“Exploring petroleum inside source kitchen”: Connotation and prospects of source rock oil and gas

Zhi YANG,Caineng ZOU

Table 1 Comparison of geology and development characteristics of conventional with unconventional oil and gas.

Resource Type Distribution Relation of source rock and reservoir Migration Accumu- lation Preservation Fluid Production process Hydrocarbon composition Recoverable resources/ (oil/t; gas/m3) Examples Composition Movable hydrocarbon Target Key technology Initial production Cumulative production Global China Conventional Oil Favorable traps at structural highs Separate Secondary High abundance; stratigraphic and lithologic reservoirs Regional and immediate caprock Liquid hydrocarbon 40%-80% movable hydrocarbon Oil with high abundance, good reservoir properties and high natural production Vertical and horizontal wells, etc. 90%- 100% movable oil 90%- 100% movable oil 4 878 ×108 200× 108 Gawal Oilfield, Daqing Oilfield Gas Favorable traps at structural highs Separate Secondary High abundance; stratigraphic and lithologic reservoirs Regional and immediate caprock Gas hydrocarbon, generally CH4 90%- 100% free gas Oil with high abundance, good reservoir properties and high natural production Vertical and horizontal wells, etc. 90%- 100% free gas 90%- 100% free gas 471 ×1012 20× 1012 North-South Pars Gas Field, Kela 2 Gas Field Retained Heavy oil +asphalt Near surface Separate Secondary Favorable trap in the drainage area Caprock and self- sealing Heavy oil Unmo- vable oil Heavy oil with poor movability and no natural pro- duction Steamflooding, gravity, steam stimulation, cooling production Almost unmovable oil Almost unmovable oil 2 146 ×108 42× 108 Heavy oil in Venezuela, asphalt sandstone in the Western Canada Basin Hydrate Stable T and P zone Separate Secondary Reservoir enrichment in coarse facies T and P conditions Domi- nant CH4 Almost no free gas Unconsolidated seabed pay zone, unstable and without natural production Pressure drop, thermal production Hardly free gas Hardly free gas 3 000 ×1012 (50- 70)× 1012 Hydrate in the northern part of the South China Sea Tight Oil Basin center or slope Direct contact or neighbor Primary or short secondary migration High abundance in the tectonic or fractured zone Good top and bottom Matured oil 20%-50% movable hydro- carbon Tight reservoirs Energizing, fracturing in horizontal wells 90%- 100% movable oil 90%- 100% movable oil (400- 600) ×108 (20- 25)× 108 Triassic in Ordos Basin, Cretaceous tight sandstone oil in Songliao Basin, Gas Basin center or slope Direct contact or neighbor Primary or short secondary migration High abundance in the tectonic or fractured zone Good top and bottom Different gas saturation, almost 60% below 90%- 100% free gas Tight reservoirs with low natural production Fracturing in horizontal wells 90%- 100% free gas 90%- 100% free gas 210× 1012 (9- 13)× 1012 Carboniferous-Permian in Ordos Basin, Triassic tight sandstone gas in Sichuan Basin Source rock Shale oil Developed shale in deep sags or slopes Same No or short inside-source primary migration Nano-pore and throat system, enrichment in the fracture development zone Good top and bottom Less mature oil and immature oil sand 0%-30% movable hydrocarbon Low or no production, low natural production In-situ thermal transformation 0%-100% movable oil 0-5% movable oil 15 000 ×108 (200- 300)× 108 Triassic shale oil in Ordos Basin Matured oil 20%-50% movable hydrocarbon Low or no production, low natural production Fracturing in horizontal wells 90%- 100% movable oil 90%- 100% movable oil Bakken shale oil in Wyckenston Basin Shale gas Near basin subsidence-sedimenta- tion center Same No or short inside-source primary migration Disperse distribution in shale, enrichment in fracture zones Good top and bottom Dry gas absorbed to kerogen, pores and free in fractures 40%-70% free gas Low production and recovery Fracturing in horizontal wells 80%- 100% free gas 30%-60% free gas 456× 1012 (10- 25)× 1012 Masalus shale gas in Appalachian Basin, Lower Paleozoic shale gas in Sichuan Basin CBM Basin or de- pression synclines Same No or short inside-source primary migration Enrichment in fractures and joints Good top and bottom Absorbed and free gas 5%-20% free gas Low production, no natural production Fracturing in horizontal wells 5%-10% free gas 0-5% free gas 256× 1012 11× 1012 Carboniferous-Permian CBM in Qinshui and Ordos Basins