Hydrate Formation Prediction And Prevention Measures In The Development Process Of Offshore Gas Field

With the development of offshore fields, especially the offshore gas field in deep water and seasonal temperature region, the effective prevention and control of hydrate is directly related to development of offshore oil and gas fields. In the process of drilling and completion, test, production and gas gathering and transportation, all have the problems of gas hydrate. Once the hydrate formed, the hydrate can jam the wellbore, throttle manifold, valves and other key parts, which will reduce production and even cause major safety accidents. At present, the hydrate prevention and control technology is more mature, therefore, safety, economic and effective process and measures to prevent the hydrate are particularly important for the offshore gas field development.The present situation of hydrate prevention and control technology and cases at home and abroad was investigated. With the analysis of the marine environment of YC13-4 field, drilling and test data, a hydrate prediction software was used to predict the gas hydrate formation conditions and possibilities. The predicting results show that, in the process of spray test after long-term shut-in restart, the undercooling degree was 3.2℃, have the risk of hydrate formation near the wellhead; During the production process, after long-term shut-in restart, due to large pressure difference, the lowest temperature was-30℃, causing serious hydrate plugging problems; while drilling, will not form hydrates.Based on the methanol inhibition test and the evaluation of kinetic inhibitors, when the concentration of methanol was 15%, it is possible to provide 4.5 ℃ undercooling degree protection, which can be used to hydrate prevention. Installation of down-hole choke was designed to inhibit hydrate formation, through the secondary throttling technology, using geothermal heating borehole fluid, the fluid temperature was higher than the temperature of hydrate formation under corresponding pressure, successfully inhibit hydrate formation, and formed a calculation method of down-hole choke setting depth.