鄂尔多斯盆地延长组长8油层组沉积及其演化特征

鄂尔多斯盆地三叠系延长组长8油层组是盆地西南、西北地区的主力产油层,近年来,随着勘探向湖盆中心推进,在湖盆中部长8油层组勘探也取得较大的突破。但是对长8油层组的沉积特征认识不足,制约了勘探部署。通过对长8油层组的物源分析,结合其层序地层演化规律,对长81油层和长82油层沉积特征、沉积相类型及其沉积相演化进行了研究,认为长8油层组主要发育东北、西北、西部和西南4大沉积体系,明确了汇水区的展布范围为甘泉-吴起-白豹-黄陵一带;建立了长82油层滨浅湖滩坝沉积模式和长81油层三角洲沉积模式;通过分析湖平面的变化对湖岸线迁移带的控制,认为长82油层和长81油层之间存在沉积体系转换面,解释了长8油层组沉积中期广泛发育煤层、煤线及植物根系的原因。

Sedimentation and Evolution Features in Chang 8 Reservoir of Yanchang Formation in Ordos Basin

Chang 8 reservoir of Yanchang Formation was the main reservoir in the southwest and northwest areas of Ordos Basin.In recent years,with the exploration extended to the center of lake basin,the exploration of Chang 8 reservoir has been breakthrough,but its sedimentary features was recognized insufficiently,therefore its exploration was limited.Through analysis of provenance in Chang 8 reservoir and in combination with the evolutionary rules of sequence stratigraphy,the depositional characteristics,its facies type and facies evolution of Chang 82 and Chang 81 reservoirs were studied.It was considered that four depositional systems were developed in Chang 8 reservoir,such as northeast,northwest,west and southwest depositional systems.It was clarified that water distribution and collection area was Ganquan-Wuqi-Baibao-Huangling Area.The depositional patterns of Chang 82 beach sandbar reservoir and Chang 81 delta deposit are established.By analyzing the control factors of lake surface changes on the transferring belt of lake shorelind,it is considered that the depositional system transform exists between Chang 81 and Chang 82 reservoirs,it presents the reasons of wide range of coal bed,coal seam and plant root system in Chang 8 reservoir.