Salt Mechanics Primer for Near-Salt and Sub-Salt Deepwater Gulf of Mexico Field Developments

The Gulf of Mexico (GoM) is the most active deepwater region in the world and provides some of the greatest challenges in scope and opportunity for the oil and gas industry. The complex geologic settings and significant water and reservoir depths necessitate high development costs, in addition to requiring innovating technology. The investment costs are substantial: because of the extreme water depths (up to 8000 feet) and considerable reservoir depths (to 30,000 feet below mudline), the cost of drilling a single well can be upwards of 50 to 100 million dollars. Central, therefore, to successful economic exploitation are developments with a minimum number of wells combined with a well service lifetime of twenty to thirty years. Many of the wells that are planned for the most significant developments will penetrate thick salt formations, and the combined drilling costs for these fields are estimated in the tens of billions of dollars. In May 2001, Sandia National Laboratories initiated a Joint Industry Project focused on the identification, quantification, and mitigation of potential well integrity issues associated with sub-salt and near-salt deepwater GoM reservoirs. The project is jointly funded by the DOE (Natural Gas and Oil Technology Partnership) and nine oil companies (BHP Billiton Petroleum, BP, ChevronTexaco, Conoco, ExxonMobil, Halliburton, Kerr-McGee, Phillips Petroleum, and Shell). This report provides an assessment of the state of the art of salt mechanics, and identifies potential well integrity issues relevant to deepwater GoM field developments. Salt deformation is discussed and a deformation mechanism map is provided for salt. A bounding steady-state strain rate contour map is constructed for deepwater GoM field developments, and the critical issue of constraint in the subsurface, and resultant necessity for numerical analyses is discussed.