东濮凹陷深层气盖层封闭性及有效性研究

Study on sealing capacity and effectiveness of deep gas cap rock in Dongpu Depression

在油气源充足的条件下,盖层的分布与封闭性能控制着油气的运移、聚集与保存,良好的盖层可以阻滞油气渗流运移并降低天然气的扩散散失,使其在盖层下聚集成藏。与油藏相比,天然气藏对盖层条件要求更高。文章从宏观、微观及时空配置关系等方面对东濮凹陷深层气盖层的特征、封盖能力及有效性进行了分析,认为东濮凹陷深层气盖层主要是沙三段的暗色泥岩及盐岩,盖层品质好、分布广、厚度大;盖层物性封闭能力以好为主,部分为中等;沙三段地层普遍存在的异常压力,对其下伏气藏构成超压封闭;深部盖层本身也是烃源岩,其中的天然气浓度高于下伏储层中的天然气浓度,烃浓度封闭作用明显;盖层初步具有封闭能力对应的封气门限时间大大早于生烃期;盖层的有效性显著。

In the condition of sufficient hydrocarbon resources,cap rock distribution and sealing capacity can control on the migration,accumulation and preservation of hydrocarbon.Good cap rock can prevent oil or gas percolation and migration,and decrease diffused dissipation of natural gas and help it to accumulate under the cap rock,which is the necessary condition for hydrocarbon accumulation.Compared with the oil reservoir,the gas reservoir needs higher condition for the cap rock.This paper analyzes the characteristics,sealing capacity and effectiveness of deep gas cap rock from macroscopic,microscopic and space-time relations.It concludes that the deep gas cap rock in Dongpu Depression mainly consists of S3 dark mudstone and halite with good quality cap rock,wide distribution and large thickness.Sealing capacity of the cap rock is mainly of good quality and partially moderate.Abnormal pressure occurs widely in S3 strata,forming overpressure sealing for underlying gas reservoir.Deep cap rock is a source rock itself,in which the gas concentration is higher than that of underlying reservoir with obvious sealing of hydrocarbon concentration.Initial sealing capacity of cap rock leads to corresponding gas-sealing threshold earlier than that of hydrocarbon generation period and the effectiveness of cap rock is obvious as well.