Hydrocarbon Accumulation Periods Of Mesozoic-Paleozoic Reservoirs In Dagang Exploration Area

The hydrocarbon source-stage analysis method,reservoir asphalt analysis and fluid inclusion technology are used to study the hydrocarbon accumulation period of the Mesozoic and Paleozoic reservoirs in Dagang exploration area systematically,The evolution law of reservoir-forming period is summarized and the differences of hydrocarbon accumulation period in different regions and strata are both analyzed.The study area mainly develops three major source rocks:C-P,Ek2 and Es3.There are three main stages of hydrocarbon generation: Early Triassic-Middle Triassic,Early Jurassic-Early Cretaceous and Late Paleogene-Present.The main hydrocarbon-generating periods of C-P source rocks in the north are Early Triassic-Middle Triassic and Guantao deposition periodQuaternary,the main hydrocarbon-generating period of the Es3 is from Shahejie deposition period-Quaternary,the main hydrocarbon-generating periods of C-P source rocks in the south are Early Jurassic-Early Cretaceous and Late Paleogene-present,and the main hydrocarbongenerating period of the Ek2 is from Late Paleogene to Quaternary.The study area developed three kinds of reservoir asphalts including carbonaceous bitumen,bitumenene bitumen and oily bitumen.The general development of oily bitumen indicates that late period of hydrocarbon have been filled in the whole area.Bitumenene bitumen and carbonaceous bitumen have undergone secondary modifications such as biodegradation and oxidation.Combined with the tectonic evolution history and hydrocarbon generation history of the study area,it is speculated that the northern part of the study area was filled with hydrocarbon before the mid-Jurassic period,and the southern part of the area was filled with hydrocarbon before the Late Cretaceous.There are both two stages of hydrocarbon inclusions in the north and south of the study area.The first stage of the northern part of the inclusions is yellow-brown fluorescence,mainly distributed on the surface of quartz particles and calcite veins.The uniform temperature range is 75?80 °C,the second phase inclusions include yellow,blue-green fluorescence,which are distributed in the fractures within quartz grains,fractures through quartz grains and calcite veins.The temperature peak ranges of them are 85?90°C and 95?100°C respectively.The first period of yellow and yellow-green fluorescent inclusions in the south are mainly distributed on the surface and fractures within quartz grains,with peak temperatures of 90?110 °C and100?110 °C;late period of yellow fluorescent inclusions are distributed in the fractures within quartz grains,of which the peak temperature is 110?120°C,and the green-blue-green fluorescent inclusions are distributed in the fractures within quartz grains and fractures through quartz grains,of which the peak temperature is 130?140°C.Combining with the burial history of reservoirs,it is determined that there are three hydrocarbon accumulation periods in the study area: Middle Triassic,Middle Jurassic-Early Cretaceous,Neogene-Quaternary,and the third period was the major stage.A systematic analysis of the accumulation period and differences of different regions and different strata in the study area is carried out.On the plane,the first period of accumulation is mainly distributed in the northern area of the study area,including buried hills such as Beidagang,Qibei and Koucun.The second period of accumulation is mainly distributed in the southern part of the study area,including Wumaying.Wang Guantun and other buried hills,the third period distributed in the whole area.On vertical,the study area have a characteristic of single-period in upper strata and multi-period in lower strata.The third period is the single period occurrred in Mesozoic reservior,while the Paleozoic reservior mainly including two periods,among which the Ordovician reservoir in the middle of the study area have three periods of hydrocabon accumulation.