A Wavelet-Based Model for Determining Asphaltene Onset Pressure

Abstract

Asphaltene onset pressure (AOP) is a significant parameter for determining the flow assurance of live oils. The solid detection system (SDS) is one of the prevalent techniques used by service laboratories to evaluate the stability of asphaltenes under reservoir conditions. The determination of AOP based on this technique entails the interpretation of recorded data, making the accuracy of the result prone to error. Accordingly, this research aimed to provide a robust computational method for determining AOP by wavelet analysis of SDS data. Changes in the curvature of transmitted light (CTL) were considered a diagnostic criterion to detect AOP. To substantiate this hypothesis, CTL was first calculated at each pressure. The discrete wavelet transform was then applied to decompose the CTL curve and compute the CTL entropy $\left( {E_{\text{CTL}} } \right)$ based on the decomposition results. Finally, a relation was established between AOP and the entropy variations of CTL $\left( {\Delta E_{\text{CTL}} } \right)$, leading to the AOP determination model. This model indicated that the maximum value of $\Delta E_{\text{CTL}}$ is at AOP. Put differently, the onset of asphaltene precipitation pressure corresponds to the highest variation in the CTL entropy. The results obtained from the AOP determination model in various reservoirs are consistent with the experimental findings.