Paleocave carbonate reservoirs; origins, burial-depth modifications, spatial complexity, and reservoir implications
Paleocave carbonate reservoirs; origins, burial-depth modifications, spatial complexity, and reservoir implications
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DOI：
10.1306/e4fd426f-1732-11d7-8645000102c1865d
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发表时间：
1999-11
期刊：
影响因子：
3.5
通讯作者：
R. Loucks
中科院分区：
文献类型：
--
作者：
R. Loucks
古洞穴系统形成了一类重要的碳酸盐岩储层，是近地表岩溶作用和后来的埋藏压实和成岩作用的产物。在现代和古代洞穴系统中，已经研究了与古洞穴储集层有关的裂缝、角砾岩和沉积物充填的特征和成因。本文利用有关这种洞穴系统的信息，重建了古洞穴储集层的一般演化及其相关的规模、孔隙网络和空间复杂性。古洞穴储集层的空间复杂性是近地表和埋藏过程的结果。近地表过程包括溶解挖掘、碎屑沉积、化学沉淀、局部破裂、角砾化和洞壁和天花板的坍塌。随着洞穴系统下沉到地下，埋葬过程开始。残留的洞穴通道通常会坍塌，早期形成的角砾岩碎屑被重新碎屑。塌陷通道周围和上方地层的差异压实作用产生了裂缝、裂隙角砾岩和马赛克角砾岩。近地表和埋藏过程结合在一起，产生了具有几个尺度的非均质性的典型的复杂储集层。古洞穴成因的油气藏通常是塌陷-古洞穴系统聚合的产物。洞穴系统中的通道聚集成更大的、相连的孔隙带是复合不整合面上的多个洞穴形成幕的组合，也是洞穴系统在埋藏过程中坍塌的结果，在那里周围的寄主地层被角砾化和破裂。这一组合过程产生了空间上复杂的储集层，这些储集层的直径可以达到数百米到数千米，通常会形成大型勘探目标。合并的塌陷古洞穴系统的最终大小、孔隙网络类型和空间复杂性是它们从表层发育到埋藏到更深的地下的产物。合并的塌陷-古洞穴储集层假说解释了观察到的储集层的规模和所涉及的空间复杂性。
Paleocave systems form an important class of carbonate reservoirs that are products of near-surface karst processes and later burial compaction and diagenesis. Features and origins of fractures, breccias, and sediment fills associated with paleocave reservoirs have been studied in modern and ancient cave systems. Information about such cave systems is used in this paper to reconstruct the general evolution of paleocave reservoirs and their associated scale, pore networks, and spatial complexities. Spatial complexities in paleocave reservoirs result from near-surface and burial processes. Near-surface processes include dissolutional excavation, clastic sedimentation, chemical precipitation, and localized fracturing, brecciation, and collapse of cave walls and ceilings. Burial processes begin as cave systems subside into the subsurface. Remaining cave passages commonly collapse and early-formed breccia clasts are rebrecciated. Differential compaction of strata around and over collapsed passages produces fractures, crackle breccias, and mosaic breccias. Near-surface and burial processes combine to produce typically complex reservoirs with several scales of heterogeneity. Hydrocarbon reservoirs of paleocave origin are commonly the product of coalesced collapsed-paleocave systems. The coalescing of passages in a cave system into larger, connected porosity zones results from a combination of multiple, cave-forming episodes at composite unconformities and from the collapse of cave systems during burial where surrounding host strata are brecciated and fractured. This combination of processes creates spatially complex reservoirs that can be hundreds to several thousands of meters across, commonly forming large exploration targets. Final size, pore-network types, and spatial complexities of coalesced collapsed-paleocave systems are products of their evolution from near-surface development through burial into the deeper subsurface. The coalesced collapsed-paleocave reservoir hypothesis explains the scale of reservoirs observed and the spatial complexities involved.