南襄盆地安棚东南区核桃园组三段深层致密油储层裂缝发育特征及控制因素

Development characteristics and controlling factors of fractures in deep⁃buried tight oil reservoirs of the 3rd member of Paleogene Hetaoyuan Formation in southeast An’peng area,Nanxiang Basin

为了探明深部致密油储层天然裂缝发育规律及其影响因素,以南襄盆地泌阳凹陷安棚东南区古近系核桃园组三段Ⅱ—Ⅵ油层组致密油藏为例,利用大量岩心、薄片、物性、成像及常规测井、注水压驱等资料,系统开展了致密油藏裂缝综合评价。该区目的层Ⅱ—Ⅵ油层组属扇三角洲前缘沉积,储层岩屑含量较高,为近源沉积;储层孔隙度与渗透率之间具有良好的正相关性。对于不同岩性砂岩储层,裂缝主要发育于细砂岩中,其次为粉砂岩,而含砾砂岩中裂缝通常不发育。目的层主要发育高角度缝及直立缝,其占比可达87.8%,低角度斜交缝和水平缝分别占比7.3%及4.9%。目的层致密储层裂缝发育主控因素主要包括岩性、沉积微相及局部构造,厚度较薄、粒度较细的单砂体或复合砂体部位裂缝通常较为发育。裂缝主要发育于前缘河道、河道侧翼、河口坝及其外缘远砂坝砂体部位,而席状砂及前缘三角洲微相中裂缝不发育。此外,裂缝还发育于构造转折端,且主要发育于正向构造的顶部及翼部。目的层裂缝主要沿着WE向、NE向分布,其次为NW向;裂缝主要形成于新近纪拗陷期(喜马拉雅晚期)。裂缝是导致致密油储层水窜的重要因素,因而要加强裂缝发育程度、扩展规模及方向的动、静态监测。

To elucidate the development patterns and influencing factors of natural fractures in deep⁃buried tight oil reservoirs,a comprehensive evaluation was conducted using a large amount of core samples,thin section,physical property data,imaging and conventional logging,water injection pressure testing and other data.The focus was on the tight oil reservoirs within theⅡ-Ⅵoil layers of the third member of the Paleogene Hetaoyuan Formation in the southeastern An’peng area of the Biyang Depression,Nanxiang Basin.These oil formations,deposited in fan⁃delta front environment,are characterized by a high content of rock debris,indicating proximal deposition.A strong positive correlation between reservoir porosity and permeability was observed.Among the various sandstone lithologies,fractures predominantly developed in fine sandstone,followed by siltstone,while gravelly sandstone generally lacked fractures.High⁃angle and vertical fractures were predominant,constituting 87.8%of the total,while low⁃angle oblique and horizontal fractures accounted for 7.3%and 4.9%,respectively.The main controlling factors for fracture development in these tight reservoirs included lithology,depositional microfacies,and local structures.Thin and fine⁃grained single or composite sand bodies typically had more deve⁃loped fractures,particularly in front channel,channel flank,mouth bar,and outer edge of distal bars.Conversely,fractures were less developed in sheet sands or delta front microfacies.Moreover,fractures primarily formed at structural inflection points,predominantly at the tops and wings of forward structures and were primarily oriented along the WE and NE directions,followed by the NW direction.These fractures predominantly formed during the Neogene depression period(late Himalayan).Fractures significantly influence water channeling in tight oil reservoirs,necessitating enhanced dynamic and static monitoring of the degree,extent,and orientation of frac⁃ture development.