深盆气基本概念与特征

深盆气的最本质特征是盆地中心饱含气。凡煤系发育、构造稳定、埋藏适中、经历过高地温演化阶段的盆地都能形成深盆气。深盆气上倾方向多因致密岩石含水而封闭，孔隙性地层的水封只是个例，它因深盆中仍不断大量供气而存在。深盆气形成于高温高压的环境中，早期地层水因汽化而与甲烷气混溶，一部分随岩性变致密加厚水膜而成为束缚水，导致深盆气盆地内无水层。但在深盆气萎缩阶段，降温降压过程可使蒸汽水“冷凝”形成深盆气中的“酸点”。“酸点”水规模小呈散点状分布，矿化度低于正常地层水矿化度。深盆气因所处演化阶段不同而具有不同的压力特征，既可以是低压的，也可以是高压的。松辽盆地、沁水盆地和西北侏罗系含煤盆地都具有深盆气形成的条件。

Key Concept and Characteristics of Deep Basin Gas Accumulation

The essence of deep basin gas accumulation is gas saturated feature in the basin center, which may present several hundred meters of gas in a well bore without water, and generally include coal bed absorbed gas, shale fracture gas, and sandstone void gas. Basin centered gas accumulation could easily happen in a basin with plenty of coal formation, moderate burial depth, tectonic constancy, and a mega temperature evolution history. Most of deep basin gas accumulations are sealed by tight reservoir water in updip direction and involve everlasting gas supply, but this is only one of deep basin gas styles. Mutual dissolution of water vapor and methane in the ancient HTHP situation and the formation of bound water in reservoir bed compaction lithogenesis led to the absence of water layers in deep basin gas accumulation.“Acid dew” which has lower salinity than formation water will present along with mutual dissolution vapor condensation during the cooling and shrinking stage of deep basin gas accumulation. Deep basin gas accumulation may have the subpressure or surpressure characteristics in different evolutionary phases. Deep basin gas accumulations are available in Songliao basin, Qinshui basin and other coal basins in Northwest China.