Research and application of drilling fluid technology for thick water-sensitive formations in the Miaoershan area of Guangxi

Abstract:

The potential for uranium exploration in the Miaoershan area of Guangxi is enormous， but part of the formations are complex， with large thickness of water-sensitive and broken formations. During drilling construction， difficulties such as hole wall collapse and excessively large bore diameter occur frequently， leading to frequent accidents in the hole， which seriously affect the construction progress. Therefore， mineral composition and microscopic characteristics of water sensitive cores in the area were analyzed. The analysis results show that there are a large amount of clay minerals such as montmorillonite， kaolinite， hydromica， etc. in the water-sensitive formations， and the microcracks are developed with serious hydration expansion. To solve above problems， new materials with film forming and wall protecting functions were optimized through indoor evaluation experiments， and a drilling fluid system with good wall protection performance was further developed， which consists of 5% film-forming agent A， 3% film-forming agent B， 1.5% modified asphalt， 1% plugging agent while drilling， 1%sealing agent， 0.6% viscosifier， 0.2% coating agent. The API filtration loss of this drilling fluid is 5~8mL， and the relative expansion reduction rate reaches over 87%. This drilling fluid can effectively inhibit hydration expansion of the water-sensitive formations， and the wall protection effect is significant. This technology has been successfully applied in three boreholes in the Miaoershan area， smoothly drilling through water-sensitive formations without any problems such as core dispersion or hole wall collapse. Good application results have been achieved， and a film forming and wall protection drilling fluid technology has been preliminarily formed for water-sensitive formations in this area.

Key words:water-sensitive formation;film-forming wall protection drilling fluid;hole wall collapse;excessively large bore diameter;uranium exploration