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. 9. Micrographs of cast thin sections of Ma5 Member dolomites from Well J-2 in Ordos Basin. (a) M57 sub-member, 3 558.10 m, with partially dissolved gypsum between grains, the dissolved pores occur along fractures (red arrow), photo No. ①; (b) M57 sub-member, 3 589.10 m, dissolved anhydrite in the fractue (red arrow), photo No. ②; (c) M57 sub-member, 3 592.01 m, dissolved fracture filled with organic matter (red arrow), photo No. ③; (d) M59 sub-member, 3 608.50 m, intergranular dissolved pores filled with organic matter (red arrow), photo No. ④; (e) M59 sub-member, 3 608.50m, intergranular dissolved pores filled with organic matter (red arrow), photo No. ⑤; (f) M510 sub-member, 3 613.17 m, dissolved fracture, photo No. ⑥.