Characteristic Of Basin System And Its Reservoirs Controlling Mechanism In Extensional And Compressive Cenozoic Basins

Earth system science,as a cross century frontier field of geosciences,shows the great potential to analyze the earth as an open thermodynamic system in a holistic way by using system theory.At the same time,the petroleum system has adopted the system theory to study the key problems of oil and gas accumulation and achieved effective application to guide exploration deployment.However,for many years,there is a lack of an intermediate scale geological system between the earth system and the petroleum system,and the analysis of oil and gas bearing basins has not been conducted as a whole according to the system theory.Whether the basin can be studied as an independent system as a whole,what basic subsystems does the basin contain,the macro commonness and difference of the basin subsystems,and the evolution characteristics of the subsystems are also lack of targeted research.Therefore,the study of the basic composition and evolution of the basin system,and the discussion of the macro control of the basin system on the distribution of oil and gas have an important reference role for deepening the study of the earth system and predicting the direction of oil and gas exploration in the basin in the future.In this paper,the Xihu Depression in the East China Sea Basin and the western Qaidam Basin are taken as the typical anatomical research objects.Based on a large amount of previous research work,drilling and logging data,geochemical data and a large number of seismic data are used to introduce the adaptive action,catastrophe mechanism,thermal dynamic coupling and other theories in the system theory.Through the systematic anatomy,genetic mechanism and difference analysis of the strata in the extensional and compressional basins,the analysis of fault system development characteristics and cycle superposition mode,as well as the catastrophe formation mechanism of fault system,the analysis of temperature-pressure system evolution mode,the analysis of temperature-pressure system controlling oil and gas distribution,forming a new basin system between the earth system and petroleum system,and discussing the control of basin system on oil and gas macro distribution.The paper has made the following achievements and understandings.(1)The basin system,as an independent geological system between the earth system and the petroleum system,is considered to be more reasonable and scientific and practical.It is proposed that the basin system consists of four subsystems,i.e.stratigraphic system(horizontal geological system),fault system(vertical geological system),temperature-pressure system(energy system),and petroleum system(fluid system),The interaction between them promotes the evolution of the basin and the formation,distribution and transformation of oil and gas.(2)A new definition is proposed that the stratigraphic system is a basin subsystem with vertically nested polycyclic sequences and horizontally widely distributed and heterogeneous lithofacies layers.It is considered that the adaptive cycles of base level,climate and tectonic movement control the vertical cycles of stratigraphic system.It is pointed out that the stratigraphic system has the characteristics of self-organized criticality(the thickness and its frequency of the strata conform to the negative power law),and that the self-adaptive effect is the main cause of the denudation of the high part of the basin and the deposition of the low part of the basin and the wide distribution of horizontal strata.It is found that the difference of base level cycle controls the difference of sequence thickness in extensional and compressional basin stratigraphic systems.It is found that the difference of base level cycles is the main cause of the thickness of HST in extensional basins being significantly higher than that in compressional basins.(3)It is found that three fault systems are developed in the early,middle and late Cenozoic in the Xihu Depression of the East China Sea Basin,while two fault systems are developed in the Qaidam Basin in the early,middle and late Cenozoic.Three fault cycle superposition models in the East China Sea basin are established,and four fault cycle superposition models in the Qaidam basin are divided.It is considered that fault is the product of catastrophe formation in a relatively short period of time.A generalized model of fault extension catastrophe connection is proposed to reveal the basic regular pattern of fault growth.(4)The coupling model of temperature and pressure system in the Xihu Depression of the East China Sea Basin is established.It is pointed out that both the slope belt and Santan deep sag develop high-pressure type compound temperature-pressure system,the central anticline belt develops single type temperature-pressure system,and the typical high-pressure type compound temperature-pressure system is developed in the western Qaidam Basin today.A typical evolution model of the basin is proposed,in which the early stage of the basin is a single type and the late stage of the basin is transformed into a high-pressure compound temperature-pressure system.It is found that the main location of oil and gas resources is near the transition surface between the shallow static pressure type and deep high-pressure type temperature-pressure system.It is pointed out that the deep and shallow sequence of the basin are potential areas for oil and gas exploration in the next step.