Effects of Sedimentary-diagenesis Evolution on Petrophysical Properties of Carbonates of Majiagou Formation in Ordos Basin

The fifth Member of Ordovician Majiagou Formation (Ma 5 Member) in the central Ordos Basin is a crucial hydrocarbon reservoir, characterized by the unique carbonate-gypsum salt rock combination sedimentary system. Studies have showed that the Ma 5 marine carbonate reservoir experienced a long and intricate geological process. Furthermore, tectonic-sedimentary patterns and subsequent diagenesis control the reservoir distribution characteristics and rock properties (including compositions, fabric and pore types, etc.) of the Ma 5 carbonate, thus affecting their seismic response ( Zhao et al., 2013 ). These complex relationships emphasize the importance of understanding the physical properties of the Ma 5 carbonate from geological-petrophysical perspective. To address this, a systematic petrophysical laboratory testing under reservoir conditions were conducted to reveal the influence of sedimentary environment on the petrophysical properties of the Ma 5 carbonates. That is, tectonic-sedimentary differentiation and multi-stage diagenesis results in complex and distinctive rock microstructure and pore structure of Ma 5 carbonate, which has strong impacts on their seismic response.