阳离子交换含量的测定及与薄膜电位的关系研究

Determination of Cation Exchange Capacity and the Relationship between Membrane Potential and Core CEC

岩心阳离子交换含量(CEC)对地层岩心水化特性有重要影响,是测井过程中的重要数据。实验选用大庆油田凝灰质砂岩岩心,通过pH计法测定岩心CEC,考察了地层水矿化度及水型、离子交换温度、岩心粒径对CEC测定值的影响。结果表明,岩心在NaHCO3溶液中浸泡时,随盐加量的增大,岩心CEC测定值减小;当矿化度大于1.00×104mg/L时,CEC基本稳定。两种地层水水型对岩心CEC测定值的影响规律基本一致,CEC均随着矿化度的增大而减小;矿化度相同时,Na2SO4地层水处理后岩心的CEC稍大于NaHCO3地层水。随离子交换温度升高,离子交换更充分,岩心CEC增大。岩心颗粒粒径越小,CEC越大;200～250目(粒径75～58μm)岩心的CEC为3.11 mmol/100 g;当岩心目数大于200目时,CEC基本稳定。对比100～120目与200～250目岩心的薄膜电位计算值与实测值,200～250目岩心的CEC测定值更准确。

Cation exchange capacity （CEC） had important influence on the hydration characteristics of formation core, which was thought as a vital data in well logging. In the experiment, the tuff sandstone cores came from Daqing oilfield. The CEC value of core was measured by pH meter method. The effect of formation water salinity, formation water type, ion exchange temperature and core grain diameter on CEC determination of cores was analyzed. The experiment results showed that the measured value of core CEC decreased with increasing salt content when the core was soaked in NaHCO3 solution. CEC value was basically stable when the salinity was greater than 1.00× 10^4 mg/L. The influence laws of two type of formation water on core CEC measurements were basically identical, that was, CEC value decreased with increasing salinity. CEC value of core processed by Na2SO4 solution was slightly greater than that by NaHCO3 formation water, when the degree of mineralization was the same. With the temperature of ion exchange rising, ion exchange was more fully and core CEC increased. The smaller core particle size, the greater CEC value was. The CEC value of 200--250 mesh （diameter 75--58 μm） core was 3.11 mmol/100 g and when the particle size was greater than 200 mesh, CEC was basically stable. The calculated value and measured value of membrane potential for 100--120 mesh and 200---250 mesh cores were compared. It showed that the measured CEC value of 200---250 mesh core was more accurate.