Mark Zwinderman - Surface Active Solutions
The application of micro-emulsion technology to the problem of oil-contaminated waste may solve the problem in many instances.
Oil-contaminated drilling waste long has been a concern for the oil and gas industry. Aside from environmental and regulatory issues, there are significant costs associated with waste disposal.
Cuttings from wells drilled with oil-based or synthetic-based muds need to be treated or disposed of safely. It is rarely possible to dispose of cuttings at the production site without treatment. This typically involves thermal ovens, can be expensive, and is energy-intensive. In many cases the treatment cannot be performed onsite, and the logistics of transporting the cuttings for treatment can be complicated, expensive, and polluting.
In harsh regions such as the North Sea, the climate can hamper operations to the extent that drill cuttings are collected on the rig with nowhere to go. Bad weather often prevents cuttings from being offloaded onto supply vessels and shipped ashore. When the rig runs out of storage space, drilling ceases and costs rise with every hour of delay. The recent emergence of the arctic exploration areas, as well as activity around the Faroe and Falkland islands, give new urgency to these operational issues.
Wash solution
Surface Active Solutions (SAS) has worked for nearly a decade on micro-emulsion technology for the treatment of oil-contaminated cuttings. The company has applied the technology over the past few years in offshore drilling activity for downhole and tank cleaning, and for treatment of oil waste from drilling operations.
Micro-emulsions can treat oil-contaminated drill cuttings simply by mixing those solids with a wash solution comprising seawater and a small dose of micro-emulsion product. The chemical characteristics of the micro-emulsion remove oil from the cuttings and prevents hydration of any clays present. This wash system also allows cuttings to be cleaned onsite at the same rate at which the cuttings are produced.
The basic principles of the wash system are familiar. Cuttings pass over the shale shakers upon return from the well. This removes most of the mud which is returned to the mud system. The cuttings are collected in a custom-designed feed hopper where they are injected with the seawater-based micro-emulsion solution.
The mixture is agitated inline and pumped through a flexible hose to a standard cuttings dryer. The end result is drill cuttings with less than 0.8% oil content. These clean, dry cuttings then can be disposed of to sea and the liquid phase passed through standard filtration for discharge.
The system allows for continuous drilling without interruptions because of stacked-up drilling waste. There is no requirement for thermal treatment, and the entire process operates efficiently at ambient temperatures – whether the cleaning is to take place in the Arctic Circle or in the Middle East, the same engineering set-up is used.
Integrating the cleaning of drill cuttings with the pit or tank cleaning and downhole cleaning operations also allows operators to reduce their costs and the risk of any weather-related delays in drilling the wells.
North Sea case study
Recently, SAS completed a wellbore clean-up in the North Sea on behalf of a major oil services company. The well in question was displaced to seawater, the annulus having been topped off with base-oil and seawater to cure losses after setting the liner hanger. The displacement to filtered and inhibited seawater was with 50-bbl base oil, a 200-bbl seawater pill, and a 100-bbl SAS product wash pill followed by filtered inhibited seawater.
A further 200 bbl of filtered inhibited seawater was pumped before the returns were called clean. The completion string was then run and the well completed and handed over to production. The total volume of waste produced from the clean-up operation was less than 500 bbl.
The first 917 bbl of returns (including the SAS product wash pill) were segregated and back loaded to shore for treatment and disposal. The remaining 1,502 bbl of brine were totally free of suspended solids and had an oil-in-water content of below 15 ppm, indicating that the well had been efficiently cleaned.
This volume of brine was discharged to sea under current EU legislation. It represented an immediate reduction in the volume of waste produced by 62%. The 917 bbl of returns were further treated onshore using a chemical treatment and physical separation process. As a result 733 bbl were rendered suitable for discharge to sewer, reducing the oil-in-water content to below 40 ppm on average, leaving only 184 bbl requiring disposal. Total reduction in waste produced from the job exceeded 92%.
