​Furthermore they alter the wetting characteristics of mineral surfaces within the reservoir, hindering oil recovery efficiency.
Asphaltenes are a complex mixture of different molecules with similar chemical characteristics which are insoluble in aliphatic solvents (e.g. heptane) but soluble in aromatic ones (e.g. toluene). Even at very low concentrations in ‘good’ solvents, they still have a propensity to form ‘nanoaggregates’ whose structure and formation remain largely unknown despite much research. Small-angle neutron scattering (SANS) has been used to examine asphaltenes in deuterated toluene in the absence and presence of laponite clay, the hypothesis being that the clay surface would enhance asphaltene aggregation. This appears to be borne out by the change in the radius of gyration (Rg) of the asphaltene nanoaggregates as a function of temperature (see figure). Hopefully this observation will help provide a route for the oil industry to predict and control asphaltene precipitation and deposition in the field.

TF Headen, NT Skipper (University College London), ES Boek (Schlumberger Cambridge Research), RK Heenan (ISIS)

Research date: December 2007