塔北轮南下奥陶统裂缝—溶洞系统

The Crack-cave System of Lower Ordovician in Lunnan Region, Tarim Basin

塔里木盆地北部轮南地区下奥陶统的裂缝和溶洞是该区油气储集的主要空间。研究区内裂缝属多成因类型,主要有构造裂缝、压溶缝合线、成岩网状收缩缝及古风化剥蚀裂缝。其中构造裂缝是主要的油气储集裂缝,它按裂缝充填程度及所充填的物质组分划分成几个亚类。研究区内溶洞也十分发育,洞径最大可达100m,地下广为分布的大型水平溶洞是古岩溶作用的产物,但绝大多数的溶洞均被充填。与溶洞相伴出现的洞顶破裂角砾岩是极好的储层。裂缝系统和溶洞系统在空间分布上既可组成裂缝一溶洞型储层,也可单独形成裂缝型储层或溶洞型储层。这几种类型的储层均表现出强烈的非均质性。

Lower Ordovician cracks and caves in Lunnan region, Tarim Basin are the best space for oil and gas accumulation. The fissures in the region consist of many original types: structure cracks, pressolved sutures, network diagenetic contraction crevices and weathered cracks of palaeosurface. Among them, the structure cracks form major reservoir of oil and gas. The crack caves are also well developed within the studied region. The maximum diameter may reach a hundred meters. The large and horizontal caves distributed extensively result from palaeokarst. However, most of the caves have been filled, The cracked breccias of cave roof are a better reservoir. The crack system and the Cave system make up a crack-cave reservoir or the crack reservoir or the cave reservoir separately. All the above types of reservoirs demonstrate intense heterogeneity.