Developmental Characteristics Of Pyrite And Its Influence On Reservoirs In Third Member Of Shahejie Formation In North Area Of Dongpu Depression

This thesis focuses on pyrites developed in reservoirs of the third section of Shahejie Formation(Es3)in the north part of Dongpu Depression.Using the observation and description of cores and casting thin sections,along with well logging data,well testing data,and other useful data,combined with former research results,this thesis studies the classifying feature and forming process of pyrite,the influence factors of pyrite development,and the relationship between pyrite and reservoir in Es3 of the study area.According to the study,pyrites in Es3 of the study area have the following characteristics:(1)the content of pyrites in reservoirs is very low,usually around 3%,only a few samples have higher content of pyrites,while most of the samples contain pyrites less than 1%;(2)the pyrites are widely spread in reservoirs,as they developed in various regions and through the whole formation from 1500 m to 5000m;(3)by observing thin sections,it is found that pyrites are varying in shapes and sizes,according to this feature,we can classify the pyrites to 6 types,such as massive pyrite,stripe pyrite,granular pyrite,and son on;(4)based on the developmental characteristics of pyrites,combined with previous studies,the pyrites can also be classified as early pyrite and later pyrite according to their formation period,each of them has its own formation mechanism under different conditions.There are various kinds of factors to impact the development of pyrites in reservoirs.After analyzing the sedimentary and diagenesis process of Es3,it is found that the main influence factors on pyrite formation include sedimentary environments,development of salt-gypsum formation,diagenesis evolution,thermal evolution of organic matter,and development of micro-fractures.These factors function together to influence the development and distribution of pyrites by controlling the sources and environment of pyrite-forming-reactions.Through researches of diagenesis process and reservoir properties,we can study the distribution law of pyrite in reservoirs,as well as study the relationship between development of pyrite and reservoir properties.It is concluded that the vertical enrichment zones of pyrite corresponds to secondary pore developmental zones and enrichment zone of Fe-bearing carbonates.Besides,as hydrocarbon-indicating minerals,the emergence of pyrite and Fe-bearing play an indicative role in the oil-berating feature of reservoirs.On the basis of hydrocarbon filling process and diagenesis evolution stages,we establish the development pattern of pyrite in the process of reservoir digenesis evolution.