Deepwater wellbore integrity can be defined as the application of relevant engineering techniques and operational measures in deepwater drilling to control related risks during the drilling process, ensuring that deepwater oil and gas wells are always in a safe state throughout their entire life cycle. Oil platform in the North Sea

In deepwater drilling, high investment, high risk, and high return are the most significant characteristics, so special attention needs to be paid to safety operations during the drilling process.

Difficulties

Harsh environment

According to international conventions, oil and gas wells with a depth greater than 500 meters are considered deepwater wells, while oil and gas wells with a depth greater than 1500 meters are considered ultra deepwater wells. In the deepwater marine environment, geological conditions and environmental factors are more complex. Firstly, the deepwater marine environment is more harsh, with frequent typhoons and extreme waves. After the superposition of

internal wave Internal waves are gravity waves that oscillate within a fluid medium, rather than on its surface. To exist, the fluid must be stratified: the density must change (continuously or discontinuously) with depth/height due to changes, for example, in ...

and ocean currents in the ocean, the deepwater flow velocity increases, resulting in extremely harsh comprehensive environmental conditions for deepwater drilling; In addition, due to the long offshore distance of deepwater drilling, it is difficult to provide material support, which also makes challenges for deepwater drilling.

Shallow geological hazards

The geological conditions in deepwater areas are complex. For example, in the South China Sea region, shallow areas usually meet with three shallow problems when drilling in deepwater areas, namely shallow gas, shallow water flow, and natural gas hydrates. During drilling operations, complex accidents such as gas invasion and overflow are prone to occur. In addition, deep strata have poor

diagenesis Diagenesis () is the process of physical and chemical changes in sediments first caused by water-rock interactions, microbial activity, and compaction after their deposition. Increased pressure and temperature only start to play a role as sedi ...

, weak pressure bearing capacity, so leakage is easy to happen, the risk of well control is high, and the treatment is difficult, which impact on deepwater wellbore integrity seriously.

Complex working environment

In the process of deepwater drilling, due to the long-term complex and dynamic changes in the marine geological environment, the relevant marine petroleum machinery and tools are more susceptible to external damage caused by surrounding marine activities. Therefore, in this complex flow field with high spatiotemporal variability, the relevant petroleum equipment and tools will undergo varying degrees of

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

, damage, and deformation. These damages will accumulate and cause irreversible leakage, perforation, and fracture to themselves, causing serious damage to deepwater wellbore integrity. In addition, due to the difficulty of timely monitoring and evaluation of leaks in deepwater oil and gas wells, traditional detection methods for onshore oil fields are no longer applicable. Therefore, timely detection of leakage points and accurate evaluation are also important difficulties in ensuring the deepwater wellbore integrity.

Testing

Schematic-representation-of-wellbore-and-formation-temperature-fields

The detection of deepwater wellbore integrity can be generally divided into two aspects from global perspective: detection of wellbore pressure and wellbore temperature. By detecting the two important indicators of temperature and pressure, the change in borehole thickness of the

casing string In drilling technology, casing string is a long section of connected oilfield pipes that is lowered into an wellbore and cemented in place. The purpose of the casing pipe is to: * Prevent the borehole from collapsing. * Prevent formation fluids ...

, as well as the location of leakage points and types of damage, can be determined. Therefore, a comprehensive assessment of deepwater wellbore integrity can be conducted.

Equipment

The commonly used detection devices are sound wave acquisition tools and electromagnetic detectors. To meet with the special environmental requirements of deepwater oil and gas wells, it is necessary to strengthen the high temperature and high pressure resistance, corrosion resistance, and airtightness of the acoustic testing instrument, so as to make the detection results more accurate. The electromagnetic detector is used to detect damage to the casing string in the wellbore. Due to the use of low magnetic material oil pipes in deepwater oil and gas wells, the response time of the electromagnetic detector will be shortened, optimizing the detection process. Generally, when used together with acoustic acquisition tools and electromagnetic detectors, the detection and analysis of deepwater wellbore integrity will be more comprehensive.

Future work

With the development of

artificial intelligence Artificial intelligence (AI) is the capability of computer, computational systems to perform tasks typically associated with human intelligence, such as learning, reasoning, problem-solving, perception, and decision-making. It is a field of re ...

technology, big data-driven methods such as

machine learning Machine learning (ML) is a field of study in artificial intelligence concerned with the development and study of Computational statistics, statistical algorithms that can learn from data and generalise to unseen data, and thus perform Task ( ...

and

deep learning Deep learning is a subset of machine learning that focuses on utilizing multilayered neural networks to perform tasks such as classification, regression, and representation learning. The field takes inspiration from biological neuroscience a ...

have provided new ideas and methods for solving engineering problems in deepwater oil and gas wells. Artificial intelligence technology is used to monitor wellbore pressure and temperature in real time, warn of abnormal values, classify risk levels, and comprehensively evaluate deepwater wellbore integrity. Then, corresponding risk control measures and well control measures are provided based on historical and near well data to reduce safety risks. Among them, timely and accurate identification of corresponding early accident risks is of great importance. Therefore, in the future, real-time monitoring of deepwater wellbore integrity, real-time warning of abnormal situations, and making accurate and timely processing methods based on artificial intelligence methods will become the development direction of petroleum engineering, offshore engineering, and computer technology.