Research on long-term anti-channeling cementing technology for complex formations in mature oilfield areas

Abstract:

After long-term waterflooding and polymer injection development， the mature oilfield are subjected to the complex working conditions including coexisting multi-pressure systems， interleaved oil and water layers， polymer contamination and active formation water invasion， as a result， the integrity of the cement sheath and the long-term inter-zonal sealing performance were insufficient， and the oil wells cannot be put into production directly， or inter-zonal channeling frequently occurs after production， which severely restricts the fine exploration of remaining oil potential and long-term stable production in mature oilfields. In view of this， firstly， experiments and mechanism analysis are carried out on formation water invasion， polymer contamination， residual false mud cake， and displacement channeling to identify the main controlling factors and propose key technical countermeasures for long-term anti-channeling cementing. Nano-silicon fluid and thixotropic agent were selected， anti-channeling parameters were optimized， and an efficient water anti-channeling cement slurry system was developed. Based on the synergistic mechanism of permeation swelling and mechanical erosion， a dual-effect composite flushing fluid was developed. The effective anti-channeling annular pressure difference standard was determined to be 3~7 MPa， and an adjustable density heavyweight spacer fluid was developed， a pressure compensation method was designed， and a full-process pressure stabilization and anti-channeling technology was established. Supporting measures such as efficient mud cake removal and enhanced centralization of key layers were implemented to form a long-term anti-channeling cementing technology for complex formations. The results show that the high-quality rate of cementing for the first and second interfaces in an eastern mature oilfield has been significantly improved. The cementing qualification rate for thin interlayers and water-flooded zones has increased from less than 60% to 100%， and the oil well production rate has increased from 85% to 100%. This effectively solves the problem of insufficient long-term sealing of the cement sheath in mature oilfield areas， providing technical support for the layered subdivision development of similar mature oilfields.