Investigation on Variations in Wettability of Reservoir Rock Induced by CO2-Brine-rock Interactions

摘要

Originally, the reservoir rock surface is hydrophilic at atmosphere pressure, because they are generally consisted of hydrophilic minerals, such as quartz, feldspar, calcite, dolomite and clay minerals. According to different hydrophilic magnitudes of different minerals and Cassie's law, the heterogeneous reservoir rock surface shows different hydrophilic magnitudes with different mineral compositions. Therefore, after CO2-brine-rock interactions, minerals dissolution and precipitation will change the mineral composition and the hydrophilic magnitude of the reservoir rock surface at the same time. The present study implemented a CO2-brine-rock system in laboratory with elevated CO2 partial pressures at 323K and 343K. Surface properties of the reservoir rock (such as wettability, surface mineral composition, surface topography and surface element composition) were respectively determined by Wilhelmy plate, XRD, SEM and EDS method before and after CO2-brine-rock interactions. The contact angle results show with the increasing CO2 partial pressure, the contact angle of water on the reservoir rock surface increases at 323K, and decreases at 343K. SEM results show minerals dissolution and precipitation were both taken placed on the reservoir rock surface after CO2-brine-rock interactions. EDS results indicate carbonate minerals dissolution plays a dominate role at 343K, and secondary carbonate minerals precipitation mainly occur at 323K. There is a close relation between the contact angle variation of water and the element mole percentage variation on the reservoir rock surface. With the increasing O, Si, Al, Na or K mole percentage, the decreasing C or Fe mole percentage, the rock surface becomes more hydrophilic.