温和氧化解聚作用下，低阶煤(褐煤、长焰煤)可高效生成高值化学品，同时煤体多尺度流动能力显著改善。针对我国低阶煤资源丰富与煤层中赋存巨量天然气的地质背景，结合低阶煤化学性质特点，提出了基于原位氧化改性的深部低煤阶煤层高值化学品与天然气共采技术构想，从氧化解聚制备羧基化学品方法、氧化改性提高煤层气采收率机理、共采技术模式、地质及工程有利条件等4方面论证了该技术可行性。调研总结发现：低阶煤具有丰富的含氧官能团(如羧基—COOH和酚羟基—OH)和侧链，为氧化解聚制备高值化学品(如羧酸)提供了关键前体结构；过氧化氢、次氯酸钠等氧化剂，在低温(<100 ℃)、常压条件下，温和氧化解聚低阶煤可高效、低成本制备羧基化学品，实现低阶煤非能源化高值利用；氧化解聚反应对低阶煤具有明显的氧化改性作用，主要表现为煤表面对甲烷的吸附能力减弱、水的疏水性增强、形成溶蚀孔与微裂缝，并可原位生成CO2，从而增加了煤层气解吸-渗流能力。围绕深部低煤阶煤层气井高效增产改造需求与枯竭煤层气井二次利用，设计了单井压裂-溶浸开采(采气为主)与群井压裂-溶浸开采(采高值化学品为主)2种技术模式。前者通过注入氧化性压裂液，合理控制压后焖井时间，充分发挥力学-化学协同改造增渗作用，返排阶段分离压裂液中高值化学品，并高效抽采天然气；后者对各枯竭气井重复改造，通过压裂缝网形成相互沟通的注采井网，持续生成、抽采高值化学品。我国巨厚(数十米～近百米)、深埋藏(500～1 000 m)低煤阶煤层分布广泛，能有效减小氧化剂及反应产物泄漏诱发的地下水污染，为共采提供了有利地质条件；现有大规模煤层气水平井及水力压裂缝网，避免了高值化学品原位制备的高额建井成本，为共采提供了有利工程条件。结论认为，利用温和氧化解聚反应，实现深部低煤阶煤层高值化学品与天然气共采，丰富了原位改性采矿理论与技术体系，有望形成煤层气增产改造新模式，增加低煤阶煤层资源开采综合经济效益。

Mild oxidative depolymerization of low-rank coal (lignite and long-flame coal) can generate high-value chemicals and improve the gas transport capacity.In view of the geological background of abundant low-rank coal resources and huge amount of natural gas in coal seams in China,the concept of in-situ oxidation modification-based co-extraction technology of high-value chemicals and gas in deep low-rank coal seams is proposed.The feasibility of this technology is studied from four aspects,including the oxidation depolymerization method to prepare carboxy chemicals,the mechanism of oxidation modification to improve coalbed methane recovery,the co-extraction technology model,and the favorable geological and engineering conditions.It is found that low rank coal has abundant oxygen-containing functional groups (such as carboxyl —COOH and phenolic hydroxyl—OH) and side chains,which provide key precursor structures for the preparation of high-value chemicals (such as carboxylic acid) by oxidative depolymerization.Under the condition of low temperature (<100 ℃) and atmospheric pressure,the mild oxidative depolymerization of low-rank coal with hydrogen peroxide,sodium hypochlorite and other oxidants can prepare carboxyl chemicals with high efficiency and low cost,and realize the non-energy high value utilization of low-rank coal.The oxidative depolymerization reaction has an obvious oxidative modification effect on low-rank coal,mainly manifested by the weakened adsorption capacity of coal surface for methane,enhanced hydrophobicity of water,formation of soluble pores and microfractures,and in-situ generation of CO2,thus increasing the desorption-percolation capacity of coal bed gas.Based on the demand for the high-efficiency production transformation of deep low coalbed methane wells and the secondary utilization of depleted coalbed methane wells,two technical models are designed:a single-well fracturing-dissolution leaching extraction (gas extraction-based) and a group-well fracturing-dissolution leaching extraction (high-value chemical extraction-based).The former is to inject oxidizing fracturing fluid,reasonably control the stewing time after fracturing,give full play to the mechanical-chemical synergistic transformation to increase seepage,separate the high-value chemicals in the fracturing fluid at the rejection stage,and efficiently extract natural gas.The latter is to repeat the transformation of each depleted gas well,form an intercommunicating injection and extraction well network through the fracture network,and continuously generate and extract high-value chemicals.China’s mega-thick (tens of meters to nearly 100 m),deep buried (500-1 000 m) low-rank coal seams are widely distributed,which can effectively reduce the groundwater pollution induced by the leakage of oxidants and reaction products,and provide favorable geological conditions for co-mining.The existing large-scale horizontal coalbed methane wells and hydraulic fracture network can avoid the high well construction cost of in-situ preparation of high-value chemicals and provide favorable engineering conditions for co-production.It is concluded that the co-exploitation of high-value chemicals and natural gas in deep low-rank coal seams can be realized by mild oxidative depolymerization reaction.It enriches the theory and technical system of in-situ modified mining in deep coal seams,is expected to form a new model of coal-bed methane production enhancement and transformation,and increases the comprehensive economic benefits of low-rank coal seam resource exploitation.

1 低阶煤主要官能团及氧化解聚制备高值化学品方法

   1.1 官能团及氧化解聚反应机理

   1.2 过氧化氢(H2O2)氧化解聚效率及机理

   1.3 次氯酸钠(NaClO)氧化解聚效率及机理

2 氧化改性作用对提高煤层气采收率的影响

   2.1 氧化改性作用对煤层气吸附-解吸影响

   2.2 氧化改性作用对煤层渗透率影响

   2.3 煤中有机显微组分对氧化改性提高采收率效果影响

3 基于原位氧化改性的深部低阶煤高值化学品与天然气共采技术构想

   3.1 低阶煤原位氧化改性概念与关键科学问题

   3.2 原位氧化改性共采高值化学品与天然气技术模式

   3.3 技术发展面临挑战

4 原位氧化改性作用下高值化学品与天然气共采可行性及战略意义

5 结论