DISCUSSION ON RELATION OF GAS ACCUMULATION MECHANISM BETWEEN DEEP BASIN AND UPPER PALEOZOIC IN THE ORDOS BASIN

The relation between gas accumulation of typical deep basin gas and Upper Paleozoic gas field in the Ordos basin was studied in detail on the basis of analysis of sandstone and shale compaction,evolution of porosity,mechanism of pressure formation,distribution of gas and water,gas migration and gas accumulation,as well as in combination with previous research.The characteristics of deep basin gas trap and Upper Paleozoic gas field were similar from the aspects of abundant accumulation,abnormal pressure,large scale gas accumulation and compacted reservoir.However,it was showed that the generation rates of gas was low with poor condition of continuous gas supply in the Upper Paleozoic hydrocarbon rocks,and the migration of gas was prevented by either rock property or lithology,forming lithologic gas reservoir or structural-lithologic gas reservoir in the condition of heterogeneous reservoir.Dynamic analysis of gas formation revealed that the resisting force for the capillary tubes in the Upper Paleozoic reservoir was so high that it prevented the remigration of gas.In fact,the gas only migrated in a very short way and then accumulated.Therefore,the gas accumulation mechanism for deep basin was not suitable for the interpretation of the genesis of the Upper Paleozoic gas pool in the Ordos basin.Comprehensive analysis indicated that the low capacity of continuous gas supply and poor connection of reservoir were the major factors differing the deep basin gas pool from the Upper Paleozoic gas pool in the Ordos basin.