钻井液-井壁界面半透膜与隔离层形成机理

在钻井液-井壁界面形成高效率半透膜是一种新的阻水思路。利用活度控制原理，半透膜具有调控水流方向的作用。半透膜通过膜污染进一步转换成隔离层之后，能阻止外来物质进入地层，起到稳定井壁和保护储层的作用。以自制纳米胶乳NM-1（平均粒径为65 nm）和无机纳米粉体NMTO为主剂，配制出纳米钻井液；用渗透压法测定了纳米钻井液的半透膜效应，膜效率为65%；采用滤失量测定法评价了钻井液的隔离层效应，API滤失量在120 min后随时间变化的增量几乎为零，其承压能力在3.5 MPa以上。将成膜后的岩心切片，用扫描电镜分析了膜的内部微观结构。研究表明，半透膜是通过纳米胶乳粒子与聚合物形成网络结构后形成，隔离层是在半透膜的基础上通过乳胶粒的变形、填充、高温黏结而形成的，其厚度为50~60 μm。

Formation mechanisms of semi-permeable membranes and isolation layers at the interface of drilling-fluids and borehole walls

The formation of high efficiency semi-permeable membranes at the interface of drilling fluids and borehole walls is a new approach to prevent formations from water. On the principle of activity control, a semi-permeable membrane can control the flow orientation of water, and provided transformed to an isolation layer via membrane contamination, semi-permeable membranes can prevent formations from the invasion of extraneous substances, playing a role in stabilizing borehole walls and safeguarding formations. The present study prepared a kind of nanometer drilling fluid using the self-made nano-latex NM-1 (65 nm in mean grain size) and inorganic nano-powder (NMTO) as the host and tested the semi-permeable membrane efficiency of this drilling fluid via the osmotic pressure method, which was 65%. The study also evaluated the effect of the drilling fluid as an isolation layer through the API filtration loss method, and the result showed that the incremental of the API filtration loss with time decreased nearly to 0 after 120 minutes and the bearing resistance to pressure increased up to 3.5 MPa. The scanning electron microscopic examination of sliced cores after membrane formation indicated that microstructures inside this semi-permeable membrane were network structures formed through the interaction of nano-latex with polymers in the drilling fluid, while isolation layers with an average thickness of 50~60μm were thermally felted through the deformation, filling and cementation of latex particles based on semi-permeable membranes.