煤炭地下气化及对中国天然气发展的战略意义

在实现碳达峰碳中和(“双碳”)目标和保障国家能源安全的双重需求驱动下，我国煤炭地下气化(UCG)迎来了新的历史发展机遇期。为科学制定技术攻关路线、加快产业化发展，按时间顺序梳理了煤炭地下气化试验历程，将其分为矿井式气化、直井/定向井气化、水平井气化3个发展阶段，探究了不同阶段推动气化技术革新的底层逻辑，从技术和非技术2个方面分析了未能产业化的原因并提出产业化发展建议。研究表明：(1) 水平井+可控注入点后退气化工艺不仅能够有效规避浅层气化在地表沉降、淡水污染方面的风险，而且在扩大煤炭纵向开发范围、提高单井控煤量、提升粗煤气品质、保障连续气化方面具有优势，是当前和今后一个时期的主流技术路线。(2) 我国是现场试验时间最长的国家，长期处于矿井式气化阶段，虽然我国中深层煤炭地下气化攻关试验刚起步，但是由于该技术攻关难度大、技术成熟度低，主要富煤国家在技术研发上基本属于同一起跑线，有希望成为我国钻井式气化技术弯道超车的新赛道。
(3) 技术适用性不强是造成矿井式、直井式气化产业化困难的主要技术原因，技术成熟度较低是制约水平井气化产业化的主要技术原因，长期稳产高产问题尚未得到彻底解决。(4) 常规天然气低成本开发和页岩气革命的冲击，民众对浅层气化诱发环境污染的担忧，政府对煤炭地下气化的政策转向，是导致国外试验终止的主要非技术原因；发展规划长期空白、科研试验主体相对单一、科研投入不足、产业扶持政策未出台、联合创新机制未建立是阻碍我国气化产业化的非技术原因。提出我国UCG产业化建议：新时期要充分认识煤炭地下气化技术的复杂性和挑战性，按照“干成”“干好”两个维度，破解“长期稳产”和“高产优产”两个核心问题，通过同步推进科研攻关和现场试验不断提高技术成熟度，在生产端采用“先物理采气后化学气化”的梯级开发方式避免与煤层气开发竞争，在利用端积极探索与油气、新能源、煤化工融合发展模式以提高经济效益。作为一种“人造气藏”的颠覆性开发方式，煤炭地下气化攻关成功后能为其他矿产资源的流态化开发提供技术借鉴，助推我国化石能源非常规开发技术实现新跨越。

Underground coal gasification and its strategic significance to the development of natural gas industry in China

Driven by the dual demands for achieving the goals of peak carbon dioxide emissions and carbon neutrality and for ensuring national energy security, underground coal gasification (UCG) in China is embracing a new historical development opportunity. To scientifically formulate a route for making technological breakthroughs in UCG and accelerate its industrialization, this study analyzed the history of UCG field tests, dividing UCG into three stages: UCG based on coal mines, vertical/directional wells, and horizontal wells. By exploring the underlying logic that propelled innovations in UCG technologies in different stages, this study delved into the technical and non-technical reasons for the failure of UCG industrialization and finally proposed suggestions. Key findings are as follows: (1) The UCG technology combining horizontal wells with the controlled retracting injection point (CRIP) process can effectively avoid the risks of surface subsidence and freshwater pollution caused by shallow gasification. Furthermore, this technology enjoys advantages in terms of expanding the vertical coal mining range, increasing single-well-controlled coals, improving the quality of raw gas, and ensuring continuous gasification. Hence, this technology serves as a mainstream technical route currently and in the future. (2) After the longest field test period, China has remained long in the stage of UGS based on coal mines. Although China is still in the initial stage of tests for breakthroughs in moderately deep UCG, it roughly keeps the same pace with other major coal-rich countries in terms of technical research and development due to the challenging technology research and low technological maturity. Therefore, China is expected to overtake these countries in the technology for UCG based on drilled wells. (3) Regarding technical reasons, limited technology applicability poses challenges in the industrialization of UCG based on coal mines and vertical wells, while low technological maturity predominantly restricts the industrialization of UGS based on horizontal wells.
Consequently, long-term stable and high gas production is yet to be achieved. (4) Concerning non-technical reasons, the termination of UCG tests abroad is primarily caused by low-cost production of conventional natural gas, the influence of the shale gas revolution, public concerns about environmental pollution caused by shallow gasification, and governments' UCG policy shift. In contrast, China's UCG industrialization is principally hindered by a prolonged gap in development planning, relatively limited entities engaging in scientific research and tests, insufficient investment in scientific research, a lack of industrial support policies, and the absence of joint innovation mechanisms. This study proposed suggestions for China's UCG industrialization. In the new era, it is necessary to thoroughly identify the complexity and challenges of UCG technology. Then, great efforts should made to achieve long-term stable production with considerably high quality. It is recommended that the technological maturity should be constantly improved through synchronous scientific research and field tests. The cascade production mode featuring physical gas extraction followed by chemical gasification should be employed to avoid competition with coalbed methane production. Meanwhile, it is necessary to actively explore the utilization mode that integrates oil and gas, new energy, and coal chemical industry for elevated economic benefits. As a revolutionary production technology for artificially created gas reservoirs, UCG, after successful achievement, can provide a technical reference for the fluidization exploitation of other mineral resources and push China's unconventional technology for fossil energy development to a new level.