The Impact of Asphaltene Nanoscience on Oilfield Evaluation

For condensates, the most important compositional variation is GOR, and the cubic equation of state (EoS) treatment of GOR variations is well developed and successful. Consequently, key reservoir attributes such as vertical and lateral connectivity, extrapolating gradients to obtain contacts for reserves estimation, and properties of the produced fluids are addressed by Downhole Fluid Analysis (DFA) on the MDT measuring GOR and light end compositional variations. In contrast, black oils are defined as having low GOR; while black oils can exhibit GOR variations, the most important compositional variation of black oil is the heavy ends, essentially the asphaltenes. However, there had been no predictive equation of state for asphaltene gradients because the (colloidal) size of asphaltene particles in crude oils had been unknown. Consequently, the gravity term was unknown. Indeed, even asphaltene molecular weight had been the subject of vigorous debate in the literature spanning six orders of magnitude.

In recent years, several major advances have taken place in asphaltene science that have been codified in the “modified Yen model” (aka Yen-Mullins model). These scientific advances have led to the first predictive asphaltene equation of state, the Flory-Huggins-Zuo equation. The FHZ equation coupled with DFA data has been shown to correctly predict connectivity in several case studies that have gone into production. To date, in each of these cases the traditional cubic EoS failed. This work has recently been extended to include heavy oils. Moreover, complex disequilibrium columns can now be modeled with this simple formalism. The confluence of advanced asphaltene science with the third generation of DFA tools enables a powerful new approach to address reservoir dynamics. In addition, this novel asphaltene nanoscience provides the primary mechanism for forming tar mats – a long standing puzzle in the oil industry. And this science provides a foundation for interfacial studies. Many oilfield case studies show the power this combined approach of new asphaltene science plus new DFA technology.