Our shore-based ENVIROCENTER water treatment system set the standard for the treatment of drilling and production-generated slop and the recycling of premium drilling fluids. Since its inception, the ENVIROCENTER water treatment system has reduced overall waste streams by as much as 90% while recovering and reusing not only drilling fluids, but also some of the residue from vessel cleaning.
Recognizing the obvious importance and benefits of source segregation of the waste stream, we incorporated that basic concept into our modular ENVIROUNIT offshore slop water treatment and recycling systems. Isolating and treating operators’ drilling slop on the rig effectively reduces the waste volume, risks and costs. What’s more, treating directly at the rig site clears the way for complete traceability of the waste stream.
Slop is generated from a variety of sources, from spills and rainwater that must be collected to avoid overboard release of contaminants to residue from cleaning operations. Most of the more heavily contaminated slop sources, however, result from completion operations and drilling fluid interfaces that can include:
■ Water contaminated with hydrocarbon
■ OBM contaminated with water and/or WBM
■ WBM contaminated with oil and/or OBM
■ Completion fluids
The ENVIROUNIT water treatment system is designed to easily and thoroughly treat all Category 1 and Category 2 liquids, which have light to moderate contamination. Category 1 offers the mildest contamination with oil content less than 1,000 ppm and solids less than 1%, while the second category includes liquids containing between 1,000 ppm to 35% oil concentration with less than 5% solids. Slop arising from either of these groupings are fully treatable with the ENVIROUNIT treatment system, with the usable base fluid recovered for reuse.
The more heavily contaminated, or Category 3, liquid contains more than 35% oil and 10% solids content, along with polymers, surfactants and other additives. While this ultra-contaminated slop can be treated through the ENVIROUNIT water treatment system at low capacity, it usually is collected and shipped to the shore-based ENVIROCENTER water treatment system for further treatment.
An ENVIROUNIT water treatment system also can be configured to meet the distinct challenges of well cleanup interfaces, which require additional pretreatment in the rig tanks. Here, the only requirement is that the rig has sufficient pit and tank capacity to allow extraction of the water phase from the interface slop before treatment. The ENVIROUNIT water treatment system has routinely demonstrated its capacity to reduce waste from interface treatments by up to 40%, and even higher if the well is displaced with seawater or brine.
ENVIROUNIT System Saves USD 10 Million in Slop Water Processing Offshore Republic of the Congo
Innovative technology reduces waste stream by 97% over 45-well deepwater development project
Reduce costs and improve QHSE of offshore slop water treatment
During a 45-well deepwater development project offshore Republic of the Congo, an operator sought a cost-effective solution for treatment, transportation, and disposal of slop water. Its two rigs—the Tungsten Explorer and Ocean Rig Apollo—were located approximately 100 km [62 mi] from the nearest supply base, presenting logistical challenges and expensive treatment and disposal options. Additionally, collection of up to 80 m3 [503 bbl] of deck water during the rainy season further complicated waste disposal operations.
The lack of slop water treatment units in the region forced the operator to collect waste in skips or dedicated pits. As storage filled up, waste was transported to an onshore third-party facility for treatment at a cost of USD 700 per metric ton. Transporting slop water waste to shore in skips typically involved numerous units and required ample supply vessel deck space. In addition, bulk shipments require that the vessel’s tanks be cleaned after offloading. Movement of containment fluids and the use of crane lifts also added to QHSE considerations. The operator requested a slop water treatment solution that would minimize offshore drilling waste, recover valuable drilling fluids for reuse, reduce personnel, lower safety risks, and lessen transportation and environmental footprint.
Deploy efficient ENVIROUNIT system to meet objectives
M-I SWACO fluid processing specialists recommended the ENVIROUNIT offshore slop water treatment system to reduce waste shipments to shore and recover valuable drilling fluids. The system uses a four-stage process to decrease slop water treatment costs and time.
■ In the separation and emulsion-breaking stage, the system recovers oil-base and synthetic-base fluid for reuse.
■ Recovered water is then mixed with a flocculent to eliminate hydrocarbons and other contamination from the water.
■ Then, the water undergoes a three-step policing filtration to guarantee discharge quality, and the water is tested to meet regulatory limits before being discharged overboard.
■ In a final dewatering stage, sludge from flocculation is processed through a filter press for drying. The filter press increases the dry substance volume from 2% to up to 70% and reduces the overall waste volume by more than 90% of its original slop water volume compared with conventional techniques.
Saved USD 10 million in slop water processing
Treated water was discharged when the total percentage of hydrocarbons was below the 30-ppm limit set by the operator. The ENVIROUNIT system provided overall improvement in the QHSE program by minimizing contaminated fluid transfers from the rig to the waste management facility as well as reducing crane lifts of skips and confined space entry for tank cleaning. The potential for spills, the number of vessel trips for transporting to shore, and the environmental footprint of the operations were also significantly reduced. After 14 months, the operator saved nearly USD 10 million in processing expenses for 16,500 m3 [103,782 bbl] of slop water. Approximately 315 m3 [1,981 bbl] of synthetic-base drilling fluid was captured for reuse in the active mud system. Only 530 m3 [3,334 bbl] of waste was sent to shore for disposal. Compared with a conventional slop management system, the overall waste stream was reduced by 97%. Average monthly savings for the operator exceed USD 500,000. Savings for the entire five-year drilling campaign has been calculated at USD 6.1 million per year and USD 30 million overall.
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