油基钻井液组分对水泥浆性能的影响及其机理

针对固井时油基钻井液与水泥浆掺混易产生接触污染进而影响施工安全的问题,开展了油基钻井液各组分对水泥浆流变性、稠化时间、抗压强度等性能影响的研究,同时结合扫描电镜、X射线衍射仪、红外光谱等手段,初步探索了油基钻井液各组分对水泥浆性能影响的机理。实验结果表明:油基钻井液的掺混会使水泥浆流变性变差、水泥石抗压强度降低,影响顶替效率及水泥环的封隔能力;柴油、主乳化剂、副乳化剂等单组分对水泥浆流变性能的影响不大,而由柴油、内部水相与乳化剂搅拌形成的乳状液则会对水泥浆性能产生几乎与油基钻井液同等程度的影响。研究结果表明:乳状液圈闭了水泥浆中的自由水,导致浆体变稠,使水泥颗粒无法与自由水有效结合,阻碍水泥浆的水化,导致水泥石结构疏松多孔,影响了水泥石的强度。对策建议:可使用添加合适表面活性剂的先导浆、隔离液等措施来缓解接触污染。

Impact of the oil-based drilling fluid components on cement slurry performances and its mechanism

When the oil-based drilling fluid is mixed with cement slurry during well cementing, contamination may occur and consequently cementing safety is threatened. In this paper, therefore, studies were made on the impact of the oil-based drilling fluid components on cement slurry performances (e.g. rheological property, thickening time and compressive strength). Meanwhile, its corresponding influential mechanism was also explored preliminarily by means of SEM, XRD and FTIR analyses. The experimental results show that the rheological property of cement slurry gets worse and the compressive strength of set cement drops when cement slurry is mixed with the oil-based drilling fluid, thus the displacement efficiency and cement sheath sealing capacity are influenced. Besides, the rheology of cement slurry is less influenced by each single component (e.g. diesel, main emulsifier and assistant emulsifiers). The effect on the rheology of cement slurry from the emulsion which is composed of diesel, aqueous salt solution phase and emulsifier is the same as that of the oil-based drilling fluid. It is indicated that the free water of the cement slurry is trapped by the emulsion, so its liquidity is obviously decreased. Thus, cement particles cannot be combined effectively with free water and cement hydration is hindered. And consequently, set cement is structurally unconsolidated and porous and its strength is damaged. It is recommended to alleviate contact contamination by using forerunning fluids and spacer fluids that are added with appropriate surfactants.