不同注入条件下地层酸蚀蚓孔扩展规律

Study on underground acid etched wormhole propagation under different injection conditions

在碳酸盐岩酸化中,地层条件下酸液流动引起的蚓孔扩展情况与实验室条件下的不同,因此有必要对地层条件下的蚓孔扩展规律进行研究。应用1种二维双重尺度连续模型并耦合1个压缩区模型进行了研究,结果表明:与实验室条件相比,地层条件下的蚓孔扩展速度较慢;定压条件下,地层流体的压缩系数越小,蚓孔扩展速度越慢,反之亦然;定流量条件下,地层流体的压缩系数越小,入口压力下降越慢,出口压力上升越快,反之亦然;由于压缩区和施工条件的影响,地层条件下的蚓孔长度存在最大值;建立表皮系数模型,通过实例分析发现,蚓孔未突破污染区域之前,定流量条件下的蚓孔扩展速度和表皮系数下降速度均大于定压条件下的结果,蚓孔突破污染区域之后,二者几乎没有差异,且注酸量存在最优值。

In carbonate acidizing, the injected acid reacts with the rock to create a high conductivity channel called wormhole in order to improve the damage in near wellbore zone. Different from experimental conditions, the acid flow is radial flow and the formation pressure increases due to fluids being compressed under reservoir condition. Both of them can influence wormhole propagation to a great extent, it is very necessary to study the wormhole propagation under reservoir condition. We use a 2D two-scale continuum model coupled with a compressed zone model to study it. The results show that the wormhole propagation velocity under reservoir condition is slower than that under experimental condition. Under constant pressure condition, the smaller the compressibility coefficient of formation fluid, the slower the propagation velocity of wormhole, and vice versa. Under constant rate condition, the smaller the compressibility coefficient of formation fluid, the slower the inlet pressure declines and the faster the outlet pressure increases, and vice versa. Due to the effect of compressed zone and implementation condition, the wormhole length has a maximal value under reservoir condition. We also develop a skin factor model to study on an example. It is found that both wormhole propagation velocity and skin factor decline velocity under constant rate condition are higher than those under constant pressure condition before wormhole breaks through the damaged zone, but both of them are very close after wormhole breaks through. Note that, the acid injection volume has an optimal value.