Managing Total Circulation Losses with Crossflow While Drilling: Case History of Practical Solutions

Abstract Lost circulation during drilling increases the drilling costs and also enhances possibility of stuck pipe. Generally, viscous mud pills with lost circulation materials and gels or cement plugs are placed to allow plugging of loss circulation zone. But in case of total circulation loss in conjunction with cross flow condition, even repeated LCM-mud plugs followed with cement plugs do not guarantee the durable sealing of lost zone. This paper discusses the properties, mechanism and placement technique for successful plugging off lost zone in such cases where very few lost circulation remedies were effective and more than several hundred cubic meter of drilling fluid and cement were already lost. Details development of a novel sealant system consisting of an elastomer combined with cross-linking polymers, activator and bridging agents which provided quick, reliable control of loss has been deliberated in this paper. Initial low viscosity of this sealant allow easy placement against the lost zones and then gel activated near wellbore to set and form a stiff, rubbery gel stick with formation sediments to eliminate further losses. This development offers a proven means of controlling severe circulation losses resulting from large fractures or vugular spaces. The composition can be engineered to produce durable cross-linked polymeric rigid gel across a vide range of densities 8.6-14 ppg and temperature 45120 deg C. Addition of accelerators or retarders during mixing controls setting time and eliminates risk of premature setting inside the string while pumping. Laboratory tests revealed effectiveness of this polymeric based sealant treatment and can improve stress around wellbore by forming a deformable, viscous and cohesive sealant inside a lost circulation fracture. Field application shows the restoration of well bore integrity in total loss with cross flow condition by the innovative approach of using this cross linked polymeric stiff rubbery gel in combination with high volume cement plug. This paper deals with aspect of important lessons learnt from the field application of the developed cross linked polymeric stiff rubbery gel to control total circulation losses in conjunction with cross-water flow.