Zou, CN; Zhu, RK; Bai, B; Yang, Z; Hou, LH; Ziia, M; Fu, JH; Shao, Y; Liu, KY; Cao, H; Yuan, XJ; Tao, SZ; Tang, XM; Wang, L; Li, TT
The research on light oil recently becomes a highlight in global unconventional petroleum development and shale oil remains as the highly promising potential unconventional petroleum. Based on the systematic investigation of petroleum geology of shale hydrocarbons in China and other countries, we propose that distributions of sweet spots of tight oil and shale oil are constrained by source roek quality, lithology, petrophysics, brittleness, gas/oil contents, and underground stress anisotropy of reservoirs. Prolific shale strata in China possess such geological features of ( I ) TOC >2% or SI >2 mg/g, (2) laminated shale, light sandstone or carbonate. (3) relatively high porosity ( porosities of tight oil or shale oil reservoir should be higher than 10 vol.% or 3 vol.% , respectively) , (4) brittle minerals contents > 40% , (5) oil saturation in the range of 60%-90%, ( 6) relatively low oil viscosity or relatively high formation pressure, (7) fair development of fractures. Similarly, good shale reservoirs in U.S. have the geological characteristics of ( I ) T()C>4% , (2) laminated shale or mud stone, (3) porosity >7 vol.%, (4) brittle minerals contents >50%, (5) oil saturation in the range of 5()%~8()%, (6) AP1>40° and pressure coefficient >1.30, (7) good development of fractures. A rock classification scheme for tight oil reservoirs, which have mixed terrigenous clastics and lacustrine carbonates sedimentary origins, is proposed to describe the Permian mixed sedimentary tight oil reservoir in the Junggar basin, and the preliminary assessment suggests that the technical recoverable reserves of tight oil and shale oil in the study area are approximately ( 20-25) xlO't and (30-60) x I0't, respectively. The key innovation and challenges of the new-era unconventional oil and gas might concentrate on the formation mechanisms of lacustrine fine-grained sediments, micrometer-nanometer scale storage structures of low permeable reservoirs, charge and migration of liquid hydmearbons in shales, and reservoir geophysical response models of tight oil and shale oil as well as resource potential assessment and enrichment patterns of tight oil and shale oil.