SCA2003-05: VARIATION OF SPECIAL CORE ANALYSIS PROPERTIES FOR INTERMEDIATE WET SANDSTONE MATERIAL

摘要

Wettability is known to influence fluid flow processes in porous media.Most North Sea sandstone reservoirs fall into the large group of intermediate wet state.However,special core analysis of intermediate wet rock shows a wide variation in properties like;end point saturation,capillary pressure and relative permeability.In this study,we find an improved understanding of the intermediate wet state by dividing the intermediate wet group into three sub-classes.Fractionally-wet(FW),where oil and water wet sites are random with respect to pore size,and mixed wet defined by water and oil wet pores that are sorted by pore size.We assume two classes of mixed wet state,where the oil wet sites are either in the large or the small pores.MWL(mixed-wet large)is defined by oil wet large pores,while MWS(mixed-wet small)refers to the smaller pores are oil wet.The USBM and Amott-Harvey wettability indices are used to group reservoir data into reservoirs with FW,MWS,and MWL behavior.Some of the main results were that the fractional-wet rock has a more robust wettability.Cleaned cores maintain a non-waterwet state,indicating that the wetting sites may be coupled to mineralogy in addition to adsorption/deposition of oil components changing the surface properties of the rock.Also MWS maintains wettability after cleaning,while the mixed wet(MWL)cores become more water wet after solvent cleaning.The average waterflood remaining oil saturation(Sorw)is lowest for MWL cores.The remaining oil saturation for the MWL rocks also show a reduced Sorw with increasing permeability,but the FW and MWS reservoirs indicate a constant Sorw independent of permeability.The type of intermediate wettability has impact on data structure needed to build representative reservoir models.In addition,the type of wettability influences the shape of relative permeability curves and also the capillary pressure relations for different classes of intermediate wettability.