| The main research area - No. 1 Sebei gas field is situates in the middle east of Chaidamu basin. The anticline structure is a third level synsedimentary anticline structure in second level structure belt of Tainan - Sebei, which is closely near the central gas generation depression. Thin interbedded sands and shale, and loose reservoir are main sedimentary character of the Quaternary system of target formation in this area.From 1956 to now, the exploration of this area has gone through three stages, over 40 years. The drilling with brine mud and the bad quality have caused the difficulty of gas and water identification, which lead to miss of gas reservoir in logging interpretation. In late over 10 years, with the improvement of resolution of seismic data processing, the application of freshwater polymer mud and digital logging, as well as the strengthening of gas test in low resistance formation and out-laying well drilling, the identification of gas reservoir is enhanced greatly, which has largely increased number and the thickness of gas reservoir and enlarged gas- bearing area of gas reservoir. Consequently, reserves of gas reservoir are still continuously increasing through several reassessments.The comprehensive geological characteristic has been fully studied in this paper. On the basis of this, closely combining production practice, the favorable gas developing regions have been determined with the methods of sedimentary facies and combination of generation, reservoir and caprock, and logging parameters interpretation maps and regression formulas have been established with logging data, as well as reprocessing, interpretation and identification of gas reservoir have been done with computer. Integrating the information and results of geology, logging, testing and geophysics, the gas reservoir distribution regularity of structure of No. 1 Sebei has been described and reserves in place of No. 1'Sebei gas field have been recalculated, which have provided a basis for next step of development in research area. The major achievements and knowledge are as follows:1. Through the reprocessing of the present logging data in No. 1 Sebei gas field, it is considered that the invasion of saturated brine mud and high density mud employed in drilling is main factors causing logging response distortion; At the same time, factors such as disunified logging series and ambiguous reservoir boundary also have effected identification of gas reservoir.2. With several surrounding calibrating method such as using overlaid difference of standard histogram of logging curve value and other histogram as calibration value etc., the non-geological factors can be eliminated generally.3. Reservoirs can be correctly identified with parameters of relative value of gamma ray andnatural potential; Plotting maps of gas saturation and content of shale have been made with experimental analysis data and identification standards have been determined.4. Under the control of sedimentary facies and sequence stratigraghy, with the contrast of single sand formation and gas- water formation by geological contrast software, mud contaminated formation and doubtful formation can be correctly understood.5. The regularity of gas and water distribution is: Regularity of gas and water is controlled by structure. Gas reserved in higher part of structure, and small scale gas reservoirs locate in top and base part of structure while the large scale gas reservoirs lie in the middle; Lower part of structure bears water, and water and gas are interbedded with unlined gas-water boundary;6. The old "reservoirs with low-middle production "were reidentified. At the same tune, part of bad reservoirs with unclear show of gas were selected from the continuous drilled production test wells to undertake test production with multilayer perforating and 43 interpreted gas reservoirs with low show of gas and 10 possible gas reservoirs were tested singly, which have help to confirm large number of new gas reservoirs. The number of re...
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