苏德尔特油田低渗透凝灰质砂岩成岩作用及储层质量差异性演化

海拉尔盆地贝尔凹陷苏德尔特油田兴安岭油层为典型的富火山物质的低渗致密砂岩储层。利用岩心观察、薄片鉴定、扫描电镜分析、压汞测试分析等方法,对兴安岭油层储层成岩作用及其控制下的储层质量演化过程进行了系统研究。结果表明,储层目前主要处于中成岩A期,整体经历了压实作用—早期方解石胶结作用/方沸石胶结作用—方沸石溶解/长石溶解作用/高岭石胶结作用/硅质胶结作用—晚期方解石胶结作用。兴安岭油层储层可以划分出强压实成岩相(I)、弱压实-方解石中强胶结成岩相(II)、中等压实-方沸石/长石强溶解成岩相(III)、中等压实-方沸石/长石中强溶解-高岭石强烈充填成岩相(IV)4种类型的成岩相。压实作用和早期方解石胶结作用导致储层孔隙度和渗透率降低,方沸石和长石的溶解作用有效提高储层孔隙度和渗透率,高岭石的沉淀作用导致储层渗透率大大降低。成岩相I和成岩相II储层质量最差,孔隙度和渗透率均较低,为典型的特低孔特低渗致密储层;成岩相III储层质量最好,具有较高的孔隙度和渗透率,为中孔—中低渗储层;成岩相IV储层质量中等,具有较高的孔隙度,但渗透率较低,为中孔(特)低渗储层。

Diagenesis and Reservoir Quality Evolution of Low Permeability Tuffaceous Sandstones in Suderte Oilfield

The reservoirs in Xing’anling Group in Suderte oil field,the Hailer basin,exhibit low to ultra-low permeability and high tuffaceous content.A comprehensive study on diagenesis and quality evolution of the low
permeable reservoirs was carried out utilizing cores,thin sections,SEM analysis,tested physical properties and mercury injection data.The results show that,the reservoirs are at the A period of the mesodiagenetic stage.The entire diagenetic sequences consist of compaction-early analcite cementation /early calcite cementation-feldspar dissolution /analcite dissolution /authigenic kaolinite precipitation /quartz cementation -late calcite cementation.Four types of diagenetic facies are identified as follows,strong compaction facies (I),weak compaction-medium to strong calcite cementation facies (II ),medium compaction-analcite /feldspar strong dissolution facies (III),and medium compaction-analcite /feldspar medium to strong dissolution-strong kaolinite cementation facies (IV ).Compaction and early calcite cementation resulted in the decrease of porosity and permeability of the reservoirs,while the dissolution of analcite and feldspar effectively improved the reservoir physical property,and the kaolinite cementation damaged the reservoir permeability.Diagenetic facies I and II have the worst reservoir quality and defined as the dense reservoirs characterized by extra-low porosity and permeability.Facies III is the best reservoir,featured by relatively high porosity and permeability,and defined as middle porosity-medium to low permeability reservoir.Facies IV developed medium reservoir quality,which is characterized by high porosity and low permeability and is defined as medium porosity and (extra ) low permeability reservoir.