深层海相碳酸盐岩优质储层的形成、保存和破坏机制——以四川盆地震旦系—志留系为例

Formation,preservation and damage mechanism of marine deep carbonate high quality reservoir rocks:Illustrated by Sinian system to Silurian in Sichuan Basin

四川盆地震旦系—志留系碳酸盐岩普遍埋藏深度超过3500 m,属深层碳酸盐岩储层范畴。宽广的潮坪相和陆棚相沉积环境从根本上决定了盆内下组合碳酸盐岩储层岩石类型主要为颗粒碳酸盐岩、晶粒结构白云岩及裂缝性灰岩。多期次的构造运动导致下组合岩溶储层发育,特别是志留纪末期的加里东运动导致从乐山—龙女寺古隆起核部由西向东依次发育震旦系、寒武系和奥陶系古岩溶带。现今下组合储层中广泛分布的沥青表明下组合曾有过广泛的油气成藏过程,形成古油藏或古气藏,亦表明下组合在油气充注时曾普遍发育优质储层。岩石学和地球化学研究表明,复杂多变、期次繁多的成岩演化和流体充注与下组合优质储层的形成、保存和破坏密切相关,总体上,对四川盆地深层海相碳酸盐岩储层而言:1)原位沉积体系、白云岩化对震旦系和寒武系优质储层发育控制作用弱、仅对奥陶系和志留系具有较强的控制作用;2)古隆起是优质储层发育的先决条件,表生岩溶与破裂作用为必备条件;3)烃类流体充注和热裂解作用早期优质储层保存的主要机制,此外,适度的重结晶作用是形成优质储层的持久动力,埋藏过程中外源侵蚀性流体溶蚀作用的储层效应有限;4)压实压溶作用、胶结充填作用是储层致密的最主要的因素。

Sinian system to Silurian （Lower group）carbonate rocks is generally buried deeper than 3500 m, which belonged to deep carbonate reservoir rocks. Broad tidal fiat and shelf depositional environment determined the lower group carbonate rock reservoirs types which were grainstones,crystalline dolomite and fractured limestone. Multiple phases of tectonic movement led to the karst reservoir rocks development in lower group, Sinian, Cambrian and Ordovician paleokarst zone had occurred by the west to east caused by Caledonian movement. Plenty of bitumen in lower group had showed that there widely developed high quality reservoir rocks and formated paleo-oil pool or paleo-gas pool. The petrological and geochemical data had showed that camplicated and multistaged diagenesis and fluid infilling had intimate relationship with formation,preservation and damage mechanism of high quality reservoir rocks. In a word, the controlling factors just for the deep carbonate reservoir rocks were as follows： 1 ） depositional environment had intensely controlling on the Ordovician and Silurian reservoirs rocks, but faintly controlling on the Sinian and Cambrian. 2 ）paleouplift was a prerequisite, and karstification and fractures were as a necessary condition. 3） infilling and thermal cracking of hydrocarbon were the main preservation mechanism, and so is moderate recrystallization. Exogenous erosion fluid had very limited effect in deep burial diagenesis. 4）compaction- pressure solution and cementation-infilling were the most important factor for densitification of reservoir rocks.