Determination of Asphaltene Stability in Crude Oils Using a Deposit Level Test Coupled with a Spot Test: A Simple and Qualitative Approach.

ABSTRACT

The main goal of this study is to monitor the stability of crude oils in terms of both precipitation and deposition magnitude with respect to time. To achieve this goal, two experimental techniques which include a deposit level test and a spot test were integrated and applied simultaneously. The method was implemented using six crude oils, namely A, B, D, E, F, and G, and tests were performed at different times which split them into short duration tests and long duration tests. All crude oils were found to exhibit potential for asphaltene precipitation and subsequent deposition at different rates. Crude oils B, G, and D were observed to have started asphaltene precipitation and subsequent deposition relatively quicker. Similarly, crude oils B, A, and F exhibit a higher potential for producing asphaltene deposits in terms of deposition level. Crude oil E produces relatively fewer deposits at comparatively slower rates. The overall result indicates that crude oil B was found to be the most risky crude oil as it produces a higher quantity of deposits at higher rates, while crude oil E proved to be the least risky. Sensitivity analysis was also performed via the computing relevancy factor to determine the relative importance of two input parameters, namely the specific gravity of crude oil and the time for two-output precipitation intensity and deposition level. Precipitation intensities were found by the implementation of an image-processing tool on spot test results. The relationship between time and precipitation intensity was found to be negligible; however, the correlation between time and deposition level was found to be strongly positive with a relevancy factor value of approximately 0.521. Similarly, the relationship of the specific gravity of oil with precipitation intensity and deposition level was found to be moderately negative and very close to each other, i.e., -0.228 and -0.247, respectively. The integration of the deposit level test with the spot test allows the continuous and simultaneously reliable monitoring of both asphaltene precipitation and deposition at different times without involving cost, complex instrumentation, or interpretation, irrespective of the type of oil. The method enables the successful determination of stability ranking of different crude oils both in terms of precipitation and deposition.