Asphaltene deposition is a major production constraint in several carbonate reservoirs in United Arab Emirates (UAE). The negative effects of asphaltene include plugging of reservoir formation, wellbore, tubing and surface production facilities and causing shutdown of certain wells. Many of these carbonate reservoirs are likely to be parts of a strategic EOR program through gas injection in the near term. However, as gas injection may further exacerbate the asphaltene problem, it is essential to investigate, as a priori, the effects of gas injection on asphaltene precipitation and deposition and this is the motivation for this study.

A critical analysis of the asphaltene problems to be faced in this particular field was carried out with both HC and CO2 gases as likely injectants under reservoir conditions. In doing so, different gas injection scenarios were studied. The results from experimental studies have been interpreted. The effects of gas injection ratio and depressurization speed on asphaltene onset pressure (AOP) have also been carefully studied. The strategy to adopt an equal-time-stepwise depressurization approach in this study yielded a more reliable result than conventional AOP detection method and also helped reduce the experimental time. In addition, asphaltene precipitation growth history and its nature as solids were studied with the aid of a high pressure microscope (HPM).

The asphaltene onset pressure is found to be affected by the way of system depressurization (frequency and time step magnitude) since it has a direct bearing on the stabilization time. Based on this study, a faster and more reliable method of AOP determination by using light scattering technique with near infrared range (NIR) light was proposed. The AOP of oil depends on the volume of injection for both HC and CO2 gases. It is noted that asphaltene deposition envelope enlargs with the increasing volume of injected gas.

Keywords:
wax remediation, wax inhibition, asphaltene remediation, paraffin remediation, hydrate remediation, hydrate inhibition, flow assurance, oilfield chemistry, scale inhibition, asphaltene inhibition
Subjects:
Production Chemistry, Metallurgy and Biology, Flow Assurance, Inhibition and remediation of hydrates, scale, paraffin / wax and asphaltene, Precipitates (paraffin, asphaltenes, etc.)
Copyright 2012, Society of Petroleum Engineers
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