Abstract:

To analyze the formation reasons of the Xushen large gas field thoroughly, this passage researches them in detail by anatomical study on conditions of sourcerock, trap, transporting pathway and cap rock and distribution relationship among them and gas field. First, by study on the distribution and geochemical characteristic of sourcerock, the major sourcerock of Xushen large gas field is mudstone source rock in coal measure strata of K₁sh, which has generating gas ability. Second, by anatomical study on conditions of the traps of Xushen large gas field, it is known that favorable reservoir facies zone combing with faults provides favorable traps for formation of large gas field. Third, by analyzing the gas transporting pathway of Xushen large gas field, there are two kinds of sourcerock faults and unconformity transporting pathway: faults from sourcerock and unconformities on top of volcanic. Faults from sourcerock of K₁sh to volcanic rock reservoir of K₁ yc provide vertical transporting pathways for gas migrating to volcanic rock of K₁yc, and unconformities on top of volcanic rock provide lateral transporting pathways for gas migrating to high positions in volcanic rock. Fourth, by research on preservation conditions of Xushen large gas field, mudstone of K₁d₂ and volcanic cap rock with high interval transit time on top of K₁yc₁ provide favorable preservation condition for formation of large gas field. In a word, above four conditions are favorable for forming Xushen large gas field.

Key words: Xujiaweizi depression, gas supply, volcanic trap, transporting pathway, cap rock, nature gas