川东地区热体制恢复及其与页岩气生成富集的关系

Organic-enriched shale is the carrier of shale gas generation and reservoir, geothermal evolution of which not only influence the maturity of organics, hydrocarbon generation capability, hydrocarbon generation stages, generation process, and transformation, but formation of micro-nano pores of organics, occurrence of shale gas within. Southern China have abundant resources of shale gas, but we unclear about the generation process, reservoir quality, changes of pore pressure about the shale under the geothermal evolution, which indication restricts the understand of gas-bearing properties and evaluation of exploration risks, because of the difficulty of reconstruction of geothermal system of the superimposed evolution of basin, by the reasons of the covered thermal record, and absence of effective geothermometer used in the Early Palaeozoic stratum, also of simple methodology...We plan to reconstructing the geothermal process of Jiaoshiba and Pengshui shale gas reservoir, which have similar original sedimentary environment, eastern Sichuan basin, China (ESC), with the method of combined multiple geothermometer. Bottom hole temperature, thermophysical property of cores, out-crop samples, Ro of shale organics, fission track of zircons, apatite and sphenes, geochronology and closure temperature of zircons, apatite and sphanes will be analyzed to reconstructing geothermal system of ESC. Combined with observation of microstructure, analyzation of reservoir porosity and permeability, and gas bearing capacity, we expect to forecasting and discovering shale gas enrichment region, and pointing out the relationship of generation and concentration of shale gas during the geothermal process.

富有机质页岩是页岩气生成和储集的母体，其受热史不仅影响有机质成熟度、生烃能力、时间和期次、持续过程，还会影响以有机质微孔为代表的储集空间、页岩气的赋存状态等要素。中国南方海相页岩气资源潜力巨大，但由于多期构造演化改造使早期热信息遭受掩盖或叠加，早古生界地层缺乏有效古温标，研究方法单一，难以系统恢复早古生代地层的热演化体制。该问题影响了页岩在热体制下生烃过程、储集性能、孔隙压力演化的统一认识，同时也制约了对高演化页岩含气性和保存条件的评价。项目拟选择四川盆地东缘原始沉积环境相近的焦石坝和彭水典型气藏做对比，基于多温标耦合反演技术恢复叠加盆地热体制（现今地温场热结构计算、Ro-AFT-(U-Th)/He-包裹体联合反演古地温场和热史），结合微观孔隙结构观察和物性测试，揭示热作用与页岩生烃（气）、富集与成藏、保存之间的内在联系，进一步提升页岩气成藏富集机制的认识，并为页岩气甜点预测提供科学依据。

以川东南地区下古生界志留系龙马溪组页岩气生成富集规律为研究目标，基于现今地温场特征分析、利用古温标数据镜质体反射率（Ro）和低温热年代学（U-Th）/He的联合反演，选择涪陵-石柱-彭水地区为典型代表，对本地区的热史综合分析。研究得到以下主要认识：.一是四川盆地东南部现今大地热流属于“温热”背景，地温梯度分布范围为16-32℃/km，涪陵页岩气田焦石坝构造高部位达最大值，热流值介于60-75mW/m2之间，沿盆地边界往南西方向逐渐降低；.二是二叠世末期峨眉山地幔柱事件对四川盆地大部分地区有重要影响，由西向东逐渐减弱，在区内有明显反映，估算的热流值最大达到70-100mW/m2，此后缓慢降低至现今的地表热流60-70mW/m2；.三是系统恢复典型剖面热史演化过程，龙马溪组的烃源岩于晚石炭世进入低成熟阶段，早二叠世进入高成熟阶段，晚二叠世初期（256Ma）进入过成熟阶段，二叠纪末进入高成熟阶段，于早三叠世达到最高阶段，并在75-105Ma左右发生阶段性抬升，对志留系（寒武系和震旦系页岩也然）的储集和逸散有明显控制；.四是在重点评价区内构造变形与演化对油气生成和富集关系的影响，尤其是深埋与抬升作用、缩短与变形程度对页岩生排烃、储集、保存、散失与富集等关系的相互作用，提出了南方复杂构造区页岩气富集机理与发育模式；.五是页岩气富集机理与主控因素认识，针对中国南方复杂构造带页岩气富集和资源分布规律，根据构造样式与页岩气富集机理，总结出了构造复杂区内简单背斜控藏型、逆断背斜控藏型等五类页岩气富集模式。