Petroleum Migration And Accumulation In Zhuanghai Buried Hill, Shengli Oilfield

Petroleum system theory and its successor, pool-forming dynamics, are being put more and more attention because of systematic and dynamic thoughts included. Study on petroleum inhomogeneous migration and systematic analysis of multi elements controlling petroleum migratioan and accumulation are more popular and difficult. In the meantime, petroleum system theory is gradually used to analyze the formation process of buried hill reservoirs, prospective petroleum exploration targets in Jiyang depression so much as throughout the world. On the basis of above researches, Zhuanghai Paleozoic and Archean buried hills in Shengli Oilfield are selected as research objects in this paper. In the paper, the dynamic process of petroleum migration and accumulation is rebuilt by systematically analyzing mulit elements, which is helpful to open out the law of pool-formation. All achievements in the paper could develop the theory of petroleum migration and accumulation in buried hills as well as provide academic guidances for petroleum exploration.Paleozoic and Archean traps in Zhuanghai area can capture sufficient petroleum from such peripheral depressions as Bozhong depression, Huanghekou depression, Wuhaozhuang depression and Chengbei depression,which lead to the huge petroleum reserves in buried hills. However, serious heterogeneity in reservoirs and in the process of petroleum migration and accumulation increases the risk of exploration and production.Research on the actual exploration&production state, together with geological background and static elements for reservoir formation, is the base of the whole systematic work. In this paper, with the guide of petroleum system theory, reservoirs are the core of the research, in addition, the process of petroleum migration and accumulation in Zbuanghai buried hills is rebuilt. Several kinds of methods, such as geological method, geophysical method, geochemical method and numerical analogy, are used to handle with numerous data to help the whole research. Dynamic fields favorable to petroleum migration and accumulation are rebuild qualitatively and quantitatively, including tectonic stress field, formation pressure field, geotemperature field and fluid potential field. Homogenization temperature can direct the research on periods and times of petroleum migration and accumulation, which is one important part of the paper. According to the configuration of static elements and dynamic processes, effective passage systems, effective migration-accumulation systems and poolforming models in buried hills are obtained. Finally, several parameters including stress characteristics, effective passage systems, preservation conditions and exploration states, are selected to evaluate the petroleum distribution in Zhuanghai buried hills.Main achievements can be summaried as follows:(1) According to statistics of homogenization temperature of fluid inclusions, three periods of petroleum migration and accumulation are identified, viz. late Dongying formation sedimentary periodearly Guantao period, late Guantao period and Minghuazhen period. Three above periods correspond to the main petroleum-discharged periods in surrounding depressions.(2) About dynamic fields favorable to petroleum migration and accumulation. Several sections with tensile strss and tensile-slip stress, such as CB30 area and 1686 area, can provide favorable pathways and spaces for petroleum migration and accumulation. The analog result of fluid potential shows that depressions correspond to higher values, while lower values to higher parts of buried hills. Besides, hydrodynamic power played positive as well as negative roles for petroleum migration, while the positive role was popular. In Zhuanghai buried hills, there exist four kinds of zones with differents fluid potential, including zone with higher values, zone with lower values, interzone between zones with higher values and lower values respectively, as well as zone with relative low values surrounded by zones with higher values. Researches prove that preferred directions of petroleum migration are controlled by values of the fluid potential and shapes of fluid potential isolines. According to the above conclusion, some practice phenomena could be explaind. There exist higher outputs in zones with lower values, which lower outputs also possiblely exist. Furthermore, interzones between zones with higher values and lower values respectively are favorale for petroleum accumulation.(3) Petroleum migration passage system in Zhuanghai area consists of higher-permeability rocks (including sandstone, carbonate rock and granitic gneiss), faults and unconformity systems. Fauts and unconformity systems are more effective to petroleum migration. Three kinds of pathways comprise three types of passage systems including rock-fault-unconformity system, rock-fault systems and rock-unconfromity system. The first type is poplar in this area, the second type exists at the edge of buried hills, while the last system only exists at the eastern slope of Changdi buried hill.(4) With the research on source rock to petroleum correlations, buried history of peripheral depressions, periods of petroleum migration and accumulation as well as chracteristics of dynamic fields and pathways, four macro effective passage systems, together with corresponding effective migration&accumulation systems are distinguished. They are Bozhong depression - Northern Zhuanghai buried hills system, Huanghekou depression - Eastern Zhuanghai system, Wuhaozhuang depression - Southern Zhuanghai system and Chengbei depression - L30 buried hill system, two former of which are more effective and advantaged.(5) Mature-High mature petroleum in Zhuanghai buried hills comes from peripheral depressions. Controlled by fluid potential, petroleum migrated through faults as well as high-permeability rocks and unconformity systems at tnree primary periods, viz. late Dongying formation sedimentary period-early Guantao period, late Guantao period and Minghuazhen period. Traps associated with effective passage pathways can trap those petroleum to form pools at the top or inside of Zhuanghai buried hills which constitute the multi-phase petroleum accumulation zone in Zhuanghai buried hills. In different migration&accumulation system, pool-formation models possess such common characters as multidepression generating petroleum, impure petroleum, multi migration powers, multi-pathway, multi-spaces, multi-direction and multi-period migration and accumulation, multi-layer bearing petroleum and multi-type reservoirs, including internal monoclinal faulted block hill petroleum reservoir, internal fold faulted block hill petroleum reservoir, internal fragmentation hill petroleum reservoir and fractured hill petroleum reservoir at the footwall of detachment fault..