塔里木盆地顺北地区奥陶系鹰山组超深层白云岩类型及成储潜力评价^*

Ultra-deep dolomite types and their reservoirs potential of the Ordovician Yingshan Formation in Shunbei area,Tarim Basin

摘要

塔里木盆地顺北地区中下奥陶统鹰山组白云岩是极具勘探潜力的岩相类型,但目前对该地区成层分布的白云岩成因及其物性差异尚无系统阐释。本研究基于详细的岩石学观察、碳氧同位素和微区微量稀土元素分析、碳酸盐岩U-Pb定年、覆压孔渗测试等资料,对鹰山组内幕成层发育的白云岩类型、成因机制进行探讨,并初步评价了不同成因白云岩的物性差异。研究发现: (1)顺北地区鹰山组下段白云岩相对发育,主要包括2类成层分布白云岩,分别是埋藏压溶白云岩(Ⅰ类)和准同生渗透—回流白云岩(Ⅱ类);(2)I类白云岩为埋藏白云石化成因,分布于低能沉积相内,为埋藏过程中缝合线建造驱动黏土矿物转化成因机制,在顺北中部地区较为发育; (3)Ⅱ类白云岩为准同生渗透—回流白云石化成因,主要分布于地貌较高、相对高能的沉积相区,在顺北西区、顺南地区相对发育; (4)Ⅰ类白云岩实测物性数据(φ: 0.3%~1.0%;K:0.003×10^-3~0.074×10^-3 μm²)低于Ⅱ类白云岩(φ: 0.4%~2.0%;K:0.009×10^-3~0.055×10^-3 μm²),但Ⅰ类白云岩的发育可提升地层中白云岩和灰岩互层的比例,具裂缝改造成储潜力。研究成果对于塔里木盆地顺北地区超深层白云岩油气勘探选区具有借鉴意义。

Abstract

Dolomites of the Ordovician Yingshan Formation,which exhibit significant exploration potential,are found in the Shunbei area of the Tarim Basin. However,there is no systematic explanation on the genesis and physical property variations of the stratified dolomite in this region. Based on detailed petrology observation,carbon and oxygen isotopes,rare earth element analysis,carbonate U-Pb chronology dating,and porosity and permeability testing under different stress states,this study discussed the types and genetic mechanisms of the inner stratified dolomites of the Yingshan Formation. Furthermore,it provides a preliminary evaluation of the differences in physical properties among dolomites of various origin. The findings can be summarized as follows: (1)The relative development of dolomites in the lower part of the Yingshan Formation located in the northern region of Shunbei area primarily consists of two types of stratified dolomites,including the buried pressure-dissolved dolomite(Class I)and the penecontemporaneous seepage reflux dolomite(Class Ⅱ). (2)The Class I dolomites,which are predominantly distributed in low-energy sedimentary facies,have their origin in burial dolomitization. This is attributed to the genetic mechanism of clay mineral transformation,driven by the formation of stylolites during the burial process. These dolomites are relatively more developed in the central part of the Shunbei area. (3)The Class II dolomites are characterized by penecontemporaneous seepage reflux dolomitization in sedimentary facies that display high geomorphology and relatively high energy. These dolomites are primarily distributed and well developed in the western and southern Shunbei area. (4)The measured physical properties of Class Ⅰ dolomites(φ: 0.3%~1.0%;K: 0.003×10^-3~0.074×10^-3 μm²)are lower than those of Class Ⅱ dolomites(φ: 0.4%~2.0%;K: 0.009×10^-3~0.055×10^-3 μm²). However,Class I dolomites can enhance the ratio of dolomite-limestone interbedding,and there are fractures to transform into reservoir potential. This study is of significant reference value for ultra-deep dolomite oil and gas exploration in the Shunbei area of the Tarim Basin.

关键词

塔里木盆地 / 鹰山组 / 白云岩类型 / 白云石化 / 储层评价

Key words

Tarim Basin / Yingshan Formation / dolomite types / dolomitization / reservoir evaluation

基金资助

*国家自然科学基金企业创新发展联合基金(编号: U21B2063)和中国石化科技部项目(编号: P24077)共同资助