Abstract:

Clastic oil pools in western-central China may be classified into three main types in accordance with their oil/gas origins，namely the internal-sourced（hydrocarbons being sourced inside the clastic sequences，the external-sourced（hydrocarbons being sourced outside the clastic sequences）and them ixed type（hydrocarbons being sourced both inside and outside the clastic sequences）.The interna-sourced pools can be subdivided into selfˉsourced（with source rocks occurringwithin the reservoir interval）and nonself-sourced（with source rocks occurring outside the reservoir intervals），while the external-sourced types can be subdivided into secondary and primary pools.The self-sourced pools in the internal-sourced category feature in both vertical and lateral adjacency of source rocks to reservoirs，which is favorable for the formation of large lithological reservoirs or highly productive structural reservoirs.The major controlling factors for hydrocarbon accumulation in this type of pools are quality hydrocarbon kitchens，upliftswithin a depression and favorable facies zones.They are the primary targets for discovering medium to large reservoirs.The formation of nonself-sourced reservoirs requires not only the existence of source rocks within the clastic sequences，but also the vertical/lateral carrier systems for hydrocarbon m igration into the upper clastic reservoirs.Theirmain controlling factors include quality hydrocarbon kitchens，carrier systems and palaeo-structures/structures.They are potential exploration targets for discovering highly productive structural reservoirs.The formation of external-sourced pools require both vertical adjacency to underlying quality kitchens or lateral adjacency to large marine reservoirs（fields）and m igration networks consisting of faults，unconform ities or carrier beds.Theirmain controlling factors are efficiency of carrier systems and scales of underlying oil/gas reservoirs.They are important targets for discoverings mall to medium secondary oil/gas reservoir clusters and larger stratigraphic reservoirs.

Key words: clastic rock, hydrocarbon kitchen, lithologic reservoir, hydrocarbon accumulation, western-central China