Abstract:

Buried hill reservoir of fault-block type is one of the important reservoirs in Bohai Bay Basin and its formation is significantly controlled by faults.In order to study the control of faults on hydrocarbon accumulation and preservation in buried hills of fault-block type, various data including 3D seismic, drilling and logging data were integrated to describe the geometry of fault planes, calculate the sealing capacity of faults, and analyze the control of fault on reservoir modification.The focus of analysis was put on the control of five major faults on the dominant pathways of hydrocarbon migration, preservation of accumulated hydrocarbons and the reservoir space for hydrocarbons.The following understandings were obtained:(1)The migration of hydrocarbons was controlled by the geometry of fault plane, carrier systems of convergence type were favorable for migration of hydrocarbons, and the section with heavy curvature could obtain high yield;(2)The sealing properties of faults after the hydrocarbons accumulation controlled the preservation of accumulated hydrocarbons and current oil-gas potentials.When the fault opening index (FOI) of faults on top of buried hills is less than 1, the vertical sealing capacity of the faults is good, the sealing conditions are good and the oil potential is high in later stage.When it is over 3, the vertical sealing capacity is poor and hydrocarbons migrate upwards to the shallow parts.(3)The modification of buried hill reservoirs by faults is reflected by the differential distribution of fractures.There is a negative correlation between the fractures density and the distance to the second-grade faults.To some extent, there is a positive correlation between production capacity and the fracture density.

Key words: sealing of faults,fault-control on reservoirs, buried hill hydrocarbon reservoir, Nanpu Sag, Bohai Bay Basin