Experimental study on ultra-low temperature drilling fluid in Arctic permafrost

Abstract

Drilling fluid in Arctic permafrost needs to have good ultra-low temperature rheology, shale inhibition, hydrate inhibition and environmental protection performance. In this work, the properties of ultra-low temperature drilling fluid and additives have been evaluated by using rheology and fluid filtration tests, shale inhibition tests, hydrate inhibition tests, thermal conductivity measurements and biotoxicity tests. Thereafter, the key additives have been optimized and the ultra-low temperature water-based drilling fluid formula was developed. The results show that the base fluid, which combined NaCl and ethylene glycol (EG), can meet the requirement of freezing point in Arctic drilling, and it also has low thermal conductivity and good hydrate inhibition. Xanthan gum (XC) and hydroxyethyl cellulose (HEC) have been selected as viscosifiers, carboxymethyl starch (CMS) as filtrate reducer and polyetheramine as shale inhibitor. The drilling fluid has good ultra-low temperature rheology with the freezing point of −32 °C. Furthermore, it has low thermal conductivity, and can inhibit shale dispersion, expansion and collapse, which is conducive to the stability of wellbore in Arctic permafrost. In addition, it can effectively inhibit hydrate formation and has good environmental protection performance. The drilling fluid invented in this study can provide technical support for ultra-low temperature drilling in Arctic permafrost.