煤层气弱凝胶和微固相双效钻井液体系

为更好满足煤层气钻井液成膜护壁和尽可能地降低对煤层气储层的伤害，实现安全、高效钻进和保护储层的目的，提出了弱凝胶和微固相双效钻井液体系。室内对其性能进行了评价，结果表明:弱凝胶和微固相双效钻井液具有良好的基础性能；具有很好抑制性、抗温性（50℃）、抗盐（NaCl、CaCl₂、MgCl₂）侵性和抗煤屑侵性；在500 mL双效钻井液中加入纤维素酶、中性α-淀粉酶、复合酶（0.1 g:0.1 g:0.1 g），最终弱凝胶和微固相钻井液降解率分别可达90.9%和83.0%；具有很好的润滑性，润滑系数分别为0.17和0.12；渗透率恢复率可达到91.3%和82.3%；显微观测可知，增大了钻井液接触角，可很好防止水锁伤害；复合生物酶不仅能降低钻井液表观黏度，在后期通过降解泥皮来降低对煤储层裂隙的伤害，可大大减小对煤层气产出影响。 

Dual-effect Drilling Fluids with Weak Gel and Micro Solids for CBM Drilling

Dual-effect drilling fluids with weak gel and micro solids have been developed to better satisfy the needs of borehole wall protection in coal bed methane (CBM) drilling, to minimize the damage to CBM pay zones by drilling fluid, and to realize safe and efficient drilling operations. Laboratory evaluation of the drilling fluids showed that they had excellent basic properties, good inhibitive capacity, temperature resistance (50℃), salt resistance (NaCl, CaCl2, MaCl2) and drilled cutting (coal) tolerance. A 500 mL weak-gel drilling fluid sample and a micro-solid drilling fluid sample treated respectively with 0.1 g cellulose, 0.1 g neutralized α-amylase and 0.1 g compound enzyme had rates of degradation of the two drilling fluid sample were 90.9% and 83.0%, respectively. The weak-gel drilling fluid and the micro-solid drilling fluid had friction coefficient of 0.17 and 0.12, respectively, and percent permeability recovery of 91.3% and 82.3%, respectively, exhibiting good lubricity and reservoir protection capacity. Observation under microscopy showed that contact angles of the two drilling fluids were increased, capable of protecting formations from being damaged by water block. The compound bio-enzyme used in the drilling fluids not only reduced the apparent viscosity of the drilling fluids, it also helped degrade mud cakes, thereby minimizing blocking of fractures in CBM zones, greatly mitigating the negative effects of mud cakes on CBM production.