Distribution of Asphaltene Deposition in the Rock Samples by Gas Injection

Abstract

Abstract Asphaltene related experiments for the samples from a Middle Eastern reservoir were conducted to assess potential problems in association with asphaltene precipitation caused by gas injection. The study involved three parts, (1) characterization of asphaltene precipitation and identification of problematic areas, (2) quantitative analysis of asphaltene deposition and its numerical modeling (3) field-scale simulation with the developed asphaltene model. Asphaltene phase behavior was measured to understand the relationship among pressure, temperature and asphaltene precipitation due to gas injection. Asphaltene onset pressure was monitored by Solids Detection System (SDS) to estimate Asphaltene Deposition Envelope (ADE), which was the useful measure to predict the risk of asphaltene deposition. The gas injection experiments confirmed asphaltene deposition in the core samples and the permeability reduction. The asphaltene content of the effluent from the core was reduced due to the deposition in the core and the amount of the deposition profile along the core sample was measured. It was found the heterogeneous distribution of the asphaltene deposition along the core. CO2 injection made relatively large amount of asphaltene deposition near the inlet of the core as the CO2 contacted oil at the upstream of the core and the mixing and dissolving to the oil were continued. Consequently, the permeability was reduced due to large deposition at the upstream. However, it did not severely affect on permeability when the asphaltene was equally distributed in the core. The laboratory-measured asphaltene precipitation and its effect on the permeability were modeled by the equation of state (EOS) and the lattice Boltzmann method (LBM). The model was used to understand field-scale behavior by the flow simulation model and it predicted asphaltene deposition around the wells. Asphaltene deposition profiles were different under near miscible and miscible conditions. The miscible conditions had more severe permeability damage around producers although the damage was barely observed around injectors. The permeability reduction was observed after the gas breakthrough. The study covers the laboratory measurements and the numerical modeling. It shows the detail analysis of asphaltene related experiments and modeling is important to identify the risk of asphaltene deposition induced by gas injection, especially CO2 injection.