Overcoming Lost Circulation While Cementing Riserless Tophole in Deepwater

摘要

In Deepwater environment,cementing the surface casing properly is critical to ensure support of the BOP stack,and allow drilling subsequent hole sections.The riserless tophole sections are prone to lost circulation while drilling through the unconsolidated formation and geological fault zones.After switching the well fluid from seawater to heavier pad mud,no drilling fluid returns or very little is observed at sea bed.This scenario makes the cementing operations challenging,as any fluid heavier than seawater may cause lost circulation and compromise the well structural support.Failure to cement the riserless casing properly has been the root cause of many NPT events and one of the top contributors to incidents where the well has been re-spudded.This paper will present the solution to the lost circulation encountered in deepwater wells in Southeast Asia.The solution uses engineered dual fibers technology to regain circulation through the thief zones and achieve structural integrity of the riserless casing. The dual fiber technology with optimized solids package together with high solid-content cement has been effectively applied to overcome losses in the deepwater riserless section.This technology can also be used on any cementing operation where lost circulation is expected,as a pill or spacer ahead of the cement slurry,given that proper assessment of the well geometry and thorough engineered design have been performed. It was absolutely critical for the operator to get cement returns to sea bed.The dual fibers technology and high solid-content cement were synergically utilized,helping to achieve circulation through the unconsolidated and faulty zones and achieve proper cementation of the surface casing.Circulation of fluids to the sea bed was verified by ROV.The job pressure profile shows that the final displacement pressure was as expected and the top of cement reached the planned depth,despite the lost circulation scenario prior to the cementing operation. The methodology presented in this paper provides solution to effectively cement the tophole in deepwater,overcoming lost circulation,helping to achieve structural integrity of the casing that will support the BOP stack and to minimize potential NPT events associated with lost circulation.