Characteristics, formation and evolution of pre-salt dolomite reservoirs in the fifth member of the Ordovician Majiagou Formation, mid-east Ordos Basin, NW China

FU Siyi,ZHANG Chenggong,CHEN Hongde,CHEN Anqing,ZHAO Junxing,SU Zhongtang,YANG Shuai,WANG Guo,MI Wentian

Fig. 2. Petrologic characteristics of pre-salt dolomite samples from the mid-eastern Ordos Basin. (a) Well J-6, 3 552.50 m, M58 sub- member, dolomicrite with anhydrite patches, ordinary thin section; (b) Well J-6, 3 552.50 m, M58 sub-member, dolomicrite is dark red, anhydrite is not luminous, photo of cathodoluminescence; (c) Well J-12, 3 674.10 m, M59 sub-member, very fine to fine crystalline dolomite, ordinary thin section; (d) Well J-12, 3 674.10 m, M59 sub-member, dolomite is dark red to orange, photo of cathodoluminescence; (e) Well JT-1, 3 633.81 m, M56 sub-member, fine crystalline dolomite with intercrystalline pores, cast thin section; (f) Well T-38, 3 630.10 m, M510 sub-member, intercrystalline dissolved pores are partially filled with coarse dolomite and organic matter, cast thin section; (g) Well J-12, 3 647.32 m, M57 sub-member, dolarenite, cast thin section; (h) Well J-12, 3 647.32 m, M57 sub-member, carbonate grains are dark red, photo of cathodoluminescence; (i) Well T-38, 3 612.00 m, M59 sub-member, intergranular dissolved pores are partially filled with quartz and organic matter, cast thin section.