The H3 Formation in the Gucheng Oilfield of China was studied to understand how sedimentary microfacies affect oil-bearing units. By analyzing core and well-log data, researchers identified four types of sedimentary microfacies in the reservoir sand body, with distributary channel and channel margin facies being the main sources of sandstone accumulation. This study helps us understand how different sedimentary environments contribute to the formation of oil reservoirs in the area.