In this paper, we present a thorough analysis of drilling methods and fluid and mechanical solutions to mitigate lost circulation (LC), as well as risk control measures undertaken, while drilling 5 wells on two platforms with severe LC zones in the reservoir. The drilling rate of penetration (ROP) was significantly reduced compared to the ROP utilized in the sections above the reservoir, along with the pump rate, to minimize enhancing fractures in a highly permeable zone. A combination of bridging, cement and resin based materials were also used in the 5 wells to mitigate and partially/fully cure losses. Risk control measures included only having a maximum of two rigs drilling in the reservoir section at the same time, rig capacities to sustain bad weather without support from boats, each rig in the vicinity having barite, lost circulation materials (LCM), and other resin based LCM materials available and having cement retainers (CRs) on standby and using them not only when curing losses but also to secure the well in the event mud/barite/chemicals on the rig could not sustain hole filling during bad weather.

Even though the losses were not completely cured in wells B and E, which led to the cessation of drilling operations before reaching the planned total depth, the LC mitigation methods used ensured access to 20 % of the net payzone in well B and 30 % in well E, a significant achievement in such severe LC zones. Evaluation of three fluid solutions used to mitigate losses showed that spotting cement through a cement retainer (CR), set close to the previous casing shoe, gave a higher possibility of curing losses compared to conventional LCM resin based LCM and directly spotting cement on loss zone with open ended drillpipe (OEDP).

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