Evaluation of the primary cement operation on the production casing in the Ekofisk field and the Eldfisk field

Abstract

The foremost goal of primary cementing is to provide zonal isolation in a well. Cementing of the casing/liner set right above the reservoir on the Ekofisk and Eldfisk fields are associated with a lot of challenges. Depletion and water flooding of a reservoir makes drilling and cementing increasingly difficult. At the Ekofisk and Eldfisk fields, the operational window above the reservoir is very narrow and difficult to predict due to the regression of fracture pressure the last 200 ft above the reservoir. This coupled with the natural faults and fractures in this area makes lost circulation a hindrance to provide zonal isolation. Cement history on the two fields shows that there is a very low chance of achieving required casing cement isolation. Historical practices within the last two years have been analysed trying to find the root causes of any failure to meet the company requirements. A review of potential solutions to solve the issue has been presented. Different studies have been made, including hydraulic simulations, to come up with suggestions on how to reach the cement target for the two fields. In addition, simulations on how to cement the entire Miocene section were performed. A study performed in WellPlanTM-Opticem revealed that there still exist some challenges before the cement design and real time jobs can be properly imported and analysed in the software. During the work lack of cement job data storage system was discovered. A new way of cement data storage was suggested and established. Collection and analyses of cement jobs during the last two years on the M-wells was performed in order to investigate if there was a trend between lost circulation and different parameters. No clear trend was found. Hydraulic simulations were performed to investigate how different parameters impact the equivalent circulating density. A colloidal light weight cement was utilized in the simulations. The main results from the simulations showed that; Warp OBM is superior to Versatec OBM system from a well cementing perspective, the expandable liner hanger imposed a very high ECD and the liner hanger dimensions needs to be taken into account in hydraulic simulations. The overall outcome of the simulations indicates a possible solution on how to cement back to the previous casing shoe.