南襄盆地安棚浅、中层系特低渗储层裂缝特征及其与深层系裂缝对比

利用野外露头、岩心、成像测井和薄片等资料,分析了南襄盆地安棚浅、中层系储层裂缝的发育特征,并与深层系裂缝特征进行了对比,最后分析了控制裂缝发育的主要因素。研究区发育有构造裂缝和成岩裂缝两种类型,以高角度构造裂缝为主,裂缝平均线密度为0.42条/m,裂缝高度通常小于0.40 m,平均为0.25 m,反映裂缝主要在层内发育。微观裂缝是沟通基质粒间孔和粒内溶孔的重要通道,它使储层孔隙的连通性变好。受喜马拉雅早期和晚期水平构造挤压应力作用,该区主要发育3组裂缝。其中,近东西向裂缝最为发育,其次为北东向和北西向裂缝。安棚油田裂缝的形成与分布受构造应力场、岩性、孔隙度、渗透率、层厚以及构造等因素的影响。在相同因素的作用下,安棚油田浅、中层系裂缝的成因类型、产状及发育特征和深层系具有相似性,但浅、中层系裂缝的发育程度略差于深层系裂缝。

Features of fractures in shallow-to mid-depth reservoirs with ultra-low permeability and their comparison with those in deep reservoirs in Anpeng oilfield, the Nanxiang Basin

Based on data of outcrops,cores,image logs and thin sections,we analyzed the features of fractures in the shallow- to mid-depth reservoirs in Anpeng oilfield of Nanxiang Basin,compared them with that of the deep reservoirs,and determined the main factors controlling the development of these fractures.The study suggests that there are two types of fractures in the shallow-to mid-depth reservoirs in the Anpeng oilfield:the tectonic fractures and the diagenetic fractures.The former of high dip-angle dominates the study area with an average linear density of 0.42/m and a height of generally less than 0.40m(averaging at 0.25m),which indicates that fractures are confined within the layers.Micro-fractures are very important channels for connecting the intergranular pores and intragranular dissolved pores,and enhance reservoir pore connectivity.Affected by horizontal tectonic compressions during the Early and Late Himalayan movements,three sets of tectonic fractures were formed in the study area,i.e.E-W,NE-SW and NW-SE striking fractures.The E-W fractures were developed better than the other two sets.The formation and distribution of these fractures in the oilfield were controlled by such factors as the tectonic stress field,lithology,porosity,permeability,layer thickness and structures.Under the same controlling factors,the fractures in the shallow- to mid-depth reservoirs of the field are thought to have the similar genetic types,occurrences and development characteristics to that of the deep reservoirs,but slightly lower degree of development than that of the deep reservoirs.