Plan Design Of Well Drilling And Completion For Injection And Production Wells Of Underground Gas Storages

As the position of natural gas energy resources rises in China’s energy strategy, the construction of underground gas storages becomes an important part of natural gas development pattern for purposes of effectively improving China’s energy strategy safety and eliminating the energy supply and demand contradiction.The National Development and Reform Committee issued the Twelfth Five-Year Plan for Natural Gas Development on Dec.3,2012. The Twelfth Five-Year Plan for Natural Gas Development clearly indicates that China will invest81.1billion yuan in the construction of24key gas storages, the working gas volume of newly increased gas storages will be about22.0billion cubic meters and the working gas volume of gas storages will account for10%of the total natural gas sale volume through making every effort; in addition, this percent will be increased to15%in2020; therefore, the importance of the construction goes without saying. However, the construction of gas storages is still in the infancy and exploration stage in China compared with foreign countries; in addition, China lags in the concept and technology of the construction and has not formed relevant technical standards yet, and matching techniques are insufficiently perfect. Especially gas storages have extremely high requirements for the quality of drilling and completion engineering of injection and production wells, and the well bore quality shall meet the needs of over50years of safety production and rapid import and export of over1.00million cubic meters of gas volume.The subject is intended to make a feasibility study of drilling and completion technologies for injection and production wells for gas storages in Changqing Oilfield according to the technical difficulties in the construction of gas storages in China at present. In addition, with the current mature techniques and domestic and foreign advanced experience, the subject is intended also to study and probe into the selection of injection and production well types for gas storages, hole structure optimization design, injection and production string optimization methods, trajectory control technology for well bores with long horizontal sections, injection and production well cementing technology, completion technology, completion tool optimization, etc. for the purpose of improving the integrity of injection and production wells. The design concept:increase the reservoir producing degree and injection-production gas volume and use horizontal injection and production wells with long horizontal sections. Large size hole structure for the fourth spud is adopted and the size of the injection-production string is increased to139.7mm. The geosteering drilling technique while drilling is used in well trajectory control, and the tools including individually designed bits, high efficiency screw drills, hydraulic oscillators, etc. are applied to meet the needs of drilling tasks in over1500m horizontal sections. The stab-in cementing method is used for surface casing; stage collars are used in production casing cementing; the technologies including air tight testing of casing, stage cementing, liner cementing, etc. are integrated and adopted; gas channeling resistant micro-expansion latex cement slurry and flexible cement slurry systems are applied. The acoustic imaging logging technique is used to evaluate cement mantle cementing quality. Based on the principle of ensuring the integrity and operation safety of well bore in a long injection-production period, the screen hanging completion method is selected, completion tools are designed with safety valves against overpressure,underpressure, fire and explosion, and wellhead equipment has remote automatic and manual shutdown functions. The air tight testing technique is used to test the integrity of injection-production strings. The materials of completion tools including downhole safety valves, permanent packers, etc. and Christmas trees all are designed for anticorrosion according to international standards ISO15156/NACE MR0175, and annular protective fluid is injected into the tubing-casing annulus.As fundamental research, the paper systematically integrates a large number of advanced drilling and completion design concepts and techniques and provides an idea of early research on scale development of gas storages on the basis of plentiful horizontal well development techniques of Changqing Oilfield with a view to improving the integrity and long-life operation of well bore. Therefore, the construction of gas storages is feasible strongly technically.