川东北元坝地区须三段钙屑砂砾岩储层特征及控制因素

Reservoir characteristics and main controlling factors of calcareous coarse clastic rocks of the third Member of Xujiahe Formation in Yuanba area,northeastern Sichuan Basin

四川盆地元坝地区须家河组三段多口井测试获得中-高产工业气流,具有良好勘探开发潜力,但其储层特征及控制因素不明确。利用岩心、薄片及分析化验资料对研究区储层岩石类型、储集空间、物性及发育控制因素进行综合研究。研究认为:储层岩石类型以钙屑砂岩和灰质砾岩为主,具有"石英、长石含量低,碳酸盐岩屑(碳酸盐砾)含量高"的特征。储集空间以粒间溶孔、粒内溶孔及裂缝为主,钙屑砂岩与灰质砾岩储层差异明显。钙屑砂岩为裂缝-孔隙型储层,而灰质砾岩为孔隙-裂缝型储层,物性总体较差,具有低孔、低渗的特征。储层发育主要受沉积微相、岩石类型、溶蚀作用及裂缝共同控制。有利沉积微相及岩石类型是优质储层发育的基础,溶蚀作用及裂缝是优质储层发育的关键。水下分流主河道中-粗粒钙屑砂岩为最有利岩相,高含量钙屑组分在后期溶蚀作用及裂缝改造下易形成优质储层。

Several wells have tested moderate-to-high industrial gas flow from the calcareous coarse clastic reservoirs the third Member of Xujiahe Formation in Yuanba Area,Northeastern Sichuan Basin,revealing its great exploration and de-velopment potential.However,the reservoir characteristics and main controlling factors are still unclear.Core,thin section and testing data are integrated to study the rock types, reservoir space, physical properties and controlling factors.The reservoirs are dominated by calcareous sandstone and limy conglomerate which featuring in low content of quartz,feldspar and high content of carbonate debris.And the reservoir space is dominated by intergranular dissolved pores,intragranular dissolved pores and fractures.The calcareous sandstone reservoirs are obviously different from the limy conglomerate reservoirs.The former is of fracture-pore type reservoir,while the latter is of pore-fracture type reservoir with low porosity and low permeability.The development of the reservoirs was mainly controlled by sedimentary microfacies,rock types,dis-solution and fractures.Besides,for the development of high-quality reservoir,favorable sedimentary microfacies and reser-voir rock types are the basis and dissolution and fractures are the key factors.The medium-coarse grained calcareous sandstone in underwater distributary channel is the most favorable faces,as the high content of calcareous component can improve the development of high quality reservoirs through dissolution and fracture modification at late stage.