川东北飞仙关组鲕滩气藏压力与成藏特征研究

川东北飞仙关组鲕滩气藏原始地层压力在平面上分布极不均匀,高异常压力区呈局部块状分布.压力分布、气藏特征、成藏演化历史综合研究发现,不同压力状态反映不同气藏类型:正常压力系统(压力系数在1.25以下),多处于台地边缘礁滩相,储层岩性以云岩为主,储集类型多为孔隙型,气藏一般甲烷含量低、储层舍大量沥青、气藏连通范围大,具边底水等特征,主要为构造或岩性-构造型气藏;异常高压或超高压系统(压力系数多达1.65以上),多处于海槽区或台内云岩欠发育区,储层岩性以灰岩为主,甲烷含量高、储层不含或含极少量的沥青,不含或有限边底水等特征,主要为裂缝型岩性气藏;而处于台地内部,介于以上两种压力状态之间的过渡类型气藏,多出现轻微高压,压力系数多在1.20～1.45,孔隙-裂缝或裂缝-孔隙型储层交替出现,气藏连通范围有限,气水特征较复杂,主要为岩性型或构造-岩性气藏特征.同时鲕滩气藏压力系数与气藏储集系数明显成反向关系,地层压力大小体现了天然气储集系统空间大小,天然气富集于正常压力系统.地层压力威因及形成过程实际上反映了优质储层发育历史、天然气的充注历史、礁滩气藏成藏历史的配置关系和相互作用过程,详细研究它们的配置关系和作用过程对正确认识飞仙关组礁滩气藏的形成和分布规律有重要的理论和现实意义.

RESEARCH ON CHARACTERISTICS OF GAS POOL PRESSURE AND ACCUMULATION OOLITIC GAS RESERVOIRS IN THE FEIXIANGUAN FORMATION, NORTHEASTERN SICHUAN BASIN

The distribution of initial reservoir pressure was extremely inhomogeneous and high abnormal pressure areas occurred in local block in the oolitic gas reservoirs of Feixianguan Forma-tion, Northeastern Sichuan. Comprehensive study of pressure distribution,gas accumulation char-acteristics and evolution history revealed that different state of pressure reflected different types of reservoir. In fact,normal pressure system (pressure coefficient less than 1.25) concentrated a-round the reef-bank on the edge of the platform in the porous dolostone, characterized by low methane content,large range of asphalt, well developed connecting with edge-bottom water. This type of reservoir mainly belonged to tectonic or litho-tectonic gas reservoir. Abnormal pressure system (pressure coefficient more than 1.65) ,occurred chiefly in the platform trough and poorly developed in the dolostone area,with limestone as the main lothology of reservoir. It was charac-terized by high methane content, without or only with little asphalt, or limited edge-bottom wa-ter,and therefore, classified as fracture lithology gas reservoir. Another type of pressure system in the platform was between the above two kinds of pressure system state with pressure coefficient of 1.20～1.45. It was characterized by alternate occurrence of porous-fracture reservoir and frac-ture pore reservoir, limited connectivity,complicated gas and water features, and divided into li-thology or tecto-lithology gas reservoir. Pressure coefficient of oolite gas pool reverses with reser-voir coefficient. Reservoir pressure value reflected the size of accumulation space and natural gas was enriched in normal pressure system. Origin of formation pressure and forming process actual-ly reflected the relation and interaction process about development history of the high quality res-ervoirs,gas-charging and reef-banks accumulation history. Detailed study on their relation and processes was of important theoretical and practical significance for correctly understanding on genetic mechanisms and distribution of oolitic gas reservoirs in Feixianguan Formation.