Study on three-phase circular micro-foam drilling fluid technology and its application in Cainan oilfield.

According to investigative data of 96 developing wells in Cainan oilfield of Xinjiang, there were 70 absorption wells, i.e., 72.9% of the wells investigated were absorption wells. The primary lost circulation zone is from 400 m to 700 m and the secondary zone is from 1800 m to 2000 m. While lost circulation occurred, no any drilling fluid returned. Due to lost circulation while drilling hampers severely ROP and makes drilling cost up, three phase circular micro foam drilling fluid system was developed to cope with severe lost circulation existing in low pressure fracture type reservoir of the upper section. The system consists of foaming agent, stabilizing agent and curing agent. It can be recycled without special degassing and aeration equipments while remains part advantages of common foam drilling fluid. Based on studies of composing, micro conformation, stability and equivalent density of micro foam drilling fluid, three phase circular micro foam drilling fluid technology was developed and was used in the field. The results showed that the drilling fluid has properties of high stability, easily preparing in site, good performance, strong resistance to fouling, as well as leak resistance and plugging effect.