高密度油基钻井液体系优选及其在页岩气水平井的应用

Optimization of high-density oil-based drilling fluid system and its application in shale gas horizontal wells

摘要:

为解决威远-长宁地区泥页岩地层井壁失稳、井眼清洁等问题，通过试验优选出适用于高密度油基钻井液体系使用的乳化剂、有机土和降滤失剂等处理剂；通过正交试验设计确定出一种适用于威远-长宁地区页岩气长短水平井使用的高密度油基钻井液体系。其最终配方比例为：5%主乳化剂+2.0%辅乳化剂+2.0%润湿剂+5%降滤失剂+2%有机土+3%CaO、油水比80∶20（25%CaCl2水溶液）。对其性能进行评价，结果表明该体系可加重密度至2.2 g/cm3，加重后性能稳定，可抗水污染达9%，抗岩屑污染至18%，具有较好的抗污染性能，页岩回收率95.11%，抑制性能好，乳化性能稳定。现场应用表明：高密度油基钻井液满足威204H378井页岩气水平井钻井施工需求，全井性能良好，无井漏，井径规则，测井未见异常，顺利完钻。

Abstract:

In order to solve the problems of wellbore instability and wellbore cleaning in shale formation in the WeiyuanChangning area, the treatment agents such as emulsifiers, organic soils and filtration reducers suitable for high-density oil-based drilling fluid systems were selected through experiments. A high-density oil-based drilling fluid system suitable for use in both long and short shale gas horizontal wells in the WeiyuanChangning area was determined by orthogonal design. The final formulation ratio is: 5% primary emulsifier + 2.0% co-emulsifier + 2.0% wetting agent + 5% filtration reducer + 2% organic soil + 3% CaO, oil to water ratio 80∶20 (25% CaCl2 aqueous solution). Evaluation on its performance shows that the system can increase the density to 2.2g/cm3, and the performance is stable after addition of weighting material. It can resist water pollution up to 9%, anti-cutting pollution to 18%, providing good anti-pollution performance with shale recovery up to 95.11%, and good inhibition performance, as well as stable emulsification performance. The field application showed that the high-density oil-based drilling fluid met the drilling requirements of the shale gas horizontal well Wei 204H378. The performance of the whole well was good: there was no well leakage, the well diameter was regular, there was no abnormities in logging, and well completing was smooth.