Impact of asphaltene precipitation on vapex performance

Abstract

The VAPEX (Vapor Extraction) is an oil recovery process, in which heavy oil or bitumen is mobilized by injection of a low molecular weight hydrocarbon solvent and is drained by gravity to a horizontal production well. It has attracted considerable attention because of its potential applicability to problematic reservoirs and the chance of in situ upgrading of the oil during the process. The objective of the current work was to determine whether the beneficial effects of asphaltene precipitation will outweigh any formation damage in Vapex operations. The effects of in situ precipitation and deposition of asphaltenes on the rate of oil drainage and the quality of the produced oil under different operating conditions were experimentally evaluated. The experiments were conducted in a physical model packed with realistic permeability sand and propane was used as the solvent. The experimental results show that the oil produced at higher injection pressures was substantially upgraded but the viscosity reduction by asphaltene precipitation did not lead to higher rates of production. The effect of viscosity reduction was negated by the accompanying damage to formation permeability. Injection of toluene with propane was successful in increasing the rate of production and the extent of upgrading was encouraging. The huff and puff injection of toluene into the production well, to remove damage from the near well zone, was not successful. It led to production of oil with higher asphaltene content and there was no improvement in the rate of oil drainage compared to lower pressure operation with minimal asphaltene precipitation.