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.

A Novel Method to Determine the Drilling Fluid Density for Gypsum-Salt Layer

2021 ◽  
Author(s):  
Jitong Liu ◽  
Wanjun Li ◽  
Haiqiu Zhou ◽  
Yixin Gu ◽  
Fuhua Jiang ◽  
...  
Keyword(s):  
Drilling Fluid ◽  
In Situ Stress ◽  
Wellbore Stability ◽  
Shrinkage Rate ◽  
Fluid Density ◽  
Salt Layer ◽  
Rock Creep ◽  
Key Factor ◽  
Well Abandonment

Abstract The reservoir underneath the salt bed usually has high formation pressure and large production rate. However, downhole complexities such as wellbore shrinkage, stuck pipe, casing deformation and brine crystallization prone to occur in the drilling and completion of the salt bed. The drilling safety is affected and may lead to the failure of drilling to the target reservoir. The drilling fluid density is the key factor to maintain the salt bed’s wellbore stability. The in-situ stress of the composite salt bed (gypsum-salt -gypsum-salt-gypsum) is usually uneven distributed. Creep deformation and wellbore shrinkage affect each other within layers. The wellbore stability is difficult to maintain. Limited theorical reference existed for drilling fluid density selection to mitigate the borehole shrinkage in the composite gypsum-salt layers. This paper established a composite gypsum-salt model based on the rock mechanism and experiments, and a safe-drilling density selection layout is formed to solve the borehole shrinkage problem. This study provides fundamental basis for drilling fluid density selection for gypsum-salt layers. The experiment results show that, with the same drilling fluid density, the borehole shrinkage rate of the minimum horizontal in-situ stress azimuth is higher than that of the maximum horizontal in-situ stress azimuth. However, the borehole shrinkage rate of the gypsum layer is higher than salt layer. The hydration expansion of the gypsum is the dominant reason for the shrinkage of the composite salt-gypsum layer. In order to mitigate the borehole diameter reduction, the drilling fluid density is determined that can lower the creep rate less than 0.001, as a result, the borehole shrinkage of salt-gypsum layer is slowed. At the same time, it is necessary to improve the salinity, filter loss and plugging ability of the drilling fluid to inhibit the creep of the soft shale formation. The research results provide technical support for the safe drilling of composite salt-gypsum layers. This achievement has been applied to 135 wells in the Amu Darya, which completely solved the of wellbore shrinkage problem caused by salt rock creep. Complexities such as stuck string and well abandonment due to high-pressure brine crystallization are eliminated. The drilling cycle is shortened by 21% and the drilling costs is reduced by 15%.

scholarly journals Artificial Interference of Stress Field in a Near-Fracture show="" $6#?=""Zone by Water Injection in a Preexisting Crack

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Yongxiang Zheng ◽  
Jianjun Liu ◽  
Bohu Zhang
Keyword(s):  
Oil And Gas ◽  
Fractured Reservoirs ◽  
Water Injection ◽  
Fluid Pressure ◽  
In Situ Stress ◽  
Stress Intervention ◽  
Oil And Gas Resources ◽  
Favorable State ◽  
Artificial Stress

The in situ stress has an important influence on fracture propagation and fault stability in deep formation. However, the development of oil and gas resources can only be determined according to the existing state of in situ stress in most cases. It is passive acceptance of existing in situ stress. Unfortunately, in some cases, the in situ stress conditions are not conducive to resource development. If the in situ stress can be interfered in some ways, the stress can be adjusted to a more favorable state. In order to explore the method of artificial interference, this paper established the calculation method of the in situ stress around the cracks based on fracture mechanics at first and obtained the redistribution law of the in situ stress. Based on the obtained redistribution law, attempts were made to interfere with the surrounding in situ stress by water injection in the preexisting crack. On this basis, the artificial stress intervention was applied. The results show that artificial interference of stress can effectively be achieved by water injection in the fracture. And changing the fluid pressure in the crack is the most effective way. By stress artificial intervention, critical pressure for water channelling in fractured reservoirs, directional propagation of cracks in hydraulic fracturing, and stress adjustment on the structural plane were applied. This study provides guidance for artificial stress intervention in the exploitation of the underground resource.

scholarly journals Experimental Investigation of the Effects of Drilling Fluid Activity on the Hydration Behavior of Shale Reservoirs in Northwestern Hunan, China

Energies ◽  
2019 ◽  
Vol 12 (16) ◽  
pp. 3151 ◽  
Author(s):  
Han Cao ◽  
Zheng Zhang ◽  
Ting Bao ◽  
Pinghe Sun ◽  
Tianyi Wang ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Drilling Fluid ◽  
Contact Angles ◽  
Wellbore Stability ◽  
Adsorption Rate ◽  
Drilling Fluids ◽  
Swelling Ratio ◽  
Gas Drilling ◽  
Surface Hydration ◽  
The Relationship

The interaction between drilling fluid and shale has a significant impact on wellbore stability during shale oil and gas drilling operations. This paper investigates the effects of the drilling fluid activity on the surface and osmotic hydration characteristics of shale. Experiments were conducted to measure the influence of drilling fluid activity on surface wettability by monitoring the evolution of fluid-shale contact angles. The relationship between drilling fluid activity and shale swelling ratio was determined to investigate the osmotic hydration behavior. The results indicate that, with increasing drilling fluid activity, the fluid–shale contact angles gradually increase—the higher the activity, the faster the adsorption rate; and the stronger the inhibition ability, the weaker the surface hydration action. The surface adsorption rate of the shale with a KCl drilling fluid was found to be the highest. Regarding the osmotic hydration action on the shale, the negative extreme swelling ratio (b) of the shale was found to be: bKCl < bCTAB < bSDBS. Moreover, based on the relationship between the shale swelling ratio and drilling fluid activity, shale hydration can be divided into complete dehydration, weak dehydration, surface hydration, and osmotic hydration, which contributes to the choice of drilling fluids to improve wellbore stability.

Machine Learning Applications in Drilling Fluid Engineering: a Review

2021 ◽  
Author(s):  
Sercan Gul
Keyword(s):  
Machine Learning ◽  
Oil And Gas ◽  
Drilling Fluid ◽  
Wellbore Stability ◽  
Drilling Fluids ◽  
Fluid Mud ◽  
Surface Cooling ◽  
Real Time Analysis ◽  
Machine Learning Applications ◽  
Drilling Operations

Abstract Drilling fluid (mud) serves various purposes in drilling operations, the most important being the primary well control barrier to prevent kicks and blowouts. Other duties include, but not limited to, maintaining wellbore stability, removing and transporting formation cuttings to the surface, cooling and lubricating downhole tools, and transmitting hydraulic energy to the drill bit. Mud quality is therefore related to most of the problems in drilling operations either directly or indirectly. The physics-based models used in the industry with drilling fluid information (i.e., cuttings transport, well hydraulics, event detection) are computationally expensive, difficult to integrate for real-time analysis, and not always applicable for all drilling conditions. For this reason, researchers have shown extensive interest in machine learning (ML) approaches to alleviate their fluid-related problems. In this study, a comprehensive review of the abundant literature on the various applications of ML in oil and gas operations, concentrating mainly on drilling fluids, is presented. It was shown that leveraging state-of-the-art supervised and unsupervised ML methods can help predict or eliminate most fluid-related issues in drilling. The review discusses various ML methods, their theory, applications, limitations, and achievements.

The Research of the Oil Base Drilling Fluid Hard Brittle Shale Sidewall Instability Mechanism

2014 ◽  
Vol 513-517 ◽  
pp. 309-313 ◽  
Author(s):  
Guang Feng Zhen ◽  
Go Lin Jing ◽  
Wei Jie Hu ◽  
Bai Sun Liao
Keyword(s):  
Drilling Fluid ◽  
Continuous Production ◽  
Exchange Capacity ◽  
Wellbore Stability ◽  
Instability Mechanism ◽  
X Ray Diffraction ◽  
X Ray ◽  
Mechanism Research ◽  
Shale Formation ◽  
Temperature Time

With the continuous production of the well development, sidewall instability phenomenon has become increasingly serious, mostly occurs in the shale formation, benefit for oilfield produced great harm. Water-based drilling fluid sidewall instability mechanism has been basically clear, the oil-base drilling fluid influence on sidewall stability is not yet concrete. So this paper mainly for oil-based drilling fluid hard brittle shale sidewall instability mechanism research. This article first from the perspective of chemistry, the hard brittle shale borehole wall instability is studied, the experiment tested respectively by the white oil and water treatment of hard brittle shale of cation exchange capacity (CEC) value, so as to analyze the same and the hydration of clay mineral equivalent after processing samples, through analysis of the temperature, time, media's impact on hard brittle shale wellbore stability. Secondly, from the Angle of mechanics, stress and mechanical properties of mud shale formation is analyzed, and the minimum drilling fluid density model, gives a variety of analysis and calculation formula. In addition, this paper adopted the X ray diffraction (XRD)

scholarly journals Theoretical preconditions for modeling wellbore stability and predicting hydraulic fracturing

2021 ◽  
pp. 41-49
Author(s):  
A.N. Popov ◽  
◽  
R.A. Ismakov ◽  
F.N. Yangirov ◽  
A.R. Yakhin ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Drilling Fluid ◽  
Fluid Pressure ◽  
Polycrystalline Diamond ◽  
Wellbore Stability ◽  
Rotary Drilling ◽  
Factors Affecting ◽  
The Stability ◽  
Diamond Bit ◽  
The Given

One of the complex technological tasks in the process of drilling is to ensure the stability of the wellbore walls, as well as their modeling for further forecasting the state of the wellbore and the likelihood of hydraulic fracturing. This is due to the fact that most of the complications and factors affecting the equilibrium state of the wall are associated with external influences. The article discusses the mechanical and partially hydraulic aspects of solving the described problems associated with modeling the stability of the wellbore walls and predicting hydraulic fracturing. As a result of calculations, the necessary data are obtained for making a decision on the density of the drilling fluid for drilling the considered interval of rocks. The assumed model of the porous rock and the given calculation formulas make it possible to fully evaluate the influence of the formation fluid pressure on the mechanical processes in the rocks when they are opened by a well. Keywords: hydraulic fracturing; blade bit; steel ball-shaped toothed bit; polycrystalline diamond bit; laser drilling; impact rope drilling; rotary drilling.

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.

scholarly journals Stability Analysis in Determining Safety Drilling Fluid Pressure Windows in Ice Drilling Boreholes

Energies ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 3378
Author(s):  
Han Zhang ◽  
Dongbin Pan ◽  
Lianghao Zhai ◽  
Ying Zhang ◽  
Chen Chen
Keyword(s):  
Stability Analysis ◽  
Oil And Gas ◽  
Drilling Fluid ◽  
Fluid Pressure ◽  
Failure Criteria ◽  
Borehole Wall ◽  
Polar Regions ◽  
Borehole Stability ◽  
Oil And Gas Exploration ◽  
The Stability

Borehole stability analysis has been well studied in oil and gas exploration when drilling through rock formations. However, a related analysis of ice borehole stability has never been conducted. This paper proposes an innovative method for estimating the drilling fluid pressure window for safe and sustainable ice drilling, which has never been put forward before. First, stress concentration on a vertical ice borehole wall was calculated, based on the common elastic theory. Then, three failure criteria, the Mogi–Coulomb, teardrop, and Derradji-Aouat criteria, were used to predict the stability of the ice borehole for an unbroken borehole wall. At the same time, fracture mechanics were used to analyze the stable critical pressure for a fissured wall. Combining with examples, our discussion shows how factors like temperature, strain rate, ice fracture toughness, ice friction coefficient, and fracture/crack length affect the stability of the borehole wall. The results indicate that the three failure criteria have similar critical pressures for unbroken borehole stability and that a fissured borehole could significantly decrease the safety drilling fluid pressure window and reduce the stability of the borehole. The proposed method enriches the theory of borehole stability and allows drillers to adjust the drilling fluid density validly in ice drilling engineering, for potential energy exploration in polar regions.

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