A Wavelet-Based Model for Determining Asphaltene Onset Pressure
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Original Paper
A Wavelet-Based Model for Determining Asphaltene Onset Pressure Mohammad Heidary
1,2
and Kazem Fouladi Hossein Abad1
Received 29 July 2020; accepted 19 September 2020
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 ðECTL Þ based on the decomposition results. Finally, a relation was established between AOP and the entropy variations of CTL ðDECTL Þ, leading to the AOP determination model. This model indicated that the maximum value of DECTL 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. KEY WORDS: Asphaltene onset pressure, Solid detection system, Curvature of transmitted light, Entropy of transmitted light curvature, Discrete wavelet transform.
INTRODUCTION One of the main factors that influence flow assurance during the primary production of oil reservoirs with main economic losses is precipitation and deposition of heavy organic components, especially asphaltene (Struchkov and Rogachev 2017). Asphaltene precipitation from live crude oils that occurs due to temperature or pressure reduction can lead to closure of flow paths within the reservoir rock (Mansourpoor et al. 2019; Kalantari and Farahbod 2019). In this regard, several studies have been conducted to investigate the impact of 1
Research Institute of Petroleum Industry (RIPI), Tehran, Iran. 2 To whom correspondence should be addressed; e-mail: [email protected]
asphaltene deposition on reservoir rock properties. The findings show that porosity and permeability decrease dramatically as a result of asphaltene deposition (Memon et al. 2017; Mohammadzadeh et al. 2019; Ghadimi et al. 2019; Mehana et al. 2019; Qian et al. 2019). There is a wealth of evidence that rock wettability changes due to the adsorption of asphaltene and resin fractions on pore walls (Amin et al. 2011; Al-Aulaqi et al. 2011; Uetani 2014; Taqvi et al. 2016). Therefore, determination of the asphaltene onset pressure (AOP) at which asphaltene molecules first begin to precipitate out of solution is indispensable for managing the asphaltene threat. The different understandings of the mechanisms behi
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