Offshore / Onshore Wastewater Treatment and Disposal
Over a two-year period from 2017 to 2019 Bordis management worked with a deep-water semi-submersible offshore Newfoundland primarily conducting intervention activities on existing wells, but also drilling new wells using synthetic oil-based mud (SBM). Regulatory requirements called for deck slops to be captured and treated before water disposal offshore. The total oil and grease (TOG) was required to be 15ppm or less.
The slops originated from accumulated precipitation and the onboard operations related to the drilling and intervention activities. Primary contaminants were BOP operating fluids, drilling fluids, and other associated hydrocarbons found in the closed deck drainage run off. If the water (slops) did not meet disposal specifications of the regulations it would need to be shipped back onshore for disposal.
Depending on the drilling unit deck shape and size, and the normal precipitation of the region and season, it isn`t uncommon to see slop accumulations greater than ~200 m3/day.
The equipment installed on the rig on a rental basis was a Dissolved Air Filtration (DAF) unit, recirculation equipment, and an EX-1000 analyzer. The equipment was onboard for a total of 607 days of which 134 days were downtime. The downtime was primarily associated with inadequate new personnel training on equipment operation.
Chemicals were also added to treat the water to lower the pH and create hydrocarbon droplets to facilitate the aeration and skimming removal process. The analyzer accuracy verification was required monthly which caused logistical problems and delays.
Over the course of the two-year period ~11,400 m3 of water was disposed over the side. The cost to the client for the treatment system and personnel was $1.73 million inclusive of the downtime. The disposal costs to client were $300/m3 if the fluid had to be returned onshore. The savings was estimated to be ~$1.7 million to client.