A Collection of Innovative Answers to Solve the Main Problematics Encountered When Drilling Deep Water Prospects

Abstract

Abstract This paper summarises the main problematics encountered when drilling deep water prospects and presents a collection of innovative technologies which would allow in a near future to solve these technical problematics as well as new and blue sky concepts to significantly reduce deep water development costs. Introduction Since 1967, TOTALFINAELF has been actively involved in deep water drilling operations but the saga really began in 1976 with the building of PELERIN and PELICAN drill ships which broke a first water depth world record by drilling a well (925 m of water) offshore Algeria. It was followed by another outstanding performance in 1982 with two wells in the Mediterranean Sea (record of 1714 m of water depth). Following these campaigns, there was a lull in deepwater drilling that lasted about ten years. However, in 1994 the exploration Offshore Angola on the bloc 17 re-activated the drilling activity in deep waters. In 1996, the exploration well GIR-1 was tested at 12500 barrels per day of API 32° oil. Two subsequent appraisal wells proved oil in place more than 1 Gbbl of oil and set in motion what would be the first major deepwater project in Golf of Guinea. Major technical challenge had to be overcome due to the specific conditions encountered. The deep and cold water conditions as well as the very specific unconsolidated nature of the reservoir required a collection of new technologies and practices. In december 2001, less than six years from discovery, TotaFinaElf brought the Girassol field into production and within six weeks a production plateau of 200,000 bpd was reached. This has been recognised by the Oil Industry as a world class achievement for which TotalFinaElf received in 2002 the prestigious OTC reward. Close to the Girassol field, other major discoveries (Rosa, Lirio, Jasmin, Cravo and Dalia) have confirmed the exceptional potentialities of the bloc 17. More recently TotalFina Elf put on stream the deepest field ever completed world wide : the Aconcagua gas field, which lies in 2200 m of water. Consequently, the Group has considered that deep off shore will become for the future a major tool of its growth and has launched an aggressive R&D program to push further and further the technico-economical deep water limits. Main Problematics Encountered When Drilling Deep Water Prospects Compared to shallow water, deep water consists of replacing part of the overburden by water. Typical geometries are presented in Fig. 1. In both cases, the target is located 3500 m from the sea level but, for the deep water case, 1800 m of overburden has been replaced by 1800 m of water whereas the reservoir located at 3300 m TVD from the mud line in the first shallow water case is only at 1500 m in the deep water case. These differences induce major consequences in terms of drilling and completion. From a drilling point of view, the key points are the following :The rig size has to support a much heavier architecture with increasing difficulties for station keeping if the rig is moored.