Breaking Through in Drilling-Waste Treatment: SINOKLE CDOF Enables Efficient Filtrate Purification and Volume Reduction
In the drilling-waste disposal process, colloid destruction (gel breaking) is the prerequisite for effective solid-liquid separation and also the most technically difficult stage. Considering that heating the waste drilling mud at the drilling site is hardly feasible, dosing electrolytes at ambient temperature to break the gel has become a relatively suitable process approach.
The gel breakers commonly used today include dilute hydrochloric acid, calcium chloride solution, magnesium chloride solution and polyaluminum chloride. Although these agents can break the drilling fluid and complete solid-liquid separation, the resulting filter-press filtrate has a high content of metal ions and high hardness. If it is recycled and reused, it will pollute the drilling fluid system significantly, not only affecting drilling fluid performance but also possibly endangering downhole operation safety. Moreover, since indicators such as chemical oxygen demand (COD), chromaticity and petroleum substances in this filtrate exceed discharge standards, it cannot be discharged directly. Its water quality mainly presents the following characteristics:
1. High salinity, which accelerates the corrosion rate and also makes the biochemical treatment of the wastewater difficult;
2. High oil content, far exceeding the water quality standards required by the various disposal outlets;
3. A large amount of scaling-prone ions;
4. High suspended solids concentration with fine particles, which easily causes formation plugging.
At present, drilling-fluid filtrate is mostly reinjected into water injection wells. However, with the full implementation of the “mud-does-not-touch-the-ground” requirement, the amount of filtrate generated keeps increasing, and relying solely on reinjection and transfer faces enormous pressure. Promoting volume-reduction treatment of waste drilling fluid and filtrate has therefore become an inevitable choice.
Application case: drilling-fluid and fracturing-fluid treatment project at an oilfield in the Republic of the Congo
Targeting the above water-quality characteristics, Shenzhen SINOKLE Technology Co., Ltd. has launched a combined “coagulation-sedimentation-flotation + CDOF” process for filtrate treatment. The process first uses the coagulation-sedimentation-flotation unit to remove most of the suspended solids and metal ions from the liquid and partially reduce COD; subsequently, CDOF ozone advanced oxidation treatment efficiently removes grease pollutants and achieves a COD removal rate of over 90%.
Bench-scale case
A filter-press filtrate sample from an oilfield was treated by coagulation-sedimentation combined with ozone oxidation. The raw sample had an oil concentration of 117 ppm; after treatment by the process, the oil content dropped to 24 ppm, a removal efficiency of 80%. The comparison of the water samples before and after treatment is shown below:
Raw water and treated water samples
After the water sample was treated by the coagulation-sedimentation-flotation and CDOF systems, its chromaticity decreased significantly, indicating that the ozone oxidation process effectively degraded the oily substances and made the water sample clear and transparent.
