In 2023

a major breakthrough of hydrocarbon exploration had been made in Triassic Yanchang Formation of Hongde area

southwestern Ordos Basin

where Hongde oilfield was discovered with 100-million-ton crude oil reserves. To clarify the geological characteristics and accumulation conditions of Yanchang Formation in Hongde area

the factors and patterns of hydrocarbon accumulation

were systematically sorted out by integrating core

well logging

3D seismic and analytical test data. Moreover

the key technologies for hydrocarbon exploration and development were summarized. The research results show that the braided river delta plain subfacies with distributary channel sand bodies are developed in the Member 8 of Yanchang Formation (Chang 8) in Hongde area

where the reservoirs have large thickness and good physical properties

demonstrating excellent conditions for oil accumulation. The source rock in the Member 7 of Yanchang Formation (Chang 7) in Hongde area is characterized with thin layer

and its total organic carbon (TOC) content is 1.16 % on average

thus indicating a low potential for supplying hydrocarbons. The crude oil in Chang 8 of Hongde area is mainly originated from the high-quality source rock of Chang 7 near the center of lake basin in the eastern part of Ordos Basin. The oil migrates laterally through the three-dimensional transport system composed of faults

fractures and high-quality reservoir sandbodies developed in Yanshanian period

and accumulates in the high parts of paleo-structures. Horizontally

the structural and structural-lithologic reservoirs developed in the west of Hongde area are characterized with the hydrocarbon accumulation mode of "lateral migration and accumulation

reservoirs controlled by fault and uplift

and enrichment characteristics controlled by physical properties of reservoirs". In contrast

the large scale of lithologic reservoirs are developed in the east of Hongde area

with the characteristic of being close to source rocks. During the petroleum exploration and development in Hongde area

the study establishes a series of key technologies focusing on 3D seismic processing and interpretation of depth migration

evaluation of reservoir fluid properties based on the integration of well logging and mud logging

and fracturing transformation for fracture controlling and reservoir stimulation. Those technologies have provided strong supports fo

r new oil and gas discoveries. The breakthrough of Hongde oilfield proves that the area far from the oil source of Tianhuan depression still has the potential for large-scale accumulation. The western margin of Ordos Basin is expected to further implement the petroleum geological reserves of more than 2×10

8

t

which is a key field for expanding the extra-source oil and gas exploration.