Diagenetic Facies Analysis of Tight Sandstone Gas Reservoir of Bashijiqike Formation in Kuqa Depression

The lithology characteristics,reservoir property and pore structure,diagenesis,diagenetic minerals,diagenetic environment,diagenetic stage and diagenetic evolution sequence of Bashijiqike Formation tight sandstone reservoirs are studied by making full use of normal thin sections,casting thin sections,cathode luminescence,scanning electron microscope analysis data and mercury injection test data.The results show the reservoirs have experienced diagenesis such as compaction,cementation,corrosion and fracturing.It is now in the phase A of middle diagenetic stage.Then five types of diagenetic facies are divided based on type and intensity of diagenesis,diagenetic minerals and their effect on the reservoir quality.They are:tight compaction facies;,carbonate cemented facies,mixed-layer illite-smectite filling facies,diagenetic micro-fracture facies and corrosion of unstable components facies.According to the various well logging response characteristics of different types of diagenetic facies,five normal logging curves which are sensitive to the diagenetic facies are chosen to characterize the diagenetic facies.They are:neutron logging(CNL),density logging(DEN),acoustic slowness(AC),natural gamma ray(GR),array induction log(M2R2).Thus we can set up the logging recognition model and standard of diagenetic facies.Actual log data of wells in Keshen area were processed using this method,and the diagenetic facies of Bashijiqike Formation reservoir in this well is figured out on the vertical profile.When the logging recognition results of diagenetic facies of Bashijiqike Formation are corresponded with the actual gas test data,it is found that the diagenetic micro-fracture facies are always coexisting with tectonic fractures.When there are no tectonic fractures,the gas bearing property of the layer with the corrosion of unstable component facies is the best,while the diagenetic facies such as tight compaction facies,carbonate cemented facies and mixed-layer illite-smectite filling facies correspond to the dry layers.It is an effective way to comprehensively evaluate the reservoir and predict the sweet spot of tight gas sandstones by analyzing the diagenetic facies.