Analysis on the influencing factors of secondary damage of seawater-based acid on sandstone reservoir

Key words:  seawater  acidizing  sandstone reservoir  secondary damage  abnormal common-ion effect

Abstract:

The damage type of seawater-base acid was analyzed by X-ray diffraction technology. And the effects of acid types, pH value, dilution ratio of seawater and electrolytes on the secondary damage were studied by the turbidity method. It is found that the damage in seawater-based acid preparation and reaction is mainly formed by MgF₂ and CaF₂. Compared with mud acid system, multi-hydrogen acid is better in mitigating the secondary damage. Increasing the amount of HCl, diluting seawater and using appropriate electrolytes can also effectively inhibit the precipitations. Based on the analysis of the acid effects, the complexation effect, and a special kind of abnormal common-ion effect, one seawater-based acid system that can eliminate the secondary damage in sandstone matrix treatmentis developed.