Oil in Ordos Basin mainly accumulates in the Mesozoic

so it is of great significance to study the oil accumulation patterns of the Mesozoic basin.This study provided an overview of the history of hydrocarbon exploration theories and discussed the oil accumulation patterns in the Mesozoic Ordos Basin based on the systematic analysis of the relationships between the Mesozoic source rocks

sedimentary facies belts

hydrocarbon migration and accumulation

and the oil reservoirs.The results show that the sedimentary facies control the distribution and development characteristics of hydrocarbon source rocks and reservoirs

whereas the diagenetic facies control the distribution and reservoir space of quality reservoirs.Pressure or fluid potentials determine the migration directions and pathways of oil and gas

thereby the coupling of facies and potentials controls the locations of hydrocarbon accumulations and traps.The Ordos Basin was a large inland down-warped basin during the deposition of the Yanchang and Yan'an Formations as the main oil-bearing layer series

featuring relatively simple structures

relatively flat-lying strata

and poorly developed fractures.Therefore

among the six major requirements for hydrocarbon accumulation

risks associated with cap rocks

traps and preservation are almost negligible.When the source rocks are ascertained in the Mesozoic Ordos Basin

the main risks are related with reservoirs

as well as hydrocarbon migration and accumulation.Thus

facies-potential coupling controls oil accumulation in the Mesozoic Ordos Basin

revealing the accumulation pattern as follows:"source rocks control the distribution of play

sedimentary facies control the occurrence of play fairways

and potentials control the location of oil reservoirs".To be specific

the source rocks in Chang 7 and Chang 9 in the Mesozoic basin control the distribution of play

and the 11 fluvial-delta systems around the basin control the distribution of play fairways.For shallow reservoirs controlled by buoyancy

the nose structural uplift plays a significant role in controlling the formation and distribution of oil reservoirs

while for the lower assemblage reservoirs controlled by abnormal pressures

the migration directions and accumulation locations are determined by the diffe-rential pressures or fluid potentials between source rock and reservoir.In addition

facies-potential coupling controls the diversity of hydrocarbon accumulation in the Mesozoic Ordos Basin seen from both planar and vertical directions

which is embodied by the "compensatory accumulation" in the shallow layers of the eastern Ordos Basin

"vertical bead-like accumulation" in the western Ordos Basin

and "abnormal pressure-controlled accumulation" in the deep Yanchang Formation.This understanding is also applicable to the exploration targets in other large down-warped petroliferous basins with higher exploration maturity.