Geological characteristics and exploration of shale oil in Chang 7 Member of Triassic Yanchang Formation, Ordos Basin, NW China

FU Jinhua,LI Shixiang,NIU Xiaobing,DENG Xiuqin,ZHOU Xinping

Table 1 Types and characteristics of rocks of shale oil of Chang 7 Member, Ordos Basin.

Rock types Type of shale oil Sedimentary characteristics Main mineral components/% Physical properties Sedimentary environment Development status Quartz Feld- spar Clay Por./ % Per./ 10-3 μm2 Find sandstone Massive- stratified fine sandstone with parallel and cross beddings Class I shale oil Gray, grayish green and grayish brown, with large-scale trough, plate and wedge- shaped cross beddings. The sandstone is high in maturity and shows scouring surface 30 45 13 7.4 0.10 Underwater distributary channel and river mouth bar in delta front facies Very developed Massive fine sandstone Light gray, gray and grayish brown, with massive and graded beddings. There are angular mud gravels and "mud wrapping gravels". It is in abrupt contact with the upper and lower strata 32 43 15 8.0 0.06 Sandy clastic flow deposit and turbidite deposit in slope break zone Very developed Silt- stone Medium-thin layered siltstone with massive beddings Class II shale oil Light grayish green and grayish, with pure quality and good sorting, massive and graded beddings, and bioturbation structures 25 40 17 6.4 0.04 Distal bar and sheet sand in delta front Developed Thin-thick layered siltstone with graded beddings Dark gray and gray black, with parallel beddings and sand ripple beddings, complete or incomplete Bouma sequences 21 48 28 4.8 0.02 Turbidite sediment Very developed Blake shale Lamellar black shale Class III shale oil Organic matter is in lamina and parallel beddings 17 16 65 1.9 <0.01 Deep lake sediment Very developed Dark mudstone Massive beddings Organic laminae is in dispersion and no beddings 19 19 60 2.1 <0.01 Semi-deep to deep lake sediment Very developed Tuff Thin tuff Tuff marker bed at the bottom of Chang 7 is stably distributed. Other tuff layers are generally thin and interbedded with shale 62 27 10 Lacustrine sediment relatively developed