| The main body of the Papuan Basin is located in Papuan New Guinea and adjacent to the Australian sea area.It is structurally located at the junction of the Australian plate,the Pacific plate and the Philippine plate and generally distributed in the northwest-southeast direction.It is a large Mesozoic-Cenozoic superimposed basin which develops on the pre-Mesozoic basement and is the only oil-gas producing basin in Papuan New Guinea as well.There are abundant oil and gas resources in the basin,however,the current level of exploration in the basin is relatively low,but with great potential.In the early exploration process,though preliminary research on stratigraphic,tectonic,sedimentary,reservoir and hydrocarbon accumulation conditions have been made,and have obtained some relevant achievements and knowledge.However,with the gradual deepening of exploration,the continuous application of new theories,new methods,and new technologies,as well as the continuous improvement of people's understanding,many geological problems need to be further studied.In this paper,on the base of the research results of tectonic evolution and sedimentary background,the evolution process of hydrocarbon-generation of main source rocks is studied through the simulation of hydrocarbon-generation of respective well.Taking geochemical analysis as the core,the types of crude oil are classified;Based on the stability of the unique carbon skeleton of biomarkers and the complex "fingerprints" characteristics,oil-gas-source correlation is made to clarify the hydrocarbon origin in Papuan area,and taking this as a guide,the migration process of oil and gas is briefly analyzed with the aid of simulation of hydrocarbon migration path and other achievements.Hence,these basic geological problems,such as where oil and gas coming from and where to go,are expounded.The main results of this thesis are as follows:(1)There are many types of depositional systems of Mesozoic in Papuan Basin,among which the reservoirs are mainly developed in delta sedimentary system,while offshore and neritic-bathyal sedimentary facies are favorable facies belts for source rock development.The tpyes of source rocks can be divided into marine-terrestrial source rocks,marine-endogenous source rocks and mixed source rocks.The Jurassic source rocks in Papuan fold belt are mixed source rocks,while in Fly platform are mainly mixed source rocks with terrestrial plants inputing and in Papuan Bay are typically terrigenous inputs;In Cretaceous,littoral-neritic argillutite is developed in weak reducing environments,the source rocks in Papuan fold belt are dominated by mixed source rocks,while in Papua Bay,terrestrial plant supply is dominant.The Cenozoic in the eastern basin mainly develops littoral-neritic argillutite belonging to mixed source rocks,which has hydrocarbon-generation potential at some degree,while marine endogenous neritic limestones are developed with low content of shale in the western basin which have limited hydrocarbon-generation potential.(2)The simulation results of single well hydrocarbon-generation show that the closer to the hydrocarbon-generating center on the plane,the higher evolution degree,and source rocks in structural high are generally late maturing.The mature centers of Mesozoic are located in the middle of Papuan fold belt as well as Wabula and Aure sag,moreover,the fore trough of Aure fold belt has been in the mature center in Cenozoic.The Middle and Lower Jurassic began to mature in Late Cretaceous,and a large amount of hydrocarbons were generated before the basin uplifting in late Cretaceous.As strata generally uplifted and denuded,hydrocarbon-generation stagnated,until Miocene with the basin re-subsiding,these source rocks entered the oil-producing windows once again.At the end of Miocene,source rocks generally matured and entered the windows of vitality up to now.During Miocene,the Upper Jurassic source rocks in the Papuan fold belt and the northern Papuan Bay have matured;The Cretaceous source rocks matured later with smaller range,and the mature centers migrated to the northwest compared to the Jurassic.(3)According to the characteristics of normal paraffin hydrocarbons "gas chromatographic fingerprints",isoprenoid alkanes,steride-terpane series fingerprints curve and stable carbon isotopes,the crude oil in Papuan Basin can be divided into three types: A,B and C.The A-type crude oil is mainly distributed in the upper Jurassic and Cretaceous reservoirs of middle-western Papuan fold belt,as well as the upper Jurassic in the northern Fly platform,which is mainly supplied by the local underlying Jurassic mature source rocks,while a small part of organic matters of A-type oil in the Miocene of the eastern Papuan fold belt comes from local Cretaceous source rocks.The B-type crude oil distributes mainly in the Miocene reservoirs in the eastern Papuan fold belt,whose main sources of organic matters are local Cretaceous source rocks at some degree of the contribution of underlying Jurassic source rocks.However,the B-type oil in the Cretaceous in the middle-western Papuan fold belt was mostly self-generating and self-storing,while the organic matters of the B-type crude oil in the southern ramp of Fly platform originate from underlying middle and lower Jurassic source rocks with higher maturity.The C-type crude oil is centralized distributing in the Neogene reservoirs in the intersection area of the Wabuda Sag,Torres Shelf and Aure sag,which is supplied by the mature source rocks of the Neogene in Papuan Bay.(4)Natural gas in the Papuan Basin is organic gas,including coaliferous gas and oil-type gas.According to the maturity evolution stages,it can be further divided into mature gas,condensate gas,pyrolysis gas and biogas.Mature gas and high mature condensate gas are distributed throughout the Papuan fold belt,mainly derived from the local Jurassic source rocks with higher maturity,it isn't ruling out the contribution of the Cretaceous humic kerogen in the eastern fold belt;It is dominated by mature gas in northern Fly platform,with partially overmature pyrolysis gas in Omati graben,presumed that it is mainly formed by the initial pyrolysis of the local higher-maturity middle and lower Jurassic source rocks.The biogas is dominantly distributed in the junction of the northern Torres shelf and Aure sag,the biogas of ASF 1 is supplied by the Pliocene premature source rocks,while that of OHP 1 is mainly originated from the Miocene premature source rock with the contributions of the Pliocene source rocks draping above the reefs.(5)The Papuan Basin is generally dominated by atmospheric pressure with unsmooth exchange of formation water and weak Hydrodynamic force,the migration dynamic of oil and gas is mainly buoyance,and the long-term successive uplifts or slopes around the hydrocarbon-generating stoves in the basin are favorable directions for hydrocarbon migration. |
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