Accumulation Characteristics And Distributing Disciplinarian Of Deep Gas Reservoirs In Dongpu Sag

This paper analyses the geochemical characteristics of the natural gas in different blocks in deep of Dongpu Sag,such as composition characteristics,isotope characteristics,maturity characteristics etc.,makes a systematic identification of different genetic types of natural gas in different parts in Dongpu Sag and distribution characteristic of different genetic types of natural gas.the paper selects there typical deep gas reservoirs in Dongpu Sag and analyses its geological characteristics,geochemical characteristics,accumulation mechanism and model for oil and gas reservoir anatomy,and analyzes the deep natural gas reservoirs in this area into the main controlling factors of accumulation.The main achievements are as follows:Composition of hydrocarbon in natural gas changed greatly in Dongpu Sag,for a overall look,methane in natural gas content from 6.26%-99.0%.It appears minimum of average value with 46.3% in the frist member of Shahejie Formation in the entire sag,with its methane concentration range from 37.1%-56.9%.With the deepening of depth,the methane content in the 2nd to 4th member of Shahejie Formation increased significantly,reaching 96.8%,respectively,the highest,99.0%,97.1%,the average reached 60% or even higher.Meanwhile,the difference between the methane content of these intervals is also very strong,low methane content is only about 10%.From the different blocks,methane content mean lower value appears in the 4th member of Shahejie Formation of Puwei area(40.1%)and the 1st member of Shahejie Formation of Wenliu(37.1%),higher values appear in the 4th member of Shahejie Formation of Wenliu area(74.8%),the 2nd member of Shahejie Formation of Qiaobai area(81.0%)and Machang area(90.2%).The ?13C1 of natural gas of Shahejie Formation in Dongpu Sag distributed widely,range from less than-48‰ to greater than-26‰,which are mainly concentrated in-40.0‰ ~-28.0‰,the gas reservoirs whose value of ?13C1 of natural gas is lighter(less than-35‰)is mainly concentrated in the southern of Wenliu area,Pucheng area,Liuzhuang area,and Qiaokou area.On the other hand,the value of ?13C1 of natural gas which is heavier(greater than-30‰)are mainly located in the northern part of Wenliu area,Hugu2 gas field,Baimiao area and Machang area.By identification analysis of the composition-isotope characteristics of gas samples in study area,It reaches following conclusions.The natural gas in Puwei area exists oil type gas,coal-derived gas and the mixed gas of them,meanwhile,it mainly composed of oil cracking gas.The type of natural gas of Wenliu area present the phenomenon of oil type gas coexist with coal-derived gas,its oil type gas originated from both of kerogen-cracking and oil-cracking.The gas in Qiaobai area gas originated from oil type gas,coal-derived gas and the mixture,its oil type gas also originated from both of kerogen-cracking and oil-cracking.The natural gas in Machang area is typical coal-derived gas.The accumulation of deep gas reservoir in Dongpu Sag controlled mainly by hydrocarbon source rock,reservoir,caprock,faults and other factors.Quality hydrocarbon source rock is oil and gas hid formed of material based.The exhibition cloth and evolution of source rock decided the center of hydrocarbon generating,currently,the reservoir has found mostlt distribution around the center of hydrocarbon generating,which is a general law of the distribution of reservoir in this area.Most area of Dongpu Sag have quality reservoir condition,generally developed sandstone of fault basin of Paleogene is the most important of the reservoir,while,the sandstone of marine-continental facies in Upper Paleozoic is also the important part of reservoir formation of this area.The cap rock of Dongpu Sag mainly divided into two sets,respectively from the unique of salt caps developed uniquely in Northern and mudstone cap rock commonly developed in entire area.The difference of cap rock between the two of Southern and Northern,is one of the main reasons of extreme imbalance of distribution of oil and gas resources between Southern and Northern.this faults extremely developed in study area,many of them are large fault which cutting the basement,being a important feature of the accumulation characteristics of reservoirs of Dongpu Sag.So complicated fault is one of the most important part of the transport system of study area.