Lithofacies Characteristics And Sweet Spots Analysis Of Fine-grained Sedimentary Rocks Of The Third Member Of The Shanhejie Formation In The Banqiao-binhai Slope Area

Wide distribution,huge thickness and abundant of organic matter are the main characteristics of the fine-grained sedimentary rock in the second and first sub-member of the third member of Shahejie formation in Banqiao-Silty Binhai Slope area,which has obtained industrial oil(gas)flow and showed a great potential for the exploration of oil and gas.Guided by sedimentology,geochemistry and reservoir geology,the study makes full use of regional geological data,core observation,logging data and abundant testing data to study the characteristic of the lithofacies assemblages and its distribution,as well as the characteristics of source rock and reservoir,in the meanwhile,the study ais to find the favourable assemblage and predicts the sweet spot.Based on core observation,X-ray diffraction analysis,thin section analysis,according to lithology and sedimentary structure,the lithofacies in the study area are studied.Six kinds of fine-grained sedimentary rock lithofacies and one kind of sandstone lithofacies are diidentified,which are laminated mudstone,thick lamellar mudstone,massive mudstone,thick lamellar silty mudstone,thick lamellar argillaceous siltstone and deformed structural fine-grained mix sedimentary rocks and fine sandstone.According to the vertical development characteristic of the lithofacies,four types of lithofacies assemblages and their characteristics are summaried in the study.Lithofacies assemblage 1: laminated mudstone-thick lamellar mudstone;assemblage2: thick lamellar silty mudstone with thick lamellar argillaceous siltstone;assemblage 3: thick lamellar argillaceous siltstone with thick lamellar silty mudstone;assemblage 4: thick lamellar argillaceous siltstone-thick lamellar silty mudstone-massive mudstone.The well connection contrasts show that the mian deposits is fan delta front in the 3th submember of the third of the shahejie formation,the fine-grained sedimentary rock is deposited in the second and the earlier first sub-member of the third of the shahejie formation,when the main deposit is lithofacies assemblage 1 and 2.And the development of fine-grained sedimentary rock is reduced obviously in the late of the first sub-member of the third of the shahejie formation,and the fan delta front and submarine fan was deposited in this period.On the plane,the fine-grained sedimentary rock is mainly developed in the central and southern parts of the area,which is distributed in a ring.The ring is can be divided into three ring zones.The main lithofacies assemblage in the inner zone is assemblage 1,in the middle zone the main lithofacies assemblage is assemblage 2,and in the outer zone the main lithofacies assemblage is assemblage 3.Based on the abundance,type and maturity of organic matter in fine-grained sedimentary rocks by the methods of rock pyrolysis and vitrinite reflectance,the assemblage 1 is considered as the favorable hydrocarbon generative lithofacies assemblage.Based on the porosity,permeability,types of reservoir space,pore structure and pore size by the methods of porositypermeability test,SEM,low-temperature nitrogen adsorption experiment,and carbon dioxide adsorption experiment,the assemblage 1 and fine sandstone lithofacies are considered as the favorable reservoir lithofacies assemblage.the assemblage 3 and fine sandstone lithofacies are considered as the favorable fracturing lithofacies assemblage by calculating brittleness index.Based on above research and combining the thickness and distribution range of lithofacies assemblage,assemblage 1 is considered as the favorable lithofacies assemblage.The sweet spots are in the inner ring zones,which located in the center of the basin.