塔里木盆地巴楚地区寒武系储层特征及主控因素

Characteristics and controlling factors of the Cambrian carbonate reservoirs in Bachu area,Tarim Basin,NW China

综合利用野外剖面、钻井岩心观察、薄片鉴定以及物性测试等资料,辅以阴极发光、碳—氧同位素和电子探针等地球化学分析手段,对巴楚地区寒武系碳酸盐岩储层特征及主控因素进行系统研究。结果表明:研究区寒武系发育盐上白云岩(丘里塔格组)、盐间云灰岩(沙依里克组)和盐下白云岩(肖尔布拉克组)3套储集层。盐上和盐下白云岩储层主要由(残余)颗粒白云岩、粉—细晶白云岩和具有微生物结构的白云岩组成,储层类型以溶蚀孔洞型和裂缝—溶蚀孔洞型为主;储层发育受沉积相和多期溶蚀作用控制:高能相带(颗粒滩、微生物丘)和膏岩—碳酸盐岩过渡相带(含膏云坪)构成储层发育的基础;准同生期层间岩溶进一步叠加改造,形成大量顺层溶蚀孔洞层,在纵向上多期叠置、横向上似层状大面积展布,控制储层规模化发育;晚期热液溶蚀沿早期高孔渗带局部调整改造,但横向影响范围有限;另外,浅埋藏期适度的白云岩化有利于颗粒滩相白云岩孔隙的保存。盐间云灰岩储层以斑状或条带状白云质灰岩为主,孔隙主要发育在与生物钻孔或生物扰动有关的潜穴部位,生物扰动对于低能相带物性的改善具有积极意义。

The main objectives of this paper are to study the features and controlling factors of the Cambrian carbonate reservoirs in Bachu area,based on the field investigation,core observation,thin-section analysis and porosity-permeability data as well as geochemical tests including cathodoluminesecnce,carbon-oxygen isotopes and trace elements.The results show that there are three sets of reservoirs of the Cambrian carbonate rocks in the study area.They are salt-overlying dolomite reservoir in the Upper Cambrian Qiulitage Formation（R1）,dolomitic limestone reservoir between salt beds in the Middle Cambrian Shayilike Formation（R2）and salt-underlying dolomite reservoir in the Lower Cambrian Xiaoerbulake Formation（R3）.The R1 and R3dolomite reservoirs,comprised of（relict）grainy dolomite,very fine to fine-crystalline dolomite and microbial dolomite,are characterized by dissolution vug and fracture-dissolution vug porosity.The development of these reservoirs is collectively controlled by the sedimentary facies and multiple-stage dissolution.The formation base of the R1 and R3reservoirs is associated with the high-energy facies such as shoal bank and microbial mound,and evaporite-carbonate transitional zones such as semi-evaporitic tidal-flat facies with anhydrite-bearing dolomite.The interbedded karstification,occurred during penecontemporaneous stage,further modified the pre-existing reservoirs and formed a series of porous layers with laminar dissolutionvugs,which stacked vertically and distributed in a larger range laterally.The hydrothermal dissolution,occurred in burial stage,locally alternated the reservoirs with high initial porosity,but the effect range is limited.Otherwise,it is significant for the porosity preservation that the moderate dolomitization of the grainy sediments occurred in the shallow burial.The R2 reservoir is composed of mottled and/or banded dolomitic limestone.The porosity of the reservoir is associated with the dolomitized burrows,suggesting the bioturbation plays a vital role for the pore creation in the low energy environment.