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Diagenesis of sandstone in the Majiashan-Xiaojianzi oilfield, Ordos basin and its effect on reservoirs

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Abstract

Integrated methods, including thin section identification, cast thin section examination, mercury penetration, scanning electron microscopy (SEM), X-ray diffraction (XRD) and fluid inclusion analysis, were used to reveal the controls of sandstone diagenesis in the Majiashan - Xiaojianzi oilfield on reservoirs. Study indicates that the diagenesis of sandstone of the Chang 61 and Chang 4+5 members in the Yanchang Formation has reached stage A of the middle diagenetic phase. The distribution of diagenetic facies exhibits a distinctive regularity: dissolution pore facies, chlorite cement facies, carbonate cement facies and compact matrix facies occur in succession from the sand bodies of subaqueous distributary channels and center of river mouth sandbars to margins and down to the subaqueous distributive bay. The physical properties of sandstone become poor successively. The favorable reservoirs are dissolution pore facies and chlorite cement facies in the sand bodies of subaqueous distributary channels and center of river mouth sandbars.
中国地质
GEOLOGY IN CHIN
34 卷第
2007
Vol.34No.2
Apr.2007
马家山小涧子油田位于鄂尔多斯盆地伊陕斜坡的西
北至马家山
南至罗卜塬
西至沙腰岘
东至王洼子
2.2×10km其勘探目的层系主要为上三叠统长 4+
油层组进一步细分为长 4+
4+
油层段
个小层埋深 1 8002 450 m储集体主要是三角洲前缘水下
分流河道及河口坝砂体西
沉积时期湖平面下降三角洲沉积占主导地位砂岩厚度最
4+沉积期湖平面有所上升三角洲沉积体系向后
退砂体平均厚度最小4+沉积期湖平面又有所下
砂体发育较好
西
研究[1- 8但就成岩阶段
成岩相及其对储层的控制
储层预测等关键问题尚未取得统一认识笔者以马家山
小涧子地区延长组长
4+段为目的层60 余口井岩
心描述的基础上通过薄片鉴定
铸体薄片
扫描电镜
X-
线衍射和包裹体分析等方法对储集层成岩作用
孔隙演化进行分析和研究旨在揭示该区砂岩储层的物性演
化规律结合砂体平面展布对储层进行综合评价和有利区
带预测为油气勘探开发提供依据
成岩程度的确定
中国石油行业一般将成岩阶段划分为同生期早成岩
中成岩期
晚成岩期和表生成岩期依据古温度
粘土矿
物组合及序列
有机质成熟度
岩石结构及孔隙特征等成岩
阶段划分的标志对本区长 4+
储层成岩阶段的划分
进行了详细研究
1.1 流体包裹体
[9流体包裹体测温实验在莱卡 MSJ600 冷热台测温系
统上完成根据室温下包裹体的成分和相态
有关的流体包裹体划分为盐水溶液包裹体
CO包裹体和烃
类包裹体
盐水溶液包裹体在本区发育丰富它的个体通常不大
μ形态各异有椭圆形
颜色则以浅色为主无色或淡黄色在石英裂隙和加大边
中都有产出
CO包裹体主要呈三相产出气体
液态
水溶液组成
这类包裹体数量较少不足包裹体总量的 5%
体明显大于盐水溶液包裹体一般大于 μ包裹体轮廓以
负晶形为主主要沿石英边部或颗粒内部发育
本区发育的液态烃包裹体数量较少个体较大透射光
下颜色以淡褐色
褐色为主荧光激发下发黄绿色主要分
布在石英加大边和微裂隙中
研究区砂岩中盐水溶液包裹体分布最为广泛在成岩
马家山小涧子油田砂岩成岩作用
及其对储层的影响
杨仁超 樊爱萍 1,韩作振 柳益群
1.山东科技大学地质科学与工程系东 青2665102.西北大学地质学系西 西710069
提要为了揭示鄂尔多斯盆地马家山小涧子油田砂岩成岩作用对储层的控制作用综合采用了薄片鉴定
铸体薄
压汞
扫描电镜
X- 射线衍射和包裹体分析等多种方法
研究认为该区延长组长
4+段砂岩成岩作用进入
了中成岩阶段的 成岩相的平面分布具有明显的规律性由水下分流河道砂体及河口砂坝中心向边缘直至水
下分流间湾依次发育溶蚀孔隙相
绿泥石胶结相
碳酸盐胶结相及压实杂基相 种成岩相类型储层物性依次变差
有利的储集相带为水下分流河道砂体和河口砂坝中心的溶蚀孔隙相和绿泥石胶结相
关键词鄂尔多斯盆地延长组砂岩储层成岩作用成岩相
中图分类号P588.21 文献标志码文章编号1000- 3657(2007)02- 0283- 06
收稿日期2006- 09- 19改回日期2006- 10- 19
基金项目国家重点基础研究发展规划项目2003CB214603资助
作者简介杨仁超1976 年生博士生讲师从事沉积学研究E- mailrc_yang@sina.com
中 国 地 质 2007
射线衍射粘土矿物含量分析
Table 1 XRD analysis of the content of clay minerls
中阶段矿物中均有产出而烃类包裹体则是中成岩阶段
的产物[9研究区与液态烃伴生的盐水溶液包裹体均一温度
分布范围为 9014主体为 110120
1.2 粘土矿物组合
射线衍射分析表明 ) , 本区粘土矿物以绿泥石
8%43%26.9%
高岭石16%52%30.5%为主
蒙混层4%43%22.8%次之伊利石12%29%
19.8%最少蒙混层比全部在 20%以下说明成岩作用
已达到中期阶段
1.3 镜质体反射率与岩石结构
经实验测定本区延长组长
4+段有机质镜质体
反射 0.71%1.05%表明有机质演化处于低成熟
熟阶段岩石类型主要为岩屑长石砂岩
长石岩屑砂岩和长
石砂岩少量岩屑石英砂岩孔隙式胶结碎屑颗粒接触紧
多以线接触为主可见缝合线状接触孔隙类型以次生孔
隙为主原生孔隙保留很少长石
岩屑的溶蚀现象较为普遍
含铁方解石
铁方解石等较晚的成岩矿物未见溶解
根据上述研究按照中国石油天然气行业碎屑岩成岩阶段
划分标准SY T5477 - 2003 将马家山小涧子油田主要储
集层延长组长
4+5 段砂岩成岩阶段确定为中成岩
成岩作用对储层的影响
沉积物在进入埋藏成岩环境之后不同的成岩作用类型
及不同的成岩作用强度对储集层的储集性能起着决定性的
作用[11- 14]压实作用对本区砂岩原生孔隙的破坏十分明显
解作用则对砂岩储层物性的改善起着至关重要的作用
结作用往往具有双重性质
2.1 压实作用
机械压实作用主要发生于成岩作用早期对埋深较浅的
地层作用较明显可造成砂岩原始孔隙的大量丧失机械压
实作用在本区主要表现为: (长石
石英等刚性颗粒发生破
2- A) ; 云母
泥岩等塑性岩屑颗粒发生弯曲
或被刚性碎屑插入; (碎屑颗粒接触更加紧密由点接触到
线接触直至凹凸接触
2.2 胶结作用
2.2.1 早成岩期绿泥石或伊蒙混层胶结
埋深增加发生水化水解作用形成自生蒙脱石
水化水解作用
产生的
Na等离子使孔隙水介质的 pH 值高于 随着埋
藏深度的增加地层温度逐渐升高碎屑岩中的蒙脱石逐渐
脱去层间水晶格重新排列形成自生伊利石蒙脱石混层[15
流体包裹体均一温度分布直方图
Fig.1 omogenization temperature distribution of fluid inclusion
284
34 期 杨仁超等马家山小涧子油田砂岩成岩作用及其对储层的影响
研究区储集砂岩成岩作用
74 井斜长石双晶断裂正交偏光, 2200.1m228 蒙混层扫描电镜1824.5m69 井绿泥石薄膜与自生石英
描电镜2197.5m69 井方解石阴极光, 2199.3m115 井石英加大边
次生盐水包裹体单偏光,2225.1m122 井自生高
岭石扫描电镜, 2197.5m74 井长石被方解石交代正交偏光, 2215.2m29 井高角度裂缝及油斑含油,2179.2 ̄2179.4m
Fig.2 iagenesis of sandstone reservoirs i the study area
A- Twin fracture of plagioclase, crossed polarized light, 2200.1 m, well Yuan74B- Illite/smectite, SEM, 1824.5 m, well Yuan 228C- Chlorite
film and authigenic quartz, SEM, 2197.5 m, well Yuan 69D- Calcite, CL, 2199.3 m, well Yuan 69E- Q uartz overgrowths and secondary saline
inclusions, plane polarized ligt, 2225.1 m, well Geng 115F- Authigenic kaolinite, SEM, 2197.5 m, well Yuan 122G- R eplacement of feldspar
by calcite, crossed polarized light, 2215.2 m, well Yuan74H- High- angle fissuresand oil stains, 2179.2- 2179.4 m, well Yuan29
2- B) , 反应式如下
4.5K+8AlKNaCaMgAl143810
20
蒙脱石
5.MgFe.5Al22350020伊利石
+2C2++2.5Fe3++2Mg2++3Si4++10H
泥质沉积物在压实成岩过程中释放出 Si2+
Al3 +
Na
Mg2+
Ca2+
Fe 这些物质随压实水一起进入砂岩
孔隙系统中与蒙脱石发生反应形成绿泥石[16]反应式如下
蒙脱石+Fe2+Mg2+绿泥石+KSiO
储层中发育的绿泥石2- C蒙混层薄膜
面充填原生孔隙使孔隙度降低另一方面绿泥石薄膜的形
成阻碍了孔隙水与颗粒的进一步反应并限制了石英次生加
大的发育有利于原生孔隙的保存[17,18
2.2.2 早成岩 期方解石
早期方解石呈微晶状填充孔隙2- D) , 降低了岩石
的孔隙度和渗透率
2.2.3 中成岩 期硅质胶结和高岭石的形成
研究区砂岩中硅质胶结物主要为石英加大边- E) ,
其次为充填粒间孔隙的自生石英小颗粒2- C
硅质胶结
交代早先形成的绿泥石和方解石表明孔隙流体性质由碱性
转化为酸性石英加大边中烃类包裹体的存在证实加大边
的形成与油气运移密切相关硅质胶结一方面堵塞孔喉并使
粒间孔隙减小另一方面增加颗粒的抗压实程度和支撑能
又有利于粒间孔隙的保存
高岭石是砂岩中常见的自生粘土矿物多充填溶蚀粒间
与自生石英伴生扫描电镜下观察呈蠕虫状或书页状
集合体2- F高岭石书页状晶形保留了良好的晶间孔
是重要的储集空间组成部分
2.2.4 中成岩 期末碳酸盐胶结
晚期方解石胶结比较常见与早期方解石有明显不同的
是晚期方解石在成分上含 Fe 为含铁方解石和铁方解石
方解石往往交代长石
岩屑等碎屑颗粒2- G) , 并堵塞溶
蚀粒间孔隙和剩余原生孔隙极大地降低了储层的孔隙度
2.3 溶蚀作用
中成岩 随着埋深和古地温的不断加大有机质成
排出大量有机酸和 CO这些物质运移进入碎屑岩后导
致孔隙水介质转化为酸性
在酸性介质条件下长石碎屑发生
溶解形成大量自生高岭石
2KAlSi2HAlSi(OH+4SiO2K
CaAlSi2HAlSi(OH)+C2+
另一方面早成岩 期形成的方解石遭受不同程度的溶
其反应机理如下
CaCOHC
, HC
CO2-
方解石分解产生的 CO2-
及孔隙流体中不断富集的 Ca 2+
Fe为晚期铁方解石的形成奠定了物质基础 [19中成岩
长石和早期方解石大量溶蚀形成粒内溶蚀孔隙和溶蚀
粒间孔隙极大地改善了储层物性
2.4 破裂作用
构造运动可以使岩石发生破裂形成裂缝[20]
研究区裂缝
以斜交缝和近垂直的高角度缝为主裂缝面多平直为构造
应力形成的剪切缝古地磁分析表明裂缝的走向以 NEE
NW 向少量裂缝与燕山期和喜马拉雅期构造应力场有
向盆地基底断裂影响[2统计结果表明
47%的裂缝为钙质或泥质半充填48%未充填仅有 5%的裂缝
285
中 国 地 质 2007
砂岩成岩相与储层评价平面图
Fig.3 Plan of diageneti aciesof sandstone and reservir assessmets
被自生矿物完全充填95%的裂缝是有效裂缝40%的裂缝
见油迹或油斑2- H
裂缝的发育进一步改善了储层的物
从而更有利于油气的运移
储集
成岩相与孔隙发育的关系
根据上述成岩现象和成岩阶段的研究以起主导作用的
成岩作用为依据将本区划分为溶蚀孔隙相
绿泥石胶结相
碳酸盐胶结相及压实杂基相等 种主要成岩相以上
岩相是根据占主导地位的成岩现象来划分的其间必然存在
重叠与交叉碳酸盐胶结相中也有粘土矿物胶结的成分
溶蚀孔隙相中随着长石的溶蚀必然产生大量的高岭石胶
绿泥石胶结相中
蒙混层等
胶结物
3.1 溶蚀孔隙相
溶蚀孔隙相中溶蚀作用对储层的改善起主导作用
成岩相分布在水下分流河道
河口坝砂体的中轴部这些部
位发育的砂岩原始孔渗条件相对较好有利于有机质热演化
过程中由于脱羧基作用产生的酸性流体优先进入溶蚀长石
和早期方解石增加孔隙度这些储层的孔隙度为 8%13%
渗透率为0.12.6×10- 3μ排驱压力为0.25×10Pa
部分属类储层少数属
类储层
3.2 绿泥石胶结相
绿泥石胶结相中胶结物以绿泥石为主常含有较多的高
岭石
蒙混层等自生矿物绿泥石胶结物有两种一种是
绿泥石薄膜如前所述绿泥石薄膜的形成阻碍了早期石英
次生加大的形成有利于原生孔隙的保存另一种为充填孔
隙的叶片状绿泥石使孔隙度降低绿泥石胶结相常沿溶蚀
孔隙相边部分布溶蚀作用相对不发育储层物性较溶蚀孔
隙相差孔隙度为 5%9%渗透率为0.05×10- 3μ排驱
压力为×10Pa属于
储层
3.3 碳酸盐胶结相
属于碳酸盐胶结相的砂岩碳酸盐胶结物含量占岩石总
体积的 10%25%最高可达 30%呈孔隙充填式胶结或嵌晶
式胶结胶结物主要为方解石
含铁方解石和铁方解石代表
成岩早期胶结而晚期未发生明显溶蚀的储层类型其孔渗性
较差该成岩相常出现在水下分流河道
河口砂坝的边部
围绕绿泥石胶结相和溶蚀孔隙相分布形成一个围绕优质储
层的
钙壳其可能的成因为在压实成岩过程中泥岩中排
出大量富含 Ca2+
Fe2+
CO2-
的孔隙水进入邻近的砂岩并在
砂体边部优先沉淀形成钙质胶结层储层孔隙度大为降低
且造成后期的成岩流体很难在其间流动因此溶蚀作用很少
加之水下分流河道砂体及河口砂坝的边部的砂岩一般
粒度细
杂基高使得最终的物性较差孔隙度一般为 2%
7%渗透率为0.030.1×10- 3μ排驱压力为11×10Pa
类储层
3.4 压实杂基相
压实杂基相多对应于水下分流间湾沉积微相主要在本
区南部发育由于此处水动力条件较弱原始沉积物粒度细
砂层很薄且泥质杂基含量高砂体原始孔隙度低
进一步抑制了成岩过程中地下流体的流动不利于薄层砂岩
的改造该成岩相中砂岩的孔隙度一般<3%渗透率为
0.03×10- 3μ排驱压力大于 10×10Pa属于致密储层
286
34
结 论
马家山小涧子油田主要储层延长组长
4+
岩作用进入了中成岩阶段
压实作用使砂岩储集空间变
孔渗性变差溶蚀作用和破裂作用大大地改善了储层的
物性胶结作用往往具有双重性质本区发育溶蚀孔隙相
绿
泥石胶结相
碳酸盐胶结相及压实杂基相 种类型不同的
成岩相油气储层性质不同溶蚀孔隙相物性最好大部分属
类储层少数属
类储层绿泥石胶结相物性次
储层碳酸盐胶结相物性较差
类储层压实杂基相属于致密储层成岩相的平面分布具有
明显的规律性由水下分流河道砂体和河口砂坝中心向边
直至水下分流间湾溶蚀孔隙相
绿泥石胶结相
碳酸盐
胶结相及压实杂基相依次分布储层物性由好变差有利的
储集相带为水下分流河道砂体和河口砂坝中心的溶蚀孔隙
相和绿泥石胶结相
参考文献(Referece
[1] 聂永生田景春夏青松鄂尔多斯盆地白豹一姬源地区上
三叠统延长组物源分析[J]. 油气地质与采收率, 2004,11(5)4- 6.
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Diagenesis of sastone in e Miashn- Xiaojiazi oilfield
dos basin ad its effect on reservoir
YAG Ren- chao FA i- ping1,2 AN Zuo- zhen LIU Yi- qun
1. Departmnt ofEarth Sciene and Engineeing handong Univrsity of Scence and Thnoloy, Qingdao 266510, Shandong Chin
2. Department of Geology, Northwest University, Xi'an 710069, Shaanxi, China
AbstctIntegrated methods, including thin section identification, cast thin section examination, mercury
penetration, scanning electron microscpy (SEM), X- ray diffracion (XR D) and fluid inclusion analysis, were
used to reveal the controls of sandsone diagenesis i he Majiasha Xiaojianzi oilfield on reservoirs. Study
indicates that the diagenesis of sadstone of the Chang 6and hang 4 embers in the Yanchang Formation
has reached stage A of the middle diageetic phase. The distribution of diagenetic facies exibits a distinctiv
regularity: dissolution pore facies, chlorite cement facies, carbonate cement facies and compact matrix facies occur
in succession from the and bodies of subaqueous distributary channels and center of river mouth sadbars to
margins and down to the sbaqueous distributive bay. The physical properties of sandstone become poor
uccessively. The favorable reservoirs are disslution pore facies nd chlorite cement facies i the sand bodies
ubaqueous distributary channels and center of river mouth andbars
Key wordsrdos basinYanchag Formationandsone reservoirdiagenesisdiagenetic facies
About the first auhor YANG Ren chao, male, born in 1976, Ph.D candidate and lecturer, specializes in
edimentologyE- mailrc_yag@sina.com.
288
Article
The structure of Jiyuan region in the Ordos Basin was relatively stable during the deposition of Chang 82. In this period, a shallow water delta depositional system was developed, the lake shore line slightly migrated in the southeast, and distributary channel and underwater distributary channel constituted the deposition framework. This paper studied the diagenesis of Chang 82 reservoir based on large amount of thin sections, core observation, SEM samples, X-ray analysis, and Cathodoluminescence analysis. The study shows that the diagenesis has double effects on the reservoir. On one hand, early development of chlorite film has a positive effect on anti-compaction. The early calcite is easy to be dissolved by organic acid, resulting in secondary pores and improving poroperm characteristics. Dissolution is the major mechanism of secondary pore formation and can greatly improve reservoir poroperm characteristics. On the other hand, compaction destroys the primary porosity formed in early digenetic process, and late ferrocalcite fills pores, resulting in local strong calcareous cementation zone. In general, the sedimentary facies and diagenetic facies control the distribution of oil and gas. The former determines the reservoir shape and dimensions. While the later modifies reservoir pore space. Late diagenesis-modified chlorite-cemented sedimentary facies with residual inter-granular pores and that with feldspar-dissolution plus residual inter-granular pores are the major reservoir spaces for hydrocarbon accumulation.
Article
With the methods of rock section, cast section, scanning electron microscope, pressured mercury testing data we made a deep research of the Zhiluo oilfield Chang 8 reservoir's lithology, physical properties, pore throat structure and pore throat types in the paper. This study trying to make a clear inquiry of this area's reserve property and which lay a significant foundation for the further work. The result defines the Chang 8 reservoir, deposited in subaquatic distributary channels, are mainly made up of feldspathic sandstone, debris- feldspathic sandstone. With interparticle pore, intragranular dissolved pore and intercrystal pore, the reservoir is characterized by low compositional maturity and middle texture maturity, which had a poor physical property and it istypical low porosity and low permeability reservoir. In the plane, the reservoirs' physical property is controlled by provenance andsedi- mentary face zones, in vertical direction, the compaction and cementation lead poor reservoir's physical property and dissolution is favorable to reservoir property.
Article
The clay mineral from the sandstone reservoir with hypabyssal intrusives is analyzed by X-diffraction. Three kinds of clay mineral assemblages are recognized at Xifeng well. They are illite-smectite mixed-layer+chilkinite+chloritoid± kaolinite±chloritoid-smectite mixed-layer assemblage, chilkinite+chloritoid±chloritoid-smectite mixed-layer assemblage and chloritoid-smectite mixed-layer+kaolinite +chilkinite +chloritoid assemblage. The average content of chilkinite in the surrounding rocks on hanging wall decreases with the increase of the distance beyond the diabase-prophyrite. The average contents of illite-smectite mixed-layer, kaolinite and chloritoid increase with the increase of the distance. The average contents of chilkinite, kaolinite and chloritoid in the surrounding rocks on bottom wall increase with the increase of the distance. But the average contents of illite-smectite mixed-layer decreases with the increase of the distance. With the increase of the illite, the porosity and thickness of the surrounding rocks increases, while the permeability of the surrounding rocks decrease.
Article
The Middle Ordovician St. Peter Sandstone occurs at depths between 1600 and 3600m in the central Michigan basin. Important modification of primary mineralogy and porosity occurred during diagenesis. The different pathways of sandstone diagenesis observed in the St. Peter Sandstone are largely dependent on primary textures and composition inherited from the environment of deposition rather than other factors, such as depth of burial or position in the basin. The relationships among primary textures and composition, diagenesis, and reservoir quality in the St. Peter Sandstone in the Michihgan subsurface. -from Authors
Article
Safaniya Member of the mid-Cretaceous Wasia Formation was deposited as fluvio-marine deltaic sediments in northeastern Saudi Arabia and the northwestern Arabian Gulf. After its deposition and initial burial, the mid-Cretaceous sequence was uplifted during Late Cretaceous structural movements. Structural traps in the region also started forming at this time, but structural growth continued during the Eocene, and new structures developed during the Plio-Pleistocene.The diagenetic mineral assemblage in the Safaniya sandstones includes kaolinite, illite, glauconite, pyrite, quartz and carbonate cements. Kaolinite and illite occur both as authigenic and detrital minerals. Authigenic kaolinite exists as skeletal and euhedral plates forming vermicules and aggregates of booklets infilling the pore spaces. Authigenic illite occurs as overgrowths of projecting laths. Quartz cement is present as syntaxial overgrowths and as microcrystalline quartz. Carbonates occur as patches and show replacement textures.Early diagenetic events include the formation of calcite, siderite, glauconite and pyrite, at or close to the sediment/water interface. Vermicular kaolinite and microcrystalline quartz probably formed by meteoric-water diagenesis during the Late Cretaceous uplift. Quartz overgrowths and the bulk of the euhedral kaolinite may have formed during the Late Cretaceous-Early Tertiary burial. Illite and ankerite were precipitated during deep burial, probably from fluids expelled from the basinal Kazhdumi shales to the east and northeast. The precipitation of authigenic minerals in the clean quartz sandstones has reduced the primary interparticle porosity by an average of about 9% of the rocks. Because the clays occur mainly as pore filling cements, their precipitation has caused only a small reduction in the permeability of these rocks.