川东南綦江地区下二叠统栖霞组沉积储层特征

Sedimentary and reservoir characteristics of Qixia Formation,Qijiang area,southeastern Sichuan Basin

2022年4月川东南綦江地区FB1井下二叠统栖霞组二段酸压测试获日产气量6.42×10^(4)m^(3),这是四川盆地栖霞组在台缘滩、环古隆起台内滩相继获得重大商业突破之后,在台内台洼边缘浅滩首次实现的重要天然气勘探突破,油气地质意义重大。为了深化对该区栖霞组沉积储层特征的认识,进一步落实有利勘探区带,指导下一步勘探部署,综合利用野外调研、岩心观察、薄片鉴定、分析化验及测井数据等资料,探究了綦江地区栖霞组沉积相展布及储层发育特征。研究结果表明:(1)綦江地区栖霞组沉积期,继承二叠系沉积前隆洼格局,形成了稳定的碳酸盐岩台地沉积,发育台洼边缘浅滩、滩间、台内洼地沉积,栖霞组一段主要为滩间沉积,栖二段上亚段和下亚段顶部发育高能滩沉积;(2)储层岩石类型主要为亮晶颗粒灰岩、细晶白云岩、灰质白云岩等,储集空间类型分为孔隙(孔洞)、裂缝两大类,结合成像测井及物性数据,总体显示出低孔隙度、特低渗透率的储层特征;(3)栖霞组储层具有显著的相控性,岩溶作用进一步优化储层,栖霞期台洼边缘转折带是天然气勘探有利区。结论认为,该研究成果可以为研究区栖霞组下一步油气勘探部署提供决策依据。

In April 2022,FB1 well in Qijiang area of southeastern Sichuan Basin achieved the gas production of 6.42×10^(4)m^(3)/d from the second member of Qixia Formation(Qixia 2 Member)after acid-fracturing test.It was the first considerable exploration breakthrough for the Qixia Formation in this basin made in intra-platform and platform-depression margin shoals followed by major commercial top in both marginal platform shoal and intra-platform shoal around paleouplift.So,in order to comprehend sedimentary and reservoir characteristics of the Qixia Formation,Qijiang area,ascertain favorable exploration zones and guide the next exploration deployment,both sedimentary-facies distribution and reservoir extension were explored for this formation by making full use of field survey,core observation,thin-section identification,assay analysis and well-logging data.Results show that(i)during the deposition of the Qixia Formation,a sort of uplift-depression pattern was inherited in this area before the Permian deposition to further grow up the stable deposition of carbonate platform where platform-depression margin shoal,inter-shoal and intra-platform depression were developed.Qixia 1 Member belongs to the inter-shoal deposition,and high-energy shoal deposits were extended at the top of the upper submember of Qixia 2 Member and the top of the lower submember;(ii)reservoir rocks are mostly composed of sparry grainstone,aplite dolomite and limy dolomite,and reservoir space can be classified into two types,i.e.,pore(vug)and fracture.Imaging well logging and physical property data indicates the overall reservoir characteristics of low porosity and extra low permeability;and(iii)with an obvious facies control,Qixia reservoirs get better under karstification.The transitional belt of platform-depression margin during the deposition of Qixia Formation is regarded as a favorable exploration area.It is deemed that these results offer a scientific decision-making basis for the following deployment in the Qixia Formation of Qijiang area.