Extended Reach, Horizontal, and Complex Design Wells: Challenges, Achievements and Cost-Benefits

Abstract

Abstract The paper describes Statoils experiences in drilling extended reach (ERD) wells, to primarily serve remote parts of widespread reservoirs and experiences in drilling horizontal and complicated wells, specially designed for optimal drainage of complex reservoirs. Several world records in extended reach drilling, conducted from the Statfjord "C" platform are summarized. The latest ERD well drilled has a horizontal reach of 7290 m. Included are also the latest plans of implementing these techniques in developing new fields. A brief summary is given on the achievements within the industry regarding other special well types, such as dual lateral, snaky, multiple arm, etc. Furthermore the paper describes technical challenges of drilling complex wells and how planning is done to cope with these challenges. Some limitations to the drilling are highlighted and solutions to drilling problems related to torque, drag, buckling, hole cleaning and surveying are given. Cost-Benefit considerations regarding ERD, horizontal and complex wells are discussed. Reducing number of platforms and/or leave out subsea templates due to ERD wells are considerable cost reducing factors. Reducing the total number of wells from a platform due to horizontal and/or complex well profiles is another major cost reducing factor. The oilfields developed in the 1970-80s had relatively significant limitations to the drainage area from each platform. The Statfjord and Gullfaks fields were initially planned to be developed with maximum 60 degree inclination wells, resulting in a maximum horizontal reach of 3000 m at the Statfjord field and 2100 m at the Gullfaks field reservoir depths. To drain the fields in an optimum way based on the technology available, called for three GBS platforms on each field. Developments and improvements in drilling technology, engineering research and field experiences have, since then, pushed the limits for available well profiles and horizontal reach distances dramatically. The purpose of drilling extended reach, horizontal and complex design wells is to drain the field in the most cost effective way. The use of these new techniques can make old nonprofitable fields profitable, prolong an existing field's economic life and make new questionable field discoveries worth developing. Today's techniques enable the reservoir, dip angles, faults and structural geology to be design factors for optimal placement of the wellpath. P. 505^