The Emeraude field in the Republic of Congo is a shallow-water field, which has been well studied and explored over the years. In May 2014, the operator decided to drill more wells in the area to be able to extract oil from Cenomanian deposits. The greatest challenge faced in drilling wells in Emeraude field was the extremely low fracture gradient due to the depleted upper Senonian reservoir. The surface section was drilled with sea water, and for the intermediate section, the water-base mud (WBM) used was 1.08 g/cm3. During drilling the intermediate section of 12 ¼-in., total losses were observed at 320 m of measured depth (MD), with total losses of approximately 1230 m3. Although losses were expected, the challenge was aggravated as the operator faced difficulties in keeping the hole full. After several unsuccessful attempts to cure the losses with lost circulation material (LCM) pills in mud, it was decided to pull out and run-in with open-ended pipe to cure the losses with a cement plug.
The cement plug was specifically engineered to remediate total losses in the depleted zone. The base cement slurry was conventional Class G cement extended with bentonitic gel that had rapid gel-strength development. The slurry was designed at 24' solid volume fraction (SVF) to be able to be dosified with engineered LCM, which is a combination of a flake-solids package and synthetic fibers. This LCM pill was engineered to engage with the cement to make a filter cake and a mesh to cure the losses.
After completing the lost circulation cement treatment, full returns were observed and the drilling continued without any issues. The solution was fit for purpose for the losses in depleted zones and was applied for the first time in the African continent. The treatment was then successfully repeated in the same well and other wells in the field. The paper uses the case study to elaborate the design process and technical advantages of the novel fiber-based cement lost circulation treatment.
