The problem of narrow safety density windows in deepwater drilling has always been one of the challenges faced in wellbore structure design and safe construction. Moreover, with the increase in water depth, the problem of narrow safety density windows becomes more prominent. To this end, at home and abroad, new equipment such as advanced deepwater drilling platforms and new process technologies such as underbalanced drilling, managed pressure drilling, aerated drilling, and dual-gradient drilling, as well as risk assessment technologies such as pre-drilling wellbore structure design and risk assessment methods based on probability and statistics have been adopted, which have solved this problem to a certain extent. Among them, risk assessment technology can quantitatively evaluate engineering risks based on theories such as risk analysis on the basis of existing equipment and processes, which is very necessary for high-risk and high-investment deepwater drilling and is conducive to achieving the goal of safe and efficient deepwater drilling. Through research, the pre-drilling wellbore structure design and risk assessment method based on probability and statistics uses logging data or seismic data of adjacent wells to probabilistically predict the safety density window of the target well, and quantitatively evaluates engineering risks such as leakage, blowout, collapse, and sticking of the existing wellbore structure design scheme before drilling, and then improves it. This method is effective for wells with abundant adjacent well data. However, with the continuous increase in the water depth of deepwater drilling and the drilling of unproven blocks, the abundance of adjacent well data is greatly limited, thus reducing the accuracy of wellbore structure risk assessment technologies such as regional probability and statistics methods. At the same time, there are currently no good methods or technologies for the quantitative evaluation of wellbore structure and engineering risks during deepwater drilling. The methods of accident statistics are mostly used to establish accident tree models, bow-tie models, safety barrier models, etc. and combine drilling conditions to macroscopically evaluate the wellbore structure and engineering risks during the drilling process, lacking a mechanistic understanding of engineering risks. With the gradual maturity and development of measurement while drilling and transmission technologies, the formation pressure and rock mechanical parameters of the drilled section, which are uncertain parameters before drilling, can be accurately determined during the drilling process. This provides a basis for the assessment of wellbore structure and engineering risks during the drilling process. The advantages of this technology can be fully utilized, combined with the theory and ideas of the pre-drilling wellbore structure risk assessment method based on probability and statistics, to seek to establish a new method for quantitatively evaluating the wellbore structure and engineering risks during deepwater drilling using logging while drilling data. Therefore, it is necessary to address the characteristics of deepwater drilling, fully utilize the advantages of technologies such as logging while drilling to seek methods to improve the prediction accuracy of formation pressure in narrow safety density windows, eliminate potential risks caused by uncertain formation parameters at the source, and on this basis, study the identification methods of engineering risks such as leakage, blowout, collapse, and sticking during the drilling process, and establish a dynamic wellbore structure risk assessment method during the drilling process. At the same time, study the uncertain parameters in the existing wellbore structure design methods and improve the design methods to minimize the risks of pre-drilling wellbore structure design.

Risk Assessment Method of Wellbore Structure in Deepwater Drilling Process

章节
发表日期：

2026年

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Yuqiang Xu

摘要

The problem of narrow safety density windows in deepwater drilling has always been one of the challenges faced in wellbore structure design and safe construction. Moreover, with the increase in water depth, the problem of narrow safety density windows becomes more prominent. To this end, at home and abroad, new equipment such as advanced deepwater drilling platforms and new process technologies such as underbalanced drilling, managed pressure drilling, aerated drilling, and dual-gradient drilling, as well as risk assessment technologies such as pre-drilling wellbore structure design and risk assessment methods based on probability and statistics have been adopted, which have solved this problem to a certain extent. Among them, risk assessment technology can quantitatively evaluate engineering risks based on theories such as risk analysis on the basis of existing equipment and processes, which is very necessary for high-risk and high-investment deepwater drilling and is conducive to achieving the goal of safe and efficient deepwater drilling. Through research, the pre-drilling wellbore structure design and risk assessment method based on probability and statistics uses logging data or seismic data of adjacent wells to probabilistically predict the safety density window of the target well, and quantitatively evaluates engineering risks such as leakage, blowout, collapse, and sticking of the existing wellbore structure design scheme before drilling, and then improves it. This method is effective for wells with abundant adjacent well data. However, with the continuous increase in the water depth of deepwater drilling and the drilling of unproven blocks, the abundance of adjacent well data is greatly limited, thus reducing the accuracy of wellbore structure risk assessment technologies such as regional probability and statistics methods. At the same time, there are currently no good methods or technologies for the quantitative evaluation of wellbore structure and engineering risks during deepwater drilling. The methods of accident statistics are mostly used to establish accident tree models, bow-tie models, safety barrier models, etc. and combine drilling conditions to macroscopically evaluate the wellbore structure and engineering risks during the drilling process, lacking a mechanistic understanding of engineering risks. With the gradual maturity and development of measurement while drilling and transmission technologies, the formation pressure and rock mechanical parameters of the drilled section, which are uncertain parameters before drilling, can be accurately determined during the drilling process. This provides a basis for the assessment of wellbore structure and engineering risks during the drilling process. The advantages of this technology can be fully utilized, combined with the theory and ideas of the pre-drilling wellbore structure risk assessment method based on probability and statistics, to seek to establish a new method for quantitatively evaluating the wellbore structure and engineering risks during deepwater drilling using logging while drilling data. Therefore, it is necessary to address the characteristics of deepwater drilling, fully utilize the advantages of technologies such as logging while drilling to seek methods to improve the prediction accuracy of formation pressure in narrow safety density windows, eliminate potential risks caused by uncertain formation parameters at the source, and on this basis, study the identification methods of engineering risks such as leakage, blowout, collapse, and sticking during the drilling process, and establish a dynamic wellbore structure risk assessment method during the drilling process. At the same time, study the uncertain parameters in the existing wellbore structure design methods and improve the design methods to minimize the risks of pre-drilling wellbore structure design.