Well Design and Well Workover to Land Deep Production Casings in the Menengai Field

摘要

Drilling has been on going at Menengai high temperature field since 2011. The wells are regular well design wells with the 20" surface casing set at 60-70m. 13 3/8" anchor casing set at about 400m depth and the 9 5/8" production casing set at between 800-1400m. The wells are targeted to be drilled to a total depth of 2500-3000m, with the slotted 7" liners run to the bottom. All the casings used are grade K55 with threaded couplings. Data from offset wells drilled earlier have helped design the depth of the production casing to avoid cold inflows into the wells. Wells located at the center of the field which are at a higher elevation have the production casings set at about 850m, while wells sited further away, the production casing has been designed to be set further deeper, to up to 1400m. A majority of the wells at the Menengai field have the production casing set at 1400m. This paper looks at designing wells with 9 5/8" K55 production casing, slurry design and the most effective method for cementing the casing to ensure an effective cement job. Cementing methods that will be discussed include cementing head and plugs, two stage cementing, C-Flex RPL from peak using the inner string method, reverse circulation cementing with inner string and flap gate valve collar and use of foam cementing. The paper looks at a number of wells which have already been completed. Pressure and temperature logs of the wells are analyzed as well as the borehole geology to identify the cold inflow zones. The remedial mechanisms available for sealing off the cold zones in completed wells are then researched and the most effective method to be applied at the Menengai field identified. The methods include use of External casing packer (ECP) and tie back design.