Application of Strong Sealing High-performance Water-based Drilling Fluid in the Horizontal Well of the Missan Oilfield

Abstract

In the Missan oilfield, because of its reservoir being "easy leakage in the up and low zones, and wellbore being collapse in the middle zone" with narrow density window, borehole instability, lost circulation, borehole collapse, sticking and other downhole complicated conditions were easily induced. A strong sealing and high performance water-based drilling fluid was mainly used to solve the problems of borehole instabilities in mud shale and muddy limestone in the horizontal wells of Missan Oilfield, for solving the problem of sidewall instability, aphysical/chemical plugging was used for strengthening the plugging of drilling fluid, improving the loading ability in formation, reducing the risk of lost circulation. The principle of "activity" regulation, permeable pressure were used to improve the semi-permeable membrane characteristics of mudstone and shale, reduce the activity of drilling fluid, inhibit the expansion ability of mudstone hydration and expansion in formation, on the basis of the static drilling fluid, permeable pressure was added to the wellbore for further improvement of borehole stability. The system in use reflects the stable rheological properties, it can be very good for plugging micro fractures, greatly improving the load ability in formation, the delaying time of borehole stability, guaranteeing the borehole stability in drilling, it provides support for the smooth drilling of the first horizontal well and consequent horizontal well drilling in Missan Oilfield.