ZOU Cai-neng1*, ZHU Ru-kai1, BAI Bin1, YANG Zhi1, HOU Lian-hua1, ZHA Ming2, FU Jin-hua3, SHAO Yu4, LIU Ke-yu1, CAO Hong1, YUAN Xuan-jun1, TAO Shi-zhen1, TANG Xiao-ming2, WANG Lan1, LI Ting-ting1
1. Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, China;
2. China University of Petroleum(Eastern China), Qingdao Shandong 266580, China;
3. Research Institute of Exploration and Development, PetroChina Changqing Oilfield Company, Xi'an 710018, China;
4. Research Institute of Exploration and Development, PetroChina Xinjiang Oilfield Company, Karamay Xinjiang 834000, China
Abstract: The research on tight 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 rock quality, lithology, petrophysics, brittleness, gas/oil contents, and underground stress anisotropy of reservoirs. Prolific shale strata in China possess such geological features of (1) TOC >2% or S1 >2 mg/g, (2) laminated shale, tight 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 (1) TOC>4%, (2) laminated shale or mudstone, (3) porosity >7 vol.%, (4) brittle minerals contents >50%, (5) oil saturation in the range of 50%~80%, (6) API>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)×108t and (30~60)×108t, 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 hydrocarbons 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.
Keywords: tight oil shale oil shale gas fine-grained sedimentology "sweet spot" assessment petrophysics mixed sedimentary rock ICP unconventional petroleum
*Corresponding Author, E-Mail: zcn@petrochina.com.cn
Bulletin of Mineralogy, Petrology and Geochemistry Vol. 34, No.1, 2015, page 191-200
