Drilling and Under-Reaming in the GOM Deepwater Ultradeep Lower Tertiary: History of a Record Run in the World’s Deepest Oil or Gas Well

摘要

Operators have been drilling deepwater prospects in the Gulf of Mexico (GOM) since the late 1980s. However, technology has evolved tremendously enabling deepwater operators to explore deeper frontiers. Many of the recent promising GOM deepwater prospects are targeting the lower tertiary sedimentary dispersal system that is regionally continuous from the coastal zone to the deepwater basin. Many of these wells seek ultradeep targets with total vertical depth (TVD) ranging from 28,000 - 35,000 ft (8534-10668 m). To reach these deep lower tertiary reservoirs in the middle Paleocene to early Eocene age (Wilcox Group), operators must overcome many drilling challenges, including wellbore integrity, borehole stability, pressure management, destructive vibrations and suboptimum drill bit and under-reamer performance when drilling at these greater depths. Due to the nature of the well construction and completion programs of these deepwater ultra-deep wells, which very often require over six casing strings, concentric expandable under-reamers are regularly used to maximize the wellbore final section size. As these lower tertiary sandstones can be highly abrasive and hard, especially under extremely high confining pressures, bit and under-reamer durability has become a huge challenge. This paper will focus on the deepest successful 12 1/4 -in under- reamer run in the world (31,400 ft or 9571 m TVD), achieved when drilling the deepest oil or gas well ever drilled., with emphasis on the selected under-reamer characteristics, bit selection and best drilling practices used.