硫酸钡结垢对岩心渗透率影响模型研究

Investigation of the Model of the Effect of Barium Sulfate Scaling on Core Permeability

油田注水过程中,含SO_4^(2-)的注入水与含Ba^(2+)地层水不配伍将导致硫酸钡垢产生,堵塞地层孔喉,造成严重的渗透率下降。建立合理的数学模型,精确地预测岩心渗透率的变化,对于选择合理的注水方案具有重要意义。首先研究了Bedrikovetsky化学动力学模型,在此基础上优化了模型的求解方法,避免了国内外已有的硫酸钡结垢动力学模型的求解方法中做出的岩心入口端Ba^(2+)与SO_4^(2-)浓度比远小于1的假设;其次,改进了模型中的三个重要参数——扩散系数、反应速率常数和地层损害系数的求取方法;最后,针对来自长庆油田的两块岩心求模型参数,对模型有限差分并在0≤T≤T_f范围内利用Runge-Kutta方法求数值解,得出了驱替至不同孔隙体积倍数时岩心中无因次Ba^(2+)浓度分布、硫酸钡结垢量分布及岩心渗透率比值的变化。结果表明:岩心中有少量的硫酸钡垢生成时,渗透率便迅速下降。随着驱替孔隙体积倍数增加,岩心中Ba^(2+)含量减小;SO_4^(2-)含量增加;岩心中结垢量增大;岩心的渗透率降低。

In the oilfield water injection,due to the incompatibility between the SO_4^(2-) in the injected water and the Ba^(2+ )in the formation water,will lead to barium sulfate scaling,plugging the formation pore and roar,and causes a serious decline in permeability. To establish a reasonable mathematical model to predict the change of core permeability accurately is of great significance for the reasonable selection of the water injection scheme. Firstly,the chemical kinetic model of Bedrikovetsky was studied,the method of solving the model was optimized,which effectively avoided the assumption at the core inlet Ba^(2+ )and SO_4^(2-) concentration ratios were much less than 1 in the solution of the existing barium sulfate scaling dynamics model. Secondly,a calculating method for the three important parameters—diffusion coefficient,reaction rate constant and formation damage coefficient in the model were improved. Finally,according to the two cores from Changqing Oilfield,the finite difference method was used and the numerical solution was obtained by using the Runge-Kutta method in the range of 0≤T≤Tf,obtained that the distribution of dimensionless Ba^(2+ )concentration and barium sulfate scaling in the core,and the variation of permeability ratio when displacement to different pore volume ratios. The results showed: When a small amount of barium sulfate was formed in the rock,the permeability decreased rapidly. With the increase of the pore volume,the Ba^(2+ )in the rock decreased; the SO_4^(2-) increased; the scale of the core increased; the permeability of the core decreased.