Study on enhancing heavy oil recovery through catalytic hydrothermal cracking using a dual in-situ strategy

The high activation temperature of catalysts and the difficulty of their dispersion in the formation are the main obstacles preventing the widespread application of catalytic hydrothermal cracking technology for heavy oil development. However, the "dual in-situ" strategy, which involves the in-situ generation of catalysts to achieve in-situ upgrading of heavy oil, holds promise as an ideal solution to overcome these challenges. Herein, a catalyst precursor suitable for the "dual in-situ" strategy was synthesized, and targeted decomposition experiments were conducted in both steam and oil-water environments typical of heavy oil thermal recovery. Additionally, oil displacement experiments in porous media were carried out, revealing the advantages and characteristics of this innovative oil displacement method in terms of heat transfer efficiency, oil displacement dynamics, and upgrading effects. The results showed that the final decomposition products of the synthesized cetyltrimethyl ammonium heptamolybdate in both steam and oil-water environments were catalytically active MoS 2 . In the oil-water environment, due to solvent and interfacial effects, MoS 3 could be converted to MoS 2 at 180–200°C, which was about 130°C lower than in a nitrogen or steam atmosphere, fully meeting the conditions for integration with heavy oil thermal recovery. Furthermore, the presence of organic groups significantly enhanced the adsorption properties of the MoS 2 generated from cetyltrimethyl ammonium heptamolybdate, with specific surface area and pore volume increasing by 110 m²/g and 0.04 cm³ /g, respectively. In the oil displacement experiments, the oil recovery after using cetyltrimethyl ammonium heptamolybdate increased by 10.3 % compared to steam flooding, and by 3.8 % compared to the direct injection of MoS 2 NPs. The in-situ generation of the catalyst resulted in reduced agglomeration and deposition, leading to significantly improved mobility and sweep efficiency. Consequently, this approach not only enhanced the upgrading and production of heavy oil but also greatly extended the durability of the effect.