智能水矿化度及离子组成对碳酸盐岩储集层矿物结垢的影响

Effects of salinity and ionic composition of smart water on mineral scaling in carbonate reservoirs during water flooding

利用碳酸盐岩岩心开展岩心驱替实验,研究了在智能水驱过程中由于矿物结垢沉淀而引起的储集层伤害风险以及注入水矿化度和离子组成对矿物结垢沉淀的影响。设计了一种新的室内岩心驱替实验程序以模拟注入水和地层水在储集层中的流动条件,考虑了注入水和地层水的原位接触时间对矿物结垢沉淀的影响。在确定了最佳接触时间之后,通过改变注入海水的矿化度和离子浓度来研究渗透率下降程度的变化。利用扫描电镜对结垢后的岩心样品进行目测分析,以研究结垢晶体形态。实验结果表明,在设定的实验条件下,CaSO_(4)和CaCO_(3)复合结垢沉淀导致的渗透率下降幅度为初始渗透率的61.0%~79.1%,注入智能水的矿化度、离子组成以及注入水与地层水的接触时间对CaSO_(4)和CaCO_(3)结垢沉淀有显著影响。扫描电镜图像显示,岩心渗透率的损失主要是由结垢晶体积聚并垂直于孔隙壁面生长造成的。

This work was conducted to study the risk of formation damage as the result of mineral scales deposition during smart waterflooding into carbonate core sample,as well as the influence of injected water salinity and ionic composition on mineral scaling and precipitation.The reservoir flowing conditions were simulated by a new laboratory core-flooding procedure,which took into count of the effect of in-situ contact time(CT)of injected water and formation water on scaling.After the optimum CT was determined,extent of permeability decline was studied by the change in the salinity and ionic composition of injection seawater.The scaled core sample was analyzed visually by scanning electron microscopy(SEM)to study the crystal morphology of the scale.Under the experimental conditions,extent of permeability decline caused by CaSO_(4 )and CaSO_(3) composite scales ranged from 61%to 79.1%of the initial permeability.The salinity and the ionic composition of injected smart water,and CT of the mixing waters had significant effects on the co-precipitation of CaSO_(4) and CaSO_(3) scales.The SEM images reveal that the loss of permeability is mainly caused by the accumulation and growth perpendicular to the pore wall of scale crystals.