Objective  The Ansai area of the Yan'an Gasfield is a "three-low gas reservoir" with low pressure, low permeability and low abundance, and has strong heterogeneity. The gas field water has high salinity, and the content of high valence ions such as Ca²⁺, Mg²⁺, Ba²⁺ and Sr²⁺ is very high. With the change of temperature and pressure in mining, the wellbore is easy to scaling and form scale plugging. For such “three low gas reservoir” with highly mineralized, targeted blocking removal is needed to improve productivity.

Method Inductively coupled plasma (ICP), X-ray diffraction (XRD), ion chromatography (IC) and other analytical methods were used to analyze the water samples and scale samples of the gas field, and the scaling trend of the gas field was studied. The chelating self-generated acid blocking removal system was developed, and the performance of the blocking removal system was evaluated.

Result The research showed that the blockages of gas wells in this area were mainly blockages such as formation water scaling, clay mineral migration and corrosion product deposition. It was determined that the main type of wellbore scale blockage in this area was carbonate scale. A CN chelating self-generated acid blcoking removal system was formed, the scale dissolution rate was 80.8%, the damage recovery rate of the scale blocking core was 73.62%, and the daily gas production increased from 2 000 m³ to more than 15 000 m³ in field application.

Conclusion  The self-generated acid blocking removal working fluid developed for the gas field in this area can not only dissolve the wellbore blocking, but also chelate the scale ions, so that it is not easy to scale, and has achieved a good effect of blocking removal in field application.