鄂尔多斯宁县-正宁地区上古生界盒8段天然气成藏特征及主控因素

鄂尔多斯宁县-正宁地区上古生界石盒子组盒₈段天然气展示了良好的勘探前景,但有效储层单层厚度薄、横向变化快,其天然气成藏特征和富集规律尚不清楚,严重制约了该区天然气勘探开发。为此,通过对研究区气藏生、储、盖、圈、运等成藏条件综合分析,总结其成藏特征和富集规律,筛选了气层敏感的测井曲线,结合储层岩性和物性特征,建立了研究区盒₈段气藏有效储层划分标准,在此基础上运用三维地震资料开展有效储层预测。结果表明:二叠系煤系烃源岩广覆式分布,处于高—过成熟阶段,为天然气成藏提供了良好的气源条件;盒₈段辫状河三角洲前缘分支河道砂岩近南北向条带状大规模展布,岩性主要为岩屑石英砂岩,次为石英砂岩,形成了天然气藏的有效储集砂体;盒₈段优势储层与下伏有效烃源岩形成“下生上储 ”型近源成藏组合,形成大面积展布的致密砂岩岩性气藏。近源有利砂体优先成藏,气藏分布及含气丰度受有效砂体展布、储层物性及通源断层控制。通过该研究落实了区内盒₈段有效储层分布,为该区域天然气下步勘探目标优选提供了依据。

Accumulation Characteristics and Main Controlling Factors of Natural Gas in the He8 Member of the Upper Paleozoic in the Ningxian-Zhengning Area,Ordos

The natural gas in the He₈ Member of the Upper Paleozoic Shihezi Formation in the Ningxian-Zhengning Area, Ordos shows a good prospect for exploration, but the single-layer thickness of the effective reservoir is thin and the lateral change is rapid, and its natural gas accumulation characteristics and enrichment law are still unclear, which seriously restricts the natural gas exploration and development in this area. To this end, through a comprehensive analysis of the accumulation conditions of gas reservoirs in the study area, such as source bed, reservoir, caprock, trap, and migration, the accumulation characteristics and enrichment laws are summarized, and the gas layer-sensitive logging curves are screened. Combined with the lithology and physical properties of the reservoir, the effective reservoir division standard of the gas reservoir in the He₈ Member of the study area is established, and on this basis, the effective reservoir prediction is carried out by using 3D seismic data. The result shows: The Permian coal-measure source rocks are widely distributed and are in the high-to-over-mature stage, providing good gas source conditions for natural gas accumulation; the branched channel sandstone at the braided river delta front of the He₈ member is distributed in large-scale stripes in the near north-south direction, the lithology is mainly detrital quartz sandstone, followed by quartz sandstone, forming an effective reservoir sand body for natural gas reservoirs; the dominant reservoir in the He₈ Member and the underlying effective source rock form "lower source and upper reservoir" type near-source accumulation assemblages, generating widely distributed tight sandstone lithologic gas reservoirs. The near-source favorable sand body is preferred for accumulation, and the distribution of gas reservoirs and gas abundance are controlled by the distribution of effective sand bodies, the physical properties of the reservoir and the faults leading to the source. Through this study, the distribution of effective reservoirs in the He₈ Member in the area has been identified, which provides a basis for the optimization of the next natural gas exploration targets in this area.