Since the commencement of horizontal well development in the Chang 7 shale oil reservoir in Qingcheng Oilfield,the degree of scaling in the wellhole has been significantly higher than in other formations within the same region.This scaling issue has adversely affected the open flow rate and the pump inspection cycle.The horizontal shale oil wells exhibit a casing pressure distribution ranging from 0.5 to 2.0 MPa and a high gas-oil ratio(greater than 100 m3/t),complicating the chemical injection process at the wellhead.The wellhole scale types are complex and variable,rendering single-type scale inhibitors inadequate for field applications.Thus,research on the scaling mechanism in shale oil wellholes and the development of efficient anti-scaling technologies are becoming imperative.By analyzing the fluid properties and scale types at different stages of shale oil development,the characteristics and key influencing factors of scaling were identified.In the initial production stage,the primary scale composition is ferrous carbonate,while in the later stages,calcium carbonate and calcium sulfate become predominant.A composite scale inhibitor tailored for shale oil and a downhole drip doser were developed and tested in 5 field wells.The results show that continuous monitoring of phosphorus content in the produced fluids ranged from 28 to 40 mg/L,with the downhole drip injection device ensuring a stable and continuous release of chemicals.The scaling rate per well decreased from 3.4 mm/a to 0.5 mm/a,and the pump inspection cycle extended from 155 days to 362 days,a 162.2%increase in pump inspection intervals.This research established a long-term anti-scaling technology for horizontal shale oil wellholes,providing a technical guidance and valuable reference experience for the efficient development and stable production of shale oil.
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