鄂尔多斯盆地南部富县地区三叠系延长组长8油层组油气成藏期次与时限

Abstract

多旋回叠合盆地的油气成藏期次与时限研究是成藏地质学研究热点及前缘领域。鄂尔多斯盆地延长组长8油层组作为深层油气勘探的重点层位，其成藏期次与时限鲜有报道。根据含油气砂岩样品的包裹体薄片岩相学与荧光分析分析，研究区存在两期不同产状的烃类流体包裹体(FI)，第一期烃类FI呈带状分布在石英加大边、石英矿物早期裂缝中，显示褐色或浅绿色荧光；第二期烃类FI分布在切穿石英及其加大边裂缝，或晚期方解石胶结物，显示浅黄色或黄绿色荧光。根据与烃类FI同期的盐水FI均一温度的测试分析，早期FI均一温度分布在85℃~135℃，峰值接近105℃；晚期分布在135℃~155℃，峰值接近145℃。结合构造热演化史，该区存在两期幕式充注成藏过程，主要成藏时限为164 Ma和 127 Ma。为盆地延长组油气成藏机理及过程研究提供了新认识。 Timing and stages of oil-gas accumulation (OGA) are hot spots and key frontier for petroleum accumulation geology in multi-cycle superimposed basin. As the important deep oil-gas reservoir of exploration, timing and stages of OGA of Chang 8 member of Yanchang formation in Ordos Basin are rarely reported. According to the lithofacies and fluorescence analysis of hydrocarbon fluid inclusions (FI) from sandstone samples, there are two different occurrence fluid inclusions for Chang 8 member of Yanchang formation in the study area. The first occurrence of hydrocarbon FI is banded in the quartz plus side, quartz mineral early cracks, showing brown or light green fluorescence. The second occurrence of the hydrocarbon FI is distributed in the cut-off quartz and its increased fissures, or late calcite cements, showing light yellow or yellowish green fluorescence. According to the test analysis of the homogeneous temperature of the salt water FI with the hydrocarbon FI, the early FI homogeneous temperature distribution is in a range of (85˚C - 135˚C) with the peak of 105˚C; the late distribution is in a range of (135˚C - 155˚C) with the peak of 145˚C. Combined with the history of tectonic thermal evolution, it reveals that the Chang 8 reservoirs went through 2-stage OGA of 164Ma and 127 Ma, which provides a new understanding for the mechanism and process of hydrocarbon accumulation in the Yanchang Formation.