The mechanism of asphaltene precipitation and its effects on interfacial properties of oil-water systems at reservoir conditions has been actively researched, since it has significant impact on oil recovery and flow in the production network. In this work, we investigate the effect of pressure-depletion induced asphaltene precipitation on interfacial properties of live-oil, brine and quartz system; and present experimental observations on hysteresis of contact angle after aging at high pressure high temperature (HPHT) conditions.

The experimental method is based on pendant drop-shape method utilizing high-resolution camera for quantitative image analysis and high-resolution digital pressure transducer in a HPHT fluid cell. The cell temperature was controlled with an accuracy of ±0.1°C. The contact angle with quartz was measured in presence of de-ionized water as surrounding medium. The experiments were started at a pressure higher than asphaltene onset pressure (AOP) and decreased below AOP in multiple discrete stages to cause asphaltene precipitation. At each pressure stage, sufficient time was given to stabilize the contact angle caused by aging and/or asphalting precipitation, and the change was recorded.

Experimental contact angle data for a system containing a live oil, brine and quartz is presented at various pressures capturing the AOP. Under isothermal condition and at a pressure above AOP, the contact angle decreases with time until stabilization implying that it is a transient process. At sequential steps, the time to achieve the equilibrium value decreases. In this study, we

  1. experimentally show that the contact angle decreases with pressure. However, an evident sharp jump is observed near the vicinity of AOP point, signifying the effect of asphaltene precipitation, especially at the three phase (quartz/oil/water) interfaces.

  2. present the experimental data of interfacial tension (IFT) between live oil and water, and study the interfacial tension (IFT) trend reversal with supplemental IFT measurements before and after asphaltene precipitation.

  3. utilize the solubility-parameter approach for asphaltene modeling to predict asphaltene precipitation from live oil at various pressures below AOP but above the saturation pressure (Psat < P < AOP).

  4. relate the amount of precipitation with change in IFT that may enable the model to predict the change in interfacial properties (IFT, contact angle) at various pressure, temperature conditions, and other oils.

Despite asphaltene effects on wettability alteration have been proposed, this is the first experimental evidence that pressure-depletion driven asphaltene precipitation alters the contact angle at realistic reservoir conditions (HPHT, live oils), including hysteresis in contact angle and IFT reversal. These data can be used as basis to establish the benchmark data, model calibration for managing and preventing/remediation asphaltene problems, and to design the proper facility and operating conditions for efficient recovery and operational processes.

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