INFLUENCE MECHANISM AND THEIR DEGREE OF SEDIMENTARY MINERAL COMPONENTS ON TIGHT SANDSTONE RESERVOIR IN THE EASTERN ORDOS BASIN, CHINA

As the rock skeleton in the rock physics models of tight sandstones, sedimentary mineral components have a significant influence on pore types, sizes, structure and connectivity. Tight sandstones are characterized as low porosity and low permeability and their formation, to a large extent, depends on sedimentary mineral components. Base on a variety of technical methods including casting thin sections observation, bulk-rock analysis, X-ray diffraction analysis of clay minerals, cathode luminescence, SEM and porosity and permeability tests, influence mechanism and their influence degrees of sedimentary mineral components on tight sandstone reservoir have been focused in the eastern Ordos Basin, China.

There is a linear relationship between quartz content and porosity, but an exponential relationship between quartz content and permeability, which reflects the supporting role of quartz on pores in tight sandstones reservoirs. With the increase of feldspar content, porosity is represented as an increase after the decrease and the feldspar content is about 12.5% in the turning point. Permeability has the same trend with porosity, but 15.0% of feldspar content in the turning point. In contrast to quartz, there is a negative correlation between clay mineral and reservoir quality on account of the destructive effect of clay minerals on microscopic pores. The effect of carbonate cement can not be ignored and plays a role of destroying pores. In addition, there is no significant regularity between reservoir quality with other cements, such as pyrite, gypsum and anhydrite. The influence degrees of sedimentary mineral components on tight sandstone reservoir have been discussed on the base of grey correlation method. The computation results show that the degree of association between quartz and porosity is maximum, however, clay mineral is minimum. In the case of permeability, the influence degrees of clay mineral is maximum.