陕西延安地区奥陶系马家沟组油气储层特征及成岩作用研究

Hydrocarbon Reservoir Characteristics and Diagenesis of Ordovician Majiagou Formation in Yan'an area

碳酸盐岩储层原始沉积以泥微晶灰岩为主,物性极差,其储集性能主要源于后期复杂成岩作用的影响。通过岩芯观察、铸体薄片、扫描电镜、阴极发光等测试分析,对延安地区鄂尔多斯盆地沉积基底奥陶系马家沟组碳酸盐岩的储层特征及成岩作用进行了详细的研究。研究表明,延安地区马家沟组马六段岩性以石灰岩、含云灰岩为主,马五段岩性以白云岩、含灰云岩为主。发育压溶缝、构造裂缝、白云石晶间孔、粒内溶孔、溶蚀孔洞、铸模孔隙等多种储集空间类型。储层主要经历海水成岩环境、大气淡水成岩环境和埋藏成岩环境,研究认为白云石化、去膏化和溶蚀作用在不同的阶段对形成孔隙有利,是建设性成岩作用;而胶结作用、压实压溶作用、膏化作用及去白云石化作用,在一定程度上使孔隙消失,为破坏性成岩作用;低重结晶及中等重结晶作用有利于孔隙的形成,但强重结晶作用往往使岩石致密成镶嵌状,对形成孔隙不利,为双重成岩作用。

The original deposition of carbonate reservoir is mainly micritic limestone with poor physical properties,and its reservoir property is mainly due to the influence of late complex diagenesis.The reservoir characteristics and diagenesis of carbonate rocks of Ordovician Majiagou formation in sedimentary basement of Ordos basin in Yan’an area was studied in detail by means of core observation,casting thin sections,scanning electron microscopy,cathode luminescence analysis.The research shows that the lithology of Ma-6 member of Majiagou formation in Yan’an area is mainly limestone and dolomite-bearing limestone,the lithology of Ma-5 member is mainly dolomite and lime-bearing dolomite.There are many types of reservoir space,such as pressure solution fissure,structural fissure,dolomite intergranular pore,intragranular dissolved pore,dissolution hole and mold pore.The reservoir mainly experiences the marine diagenetic environment,the atmospheric freshwater diagenetic environment and the buried diagenetic environment.It is considered that dolomitization,degypsification and dissolution are constructive diagenesis,which are beneficial to pore formation at different stages.However,cementation,compaction,gypsification and dedolomitization are destructive diagenesis,which make pores disappeared to some extent.Low recrystallization and medium recrystallization are conducive to the formation of pores,but strong recrystallization often makes the rocks compact into Mosaic,which is unfavorable to the formation of pores,and is a dual diagenesis.