Oilfield & Energies
Development of OSPAR compliant solutions for oil-field emulsions 12th February 2020
By Hans Oskarsson, Per-Erik Hellberg and Han Bevinkatti of Nouryon
Hans Oskarsson, Per-Erik Hellberg and Han Bevinkatti outline the approach taken to develop Nouryon’s novel OSPAR-compliant demul
One of the major challenges associated with oil and gas production is the separation of oil from water. Produced crude is almost always accompanied with a percentage of water and this water content can make up almost 90% of the produced fluid. Higher production rates are always desirable but that also means shorter residence times in separation units, which are used to separate oil and gas from water. This becomes even more challenging when faced on offshore production facilities due to the lack of space available on platforms. Furthermore, the last decade has seen increasingly strict regulations on the type of chemistry that can be applied on offshore fields. Considering that offshore production accounts for nearly 30 percent of the global oil production, there is a growing need for environmentally-acceptable and cost-competitive materials. As an example, the North Sea accounts for 10% of global offshore production and there are few chemistries that meet regulatory requirements laid out by the OSPAR convention. Areas that previously did not have regulatory requirements for their offshore operations have also begun to implement them. Nouryon has been producing demulsifier chemistries for the oilfield for decades and has recently launched a range of OSPAR-compliant demulsifier chemistries. This article details the approach we took to develop these novel chemistries.
Crude oil demulsifiers are generally considered as high molecular weight “amphiphilic polymers” with surface active properties. While alkylphenol derivatives are banned in OSPAR areas, other popular demulsifier chemistries like epoxy resins and polyamine-based alkoxylates, which often achieve good treatment of crude with low Basic Sediment & Water content (BS&W), typically are highly lipophilic products with high molecular weight and very weak biodegradation.
In order to enhance the biodegradation of these polymeric/oligomeric amphiphilic structures, our strategy was to introduce labile bonds in the polymer backbone, such as esters, amides and/or acetal bonds that have proven to be effective in designing biodegradable polymers. Such labile bonds are responsive to a change in pH or an attack from microorganisms resulting in primary degradation and release of smaller fragments. If the polymer is designed in the right way, such fragments may then further degrade, thus leading to ‘safe biodegradation’, meaning that the building blocks connected by weak links are known to biodegrade further and that they, as well as their breakdown species, are harmless to aquatic life.
The starting point for the design of the candidate polymers was based on previous experience of structure activity relationships for demulsifier chemistries, such as polymer shape and size, as well as estimated structure at the oil/water interphase (packing and geometry). In addition to the functionality, biodegradation and eco-toxicity aspects, the building blocks were also carefully selected based on commercial availability, cost and feasibility of synthesis/production. Another factor taken into account was if the chemistry could be derived from natural sources. After a first broad screening of ideas, 17 suggestions were brought forth incorporating the concepts mentioned above. Following a preliminary evaluation of these ideas with respect to their synthetic viability, raw-material costs and ease of production, this was then narrowed down to 13 broad ideas to take forward. These included chemistry types such as poly-esters, poly-amides and carbohydrates. Building-blocks with either hydrophilic or hydrophobic character were used in combination with weak links to connect to amphiphilic polymers with high interfacial activity.
Following a small-scale synthesis approach, the reactions for the selected 13 classes of chemistries were explored yielding 176 synthesized samples. Only one of the selected classes was discontinued due to difficulties with the synthesis. For basic screening of rate of separation and further performance of new candidate demulsifiers, the Turbiscan Lab Expert instrument was used. The Turbiscan instrument is an automated vertical scan analyzer that can be used for studying the stability of concentrated emulsions. The temperature of the measuring cell of the instrument can be set between +25ºC and +60ºC. After lab evaluations using Turbiscan on a North Sea crude, it was decided to pursue 5 out of the 13 ideas (chemistry types) and synthesis of promising samples was repeated in order to certify reproducibility of synthesis as well as performance. This work resulted in 20 promising samples (different specific structures), which were made on a slightly bigger scale and submitted for field evaluation along with some preliminary data on their RSN (Relative Solubility Number) values and solubility in different solvent systems.
The best performing samples after the first wave of field testing were subject to another round of lab evaluation—this time with partly different crudes and/or alternative methodology. In these extended test conditions, some of the new candidates proved to perform equal to or better than best-in-class commercial demulsifiers. Performance of the new tentative demulsifiers was evaluated in field on various, fresh crudes in different locations, globally. Samples were used as single bases, to check their performance as dropper, treater or polisher/dryer. The best performing demulsifier candidates selected after our lab and field evaluations were screened for biodegradation and aquatoxicity. All samples had screening biodegradation data >20 percent after 28 days and several of them showed promising rate of biodegradation with a potential to reach >60 percent after 28 days.
The principle used to design these new demulsifiers while ensuring that the raw materials selected were cost-competitive was an essential first step. The use of Turbiscan methods for initial laboratory screening prior to field testing allowed for a wide range of candidate chemistries to be screened in a shorter time frame. Verification through field testing and benchmarking against best-in-class products on a variety of crude oils was crucial in finalizing chemistries to send for biodegradability and aquatoxicity screening. It was through this approach and co-operation with key partners that we were able to launch our high performance OSPAR-compliant range of demulsifiers – the Witbreak NEO-100 series.