鄂尔多斯盆地东部上古生界石千峰组低压气藏特征

Characteristics of Underpressured Gas Pool in Upper Paleozoic Shiqianfeng Formation of Eastern Ordos Basin

鄂尔多斯盆地的气源主要来自于山西组 -太原组的海陆交互相煤系地层 ,上石盒子组沉积了一套巨厚的泥岩 ,具有很强的封盖能力 ,天然气很难穿层运移 .近年来 ,相继在盆地东部的石千峰组地层中发现了一系列次生气藏 ,其形成机理逐步引起了勘探家的关注 .根据次生气藏的特点 ,结合包裹体测试计算 ,认为其形成原因主要是由于下部超压地层进行超压释放 ,从而在区域性盖层内部形成一系列泄压通道 ,原生气藏泄漏而形成的 .形成过程主要经历了下部高温高压原生气藏的形成、原生气藏泄压与次生气藏的形成、次生气藏的长时间调整 3个阶段 .

The gas source in Ordos basin mainly comes from the alternate marine-continental coal-bearing measures of Shanxi and Taiyuan formations. The Upper Shihezi Formation with a vast thick mudstone layer can be taken as a very good seal, so it is difficult for natural gas to pass through. Recently, some secondary gas pools have been found in Shiqianfeng Formation lying above the Upper Shihezi Formation in eastern Ordos basin. In this paper, according to the properties of secondary gas pools and the inclusion data, the secondary gas pools are thought to be formed due to the leakage of the original gas pools penetrating through the regional caprock when the overpressures within lower overpressured strata release. The forming process of gas reservoirs includes three stages, that is, the formation of the primary gas pools with high temperature and high pressure, the leakage of the primary gas pools and the formation of the secondary gas pools, and late adjustment and maintenance of the secondary pools.