Salinity-Based Pump & Dump Strategy for Drilling Salt with Supersaturated Fluids

Abstract

Riserless drilling with weighted mud systems, commonly referred to as a "Pump & Dump" drilling strategy, is an established drilling technique used on deepwater wells with shallow hazards. Large holes and high flow rates result in very large volumes of fluid being required to drill to total depth (TD), circulate the well clean and cement the conductor casing string. Fluids management becomes a major issue in the riserless hole section. In the Gulf of Mexico, mud is often densified in excess of well requirements and then blended with seawater in a "Cut-Back" operation to reach the desired density to pump downhole.When riserless drilling into salt, a Pump & Dump strategy is often used. Dilution with seawater, however, results in an undersaturated fluid. This fluid leaches the salt resulting in substantial hole enlargement. The hole enlargement can result in poor cementing jobs that require remediation or even an additional string of casing. A unique operation has been employed in the Santos Basin of Brazil where a supersaturated brine fluid was used to conduct a pump & dump operation with the goal of drilling with a saturated brine fluid and minimizing hole enlargement. This paper details the planning of the operation, fluid design, and pilot testing. Fluids management, equipment rig up, and results are discussed in detail. The operation has been successfully executed twice with both operations achieving the set objectives for the wells. Unforeseen complications that were encountered are discussed along with lessons learned that have been applied to subsequent operations.