GOM Deepwater Field-Development Challenges at Green Canyon 468

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 137220, ’GOM Deepwater Field Development Challenges at Green Canyon 468 Pony,’ by M.H. Weatherl, Hess Corporation, originally prepared for the 2010 SPE Deepwater Drilling and Completions Conference, Galveston, Texas, 5-6 October. The paper has not been peer reviewed. The deepwater Gulf of Mexico (GOM) has proved in recent years to be one of the most prolific oil-production provinces in the world. The bulk of the new reserves and production in this area flow from subsalt, Miocene reservoirs. In the summer of 2005, the Green Canyon 468 “Pony” discovery well was drilled. Information collected during appraisal drilling provided significant insight into subsalt oil reservoirs that exist in this area at depths between 28,000 and 31,000 ft true vertical depth (TVD). Introduction The Pony area currently consists of Green Canyon Blocks 468 and 469, approximately 175 miles south of New Orleans in 3,500 ft of water. The field is within a 30-mile radius of numerous discoveries and established production from fields including Genesis and Brutus to the north and Tahiti, Holstein, and Shenzi to the south and east. From a well-construction perspective, Pony is characterized by geologic complexity and numerous design challenges. Many aspects of well design are common among 30,000-ft-plus-TVD GOM subsalt plays. However, one differentiating feature of this field is the severity of the subsalt pore-pressure/fracture-gradient regression. The area is characterized by a very thick salt section that ranges between 16,000 and 18,000 ft of total vertical thickness across the structure. Pore pressure ranges from ±15 lbm/gal mud weight equivalent (MWE) at the base of salt at 22,000 ft TVD to less than 10 lbm/gal MWE in the deepest pay interval near 31,000 ft TVD. Exploration vs. Production Well The majority of wells drilled to date in the deepwater GOM are exploration and appraisal. Furthermore, the necessary evolution of well design and increased complexity moving from an “expendable” exploration well to a “keeper” production well are under-stood fully by only a relatively few operators with firsthand experience. Fields with development wells with the level of complexity analogous to that found at Pony are very few (Fig. 1). During exploration and early appraisal drilling, extremely high well cost can result in the challenge of balancing the need for additional appraisal drilling with controlling high presanction costs. A classic issue in an area such as Pony where exploration and appraisal wells exceed USD 100 million each is the recurring question, “Can we keep this well as a producer if we find pay?” The usual answer, which can be a source of contentious debate, is “probably not.” The rational behind this conclusion can be addressed best in the form of a business proposition.