低渗透砂岩天然气运移和聚集模拟实验

摘要

低渗透砂岩气藏勘探表明，其形成与分布具有独特的特征，很难用常规天然气成藏理论进行解释与描述。在低渗透砂岩天然气岩心充注模拟实验的基础上，对低渗透砂岩天然气藏的运移和聚集特征进行了研究。研究结果表明：气体在低渗透砂岩中的运移需要克服储层的最小阻力和最大阻力，当运移动力位于二者之间时，气体的主要运移方式表现为非达西流；运移动力小于最小阻力时，气体的运移方式为扩散；运移动力大于最大阻力时，气体的运移方式为达西流。正是这种复杂的气体运移方式，导致了低渗透砂岩中复杂的气水分布关系。天然气的聚集成藏过程主要受运聚动力、储层物性和束缚水饱和度控制。随运聚动力的增加，含气饱和度逐渐增加，并在束缚水的影响下最终趋于稳定，含气饱和度一般小于60％。在相同的动力下，渗透率越大的储层含气饱和度越大，这也是“甜点”成藏的主要原因。%The explorations of gas reservoirs in low-permeability sandstones have indicated that they have unique characteristics, hence are difficult to interpret and describe with conventional natural gas accumulation theories. Based on the experiments of natural gas charging of cores, the migration and accumulation characteristics of natu-ral gas in low-permeability sandstone reservoirs were studied. It has been concluded that the main gas migration way is diffusion when the driving force is less than the minimum reservoir resistance;the main migration way is non-Darcy flow when the driving force is between the minimum and maximum reservoir resistance;the main mi-gration way is Darcy flow when the driving force is more than the maximum reservoir resistance. It is this complex gas migration and accumulation way that leads to complicated gas water distribution relationship in low-permeabi-lity sandstones. The process of gas migration and accumulation is controlled by the driving force of gas migration and accumulation, sandstone physical properties and bound water saturation. With the increase of driving force, gas saturation gradually improves and finally becomes stable ( usually less than 60%) due to the influence of bound water in sandstone reservoirs. With the same driving force, gas saturation increases with the improvement of permeability, which explains the accumulation of “desserts”.