山西沁水盆地天然气封存箱成藏机理与模式

依据沁水盆地现有勘探资料及研究成果，从构造特征、地下水及天然气分布等方面出发，综合分析盆地内天然气封存箱成藏模式。盆地内水动力条件复杂，地层水可依次划分为补水带、强径流带、弱径流带、交替阻滞带及泄水带5个区带。根据地下水动力条件与地层水矿化度的关系，并结合地层水矿化度的变化趋势与盆地内地层含气量的展布特征，提出了由煤岩、泥岩等致密岩层组成的顶、底板，形成了在盆地内广泛展布的近同心圆状的“饼状”箱体模式。同时，还进一步分析了盆地内致密砂岩气的成藏机理及封闭机理，发现区内“饼状”箱体可分为上、下两层，上层为3^#煤层上部山西组致密砂岩段箱体，下层为3^#煤层与15^#煤层之间的致密砂岩段箱体。上、下封存箱封存机理虽然不同，但自盆地边缘到盆地内部，再到盆地边缘，“饼状”箱体稳定展布。

Accumulation Mechanism and Model of Natural Gas Compartment in Qinshui Basin of Shanxi,China

Based on the existing exploration data and research findings in Qinshui Basin, the accumulation model of natural gas compartment was set up by comprehensive analysis of structure characteristics, formation water composition and natural gas distribution. The hydrodynamic conditions are very complex, and the formation water can be divided into five zones in turn, including water supply zone, strong runoff zone, weak runoff zone, alternating block zone and discharge zone. According to the relationship between hydrodynamic and salinity of formation water, the change rules of formation water salinity and distribution of formation gas content were studied. Then, it is proposed that the roof and floor combined by tight formations (coal, mudstone, etc.) form the model of widely distributed and nearly concentric “discus” box. Meantime, the accumulation mechanism and sealing mechanism of tight sandstone gas in Qinshui Basin were analyzed. It is found that the “discus” box can be divided into the upper and lower layers. The upper layer is tight sandstone of Shanxi Formation above No.3 coal bed; the lower layer is tight sandstone between No.3 and No.15 coal beds. Although the sealing mechanism of upper and lower layers is different, the distribution of “discus” box is stable from the edge to the interior, then to the edge of Qinshui Basin.