Penglai 9-1 oilfield has been the first large-scale field found in weathering crust reservoirs of the Mesozoic bu-ried granite hills in coast waters of China in recent years.In this brand new area of exploration

reservoir characterization and its forming mechanism are considered essential for efficient and successful exploration.Thin section

SEM

and clay mineral X-diffraction analyses were combined with logging data to provide insight into uncertainties of the area.The results show that the buried granite hills can be divided into soil zone

sand-conglomerate weathering zone

fracture zone and base rock zone

and reservoiring space in them changes in a regular pattern from pore to fracture-pore

pore-fracture and fracture

from the surface to the center as weathering and leaching gradually weaken.Horizontally

granite reservoirs are continuously and widely distributed and paralleled to the top of the buried hills.Thicker reservoirs are mainly developed near large-scale faults with intensive activities and paleogeomorphic slope areas.The paper proposes that the reservoirs were controlled mainly by epigenic karstification

organic acid dissolution

structural deformation and micro-palaeogeomorphology.The significance of the understanding may be felt in the future exploration and development of oil and gas in weathering curst reservoirs of buried granite hills intruded during Yanshan period.