Abstract: The Chang 7 shale oil reservoir in Qingcheng Oilfield has achieved large-scale economic development by applying technologies such as long horizontal well fracturing, energy boosting, and volumetric fracturing integrating imbibition. However, some oil wells experience significant scale deposition and blockage in the near-wellbore zone, leading to rapid decline in production, and conventional acid systems have proven ineffective for restoring productivity. By analyzing the scaling characteristics and chemical composition of the sand scale deposits recovered during sand washing, as well as the ion composition of the produced water, the mechanisms of formation scaling were investigated. Based on this analysis, a long-lasting composite organic acid system was developed, specifically targeting scale removal in horizontal shale oil wells in the Qingcheng Oilfield. The research results show that significant scaling ions in the produced water precipitate in the near-wellbore zone, encapsulating proppant and gradually filling pore spaces. The primary scale type is carbonate, with some wells found barium and strontium sulfate scales. The developed composite organic acid system achieved an over 80% dissolution rate of the scale samples, with a corrosion rate of only 1.920 g/(m²·h) on N80 steel and a scale prevention efficiency exceeding 85%. The system showed good compatibility with formation water, offering excellent long-term scale removal and corrosion inhibition performance. Field application in five horizontal shale oil wells in the Qingcheng Oilfield shows that the average oil production for each well was increased from 3.5 t/d to 5.1 t/d, and the effective period was extended from 190 days to over 450 days, achieving remarkable production enhancement effect. This technology provides valuable guidance and experience for the efficient development of similar unconventional shale oil reservoirs.