井壁强化与堵漏双作用可钻水泥实验研究

针对常规复合堵漏材料之间无胶结、易被钻井液冲刷、使用油井水泥堵漏会造成新井眼的问题，研究开发了井壁强化与堵漏双作用可钻水泥。将超细碳酸钙粉体加入新型胶凝材料硫铝酸盐水泥中，调节胶凝材料的可钻性，研究表明，当超细碳酸钙粉体的加入量不大于7%时，水泥凝胶材料的强度随粉体加入量的增加而增加，而当粉体的加入量大于7%时，水泥凝胶材料的强度随粉体加入量的增加而减小，即可钻性变好；在硫铝酸盐中加入0.4%减水剂、0.3%提黏剂、0.6%缓凝剂时，其稠化时间达到155 min，为安全施工提供了条件；在可钻水泥中加入12%鳞片状云母、1%纤维、1.5%石灰岩颗粒作为堵漏剂，较好地增强了体系堵漏性能，能够较好地封堵3 mm和5 mm缝板裂缝。可钻水泥的研发为实现钻井过程中井壁强化与堵漏双作用提供了技术保障。 

Experimental Study on Drillable Set Cement Capable of Strengthening Borehole Wall and Controlling Lost Circulation

Conventional compound lost circulation materials (LCMs) have no cementation among their particles. When these LCMs are put into the hole to stop mud losses, they are quite easy to be eroded away by the flow of drilling fluid. Cement slurry is another LCM frequently used to deal with severe mud losses, with a shortage of being easy to make new "hole" in a hole that uses cement slurry to stop mud losses. A Laboratory study has been conducted on drillable cement LCM. In this study, ultra-fine calcium carbonate was added into sulphoaluminate cement, a new gel material with adjustable drillability. It was found that when the concentration of ultrafine calcium carbonate in the cement slurry was not greater than 7%, the strength of the cement slurry was increasing with increase in the concentration of ultra-fine calcium carbonate. When the concentration of calcium carbonate was greater than 7%, the strength of the cement slurry was decreasing with increase in the concentration of ultra-fine calcium carbonate, i.e., the drillability of the cement was getting better. A sulphoaluminate cement treated with 0.4% water reducer, 0.3% viscosifier and 0.6% retarder had thickening time of 155 min, satisfying the needs of safe operation. A new lost circulation material was thus formulated by adding 12% scaly mica, 1% fiber and 1.5% limestone powders. This lost circulation material can be used to plug slots of 3 mm and 5 mm width, respectively. This drillable cement has provided a technical support for borehole wall strengthening and lost circulation control in drilling operations.