碳酸盐岩储层多尺度孔洞缝的识别与表征——以川西北双鱼石构造中二叠统栖霞组白云岩储层为例

对于具有强非均质性的多尺度储集空间的碳酸盐岩储层,仅采用单一的测试手段难以识别出所有的储集空间。为了给碳酸盐岩油气藏精细刻画及高效开发提供技术支撑,以四川盆地西北部双鱼石构造中二叠统栖霞组白云岩储层为研究对象,针对其发育多个尺度的孔洞缝,采用岩心图像采集仪和双能CT对不同尺度岩心的孔洞缝进行刻画,借助三维可视化软件对重构孔隙空间进行定量化分析,实现了不同尺度下孔洞缝的搭配关系表征以及储集类型划分,并建立了一套基于几何学参数识别裂缝、溶洞的方法。研究结果表明:(1)该区栖霞组储层发育多个尺度的孔洞缝储集空间,可划分为3大类6种类型,孔隙以晶间溶孔、晶间孔为主,溶洞以小洞为主,裂缝以斜交缝为主;(2)建立起了一套基于几何学参数识别裂缝、溶洞的方法,球形度小于0.43、球半径比小于0.41为裂缝识别标准,等效球半径大于2 mm为溶洞识别表征;(3)栖霞组储层的孔隙以直径介于0.02～2.00 mm的大孔隙为主,溶洞以2.00～10.00mm的小洞为主,发育多个级别的裂缝;(4)栖霞组白云岩储集类型以裂缝—孔洞型、裂缝—孔隙型为主,缝洞发育程度是影响该储层物性的关键因素,栖霞组裂缝发育的储集类型占比超过50%,渗流能力较好。

Identification and characterization of multi-scale pores,vugs and fractures in carbonate reservoirs: A case study of the Middle Permian Qixia dolomite reservoirs in the Shuangyushi Structure of the northwestern Sichuan Basin

As for the carbonate reservoirs with strong heterogeneity and multi-scale reservoir spaces, it is difficult to identify all the reservoir spaces using only one single test method. In order to provide technical support for a fine characterization and efficient development of carbonate oil and gas reservoirs, this paper took the dolomite reservoir of Middle Permian Qixia Formation in the Shuangyushi structure of the northwestern Sichuan Basin as the research object. Considering there are multi-scale pores, vugs and fractures developed in the reservoir, core image acquisition instrument and dual-energy CT were used to characterize pores, vugs and fractures in the cores of different scales, and the 3D visualization software was applied to quantitatively analyze the reconstructed pore spaces. In this way, the characterization of the matching relationship of pores, vugs and fractures at different scales and the division of reservoir types were realized, and a set of methods for fracture and vug identification based on geometric parameters was developed. And the following research results were obtained. First, multi-scale reservoir spaces of pores, vugs and fractures are developed in the reservoirs of Qixia Formation in this area, and they can be divided into 6 types of 3 categories. Pores are dominated by intercrystalline dissolution pores and intergranular pores, vugs are mainly small ones, and fractures are mainly diagonal fractures. Second, a set of methods for fracture and vug identification based on geometric parameter is set up. And it takes the sphericity <0.43 and the spherical radius ratio <0.41 as the fracture identification standard and the equivalent spherical radius >2 mm as the vug identification standard. Third, the pores in the reservoirs of Qixia Formation are mainly large pores with a diameter ranging from 0.02 to 2.00 mm, the vugs are mainly small with a diameter ranging from 2.00 to 10.00 mm, and fractures of multiple scales are developed. Fourth, the Qixia Formation dolomite reservoirs are mainly of fracture–vug type and fracture–pore type. The development degree of fractures and vugs is a key factor affecting the physical properties of the Qixia Formation reservoirs. The reservoir types with developed fractures in the Qixia Formation account for more than 50%. Therefore, its percolation capacity is better.