煤层气井沙试3井钻井液体系的研究与应用

Study and application of the drilling fluid for test well Shashi3.

吐哈盆地沙尔湖区块的储层是煤层气地层,井深在600～900m之间,煤层面积大,煤层厚,具有良好的开发前景。该区块煤层的压力系数低,裂缝发育,易垮塌,因此防漏防塌是钻井液技术的重点。沙试1井采用聚合物钻井液钻井,发生恶性漏失,严重破坏了煤层。经过调研,决定在沙试3井采用可循环微泡钻井液体系,并在室内对可循环微泡钻井液的配方进行了优选。在沙试3井二开井段的现场应用中,将微泡钻井液密度降低到0.70～0.80g/cm3,同时提高微泡堵漏浆中的堵漏剂浓度,有效地封堵了漏层。煤层平均取心收获率达到80%以上,取得了良好的效果,为煤层气井的钻探提供了可借鉴的经验。

In Shaerhu Block of Tuha Basin, there is abundant coalbed methane resource trapped in depth from 600 to 900 m. Because of the low pressure coefficient and mature fissures, caving/collapse is easy to occur, thus anti-lost circulation and collapse property becomes an important issue in the drilling fluid design. When a polymer drilling fluid was employed in Shashi1 well, an drilled test well, severe lost circulation appeared, resulting in serious damage to the coalbed. Based on investigation on the drilling fluids used in other places, circable micro-bubble drilling fluid system was determined to serve in well Shshi3, and the composition was optimized in lab. In field implementation of this fluid during the second opening interval, the drilling fluid density was lowered to 0.70~0.80 g/cm 3, and the plugging agent concentrate of the plugging slurry was increased. As a result, the thief zone was sealed successfully and the average core recovery ratio was more than 80%. The drilling experience of Shashi3 well is valuable to coalbed gas exploration.