (NPs) to enhance the properties and improve the performance of muds. NP can be defined as a simple particle structure with a size in the range of nanometers. The effectiveness of NPs can be accredited to their small size and high surface-area-to-volume ratio. Using NPs showed promising enhancements on the rheological and filtration characteristics as well as thermal stability and carrying capacity of the drilling fluid. Moreover, adding NPs to the drilling mud was found to minimize the shale permeability and thus, promote wellbore stability. The swelling and collapse of shale formations is expected under drilling with water-based mud, which might complicate the drilling operation. In the present work four types of NPs (nanosilica, nanoaluminium, nanotitanium, and nano copper oxide) were tested as promising additives to improve the characteristics of KCL-Polymer mud, which is mainly used to drill shaly formations. The impact of NPs-type, -size, and -concentration were thoroughly investigated using standard viscometer and API filter press. The results showed higher potential of nanotitanium and nanoaluminium to enhance the mud properties when used at small concentrations (0.3–0.5 wt.%). This research paper discusses a latest application and presents the most valuable findings concerning the efficient use of NPs in the drilling fluid industry. On this basis, different recommendations are stated, which might help researchers to better understand NPs’ functionality in this area of application and promote using NPs-based drilling muds as cost-effective and environmental-friendly fluids to drill the Egyptian oil and gas wells.

scholarly journals Study on Wellbore Stability and Instability Mechanism in Piedmont Structures

2015 ◽  
Vol 8 (1) ◽  
pp. 208-213
Author(s):  
Qiang Tan ◽  
Baohua Yu ◽  
Jingen Deng ◽  
Kai Zhao ◽  
Jianguo Chen
Keyword(s):  
Oil And Gas ◽  
Drilling Fluid ◽  
Fluid Pressure ◽  
Tectonic Stress ◽  
Mechanical Analysis ◽  
In Situ Stress ◽  
Wellbore Stability ◽  
Instability Mechanism ◽  
Sealing Ability ◽  
Stability And Instability

Piedmont tectonic belts are rich of oil and gas resources, however the intense tectonic stress and broken formation may cause great drilling problems in piedmont structures such as borehole collapse, lost circulation and gas cutting. Through analysis of in situ stress properties, bedding structure and mechanical characteristics, wellbore instability mechanism was expounded from rock mechanics, chemistry of drilling fluid and drilling technology. The high tectonic stress, formation strength decreasing and fluid pressure rising after mud filtrate seepage are main reasons for borehole collapse. The methods of calculating collapse and fracture pressure and determining drilling safety density window were put forward based on mechanical analysis. In order to reduce drilling problems in piedmont structures, some countermeasures should be taken from optimizing well track and casing program, using proper mud density, improving inhibitive and sealing ability of drilling fluid. Good sealing ability can reduce seepage and cut off pressure transmission, enhancing the effective support force. This is the key technology of maintaining wellbore stability in hard brittle shale in piedmont structures.

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