Drilling Optimization on Gyda Development Project: A Case Study

ABSTRACT BP Norway's North Sea Gyda Field development commenced when a nine slot template was installed and the first template well spudded in November 1987. Eight template wells were then drilled successfully, significantly under budget and well before the jacket installation in September 1989. The Gyda Field development drilling program was identified as a candidate for an optimized slim-hole well design which resulted in significant cost and drilling time savings. INTRODUCTION The Gyda Field is located in the Southern part of the Norwegian Offshore Continental Shelf in License Block 2/1. The field is located 270 km South Yest of Stavanger and 43 km North Yest of the Ekofisk Centre. The water depth is 66 m. (Refer to Figure 1.) The field was discovered in 1980 when BP drilled the third exploration well on the License 019B. The field was declared commercial in January 1987 subsequent to another five wells being drilled on the License. The Development Plan estimated recoverable reserves Of 32 million m3 (202 MMSTB) of oil and 3.2 million m3 (20 MMB) of NGL's of which c. 3 billion m3 (110 billion SCF) of dry gas sales are expected. The Gyda Development Scheme is based on a single Production/Drilling/Quarters platform concept. The scheme includes a 30 well drilling program of which eight of the wells were pre-drilled. The pre-drilled wells were drilled through a sub-sea template by a semi-submersible drilling rig prior to jacket installation. This philosophy was followed to permit plateau production to be reached soon after the completion of the platform facilities. At the planning stage, the eight well template drilling operation with a slim-hole well design was estimated at 636 days at an unescalated budget cost of NOK 707.6 million (US$ 102 million). Detailed planning, teamwork and the application of the appropriate technology resulted in a final duration of 477 days and an actual total all inclusive cost of NOK 385.9 million (US$ 55.6 million). This paper describes the factors which enabled optimized drilling performance to be achieved. SUB-SEA TEMPLATE INSTALLATION The template comprised a 9 slot unitized design with two rows of four receptacles plus one additional receptacle to one side. The template design featured three support pile housings with mud mats and two jacket location pile housings. (Refer to Figure 2.) The Gyda Template was installed in November 1987 in four days. The installation program covered emplacement from a crane barge, leveling, piling of template support and jacket location piles, removal of mud mats and cutting the jacket location piles from the template. The template structure was designed only to be capable of supporting the weight of one conductor. This concept allows a conductor to be temporarily supported while cementing but prevents any permanent loading of the template. A retrievable gimbals was used below the guide base. It acted as an interface between the 30" wellhead housing and the well slot receptacle and enabled the release of any pre-load. This could be unlatched using a surface run tool even when the full conductor load had been applied to the receptacle.