一种环保型合成基钻井液在页岩气水平井中的应用

Application of an environmentally-friendly synthetic base drilling fluid to horizontal drilling of shale gas wells

页岩失稳坍塌是目前困扰中国页岩气水平井大规模钻探的关键因素之一。合成基钻井液因其强抑制性强,在国外被广泛用于页岩气水平井钻井。借鉴国外的相关经验,选用气制油Saraline 185作为基础油,通过室内实验得到了合成基钻井液的基本配方,再采用醋酸钾替代氯化钙作为水相抑制剂,既增强了体系的抑制性又简化了配制工艺。之后对其基本性能开展了实验评价:加重至2.40g/cm3的钻井液流变性能良好,破乳电压较高;在130℃条件下热滚老化实验,测量其性能并与热滚老化前的性能对比,流变性及破乳电压变化都不大。在四川盆地对外合作的富顺区块成功进行了3口页岩气水平井的应用试验,在长达2 000m的大斜度及水平井段中,返出的页岩岩屑棱角分明,粉碎后的岩屑内部干燥,起下钻井眼顺畅,斜井段平均机械钻速5.33m/h,复合钻进平均机械钻速8.8m/h。完井作业的电测、下套管、固井顺利,表明该钻井液完全满足上述区块页岩气钻井的需要。

The shales＇ instability and susceptibility to collapse is currently a crucial problem bottlenecking the large scale horizontal drilling of shale gas wells. The synthetic base drilling fluid, due to its strong inhibition, has been widely applied abroad to horizontal drilling of shale gas wells. Learning experience from foreign countries, we prepared a new drilling fluid as follows： take the Shell GTL Saraline 185V as the base oil to obtain the basic formulation of synthetic drilling fluid through indoor tests; then adopt the po- tassium acetate as the water-phase inhibitor in substitution of calcium chloride so as to strengthen the system inhibition and simplify the preparation process. Finally, its basic performance was evaluated in experimental tests, the result of which demonstrated that this prepared drilling fluid with density increased to 2.40 g/cm3 has excellent rheological property and relatively high emulsion-breaking voltage. According to the comparison of performance before and after the hot-rolling aging experiment at 130℃, the rheological property and emulsion-breaking voltage show very little change. Pilot tests have been successfully conducted in horizontal drilling of 3 shale gas wells in the foreign-cooperative Fushun Block in the Sichuan Basin. In the horizontal well section with the length of 2000 m and high inclination, the returning shale cuttings had angular shapes; the pulverized cuttings were dry inside; the wellbore was smooth in pipe tripping; the average mechanical drilling speed of the deviated section reached 5. 33 m/h, while that of compound drilling 8.8 m/h; and the electrical logging, casing running and cementing proceeded smoothly in the well completion. All these above indicate that this drilling fluid fully meets the requirements of shale gas drilling.