Salinity-Based Pump-and-Dump Strategy for Drilling Salt With Supersaturated Fluids

Abstract

Riserless drilling with weighted-drilling-fluid systems, commonly referred to as a "pump-and-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 performing riserless drilling into salt, a pump-and-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-and-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 executed successfully 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.

Subsurface Containment Assurance Program - Key Element Overview and Best Practice Examples

“…In the former case, formation damage may compromise casing cement or lead to fracturing near a casing shoe, which could then either propagate up to the surface or laterally to connect closely spaced wells, leading to local subsidence of the overburden. In the latter case, reduction of mud weight by dilution with seawater (e.g., the pump-and-dump strategy) can lead to unfavorable chemical reactions with salt bodies and wellbore enlargement (Akers, 2011); the returns to the seafloor can undermine the ability of the seafloor to support foundation pilings, as for tension-leg platforms, by eroding near-surface sediments (Winker and Stancliffe, 2007b). Narrow drilling windows and prevention of lost circulation are currently being addressed by a variety of solutions including wellbore-strengthening technology (i.e., chemically activated cross-linking polymers that can limit mud loss into more permeable formations), dual-gradient and managed-pressure drilling (Smith et al, 1999;Myers, 2008), flat-rheology (i.e., temperature-insensitive) synthetic drilling mud, and improved monitoring of the drilling process (McLean et al, 2010).…”