Characteristics and controlling factors of deep-water gravity flow sandstone reservoir in the Chang 73 sub-member in Ordos Basin: Case study of Well CY1 in Huachi area

  • Liming XU , 1, 2 ,
  • Qiheng GUO 1, 3 ,
  • Yuanbo LIU 4 ,
  • Jiangyan LIU 1, 3 ,
  • Xinping ZHOU 1, 3 ,
  • Shixiang LI , 1, 3
Expand
  • 1. National Engineering Laboratory for Exploration and Development of Low Permeability Oil & Gas Fields,Xi’an 710018,China
  • 2. PetroChina Changqing Oilfield Company,Xi’an 710018,China
  • 3. Exploration and Development Research Institute of PetroChina Changqing Oilfield Company,Xi’an 710018,China
  • 4. No. 1 Oil Production plant,Changqing Oilfield Company,PetroChina,Yan'an 716000,China

Received date: 2021-07-01

  Revised date: 2021-08-03

  Online published: 2021-12-27

Supported by

The National Basic Research Program of China(973 Program)(2014CB239003)

Highlights

The gravity flow-derived sandstone developed in the Chang 73 sub-member shale strata is a realistic replacement target for shale oil reserves and production in the Changqing Oilfield, but the research on the characteristics of the Chang 73 sub-member sandstone reservoir and shale oil enrichment controlling factors are weak. Based on the data from the Well CY1, the Chang 73 sub-member fully coring well, using X-ray diffraction, scanning electron microscopy, high-pressure mercury intrusion and nuclear magnetic resonance test data, combined with thin section and core data, an in-depth analysis of the macro and micro of the Chang 73 sub-member sandstone reservoir characteristics, and the controlling factors of storage capacity and oiliness were carried out. The results show that the Chang 73 sub-member mainly develops gray massive lithic feldspar, lithic feldspar and feldspar lithic siltstone, and a small amount of fine sandstone, which is characterized by typical low porosity and low permeability. The reservoir space is mainly composed of intergranular pores, feldspar dissolved pores, clay mineral intercrystalline pores, intragranular dissolved pores and micro-cracks, and widely developed micro-nano pore throats make it have a certain storage capacity; the micro-pore structure of the Chang 73 sub-member is mainly divided into three categories A, B, and C. The median pore throat radius and the micro pore throat sorting coefficient are the main parameters that control the median saturation pressure, the maximum mercury inlet saturation and the mercury removal efficiency, and determine the enrichment degree and seepage capacity of shale oil on the micro scale; the mineral composition, grain size, and micro-pore structure of the Chang 73 sub-member sandstone jointly control the storage capacity of the Chang 73 sub-member sandstone, and the pressurization of hydrocarbon generation promotes the hydrocarbon quality in the Chang 73 sub-member black shale. Hydrocarbons accumulate toward the adjacent sandstone with good seepage ability. Intergranular pores, feldspar dissolution pores and micro-cracks are the main storage spaces for free hydrocarbons. Clay minerals are the main storage spaces for adsorbed hydrocarbons. Finding sandstones with high felsic mineral content, low clay mineral content, and weak calcite cementation in the Chang 73 sub-member mud shale strata is the main goal of shale oil exploration and development; the porosity represented by type A and B pore structures is greater than 5%, and the sandstone with permeability higher than 0.05×10-3 μm2 is the dominant reservoir of the Chang 73 sub-member. The sandstone represented by type C pore structure is difficult to charge with oil and gas, and its physical properties and seepage capacity are poor, which is not conducive to the accumulation and production of shale oil.

Cite this article

Liming XU , Qiheng GUO , Yuanbo LIU , Jiangyan LIU , Xinping ZHOU , Shixiang LI . Characteristics and controlling factors of deep-water gravity flow sandstone reservoir in the Chang 73 sub-member in Ordos Basin: Case study of Well CY1 in Huachi area[J]. Natural Gas Geoscience, 2021 , 32(12) : 1797 -1809 . DOI: 10.11764/j.issn.1672-1926.2021.08.008

0 引言

页岩油(气)革命的发生使美国油气对外依存度大幅度下降,页岩油气资源成为全球勘探开发的热点1-2。中国陆相页岩油资源非常丰富,与北美海相页岩油相比,中国陆相页岩油受湖盆沉积环境及规模的影响,储层类型多样且非均质性强3-5。根据岩性组合和沉积特征,可分为夹层型、混积型、纯页岩型3类6。借鉴北美成功的经验和技术,中国相继在以夹层型页岩油为代表的鄂尔多斯盆地7-8、松辽盆地9和以混积型页岩油为代表的准噶尔盆地10-11、渤海湾盆地12-13取得了陆相页岩油的工业化突破,其中大庆油田和大港油田针对纯页岩型页岩油部署的多口井也获得了工业油流14-15,证实中国陆相多类型页岩油均具有一定的勘探开发潜力。
页岩油储集层表现出低孔、特低渗、可动性差的特点,优选出高品质的储集层是决定页岩油能否商业开采的关键16-17。国内外页岩油勘探开发经验表明富有机质泥页岩层系内部夹层的发育程度是决定页岩油富集高产、稳产的关键因素18-20。夹层储集性能及含油性不仅受与其间互的富有机质泥页岩地球化学参数的影响,还与夹层的沉积微相、岩石组分、物性、微观孔隙结构及成岩演化密切相关21-22。致密砂岩夹层储集空间以微纳米孔喉为主,微观孔隙结构不仅影响页岩油的储集性能,还与渗流机理及驱油效率密切相关23-26。根据沉积旋回、岩性组合和地层厚度,长7段自上而下可划分为长71、长72、长73共3个亚段,长庆油田围绕鄂尔多斯盆地长71、长72亚段泥页岩层系中的砂岩夹层“甜点”,率先建成了国内第一个百万吨整装页岩油示范区7-8。长73亚段泥页岩层系中也发育重力流成因的砂岩夹层,2019年部署的2口风险水平探井在长73亚段泥页岩层系中试油均获百吨以上高产27,虽然多口水平井压裂示踪结果显示长7段纯泥页岩对产量也有一定的贡献,但长7段页理型页岩油还有待进一步评价,在长73亚段寻找夹层型页岩油“甜点”是长庆油田页岩油增储上产的重大接替领域。目前对长73亚段的研究主要集中在烃源岩评价、沉积环境等方面28-29,砂岩夹层储层特征的研究主要集中在长71、长72亚段,针对长73亚段泥页岩层系中的砂岩夹层研究也多限于砂体刻画和搬运机制30,缺乏对储层特征及控制因素的研究。本文基于鄂尔多斯盆地湖盆中部华池地区的CY1井长73亚段全取心井资料,对长73亚段砂岩储层的宏、微观特征进行了精细刻画,并对储集能力和含油性控制因素进行深入分析,以期为长73亚段页岩油储层“甜点”优选提供指导。

1 地质概况

鄂尔多斯盆地位于中国大陆中部,是一个多旋回的叠合含油气盆地,为中国内陆第二大沉积盆地,面积约为37×104 km2 (盆地本部为25×104 km2),根据现今盆地构造形态及演化历史,划分出西缘逆冲带、天环坳陷、伊陕斜坡、晋西挠褶带、伊盟隆起及渭北隆起共6个二级构造单元31图1)。晚三叠世延长期发育大型克拉通拗陷湖盆,整体具有盆大、坡缓、水浅、源多、构造稳定的特征,沉积了一套厚逾1 000 m的河湖相碎屑岩,自上而下依次划分为长1—长10共10个段32-33
图1 鄂尔多斯盆地构造划区(a)及长7段地层综合柱状图(b)(修改自文献[34])

Fig.1 Tectonic division(a) and stratigraphic column(b) of the Chang 7 Member, Ordos Basin(revised from Ref.[34])

长7段沉积期是鄂尔多盆地中生界最大湖泛期,也是湖盆热流体活动的高峰期,湖泊藻类和浮游生物的繁盛为富有机质泥页岩沉积奠定了物质基础,该时期适宜的温度、大面积深水区、强还原性的古沉积环境,导致长73亚段有机质大量发育和富集保存,既形成了一套优质烃源岩,同时也为大规模页岩油的富集创造了有利的物质条件7-832-33。长7段频繁发育的重力流砂体与烃源岩互层共生,独特的地质条件和有利的成藏配置形成了源内油藏的规模富集。

2 砂质储层特征

2.1 岩石学特征

CY1井位于延长期湖盆中部的半深湖—深湖区域(图1),该井长73亚段泥页岩层系中发育的储集砂体来自于湖盆西南缘三角洲前缘沉积物的失稳滑脱和搬运形成的重力流砂体,受烃源岩强生排烃就近持续充注影响,该重力流砂体是延长组湖盆中部页岩油勘探的重要“甜点”30。砂岩主要为灰色块状岩屑质长石、岩屑长石和长石岩屑粉砂岩,发育少量的细砂岩;分选中等—好,磨圆棱角—次棱角状,结构成熟度中等;以颗粒支撑结构为主,颗粒之间点、线接触,胶结类型主要为接触胶结(图2图3);岩屑主要为火成岩岩屑和变质岩岩屑,部分样品含有较多的云母;长石和石英矿物总含量普遍在80%以上,黏土矿物含量在10%左右,碳酸盐岩矿物含量在3%左右,粉砂岩中含有少量的黄铁矿[图2(b)]。
图2 CY1井长73亚段砂岩类型及矿物组成

Fig.2 Types and mineral composition of the sandstone, Chang 73 sub-member of Well CY1

图3 CY1井长73亚段砂岩特征

(a)2 043.53 m,灰色块状粉砂岩;(b)2 050.81 m,灰黑色块状粉砂岩;(c)2 045.81 m,粉砂岩中的泥质撕裂屑;(d)2 007.41 m,岩屑长石粉砂岩中的泥质撕裂屑,单偏光;(e)2 040.32 m,岩屑质长石粉砂岩,单偏光,(f)2 040.32 m,岩屑质长石粉砂岩,正交光,与(e)同一视域

Fig.3 Characteristics of sandstone in the Chang 73 sub-member of Well CY1

2.2 物性特征

CY1井砂岩的孔隙度主要分布在2%~8%之间,平均孔隙度为4.7%(图4);渗透率主要分布在(0.03~0.07)×10-3 μm2之间,平均渗透率为0.05×10-3 μm2图4),砂岩储层的孔隙度和渗透率明显低于长71、长72亚段;孔隙度和渗透率在整体趋势上具有一定的正相关性,随着深度的增加,孔隙度整体有下降趋势[图4(a)];粉砂岩的面孔率平均为0.27%,细砂岩的面孔率平均为0.62%,明显高于粉砂岩(图5)。
图4 CY1井长73亚段砂岩物性特征

Fig.4 Storage characteristics of sandstone in Chang 73 sub-member of Well CY1

图5 CY1井长73亚段砂岩面孔率柱状图

Fig.5 Histogram of the borehole ratio of sandstone in the Chang 73 sub-member of Well CY1

2.3 储集空间

CY1井长73亚段砂岩储层主要发育粒间孔、长石溶孔、黏土矿物晶间孔、粒内溶孔和微裂缝(图6)。粒间孔普遍被黏土矿物充填,氩离子抛光扫描电镜显示粒间孔非均质性强,局部粒间孔隙发育程度高[图6(a)—图6(c)];长石溶蚀孔极为发育,铸体薄片和扫描电镜下明显可以见到长石沿着解理方向溶蚀现象[图6(d),图6(e)];黏土矿物主要为绿泥石,围绕粒间孔隙呈衬边式分布,黏土矿物晶间孔发育[图6(f),图6(g)];少量长石发育孤立状的粒内溶孔,不连通的粒内溶孔对储层物性没有贡献[图6(h)];砂岩中发育未被方解石胶结的微裂缝,是油气运移的优势通道[图6(i)]。与长71、长72亚段砂岩储集空间类型相似,粒间孔、长石溶孔是页岩油聚集的主要空间。
图6 CY1井长73亚段砂岩储集空间

(a)岩屑长石粉砂岩,2 028.71 m,粒间孔;(b)岩屑长石粉砂岩,2 027.56 m,粒间孔;(c)岩屑质长石粉砂岩,2 013.9 m,粒间孔;(d)岩屑质长石粉砂岩,2 053.11 m,长石溶孔;(e)岩屑长石粉砂岩,2 054.40 m,长石溶孔;(f)长石岩屑粉砂岩,2 039.04 m,黏土矿物晶间孔;(g)长石岩屑粉砂岩,2 030.86 m,绿泥石膜;(h)长石岩屑粉砂岩,2 055.73 m,粒内溶孔(i),长石岩屑粉砂岩2 053.55 m,微裂缝

Fig.6 Characteristics of sandstone reservoir in the Chang 73 sub-member of Well CY1

2.4 孔隙结构特征

2.4.1 高压压汞

根据压汞曲线特征及参数,将砂岩储层孔隙结构分为A、B、C 3类(表1)。A类曲线平均排驱压力为5.36 MPa,平均饱和度中值压力为21.69 MPa,平均分选系数为1.35,平均孔喉半径中值为0.035 μm,平均退汞效率为20.51%,平均最大进汞饱和度为83.90%,毛管压力在10 MPa左右进汞量明显增加,孔喉大小相对比较均匀,存在明显的峰值[图7(a)];B类曲线平均排驱压力为4.35 MPa,平均饱和度中值压力为36.41 MPa,平均分选系数为2.20,平均孔喉半径中值为0.022 μm,平均最大进汞饱和度为69.89%,平均退汞效率为18.36%,与A类曲线相比,毛管压力在10 MPa左右不存在明显的平台,孔喉分布呈单峰态,但与A类曲线相比,优势孔喉分布集中性相对较差[图7(b)];C类曲线平均排驱压力为11.19 MPa,平均饱和度中值压力为170.54 MPa,分选系数为2.27,平均孔喉半径中值为0.005 μm,平均退汞效率为15.70%,平均最大进汞饱和度为54.99%,与A、B类曲线相比,进汞曲线斜率大,中值压力明显增大,孔喉大小差异大,不存在明显的峰值[图7(c)]。A类曲线进汞饱和度和退供效率最高,孔喉分布均匀,油气充注所需要的压力小,表征的孔隙结构是CY1井最优势的储集层,B类次之,C类最差,3种曲线都表明渗透率主要由相对较大的孔喉贡献,小孔喉对渗透率基本没有贡献。
表1 CY1井长73亚段砂岩微观孔隙结构分类及参数

Table 1 Classification and parameters of micro-pore structure of sandstone in the Chang 73 sub-member of Well CY1

孔隙结构类型 孔隙度 /% 渗透率 /(10-3 μm2 排驱压力 /MPa 饱和度中值压力/MPa 最大进汞饱和度/% 退汞效率 /% 孔喉半径中值 /μm 最大孔喉半径 /μm 分选系数
A (n=10) (4.6~9.6) /7.3 (0.050~0.084) /0.067

(4.12~5.50)

/5.36

(13.41~27.50)

/21.69

(81.05~85.59)

/83.90

(17.25~27.64)

/20.51

(0.027~0.055/0.035

(0.133~0.179)

/0.138

(1.03~1.98)/1.35
B (n=8) (3.1~8.2) /5.5

(0.048~0.058)

/0.055

(2.94~7.57)

/4.35

(23.05~50.49)

/36.41

(63.25~75.54)

/69.89

(15.89~22.24)

/18.36

(0.018~0.032)

/0.022

(0.097~0.250)

/0.185

(1.77~2.47)/2.20
C (n=6) (2.1~4.9) /3.1

(0.020~0.056)

/0.039

(4.60~27.54)

/11.19

(73.03~243.23)

/170.54

(52.33~62.09)

/54.99

(12.04~21.66)

/15.70

(0.003~0.010)

/0.005

(0.067~0.160)

/0.100

(1.72~3.00)/2.27

注: n=样品数 (4.6~9.6)/7.3=(最小值—最大值)/平均值

图7 CY1井长73亚段砂岩高压压汞曲线类型

Fig.7 Types of high pressure mercury injection curve of Chang 73 sub-member sandstone in Well CY1

2.4.2 微米CT扫描

微米CT实验可以获取微米尺度下的孔隙三维重构图像,更加直观地展示微观储层孔喉特征。实验结果显示长73亚段储层虽然致密,但微纳米孔喉发育,为页岩油规模聚集成藏奠定了基础(图8)。粉砂岩和细砂岩平均孔喉半径相近,但测试的粉砂岩的喉道平均长度明显大于细砂岩,可以使更多的孔隙连通,因此粉砂岩的连通体积百分比明显高于细砂岩。
图8 CY1井长73亚段砂岩纳米CT扫描特征

Fig.8 Nano CT scanning features of sandstone in the Chang 73 sub-member of Well CY1

2.4.3 含油性特征

钻井现场岩心核磁共振显示CY1井的含油饱和度主要分布在30%~70%之间,平均含油饱和度为50%,可动流体饱和度主要分布在5%~20%之间,平均可动流体饱和度为11%。CY1水平井共钻遇砂层944.4 m,砂层测井解释为油层900.7 m,砂层中油层钻遇率高达95%。长73亚段重力流沉积砂体被厚层的富有机质泥页岩包裹,受烃源岩生烃增压的影响,长73亚段砂岩具有普遍含油且含油饱和度高的特征,钻遇砂体就相当于钻遇油层。荧光薄片显示,CY1井砂岩中孔隙尺度较大的粒间孔和孔隙尺度较小的长石粒内溶孔及刚性矿物粒内裂缝普遍含有蓝色油质沥青,说明长73亚段多类型多尺度的孔喉均是页岩油的有利储集空间(图9)。
图9 CY1井长73亚段砂岩荧光照片

(a)2 021.77 m,岩屑长石粉砂岩,粒间孔蓝色油质沥青充填;(b)2 027.52 m,岩屑长石粉砂岩,长石粒内溶孔蓝色油质沥青充填;(c)2 032.34 m,岩屑质长石粉砂岩,粒内裂缝蓝色油质沥青充填;(d)—(f)为(a)—(c)对应的荧光照片

Fig.9 Fluorescence photo of sandstone in the Chang 73 sub-member of Well CY1

3 储层控制因素

3.1 矿物组分对储集能力的影响

CY1井的矿物组成主要为石英、长石、黏土矿物和碳酸盐矿物,碳酸盐矿物的含量与孔隙度存在明显的负相关性(相关系数为0.62)[图10(a)],碳酸盐矿物的胶结作用对储层物性破坏较大,使孔隙结构进一步复杂化,不利于页岩油的充注和开采,碳酸盐矿物胶结作用强烈的样品普遍对应C类压汞曲线。石英、长石和黏土矿物单矿物含量与孔隙度相关性差,但3种矿物总含量与孔隙度呈明显的正相关性(相关系数为0.61)[图10(b)],说明刚性矿物粒间孔、粒内溶孔及黏土矿物均对储层孔隙度具有一定贡献。CY1井砂岩中黏土矿物主要为绿泥石及伊利石,绿泥石膜的发育导致粒间孔和喉道半径缩小,伊利石普遍呈搭桥状沿着孔隙及喉道分布,导致孔隙结构复杂化,虽然黏土矿物晶间孔的发育提高了致密砂岩的孔隙度,但其存在使微观孔隙结构复杂化,砂岩的核磁可动流体饱和度与长英质矿物含量成正比[图10(c)]、与黏土矿物含量成反比[图10(d)]也说明了这一现象。对于低孔低渗的致密储层来说,微观孔隙结构是控制渗流的主要因素,高的碳酸盐胶结物和黏土矿物造成微观孔隙非均质性增强,不利于页岩油的储集和采出。
图10 CY1井长73亚段矿物组分与储集能力散点图

Fig.10 Scatter plot of mineral composition and storage capacity of the Chang 73 sub-member of Well CY1

3.2 微观储层结构对储集能力的影响

研究区微观孔隙结构类型可以划分为A、B、C 3类,主要依据排驱压力、饱和度中值压力和最大进汞饱和度。排驱压力主要取决于岩石中最大连通孔喉半径,因此与最大孔喉半径成正比,最大孔喉半径越大,油气开始充注时所需要的压力也最小[图11(a)]。饱和度中值压力的大小决定了油气持续充注的难易程度,最终也决定了含油饱和度的高低,饱和度中值压力与孔喉半径中值呈明显的负相关,孔喉半径中值越大,饱和度中值压力越小[图11(b)]。C类曲线中虽然有部分样品排驱压力明显小于A、B类曲线,但由于孔喉半径中值小,饱和度中值压力普遍高于100 MPa,导致最终的进汞饱和度也较低。分选系数反映了孔喉分布的均值程度,分选系数值越小,代表孔喉分布越集中。分选系数与孔隙度[图11(c)]、渗透率[图11(d)]、最大进汞饱和度[图11(e)]、退汞效率[图11(f)]呈明显的负相关,即孔喉分布越集中,储集物性也越好,越有利于油气的充注和排出。
图11 CY1井长73亚段高压压汞参数与储集能力散点图

Fig.11 Scatter diagram of high-pressure mercury injection parameters and storage capacity of the Chang 73 sub-member of Well CY1

研究发现渗透率小于0.06×10-3 μm2、孔隙度小于6%时,最大进汞饱和度随着孔隙度和渗透率的增大而增大;渗透率大于0.06×10-3 μm2、孔隙度大于6%时,最大进汞饱和度维持在85%左右[图12(a),图12(b)],A类压汞曲线的孔隙度普遍大于6%、渗透率高于0.06×10-3 μm2,因此最大进汞饱和度也普遍高于80%。
图12 CY1井长73亚段砂岩粒度、含油性与储集物性散点图

Fig.12 Scatter plot of sandstone grain size, oil-bearing properties and reservoir properties of the Chang 73 sub-member of Well CY1

3.3 砂岩粒度对储层能力的影响

CY1井砂岩的粒度与渗透率相关性不明显,但与孔隙度[图12(c)]、孔隙半径中值[图12(d)]呈正相关,最大进汞饱和度、退汞效率本身就取决于储集层的物性和微观孔喉大小,因此粒度与最大进汞饱和度和退汞效率呈正相关。这种相关性表明长73亚段砂岩粒度越大,油气的充注程度和采收率也更高。

3.4 储集物性对含油性影响

长73亚段烃源岩热演化程度适中,已达生油成熟阶段,处于生油高峰期,适中的有机质成熟度形成的源内自生自储持续充注高压是长73亚段砂岩高含油饱和度页岩油富集的主要动力。CY1井的含油饱和度与孔隙度相关性不明显,但与渗透率具有一定的相关性。渗透率小于0.1×10-3 μm2时,含油饱和度和可动流体饱和度与渗透率呈正相关,渗透率高于0.1×10-3 μm2时,含油饱和度普遍高于40%,可动流体饱和度普遍高于10%[图12(e),图12(f)],渗透率是控制长73亚段砂质储集层中页岩油规模富集的主要因素。

4 页岩油富集模式与“甜点”特征

长73亚段沉积期是整个长7段湖泊发育的鼎盛期,整体为半深湖—深湖环境,沉积了一套稳定的厚层富有机质泥页岩。长73亚段沉积期活跃的火山活动不仅为生物勃发提供了丰富的营养元素,火山活动引起的地震还为湖盆中部重力流砂体的发育提供了动力7-8。长73亚段富有机质泥页岩有机质生烃在满足自身吸附的情况下,生成的轻质烃类优先向与其相邻的物性和渗流能力较好的砂岩运移,生烃增加是页岩油富集的主要动力,泥页岩中由于高有机质、高黏土矿物含量的影响,烃类主要以吸附态为主,砂岩是游离态页岩油主要储集体。纳米CT扫描结果表明长73亚段砂体中发育大量微纳米孔喉,使其具有一定的储集能力。前人研究表明可动油主要赋存在大孔隙中,黏土矿物由于孔隙直径和比表面积均较大,吸附能力强,是砂岩中吸附烃主要储存空间36;广泛发育的孔隙直径较大的刚性矿物支撑的粒间孔、长石溶蚀孔及微裂缝是游离烃的主要储集空间(图13)。
图13 页岩油“甜点”聚集模式示意

Fig.13 Schematic diagram of shale oil “sweet spot” accumulation mode

长73亚段砂岩普遍被厚层的富有机质泥页岩包裹,含油饱和度高,CY1水平井在钻遇率明显低于长71、长72亚段水平井的情况下试油获得了百吨高产,证实了长73亚段砂岩潜力巨大,是长7段页岩油增产上产的现实性接替领域。砂岩的矿物组成、粒度、微观孔隙结构共同控制着长73亚段砂岩的储集能力。在长73亚段泥页岩层系中寻找长英质矿物含量高、黏土矿物含量少、方解石胶结作用弱的砂岩是主要目标;粒度与储集能力的关系表明长73亚段的细砂岩比粉砂岩更有利于高饱和度页岩油的规模富集。微观孔隙结构直接影响着长73亚段砂岩储层的储集能力和渗流能力,并最终决定着页岩油含油规模和产能的差异分布,A、B类孔隙结构有利于页岩油的充注,C类孔隙结构不利于页岩油充注,参考储层物性与孔隙结构和含油性的关系,本文将孔隙度大于5%、渗透率高于0.05×10-3 μm2砂岩定为“甜点”段。

5 结论

(1)鄂尔多斯盆地华池地区长73亚段主要发育灰色块状岩屑质长石、岩屑长石和长石岩屑粉砂岩,发育少量的细砂岩;储集层储集空间主要为粒间孔、长石溶孔、黏土矿物晶间孔、粒内溶孔和微裂缝,广泛发育的微纳米孔喉使其具有一定的储集能力。
(2)长73亚段微观孔隙结构主要分为A、B、C 3类,孔喉半径中值和微观孔喉分选系数是控制饱和度中值压力、最大进汞饱和度和退汞效率的主要参数,影响微观尺度上页岩油的富集程度和渗流能力;以A、B类孔隙结构为代表的孔隙度大于5%,渗透率高于0.05×10-3 μm2砂岩是长73亚段优势储集层,C类孔隙结构代表的砂岩油气充注难度大,物性及渗流能力差,不利于页岩油的聚集和采出。
(3)长73亚段砂岩的矿物组成、粒度、微观孔隙结构共同控制着储集能力, 生烃增压促使长73亚段黑色页岩中的轻质烃向与其相邻的渗流能力较好的砂岩聚集,粒间孔、长石溶蚀孔及微裂缝是游离烃的主要储集空间,黏土矿物是吸附烃的主要赋存空间,在长73亚段泥页岩层系中寻找长英质矿物含量高、黏土矿物含量少、方解石胶结作用弱的砂岩是页岩油勘探开发的主要目标。
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