冯地坑-洪德地区延长组长8-长4+5致密砂岩储层特征

Sandstone reservoir features of the Chang 8 and Chang 4+5 members in the Yanchang formation of Fengdikeng-Hongde area

冯地坑—洪德地区延长组长8-长4+5油层组是勘探的重点,因其储层属于低孔低渗的致密砂岩储层,弄清该区的储层特征及其控制因素具有重大意义。利用区域地质资料,通过岩心观察、镜下薄片、扫描电镜及孔渗、压汞等一系列实验测试分析,研究结果表明:储层主要以长石砂岩、岩屑长石砂岩为主,整体上具有粒度较细、结构成熟度和成分成熟度较低的特点;由于压实和压溶作用、胶结作用、交代作用、溶解作用等成岩作用影响,储层储集空间以粒间孔和长石溶孔为主,孔喉类型为细孔-细喉型和细孔-微喉型,物性以低孔低渗为特征,且孔渗相关性好。研究认为储层发育主要受岩石类型、沉积相、砂体厚度和成岩作用的影响;在压实作用较弱、溶蚀作用相对发育的构造高部位,位于水下(平原)分流河道、河口坝微相发育区的细粒长石砂岩和岩屑长石砂岩是相对优质的储层类型。

Chang 8 - Chang 4 ＋ 5 oil reservoir is the major exploration target in Fengdikeng-Hongde are- a. It is important to investigate the reservoir characteristics and controlling factors in this area with low porosity and low permeability for tight sandstone reservoir. Through core observation and geologic infor- mation, by using the data of thin section, scanning electron microscope, pore/permeability and pressured- mercury testing, it implies that the reservoir rock of Chang 8 and Chang 4 ＋ 5 members in the Yanchang Formation of Fengdikeng-Hongde area are mainly fine grained, low textural and compositional maturity arkose and lithic arkose. Due to the influence of diagenesis of compaction, pressure solution, cementa- tion, metasomasis and dissolution, the reservoir space of reservoir rock are mainly intergranular pore andfeldspar dissolution pore with the feature of fine pore-fine throat, fine pore-micro throat, low porosity and low permeability and good correlation of pore and permeability. The development of reservoir in study ar- ea is mainly influenced by rock type, sedimentary facies, thickness of sand body and diagenesis. The study implies that the relatively coarse grain rock arkose and debris feldspar reservoir at structural high part with feeble compaction and strong dissolution in microfacies of underwater distributary channel and mouth bar are relatively high-quality reservoir type.