关键词: 油气井, 固井, 水泥环, 密封性

Abstract: With the efforts for exploration and development continually strengthened, the downhole geological conditions become more and more difficult while the wellbore structure is also complicated. As a result, the failure of cement sheath after cementing job becomes a critical problem. This article focuses on the failure of cement sheath caused by the inner characteristics of cement sheath or external conditions. It also makes analysis of cement sheath sealing challenged by cementing of complicated deep wells and super-deep wells, cementing of complicated natural gas wells, cementing of complicated acidic gas wells, cementing of shale gas wells and tight oil and gas wells, cementing of gas storage depot, cementing of complicated wells on overseas blocks, and cementing of offshore low-temperature deepwater wells. The current technological measures for assurance of long-term cement sheath sealing are proposed to improve the replacement efficiency. Balanced pressure is adopted to cement the well while the slurry system is designed to meet the requirements for sealing and cementing. The mechanical functions of cement slurry should be able to meet the changes in downhole temperature, pressure and stress. The next stage of research work is also planned on the basis of the above-mentioned efforts.

Key words: oil and gas wells; cementing; cement sheath; sealing