中国页岩气特征、挑战及前景(二)

Shale gas in China:characteristics,challenges and prospects(Ⅱ)

重点阐述中国页岩气工业化进展、“甜点区”评价标准与勘探开发技术、成功经验、面临挑战及发展前景。根据四川盆地涪陵、长宁、威远等页岩气田地质与工程参数，指出中国页岩气具有特殊性。中国南方特大型海相高演化（R0值2．0％～3．5％）、超高压（压力系数1．3～2．1）页岩气田的发现，对中国乃至世界古老海相页岩气勘探开发具有重要科学意义与实践价值。提出“经济甜点区”须具备“含气性优、可压性优、效益性优”等特征，“四高”（高TOC值（大于3．0％）、高孔隙度（大于3．0％）、高含气量（大于3．0m3／t）、高地层压力（压力系数大于1．3））、“两发育”（页岩层理、天然微裂缝）是富集高产段与水平井轨迹选择的关键指标，水平井巷道必须控制在上奥陶统五峰组一下志留统龙马溪组底部高压封存箱中部。提出“微气藏”群压裂形成“人工页岩气藏”的模式，揭示“压后焖井、控压限产”机制。形成了三维地震与压裂微地震监测、水平井、“工厂化”生产模式等关键技术和“甜点区”优选、水平井巷道控制、水平段长度优化、“工厂化”生产模式等成功经验。页岩气资源的不确定性、3500m以深勘探开发关键技术与装备突破、低成本生产、水资源与安全环保是中国页岩气实现规模开采面临的4大挑战。预测中国南方海相页岩气可采资源量约8．8×10^12m3，四川盆地有利区面积4．0×10^4km2、可采资源量4．5×10^12m3，2020年中国页岩气勘探开发有望实现“理论、技术、生产和成本”4个一体化革命，产能达到（200～300）×10^8m3／a。未来有望在四川盆地常规加非常规天然气产量一起建成“西南大庆（气大庆）”。

This paper mainly discusses the industrialization progress, ＂sweet spot＂ evaluation criterion, E＆P technologies, success experiences, challenges and prospects of China＇s shale gas. Based on the geologic and engineering parameters of the Fuling, Changning and Weiyuan shale gas fields in the Sichuan Basin, this paper points out that China＇s shale gas has its particularity. The discoveries of super-giant marine shale gas fields with high evolution degree （R0=2.0%-3.5%） and ultrahigh pressure （pressure coefficient=1.3-2.1） in southern China is of important scientific significance and practical value to ancient marine shale gas exploration and development to China and even the world. It＇s proposed that shale gas ＂sweet spots＂ must be characterized by high gas content, excellent frackability and good economy etc. The key indicators to determine the shale gas enrichment interval and trajectory of horizontal wells include ＂four highs＂, that is high TOC （〉3.0%）, high porosity （〉3.0%）, high gas content （〉3.0 m3/t） and high formation pressure （pressure coefficient〉l.3）, and ＂two well-developed＂ （well-developed beddings and well-developed micro-fractures）. It＇s suggested that horizontal well laneway be designed in the middle of high pressure compartment between the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation. The mode of forming ＂artificial shale gas reservoir＂ by ＂fracturing micro-reservoir group＂ is proposed and the mechanism of ＂closing-in after fracturing, limiting production through pressure control＂ is revealed. Several key technologies （such as three-dimensional seismic survey and micro-seismic monitoring of fracturing, horizontal wells, ＂factory-like＂ production mode, etc.） were formed. Some successful experiences （such as ＂sweet spot＂ selection, horizontal well laneway control, horizontal length optimization and ＂factory-like＂ production mode, etc.） were obtained. The four main challenges to realize large-scale production of shale gas in China include uncertainty of shale gas resources, breakthroughs in key technologies and equipment of shale gas exploration and development below 3 500 m, lower cost of production, as well as water resources and environment protection. It is predicted that the recoverable resources of the Lower Paleozoic marine shale gas in southern China are approximately 8.8×1012 m3, among which the recoverable resources in the Sichuan Basin are 4.5× 1012 m3 in the favorable area of 4.0× 104 km2. The productivity of （200-300）×10s m3/a is predicted to be realized by 2020 when the integrated revolution of ＂theory, technology, production and cost＂ is realized in Chinese shale gas exploration and development. It is expected in the future to be built ＂Southwest Daqing Oilfield （Gas Daqing）＂ in Sichuan Basin with conventional and unconventional natural gas production.