Fracture development and hydrocarbon accumulation in tight sandstone reservoirs of the Paleogene Huagang Formation in the central reversal tectonic belt of the Xihu Sag, East China Sea

ZHOU Xinhuai,XU Guosheng,CUI Hengyuan,ZHANG Wu

Table 5 Dating results of 40Ar/38Ar isotopes of autogenic illite in the Xihu Sag.

Well Depth/m Layer K2O/ % 40K/ (10-7 mol·g-1) 40Ar/38Ar 38Ar/36Ar 40Ar*/ (10-10 mol·g-1) 40Ar*/40Ar/ % 40Ar*/40K Age/Ma B-2 3 699.30-3 716.20 H3 9.08 2.18 1.004 5 689.496 6 1.18 56.37 0.000 5 9.35±0.16 B-2 3 808.90-3 820.90 H3 9.15 2.19 1.051 6 779.816 8 1.45 63.05 0.000 7 11.32±0.21 B-1 3 855.00-3 861.00 H3 9.99 2.40 0.996 6 797.154 0 1.32 61.83 0.000 5 9.44±0.16 B-2 4 005.70-4 014.10 H4 9.66 2.32 1.031 3 763.412 3 1.36 61.53 0.000 6 10.05±0.19 A-2 3 597.50-3 618.10 H3 9.40 2.25 1.157 8 790.793 9 1.50 66.89 0.000 7 11.40±0.21