RESEARCH TO THE NATURAL GAS INCLUSIONS CONTAINED IN CALCITE VEIN FILLED IN A BIG FAULT BELT ACROSS THE MIDDLE OF ORDOS BASIN

Himalayan tectonic movement has significant influence on the geology evolution and the oil-gas reservoir formation in the Ordos Basin.Large numbers of natural gas inclusions were found in the calcite vein filled in the structure joint and the fractures in the area of Triassic outcrop near the south margin of Mizi big natural gas field in the Eastern Ordos Basin.Analysis results shown that the organic inclusions formed at the temperature of 130～140℃ with H₂S of 21.1% and total gaseous hydrocarbon of 78.9% including C₄ of 51.8%.The organic matter of the natural gas inclusions is mainly saturated hydrocarbon of C₁₉-C₂₇ with the even carbon dominance.It is proposed that natural gas of the inclusions came from the carbonate source rock,which is also the main source rock of the Mizi big natural gas field.It is indicated that the natural gas inclusion was the marker of the natural gas migration from the Paleozoic gas reservoir through the structure joint and the fracture due to the Himalayan tectonic movement.