Quantitative research on tight oil microscopic state of Chang 7 Member of Triassic Yanchang Formation in Ordos Basin, NW China

Abstract

With nuclear magnetic resonance (NMR) and micrometer-nanometer CT Scanning technology, quantitative research was carried out of the micro-existing state of tight oil in the Chang7 Member of the Triassic Yanchang Formation in the Ordos Basin. The total reserves of the tight oil in the reservoirs were determined using NMR technology. The initial oil saturation was measured as 63.99%. The 2-D slice images of the tight oil reservoirs were obtained using CT Scanning technology, and the 3-D images were acquired after digital synthesis processing. Accordingly, the existence states of the tight oil in the reservoirs are divided into six types, namely thin film form, cluster form, throat form, emulsion form, particle form and isolation form. It is found by quantitative calculation of the contents of tight oil in different existence states of tight oil that the emulsion form and thin film form are the main existence states, which account for 70% of the total amount of the tight oil in the reservoirs, followed by the cluster and particle forms. The contents of isolation form and throat form tight oil are low. The contents of tight oil in various existence states are related to initial water saturation, clay mineral content and pores structure of the reservoirs. Key words: tight oil, microscopic state, quantitative research, Ordos Basin, Triassic Yanchang Formation