马1C井欠平衡钻井液技术

马1C井是在马1井上实施欠平衡钻井的一口套管开窗侧钻井。马1井是吐哈油田三塘湖盆地马朗凹陷牛圈湖构造带牛圈湖1号背斜上的一口预探井。通过对马1C井的地层岩性、储层特性、地层稳定性和可钻性、地层压力等多方面分析，室内对马1C井欠平衡钻井液进行了试验研究，确定出低密度油基钻井液的配方。经现场应用表明，低密度油基钻井液密度为0．87－0．88g/cm^3，在欠平衡钻进过程中处于负压状态，达到了保护油气层的目的；钻井过程中始终有溢流发生，3次自动点火成功，着火持续时间最长达35min，火焰最高约6m；岩屑返出均匀，无坍塌现象，机械钻速最高达30m/h，是马1井对应井段机械钻速（8．5m/h)的3．5倍；低密度油基钻井液性能稳定，较好地保护了油气层，确保了马1C井套管开窗和欠平衡钻井施工顺利。

Under-balanced drilling fluid technology for Well Ma-1C

Well Ma-1C is a casing side tracking hole of Well Ma-1, which is an exploratory well in Tuha oilfield. Based on the analysis to formation lithology, formation characteristics, formation stability and drillability, and formation pressure, etc, together with the laboratory study on the under-balanced drilling fluid for well Ma-1C, the formulation for low weight oil-based drilling fluid is determined. Field using shows that the density of the drilling fluid is kept between 0. 87-0. 88 g/cm3, and under-pressure state is maintained during under-balanced drilling, formation is effectively protected. Overflow is always on during drilling, and the max. burning time is 35 minutes, the flame is as high as 6 m. Return of cuttings is even and no hole collapse is found, and the max, ROP is 30 m/h, which is 3. 5 times of Well Ma-1. The low-density oil based mud displays stable performances and effectively protects formation, and casing milling and under-balanced drilling are smoothly carried out.