The use of drilling fluid te of strong inhibition, anti-high temperature and anti-collapse in Well Dong-8

Well Dong-8 is an important exploratory vertical well placed in Junggar Basin by SINOPEC. Its total depth is 5 580 m. Tight hole was frequently met during tripping in the upper part of the well, and in the lower part, the Jurassic coalbeds were deposited. Moreover, the formation pressure was anomalous and wellbore instability was severe during drilling. The Sangonghe Formation has high-pressure saltwater layers and is contaminated by bicarbonate fluid, so the rheology of drilling fluid under high density is not easily controlled. In view of its geologic characteristics and through indoor studies, it was determined that the aluminum-amine strong inhibition and anti-sloughing drilling fluid system and high-temperature film forming anti-sloughing drilling fluid system are used. Field application results show that the drilling fluid systems used have overcome the difficulties of tight hole in the upper soft mudstone, sticking in sandstone section and instability of Jurassic wellbore. The average enlargement rate of the entire hole was only 7.02%, which was quite satisfactory.