Anti-sloughing Mechanism Study and Application of Circulating Micro-foam Drilling Fluid

Micro-foam drilling fluid is one of the best muds to effectively resolve the lost circulation, but its effectiveness of well bore stability is unknown. It becomes one of the key elements to choose it or not. Seven mechanisms of micro-foam drilling fluid to stabilize wellbore were generalized and proposed. The wellbore stability effectiveness of commonly water-base drilling fluid and micro-foam drilling fluid was comparatively studied in lab. The results indicated that the micro-foam drilling fluid had a more powerful capability to stabilize the wellbore than water-base drilling fluid, which provides a theory foundation and experiment basis for choosing micro-foam drilling fluid or not. The successful field test indicated that micro-foam drilling fluid could not only effectively avoid sloughing and lost circulation, but also improve the ROP, protect reservoir and save the drilling cost.