川东地区下二叠统梁山组页岩钻进预防卡钻技术

四川盆地川东地区石炭系气藏目前采用定向井、水平井方式开发,钻进至气藏的盖层下二叠统梁山组(页岩夹煤线)时,井斜角已超过了60°,钻进的关键在于预防大斜度井段的页岩段出现井壁垮塌、压裂井漏的复杂情况,这样才能安全钻至石炭系顶部。针对该段钻进难点,研究试验总结了一套钻过梁山组的工程安全预警及卡钻事故预防技术措施:1以邻井实钻厚度、岩性组合为依据,把钻时录井测量的钻时变化作为判断钻头进入梁山组的工程预警指标,并采用岩屑录井及循环观察的手段对其岩性进行证实确认;2工程实施中采取了简化钻具组合、钻进1m后退2m的划眼措施预防垮塌卡钻;3保持合理的钻井液密度与润滑性,加入力学封堵剂来增强地层的胶结力和改善泥饼质量,增强井壁稳定性;4检测记录钻进中的摩阻,用循环、划眼的方法检查大斜度井段的沉砂及梁山组井壁稳定情况,确保起下钻作业的安全。

Pipe-stuck prevention technology in shale drilling at the Lower Permian Liangshan Fm in the eastern Sichuan Basin

Currently the Carboniferous gas reservoirs in the eastern Sichuan Basin have been developed through directional and horizontal well drilling. And the inclination angle exceeds 60° when drilling into the Liangshan Fm at the cap rocks of gas (shales mingled with coal seams). The key point for drilling is to avoid such complex problems as well wall collapse and circulation loss at the shale intervals with high inclination angles. Only in this way, it is possible to drill into the top of Carboniferous strata safely. To this end, a set of technologies and measures for project safety precautions and pipe stuck preventions were summarized from research and tests. We first took the drilling time changes measured in drilling time logging as a project warning indicator for drilling into the Liangshan Fm according to the actual drilling thickness and lithological association of adjacent wells, and then adopted the cutting logging and circulation observation measures to confirm the lithology. In addition, we took such ramp down measures as simplifying BHA and drilling 1 m and back reaming 2 m to prevent collapse and pipe stuck complexities. Meanwhile, we kept the unctuosity and density of drilling fluid at an appropriate degree and injected a kind of mechanical blocking agent to increase the cementation strength of strata and to improve the quality of mud cakes and strengthen the stability of well wall. Finally, we monitored and recorded the friction and resistance during drilling, and took circulation and reaming measures to inspect the sand settling of wells with high deviation angles and stability of well wall at the Liangshan Fm so as to ensure the safety of tripping operation.