Mechanism analysis and preventive measures of drill jam caused by salt water overflow derivative sedimentation in Kuqa mountain front

The Paleogene in the piedmont structure of the Tarim Basin develops composite salt-gypsum layers and inter-salt high-pressure brine layers and is found with complicated pressure systems. To deal with the cutting settling and bit/string sticking after well killing for brine kick, the brine contamination resistance of water- and oil- based drilling fluids was investigated via laboratory experiments. Moreover, based on the Herschel-Bulkley fluid, an annular solid settling model was built to analyze the effects of various factors on solid settling. The field case study was performed, and technical strategies were developed to prevent cutting settling and tool sticking related to brine kick. The research shows that solid flocculent solids occur in water-based drilling fluids contaminated by brine and such drilling fluids barely maintain their cutting suspension capacity, which results in cutting settling-induced tool sticking after solids build up in the annulus. With the increasing solid particle radius, the solid settling velocity, solid build-up height in the annulus and shut-in time grow rapidly. In addition, the application of oil-based drilling fluids, preparation of standby weighted killing fluids with a volume 1-1.5 times that of the well volume, installation of the rotating control head, lifting BHA to the safe well section and rapidly relieving invaded fluids via the driller’s approach are technical measures to prevent cutting settling and tool sticking related to brine kick. The findings of this research provide technical support for the safe, cost-effective, high-efficiency development of sub-salt hydrocarbons in the piedmont structure.