Modeling Offshore Drill Cuttings Discharge

摘要

Offshore discharge of drill cuttings is an important waste management option for the oil and gas industry. The objective of this paper is to describe results of a numerical simulation study of drill cuttings dispersion in the ocean environment and accumulation on the seabed. The Offshore Operators Committee Mud and Produced Water Discharge Model (OOC Model) was used to simulate drill cuttings dispersion and seabed accumulation. The model was set up to simulate discharge from a 17-day drilling operation in three water depths (37 m, 65 m, and 502 m). Key input parameters to the OOC model include ocean current conditions, drill cuttings particle fall velocity, water column salinity and temperature. Drill cuttings drilled with non-aqueous drilling fluids (NADF) were treated with solid control technology followed by secondary treatment technology. Particle fall velocity was measured using a fall velocity test rig consisting of a 15-foot high settling column. Ocean currents, water column salinity and temperature were obtained from a field measurement campaign in northern Gulf of Mexico. Simulation results showed that impacts on the seabed are limited to approximately between 100 and 400 m radius from the discharge point for all three water depths. Ocean current speed and direction during the drilling operation play an important role in predicting spatial accumulation of drill cuttings and hydrocarbon loadings on the seabed within a 4000 m × 4000 m simulation domain. Particle fall velocity and water depths are two important factors that also affect drill cuttings accumulation on the seabed. In the two shallow water locations, 85% and 93% of the total discharged drill cuttings settled in the simulation domain, respectively. In the deep water location, approximately 54% of the drill cuttings settled. This paper presents results from a comprehensive modeling study of offshore drill cuttings dispersion and deposition using realistic conditions. Measured ocean current conditions and particle fall velocity enabled more realistic predictions of drill cuttings fate and transport in the marine environment. This study demonstrates the value of dispersion modeling in the offshore environmental impact assessments: better understanding potential impacts from marine discharges of drilling waste, providing guidance on pre- and post-drilling monitoring field studies and in the decision making process of drill cutting management options.