新型弱凝胶水基钻井液研制及作用机理分析

Development and Working Mechanism Analysis of a New Weak Gel Water Base Drilling Fluid

目前弱凝胶钻井液存在抗温、抗盐和封堵性能差等问题,限制了其推广使用。研制出一种新的弱凝胶成胶剂,其抗温达150℃,抗钙可达4 000 mg/L。以该成胶剂和优选出的降滤失剂IMPERMEX、封堵剂JA为主剂,以CX-215和KCl作抑制剂,形成了一种新型弱凝胶水基钻井液。评价结果表明:该钻井液在接近静止状态下的黏度可达90 000m Pa·s,剪切后黏度快速下降,且静切力表现出无时间依赖性,属于快的弱凝胶体系;具有好的降滤失和稳定井壁能力。环境扫描电镜和蔡司体显微镜分析结果表明,该钻井液微观结构由三维空间网状结构与包裹、镶嵌在网状结构节点上的溶胶颗粒组成,是一种具有独特空间结构的复杂胶体分散体系;该钻井液在微裂缝内能形成具有良好压缩性的致密封堵层,封闭岩石通道,具有良好的井壁稳定作用。

A new weak gel water base drilling fluid was formulated with a new developed weak gel agent as the main additive and other additives such as filter loss reducer,shale inhibitor and sealing and plugging agent selected through experiment.Laboratory experiment shows that this drilling fluid has unique rheological behavior,i.e.,it has high viscosity at low shear rates,and weak gel is formed quickly within the fluid.This drilling fluid has very good filtration property and superior performance in shale inhibition.The properties of this drilling fluid remain stable at 150℃ or when contaminated by calcium of 4 000 mg/L.Study with SEM and Zeiss microscope shows that sol particles are encapsulated and embedded at the nodal points of a 3D network developed within the drilling fluid.This drilling fluid can form dense sealing layers with good compressibility in formations full of micro fractures or fissures,preventing water from entering into the formations,thus inhibiting the hydration and swelling of shale or formations with high content of clays.