致密气藏成藏动力及成藏模式——以鄂尔多斯盆地L区块山_1储层为例

Study on Dynamics and Models of Hydrocarbon Accumulations of Tight Sandstone Gas Reservoir:Taking Shan 1 Formation of Block L in Ordos Basin as an Example

研究区主力产气层山1储层属于致密气藏,为了摸清有效储集层的形成机制、寻找勘探开发的有利区域,应用铸体薄片、扫描电镜、核磁共振、恒速压汞等实验手段开展成藏动力及成藏模式研究。结果表明:早白垩世为天然气充注的主要成藏期,水相封存天然气分子的最小孔喉半径和天然气充注的孔喉半径下限分别为0.093μm和0.25μm,天然气充注的最大毛细管阻力为1.16MPa,流体过剩压力是致密砂岩气藏天然气运移的主要动力和阻力;天然气主要聚集在过剩压力高值背景下的低值区,山1段过剩压力小于6 MPa的区域有利于天然气的聚集,隔夹层密度越小、厚度越薄的区域含气饱和度越高;研究区天然气充注模式存在4种模式,煤层连续发育厚度大、储层整体特征优,源储层间压差大、储层顶面的隔夹层和大段较厚泥岩产生的欠压实过剩压力有利于储层段的天然气保存,成为天然气开发的"甜点"。

Shan 1 Formation in the study area belongs to tight gas reservoir. In the formation mechanism of effective reservoir, and to find the favorable area order to understand for exploration development, the authors carry out a research on the accumulation dynamics and the accumulation model through application of casting thin sections, scanning electron microscopy, nuclear magnetic resonance （NMR）, and constant speed mercury iniection experiment, etc.. The results show that： The Early Cretaceous is the main period for gas accumulation, the pore-throat radius of water sealed gas molecules is 0.093 μm,the pore-throat radius cutoff of gas filling is 0.25μm, and the maximum capillary resistance of gas filling is 1.16 MPa; The fluid overpressure in tight sandstone gas reservoir is the main force and resistance of gas migration; Natural gas is mainly gathered in a low overpressune area under high overpressure background; The area whih overpressure less than 6 MPa is advantageous for gas gathering, and the smaller the density and the thickness of isolation layers are, the higher their saturation is; There are four gas filling patterns in the study area. Coal seam with large thickness of continuous development, optimal overall characteristics of reservoir, pressure difference between source bed and reservoir, interlayer and overpressure are beneficial to preserve natural gas, which become ＂sweet spots＂ of the development of natural gas.