长6致密砂岩油藏储层孔隙结构特征及孔缝组合模式

为了研究致密油孔隙结构特征及与石油渗流关系，利用F200场扫描电镜对鄂尔多斯甘谷驿油田致密油样品进行微观分析，建立该样品储层的微观孔隙裂缝体系，进一步通过压汞实验了解孔喉分布及不同孔径孔、缝对渗透率的贡献率，结合样品电镜扫描观察结果推断孔隙、裂缝储集渗流油气有效性。研究结果表明，该区致密油储层主要孔隙有原生孔、粒内溶孔、粒间基质溶蚀孔及晶间孔4种类型，油气主要储存在粒内、粒间溶孔中，原生粒间孔仅为次要储油空间，大量纳米级孔隙成为储油主体。而裂隙主要为微裂缝，由方解石解理缝、溶蚀缝及成岩收缩缝构成，其中方解石解理缝和溶蚀缝构成渗流运移主要通道，微裂缝与人工裂缝结合形成裂缝网络。微孔(小于2 nm)对油气储存有效，对油气渗流则不起作用。因此该区致密油储油渗流孔隙结构总结为“纳米溶孔储油，微裂缝人工压裂缝渗流”。据此将不同孔缝组合划分为3种模式:溶蚀孔缝组合模式、方解石解理缝+溶蚀孔组合模式、裂缝或孔隙单独存在模式。其中溶蚀孔缝组合模式和方解石解理缝+溶蚀孔组合模式流体渗流阻力小，在甜点区选择时应重点关注。

Pore structural characteristics and pore-fracture combination modes of reservoirs in Chang 6 tight sandstone oil reservoirs

In order to research the relationships between the pore structural characteristics and the oil flowing in tight oil reservoirs, F200 field scanning electron microscope (SEM) was used to microscopically analyze the tight oil samples of Ganguyi Oilfield in the Ordos Basin, and the microscopic pore-fracture system of the sample reservoir was established. Then, the distribution of pore throats and the contribution rate of pores and fractures of different sizes to the permeability were analyzed by conducting mercury injection experiments. Finally, combined with the SEM results of the samples, the effectiveness of pores and fractures to hydrocarbon storage and flow was inferred. It is indicated that the pores in the tight oil reservoirs in this area are mainly divided into four types, i.e., primary pore, intragranular dissolved pore, intergranular (matrix) dissolved pore and intercrystalline pore. Intragranular and intergranular dissolved pores are the main reservoir space of oil and gas, primary intergranular pore is merely the secondary reservoir space of oil, and a great number of nano-scale pores are the main reservoir space of oil. Micro-fractures are dominant and they are mainly composed of calcite cleavage fissure, dissolved fracture and diagenetic contraction fracture, among which the former two are the main pathway of flow and migration. Micro-fractures and hydraulic fractures constitute fracture networks. Micro-pores (< 2 nm) are effective for oil and gas storage, but ineffective for oil and gas flowing. Thus, it is concluded that the oil storage and flowing pores of tight oil reservoirs in this area are in the mode of "nano-scale dissolved pores acting as oil reservoir space, and micro-fractures and hydraulic fractures acting as oil flowing pathway". Accordingly, pore-fracture combinations are divided into three modes, i.e., dissolved pore-fracture combination mode, calcite cleavage fissure+dissolved pore combination mode and independent fracture or pore mode. The first two combination modes have small resistance to fluid flow and they shall be focused on when sweet spots are selected.