摘要
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?
Even if coalbed methane (CBM) is mainly defined as sorption gas on the inner surface of coal, there still is a contradiction between the preservation and loss. The mechanism of CBM pool trap is capillary trap, mass concentration difference (gradient) trap and pressure trap. Three different trap types may be recognized according to the trap mechanism. There are selftrap in which mechanism of CBM pool trap is mainly capillary trap, surrounding rocks and their suitable hydrological trap in which mechanism of CBM pool trap is mainly pressure and capillary trap, and mixed trap in which mechanism of CBM pool trap is capillary, mass concentration difference and pressure traps. The trap feature of selftrap mainly depends on the developing features of the pore_fracture system of coal reservoirs. The CBM pool of selftrap usually is high content of gas. The gas saturation of the CBM pool in the surrounding rocks and their suitable hydrological trap mainly depends on the following factors: (1) the lithotypes and their thickness of continuous deposits; (2) the CBM (or gas) mass concentration of CBM pool (or in other rocks) nearby; (3) the presence of a simple tectonic condition; (4) the relative stable hydrological condition; (5) the distance between the regional unconformity and a CBM pool, and the presence of faults between them. The three scale traps are recognized according to the trapping scales. The first degree trap is non_coalbearing strata trapping several CBM pools in the coal_bearing strata. The second degree trap is other rocks in the coal_bearing strata trapping one coalbed and its roof and floor rocks. The third degree trap is the roof and floor rocks trapping their coalbed. The CBM pool trapping condition is very important for the CBM preservation and high_production. The hydrological condition is key factor which affects the CBM preservation. Recognizing the difference of CBM pool traps among the different geological conditions and searching for the good trapping conditions of CBM pool are very important research contents for selecting good exploration area in North China.
出处
《地球科学（中国地质大学学报）》
EI
CSCD
北大核心
1999年第1期49-53,共5页
Earth Science-Journal of China University of Geosciences
基金
国家"八五"攻关项目
