Study and Application of Snubbing Technology for Low Pressure Gas Well

Abstract

Abstract With the further development of natural gas, the quantity of gas well has been increasing year by yearin China, the demands for well completion and workover are growing. At present, more than 70% of gas wells are low yield and low pressurein China, in order to protect the reservoir and make the production stably, it's an urgent need to use snubbing technology for low pressure gas well. Snubbing technology faces several challenges for low pressure gas well, such as high risk, complex downhole conditions, high cost, low operation efficiency, etc. High efficiency, low cost and low risk are crucial targets for gas well snubbing. To achieve this target, we developed a set of snubbing wellhead for low pressure gas well which operation pressure is less than 14MPa. Some key technologies are formed, such as airtight makeup and breakout device, gas sealing system, rotating slips etc. The unit can realize pipe tripping and rotating operation with high efficiency and low risk in low pressure gas well, it's composed of lifting system, gas sealing system, working BOP stacks, airtight makeup and breakout device, security BOP stacks. The main working principle is adopted liquid to seal gas, the gas sealing system is composed of two sets of annular preventers, and a length of liquid which has 3-4MPa pressure is sealed between them. When it comes to begin snubbing operation, the gas sealing system can realize effective sealing within the wellbore pressure and also achieve the purpose of tubing lubrication, the safety and reliability can be well guaranteed when it works with BOP stacks. The airtight makeup and breakout device is equipped between the working BOP stacks and security BOP stacks, cooperate with the rotating slips, tubing joints can be screwed on and off at the bottom of the snubbing wellhead when it meets special snubbing work conditions, such as no tubing plug or tubing leakage. The pilot test of this technology is carried out in Jilin oilfield, operation cost is reduced about 50%, and it makes the production development more effectively and economically. The annual demands of snubbing operation for low pressure gas wellare probably more than2000 wells each year in China, This technology has the advantages of high efficiency, low risk and low cost, the application prospectis broad.