饱和盐水钻井液对高膨胀凝灰岩的防塌机理分析

摘要

To solve the problems with drill pipe sticking caused by high-expansion and collapse tuff, the drilling lfuid has been developed in early stage research, and the anti-caving mechanism of the saturated saltwater drilling lfuid is discussed in this paper. Here, by discussing the functions of the soluble starch, NaCl, NaOH, tuff extracting solution and the wall iflm components, the anti-water and anti-caving function of the drilling lfuid is studied. By designing incremental solvent anti-sloughing experiments and comparing the dissolution ion state, the anti-dissolving function is studied too. Researches show that, the soluble starch of the formula lfocculates along the crack when it loses water, and the lfocculation may block the channels along which the solution go into the tuff, and, soluble starch provides the basis for NaCl crystallization; the adding of NaOH contributes to the NaCl crystallization and NaOH can prevent the salt solution; saturated NaCl can block the solution of the salt in tuff and NaCl crystallization can block the channels; the tuff extracting solution plays an important role in preventing dissolution of the salt solution, and in helping the crystal formation. After the well tuff absorbs water, under the common action of NaCl and other components, the hybrid iflm which contained NaCl crystallization is formed on the well wall. All the lfocculation, crystallization and iflm prevent water inifltration into the tuff. The quantitative and qualitative analysis shows that the leaching of soluble matters plays an important part in tuff breakdown and collapse. The quantitative analysis of the leached material shows that, the drilling lfuid not only prevents collapse and obstructs water obstructing physically, but also it pre-vents dissolution and collapse chemically.%针对高膨胀快速垮塌凝灰岩带来的钻井卡钻问题，前期研究中研制了饱和盐水防塌钻井液，对该钻井液的防塌机理进行研究。通过讨论可溶淀粉、NaCl、NaOH和凝灰岩浸提液的作用、井壁膜组分等分析钻井液的阻水防塌作用；通过设计增量溶剂防塌实验并对比溶出离子状态，分析钻井液对凝灰岩中可溶物的阻溶防塌作用。研究认为：配方中的可溶淀粉沿微裂缝失水絮凝，淀粉絮凝可堵塞溶液进入凝灰岩的通道，淀粉还为NaCl结晶提供结晶和生长的基础；NaOH的加入有助于淀粉絮凝和NaCl结晶，并对可溶物的溶解有增进阻碍作用；饱和NaCl有阻止凝灰岩中可溶物溶出和结晶堵塞的双重作用；凝灰岩浸提液对阻溶及助结晶有重要作用。井壁凝灰岩吸水后，钻井液中的NaCl和可溶淀粉在其他成分的共同作用下，在井壁形成含NaCl结晶的混合膜，絮凝、结晶及成膜均阻碍了水渗入凝灰岩中。由定性和定量分析得到可溶物的溶出在凝灰岩分解垮塌中起重要作用的结论。对溶出物质的定量分析表明，钻井液不仅从物理上隔水防塌，也从化学上阻溶防塌。