As a part of an integrated improved oil recovery project, it was required to evaluate asphaltene formation arising from contacting nitrogen gas with the reservoir fluid. This paper discusses the experimental work associated with the asphaltene evaluation.
The subject reservoir was known to have operational problems due to asphaltene precipitation during primary production. Hence, laboratory experiments using the transmittance of an optimized laser light in the near infrared (NIR) wavelength (~1600 nm) were used to first define the pressure-temperature regions of asphaltene instability of the reservoir fluid. Subsequently, several light transmittance experiments were conducted to evaluate the asphaltene instability regions by contacting various molar concentrations (5, 10, & 20%) of nitrogen gas with the reservoir fluid. Also, measurements were conducted to quantify the bulk precipitation of asphaltene with various molar concentrations of nitrogen.
Results indicated that nitrogen gas aggravated the asphaltene instability, and also, increased the bulk precipitation amount with increasing concentrations of nitrogen gas in the reservoir fluid. The aggravated asphaltene instability could potentially nullify any expected benefits of improved oil recovery with nitrogen injection as pressure maintenance.