库车山前盐水溢流衍生沉砂卡钻机理分析与预防对策

塔里木山前构造古近系发育复合盐膏层，盐间发育高压盐水层，压力系统复杂。为解决盐水溢流压井后发生的沉砂卡钻难题，通过室内实验评价了水基和油基钻井液抗盐水污染能力，建立了基于赫巴流体的环空固相沉降模型，分析不同因素对环空固相沉降的影响规律，并开展现场实例分析，制定了预防盐水溢流衍生沉砂卡钻技术对策。研究结果表明:水基钻井液被盐水污染后固相絮凝，几乎丧失悬浮能力，导致固相在环空沉降堆积引发沉砂卡钻；固相颗粒沉降速度、环空堆积高度和关井时间随固相粒径增大而快速增加；采用油基钻井液、储备井筒容积1~1.5倍以上的重浆、安装旋转控制头、上提活动钻具至安全井段、司钻法快速排出溢流等措施可预防盐水溢流衍生沉砂卡钻的发生。研究结果可为山前盐下油气资源的安全经济高效开发提供技术支撑。

Mechanism analysis and preventive measures of drill jam caused by salt water overflow derivative sedimentation in Kuqa mountain front

The Paleogene in the piedmont structure of the Tarim Basin develops composite salt-gypsum layers and inter-salt high-pressure brine layers and is found with complicated pressure systems. To deal with the cutting settling and bit/string sticking after well killing for brine kick, the brine contamination resistance of water- and oil- based drilling fluids was investigated via laboratory experiments. Moreover, based on the Herschel-Bulkley fluid, an annular solid settling model was built to analyze the effects of various factors on solid settling. The field case study was performed, and technical strategies were developed to prevent cutting settling and tool sticking related to brine kick. The research shows that solid flocculent solids occur in water-based drilling fluids contaminated by brine and such drilling fluids barely maintain their cutting suspension capacity, which results in cutting settling-induced tool sticking after solids build up in the annulus. With the increasing solid particle radius, the solid settling velocity, solid build-up height in the annulus and shut-in time grow rapidly. In addition, the application of oil-based drilling fluids, preparation of standby weighted killing fluids with a volume 1-1.5 times that of the well volume, installation of the rotating control head, lifting BHA to the safe well section and rapidly relieving invaded fluids via the driller’s approach are technical measures to prevent cutting settling and tool sticking related to brine kick. The findings of this research provide technical support for the safe, cost-effective, high-efficiency development of sub-salt hydrocarbons in the piedmont structure.