Supercritical water upgrading of heavy oil: Effects of reservoir minerals on pyrolysis product distribution

Abstract

Supercritical water upgrading (SCWU) is a promising technology for heavy oil recovery and refining, in which minerals could act as catalysts, but the effect on the upgraded product distribution remains unclear. In this study, heavy oil upgrading experiments in supercritical water (SCW) were carried out at 400°C and 25 MPa to investigate the effects of reservoir minerals such as quartz, carbonate, feldspar and clay minerals on the upgrading process. The result indicated that carbonate minerals and clay-bearing minerals produced noticeable benefits to the SCWU of heavy oil process. In carbonate minerals, dolomite showed the strongest catalytic effect in promoting hydrothermal cracking of hydrocarbon macromolecules, with a 5.6 % reduction in heavy fraction and a 12.2 % increase in light fraction of the upgraded oil. Clay-bearing minerals mainly exhibited oil-enhancing and coking-inhibiting benefits, calcium montmorillonite exhibited the most significant increase in oil production of 9 %, while zeolite most significantly reduced the coke activation energy by 62 %. Regarding the catalytic mechanism, the catalytic effect of carbonates originated from the MgO and CaO sites on the surface. For clay minerals, the acidic catalytic sites exist in the interlayer domains of montmorillonite and in the pores of zeolite provided higher catalytic efficiencies in oil production. This study demonstrated the feasibility of using natural minerals as inexpensive catalysts for supercritical water upgrading of heavy oil.