Research and application of low-solid film-forming flushing fluid for hard-brittle fractured formations

Abstract:

To address the frequent technical challenges of borehole collapse， block falling， and pipe sticking encountered in multiple drill holes penetrating fractured formations in a mining area of Nandan County， based on a systematic analysis of the geological characteristics of the mining area， this study proposes technical countermeasures to wellbore stabilization using flushing fluid， and field application was carried out. Influenced by the Danchi fault zone， the siliceous mudstone rock mass exhibits extremely developed joints and fissures， displaying hard-brittle fractured characteristics. Under mechanical disturbance， the interlayer structure is highly susceptible to instability failure， forming brecciated and fragmented spalled materials which further trigger large-scale block falling and collapse-induced pipe sticking. Therefore， multiple flushing fluid formulations were explored， including low-solid plant gum systems， low-clay-phase silicate anti-collapse systems， and low-solid film-forming systems. Ultimately， a low-solid film-forming PAC-LV+PVA1788 flushing fluid system suitable for the fractured formations in this mining area was developed. The system utilizes the skeleton role of clay particles within the low-solid-phase system. Under the GSP dispersion and activation， PAC-LV particle bridging and PVA1788 hydrophobic anchoring synergistically form a film， rapidly generating a dense and tough internal/external mud cake on the siliceous mudstone borehole wall. This system combines the dual functions of physical plugging and chemical consolidation， effectively solving the engineering challenge of long-term micro-fracture plugging in hard-brittle fractured formations. Field application has yielded favorable results， providing strong technical support for the prospecting breakthrough of critical metals such as tin， antimony， and indium in Guangxi.