In-situ formation of molybdenum disulfide nanoparticle and its catalytic performance in heavy oil long-term aquathermolysis

Abstract

Heavy oil is an important unconventional petroleum resource due to its abundant reserve, but the reduction of viscosity is a prerequisite for its effective exploitation. Researchers are trying to develop heavy oil catalytic aquathermolysis technologies for their merit of irreversible viscosity reduction through in-situ upgrading. The key point of catalytic aquathermolysis is the in-situ formation of high active catalytic phase. In this study, we have demonstrated that the precursor (NH₄)₂MoS₄ was fully decomposed into MoS₂ nanoparticles at relatively low temperature of 200°C after 90 minutes. The decomposition of (NH₄)₂MoS₄ in aquathermolysis was significantly different from its decomposition process under hydrogen and vacuum atmospheres. The laboratory experimental results showed that the heavy oil viscosity reduction rate was above 85 % with the action of in- situ formed MoS₂ nanoparticles after aquathermolysis. The sulfur content of heavy oil and asphaltene, asphaltenes and aromatics contents of heavy oil were decreased significantly, indicating that the cracking and ring opening reactions did take place. In the oilfield experiment, the precursor (NH₄)₂MoS₄ was injected into the reservoir along with steam. After one-time injection, the catalytic effect could be sustained for at least four months. The maximum viscosity reduction rate was as high as 90 % during the first week, and still around 70 % in the 4th month. The molecular structural analysis of the produced heavy oil proved that the asphaltenes has been effectively cracked during the in-situ catalytic aquathermolysis. Both the laboratory and oilfield experimental results demonstrated that (NH₄)₂MoS₄ precursor could form MoS₂ nanoparticle and effectively catalyze the upgrading reactions of heavy oil. We hope that this study will provide a new catalyst development strategy for the catalytic aquathermolysis exploitation technology of heavy oil.