海上高温高压天然气水平井临时隔离储层悬空水泥塞技术

南海西部高温高压水平井采取悬空水泥塞临时隔离高温高压储层。水泥塞质量要求高，处于大井斜高温高压井段，水泥塞底部距小井眼储层水平段斜深仅150 m、垂深仅40 m左右。注水泥塞作业对井底的波动压力大，水泥浆防窜和防漏矛盾突出。在高密度油基钻井液环境下注水泥塞，泥饼清洗困难，影响胶结质量。水泥浆用量少，易混浆和被钻井液污染。因此，通过提前转化钻井液、优化注水泥塞管柱结构、提高水泥塞支撑能力、优化前置液、水泥浆和水泥浆附加量、提高顶替效率工艺、优化替浆量精确设计及计量工艺、创新水泥塞管柱内壁清洁新工艺等方面的研究，形成海上高温高压天然气水平井储层临时封井悬空水泥塞技术。该技术在中国南海西部海域莺琼盆地7口高温高压水平开发井中应用，一次注水泥塞成功率为100%，为高温高压大斜度井段、高密度油基钻井液环境以及小井眼复杂工况下悬空水泥塞质量的提升提供了技术参考。 

Running Suspended Cement Plug to Temporarily Isolate Reservoir in an Offshore HTHP Horizontal Gas Well

Suspended cement plug was run in a high temperature high pressure (HTHP) horizontal well in the west of South China Sea to temporarily isolate the HTHP reservoir. The cement plug was required to run in the highly deviated HTHP hole section, the bottom of which was only 150 m (MD) or 40 m (TVD) away from the reservoir penetrated by a horizontal slim hole section. Caution should be taken to prevent slurry channeling and loss during injection of cement slurry because of pressure fluctuation on the bottom of the hole. Cement plug run into a well drilled with high density oil base mud makes mud cake cleaning very difficult and the quality of cementation is thus reduced. If low volume of cement slurry is used, the cement slurry is easy to get contaminated by drilling fluid. Several measures were taken to avoid these problems, such as converting the drilling fluid in advance, optimizing pipe structure for slurry injection, increasing the support capacity of the cement plug, optimizing the prepad fluid, cement slurry composition and surplus volume of cement slurry, improving displacing efficiency, optimizing volume of displacement and technique of displacement and using new technology of cleaning the internal pipe wall of the cementing slurry injection string etc. With these measures, a set of technology for running suspended cement plug in offshore HTHP horizontal gas well to isolate reservoir was presented. This technology has been successfully applied on 7 HTHP horizontal wells drilled in the Ying-Qiong basin, west of South China Sea, providing a technical reference for running suspended cement plug in HTHP highly deviated holes drilled with high density oil base mud.