Abstract:
The profile control in edge/bottom water reservoirs requires a large volume of plugging agents with superior anti-dilution and salt resistance properties. Based on the resource recycling principle, development of a series of plugging agents by utilizing oil sludge for profile control in edge/bottom water reservoirs offers potential economic and environmental advantages. Therefore, it is particularly important to evaluate the dynamic and static performance of plugging agents. By using the sludge from settling tanks at the combined station in the operation area of Jiqing Oilfield as raw material, adding non-ionic polyoxyethylene ether emulsifier, self-crosslinking hydrophobic association polymer, and curing agent, three distinct plugging agents with different plugging strengths and functions, namely, sludge emulsification, sludge gel, and sludge solidification, were developed. The performance of three plugging agents was assessed via such indicators as gelling time, viscosity, anti-dilution performance, and selective plugging capacity. Research has shown that the developed oil sludge plugging agent can increase the sludge carrying capacity to 30-40%. Among them, the emulsified oil sludge plugging agent achieves 40% sludge carrying capacity with a plugging efficiency over 75%, and can serve as a green main slug for treating oil sludge. The oil sludge gel plugging agent exhibits viscosity of the base fluid less than
1000 mPa·s with excellent injectivity. After 120 days at 90 ℃ with 1∶3 mass ratio of gel plugging agent to formation water, the gelling viscosity stabilizes at around 9 000 mPa·s, confirming anti-dilution stability. The solidification plugging agent maintains plugging efficiency over 90% at 150 ℃ and is suitable as tail slug to protect the preceding slugs. The results showed that the designed mud barrier slug combination was applied in edge/bottom water reservoirs in Jiqing Oilfield operation area, with such strategy as "leading slug-deep barrier construction, main slug-green coning suppression, tail slug-high-efficiency channeling sealing". Field trials in 7 wells cumulatively treated 28 800 m
3 oil sludge, saved about 19.87 million RMB in oil sludge disposal costs, and increased oil production by
4 011.6 t, demonstrating effective water shut-off. Oil sludge-based plugging agents achieve dual goals of efficient water control and sludge recycling via the mud-barrier slug technology, providing a valuable solution for eco-friendly EOR.