Abstract
Hydrate formation risk is an important challenge in the development of deep-water gas field. Considering the characteristics of the Lingshui (LS) gas field in the South China Sea and the difference of well structures, a model for calculating wellbore temperature and pressure in deep-water gas production well is proposed and verified by the field data. Combining the hydrate equilibrium models with varied gas components, the prediction method of hydrate formation region in deep-water gas well in the South China Sea is obtained. The hydrate formation regions under different operating conditions for a deep-water gas well in the South China Sea were given by the proposed model. The results show that no hydrate formation risk exists in the production operation, but the risk exists in the shut-in and testing operations. Meanwhile, the determination of the hydrate inhibitor injection parameters during the testing operation is studied, and the influence of the inhibitors’ injection concentration and pressure on preventing gas hydrates is analyzed. This work provides useful advice for the prediction and prevention of hydrate formation risk in the development of deep-water gas fields, especially in the South China Sea.
Highlights
The South China Sea is one of the four major oil and gas accumulations in the world, with about 23-30 billion tons of petroleum geological reserves, and accounts for one-third of China’s total oil and gas resources, 70% of which is located in the deep-water area of 1.537 million square kilometers [1]
By calculating the hydrate phase equilibrium conditions under different injection concentrations of methanol and ethylene glycol, the hydrate inhibitor injection plates under different test yields can be obtained, as shown in Figures 8 and 9. It can be seen from the figure that with the increase of test production and inhibitor injection concentration, the wellbore temperature pressure curve and hydrate phase equilibrium curve gradually deviate, indicating that the hydrate formation region in the wellbore decreases at this time
Considering the characteristics of Lingshui gas field in the South China Sea, based on the calculation model of temperature and pressure field in deep-water wellbore and hydrate phase equilibrium conditions, this paper establishes a quantitative prediction method of hydrate formation region, analyzes the hydrate risk existing in the wellbore under different production stages in the development of Lingshui gas field in the deep-water region, and obtains the following understandings: hydrate prevention measures are not needed in the whole normal production stage
Summary
The South China Sea is one of the four major oil and gas accumulations in the world, with about 23-30 billion tons of petroleum geological reserves, and accounts for one-third of China’s total oil and gas resources, 70% of which is located in the deep-water area of 1.537 million square kilometers [1]. Considering wellbore structure, string structure, operation conditions, and other factors, Wang et al [25, 26] comprehensively established the calculation model of temperature and pressure field of deep-water wellbore and the model of hydrate formation and deposition plugging in string. The model can realize the quantitative prediction of hydrate formation region in deep-water wellbore under different working conditions and reveals hydrate formation risk under different working conditions in the process of deep-water gas field development.
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