Genetic Types And Geophysical Response Characteristics Of Sand Bodies In The Middle Sub-member Of The Third Member Of Shahejie Formation In Xianhe Area, Dongying Sag

Deep-water gravity flow sand bodies are favorable reservoirs of hydrocarbon,being rich in oil or gas resources and playing a key role in hydrocarbon exploration and development.The deep-water gravity flow sand bodies have been extensively developed in the Middle Sub-member of the Third Member of Shahejie Formation of the Xianhe area in Dongying Sag.Because of their thin layers,small distribution range,complicated lithofacies assemblages,and less aware of genetic types and geophysical response of deep-water gravity flow sand body,the previous understanding is difficult to meet the needs of today's fine exploration.Based on these problems,the paper systematically researches the delta–gravity flow deposits in the Middle section of the Third Member of Shahejie Formation of the Xianhe area on the basis of former research results and through fully utilization of seismic,drilling,well logging and laboratory testing data.The detailed classification of gravity flow sand bodies and the geophysical response characteristics of different genetic types of sand body are identified.Then the developing characteristics and evolutional laws of sand bodies are revealed,thus providing theoretical guidance for the subsequent reservoir prediction.The main conclusions of the thesis are as follows:(1)Considering the clearly progradational configuration in delta–gravity flow deposits,the study combines seismic reflection characteristics with stratigraphic sequence characteristics of delta foreset bodies.According to the development phase of delta foreset bodies,the Middle Sub-member of the Third Member of Shahejie Formation is divided into six sand groups in Niuzhuang–Xianhe areas and is divided into four sand groups in Xianhe areas.Gravity flow sand bodies mainly develp in the 2nd and 3rd sand groups.(2)two types and six subtypes of genetic sand bodies and thirteen lithofacies types are determined for the Middle Sub-member of the Third Member of Shahejie Formation in Xianhe areas.To be specific,the sand bodies of subaquatic distributary channel,estuary dam and frontal sheet deposits belong to tractive current deposits of delta front and mainly develop in the upper of the 1st sand group.The slide-slump deposits,sandy debris flow deposits,turbidites(turbidite channel and lobes)belong to gravity flow deposits and mainly develop in the 2nd and 3rd sand groups.Besides,a large scale mass transported deposits(MTDs)is identified for the first time in the study area and it shows cliff wall,pressure ridge and anti-imbricated seismic reflection characteristics on seismic profile.(3)The seismic forward modeling experiments are conducted based on lithological association of gravity flow sand bodies,indicating that thickness of sand bodies,configuration relationship between sandstone and mudstone,mudstone interval thickness between two sand bodies and wave impedance difference are the main factors influencing seismic response characteristics of gravity flow thin-bed sand bodies.The effect of mudstone interval thickness between two sand bodies is the most significant.It points out that 35Hz~40Hz seismic data volume after frequency division processing can greatly increase the recognition precision of gravity flow sand bodies.(4)The differential development of sand bodies is a result of the coupling of sediment supply,lake level variation,synsedimentary fault and depositional topography in Xianhe areas.On the whole,with the continuous retrogradation of Dongying delta,the Middle Sub-member of the Third Member of Shahejie Formation in Xianhe areas has undergone the evolution of deep-lacustrine mudstone deposits — distributary channel and lobe of turbidites — turbidite channel deposits and sandy debris flow deposits — slide-slump deposits and delta front deposits.The detailed classification of deep-water gravity flow sand bodies is realized,and identification marks and geophysical response characteristics of different genetic types of sand body are determined.Furthermore,the developing characteristics and evolutional laws of sand bodies are revealed in the paper.The research results can provide theoretical guidance for the subsequent reservoir prediction and have certain reference significance for other similar researches.