鄂尔多斯盆地陇东地区上古生界天然气成藏模式

Hydrocarbon Accumulation Patterns of the Upper Paleozoic Gas in the Longdong Area,Ordos Basin

主要基于鄂尔多斯盆地陇东地区上古生界天然气成藏地球化学特征、流体包裹体特征、生烃增压数值模拟等研究对天然气运移动力、运移方式和成藏过程进行了分析,建立了天然气成藏模式。研究表明,鄂尔多斯盆地陇东地区上古生界山西组山1段(P_1s_1)、石盒子组盒8段(P_2h_8)天然气除了生烃增压驱动运移外,还具有明显的扩散运移特征,且盒8段相对更加明显。石炭系—二叠系烃源岩生烃增压驱动的天然气运移距离纵向上主要到达山1段底部,扩散作用对于天然气从山1段至盒8段的运移具有重要贡献。天然气在烃源岩生烃超压和浓度梯度驱动下通过基质孔隙和裂缝运移进入山1段储层,在山1段直接盖层之下聚集形成山1段气藏,若山1段直接盖层不发育,则进一步以垂向扩散运移为主进入盒8段有利部位聚集形成盒8段气藏。

Based on the natural gas reservoir geochemical behaviors,characteristics of fluid inclusions and numerical simulation of hydrocarbon generation pressurization,the gas driving force of migration,migration style and the accumulation process of the Upper Paleozoic have been analyzed in the Longdong area of Ordos Basin,and it also established natural gas accumulation patterns.It has been conformed that the gas of the first member of Shaanxi Formation（P2s_1）and the eighth member of Xiashihezi Formation（P_2h_8is not only driven by the overpressure-driven surge flow,but also has an obvious diffusion migration characteristic.Moreover,the natural gas of P_2h_8 is more obvious.The natural gas migration distance,in vertical,mainly arrives to the bottom of P_2s_1,which phenomenon is caused by the C-P hydrocarbon generation pressurization.The diffusion migration has an important contribution to the gas migration from P_2s_1 to P_2h_8.The gas,which is the overpressure-driven by the hydrocarbon generation and diffusion-driven by the gradient of gas molecule concentration,spills into P_2s_1 reservoir through matrix porosity and fracture.It could directly accumulate and form P_2s_1 reservoirs under P_2s_1 direct caprock development,or further vertically migrate into the advantageous parts of P_2h_8 to accumulate and form gas reservoirs.