Influence Of Fault Activity On Hydrocarbon Accumulation In Jiyang Depression In The Cenozoic

The Jiyang Depression is a Cenozoic fault basin developed under the background of strike-slip-extension.The faults have both extension and strike-slip activities.The change of stress field in each period will also affect the inherited faults.However,the study on the characteristics of fault strike-slip activities,the effects of stress field changes and the differences of fault activities in different regions is insufficient.The paper analyzes the fault activity patterns from the geometry and kinematics,analyzes the activity characteristics,compares the differences of fault activities in different regions and analyzes the influence of fault activity on hydrocarbon accumulation.The following understandings are obtained:Firstly,based on the seismic data,the static characteristics of faults in the study area are analyzed.It is found that there are mainly three groups of faults in NW,NE and near EW directions in the basin.The extensional tectonic style is dominant.The Linnan subsag in the south and the eastern coastal area in the east develop extension-strike-slip structural styles.Secondly,through the calculation of fault activity,the extensional characteristics of faults controlling depressions and subsag in different sags are analyzed and compared.The faults are divided into three types: early faults,inheritance faults,late faults.Inheritance faults and late faults are both further divided into two types and the activity peak period and the decline period move back from southwest to northeast.It is considered that there are two strike-slip mechanisms.The Jiyang Depression is divided into three strike-slip regions.By calculating the strike-slip volume of faults and analyzing seismic profiles and balanced profiles,it is concluded that the main strike-slip periods in Linnan Subsag are Es2 and Ed.The main strike-slip period in the coastal area is the Neogene.The strike-slip strength in the central area is related to the fault strike and regional stress.Finally,the influence of fault activity on hydrocarbon accumulation is analyzed: fault activity controls the transition of depression from NW-trending inverted basin to NE-trending tension-torsion basin;oblique slip movement affects the development location,facies type,distribution pattern and depositional thickness of sedimentary system;oil source faults are the main channels of four kinds of transport systems in the work area,and strike-slip activity promotes the dominant migration direction of oil and gas and transports of oil and gas along the strike-slip direction the strike transport complements the migration;Two main modle of oil and gas accumulation containing enrichment in upper stratum and enrichment in lower stratum are summarized.Generally speaking,extensional movement affects the vertical combination of source,reservoir and cap,determines the lateral distribution and reserves scale of compound oil and gas accumulation zones;strike-slip movement remoulds the distribution of oil and gas,and oil and gas enriches in strong strike-slip zones.Oil and gas distribute in zones around sags with faults as the main body and the oil and gas enrichment layer in the southwest to the north is becoming higher.