海相碳酸盐岩成岩作用与排烃特征

Diagenesis and Expulsion efficiency of Marine Carbonate Rock

与泥页岩以缓慢压实为主的成岩作用不同,碳酸盐岩的成岩以胶结和交代作用为主,并在浅埋处几乎失去其所有的原生孔隙和沉积水。碳酸盐岩在埋藏条件下处于近完全封闭的压实流环境中,深埋和地温升高除形成小规模的压溶作用(如缝合线)外,其他类型的成岩作用很微弱。在进入有机质生烃的门限深度后,低丰度有机质虽可生成一定数量的烃类,但碳酸盐岩不像泥岩那样可以脱出大量压实水,烃的运移既无"载体",又无异常高压作为动力和造缝条件,烃类很难大规模运移。在其后的成岩作用中,烃类或分散于封闭的晶间孔隙中,或与矿物结合形成晶包有机质和包裹体有机质,造成碳酸盐岩含烃率常常高于泥页岩。

Being different from diagenesis of argillutite that is mainly secular compaction, the diagenesis of carbonate rock is mainly cementation and metasomatism so that carbonate rock almost lose all of primary pores and deposi- tional water in it. The carbonate rock is in the perfectly enclosed environment of compacting fluid with deep burial. Besides of small-scaled pressure solution that is formed by deep burial and geothermal rise, other styles of diagen- esis are faint. After organic matter enter the depth of hydrocarbon generation threshold, low abundance of organic matter may generate an amount of hydrocarbon but carbonate rock may not cast off such same great deal of com- paction water as the argUlutite. Due to neither carrier of hydrocarbon migration nor dynamics of abnormal pressure with fracture-generating condition, hydrocarbon compounds are difficult to come out from its parent rock in large scale. Hydrocarbon compounds may be dispersed in disconnected intercrystalline pores and form crystal-wrapped organic matter combined with minerals and inclusion enclave organic matter, which results in hydrocarbon percentage of carbonate rock commonly higher than that of argillutite.