我国煤层气储层异常压力的成因分析

通过分析我国煤区大量的煤储层压力资料,对引起煤储层异常压力的成因、成压环境、成压机制、压力类型特征进行系统研究表明,煤层埋藏过程、生气作用是地质历史中煤层高异常压力形成的主要成压机制,而煤层割理与煤盖层突破在引起大规模流体向外运移过程中扮演着极为重要的降压角色,水热作用、构造应力、水动力等在不同时期,不同部位具双重性;后期的抬升、剥蚀作用、上覆负荷应力减小、封盖条件的破坏,尤其是近地表的水文地质条件的改变,是控制现今煤层压力分布的主要原因;煤层气储层异常压力表现特征主要有4种类型：1)水动力封闭型,2)自封闭型,3)弱开启型,4)强开启型;地质构造演化复杂、地层抬升剥蚀强烈、地形差别大、渗透率低、应力分布复杂、区域水文地质条件变化较大等诸多因素是造成我国煤层低压的原因。

GENETIC ANALYSIS ON THE ABNORMAL PRESSURE OF THE GAS RESERVOIRS IN THE COAL LAYERS IN CHINA

On the basis of analysis on the pressure data from the coal layer gas reservoirs in China,this paper thoroughly described the genesis,the environment conditions and the characteristics and types of the abnormal pressure in the coal layer-related gas reservoirs,and analyzed the reasons for the low pressure in the coal layers in China.The study showed that pressure-forming mechanism was resulted from the high abnormal pressure during the burial process and the gas formation in the geological history,and the joints and outbursts of the cap rocks played an important role in the process of large-scale outward migration of fluid.In addition,the water heating,tectonic stress and hydrodynamics are of dual effects at different periods and different locations.The uplift in the late stage,the erosion,the decrease of overlying loading pressure,the destruction of capping condition,especially the change of hydrogeological condition near the surface of the earth,were the main fctors controlling the current pressure distribution in the coal layers.Four types of abnormal pressure of the gas-bearing coal layers were recognized as (1) self confining typem,(2) hydrodynamic confining type,(3) weakly opening type and (4) strongly opening type.Finally,the reasons for the low pressure of the coal layers in China were concluded as such factors as the complexity of the tectonic evolution,the strong erosion due to the strata uplifting,the sapparent difference in topography,the low permeability,the complexity of the stress distribution and the variation of the regional hydrogeological condition.