不同剪切作用下水合物钻井液微观结构试验研究

An Experimental Study on Microstructures of Drilling Fluids in Hydrate Formation under Different Shearing Actions

在钻进水合物地层过程中,井壁附近水合物的分解和环空中水合物的分解与再形成,很可能会引起井壁失稳坍塌以及环空堵塞等复杂情况,从而影响钻井的顺利进行。在此过程中,由各组分相互作用形成的钻井液微观结构起到了至关重要的作用。但由于多组分钻井液的微观结构非常复杂,文中仅针对组分简单的水基聚合物钻井液(NaCl、CMC、PVPK90相互组合),考虑钻井液在井底钻头与环空处所受的不同剪切作用(分别为600r/min和6000r/min),结合冷冻干燥方法,利用扫描电子显微镜观测了这两种剪切作用后不同组分的水基聚合物钻井液相应的微观结构。结果表明,聚合物分子以网络骨架结构形式悬浮于钻井液中,一小部分水分子、无机盐离子等被吸附在聚合物骨架结构表面上,大部分水分子、无机盐离子等小分子物质游离于聚合物网络骨架孔隙中;对于环空中含水合物的岩屑,热量主要通过网络骨架结构的热传导与充填其中流体的对流导热而传递至岩屑表面,而后通过热传导进一步向岩屑内部传递;钻井液的微观结构随着剪切作用、浓度与组分的改变而发生变化,这就对上述的传热过程产生影响,进而对钻井液中水合物分解的传热特性产生影响。

The dissociation of hydrates near the borehole wall and the dissociation or reformation of hydrates in the annulus can cause some down hole problems, such as changing properties of drilling fluids, plugging in the annulus and wellborc collapse, which have a direct influence on drilling opera- tion. The microstructures of drilling fluids formed by the interactions among their components have played an important role in the process. Because micro- structures of drilling fluids are very complex, only waler-based drilling fluids consisting of some simple components （ NaC1, CMC and PVPKg0） are re- searched. Eonsidering different shearing actions in the drill bit and in the annulus, and using the freeze-drying method and scanning electron microscopy, the corresponding microstructures of the water-based polymer drilling fluids are observed after two kinds of the shearing action （600r/min and 6000r/min, respectively）. The results show that polymer molecules form a net framework stnicture in drilling fluids, some part of H20 molecules and mineral salt ions is adsorbed on the surface of the net framework, other part of H20 molecules and mineral salt ions is wandering in the pores of the net framework. For cut- tings with hydrate in the annulus, heat is transfered to the surface of cuttings through the heat conduction of the net framework and the convection of the fluids in the net framework, and further into cuttings through the heat conduction. The microstructures of water-based polymer drilling fluids change with shearing actions, components and concentration, which affect the above-mentioned heat transfer process and then the heat-transfer characteristic of the dissociation of hydrates in drilling fluids.