Plugging mechanism and technical countermeasures for weak gel flooding in unconsolidated sandstone reservoirs

doi:10.3969/j.issn.1006-6535.2025.06.017

Abstract

Abstract: Aiming at the problem of successive plugging in oil wells during the late stage of weak gel flooding in the unconsolidated sandstone reservoir of Bohai L Oilfield, research on the plugging mechanism and plug removal technical countermeasures for weak gel flooding oil wells in this reservoir was carried out. The results indicate that the plugging material in oil wells consists of water, heavy components of crude oil, polymer and inorganic matter with contents of 63.99%, 14.82%, 14.48% and 6.71% respectively. Among the inorganic matter, the contents of CaCO₃, MgCO₃ and SiO₂ are 60.00%, 20.50% and 13.00% respectively.Among the heavy components of crude oil, the contents of alkanes, aromatic hydrocarbons, resins and asphaltenes are 13.78%, 9.97%, 32.84%, and 43.40% respectively. The limited space on offshore platforms causes a large amount of insufficiently matured polymer gel particles to accumulate on the screen during weak gel injection. These particles subsequently mature slowly to form flexible gel bodies, which entrain mud and sand during migration to form multi-component encapsulated plugging material. During production, they cause plugging again due to the constraints of the screen and pump inlets. To remove on-site plugging, the best depolymerizer combination "0.05% potassium persulfate + 0.05% ferrous sulfate + 0.10% citric acid", organic solvent combination "30.00% diesel oil + 20.00% dimethyl sulfoxide + 2.00% sodium dodecyl sulfate + 0.50% penetrant" and scale dissolver combination "10% hydrochloric acid + 4% hydrofluoric acid + 1% corrosion inhibitor Lan826" were preferentially selected. On site, by alternately injecting slugs of depolymerizer, organic solvent, and scale dissolver, the composite plugging material near the oil well was effectively removed, with significant liquid and oil increase performance. The daily liquid production increased by 166.4%, and the daily oil production increased by 185.3%. This research can provide reference for oil well plug removal in offshore oilfields.

Key words: unconsolidated sandstone, weak gel flooding, plugging material, formation mechanism, technical countermeasures

CLC Number:

TE358

GAO Jianchong, LIU Yigang, LU Xiangguo, LIU Jinxiang, HE Xin, MENG Xinzhi, WANG Yuqing, HUANG Wenjing. Plugging mechanism and technical countermeasures for weak gel flooding in unconsolidated sandstone reservoirs[J]. Special Oil & Gas Reservoirs, 2025, 32(6): 141-149.

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