| The Shaximiao Formation is an important reservoir in the central Sichuan area.Natural gas mainly comes from the source layer of Xujiahe Formation in the lower western Sichuan and the hydrocarbon generation layer of Da ’anzhai Member in the central Sichuan,which belongs to remote source and multi-source hydrocarbon supply.Therefore,the transport system of fault,sand body and fault-sand combination is of great significance for the transport and accumulation of natural gas in the study area.In this paper,the properties,distribution and combination forms of faults and sand bodies in the study area are defined through logging and seismic interpretation data.In combination with physical experiment simulation,analysis and testing experiments,the control function of fault sand combination in gas reservoir formation is studied.The main conclusions are as follows:(1)The faults in the study area can be divided into two types: one is the gas source fault that cuts through the source rock of Xujiahe Formation and the reservoir of Shaximiao Formation,which controls the distribution pattern and main migration direction of natural gas in the central Sichuan Basin;The other is the transport fault developed only in the Jurassic,which plays a secondary role in regulating the natural gas diverted from the side of the gas source fault.(2)The matching relationship between gas source fault active period and source rock hydrocarbon expulsion period is different in different blocks.Longquanshan fault in Jianyang area is the most active,and it is active in Xujiahe Formation,Ziliujing Formation and Shaximiao Formation.Some faults are still active in the late period.The active period can be well matched with the hydrocarbon expulsion period of the third member of the Xueshu Formation(mid-Jurassic)and the fifth member of the Xueshu Formation(mid-late Jurassic).The Jiao(1)fault in the Santai-Yanting area began to move in the Xujiahe Formation and stopped in the middle-late Shaximiao Formation.The active period was poorly matched with the hydrocarbon expulsion period of the Da ’anzhai member source strata(late Jurassic hydrocarbon expulsion),but the fault still had the conditions for migration.(3)The physical property and connectivity of the sand body have certain influence on the migration and accumulation of natural gas.The better the physical property is,the higher the gas saturation in the sand body is.However,there is no positive correlation between gas saturation and sand ratio,and the sand ratio is more likely to transport and accumulate in the position of 0.45～0.65.(4)On the basis of similarity processing based on typical seismic profiles and two-dimensional simulation experiment of sand failure,combined with the characteristics of natural gas migration and accumulation in actual gas reservoir profiles,four sand failure and reservoir control mechanisms are summarized: The reverse up-lift down-dip type,the forward up-lift down-dip type,the vertical fault type,and the single fault type with more sand,among which,the natural gas migrating along the vertical fault is more likely to have lateral shunt to the side lifted up by the sand body,while the vertical fault has poor lateral shunt effect to both sides of the sand body.(5)The dip Angle and connecting point of fault and sand body play an important role in the formation of gas reservoir.In the fault-sand combination of gas source fault,more natural gas will be charged on the side raised by sand body;After the sand body butt with the gas source fault(such as Longquanshan and Jiao(1)fault),the natural gas in the fault will divert more laterally to the sand body with more connected points and larger contact area. |
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