四川盆地中三叠统雷口坡组是盆地内主要的产气层系之一,目前已发现中坝、卧龙河、龙岗、磨溪等气田.川中雷口坡组主要由一套浅灰—褐灰色中—厚层块状的白云岩、膏岩和石灰岩不等厚互层组成,从下至上分为四段,界线清晰,其中雷一段又分为两个亚段,雷四段分为三个亚段(图1).20世纪50年代开始,Moody (1959)、North(1985)、Schreiber(1988)等人先后在其专著中论述过油气和膏盐岩的关系,许靖华(1985)、王东旭(2005)、彭文绪(2008)等人也认为,膏岩不仅利于油气的保存,也利于下部岩层形成异常高压而产生裂缝,还能产生有机酸使下部地层形成较好的次生孔隙[1,2],在一定程度上促进油气储层的形成.但由于印支运动的影响,雷口坡组顶部发生了不同程度的剥蚀[3,4],这给宏微观研究带来了一定困难.

Research on Sinian Dengying Formation in central Sichuan by adopting combined macroscopic and microscopic methods shows that the main reservoir rocks are dolarenite, karst breccia, grained dolomite and algae dolomite, the reservoir space is dominated by emposieu and karst caves, and the reservoir is of relatively low quality, appearing as fracture-cavity type with low porosity and low permeability. The reservoir of Dengying Formation in the study area was formed by deposition and diagenesis. Dolarenite, grained dolomite and algae dolomite were deposited in a strong hydropower environment with the development of primary pores, which provided favorable material base for later strong karstification. 2nd member and 4th member were uplifted by Tongwan movement; hence the strata were exposed at the land surface for a long time and received atmospheric water together with mixed water reformation, leading to karstification. Through the weathering crust formed by karstification near the land surface, atmospheric fresh water and mixed water continued seeping into and dissolving the lower part of the formation. Strong karstification could create karstic collapse breccias and a great quantity of dissolution pore -caves in the lower part of the formation. Deposition and diagenesis provided favorable conditions for secondary porosity and improved the properties of reservoir rocks, while tectonic action in the later time formed a lot of cracks, providing the permeability for the reservoir.

The diagenesis,diagenetic evoluation,reservoir pore evoluation and characteristics were analyzed in detail by using macro and micro methods and using carbonate in Dengying Formation of Central Sichuan Basin as object of study.The common diageneses in the studied area were compaction,pressolution,cementation,packing,silicatization,heavy crystallization and denudation.Among those,heavy crystallization and denudation were constructive for reservoir development,however,compaction,pressolution,cementation and packing and silicatization were destructive.The influences of diageneses on the formation of reservoirs are discussed.Finally,according to the order of diagenesis and pore evoluton characteristics in diagenesis,diagenetic sequence and pore evolution are summarized in Dengying Formation.