An experimental approach to investigating permeability reduction caused by solvent-induced asphaltene deposition in porous media

Abstract

Permeability reduction resulting from asphaltene deposition in porous media needs to be accounted for by reservoir simulators. Two questions have to be answered in order to quantify the reduction in permeability. The first question is how much asphaltene is deposited in porous media and the second one is how much permeability reduction is associated with a certain amount of asphaltene deposition. This article focuses on answering the latter by conducting laboratory experiments. Sand packs with known porosity, permeability, and sand grain size distribution were saturated with oil. Heptane was used to flood the oil-saturated sand packs. After flooding with heptane, each sand pack was divided into ten smaller sand packs and the permeability of each small sand pack as well as the amount of deposited asphaltene in each one of them were measured. A method was developed to quantify the amount of deposited asphaltene within different cross sections of the sand packs. Results have been reported in terms of the mass of asphaltene in milligrams deposited on one gram of sand grain. The formation damage factor for each sand pack segment has been reported as the ratio between the permeability of the segment before extracting asphaltene to its permeability after extracting asphaltene. This ratio varied between 0.4–0.9. Asphaltene deposition varied between 1–20 mg/1 g of sand grain. Comparing the experimental results with the result predicted by one of the current correlations showed that the correlation does not accurately predict permeability reduction.