Leakage Analysis Of Casing Connection In High-Pressure Gas Wells

The development of deep-water gas fields has put forward higher requirements on the performance of gas well casing string.The factors such as high pressure,uneven external load and complex ocean loads have brought great hidden danger to the safety of gas wells in deep water and high pressure wells.In recent years,China has intensified research work on marine deep-water drilling and completion to improve the engineering design theory of deep-water drilling to meet the challenges of safe production brought about by the complex well conditions in deep-water high-pressure gas wells.Due to the complex external environmental loading of deep water drilling,there are many risk factors for the casing during operation,which have a profound impact on deep-water drilling,completion and cementing quality.In this paper,according to the weak link of casing string,the stress state and the airtight integrality of joints in deep-water high-pressure gas well casing joints under various working conditions are analyzed.Firstly,according to the complex sea conditions in the deep sea of the South China Sea,the stress state of the joints of the casing string is analyzed under the influence of the ocean load and the casing column's gravity load.Secondly,study the sealing mechanism of the metal seal and seal ring of special threaded sleeve joints.The finite element model of the casing joint was established,and the effects of internal and external high pressure,local extrusion and elliptical external loading on the seal integrity of the casing joint were analyzed.Then,the local simplified mechanical model of the main seal structure of the casing joint was established.According to the fluid seal theory,the leakage rate of the casing seal structure was quantitatively estimated.Through the study of the airtightness of the casing joint,the contact stress of the main sealing and the auxiliary sealing structure of the casing joint under complex sea conditions is obtained,which provides a basis for evaluating the sealing performance.The leakage rate of mesoscopic-scale leakage through the micro-gap of the main seal structure of the casing joint is obtained by numerical calculation,which can be used as the evaluation basis for the sealing performance of the casing joint under high-pressure well conditions.