A Study On The Main Controlling Factors Of The Xujiahe Formation In The South Of Shu

Under the guidance of sedimentology,tectonics,reservoir geology,organic geochemistry,hydrocarbon accumulation,by means of boring,logging,and analyzing seismic data,this paper primarily studies the types and distribution of hydrocarbon rocks,depostional reservoirs and gas reservoirs as well as the main controlling factors of oil and gas accumulation.Hydrocarbon rocks in the studies area are mainly sourced from dark argillaceous rocks and a small amount of coal seams,and are mainly found in Xujiahe Formation Section ?,?,? and Subsection ?2 vertically,with gross thickness of 30m to 330m and distribution thick in the west and thin in the east.Hydrocarbon rocks commonly feature high content of organic carbon,where type ? prevails.Results of vitrinite reflectance show that Upper Triassic hydrocarbon rocks are maturely evolved and have entered oil threshold.The hydrocarbon rocks are projected to have discharged 315455×108m3 hydrocarbon in total with 75442×108m3 coming from the coal seams.This provided favorable material foundation for natural gas accumulation.Reservoirs of Xujiahe Formation mainly are found in Xujiahe Formation Section ? and ?,with great gross thickness and extensive distribution.Reservoirs in Zigong areas are mainly found in Xujiahe Formation Section ?,Sub-section ?1,Sub-section?3occasionally found in Section ?;reservoirs in Luzhou areas,however,are more present in Xujiahe Section ? than they are in Section ?,with significant horizontal difference between reservoirs.Reservoir rocks in Xujiahe Formation are dominated by feldspar lithic sandstone and lithic feldspar sandstone.Reservoir space includes residual intergranular pores,inter-grain pores and intragranular dissolution pores.The reservoir type is fissure-pore type.The reservoirs are primarily subject to the joint control of sedimentary facies,rock facies and diagenesis.The braided primary distributary channels had a controlling effect on the distribution of favorable reservoir sand bodies.Based on sections of typical gas reservoirs and findings of other researchers,the gas reservoir types of Xujiahe Formation are mainly structural-lithologic composite trap gas reservoirs and lithologic trap gas reservoirs.The oil and gas were mainly sourced from autogenetic coal measure source rocks,as well as the underlaying deep gas sources in some areas.Sandstones in Xujiahe Formation were densificated in early to mid Cretaceous,generated hydrocarbonate most in late Cretaceous and saw fissures mainly in late Cretaceous to the Tertiary period.The structure traps were formed in early Jurassic,and feature inheritance "activization" that is also seen in the initial accumulation in early-mid Yanshan period and the sealing in late Yanshan period and the original gas reservoirs in Xishan period.Gas reservoirs in Xujiahe Formation were mainly subject to the comprehensive control of unbalanced distribution of gas generating intensity in plane,sand bodies distribution of primary distributary channels,multi phases of paleostructure traps,faults(fissions)and preserving conditions.