深水钻井面临低温、安全密度窗口窄、浅层气易形成气体水合物、井壁易失稳等技术难题,对深水钻井液提出了更高的要求.以Saraline 185V气制油为基油,通过优选乳化剂、有机土、降滤失剂及其他处理剂,构建了一套适合深水钻井的FLAT-PRO深水恒流变合成基钻井液体系.综合性能评价结果表明:该钻井液在4~65℃下流变性能稳定,具有恒流变特性,能有效保护储层,其渗透率恢复值大于90%,能抗10%海水、15%钻屑污染,易降解,满足环保要求.南海LS-A超深水井水深为1699.3 m,预测主要目的层温度为34.6~36℃,φ508 mm套管鞋处的地层承压能力系数低于1.14,安全密度窗口窄,如何控制ECD值、预防井漏是该井的作业控点,因此选择密度为1.03 g/cm3的FLAT-PRO钻井液开钻.钻进过程中,使用FSVIS调整流变性,维护黏度在50~70 s,动切力在8~15 Pa,φ6读数为7~15,φ3读数为6~12,用2%PF-HFR控制滤失量,应用井段起下钻顺利,电测顺利,井径规则,没有出现任何复杂情况.应用结果表明,FALT-PRO深水恒流变合成基钻井液在不同温度下的流变性能稳定,抑制性好,润滑性强,能获得较低的ECD值,满足深水钻井的要求.%Technical problems encountered in deepwater drilling, such as low temperature, narrow drilling window, formation of gas hydrate by shallow natural gas and hole sloughing etc. have posed rigorous requirements to drilling fluids. Using GTL Saraline 185V as the base fluid, a deepwater synthetic base drilling fluid, FLAT-PRO, was developed based on optimizing the emulsifier, organo-clay, filter loss reducer and other additives. Laboratory evaluation results showed that FLAT-PRO had stable constant rheology at 4-65 ℃. In permeability test, a permeability recovery of higher than 90% was obtained. This performed very well even when was contaminated with 10% seawater and 10% drilled cuttings. FLAT-PRO was easy to degrade, satisfying the need of environmental protection. An offshore well, LS-A, drilled in South China Sea, with water depth of 1,699.3 m, had formation (main target) temperatures between 34.6 ℃and 36 ℃. The coefficient of formation pressure at the shoe of the ?508 mm casing string was lower than 1.14, indicating a narrow safe drilling window. How to control ECD and mud losses were the major concerns of the drilling operation. FLAT-PRO with a density of 1.03 g/cm3 was used in spudding the well, and FSVIS was chosen to maintain the rheology of the drilling fluid. During drilling, rheological parameters of the drilling fluid were maintained as follows: FV = 50-70 s, YP = 8-15 Pa, φ6 reading = 7-15, andφ3 reading = 6-12. 2% of HFR was used in filtration control. Drilling, tripping and wireline logging were all successful performed. Filed application showed that the deepwater constant rheology FLAT-PRO drilling fluid had stable rheology at different temperatures, good inhibitive capacity, and superior lubricity, thereby maintaining low ECD during drilling and satisfying the needs for deepwater drilling.
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