Casing-While-Drilling 24-in. Surface Section Enables Operator to Add One Extra Slot to the Existing Drilling Template and Cut Operation Costs in Offshore Congo

Abstract

Abstract Foukanda permit is situated offshore Congo to the north of Kitina platform and to the west of Pointe Noire town. The Foukanda platform comprised a drilling template with eight slots, all of which were drilled through a 30-in. conductor casing that was laid on sea-bottom and connected to the platform's drilling template, and all were directional wells. The operator wanted to drill another well to explore another structure of the reservoir, but this was not possible with the existing template. The custom way of securing an extra slot was that which involved setting of a 30-in. diverter with 2° angle to the sea bottom, conventionally drilling some length of new hole with a 26-in. roller cone bit and then running and cementing a 20-in. casing through this 30-in. diverter and with free returns to sea bottom. This method had a negative aspect, which was the difficulty of re-entering the 26-in. hole with the 20-in. casing because of the sag of the conventional drilling assembly at the exit of the 30-in. diverter. To resolve this problem, the operator opted for an innovative drilling technique: drilling with casing. A 24-in. casing drilling bit was manufactured on purpose and was run through the diverter on a 20-in. casing string which drilled 66 m of new formation at 2° inclination and with returns to the seabed. The casing was cemented in place and the casing drilling bit was than successfully drilled out with a roller cone bit. This operation enabled the operator to secure the extra slot, to get out of the existing wells trajectory and to save the costs associated with difficulties to re-enter the hole. In this paper, the authors will describe the casing drilling bit technology, the planning of operations, the implementation, and the results compared to conventional drilling. Introduction At the Foukanda field offshore Congo (Fig. 1), the operator faced a frequent dilemma of needing to drill new wells from an offshore platform when all the slots on the seabed template have been drilled. The quandary is even more pronounced in today's environment with maturing offshore oilfields and the compelling need to increase production from new structures. One of the more obvious solutions to this problem is to drill new wells alongside existing wellbores, thus negating the use of the sub-sea template. Since all or most of the existing wells are deviated, this solution requires measures to be taken against collision with the template or the existing wells. Consequently, precise positioning of the well is crucial, which is the primary reason the template is used in the first place. Furthermore, directional control of the surface section may also be required. This is the problem the operator was faced with the Foukanda operation. The Foukanda platform has a sub-sea template with eight available slots, as shown in Fig. 2. All eight wells were drilled and most of them were deviated in different directions (Fig. 3). The operator wanted to drill another well, thereby increasing production of the field, but as described above, few options were available.