溶洞—裂缝性井漏情况下水泥堵漏形成混浆的原因分析及预防措施

REASONS FOR GENERATING MIXED SLURRY OWING TO LOSS CIRCULATION CONTROL BY CEMENTING IN SOLUTION CAVITYFRACTURED FORMATION AND SOME PREVENTIVE MEASURES

川渝地区碳酸盐岩地层 ,由于强烈的地质运动和地下水的溶蚀作用 ,存在着许多裂缝和溶洞。在钻井过程中 ,常因钻遇裂缝和溶洞而发生恶性井漏失返 ,此时井内有一定动、静液面但不在井口。针对这种恶性井漏 ,常采用水泥或水泥混合其它材料堵漏。在注水泥堵漏施工作业中 ,由于水泥浆与钻井液密度值相差较大等多种原因 ,往往形成较多的混浆 ,影响水泥胶结质量 ,甚至难以形成有效的水泥塞 ,致使水泥堵漏失败。文章在水泥堵漏施工工艺方面对形成混浆的原因进行了定量的分析 ,提出了确定合理的堵漏钻具下入深度、控制水泥浆密度。

There are a great number of fratures and solution cavities in carbonate formations in Sichuan-Chongqing region because of strong crustal movements and underground water erosion. A vicious loss circulation always occurred because of drilling into fractures and solution cavities and the producing fluid and static liquid levels were often found in the well and below the wellhead. In consideration of such a vicious loss circulation, the cement or the cement mixed with the other materials was commonly adopted for controlling the loss circulation. In the work of loss circulation control by cementing, much mixed slurry is often formed owing to many reasons as a larger density difference between the slurry and the drilling fluid, which influences cement bond quality. Sometime it was even difficult to form an effective cementing plug, thus making a failure in the loss circulation control by cementing. Finally, the reasons for generating mixed slurry in actural operation are quantitatively analyzed and some preventive measures of reducing the slurry's being mixed by drilling fluid, as a reasonable drill string running-in depth, controlling slurry density and injecting preflush high-density drilling fluid, etc., are proposed in the paper.