Asphaltenes: A Complex and Challenging Flow Assurance Issue To Measure and Quantify Risk

Abstract

Asphaltenes represent a highly polar component of crude oil, insoluble in n-alkanes and soluble in aromatic solvents. The interactions between asphaltene-water, asphaltene-clay, or asphaltene-asphaltene molecules can cause severe flow assurance issues in an oil field. Such issues could lead to pore-throat blockages within the reservoir and the plugging of production and transportation flowlines. To overcome these issues, it is necessary to first understand the overall stability and dispersancy state of the asphaltenes within the native crude. Most techniques currently used 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 or precipitants. The addition of these chemicals alters the nature and thermodynamic equilibrium of the various solubility fractions within the crude oil. Moreover, the performance of asphaltene inhibitor (AI) on low-asphaltene crude oil samples is very difficult to analyze using traditional optical transmission methods. Researchers from Clariant Oil Services have recently created a more efficient method to evaluate asphaltene stability and inhibitor efficiency using native crude oil samples. This technique can overcome the limitations associated with the optical transmission method. It also presents a more realistic approach to understanding asphaltene stability since it investigates the state of asphaltene within the native crude oil medium rather than the pseudo system of oil precipitant. A Novel Technique For the first time, AI performance is being evaluated by measuring the thermoelectric properties of the native crude oil medium using asphaltene differential aggregation probe test, or ADAPT methodology. For the performance testing part of this work, asphaltene inhibitors were examined. Analyzing multiple crude oil samples with a high degree of variation provides the opportunity to foster a better understanding of asphaltene behavior in bulk crude oil samples. It enables the development of a universal testing method for assessing asphaltene stability and inhibitor performance. It is important to note that interactions between crude oil constituents and a given AI formulation are specific since each oil sample may respond differently. To corroborate this behavior using ADAPT, one of Clariant’s AI formulations (AI-1) was tested together with 10 crude oil samples as shown in Fig. 1, where blank and treated crude oil samples are represented with blue and red bars, respectively. Fig. 2 shows the ADAPT readings for the blank (blue bars) and treated (red bars) crude oil samples. The blank oil samples have a minimum reading of 2.24 units for Oil 6 as com-pared to the maximum value measured of 6.02 units for Oil 2. The addition of 500 ppm of AI-1 formulation to each of the crude oil samples increased overall asphaltene dispersancy and resulted in higher ADAPT readings.