| dc.description.abstract | Scale deposition is a common water related production problem in the oil and gas industry that can lead to damage and reduced production. Scale deposition occurs from sparingly inorganic salts that create an organic precipitate from two incompatible water mixtures. The two most common scales are CaCO3 and BaSO4. Scale inhibitors (SIs) are commonly used to prevent the formation of scale in producing wells. With an increasing demand for more green oilfield chemicals by organisations such as the Oslo-Paris convention (OSPAR), green SIs have become prominent. A common type of SI would be phosphonates. Methylenephosphonate functional groups have been reported to yield efficient scale inhibition and strong adsorption onto the reservoir rock. To get a SI with high biodegradability is difficult, but by phosphonation, the goal was to gain effective scale inhibition and biodegradability by using starting materials claimed to have good biodegradability. The phosphonation of SIs was done via Moedritzi-Irani synthesis where methylenephosphonate groups were attached. Each SI was tested for calcium compatibility, biodegradability by the OECD 306 test in seawater for 28 days, and scale inhibition against calcite and barite scaling on a high-pressure dynamic tube blocking rig. There were two projects, project A and B.
Project A involved synthesis of one, two and three methylenephosphonate groups to tetrasodiumiminodisuccinate (TSIDS) (claimed to have good biodegradability), and the related chemicals tetrasodium ethylenediaminodisuccinate (TSEDAS), and diethylenetriamine Bis-N,N-Succinic Acid (DETAS), respectively. All synthesized SIs showed poor barite inhibition. Calcium compatibility testing showed excellent results for phosphonated TSEDAS (TSEDAS-P) and moderate for phosphonated TSIDS (TSIDS-P). TSEDAS-P also gave excellent inhibition against calcite scale which would make downhole squeeze treatment a possible option. TSIDS-P showed moderate calcite scale inhibition but precipitated at high concentrations of SI during calcium compatibility testing. This indicated that it was not suitable for squeeze treatment, however, continuous injection topside could be an option if the calcium concentration is moderate to low. TSIDS-P yielded exceptional biodegradability in seawater (OECD306 BOD28: 72.56%) and was considered as readily biodegradable. On the other hand, TSEDAS-P yielded poor seawater biodegradability (2.68%). Phosphonated DETAS (DETAS-P) was only partially soluble as a SI resulting in poor calcite and barite inhibition. No further testing was pursued.
Project B included the phosphonation of glucosamine, a monomer of the natural polymer chitosan. Ball milling was used to synthesize phosphonated glucosamine where results indicated moderate inhibition against calcite scale and poor inhibition against barite scale. Phosphonated glucosamine showed moderate calcium compatibility with only some cloudiness to the solutions when mixing high concentrations. This is not expected to be detrimental for injection as a squeeze treatment. Therefore, the SI could be used for squeeze treatment applications. When tested for seawater biodegradability, the average result was 21% biodegradability. | |
