川北地区灯四段台内丘滩储层特征及主控因素

Intra-platform mound and shoal reservoirs of Dengying 4 Member,northern Sichuan Basin:Characteristics and main influential factors

台内丘滩是四川盆地上震旦统灯影组天然气勘探的重要后备领域,为了落实灯影组四段(以下简称灯四段)优质储层主控因素与展布特征,以川北地区灯影组台内钻井和野外露头为研究对象,通过岩心观察、薄片鉴定、储层物性等研究,对灯四段储集层基本特征及主控因素进行了综合分析。研究结果表明:(1)川北地区灯四段台内丘滩储集层岩性主要为藻粘结白云岩、藻砂屑白云岩、藻叠层白云岩和藻纹层白云岩,储集空间以晶间(溶)孔、藻格架孔、粒间溶孔以及裂缝为主;(2)台内丘滩优质储层展布主要受沉积相带控制,藻丘和浅滩沉积微相是储集层发育的有利沉积相带;(3)多期溶蚀作用能有效提升储层性能,其中早成岩期岩溶是优质储层形成的基础,埋藏期溶蚀能有效扩大储集空间,第一期埋藏溶蚀作用强度从灯四段顶部向下逐渐减弱,第二期埋藏溶蚀作用造成早期孔洞储集层进一步溶蚀扩大,形成现今储集空间。结论认为,受汉南古陆和宣汉—开江古隆起控制,在坡折带发育近南北向的台内丘滩条带,是灯四段油气勘探的有利地区。

Intra-platform mound and shoal emerges as a newly important domain for natural-gas exploration in the Upper Sinian Dengying Formation of Sichuan Basin.In order to determine the main influential factors and extensional characteris-tics of quality Dengying 4 Member,both intra-platform drilling and field outcrop on the member in northern basin were taken as objectives to comprehensively analyze basic characteristics and main control factors of Dengying 4 reservoirs through core observation,thin-section identification and reservoirs'physical property.Results show that(i)lithologically,in-tra-platform mound and shoal reservoirs of Dengying 4 Member in northern Sichuan Basin are dominated by algae bound dolomite,algal dolarenite,algae stromatolite dolomite and algae laminated dolomite,and their space is elementally com-posed of intercrystalline(dissolution)pore,algae frame pore,intergranular dissolution pore and fracture;(ii)for those intra-platform mound and shoal reservoirs with high quality,the distribution is primarily affected by sedimentary facies belts,like algae mound and shallow shoal microfacies conducive to reservoir development;and(iii)multi-episode dissolution can improve reservoir performance with effect,among which karst in the early diagenesis period is the foundation to form quali-ty reservoirs,and dissolution in the burial period can actively expand reservoir space.The intensity in the first buried dis-solution period fells into a decline downward from the top Dengying 4 Member,and the second period causes early porous-vuggy reservoirs further dissolved and expanded,forming today's reservoir space.In conclusion,controlled by Hannan an-cient land and Xuanhan-Kaijiang paleo-uplift,the near NS-strike intra-platform mound and shoal belt developed in slope break zones,grows into a favorable area for oil and gas exploration in Dengying 4 Member.