Fault Feature And Its Controlling Effect On Hydrocarbon Accumulation In Weibei Sag

Many types of structural traps have been found in Weibei Sag,in which the primary type is fault block reservoir due to the well-developed faults.The faults have significant controlling effect on the accumulation and preservation of hydrocarbon,and for the purpose of acknowledging hydrocarbon geological conditions of Weibei Sag and discussing the controlling effect of faults on hydrocarbon distribution features,it is necessary to enhance the understanding of formation and evolution process.Based on the 3-D seismic survey data,the basic geometry and kinematics characteristics of the faults is systematically studied:the faults can be grouped into 4 fault systems according to the directions horizontally;the fault configurations varies from strike-slip type in the east to extensional normal fault type in the west.The fault activity of boundary faults and fault systems were evaluated by using strata subsidence and fault activity rate,combining with the accumulation period,the relationship between fault activity and hydrocarbon accumulation was clarified.In the current fault sealing assessment,the lateral fault sealing are studied using lithologic juxtaposition and SGR,and the vertical fault sealing are studied using fault plane normal pressure and fault tightness index,based on the lateral and vertical fault sealing evaluation the fault sealing characteristics were synthetically assessed.Results showed that fault sealing were significantly controlled by fault strike,it demonstrated that the fault sealing decreased in the following sequence of NW,NNE,NE,EW in general,and the fault sealing in footwall was better than in the hanging wall,and the fault showed good sealing when its displacement was greater than 40m.In the fault sealing history assessment,the fault active and stationary stages were defined using fault activity rate method.Based on tectonic stress history the paleo-stress variation was calculated,the fault sealing history was restored.The results showed that the NNE faults linked the traps and the source rocks vertically and horizontally in the oil accumulation stage while the NW and NE faults became great oil barricades which led to reservoir forming during the same time.Based on the summary of petroleum accumulation conditions in study area,combined with fluid inclusion measurement,hydrocarbon history from generation to expulsion and burial-thermal evolution history of strata,2 accumulation stages were divided:the later stage of Kongdian formation and Shahejie formation deposition.The relationship between fault and those factors including hydrocarbon source rock,reservoir,petroleum migration and accumulation were discussed,the fault effects on basin-forming and source-rock-controlling,petroleum-migration and petroleum-sealing were illuminated.Finally,the fault controlling effects on hydrocarbon accumulation were summarized:the constant activity of boundary primary and secondary faults led to the formation of reservoir depression and large-scale trap belts;the 3^rd degree faults linked the source rocks and traps which migrated and distributed the oil and gas;part 3^rd degree faults and 4^th degree faults sealed the oil and gas in which the complicated fault block reservoirs were formed.