Quantitative Evaluation Method for Sedimentation Stability of Oil Well Workover Fluids by Spectral Analysis

Under long-term high-temperature and static conditions, high-density workover fluid settles, increasing the risks of workover operations. In order to achieve a quantitative assessment of the sedimentation stability of oil well workover fluids, this study adopted spectral analysis to conduct stability tests on water dispersions of barite with different concentrations. Meanwhile, a comprehensive assessment was conducted on the sedimentation rate of the well repair fluid, the size of solid particles and the changes in the thickness of the sedimentary layer in 1# Well, 2# Well and 3# Well. With the increase in barite concentration, its sedimentation behavior changes from free sedimentation at low concentrations to flocculation sedimentation at high concentrations, and the sedimentation rate shows a slowing trend. The increase in sedimentation rate is positively correlated with the increase in density, and the intensity of the initial backscattered light at the bottom of the well also increases accordingly. In addition, during the sedimentation process of sediment, the variation pattern of particle velocity shows the characteristics of being relatively fast in the early stage and gradually accelerating in the middle and later stages. The results show that the average particle size of barite solution is 4.93 μm, and the average particle size of the three workover fluids is 87.5 μm. The deposition thickness range of barite solution is 5–50 mm, and that of the three workover fluids is 25–51.58 mm. It provides data support for the rapid quantitative evaluation of the long-term stability of oil well workover fluids.