鄂尔多斯盆地延安地区本溪组高分辨率层序地层与沉积特征

High-resolution sequence stratigraphy and sedimentary characteristics of Benxi Formation in Yan’an area of Ordos Basin

鄂尔多斯盆地延安地区油气资源储藏丰富,本溪组是重要的勘探层段之一,但其沉积环境复杂,砂体分布及沉积演化特征不明确,制约了该地区天然气勘探开发的进程。因此,加强对延安地区本溪组地质学方面的研究,尤其是层序地层、沉积特征及演化的研究,将对该地区的古地理重建、油气勘探及开发提供有利的理论支撑。以高分辨率层序地层学、沉积岩石学、测井地质学和沉积学为理论指导,研究了鄂尔多斯盆地延安地区晚古生代本溪组的地层和沉积特征,确定了其层序地层单元划分、等时地层格架、沉积相类型及演化过程。研究结果表明,在层序地层方面,本溪组内可以识别出1个长期基准面旋回、2个中期基准面旋回和多个短期旋回;在沉积相类型方面,识别出12种岩石类型和7种岩相组合,据此认为延安地区本溪组发育潮坪和障壁岛—潟湖沉积相,进而识别出潮道、砂坪、混合坪、泥坪、泥炭坪、障壁岛砂坝、潟湖泥等沉积微相;在沉积相展布方面,研究区西南部和南部以潮坪沉积为主,东北部和北部以障壁岛—潟湖沉积为主,本1段和本2段的沉积格局基本一致。

The oil and gas resources in Yan’an area of Ordos Basin are abundant,and Benxi Formation is one of the important exploration intervals.However,its sedimentary environment is complex,and the distribution of sand bodies and sedimentary evolution characteristics are not clear,which restricts the process of natural gas exploration and development in this area.Therefore,strengthening the study of geology of Benxi Formation in Yan’an area,especially the study of sequence stratigraphy,sedimentary characteristics and evolution,will provide favorable theoretical support for paleogeographic reconstruction,oil and gas exploration and development in this area.Based on the theories of high-resolution sequence stratigraphy,sedimentary petrology,logging geology and sedimentology,the stratigraphic and sedimentary characteristics of the late Paleozoic Benxi Formation in Yan’an area of Ordos Basin were studied,and the sequence stratigraphic unit division,isochronous stratigraphic framework,sedimentary facies types and evolution process were determined.The results show that in terms of sequence stratigraphy,one long-term base-level cycle,two medium-term base-level cycles and multiple short-term cycles can be identified in Benxi Formation.In terms of sedimentary facies types,12 types of lithofacies and 7 lithofacies combinations were identified.According to this,it is considered that tidal flat and barrier island-lagoon sedimentary facies were developed in Benxi Formation in Yan’an area,and sedimentary microfacies such as tidal channel,sand flat,mixed flat,mud flat,peat flat,barrier island and lagoon sediments were identified.In terms of sedimentary facies distribution,tidal flat deposits are mainly developed in the southwest and south,and barrier island-lagoon deposits are mainly developed in the northeast and north.The sedimentary patterns of Ben 1 section and Ben 2 section are basically consistent.