The gas accumulation regularity is analyzed by studying the hydrocarbon source rocks,the characteristics of reservoir and the distribution of Ordovician oil and gas in the northwest Ordos Basin.The Ordovician hydrocarbon source rocks mainly distribute in the Upper Ordovician Wulalike Formation and Lashizhong Formation with mud and grey mud as main lithology,and reservoirs occur in the Kelimoli Formation and Zhuozishan Formation of Middle Ordovician.Based on the rock type and pore combination characteristics...