中煤阶煤层气高饱和—超饱和带的成藏模式和勘探方向

中国低、中、高煤阶煤层气的资源量各占总资源量的1/3，中煤阶煤层气的勘探开发取得了一定的进展。在解剖分析鄂尔多斯盆地东缘保德区块、临兴区块和准噶尔盆地白杨河矿区、白家海凸起等地区的煤层气分布深度、成因以及高饱和—超饱和带分布特征的基础上，总结出煤层气高饱和—超饱和带的成藏模式。研究表明：①在中国中—西部盆地中，中煤阶煤层存在的深度和深度区间很大，这为中煤阶煤层气的开发提供了巨大的埋深空间，此外，中煤阶煤层气以热成因气为主，个别区块的浅层有一定程度的次生生物气补给；②针对中国煤储层渗透率低的现实，寻找高含气饱和—超含气饱和带是高效开发煤层气的关键，其中，煤层气的高饱和—超饱和带包括次生生物气补充型、二次热生烃补充型和深层型3种；③次生生物气补充型高饱和—超饱和带出现在浅层淡水入渗的影响范围内，二次热生烃补充型高饱和—超饱和带出现的深度与岩浆侵入影响的深度有关，这2种成藏模式出现在局部地区，深层高饱和—超饱和带从机理上来看较普遍，且已得到勘探实践的证实；④在积极探索次生生物气补充型和二次热生烃补充型高饱和—超饱和带的同时，寻找深层超饱和煤层气的"甜点区"，这可能成为中国煤层气未来勘探开发的重要发展方向；5利用常规油气井对深层煤层气进行探索可能是深层高饱和—超饱和带煤层气开发最有效的方式，而对于新钻的穿过深层煤层的常规油气井，应注意煤层取样和煤储层评价工作，以尽快发现更多的深层超饱和煤层气。

Accumulation model and exploration direction of high- to over-saturation zone of the midium-rank coalbed methane

In China, the low-, medium-and high-rank coalbed methane (CBM) resources account for 1/3 of the total resource amount, respectively. The exploration and development of medium-rank CBM has made some progress. Based on analyzing the distribution depth, genesis, and distribution characteristics of CBM in Baode and Linxing blocks of the eastern margin of Ordos Basin, Baiyanghe mining area and Baijiahai uplift of Junggar Basin, and other areas, this paper summarizes the accumulation model of the high-to over-saturation zone of CBM. (1) In the central and western basins of China, the depth and depth interval of the medium-rank coalbeds are very large, providing a huge burial depth space for the development of medium-rank CBM. In addition, the medium-rank CBM is dominated by thermogenic gas, and a certain amount of secondary biogenic gas is supplied to the shallow layers of individual blocks. (2) In view of the low permeability of coal reservoirs in China, exploring high or over saturation gas zones are the key for the efficient development of CBM. Three types of high-to over-saturation CBM zones are secondary biogenic gas supplement type, secondary thermal generation of hydrocarbon supplement type, and deep layer type, respectively. (3) The high-to over-saturation zone recharged by secondary biogenic gas appears in the influence range of shallow freshwater infiltration. The depth of the high-to over-saturation zone recharged by secondary thermal generation of hydrocarbon is related to the depth range of magma intrusion. These two accumulation models appear in local areas. The deep high-to over-saturation zones are common as judged in terms of mechanism, and have been confirmed by exploration practices. (4) To search for the "sweet spot" of deep over-saturation CBM in China during actively exploring the high-to over-saturation zones recharged by secondary biogenic gas and secondary thermal generation of hydrocarbon may become an important development direction for China's CBM exploration and development in the future. (5) Using conventional oil and gas wells to explore deep CBM may be the most effective way to develop CBM in the deep high-to over-saturation zone. For newly drilled conventional oil and gas wells that penetrate through deep coalbeds, attention should be paid to coalbed sampling and coal reservoir evaluation, so as to discover more over-saturation CBM at depth as soon as possible.