鄂尔多斯盆地神木—米脂地区上古生界天然气藏压力分布特征

Pressure distribution in upper Paleozoic gas reservoirs in Shenmu-Mizhi area of Ordos Basin

统计鄂尔多斯盆地上古生界90余口钻井140多个含气层位压力测试数据,通过压力系数频数统计综合分析研究区上古生界不同含气层段的压力分布特征。研究表明:上古生界天然气藏压力随层位变浅而降低,同一气层体系内部由南向北压力逐渐降低。结合烃源岩演化、天然气组分对比、成藏与构造运动的时间耦合关系,综合分析认为:原生气藏于早白垩末期形成,烃供应不足初步造成两区块压力南北分异;q5次生气藏于晚白垩世形成,构造运动使神木地区原生气藏垂向泄露形成q5超低压次生气藏,也导致了气藏后期的调整逸散,进一步扩大了其与米脂地区原生气藏的压力差。

Statistics of pressure test data of over 140 gas-bearing horizons from more than 90 wells drilled in the upper Paleozoic of Ordos Basin have been analyzed through pressure coefficient frequency to manifest pressure distribution in different Paleozoic intervals.The study shows that the pressure of the Paleozoic gas reservoirs decreases with depth becoming shallower,and decreases gradually from south to north within a same gas-bearing system.Comprehensive analysis of source rock evolution,gas composition correlation,and the time coupling relation between gas accumulation and tectonic movement indicates that the primary gas pool was formed in the end of early Cretaceous,and insufficient gas supply had resulted in pressure differentiation in Shenmu and Mizhi area;the q5 secondary gas pool with extra low pressure was formed in late Cretaceous by vertical leaking from the primary gas pool in Shenmu area due to tectonic movement,which also resulted in later gas effusion and dissipation,further amplified the pressure difference contrasting to the primary gas pool in Mizhi area.