陇东地区前侏罗纪古地貌及油藏成藏规律研究

Research on Palaeogeomorphic Features of Pre-Jurassic and Accumulation Regularity of Oil Reservoir in the Area of Eastern Gansu,Ordos Basin

陇东地区以往对油气地质方面的研究多聚焦于三叠系,侏罗系的研究相对比较零散,缺乏整体性、系统性;限于当时的基础资料、研究目的及认识,研究的精度和深度有一定的局限性,精细地质刻画及与生产实践的结合程度较低。对陇东地区古地貌特征和成藏规律的研究,作为对全盆地地质资料的补充和佐证,无疑具有其必然性和必要性。本文采用残留厚度和补偿厚度印模法及沉积地质综合方法恢复出陇东地区前侏罗纪古地貌形态,并首次做出其三维模拟还原图;依据已探明油藏空间分布,结合地貌形态、成藏条件等分析,总结出研究区古地貌油藏六种成藏模式。勘探实践证实,古地貌油藏受控因素多,古地貌形态特征仅仅是受控因素之一。

In previous achievements,depositional system,paleogeomorphology,geological evolutionary and sedimentary characteristics of Ordos basin has been quite clearly recognized.However,the research precision and depth in local area still has certain limitation.As geological data＇s supplement and corroborative evidence of Ordos basin,the research on precise depiction of geological features,sedimentary characteristics as well as their matching relationship with practical production in local area,undoubtedly,has its necessity and inevitability.Most of the previous researches on petroleum geology in the eastern Gansu were focused on Triassic,and the research on Jurassic is few,scatter,and lacking of integration and systematicness.The petroleum exploration history on Jurassic went through three stages：most of the achievements are mainly on regional geological surveying,researches on Jurassic are few（before 1970s）;Several oil fields of Jurassic,such as Maling,Yuancheng,were successively founded in study area,and Fuxian Formation,Yan＇an Formation of Jurassic become the major explorative horizon（form 1970 to 2000）;New oil reservoirs of Y10,Y9 and Y8 member of Yan＇an Formation are founded continuously in local regional（from 2000 to now） .In the past few years,exploration practice indicated that Y10 and Y9 members are the main oil-bearing layer of Yan＇an Formation,owning great resource potential.Paleogeomorphic form is the basic factor of Y8-Y10 oil reservoir.In view of petroleum accumulation of Jurassic controlled by paleogeomorphic forms,this paper will rebuild the paleogeomorphic formwork of pre-Jurassic,and first make up the 3D simulation restored maps,which are based on geological analysis（such as sedimentary background,tectonic setting）,changing tendency of sand layer thickness and formation thickness of each members（especially the formation thickness of Y10 Formation）,calculating key parameters（such as ancient landform evaluation difference,slope gradient,paleocurrent direction）,combining with seismic data and so on,adopting remnant thickness-compensation cast and synthesis method of sedimentary geology.First,according to the stratum development features,five paleogeomorphic units are divided：erosion valley,paleo-upland,paleo-slope,paleo-terrace,interchannel mound.There are three paleo-uplands,four ancient rivers,six interchannel mounds and one platform in eastern Gansu area.Between paleo-uplands and ancient rivers,there are slopes and terraces from high to low in order,which are strictly controlled sedimentary facies and compaction-drape tectonic of Fuxian formation and lower Yan＇an formation.Second,according to spatial distribution of oil reservoir already founded and combined with analysis of paleogeomorphic features and reservoir forming conditions,six paleogeomorphic reservoir models are summed up in the study area：edge of deep dissection valley-delta front,edge of deep dissection valley-delta plain,ancient valley-delta plain,paleo-terrace-delta plain,paleo-upland-delta plain,and interchannel mound-delta plain combination models.Exploration practices shows that formation conditions are very complicated,which is controlled by many factors,and paleogeomorphic features is only one of the important factors.