The Sedimentary Facies Types And Reservoir Characteristics Of The Second Member Of Xujiahe Formation In The Malubei Area,Northeastern Sichuan Basin

The paper takes the second member of Sinian Xujiahe Formation?T₃x²?in Malubei area of northeastern Sichuan as the research object.Through the field exploration,core observation,microscopic slice identification,combined with physical data,drilling and logging data,conventional logging data interpretation,and imaging logging interpretation,the sedimentary facies type,reservoir petrology,diagenesis characteristics,physical characteristics,pore characteristics,reservoir control factors of the second member of Xujiahe Formation were determined.The thickness of T₃x² is generally distributed in the range of 66?201m.According to the characteristics of the lake surface logging identification,five quasi-sequences were identified in the sandstone of the second member of the Xujiahe Formation in the Malubei area,which were PS1,PS2,PS3,PS4 and PS5 from bottom to top.The quasi-sequence PS1 is only developed in a local well location;The pseudo-sequence PS2 is thicker in the northeast and thinner in the southwest.The quasi-sequences PS3,PS4,and PS5 are all thickened in the southwest direction.The second section of the study area is the lacustrine facies and braided river delta facies.The braided river delta plain,the braided river delta front and the coastal shallow lake subfacies are developed at different sedimentary locations.The sedimentary facies of the T₃x² of the study area are the lacustrine facies and the braided river delta facies,The braided river delta plain,the braided river delta front and the shore-shallow lake subfacies are developed at different sedimentary locations,and nine types of microfacies:branch channel,flood plain,underwater distributary channel,river channel,estuary dam,sheet sand,distal bar,beach bar and shore shallow lake mudstone.The reservoir rocks in the upper sub-segment of the T₃x² of the study area are mainly lithic sandstone and lithic quartz sandstone;the reservoir rocks in the lower sub-segment are mainly lithic quartz sandstone and quartz sandstone.The type of reservoir space in the upper sub-segment of the T₃x² is mainly crack,and a small amount of intergranular and intragranular dissolved pores;the type in the lower sub-segment is mainly residual intergranular and micro-cracks.The T₃x² of the study area has a total of 58 physical properties,and they are all distributed in the upper subsection,Physical property analysis results show:porosity is generally less than 5%,and permeability is mainly distributed between 0.01-0.05m D,Belong to ultra-low porosity,ultra low permeability sandstone.The diagenesis of the sandstones of T₃x² in the study area occurred from the early to late relative sequence of Compaction—chlorite film—calcite metastasis—quartz phase I increase—chlorite lining/illite lining—pressure dissolution—clay minerals Yili petrochemical—quartz phase II increase—calcite filling pores.Among them,the effect of compaction on the sandstone pores is very strong.The sandstone pores in the early diagenetic period have been lost a lot,leading to less development of diagenesis in the later period.According to the comprehensive study,the main factors controlling the physical properties of T₃x² in Malubei area are the deep compaction and strong compaction in the middle and late stages of burial,which caused the early disappearance of large pores.After deep compaction and compaction,it has undergone three-stage tectonic movement.Under the strong compression of structure,many cracks—microcracks—all kinds of faults are formed,and micropores are communicated to form a reservoir with low porosity but no low permeability.the second member of Sinian Xujiahe Formation in Malubei area is obviously controlled by structure.