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

Table 1. Composition and isotopic compositions of the gases in Ordovician deep sub-salt.

Well No. Horizon Gas components /% Dryness Coefficient δ13C /‰ C1 C2 C3 iC4 nC4 CO2 N2 Hydrocarbon content C1 C2 C3 LT1 Ma 57 96.871 1.794 0.280 0.146 0.070 0.067 0.665 99.268 0.976 -39.30 -23.80 -19.70 TG74 Ma 57 88.636 0.764 0.118 0.820 8.310 89.518 0.989 -40.08 -29.72 -21.16 MI104 Ma 4 97.708 1.027 0.286 0.121 0.068 0.267 0.221 99.210 0.985 -42.26 -25.38 TG51 Ma 4 87.565 2.356 0.612 0.271 0.132 8.869 91.131 0.961 -42.10 -26.20 TG52 Ma 4 92.116 4.558 0.895 0.148 1.270 98.571 0.935 -41.70 -25.80 -24.60 TA36 Ma 4 82.241 0.037 0.004 0.001 0.001 11.491 6.224 82.284 0.999 -37.29 -33.03 -25.80 TA37 Ma 4 88.053 0.082 0.010 0.005 0.003 6.167 5.674 88.159 0.999 -38.20 -30.71 -20.00 TA90 Ma 3 97.861 1.329 0.182 0.054 0.030 0.200 0.326 99.474 0.984 -40.50 -29.20 -24.10 TA59 Ma 4 40.244 0.095 0.035 0.005 0.017 2.954 56.592 40.454 0.995 -38.45 MT1 Ma 4 93.265 3.077 0.967 0.526 0.305 0.516 0.864 98.599 0.947 -45.09 -26.03 -24.28 LT2 Ma 3 7.310 0.070 0.010 92.601 0.009 7.390 0.989