Unusual Asphaltene Phase Behavior of Fluids from Lake Maracaibo, Venezuela

Abstract

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.