Early Detection and Assessment of Asphaltene Precipitation and Gas Hydrate Formation at Field Conditions

Abstract

Abstract The detection of asphaltene precipitation and gas hydrate formation is critical to preventing production losses and to optimize strategies for mitigation and remediation. Likewise, the evaluation of some flow properties (e.g., viscosity and yield stress) of the slurries formed for asphaltenes and hydrates are paramount when developing and testing prediction tools for safe field operations. Several complications must be considered when dealing with asphaltenes and hydrates at field conditions, e.g., harsher conditions (especially high or extremely high pressure), the variation of fluid composition over time, and the lack of information on the thermodynamic conditions at which those solids (asphaltenes and hydrates) form. One possibility to face this challenge is to use field information to calibrate existing prediction models/tools and make them applicable for new field conditions. Hence, there is interest in industry to develop new tools that allow the detection of asphaltenes and hydrates in the early stages of their formation. In this work, acoustic and nuclear magnetic resonance (NMR) measurements are utilized to detect asphaltene precipitation in crude and model oils. Asphaltene detection was performed at ambient pressure and at CO2 pressurized conditions. Acoustic and NMR measurements were sensitive to the asphaltene concentration in the tested oils. In addition, rheological properties such as viscosity and yield stress were determined for hydrate slurries in crude oil systems at different water volume fractions, salt (NaCl) concentrations and gas compositions. Gas hydrate slurry formed from a CO2-rich gas exhibited a phase inversion in rheological experiments (external phase changed from oil to water), which was possibly promoted by the CO2-activated natural surfactants of the crude oil.