Genesis and distribution of unconventional oil

Unconventional oil refers to the petroleum that is produced with high cost and advanced technology other than conventional methods and mainly includes three categories: heavy oil oil sand,oil shale and shale(tight) oil.The first category is heavy oil and oil sand that is evolved from conventional oil undergoing biological degradation and water washing.With wide distribution and huge potentials,the heavy oil and oil sand have been exploited to a large extent.The oil shale is the mixture of kerogen and inorganic substances such as clay and fine grain minerals.The organic matters have high abundance yet are immature,which can generate oil through artificial heating.The oil shale is discovered very early and widely distributed,and the U.S.accounts for the highest proportion.The third category is the shale(tight) oil.Since it occurs in the particularly low pore and seepage reservoirs retained in the hydrocarbon source rock with higher maturity and excessive organic matters,oil can be produced only through artificial cracks by reservoir fracturing.Shale(tight) oil has been produced in the U.S.and Canada,but the exploration potentials and global distribution need further research.