Abstract: The calcarenaceous sandstone reservoirs in the 3rd member of the Xujiahe Formation in the Yuanba area are lithologic ones featured by source and reservoir coexistence, high migration efficiency, favorable accumulation condition and overall gas-bearing capacity. Reservoirs mainly develop in the high-energy channel sandstones of braided river delta. The calcarenaceous high-energy channel sandstones in the 3rd member of the Xujiahe Formation in the northwestern Yuanba area are characterized by low GR (smooth box-like or toothed box-like gamma curves), high resistance, high carbonate debris content, low quartz content, and wide spread of dissolution pores and cracks. The big thickness of calcarenaceous high-energy channel sandstones provides the basement for the enrichment of natural gas in the 3rd member of the Xujiahe Formation. Near source, high carbonate debris content, high compression strength and high dissolution degree are the keys for the enrichment of natural gas in the 3rd member of the Xujiahe Formation. The explorations of calcarenaceous sandstone reservoirs in the 3rd member of the Xujiahe Formation should be focused on the near-source and high-energy channel sandstones with thick calcareous debris sandstone, high calcareous content and low quartz content.