Unusual Asphaltene Phase Behavior of Fluids from Lake Maracaibo, Venezuela

Abstract

Reservoir fluids from Lake Maracaibo have reportedly caused asphaltene operational problems ranging from plugging of wellbores, pipelines and flowlines to clogging of surface facilities (Garcia et al, 2001). Production of fluids from some part of the region has been dramatically reduced due to asphaltene precipitation and deposition (Vasquez, 2010). Asphaltene and wax precipitation is a serious problem in production, transport and processing of reservoir fluids. Of particular concern are the effects of asphaltene precipitation and their potential to disrupt production due to deposition in the near-wellbore regions and production tubulars. This phenomenon is directly influenced by changes in temperature, pressure and composition. Commonly, low temperatures increase the probability of asphaltene precipitation; however, experimental studies on the fluid under study demonstrated unusual asphaltene phase behavior. This project involved experimental studies on fluid phase behavior as part of a formation damage investigation. The main challenges with fluids from the Maracaibo area are the relative high H2S content (1–3%), high reservoir temperature (270°F) and the asphaltenic nature of the crudes. In this study, the asphaltene precipitation envelope was determined using Near Infrared (NIR) Solid Detection System (SDS), High Pressure Microscope (HPM), Particle Size Analysis (PSA) and gravimetric techniques. As expected, a significant amount of asphaltene was observed to precipitate during depressurization. However, reversibility of the precipitated asphaltene was also observed below the bubble point and during re-pressurization. What was unusual about this fluid was the unconventional asphaltene precipitation onset conditions found at low temperatures. For most crude oils worldwide, asphaltene precipitation onset pressure increases at lower temperatures; however, the fluids considered in this work have shown a non typical behavior wherein the asphaltene onset pressure decreases with decreasing temperature. Such behavior was earlier presented by Ting et al, 2003 on the Maracaibo oils; however, no reports have been published since.

Systematic Evaluation of Asphaltene Formation Damage of Reservoir Fluids from Lake Maracaibo, Venezuela

“…The AOP and saturation pressure on the blended sample were found to be 4250 +/-250 psia and 2800 psia. These results were in agreement with the measurements performed in our earlier work (Gonzalez et al, 2012).…”

“…Generally the asphaltene onset pressure increases with a decrease in temperature, however, in this case the asphaltene onset pressure decreased with decrease in temperature. The results of the asphaltene precipitation study were reported in our earlier publication (Gonzalez at al, 2012).…”

“…The results of this work are published earlier (Gonzalez et al, 2012). A quick asphaltene onset pressure (AOP) measurement and saturation pressure measurement was also done on the blended samples.…”

A theoretically modified PC-SAFT equation of state for predicting asphaltene onset pressures at low temperatures

“…It is also important to highlight that the amply literature related to thermodynamic models to predict AOPs of petroleum reservoir fluids, included very recent works [187], intrinsically assume the AOPs are true liquid-liquid equilibria. Thus, the approach used in this work is the conventional one followed by hundreds of papers published in the literature (e.g., [114]- [120], [123], [138], [142], [143], [187]).…”

“…This could explain, in part, the tendency of PC-SAFT to over-predict the onsets of asphaltene precipitation and polymer cloud points at low temperatures [78], [123].…”