The behavior of asphaltene in live oils was investigated using a fully visual PVT cell equipped with a laser-based particle detection system. Through a series of isothermal pressure depletion experiments, the asphaltene stability envelope was established for several Gulf of Mexico oils. These tests were performed under pressure and temperature conditions typical of a field production system. Evidence of asphaltene precipitation above and redissolution below the saturation pressure was observed. Significantly, these tests also showed that pressure depletion-induced asphaltene precipitation is a highly reversible process. This latter observation helps to resolve a long-running debate in the literature concerning the reversibility of the asphaltene precipitation and flocculation process.

The phase behavior of microemulsions of brine, hydrocarbon, alcohol, and a pure alkyl aryl sulfonate-sodium 4-( I-heptylnonyl)benzenesulfonate (SHBS or Texas I )-was investigated as a function of the concentration of salt (NaCI, MgCI 2 , or CaCI 2 ), the hydrocarbon (n-alkanes, octane to hexadecane), the alcohol (butyl and amyl isomers), the concentration of surfactant, and temperature. The phase behavior mimics that of similar systems with the commercial surfactant Witco TRS 10-80™. The phase volumes follow published trends, though with exceptions.A mathematical framework is presented for modeling phase behavior in a manner consistent with the thermodynamically required critical tie lines and plait point progressions from the critical endpoints. Hand's scheme for modeling binodals and Pope and Nelson's approach to modeling the evolution of the surfactant-rich third phase are extended to satisfy these requirements. An examination of model-generated progressions of temary phase diagrams enhances understanding of the experimental data and reveals correlations of relative phase volumes (volume uptakes) with location of the mixing point (overall composition) relative to the height of the three-phase region and the locations of the critical tie lines (critical endpoints and conjugate phases). The correlations account, on thermodynamic grounds, for cases in which the surfactant is present in more than one phase or the phase volumes change discontinuously, both cases being observed in the experimental study.