Accumulation conditions and exploration directions of Ordovician lower assemblage natural gas, Ordos Basin, NW China

XU Wanglin,LI Jianzhong,LIU Xinshe,LI Ningxi,ZHANG Caili,ZHANG Yueqiao,FU Ling,BAI Ying,HUANG Zhengliang,GAO Jianrong,SUN Yuanshi,SONG Wei

Fig. 6. Source rocks and reservoirs in the Ordovician lower assemblage. (a) At 3 816.06 m in Ma 2 Member of Well TA112, gypsum-bearing argillaceous dolomite, 6 black bands with an average TOC of 0.51%; (b) At 3 867.35 m in Ma 3 Member of Well JN6, dolomitic mudstone with interbedded gypsum rock, common thin slices, plane-polarized light; (c) At 3 670.52 m in Ma 3 Member of Well TA95, algae mass argillaceous dolomite, TOC of 1.45%; (d) At 4 095.50 m in Ma 3 Member of Well TA102, fractures and pores developed in the gypsum-bearing micrite dolomite, with a diameter of 20 μm to several millimeters, filled with black organic matter, common thin slices, plane-polarized light; (e) At 3 743.67 m in Ma 3 Member of Well TA112, the kerogen microscopic components are mainly the amorphous sapropel, transparent thin slices, plane-polarized light; (f) At 3817.67 m in Ma 2 Member of Well TA112, marine vitrinite micrograph, reflective thin slices, plane-polarized light; (g) At 3713.18 m of Well TAO112, fine-crystalline dolomite, intercrystalline pores, cast thin slices, plane-polarized light; (h) At 3964.55 m of Well SH367, dissolved cavities, core photos; (i) At 3509.82 m of Well TA112, coarse powder crystalline structure, dolomite is self-shaped rhombus with semi-filled micro-fractures, cast thin slices, plane-polarized light.