莺琼盆地高温高压窄安全密度窗口钻井关键技术

南海莺琼盆地高温高压井安全密度窗口极窄，部分井甚至无窗口，钻进过程中溢流、井漏、喷漏同层等复杂情况频发，多口井被迫提前完钻甚至报废。为解决窄安全密度窗口引起的钻井问题，经过多年的实践与摸索，通过优化套管下深拓宽安全密度窗口、薄弱地层挤水泥提高地层承压能力、使用小尺寸钻具显著降低循环压耗、优选抗高温弹性堵漏材料对诱导裂缝进行堵漏、使用纳米防漏隔离液及锰矿粉高密度水泥浆应对窄安全密度窗口固井漏失与压稳问题，形成一套针对高温高压窄安全密度窗口的钻井技术及配套工艺，详细探讨了各项技术原理及现场应用效果。南海西部莺琼盆地十几口高温高压探井的应用结果表明，该技术有效应对了井底温度高达212 ℃、地层压力系数超过2.30、窄安全密度窗口仅为0.04等恶劣井况，钻井复杂情况发生率得到显著降低，为类似窄安全密度窗口钻井提供借鉴。

Key drilling technologies for HTHP wells with narrow safety density window in the Yingqiong Basin

The safety density window of the high temperature and high pressure (HTHP) wells in the Yingqiong Basin of the South China Sea are quite narrow, and even some of them have no windows, so complex downhole accidents happen frequently in the process of drilling, e.g. overflow, mud loss, and coexistence of blowout and mud loss in the same interval, and consequently many wells are forced to be completed ahead of schedule and even abandoned. In order to solve the drilling problems caused by narrow safety density window, a set of drilling technologies and support process for HTHP wells with narrow safety density window have been formed based on years’ practice and exploration, such as optimizing the casing depth to widen the safety density window, injecting the cement into the weak formation to increase its pressure bearing capacity, adopting small-size drilling tools to reduce the circulating pressure loss significantly, selecting high-temperature elastic lost circulation material (LCM) to plug the induced fractures, and applying nano-meter loss circulation spacer and high-density slurry of manganese tetraoxide to deal with the cementing fluid loss and pressure stabilization of narrow safety density window. In this paper, the principles and field application effects of all these technologies were discussed in detail. These technologies are applied in over 10 HTHP exploration wells in the Yingqiong Basin, western South China Sea. It is shown that these technologies can effectively cope with the harsh well conditions, e.g. bottom hole pressure as high as 212 ℃, formation pressure coefficient over 2.30 and safety density window as narrow as 0.04. And as a result, the occurrence rate of drilling complexities is reduced greatly. The research results provide the reference for the similar wells with narrow safety density window.