塔里木盆地柯坪露头区寒武系肖尔布拉克组储集层地质建模及其意义

Reservoir geological modeling and significance of Cambrian Xiaoerblak Formation in Keping outcrop area,Tarim Basin,NW China

通过对塔里木盆地柯坪露头区寒武系盐下肖尔布拉克组系统解剖,在实测7条剖面,观察超过1000块薄片,分析556个样品物性及大量地球化学测试的基础上,建立了28 km长度范围油藏尺度的储集层地质模型。肖尔布拉克组厚度为158~178 m,可划分为3段5个亚段,主要发育层纹石、凝块石、泡沫绵层石、叠层石、核形石、藻砂屑/残余颗粒结构的晶粒白云岩和泥粒/粒泥/泥质白云岩,自下而上的相序组合构成碳酸盐缓坡背景下的以“微生物层-微生物丘滩-潮坪”为主的沉积体系。识别出微生物格架溶孔、溶蚀孔洞、粒间/内溶孔和晶间溶孔5种主要储集空间类型,认为孔隙发育具有明显的岩相选择性,泡沫绵层石白云岩平均孔隙度最高,凝块石、核形石和藻砂屑白云岩次之;储集层综合评价为中高孔、中低渗孔隙-孔洞型储集层。揭示肖尔布拉克组白云岩主要形成于准同生—早成岩期,白云石化流体为海源流体;储集层主要受沉积相、微生物类型、高频层序界面和早期白云石化作用共同控制;Ⅰ、Ⅱ类优质储集层平均厚度为41.2 m,平均储地比为25.6%,具有规模潜力,预测古隆起围斜部位的中缓坡丘滩带是储集层发育的有利区。

Take the Cambrian Xiaoerblak Formation in the Keping outcrop area as an example,a 28 km reservoir scale geological model was built based on description of 7 profiles,observation of more than 1000 thin sections,petrophysical analysis of 556 samples and many geochemical tests.The Xiaoerblak Formation,158–178 m thick,is divided into three members and 5 submembers,and is composed of laminated microbialite dolomite(LMD),thrombolite dolomite(TD),foamy-stromatolite dolomite(FSD),oncolite dolomite(OD),grain dolomite(GD)/crystalline dolomite with grain ghost and micritic dolomite(MD)/argillaceous dolomite.The petrology features show that its sediment sequence is micro-organism layer–microbial mound/shoal–tidal flat in carbonate ramp background from bottom up.The reservoir has 5 types of pores,namely,framework pore,dissolved vug,intergranular and intragranular dissolved pore and intercrystalline dissolved pore,as main reservoir space.It is found that the development of pore has high lithofacies selectivity,FSD has the highest average porosity,TD,OD and GD come second.The reservoir is pore-vug reservoir with medium-high porosity and medium-low permeability.The dolomite of Xiaoerblak Formation was formed in para-syngenetic to early diagenetic stage through dolomitization caused by seawater.The reservoir development is jointly controlled by sedimentary facies,micro-organism type,high frequency sequence interface and early dolomitization.The classⅠandⅡreservoirs,with an average thickness of 41.2 m and average reservoir-stratum ratio of about 25.6%,have significant potential.It is predicted that the microbial mounds and shoals in the middle ramp around the ancient uplift are the favorable zones for reservoir development.