CO2对高密度水基钻井液性能影响规律及机理分析

准确判断污染物浓度以及其对钻井液影响规律和内在机制是制定有效的CO₂污染防治措施的重要前提，基于酸碱指示变色原理，改进了钻井液中碱度现场定量检测方法，提高测量的准确性和可操作性；采用现场取样跟踪分析以及室内模拟评价相结合的方法，研究了CO₂对高密度水基钻井液流变性和滤失造壁性的影响规律，并从胶体化学的角度出发，开展了CO₂对钻井液黏土胶体颗粒界面Zeta电位、粒度分布以及处理剂吸附影响的实验研究，分析了其作用机理。研究表明，高密度水基钻井液中碳酸根和碳酸氢根存在临界污染浓度，超过此浓度后，钻井液结构黏度和滤失量随其浓度增加而增加；碳酸根和碳酸氢根离子改变了黏土颗粒溶剂化程度和颗粒尺寸，主要表现为黏土胶体颗粒界面电动电势降低、亚微米级粒子减少，粗颗粒增多，黏土颗粒对护胶剂的吸附量减少，导致高密度钻井液黏土颗粒向聚结方向转化并缔合形成三维网络结构的胶凝状态，揭示了宏观性能变化内在机制。 

Analyses of the Effects of CO2 on the Properties of High-Density Water Base Drilling Fluid and the Mechanisms of the Effects

The preparation of measures to prevent and control CO2 contamination requires an accurate determination of the concentration of contaminants and an understanding of the patterns in which the contaminants affect the properties of drilling fluids. Field quantitative method of determining the alkalinity of drilling fluids was improved, based on the principle of color change with acid/base indicators, to have a better accuracy and operability. Analyses of feld sampling and laboratory evaluation were performed to study the effects of CO2 on the rheology and fltration property of high-density water base drilling fluids. Study was also conducted on the effects of CO2 on the Zeta-potential of the surfaces of clays used in drilling fluids, particle size distribution of clays and adsorption of mud additives from the point of view of colloid chemistry, and on the mechanisms of the effects. The studies showed that the concentrations of carbonate and bicarbonate ions in high-density water base drilling fluids have critical values; when the concentrations of carbonate and bicarbonate ions exceeds the critical values, the structural viscosity and fltration rate of drilling fluid increase with the increase in the concentrations of the carbonate/bicarbonate ions. Carbonate/bicarbonate ions have altered the extent of the solubilization and the sizes of clay particles, which can be seen from the decrease in the Zeta-potential of the surfaces of clay particles, the decrease in the number of submicron-sized particles and the increase in the number coarse particles. Decrease in the adsorption quantity of colloid protective agents by clay particles results in the coalescence of clay particles and association of the clay particles to form a gel with 3D network structure. These phenomena have revealed the intrinsic mechanisms governing the macro property changes.