Studies On The Control Of Faults On Hydrocarbon Accumulation In Neogene Of Chengdao Area

Neogene hydrocarbon reservoirs in Chengdao area have the characteristics of "lower generation,upper storage" and "accumulation outside source rock zone".The migration,accumulation and distribution of hydrocarbon are closely related to faults.It is of great theoretical and practical value to study the genetic relationship between faults and Neogene reservoirs.In this paper,the relationship between faults and Neogene hydrocarbon accumulation in Chengdao area is systematically studied for the purpose of deeply discussing the mechanism of the impact of faults on hydrocarbon accumulation.According to the difference of hydrocarbon enrichment characteristics and the corresponding relationship between source and reservoir,Chengdao area is divided into three hydrocarbon migration and accumulation systems with the boundary of Chengbei 20 fault and Chengbei 30 fault.The oil in Chengbei Fault Zone and Drape Anticline Zone is originated from source rocks of the third and first member in Chengbei Sag.The Neogene oil is mainly concentrated in upper Guanshan and Minghuazhen Formations,and the accumulation period is from the mid-deposition period of Minghuazhen Formation.to present.The oil in Zhuanghai Fault Zone is originated from Zhuandong Sag.The Neogene oil is mainly concentrated in the lower Guanxia section.The accumulation period is from the beginning of Minghuazhen to the present.The oil in the Eastern Slope Zone is originated from the south depression of Bozhong sag.The distribution of the oil in Neogene is limited,and the accumulation period is from the beginning of Minghuazhen period to the present.Combining with regional geological background,fault types are classified,and fault activity is evaluated quantitatively.On this base,the relationship between difference of fault activity and hydrocarbon accumulation is analyzed.According to the cutting relationship and combination pattern of faults,the faults in Chengdao area are divided into three types: oil source faults,oil source faults branches and secondary conductive faults.Based on the hydrocarbon enrichment characteristics of Neogene,it is determined that fault activity rate greater than 15m/Myr and 10m/Myr are the threshold conditions for the effective transmission of oil source faults and secondary faults,respectively.The difference of fault activity in different tectonic zones leads to the uneven distribution of oil and gas in Neogene.The fault activity rate of Chengbei fault zone is the highest and the activity time is the longest,which matches the hydrocarbon generation and expulsion period of source rocks best.The hydrocarbon enrichment degree of Neogene is the highest,and oil and gas are mainly concentrated in upper Guanshan and Minghuazhen Formations;the fault activity of Zhuanghai fault zone is the second,and the hydrocarbon enrichment degree of Neogene is the second.Lower than the Chengbei fault zone,oil and gas are mainly concentrated in the lower part of Guanxia section;the eastern slope zone of Chengdao has the smallest fault activity rate and time,the weakest vertical fault conduction and the lowest hydrocarbon enrichment in Neogene.On the basis of geological statistics and physical simulation,it is proposed that the hydrocarbon enrichment degree of Neogene is mainly controlled by three factors: fault activity,static characteristics of fault and hydrocarbon supply ability of source rocks in contact with fault sections.Based on the fuzzy valuation method and multiple linear regression method,a quantitative evaluation method for hydrocarbon transport capacity of fault in shallow strata is established.The evaluation results and hydrocarbon enrichment degree of Neogene in the study area are obtained.The high coupling degree proves the feasibility of this method,and the fault conductivity controls the enrichment degree of Neogene oil and gas.Based on the internal structure and fluid behavior of fault zones and stress analysis,the equilibrium relationship between the vertical opening and closing characteristics of faults controlled by the external compressive stress in the vertical direction of the fault section during oil and gas filling period and the pressure resistance produced by fault rock skeleton and pore fluid is proposed.The fault sealing coefficient S is used to quantitatively characterize the vertical closure of faults,and a quantitative characterization of the vertical closure of faults is established accordingly.Quantitative evaluation criteria for vertical opening and closing of faults in the study area.On the basis of SGR method for lateral fault sealing oil and gas,by restoring parameters such as fault ancient fault distance and paleomud content during hydrocarbon accumulation period,a set of evaluation methods for paleolateral fault sealing is established.The effectiveness of fault traps can only be guaranteed near faults that meet lateral shielding conditions during hydrocarbon accumulation period and now.The accuracy of the improved method is higher than that of the original method.The method is proved to be feasible.Based on geological statistical analysis and physical simulation experiments,the statistical relationship between oil-bearing property of Neogene fluvial sand body and various geological parameters is established.It is pointed out that fault type,sand body type,fault-sand collocation relationship,distance from transporting fault,hydrocarbon supply ability of source rock and reservoir physical properties control selective hydrocarbon filling.By establishing the statistical relationship between trap fullness and various quantitative parameters,it is pointed out that the Neogene trap fullness is controlled by fault activity,fault sealing,distance from oil source faults,Caprock Sealing capacity,residual pressure of hydrocarbon expulsion from source rocks,volume of sand body and distribution characteristics of sand body.The correlation coefficient is used to evaluate these geological parameters to characterize oil and gas fullness of different types of fault-sand configuration.Effectiveness and quantitative prediction model of Neogene trap filling degree in the study area were established by multiple linear regression method.On the basis of defining the space-time validity of macro-transport system and the filling mechanism of micro-sand body in the study area,the "near-source hydrocarbon-fault vertical Transport-source T" accumulation model in Chengbei fault zone,the "far-source hydrocarbon-fault-sand composite transport-fault step zone" accumulation model in Zhuanghai fault zone and the "far-source hydrocarbon-sand lateral transport-slope zone" accumulation model in Chengdao eastern slope zone are established.