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  地质与资源 2023, Vol. 32 Issue (6): 750-761  
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引用本文
云念寒, 王芙蓉, 侯宇光, 曾宏斌, 杨荣岩. 潜江凹陷页岩岩相对页岩油储层的控制作用[J]. 地质与资源, 2023, 32(6): 750-761.  
YUN Nian-han, WANG Fu-rong, HOU Yu-guang, ZENG Hong-bin, YANG Rong-yan. CONTROL OF SHALE LITHOFACIES ON THE SHALE OIL RESERVOIR IN QIANJIANG SAG[J]. Geology and Resources, 2023, 32(6): 750-761.  

潜江凹陷页岩岩相对页岩油储层的控制作用
云念寒 , 王芙蓉 , 侯宇光 , 曾宏斌 , 杨荣岩     
中国地质大学 构造与油气资源教育部重点实验室, 湖北 武汉 430074
摘要:在岩心观察与岩石薄片鉴定的基础上, 结合XRD技术、氩离子抛光扫描电镜、低温氮气吸附实验、高压压汞测试和岩石热解分析, 对江汉盆地潜江凹陷潜江组页岩储层的岩石矿物组成、孔渗和孔隙结构、地球化学特征等进行分析. 研究表明, 潜江凹陷潜江组页岩主要矿物组成为白云石和黏土矿物, 主要发育块状灰质泥岩相、纹层状灰质泥岩相、块状云质泥岩相、纹层状云质泥岩相以及块状泥质云岩相和纹层状泥质云岩相. 页岩储层主要发育碳酸盐矿物晶间孔和黏土矿物层间孔, 孔径主要分布在2~200 nm, 孔隙度多低于20%, 渗透率主要为0.1×10-3~100×10-3 μm2, 为低孔低渗-特低渗储层. 其中黏土矿物有利于页岩储层微孔和介孔的发育, 白云石有利于大孔发育, 且生物成因的白云石有助于有机碳的富集和滞留烃的赋存. 储层整体表现为纹层状页岩比块状页岩具有相对较高的孔径、较好的孔隙连通性和含油性, 尤其在纹层状泥质云岩相中, 孔隙度介于5%~15%, 渗透率处于1×10-3~10×10-3 μm2, 主要孔径为50~200 nm, 连通孔径主要为50~100 nm, TOC含量在1%~3%, S1含量分布在5×10-3~35×10-3, OSI值多处于400×10-3, 是潜江组页岩油储层的优势岩相.
关键词页岩油储层    孔隙结构    页岩岩相    潜江组    潜江凹陷    江汉盆地    
中图分类号:P618.13            文献标志码:A            文章编号:1671-1947(2023)06-0750-12
CONTROL OF SHALE LITHOFACIES ON THE SHALE OIL RESERVOIR IN QIANJIANG SAG
YUN Nian-han , WANG Fu-rong , HOU Yu-guang , ZENG Hong-bin , YANG Rong-yan     
Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences, Wuhan 430074, China
Abstract: The rock mineral compositions, porosity-permeability, pore structure and geochemical characteristics of the shale reservoir of Qianjiang Formation in Qianjiang Sag, Jianghan Basin, are studied on the basis of core observation and rock slice identification, combined with XRD technology, argon ion polishing scanning electron microscopy, low temperature nitrogen adsorption experiment, high pressure Hg injection test and rock pyrolysis analysis. The results show that the shale of Qianjiang Formation is mainly composed of dolomite and clay minerals, developed with massive calcareous mudstone facies, laminated calcareous mudstone facies, massive dolomitic mudstone facies, laminated dolomitic mudstone facies, massive argillaceous dolomite facies and laminated argillaceous dolomite facies. The carbonate mineral intercrystalline pores and clay mineral interlayer pores are mainly developed in the shale reservoir, with the pore size of 2-200 nm, the porosity mostly lower than 20%, and the permeability of 0.1×10-3-100×10-3 μm2, belonging to low porosity and low-extra low permeability reservoir. Clay minerals are conducive to the development of micropores and mesopores in shale reservoirs, while the dolomites contribute to the development of macropores, and biogenic dolomites help the accumulation of organic carbon and occurrence of residual hydrocarbon. Generally, the laminated shale has higher pore size, better pore connectivity and oil content than the massive shale dose. Especially the laminated argillaceous dolomite facies, with porosity of 5%-15%, permeability of 1×10-3-10×10-3 μm2, main pore size of 50-200 nm, connected pore size of 50-100 nm, TOC content of 1%-3%, S1 content of 5×10-3-35×10-3 and OSI value mostly 400×10-3, is the dominant lithofacies of shale oil reservoir in Qianjiang Formation.
Key words: shale oil reservoir    pore structure    shale facies    Qianjiang Formation    Qianjiang Sag    Jianghan Basin    

0 前言

岩相是岩石的一种基本特征,通常反映一定的沉积环境和沉积过程 [1],也可以反映岩石学特征和沉积微相特征 [2]. 近年来随着页岩油气勘探工作的深入,石油地质学家发现虽然泥页岩矿物成分复杂、非均质性较强,但是其有机质的成熟度、天然气的含量及气体赋存状态都与页岩中有机质的含量及矿物组成关系密切 [3],如Jacobi等 [4]证实了页岩岩相与TOC以及孔隙度的分布有密切联系,Mitra等 [5]证实页岩岩相在TOC预测、岩石物理学分析、孔隙度分析和甜点预测方面具有十分重要的作用. 同时国外在Bakken组页岩、Barnett页岩、Marcellus页岩和Woodford页岩等非常规页岩储层油气勘探和开发中,基于页岩层理、结构、生物、矿物组成、岩性等方面开展富有机质页岩岩相研究,已取得了广泛的成功 [6-9].

相比海相页岩油储层来说,中国陆相页岩油储层的矿物组成更为多样、岩石类型更为丰富、叠置关系更为复杂,众多学者对鄂尔多斯盆地页岩、渤海湾盆地济阳拗陷页岩、黄骅拗陷沧东凹陷页岩开展岩相研究,对于油气勘探均有一定的指示意义. 冯增昭 [10]、沈骋等 [11]认为不同岩相储集层形成条件存在差异,导致其矿物组成和有机碳含量存在较大差异,进而导致储层孔隙度以及页岩油的赋存机制存在差异;王圣柱、王勇、徐兴友、李士超等 [12-15]认为纹层状岩相的水平渗透率相对较高,孔渗条件好,富有机质页岩有机质多呈网状分布,含油性较好;柳波等 [16]认为块状高有机质页岩孔隙多孤立,中等有机质含量时,生油潜力好且孔隙发育较好;Iqbal等 [17]、Shang等 [18]认为富含泥质的页岩微孔及有机质较为发育.

江汉盆地潜江凹陷古近系潜江组页岩含油性好,可采资源量丰富,具有较大的勘探潜力. 近年来,众多学者对潜江凹陷潜江组页岩开展了不同程度的研究,主要集中在页岩的岩石学组成、地球化学性质以及储层特征等方面:孙中良、Huang等 [19-20]认为矿物组成以白云石、方解石、黏土矿物以及石英和长石为主;李乐等 [21]认为潜江凹陷页岩储层孔隙特征为高-中孔、特低渗;徐二社、刘心蕊等 [22-23]认为潜江组34油组第10韵律层为最有利于页岩油富集的层系;Wang、Hou等 [24-25]认为该层段为缺氧环境,有利于有机质的发育及保存,而对页岩岩相对储层的控制关系的研究较为缺乏.

潜江凹陷潜江组页岩储层矿物成分复杂、岩性多样、岩相变化快,储层孔隙类型多、结构复杂,导致页岩油富集规律的研究难度增大. 为此,本研究在前人研究的基础上,以潜江凹陷钻井中潜江组页岩为研究对象,通过XRD分析、氩离子抛光扫描电镜、低温氮气吸附、高压压汞和岩石热解分析等方法,对比研究不同岩相的岩石学特征、孔隙特征以及含油性特征,分析造成差异的相关地质因素,建立岩相与孔隙结构及含油性的关系,最终明确优势岩相,为下一步勘探部署提供依据.

1 地质概况

潜江凹陷位于江汉盆地中部,面积达2 530 km2. 北部与荆门凹陷、乐乡关地垒、汉水凹陷相连,东部与江陵凹陷相邻,南部以通海口凸起为界,西部与岳口低凸起相连. 始新世晚期到渐新世早期,潜北大断裂活动强烈,断裂前缘快速下陷,北东向构造特征弱化,北西向隆升的构造趋势得以加强 [26-27](图 1). 江汉盆地潜江组地层沉积时期以亚热带干旱为主,且与潮湿环境交替较为频繁. 因此,潜江组在纵向上显示出化学蒸发沉积与陆源碎屑沉积交替出现的特征 [28],地层长期处于封闭性强、蒸发性强以及高盐度环境,具有周期性浅水-半深水盐湖沉积特点 [29],最终沉积形成了巨厚的潜江组含盐系地层,普遍发育泥页岩,油气显示丰富. 与北美及中国其他地区的相比,潜江组盐间地层页岩具有“高黏土、低石英、高碳酸盐”的矿物特征,同时页岩中又含有一定量的蒸发盐类矿物,对页岩油储层的孔隙和含油性产生了较大的影响. 潜江组按地层层序自下而上可分为潜四段(Eq4)、潜三段(Eq3)、潜二段(Eq2)和潜一段(Eq1),其中潜三下段和潜四下段是页岩油勘探最有利层段 [22].

图 1 潜江凹陷构造位置及取样井位图(据文献[27]修改) Fig.1 Tectonic map with sampling well location of Qianjiang Sag (Modified from Reference [27]) 1-砂泥岩相区(sandy mudstone facies);2-咸淡过渡区(saline water-freshwater transition zone);3-盐韵律区(salt rhythm area);4-砂岩尖灭线(pinch-out line of sandstone);5-岩盐尖灭线(pinch-out line of rock salt);6-地层尖灭线(stratigraphic pinch-out line);7-凸起边界(boundary of uplift);8-断层(fault);9-物源方向(source direction);10-取样井(sampling well)
2 分析方法与样品

受北部单向碎屑物源的影响,本次实验所用样品取自潜江凹陷北部周矶向斜带BX7井以及南部蚌湖洼陷BYY2井的潜34油组10韵律(图 1),共37块岩心样. BX7井样品的深度为3 046~3 062 m,岩相多为浅灰色块状云-灰质泥岩相,TOC含量0.32%~2.58%,平均含量为1.40%;BYY2井样品的深度为2 813~2 823 m,岩相多为纹层状黄褐色泥质云岩相和云质泥岩相,TOC含量0.49%~2.91%,平均含量为1.58%.

XRD分析采用D8 DISCOVER X射线衍射仪,通过对材料进行X射线衍射,分析其衍射图谱,从而计算出特征X射线的波长,进而可根据已有资料查出试样中所含的元素.

低温氮气吸附试验采用ASAP2020全自动比表面及孔径分析仪进行测试. 该仪器孔径测量范围为0.35~500.00 nm,测试条件为:低温-195.8 ℃,压力97.3~127.0 kPa,样品要求0.18~0.28 mm (80~60目),以纯度大于99.999%的氮气为吸附质. 根据BET方程计算出页岩的比表面积,应用BJH理论和Kelvin方程求出孔隙所对应的分布情况.

高压压汞分析采用Autopore Ⅳ 9520高压压汞仪进行测试. 利用汞对一般固体不润湿的特性进行分析,根据相关资料得出孔径分布情况. 最大进汞压力为413 MPa,孔喉测试范围为3 nm~ 800 μm,样品为1 cm3的立方体.

索式抽提实验采用经典索氏提取器,以丙酮、氯仿、甲醇(体积比19 : 16 : 15)的三元溶剂为抽提剂,在70~90 ℃温度条件下对样品进行抽提. 以上分析测试均在中国地质大学(武汉)构造与油气教育部重点实验室完成.

孔隙度采用氦孔隙度测量仪JS 100007,渗透率采用高低渗透率测定仪JS 100006和JS 100010,实验在江汉油田分公司勘探开发研究院石油地质测试中心完成.

场发射扫描电镜采用日本日立冷场发射扫描电子显微镜,型号为SU8010,测试条件为加速电压:0.1~30 kV、0.1 kV/步,在中国科学院微生物研究所完成.

3 实验结果 3.1 储层的矿物成分及地球化学特征

XRD分析数据显示,BX7井及BYY2井样品的矿物成分主要为白云石和黏土矿物,其次为方解石和石英,以及少量长石、黄铁矿、石膏和岩盐.

两口井页岩样品中矿物含量存在差异,主要表现在黏土矿物和白云石的含量不同. BYY2井样品黏土矿物平均含量为15.42%,而BX7井样品黏土矿物平均含量为25.5%;BYY2井样品白云石平均含量为44.89%,而BX7井白云石平均含量为29.9% (表 1).

表 1 样品矿物组分及地球化学特征 Table 1 Mineral compositions and geochemical characteristics of shale samples

两口井页岩样品中含油性参数也存在差异,主要表现在TOC含量、S1含量和OSI值. BYY2井页岩样品中含油性参数相对较高,TOC含量多为1%~3%,S1含量多为0~15×10-3,平均为10.14×10-3,OSI值多为300×10-3~800×10-3,平均为793×10-3,为含油且具有较高产油性的岩层. BX7井页岩样品TOC含量多为1%~2%,S1含量多为0~5×10-3,平均为4.24×10-3,OSI值多为200×10-3~400×10-3,平均321.71×10-3,为含油且具有产油性的岩层.

以“碎屑(石英、长石以及黏土矿物)-方解石-白云石”三端元分类法进行页岩岩相划分. 同时结合岩心观察发现:BX7井页岩样品主要为浅灰色,块状构造,主要发育块状灰质泥岩相以及块状云质泥岩相;BYY2井页岩样品从浅灰色到深灰色均有,夹有黄褐色泥质岩层,主要发育纹层状泥质云岩相并夹有黄褐色纹层状灰质泥岩相(图 2).

图 2 样品岩相划分散点图 Fig.2 Lithofacies classification diagram of shale samples I-泥岩相(mudstone facies);II-灰质泥岩相(calcareous mudstone facies);III-云质泥岩相(dolomitic mudstone facies);IV-泥质灰岩相(argillaceous limestone facies);V-泥质云岩相(argillaceous dolomite facies);VI-云质灰岩相(dolomitic limestone facies);VII-灰质云岩相(calcareous dolomite facies);VIII-灰岩相(limestone facies);IX-白云岩相(dolomite facies);1-BX7井(BX7 well);2-BYY2井(BYY2 well)
3.2 孔隙结构

两口井页岩样品的脱附曲线出现了2种明显不同的迟滞环曲线 [30],块状页岩相和纹层状页岩相样品孔隙结构具有较大差异. 块状页岩样品孔隙为圆柱形、平行板状狭缝形以及墨水瓶形三者混合(图 3a),纹层状页岩样品孔隙结构多为四周开放的平行板状狭缝孔隙(图 3b).

图 3 样品孔隙结构 Fig.3 Pore structures of shale samples a-块状页岩样品低温氮气吸附-脱附曲线(low temperature nitrogen adsorption-desorption curves of massive shale samples);b-纹层状页岩样品低温氮气吸附-脱附曲线(low temperature nitrogen adsorption-desorption curves of laminated shale samples);c-孔径分布曲线(氮气吸附)(pore-size distribution curves,nitrogen adsorption);d-孔径分布曲线(进汞增量)(pore-size distribution curves,incremental intrusion Hg);1-块状云质泥岩相(massive dolomitic mudstone facies);2-块状灰质泥岩相(massive calcareous mudstone facies);3-纹层状泥质云岩相(laminated argillaceous dolomite facies);4-纹层状云质泥岩相(laminated dolomitic mudstone facies);5-纹层状灰质泥岩相(laminated calcareous mudstone facies)

低温氮气吸附-脱吸附曲线显示,样品的孔径多为2~100 nm,其中块状页岩样品孔径多小于10 nm,纹层状页岩样品孔径主要集中在10~100 nm(图 3c). 高压压汞实验结果进一步表明,样品的孔径主要集中在10~200 nm之间,且不同岩相样品的进汞曲线和孔径分布存在较大差异,其中纹层状云质泥岩相、纹层状泥质云岩相中大孔最为发育,孔隙体积也相对较大(图 3d).

3.3 孔隙类型

氩离子抛光扫描电镜结果显示,潜江组页岩样品的孔隙类型主要有粒间孔、碳酸盐晶间孔、黏土矿物层间孔,部分孔隙内可见黑色的有机质充填. 其中粒间孔主要发育于碳酸盐矿物之间以及黏土矿物颗粒间及颗粒边缘,孔径大小不一,部分孔隙边缘可见有机质赋存(图 4a);晶间孔主要发育在白云石晶体之间,多数情况下呈现出规则的多面体状,孔径较大,连通性好(图 4bc);黏土矿物层间孔主要分布在黏土矿物之间,孔径普遍较低,多为纳米级,孔隙形状多为狭长状、扁平状(图 4d).

图 4 页岩扫描电镜图 Fig.4 SEM photographs of shale samples a-BX7井,块状云质泥岩相样品,主要发育碳酸盐矿物粒间孔和黏土矿物层间孔,部分碳酸盐矿物内可见粒内孔,部分孔隙内可见少量滞留烃赋存;b-BX7井,块状泥质云岩相样品,可见黏土矿物中发育少量的层间孔,白云石颗粒接触紧密,仅见少量的粒内溶孔;c-BYY2井,纹层状泥质云岩相样品,广泛发育白云石(粒)晶间孔,滞留烃富集;d-BYY2井,纹层状泥质云岩相样品,黏土矿物间层间孔发育,部分孔隙内可见滞留烃赋存
4 讨论 4.1 岩相对储层孔隙的影响

潜江凹陷潜江组页岩样品实测的孔隙度小于20%,大部分处于5%~10%的范围内;渗透率主要分布范围为0.1×10-3~100×10-3 μm2,平均值为46×10-3 μm2(表 2). 整体来看,潜江组盐间页岩属于低孔低渗-特低渗储层,孔隙度渗透率的发育与岩相之间没有明显的对应关系. 比较而言,块状岩相的页岩样品的渗透率较高,与样品发育裂缝有关;纹层状岩相的页岩样品孔隙度较为发育.

表 2 样品不同岩相孔渗数据统计表 Table 2 Porosity and permeability data of shale samples in different lithofacies

相对而言,岩相对孔径的影响较为明显(图 56).

图 5 样品全孔径分布曲线 Fig.5 Full-scale pore size distribution curves of shale samples 1-块状云质泥岩相(氮气吸附)(massive dolomitic mudstone facies,nitrogen adsorption);2-块状云质泥岩相(高压压汞)(massive dolomitic mudstone facies,high pressure Hg injection);3-块状灰质泥岩相(氮气吸附)(massive calcareous mudstone facies,nitrogen adsorption);4-块状灰质泥岩相(高压压汞)(massive calcareous mudstone facies,high pressure Hg injection);5-纹层状泥质云岩相(氮气吸附)(laminated argillaceous dolomite facies,nitrogen adsorption);6-纹层状泥质云岩相(高压压汞)(laminated argillaceous dolomite facies,high pressure Hg injection);7-纹层状灰质泥岩相(氮气吸附)(laminated calcareous mudstone facies,nitrogen adsorption);8-纹层状灰质泥岩相(高压压汞)(laminated calcareous mudstone facies,high pressure Hg injection);9-纹层状云质泥岩相(氮气吸附)(laminated dolomitic mudstone facies,nitrogen adsorption);10-纹层状云质泥岩相(高压压汞)(laminated dolomitic mudstone facies,high pressure Hg injection)
图 6 样品抽提前后氮气吸附曲线与进汞量曲线 Fig.6 Nitrogen adsorption and incremental intrusion Hg curves before and after extraction of shale samples a,c-块状(massive);b,d-纹层状(laminated);1-灰质泥岩相(抽提前)(calcareous mudstone facies,before extraction);2-灰质泥岩相(抽提后)(calcareous mudstone facies,after extraction);3-云质泥岩相(抽提前)(dolomitic mudstone facies,before extraction);4-云质泥岩相(抽提后) (dolomitic mudstone facies,after extraction)

低温氮气吸附试验中页岩样品不同孔径下孔体积分布以及高压压汞试验中页岩样品不同孔径下进汞量分布显示,潜江凹陷潜江组页岩样品孔径分布复杂,孔径分布曲线呈多峰型,不同孔径的孔隙均有发育,其中块状云质泥岩相以及块状灰质泥岩相以微孔为主(图 5a),孔径主要分布在2~8 nm;而纹层状泥质云岩相以及纹层状灰质泥岩相的微孔、介孔和大孔均发育较好,孔径主要分布在2 nm左右和40~50 nm,部分微米级孔隙(图 5b);纹层状云质泥岩相样品孔隙发育相对均匀,以介孔和大孔为主,孔径主要集中在50~200 nm (图 5c).

抽提前后氮气吸附以及高压压汞增加的孔隙体积是滞留烃所占据的空间,可以用来表示页岩的孔隙连通性 [30]. 抽提前后孔径分布曲线显示,块状样品的氮气吸附以及高压压汞进汞量的增加主要集中在2~20 nm的介孔,而纹层状样品的曲线则呈现出双峰,分别在2~5 nm以及10~100 nm之间,且增量整体较大于块状样品(图 6),说明岩相不仅影响了孔隙的大小,也影响了孔隙的连通性.

扫描电镜显示页岩储层中孔隙主要为碳酸盐矿物晶间孔,部分为黏土矿物层间孔(图 4). 纹层状页岩相中泥晶白云石颗粒多呈环状聚集,晶间孔十分发育,孔径较大 [31]. 汪品先认为藻类勃发诱发湖水中碳酸盐的周期性化学沉淀是许多湖相纹层的形成机理 [32],但以块状为主的样品中,化学沉淀的白云石占主体地位,压实作用强,颗粒接触紧密 [33],反而不利于孔隙的发育(图 4b). 比较而言,纹层状岩相样品比块状岩相样品的孔隙体积总体较高,且介孔和大孔相对发育(图 7). 页岩储层中的黏土矿物有利于层间孔的发育,但由于黏土矿物极易挤压变形,黏土矿物的含量越高,孔隙受压实作用遭受破坏,整体表现为介孔相对发育,纹层状岩相样品在白云石含量为30%~40%时介孔及大孔更为发育(图 7).

图 7 样品孔隙与矿物含量相关性散点图 Fig.7 Scatter diagrams showing the correlation between pore and mineral contents of shale samples I-白云石(dolomite);II-黏土矿物(clay mineral);1-块状云质泥岩相(massive dolomitic mudstone facies);2-纹层状云质泥岩相(laminated dolomitic mudstone facies);3-纹层状泥质云岩相(laminated argillaceous dolomite facies);4-块状灰质泥岩相(massive calcareous mudstone facies);5-纹层状灰质云岩相(laminated calcareous dolomite facies)
4.2 岩相对含油性的影响

两口井的页岩样品的TOC含量和S1含量普遍较高,TOC含量介于1%~3%,S1含量介于0~35×10-3,且两者具有较为明显的正相关性. 比较而言,纹层状岩相的页岩样品的TOC含量高,部分可高达3%,绝大多数样品的S1含量高于5×10-3;块状岩相的页岩样品TOC含量多低于2%,S1含量多低于5×10-3 (表 3),其中纹层状泥质云岩相具有相对高的TOC含量和S1含量.

表 3 样品不同岩相含油性数据统计表 Table 3 Oil-bearing property data of shale samples in different lithofacies

页岩矿物组成在一定程度上影响页岩油储层中的有机质富集和滞留烃的赋存. 黏土矿物多为陆源碎屑,可以携带部分有机质进入,但是由于潜江凹陷有机质来源主要为水生藻类及细菌 [34],陆源碎屑所携带的有机质贡献较小,在一定程度上会稀释有机质的浓度,表现为黏土矿物与TOC含量多为负相关关系(图 8). 黏土矿物中多发育微小孔径,不利于滞留烃(S1)的大量赋存,与S1含量、OSI值也多呈现负相关性(图 8). 白云石含量与TOC含量、S1含量及OSI值均有一定程度的正相关性,其中纹层状样品的相关性更强(图 8),主要是由于这类样品多形成于还原性较强的湖泊深水区,有机质保存良好,纹层大部分呈微波状且物质组成较为复杂,高有机质含量反映了其沉积时期微生物勃发,创造了有利于碳酸盐矿物形成的沉积环境 [29].

图 8 样品地球化学参数与不同矿物含量分布相关性散点图 Fig.8 Correlations between geochemical parameters and mineral contents of shale samples 1-块状云质泥岩相(massive dolomitic mudstone facies);2-块状泥质云岩相(massive argillaceous dolomite facies);3-块状灰质泥岩相(massive calcareous mudstone facies);4-纹层状云质泥岩相(laminated dolomitic mudstone facies);5-纹层状泥质云岩相(laminated argillaceous dolomite facies);6-纹层状灰质泥岩相(laminated calcareous mudstone facies)

相比较而言,纹层状泥质云岩相具有良好的孔渗性,孔隙度一般为5%~15%,渗透率为1×10-3~10×10-3 μm2,而且纹层状泥质云岩相的页岩具有较高的TOC含量、S1含量和OSI值,其中TOC含量为1%~2.5%,S1含量为7×10-3~30.5×10-3,OSI值范围为357.51×10-3~1 350.49×10-3,是潜江组盐间地层页岩油勘探的优质岩相(图 9).

图 9 潜江凹陷潜34-10韵律综合柱状图 Fig.9 Comprehensive stratigraphic column of Eq34-10 rhythm in Qianjiang Sag a-BX7井(BX7 well);b-BYY2井(BYY2 well);1-石英(quartz);2-辉长石(gabbro);3-斜长石(plagioclase);4-黏土(clay);5-方解石(calcite);6-白云石(dolomite);7-硬石膏(anhydrite);8-黄铁矿(pyrite);9-石盐(halite);10-钙芒硝(glauberite)
5 结论

(1) 研究区潜江组页岩矿物成分复杂,主要为白云石、黏土矿物、方解石、石英,以及少量长石、黄铁矿、石膏和岩盐,其中白云石和黏土矿物占主导地位. 主要发育灰质泥岩相、云质泥岩相、泥质云岩相三大类.

(2) 潜江组页岩主要发育碳酸盐岩晶间孔、黏土矿物层间孔,孔径分布范围主要为2~200 nm,孔隙度多低于20%,渗透率主要为0.1×10-3~100×10-3 μm2,为低孔低渗-特低渗储层.

(3) 潜江组页岩TOC含量较高,大多在1%~2.5%,S1含量多处于5×10-3~10×10-3,OSI值介于200×10-3~800×10-3,具有良好的生油性;生物成因的白云石含量与TOC含量、S1含量及OSI值均有一定程度的正相关性;纹层状页岩比块状页岩具有相对较高的孔径、较好的孔隙连通性和含油性,是潜江组盐间地层优势岩相.

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