SIMULATION EXPERIMENT ON THE EFFECT OF HYDRODYNAMICS ON ALTERATION OF ORTHOCLASE UNDER RESERVOIR CONDITIONS

Abstract

The dissolution of feldspar is the main mechanism for the formation of secondary pores in deep sandstone reservoirs, which is controlled by pore fluid properties and fluid dynamics. The simulation experiment analyzed the effect of different fluid/rock ratios (hydrodynamics) on the orthoclase dissolution kinetics under reservoir diagenesis conditions. The experimental temperature was set at 100°C; the solutions were divided into acetic acid solutions and hydrochloric acid solutions, with pH values at 2 and 4; the reaction time was between 30 days and 80 days. The experimental results show that the fluid/rock ratio is an important factor controlling the feldspar dissolution. The higher the fluid/rock ratio, the stronger the fluid’s ability to dissolve at orthoclase, and the more the release of Al and Si. With the increase of fluid/rock ratio, it is possible to observe more noticeable dissolution characteristics from the feldspar morphology. The lower the fluid/rock ratio, the higher the concentration of Al and Si ions released by orthoclase dissolution, and the easier it is to cause the precipitation of clay minerals, which is not conducive to the improvement of reservoir physical properties. The fluid/rock ratio is an important controlling factor on the formation and distribution of authigenic minerals such as kaolinite. The research results are of great implications in the feldspar dissolution to form secondary pores in the burial diagenesis process. In the sandstone-shale contacts or sandstone reservoirs with good initial physical properties, the strong fluid flow is conducive to the secondary pores formation. The experimental findings are helpful for us to understand better the process and mechanism of feldspar alteration and secondary pores formation.