Effect of Reservoir Microstructure on the Organic Solid Phase Deposition During CO2 Displacement

Abstract

CO2 displacement is the primary method for the enhanced oil recovery. It could improve the oil production efficiency and reduce the greenhouse effects. However, the injection of CO2 into reservoir structures may trigger a series of the reactions such as the variation of petrophysical parameters, the component dissolution and the deposition of the organic solid phase. Among them, the organic solid phase deposition is a cumbersome problem in all steps of the petroleum industry including exploitation, production and transportation, since it has a negative effect on the oil systems. As we all know, CO2 displacement technology has been widely used for the conventional reservoirs. However, with the recent applications of carbon dioxide displacement in extra-low permeability and ultra-low permeability reservoirs (microstructures and nano-scale pores may be complex), it is essential to explore the law of the organic solid phase precipitation, deposition and mitigation in nano-scale reservoir spaces. This study works on the key factors that can affect the organic solid phase deposition in nano-scale reservoir spaces during the CO2 displacement. The related injection experiments were carried out based on the three key parameters about the pore sizes, thickness and heterogeneity. The three types of filtration membranes (0.1, 10, and 100 nm) were used and the solid deposition weight percentages for the produced and unproduced oil were measured during the whole steps. The results show that the solid weight percent with the filtration membranes of 100 nm is close to that of the normal crude oil. And the organic solid phase deposition become worse with the increase of the thickness and heterogeneity of the filtration membrane, which indicates that in actual extra-low permeability and ultra-low permeability formations, the solid phase deposition would be much more serious due to the smaller pore size and extreme heterogeneity.