Offshore Drilling in the North Sea

Introduction Much has been learned during the first 3 years of drilling in the U.K. sector of the North Sea. Generally, conditions have been difficult. Although few conditions can be pointed out as being the worst known, many of pointed out as being the worst known, many of the conditions are among the worst and require considerable attention to engineering and plannings. plannings. This paper discusses various aspects of planning and drilling exploratory and planning and drilling exploratory and development wells in the North Sea. It covers the initial planning of equipment to drill exploratory wells; some of the problems encountered in drilling these wells; Phillips' solution to these problems, and finally the planning of a directional drilling program for shallow gas production from a fixed platform of limited production from a fixed platform of limited area. Prior to selecting drilling equipment for a project like this, consideration must be given to the weather conditions, water depths, drilling depths, rig mobility, availability and logistics of moving materials and supplies, means of transportation and numerous lesser considerations. This paper presents one major operator's solution to the many problems and considerations. There are other ways of doing many of these things and reaching the same end point. There are other problems which we did not encounter. We believe that, in general, we have used a practical and economical approach to drilling in the North Sea. EXPLORATORY DRILLING EQUIPMENT Since most of the Phillips group's concessions were in water of less than 200-ft depth, a self-elevating platform-type rig was selected rather than a floater or semisubmersible. The self-elevating rig was preferred to a fixed platform-type for exploratory operations because platform-type for exploratory operations because of mobility and to a semisubmersible because of fixed position and increased efficiency by eliminating wave motion. Because of severe weather in the North Sea and availability of rigs for deep water operation, it was decided to contract The Offshore Co. to build a new rig for this operation. Consequently arrangements were made to construct the North Star drilling rig at John Brown shipyard in Clydebank, Scotland. As originally equipped, the North Star rig is capable of drilling in 150-ft water depths in the North Sea. Additional leg sections can be installed to increase the water depth capability to 200 ft. We did not find this necessary in our exploration program. The general appearance of the platform can be seen in Fig, 1. The dimensions and capacities of the barge hull equipment are as follows.