Question regarding metals causing high conductivity in crude oil.

Question:

I would like to know besides Na, Ca and Mg which major metals or materials can cause high conductivity in crudes consequently affecting the desalter operation efficiency. Is it wise to know and monitor the metals distribution?

Comments:

Water in crude oil increases conductivity³. Metals in crude oil can be present as inorganic or organic compounds and include vanadium, nickel and iron. The vanadium and nickel are mostly present as porphyrins. The crude oil also contains asphaltenes with polyaromatic cores containing nitrogen, sulfur, oxygen, vanadium and nickel.  The polyaromatic cores are believed to interact strongly with electrical fields^1,2 and thus negatively impact desalter operation.

Dilution of low conductivity crudes with toluene or DOBA crude resulted in substantial increases in electrical conductivity (cf. Reference 3). This increase in conductivity may be due to dissociation of the asphaltene aggregates, thereby exposing “the active sites” that interact strongly with the electric fields and that are otherwise shielded by the asphaltene aggregate structure or are complexed with resins¹. This shows that electrical conductivity numbers are not necessarily additive when blending different crudes at the refinery to meet total acid number specs.

References:

1. Hasnaoui, N., Achard, C., Rogalski, M., and Behar, Revue de L’Institute Francais Du Petrole. 1998, 53(1), Jan-Feb.
2. Kendall, E. J.M., Journal of Canadian Petroleum, 1978, July-Sept, p. 37-38
3. Potter, A.C., Crude Oil Conductivity Presentation, February 2007, retrieved from Internet.