A Study On The Heterogeneity Of Chang8₁ Reservoirs In A Certain Area Of Longdong

Triassic Yanchang Maling oilfield,Changqing Oilfield is one of the 8₁ main producing areas,be the most changeful structure of sandstone reservoir inside the area,rock particles,small pore throat,poor physical properties,but have great potential of oil and gas,the research has realistic economic significance and far-reaching academic value of the.In this paper,petroleum geology,sedimentary petrology,reservoir geology and other disciplines of knowledge theory as the guiding ideology,combining the core and logging data,based on respect for the former achievements and experience of the adjacent area,the area was divided into layers,and in turn in the study of reservoir sedimentary facies,petrology the characteristics of reservoir,diagenesis,reservoir characteristics.After that,the microscopic heterogeneity of reservoir is analyzed respectively in three parts: reservoir particles,interstitial materials and pore throat characteristics.Finally,combined with the above analysis,the micro heterogeneity of reservoir is evaluated,and the following results and understanding are obtained.In the study area,Yanchang Formation group 8₁ mainly developed delta front sediments,mainly showing sedimentary microfacies such as natural levee,subaqueous distributary channel,turbidite fan,distributary Bay and mouth bar.According to core analysis and thin section observation,the main reservoir types of Triassic Yanchang Formation 8₁ reservoir in this area are light grey,gray lithic feldspathic sandstone and feldspathic lithic sandstone,and a small amount of lithic sandstone.Low structural maturity.Sorting with medium well,roundness SEQ angular,contact main point-line contact,line contact,lithic quartz,mica,silty rock debris.Cements consist mainly of iron,calcite and calcite.The diagenesis of Chang 8₁ reservoir includes compaction,cementation,metasomatism,dissolution and so on.Through the analysis of clay minerals,that the Chang 8₁ reservoir sandstone in the late diagenetic stage A.The porosity of Chang 8₁ reservoir is 1.24-13.82%,the average is 8.71%,and the permeability is between0.002-5.58 m D.The microscopic heterogeneity of reservoir is studied by studying the characteristics of reservoir particles,interstitial materials and pore throat.The grain size of Chang 8₁ reservoir is generally fine,dominated by fine sandstone,followed by medium sand and silty sand,and contains a small amount of coarse sand rock.The average fine sandstone in clastic particles is 70.5%,and that of siltstone is 11.11%.The content of interstitial materials accountedfor 15.28%,of which the carbonate cement content accounted for 6.04%,accounted for 0.82% of the content of siliceous cement and clay mineral content of cement accounted for 8.91%,the average content of illite clay mineral accounted for 3.18%,the average content of chlorite accounted for 3.13%,accounted for 0.5% of the average content of kaolinite,illite mixed layer average content accounted for 2.1%,0.05% increase of feldspar.The reservoir is mainly intergranular pore,feldspar dissolved pores and the combination of both the main reservoir space;throat type flake or curved lamellar throat,tube shaped throat and neck throat at times;combination type mainly for large-hole micro throat type.According to the study of microscopic reservoir heterogeneity,reservoir pore structure in the study area is mainly divided into four types: the first type of pore structure of high velocity and high flow;class II pore structure but low flow and high flow rate;flow and flow rate of class III and IV pore structure are relatively low,which belongs to the non Darcy flow.The above results show that the Chang 8₁ reservoir has strong microscopic heterogeneity.