基于轨迹优化扩展大位移井窄安全密度窗口

S区块位于俄罗斯萨哈林岛东部海域，计划采用大位移井海气陆采技术进行开发。该区设计井深达12 000 m（垂深为2 800 m），水平位移约11 000 m，水平位移与垂直深度之比达3.93，初步设计四开井身结构。以往直井钻探表明，该区奥科贝凯组（Okobykaiskiy）下部及达吉组（Daginskiy）地层安全钻井液密度窗口窄（约0.3~0.4 g/cm3）、漏、塌、卡风险高，而大位移开发井相应井段窄安全密度窗口问题愈加突出。针对当前对于扩展窄安全密度窗口相关研究的不足、特别是局限于通过钻井液性能优化扩展安全密度窗口的现状，围绕窄安全密度窗口大位移井钻井难题，提出应综合力学、化学多手段全方位扩展窄安全密度窗口:首先，自井眼轨迹设计环节将优化井身剖面、改善井周围岩应力状态、扩展安全密度窗口有机结合起来，开展井眼轨迹主要参数对安全密度窗口的影响规律分析，在此基础上，兼顾井眼轨迹控制难度及施工摩阻等因素优化井眼轨迹，降低坍塌压力、提高地层破裂压力，实现安全密度窗口的先期扩展，为后续通过优化钻井液性能等手段进一步提高安全密度窗口奠定良好基础，并最终为窄安全密度窗口安全、高效钻井创造有利条件。研究形成的扩展密度窗口相关技术在S区块大位移井钻井设计中成功应用，使得目标层段安全密度窗口较轨迹优化前扩展幅度达25%~100%，对窄安全密度窗口难题的应对及防治具有指导意义。 

Trajectory Optimization of Extended Reach Well to Widen Safe Drilling Window

Extended reach well technology has been used to produce the natural gas in the offshore area from onshore in developing the Block S located in the east of Sakhalin, Russia. The designed well depth (MD) was 12,000 m (TVD 2,800 m) and the horizontal displacement was about 11,000 m. The ratio of horizontal displacement to vertical depth was 3.93. The wells were designed to have four intervals. It was found from the previous experiences that the lower Okobykaiskiy formation and the Daginskiy formation had narrow safe drilling windows (0.3-0.4 g/cm3), downhole problems such as lost circulation, borehole wall collapse and pipe sticking etc. were drilling risks that needed to be considered, especially in drilling extended reach wells. Researches on how to widen narrow safe drilling window were inadequate to meet field requirement, most of which were focused on the optimization of drilling fluid properties to widen the safe drilling window. To solve the narrow safe drilling window problem in extended reach well drilling, mechanical and chemical measurements shall be adopted. First, well profile optimization, improvement of stress state around the borehole and widening of safe drilling window should all be taken into account in the well trajectory designing stage. In this stage, the effects of the main well trajectory parameters on safe drilling window should be analyzed. Based on the analyses, the well trajectory was optimized to reduce borehole collapse pressure and increase formation fracture pressure, thereby realizing the widening of safe drilling window through mechanical method, which in turn paved the way for further widening safe drilling window through chemical method, and created favorable conditions for efficient drilling in areas with narrow safe drilling windows. The technologies of widening safe drilling window obtained have been used successfully in drilling the extended reach wells in Block S, with the safe drilling window widened by 25%-100% compared with the safe drilling window prior to the well trajectory optimization. This work is of importance in dealing with narrow safe drilling window problem.