Objective Severe neck contraction was identified in two gas injection-production wells during the pressurized cavern testing at Jintan Salt Cavern Gas Storage in 2019. They experienced a remarkable volume reduction of 66% and 72%, respectively, compared to the testing results in 2013. To prevent potential blockages in the neck segments due to further contraction and ensure the continued safe and stable operation of these wells, it is crucial to explore the causes of cavern neck contraction and implement targeted preventive and remedial measures.

Methods The study was based on extensive data gathered from the two caverns, encompassing information on production operation, neck shape measurements, local geological conditions, and mechanical parameters of the rock salt. Various methods were employed to investigate the factors behind neck contraction, such as numerical simulation analysis, multiarm caliper measurements, and downhole TV monitoring.

Results The production and operation of the two caverns were found to align with the design specifications. According to numerical simulation results, the maximum creep contraction in the neck radius was 7.62 mm within the design pressure range of 7 to 15 MPa, with pressure demonstrating minimal impact on neck contraction. The results from the multiarm caliper measurements closely matched the sonar-derived data, effectively ruling out measurement errors. Downhole TV monitoring uncovered a significant presence of salt crystals at the site of neck contraction.

Conclusion The operation of the salt cavern gas storage within the design pressure range proved effective in preventing neck contraction induced by creep. The main cause of neck contraction was attributed to salt crystallization, primarily triggered by the recrystallization of rock salt due to condensate water attaching to the neck during injection and production operations. Consequently, this paper introduces preventive measures, such as optimizing monitoring methods and cycles, refining the process design of neck segments, and addressing residual brine in the caverns. Additionally, the utilization of jet cleaning technology with coiled tubing is proposed as a remedial measure.