Experimental study on the mechanism of associated gas generation by heavy oil aquathermolysis and thermal cracking during steam injection

Abstract

Previously, we proposed an innovative method for heavy oil recovery known as the ISSG-SAGD (in-situ solvent generation enhanced steam assisted gravity drainage) technique. This technology can improve heavy oil recovery efficiency, reduce steam consumption, and mitigate acid gas emissions. However, the reaction kinetic model used in numerical simulation was derived from literature reports and reasonable assumptions, lacking experimental validation. This study addresses this gap by conducting a series of experiments to investigate the mechanism of associated gas generation under steam injection conditions. We differentiated the reaction temperature window of aquathermolysis and thermal cracking based on the quantity and composition of the associated gas generated. The study revealed that aquathermolysis, occurring at 240–280℃, produces a small amount of associated gas (gasification degree of 0.32 %), predominantly CO2 (about 68 %). In contrast, thermal cracking, occurring at temperatures up to 380℃, significantly increases gas generation (gasification degree of 14.33 %), with light hydrocarbons (C1–5) constituting about 80 % of the gas produced. The reaction rate was found to be proportional to the reaction temperature and time. The SARA analysis showed that saturates and aromatics content increased, while resins and asphaltenes decreased after both reactions. A kinetic model for associated gas generation was established, and kinetic parameters such as activation energies and frequency factors were derived using the Arrhenius method. For example, the activation energy for CO2 generation increased from 18.19 kJ/mol during aquathermolysis to 147.58 kJ/mol during thermal cracking. This study provides a comprehensive understanding of the associated gas generation mechanisms and characteristics under steam injection, supporting the feasibility and potential application of the ISSG-SAGD technique in heavy oil recovery.