硅酸盐钻井液体系在鄂尔多斯盆地东胜气田的应用

Application of silicate-based drilling fluid system in Dongsheng Gasfield,the Ordos Basin

鄂尔多斯盆地东胜气田二叠系石千峰组、石盒子组发育大段泥页岩,在钻井施工中井壁失稳现象频发。结合东胜气田地层特征,分析井壁失稳原因,研究硅酸盐的封堵性和抑制性,优选形成硅酸盐钻井液配方,并对其抑制性及封堵性进行实验研究。研究结果表明:(1)石千峰组、石盒子组泥页岩中黏土矿物平均含量为56%,以伊蒙混层为主,伊利石次之;泥页岩原生层理及微裂缝,黏土矿物中伊利石、蒙脱石的水化膨胀性能差异是井壁失稳的主要原因。(2)自主研发的硅酸盐钻井液体系具有较强的抑制泥页岩水化膨胀的能力,较强的微小裂缝封堵能力;当该体系中硅酸盐的模数为2.8~3.0、加量3%、p H值维持在11以上时,硅酸盐钻井液的抑制效果更好;同时该体系中的硅酸盐与地层矿物反应生成絮状沉淀,可封堵地层微小裂缝和孔隙,阻止滤液深度侵入,维持了井壁稳定。(3)通过在东胜气田两口井的现场试验,达到了环境保护和井壁稳定的目的,取得了较好的应用效果。该研究成果为其他类似地质条件钻井液的应用提供了借鉴经验。

In Dongsheng Gasfield of the Ordos Basin, massive mud shale is developed in the Shiqianfeng and Shihezi For- mations of Permian, so borehole instability occurs frequently during well drilling. In this paper, the reasons for the borehole instability were analyzed depending on the stratigraphic characteristics of Dongsheng Gasfield. After the plugging and inhibi- tion performances of silicate were investigated, the formula of silicate-based drilling fluid was optimized and its plugging and inhibition performances were experimentally studied. The results show that clay minerals in the mud shale of Shiqianfeng and Shihezi Formations are primarily illite/smectite formation and secondarily illite, and their average content is 56%. The main reasons for the borehole instability are the primary bedding and micro fractures in mud shale and the difference of hydrate expansion performance between illite and smectite. The independently developed silicate-based drilling fluid system is char- acterized by higher inhibition on hydrate expansion of mud shale and stronger plugging on micro fractures. The silicate-based drilling fluid presents better inhibition performance when its silicate module, dosage and pH value are 2.8-3.0, 3% and 11, re- spectively. The silicate in this system reacts with the formation minerals to generate flocks which can plug micro fractures and pores in the strata, preventing further invasion of filtrate. As a result, the borehole is kept stable. This drilling fluid system was tested practically at two wells in Dongsheng Gasfield. The application result is better, reaching the target of environmental pro- tection and borehole stabilization. The study results can be used as the reference and experience for the application of drilling fluids in similar geological conditions.