Study On Diagenetic Evolution And Hydrocarbon Accumulation Of Tight Sandstone Reservoirs

The Chang 6 reservoir in the Zaoyuan exploration area is dense,with poor physical properties and strong heterogeneity.In order to quantitatively analyze the relationship between various diagenesis and hydrocarbon accumulation,this article first comprehensively describes the core observation and the description of the sedimentary structure.Using rock flakes,cast flakes,scanning electron microscope,high-pressure mercury intrusion,temperature measurement of inclusions and other analysis methods.Based on the simulation of basins in the study area,the history of lithological tightness of reservoirs and the history of oil and gas accumulation and charging were restored.The quantitative analysis of pore evolution in each diagenetic stage of the reservoirs explored the coupling relationship between diagenesis and accumulation of tight sandstones.The lithology of Chang 6 in the study area is mainly siltstone and dark argillaceous sandstone,and there is a thin layer of fine sandstone in the oil shale reservoir.The thickness of each small layer in the Chang 6 formation is between 17?42m and the total thickness is 85?120m.The porosity of Chang 6 is 8.29%,and the permeability is 0.967×10^-3um².The particle size of the rock is between 0.03 mm and 0.25 mm.The cumulative probability curve is mostly shown as a two-stage diversion channel under water,followed by the third section of the estuary.The main types are intergranular pores,followed by feldspar dissolved pores;pore throat types are mostly "small pores-fine throat type".The paleotemperature of the Chang 6 reservoir in the study area is between 60?120 ?,with an average of 95?;the RO value is between 0.56?1.12%,and the mode is between0.73?0.93%;the maximum pyrolysis peak temperature Tmax is 400?500?,the mode is between 450?500?,with an average of 455?;point-to-point and point-line contact are the main types of particles,and the reservoir evolution has reached the stage A of diagenetic rocks.The original porosity in the study area was 32.4%?38.5%,with an average value of35.8%.During the syngeneic phase—early diagenetic phase A?beginning to deposit ?210Ma?,the reservoir was mainly affected by compaction and the porosity was reduced by14.65%.Early stage diagenetic stage B?210Ma ? 185Ma?reservoirs under reduced and cemented diagenesis reduced pores by 5.12% and 2.23%,respectively.The stage A of the diagenetic rocks?185Ma?110Ma?is a complex reservoir pore evolution period.Compaction and cementation reduce the porosity by 7% and 2.5%,and dissolution increases the porosity by 5.5%.Generally,it is a process of reducing porosity?Pore reduction of 4%?,remaining porosity of 10%,and the reservoir has been densified?Middle Jurassic-Late Jurassic?.The compaction and cementation of the diagenetic stage B?110Ma?198Ma?reduced the pores by 1.03% and 0.67%,the total pores decreased by 1.7%,and the final porosity was 8.29%.The first phase of inclusion temperature: 95?105 ?;the second phase of 120?135 ?,the main peak temperature is 120 ? 125 ?.The migration period of liquid hydrocarbon charging is about 123 ? 98 Ma?middle and late Early Cretaceous?;combined with the paleo-geothermal history,pore evolution characteristics and reservoir-forming period of the basin,the Chang 6 reservoir has the formation of “tightening first,then reservoir-forming”The characteristics of reservoir coupling are controlled by source rock,structure,sedimentary facies,sand body distribution and reservoir-caprock combination.