Geological characteristics and resource potential of shale gas in China

With Sichuan Basin as focus, this paper introduces the depositional environment, geochemical and reservoir characteristics, gas concentration and prospective resource potential of three different types of shale in China: marine shale, marine-terrigenous shale and terrigenous shale. Marine shale features high organic abundance (TOC: 1.0%–5.5%), high-over maturity (Ro: 2%–5%), rich accumulation of shale gas (gas concentration: 1.17–6.02 m3/t) and mainly continental shelf deposition, mainly distributed in the Paleozoic in the Yangtze area, Southern China, the Paleozoic in Northern China Platform and the Cambrian-Ordovician in Tarim Basin; Marine-terrigenous coalbed carbonaceous shale has high organic abundance (TOC: 2.6%–5.4%) and medium maturity (Ro: 1.1%–2.5%); terrigenous shale in the Mesozoic and Cenozoic has high organic abundance (TOC: 0.5%–22.0%) and mid-low maturity (Ro: 0.6–1.5%). The study on shale reservoirs in the Lower Paleozoic in Sichuan Basin discoveried nanometer-sized pores for the first time, and Cambrian and Silurian marine shale developed lots of micro- and nanometer-sized pores (100–200 nm), which is quite similar to the conditions in North America. Through comprehensive evaluation, it is thought that several shale gas intervals in Sichuan Basin are the practical targets for shale gas exploration and development, and that the Weiyuan-Changning area in the Mid-South of Sichuan Basin, which is characterized by high thermal evolution degree (Ro: 2.0%–4.0%), high porosity (3.0%–4.8%), high gas concentration (2.82–3.28 m3/t), high brittle mineral content (40%–80%) and proper burial depth (1500–4500 m), is the core area for shale gas exploration and development, the daily gas production for Well Wei 201 is 1×104–2×104 m3. ： 以四川盆地为重点，介绍中国海相、海陆过渡相、陆相三大类型页岩形成的沉积环境、地球化学与储集层特征、含气量与远景资源量。中国海相页岩是一套高有机质丰度（TOC为1.0%～5.5%）、高—过成熟（Ro值为2.0%～5.0%）、富含页岩气（含气量1.17～6.02 m3/t）、以陆棚相为主的沉积，主要分布在华南扬子地区古生界、华北地台古生界和塔里木盆地寒武系—奥陶系；海陆过渡相煤系炭质页岩有机质丰度高（TOC为2.6%～5.4%）、成熟度适中（Ro值为1.1%～2.5%）；中新生界陆相页岩有机质丰度高（TOC为0.5%～22.0%）、低熟—成熟（Ro值为0.6%～1.5%）。在对四川盆地下古生界页岩储集层研究中首次发现，寒武系和志留系海相页岩发育大量与北美地区相似的微米—纳米级孔隙。综合评价认为四川盆地发育的多套页岩气层系是勘探开发的现实领域，四川盆地中南部威远—长宁等地区的寒武系和志留系是页岩气勘探开发的核心区与层系，其特点是：热演化程度较高（Ro值为2.0%～4.0%）、孔隙度较高（3.0%～4.8%），含气量较高（2.82～3.28 m3/t）、脆性矿物含量较高（40%～80%）、埋深适中（1 500～4 500 m），有利于开采。图7表7参38