The Study Of Geological Character And Favorable Areas Of Shallow Gas Pool In Heidimiao Oil Layer In The South Of Daqing Placanticline

Based on the theories of sedimentology, petroleum geolgoy, architectonic geology, reservoir geology, seismostratigraphy and well logging geolgy, starting from the study of fine describe of structure, trap assessment, analysis of sedimentary microfacies, law of sandbody distribution, reservoir characteristic and character of gas pool, and by means of adopting the theory of weight and method of grey relational analysis to evaluate the favorable areas of shallow gas pool in Heidimiao oil layer in the south of Daqing placanticline. Results showing: Firstly, the Putaohua structural zone and Puxi structural zone are the main structural zone in work area. Fractures are presented dense distribution in plane, the fractures tend towards north-west and north-east-east, but the former is given priority to, the latter is the result of adjusting the former to metamorphose. The faults that straightly extending to Heidimiao oil layer is the main passage of gas transfer, and the natural gas collection is close related to the distribution of fault. Secondly, the sedimentary facies of nen-3¹ and nen-3² is mainly half deep-lake to deep-lake. The lake basin shrinks when nen-3³ comes into being, as well as the half deep-lake to deep-lake facies are translated into deltaic front in Pubei and Punan areas. The lake basin keeps on shrinking when nen-4 segment comes into being, and because the influence of river is increased, it turns into deltaic front sub-facies, microfacies of distributary channel under water are quite developed. The mostly sedimentary microfacies in work area is distributary channel under water, distributary clearance, mouth bar and far off sandstone. Thirdly, distributing of sandstone is preferably in Pubei and Aobaota areas and of a sort in Punan area. Single sandstone is all relatively isolated, connectivity is not well from landscape orientation. Sandstone in nen-4 segment is better than that in nen-3 segment, sandstone in nen-3 segment is hardly developed but nen-3 . Fourthly, the main composition of framework grain of sandstone reservoir is feldspar and rock debris, the character of grain structure is silt sand and fine sand, psephicity of sand grain is levity, riddling is middling to good, it belongs to early diagenesis phase. The reservoir has high porosity and permeability, it's favorable to form gas pool. Fifthly, natural gas is mainly from source bed in nen-1 segment and Qingshankou Formation, a little from source bed in other horizon. Natural gas released from source bed because of exceed press, natural gas transfer along the unsealed fault of T₁-T₀₆ or T₂-T₀₆ up to the fault nose structure and fault-lithologic trap in Heidimiao oil layer to form gas pool, or along the sandstone lateral migration with stone's throw and turn into the structure-lithologic trap or samdwich anticline to form gas pool.