鄂尔多斯盆地苏里格气田上古生界气藏充注动力计算方法

鄂尔多斯盆地苏里格气田上古生界气藏含气特征复杂,开发难度大。为此,从充注动力的角度分析了不同区带、不同层位成藏充注动力的差异性及其对该区气藏含气性的控制作用。首先根据该区上古生界气藏的地质特征,建立了气田的充注成藏模式,认为充注动力的主要类型为源储流体势差,其成因为烃源岩生烃增压产生的流体过剩压力;在此基础上采用泥岩压实的方法计算了成藏期烃源岩与储层的流体过剩压力和压差。计算结果表明:烃源岩的流体过剩压力介于13.0~22.0 MPa,源储之间的流体过剩压差介于3.5~9.5 MPa,流体过剩压力从烃源岩向储层或更外围地层整体呈逐渐减小的趋势。进一步将典型井烃源岩产生的流体过剩压力、源储压差与区域的生烃强度相比较,发现区域生烃强度越高,则流体过剩压力与压差就越大,表明成藏期的充注动力越强劲。结论认为:充注动力对该区气藏的含气性具有重要的控制作用,在储层物性、烃源岩与储层配置条件基本相当的条件下,充注动力越大,则储层含气饱和度越高。

A calculation method for the charging dynamics of Upper Paleozoic gas reservoirs in the Sulige Gas Field,Ordos Basin

In the Sulige Gas Field, Ordos Basin, the Upper Paleozoic gas reservoirs are difficult to develop due to their complicated gas-bearing features. In this paper, a series of analysis was made on the difference of charging dynamics during hydrocarbon accumulation at different zones and horizons and its controlling effects on the gas-bearing potential of gas reservoirs in this area. Firstly, the hydrocarbon charging and accumulation mode of the Sulige Gas Field was established based on the geological features of the Upper Paleozoic gas reservoirs. It is indicated that the charging dynamics is mainly derived from source–reservoir fluid potential difference, which is produced by the liquid excess pressure due to the pressure increase during the hydrocarbon generation of source rocks. Secondly, the liquid excess pressure of source rocks and reservoirs during hydrocarbon accumulation and their difference were calculated by means of shale compaction. According to the calculation results, fluid excess pressure of source rocks is 13–22 MPa and fluid excess pressure difference between source rocks and reservoirs is about 3.5–9.5 MPa. Besides, fluid excess pressure, on the whole, decreases gradually from source rocks to reservoirs or to the farther layers. And thirdly, the relation between the regional hydrocarbon-generating intensity and the fluid excess pressure and source–reservoir pressure difference caused by source rocks in the typical wells was analyzed. It is indicated that the greater the hydrocarbon-generating intensity is, the higher the fluid excess pressure and the larger the pressure difference. Correspondingly, the charging dynamics during hydrocarbon accumulation is stronger. To sum up, charging dynamics plays an important role in controlling the gas-bearing potential of gas reservoirs in this area. Given basically similar reservoir properties and source–reservoir assemblage, the stronger the charging dynamics, the higher the gas saturation.