顺煤层钻进用可降解聚合物钻井液

沁水盆地南部寺河矿区15号煤含气量高，埋深较浅，具有良好的煤层气开发潜力。针对15号煤煤体结构复杂和顶底板为富含水层的灰岩，在顺煤层钻进时主要存在的携屑困难、井壁失稳、容易漏失和储层污染难题，研发了微固相可降解聚合物钻井液体系。通过煤粉悬浮、煤岩取心模拟护壁、黏度衰减和渗透率恢复实验评价了该体系的基本性能。实验结果表明，该体系携带岩屑效果好，抑制作用强，能够减小井眼扩径，同时配合生物酶的降解作用，储层渗透率伤害率可以从50%降低到25%。该钻井液在中国首个煤层气工厂化钻井平台X-2井进行现场试用，钻井液密度为1.01~1.03g/cm3，漏斗黏度为35~40s，API滤失量小于15mL，pH值为8~10，加入生物酶后黏度降低40%，顺煤层段成功钻进900m。 

Degradable Polymer Drilling Fluids for In-seam Drilling

The #15 coal seam buried shallow in the Sihe coal mine in the south of Qinshui Basin has high content of coal bed methane (CBM) and is thus prospective in CBM mining. The #15 coal seam has a complex structure and its top and bottom are both limestone rich in water. In-seam drilling in the #15 coal seam has been encountering problems such as difficulty in cuttings carrying, borehole wall collapse, lost circulation and drilling fluid contamination to the coal seam. A degradable polymer drilling fluid has been developed to deal with these problems. The polymer drilling fluid was evaluated in laboratory through suspension of coal fines, simulation of borehole wall stabilizing with coring, viscosity attenuation and test on permeability return. The results have proved that the polymer drilling fluid has good cuttings carrying capacity and strong inhibitive capacity, mitigating borehole washout. Using bio-enzyme, formation permeability impairment of the target zones by drilling fluid can be reduced from 50%to 25%. This polymer drilling fluid has been tried in the platform X-2, the first industrial CBM drilling platform, with its properties as these: density 1.01-1.03 g/cm3, FV 35-40 sec, API Fl less than 15 mL, and pH 8-10. Addition of bio-enzyme reduced the viscosity of the drilling fluid by 40%. 900 m footage in the coal bed has been successfully drilled with this degradable polymer drilling fluid.