遇水快速膨胀胶凝堵漏技术在长宁页岩气区块的应用

长宁页岩气区块地表为喀斯特地貌，地下溶洞暗河发育，在表层钻进过程中地层出水严重且常发生失返性漏失。针对表层出水漏失难题，先后采用桥浆、高失水堵漏材料、水泥浆、智能凝胶等系列堵漏材料，但堵漏效果差且容易出现复漏。为此室内研发出一种遇水快速膨胀胶凝的堵漏材料，堵漏机理为“膨胀+交联+充填”，堵漏材料遇到地层水后可以与其混合发生交联反应，同时发生膨胀反应，释放CO₂气体促使堵漏材料快速膨胀数倍体积，形成不透水的无毒弹性胶状体；借助CO₂气体压力可将未固化的弹性胶状体进一步压入并充填漏层的孔隙，起到膨胀与弹性堵水的效果。通过配方优化形成遇水快速膨胀胶凝堵漏浆，性能评价表明，堵漏浆胶凝时间在15～70 min范围内可控，膨胀率为250%～350%，可以锁住3倍体积的蒸馏水和5倍体积水基钻井液；在CDL-Ⅱ型高温高压堵漏试验仪中对4～3 mm、5～4 mm模拟漏失通道承压分别达到3.8、1.7 MPa，复合桥浆堵漏后承压能力提高至6.25、5.2 MPa。现场应用一次性封堵出水漏层，提高承压能力5.8 MPa，解决表层出水漏失难题并保障了安全钻进。 

Application of a Fast-swelling Gel Lost Circulation Material in Shale Gas Drilling in Block Changning

Shale gas drilling in block Changning is conducted in an area with karst landform at the surface and underground cavern and underground rivers resulting in severe water kick and lost return during drilling in surface formations. To address these problems, bridging slurries, high filtration rate lost circulation material (LCM), cement slurries and smart gels were used to stop mud losses, however the results of applying these LCMs were not satisfactory, and the mud losses started again after a while of applying the LCMs. A gel that is able to fast swell when intact with water was developed in an effort to address the problems effectively and efficiently. The mechanisms of this gel are "swelling+crosslinking+filling"; when in contact with water, a crosslinking reaction takes place in the gel water mixture, and the mixture swells and releases CO2 which makes the gel swell further to a volume that is several times of its original volume. The crosslinked gel finally becomes an elastic water-tight non-toxic gel. CO2 inside the gel drives the non-crosslinked elastic gel into the formation pores in the thief zones, inhibiting water kick by swelling and elasticity. Laboratory evaluation of a fastswelling gel LCM formulated with optimized additives showed that the gelling time of the LCM is between 15 min and 70 min, it is able to expand to 250% to 350% of its original volume, and to block distilled water or water base drilling fluid that is 3 or 5 times by volume of the gel LCM, respectively. Test of the gel LCM on a model CDL-Ⅱ HTHP LCM tester showed that, using 4-3 mm and 5-4 mm simulated channels for mud loss, the pressure bearing capacity of the plugged channels were 3.8 MPa and 1.7 MPa, respectively.Test of a compound LCM mixed with the gel LCM and a bridging LCM showed that the pressure bearing capacity of the plugged channels were increased to 6.25 MPa and 5.2 MPa, respectively. In a field application, a water production zone was plugged at the first try of the gel LCM, and the pressure bearing capacity of the plugged water production zone was increased to 5.8 MPa, resolving water production when drilling the top formations and ensuring safe drilling.