A Novel Thermo-Electric Technique to Evaluate Asphaltene Stability and Inhibitor Efficiency in Native Crude Oil Medium

Abstract

Asphaltenes represent the most polar solubility fraction of crude oil. The polar-polar interactions between asphaltene-water, asphaltene-clay, or asphaltene-asphaltene molecules can cause severe flow assurance issues in the oilfield such as formation of highly stable emulsion, pore-throat blockages within the reservoir, and plugging of production and transportation flowlines. A novel approach of understanding these polar interactions through thermo-electric measurements is presented in this study, which can evaluate overall asphaltene stability in native crude oil. Most of the techniques currently being used to assess asphaltene stability and efficiency of different asphaltene inhibitors on preventing asphaltene deposition are based on light scattering and transmittance phenomenon. Since crude oils are intrinsically dark colored, these techniques require dilution of the oil sample with solvents like toluene and xylene or precipitants like pentane and heptane. Addition of these chemicals alters the nature and thermodynamic equilibrium of crude oil solubility fractions. Thus, a novel approach of measuring the thermo-electric properties of crude oil and crude oil-asphaltene inhibitor mixtures was developed and tested using a custom-built capacitor setup. The thermo-electric measurements were conducted on 10 different crude oil samples. These samples were altogether tested with 10 asphaltene inhibitors (AI). Measured data was used to indirectly estimate the polarity of the test sample, which is related to the dispersion efficiency of the asphaltene inhibitor. A standard light scattering technique was also used to analyze the oil and oil-inhibitor samples and the results were compared to the thermo-electric method outcomes. It should be noted that some of the oil samples tested in this study were obtained from production systems having asphaltene deposition issues and undergoing effective prevention and remediation treatment. Therefore, it is important for the success of the new technique to not only correlate with the standard light scattering test results but also be able to precisely the efficacy of asphaltene inhibitors for each of the test oil samples. From the results obtained, it was observed that using the thermo-electric method, the asphaltene inhibitors can be accurately screened for all the oil samples and the inhibitor efficiency analyzed in terms of its dosage curve, also agrees well with the conditions observed in the field. A strong correlation between the results obtained from the thermo-electric technique and the light scattering method indicates the validity and higher-level accuracy of the innovative technique. Moreover, direct application of this method on the production platform at the well-head using the native crude oil sample highlights the versitality of this novel method. In addition to testing overall asphaltene stability and inhibitor efficiency, the method can also be used to monitor and optimize the field scale production scenario.