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煤层气是一种以吸附气为主的天然气，其保存与散失的矛盾仍十分突出．毛细封闭、质量浓度差封闭和压力封闭是煤层气藏封闭的主要表现形式．根据这３种不同封闭机理对煤层气藏的作用特点的不同，可以分为以压力封闭和围岩中毛细封闭为主的他封闭型，以毛细封闭和质量浓度差封闭为主的自封闭型，以及３种封闭共同作用的混合封闭型．自封闭型煤层气藏的封闭特征主要取决于煤储层自身的孔裂隙系统发育特征，其含气量通常较高．而他封闭型煤层气藏的含气饱和度受下列因素的制约：（１）连续沉积的围岩岩性及其厚度；（２）相邻煤层气藏中煤层气（或烃）质量浓度的高低；（３）构造条件是否简单稳定；（４）水文地质条件是否稳定；（５）区域不整合界面与煤层气藏之间的垂直距离及其连通状况．煤层气藏的外部封闭按规模可分为３级：第１级封闭是煤系围岩对煤系内若干煤层气藏的封闭；第２级封闭是煤系内其他岩系对某一煤层气藏及其顶底板构成的封闭；第３级封闭是顶底板围岩对某一特定煤层气藏的封闭．煤层气藏封闭条件的优劣是决定煤层气藏保存与高产的关键因素之一，而水文地质条件是影响煤层气藏封闭的关键．认识华北不同地质条件下各煤层气藏封闭特征的差异、寻找封闭条件良好的煤层气藏是今后煤层气勘探?
CBM is a kind of natural gas mainly composed of adsorbed gas, and its contradiction between preservation and dissipation is still outstanding. The closed capillaries, poor mass concentration and pressure sealing are the main manifestations of the closed CBM reservoir. According to the different characteristics of the three different sealing mechanisms on the CBM reservoir, it can be divided into closed-type pressure-confined and capillary-type enclosed in the surrounding rock, closed-type with closed capillary and closed mass concentration , As well as three kinds of closed interaction of the mixed closed type. The closed characteristics of self-enclosed CBM reservoirs mainly depend on the development of pore-fractured systems in coal reservoirs, which usually have high gas content. The gas saturation of a closed coalbed methane reservoir is constrained by the following factors: (1) the lithology and thickness of the surrounding rock continuously deposited; (2) the mass concentration of CBM (or hydrocarbon) in the adjacent coalbed methane reservoir (3) Whether the structural conditions are simple and stable; (4) Whether the hydrogeological conditions are stable; (5) The vertical distance between the regional unconformity interface and the coalbed methane reservoir and its connectivity. The external sealing of coalbed methane reservoirs can be divided into three levels according to the scale: the first level seal is the closure of some CBM reservoirs in the coal measure in the coal measures; the second level seal is the seal of some other coal measures within a coal measure to a certain CBM Tibet and its top floor constitute a closed; Level 3 closure is top and bottom wall rock for a particular coalbed methane reservoir closure. The pros and cons of sealing conditions of CBM reservoirs is one of the key factors that determine the preservation and high yield of CBM reservoirs, and the hydrogeological conditions are the key factors affecting the closure of CBM reservoirs. Recognizing the differences in the sealing characteristics of coalbed methane reservoirs under different geological conditions in North China, looking for coalbed methane reservoirs with good closed conditions is the future CBM exploration?