Controlling and Documenting Dispersant Effectiveness During Subsea Dispersant Injection (SSDI) - A Novel System for Dispersant Dosage and In-Situ Monitoring of Oil Droplet and Gas Bubble Sizes

Abstract

Abstract Subsea dispersant injection (SSDI) has been implemented as a response method since it was first used in large-scale during the Macondo subsea blow-out in the Gulf of Mexico in 2010. Oil and gas operators have access to SSDI equipment through multiple suppliers of response equipment. This equipment is a crucial part of the capping and containment package offered in the event of a subsea blow-out. The concept is used to ensure access to the spill site (remove surface oil), improve working conditions (reduce exposure to volatile oil components) and finally be used as a response option to reduce environmental impact form the spill (reduce surfacing & stranding of oil and increase natural biodegradation of dispersed oil as small droplets). However, a subsea blow-out of 12 000 m3/day, would require 800–1600 m3 of dispersant for the first week with a dosage of 1–2%. Controlling the dispersant dosage could be critical, especially, since the initial volume of available dispersants could be limited. This paper presents a new system for automatic dispersant dosage control. The system monitors the size distribution of the released oil droplets and gas bubbles. The injected dosage of dispersant is then automatically adjusted to obtain a desired oil droplet size. The dispersant dosage from a hydraulically operated valve is adjusted based on a real-time signal from a silhouette camera (SilCam) positioned in the rising oil & gas plume. The SilCam is used to quantify oil droplet and gas bubble distributions. The SilCam can be held in place by a Remote operated Vehicle (ROV) and all signals are brought to the operator onboard the supply vessel via the ROV's umbilical cord. The concept is tested by down-scaled experiments at SINTEF and verified in full-scale by Oceaneering in a large ROV test pool. This study was headed by Oceanering in close cooperation with SINTEF and funded by the Norwegian Research Council and multiple Norwegian energy companies; Equinor Petroleum AS, Lundin Norge AS, ENI Norge AS, Total E&P Norge AS and ConocoPhillips Scandinavia AS.