Asphaltene Precipitation from Live Oils:  An Experimental Investigation of Onset Conditions and Reversibility

Abstract

The behavior of asphaltene in live oils was investigated using a fully visual PVT cell equipped with a laser-based particle detection system. Through a series of isothermal pressure depletion experiments, the asphaltene stability envelope was established for several Gulf of Mexico oils. These tests were performed under pressure and temperature conditions typical of a field production system. Evidence of asphaltene precipitation above and redissolution below the saturation pressure was observed. Significantly, these tests also showed that pressure depletion-induced asphaltene precipitation is a highly reversible process. This latter observation helps to resolve a long-running debate in the literature concerning the reversibility of the asphaltene precipitation and flocculation process.

Characterisation of Asphaltenes and Modelling of Flocculation – State of the Art

“…When the light transmitted starts to increase slightly as the pressure is reduced, the redissolution threshold has been reached. Hammami et al (2000) obtained the same type of results on oils from the Gulf of Mexico. Like the previous authors, they observe that although this technique can be used to determine the flocculation point, and with certain precautions the redissolution threshold, observation of possible reversibility may prove difficult due to the deposits which form on the surface of the cell and which take a long time to dissolve.…”

“…Several studies show that the flocculation point is generally located at a pressure Percentage of soluble asphaltenes in a reservoir fluid during depletion (taken from Kahir and Jamaluddin, 1999. ) greater than the fluid saturation pressure and that maximum flocculation occurs at the saturation pressure (Jamaluddin et al, 2001;Hammami et al, 2000;Jiang et al, 1990). Kabir and Jamaluddin (1999), Edmonds et al (1999), Szewczyk and Béhar (1999) determined experimentally the percentage of soluble asphaltenes in a reservoir fluid during depletion and obtained the graph shown on Figure 5, extracted from studies conducted by Kabir and Jamaluddin (1999).…”

“…Ramos et al (1997) also indicate that the flocculation process is reversible. Recent measurements taken in a PVT cell equipped with a laser solid detection system (SDS) indicated that flocculation can be reversed by alternating decompression and recompression steps (Hammami et al, 2000). These measurements are extremely important since the results were obtaining without sampling likely to modify the system.…”

溶解パラメーター推算にPeng-Robinson状態方程式を使用した簡易アルゴリズムによるアスファルテン析出挙動の予測

“…Then, mass spectroscopy of asphaltene was performed. Details of the experimental technique to evaluate the amount of asphaltene precipitation during the pressure depletion sequence at reservoir temperature were given previously 20) . The asphaltene detection system consisted of a variable volume, visual PVT cell retrofit with fiber optic light transmission probes (source and detector) to measure the onset of organic solid precipitation (due to tem- perature, pressure, and/or compositional change) confluid bubble-point pressure as well as liquid density and currently with fluid volumetric data.…”

“…cycles. Power of transmitted light (PTL) refers to the The system components were mounted across the fullamount of light passing through the oil sample and caplength PVT cell windows and a reference scan of the tured by the receiving fiber optic cable 20) . light transmittance through the oil performed.…”