Abstract:

 To predict the reservoir type and quality of the tight sandstones of  the Member 3 of the Denglouku Formation in the deep horizons of the Xujiaweizi Fault Depression, Songliao Basin, the diageneses of clastic rocks are divided into the period A of early diagenetic stage, the period B of early diagenetic stage, the subperiod A1 of middle diagenetic stage, the subperiod A2 of middle diagenetic stage, the subperiod B1 of middle diagenetic stage, the subperiod B2 of middle diagenetic stage, the period A of late diagenetic stage and the period B of late diagenetic stage on the base of the exploration results of the deep horizons and the reservoir testing data. The tight sandstone reservoirs in the period A and period B of late diagenetic stage can not produce commercial gas flows. As the result of statistical analysis of the reservoir porosity and permeability data show, the tight sandstone reservoir property or reservoir qualities in the Xujiaweizi Fault Depression are dominantly controlled by sedimentary facies and diageneses, and the combinations of different sedimentary facies and diagenetic facies form three kinds of different tight sandstone reservoirs, typeⅡ, typeⅢ, and type Ⅳ. By modeling the variation of paleotemperature, vitrinite reflectance, sterane isomerization, clay mineral transformation, and authigenic quartz formation with time, the diagenetic evolution history is modeled and the lateral distribution of the diagentic stage and diagentic facies are predicted. Considering the integrated effects of sedimentary facies and diageneses on the reservoir property, the tight sandstone reservoir types and quality of the Member 3 of the Denglouku Formation are predicted laterally by diagenetic numerical modeling and diagenetic facies analysis combining the sedimentary facies. At present the well producing commercial gas flows are mainly located in the reservoirs of typeⅡ or typeⅢ.No commercial gas flow is produced in the tight sandstone reservoirs of type Ⅳ which are mainly distributed in the period A and the period B of late diagenetic stage or located in the shallow lake facies. The main factor caused the diagenetic differences is depth.

Key words: tight sandstone gas, unconventional oil and gas, diagenesis, diagenetic facies, diagenetic facies law, lowpermeability reservoirs, Xujiaweizi Fault Depression