利用工业CT对致密砂岩裂缝三维定量评价——以塔里木盆地库车凹陷巴什基奇克组砂岩为例

doi:10.11867/j.issn.1001-8166.2018.02.0213

地球科学进展 ›› 2018, Vol. 33 ›› Issue (2): 213 -224. doi: 10.11867/j.issn.1001-8166.2018.02.0213

新学科·新技术·新发现上一篇

利用工业CT对致密砂岩裂缝三维定量评价——以塔里木盆地库车凹陷巴什基奇克组砂岩为例

张亦弛(

), 马新仿 ^*(

), 张士诚, 韩珊, 秦思捷, 张弛

中国石油大学(北京)石油工程学院,北京 102249

收稿日期:2017-07-27 修回日期:2017-12-04 出版日期:2018-02-20
通讯作者: 马新仿 E-mail:9665095@qq.com;552943533@qq.com
基金资助:
国家自然科学基金项目“致密油压裂水平井渗流机理研究”(编号:51574255)资助

Three-dimensional Quantitative Fracture Analysis of Tight Gas Sandstones Using Industrial Computed Tomography: A Case of Bashijiqike Member in Tarim Basin

Yichi Zhang( ), Xinfang Ma ^*( ), Shicheng Zhang, Shan Han, Sijie Qin, Chi Zhang

China University of Petroleum, Beijing 102249, China

Received:2017-07-27 Revised:2017-12-04 Online:2018-02-20 Published:2018-02-20
Contact: Xinfang Ma E-mail:9665095@qq.com;552943533@qq.com
About author:
First authors:Zhang Yichi(1991-),male,Yizheng City, Jiangsu Province,Master student. Research areas include oil and natural gas engineering. E-mail:9665095@qq.com
Supported by:
Project supported by the National Natural Science Foundation of China “The research of Horizontal Well fracturing in tight oil reservoirs”(No.51574255)

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利用高分辨率工业CT成像系统(ICT)对致密砂岩裂缝进行三维定量评价具有不破坏样品的优点。利用二维切片、三维可视化软件对裂缝网格进行定量评价,首先扫描岩心样品产生灰度图像,同时测量相对应的裂缝面积、长度、张开度、孔隙度和密度;利用体积渲染软件对二维切片进行叠加产生完整的三维图像,开启的裂缝被标注蓝绿色、方解石充填的裂缝被标注品红色;利用三维计数方法计算开启的裂缝和开裂缝的比表面积、体积、裂缝孔隙度和张开度。通过ICT技术在大气压力下计算裂缝孔隙度和张开度比成像测井技术在地层真实压力下计算的数值要大,最后通过计算裂缝渗透率判断裂缝之间的连通性。裂缝密度的分布、裂缝的张开度决定了致密砂岩储层渗透率和产量。

关键词: ICT, 裂缝, 巴什基奇克组, 砂岩, 塔里木盆地

Fractures are the main fluid-flow pathways in tight-oil sandstones, and they have significant influence on tight-oil distribution, exploration, and development. Cores and image logs are commonly unavailable because of their high costs. Therefore, employing conventional logs for fracture detection is imperative for tight-oil sandstones. Fractures, such as intragranular fractures, grain-edge fractures, and transgranular fractures, are abundant in the tight sandstones. Fractures improve storage and permeability and impact distribution of natural gas. Tight gas sandstone samples are imaged at high resolution industrial X-ray computed tomography (ICT) systems to provide a three-dimensional quantitative characterization of the fracture geometries. ICT has the advantage of performing three-dimensional fracture imaging in a nondestructive way. Fracture networks were quantitatively analyzed using a combination of 2-D slice analysis and 3-D visualization and counting. The core samples were firstly scanned to produce grayscale slices, and the corresponding fracture area, length, aperture and fracture porosity as well as fracture density were measured. Then, the 2-D slices were stacked to create a complete 3-D image using volume-rendering software. The open fractures (vug) were colored cyan whereas the calcite-filled fractures (high density objects) were colored magenta. The surface area and volume of both open fractures and high density fractures were calculated by 3-D counting. Then, the fracture porosity and fracture aperture were estimated by 3-D counting. The fracture porosity and aperture from ICT analysis performed at atmospheric pressure were higher than those calculated from image logs at reservoir conditions. At last, the fracture connectivity was determined through the comparison of fracture parameters with permeability. Distribution of fracture density and fracture aperture determined the permeability and producibility of tight gas sandstones. Altogether, combined X-ray tomography, image processing help visualize and quantify the complexity and heterogeneity of naturally fractured geological samples in views of applications to integrated reservoir petrophysical and geomechanical characterization.

Key words: ICT, Fracture, Bashijiqike Formation, Sandstone, Tarim Basin.

中图分类号:

P618.13

图1 ICT二维切片(a),(b)和连续二维切片(c)叠加重构三维模型

Fig.1 Example of ICT 2D slices (a),(b) and the reconstructed 3D volume (c) by a stack of contiguous slices

图2 岩心和成像测井资料分析裂缝
GR.自然伽马曲线;M2R3,M2Rx.电阻率曲线;AC.声波测井曲线;FVDC.裂缝密度;FVTL.裂缝长度;FVPA.裂缝孔隙度;FVA.裂缝张开度

Fig.2 Fracture analysis using a combination of cores and image logs
GR: Gamma Ray. M2R3 and M2Rx:High definition induction log. AC: Acoustic log. FVDC: Corrected Fracture Density.
FVTL: Fracture length. FVPA: Apparent Fracture Porosity. FVA: Fracture aperture

图3 ICT分析岩心分割体
(a) ks 2-2-8井,6 718.42~6 718.71 m,一条方解石充填的裂缝,裂缝长度0.1 mm;(b)6 680.42 m,4条张开度为0.4~0.8 mm的方解石充填的裂缝;(c)6 767.5 m,2条发育在岩心边缘的诱导缝;(d)6 734.84 m,无裂缝发育;(e)通过CT圆周扫描图像测量裂缝的倾向和倾角;(f)二维切片分析开启裂缝和高密度裂缝的长度、张开度

Fig.3 ICT analysis of core segments
(a) A long, calcite-filled, hair-line (0.1 mm), Well ks 2-2-8; 6 718.42~6 718.71 m. (b) Segment 6 680.42 m: Four, thin-aperture (0.4~0.8 mm),calcite-filled. (c) Segment 6 767.5 m: Two coring induced petal fractures on the edge of the core. (d)Segment 6 734.83 m; No fractures. (e) The directional fracture measurements (azimuth and dip) were conducted on the circumferential CAT scan images. (f) Two-dimensional slice analysis of fracture length and aperture for both vugs (open fracture) and high density (closed fracture) objects

图4 CT模型下的裂缝参数相互关系图
(a)开启的裂缝长度与张开度交会图;(b)方解石充填的裂缝长度与张开度交会图;(c)切片中裂缝张开度与裂缝面积交会图;(d)裂缝长宽比与圆度交会图

Fig.4 Crossplots showing the relationships between parameters of fracture in CT model
(a) Open fracture aperture and fracture length.(b) Calcite-filled fracture aperture and fracture length. (c) Fracture area in a slice and fracture aperture. (d) Crossplot of degree of roundness and length to width ratio for open fractures

图5 ICT重构内部结构
(a)ICT圆周测量;(b)CT重构图像;(c)三维体积渲染开启的裂缝(蓝绿色);(d)三维体积渲染方解石充填的裂缝

Fig.5 Interior structure reconstructed by ICT analysis
(a) ICT Circumferential View. (b) Images reconstructed by computed tomography. (c) 3-D Volume-rendering of open fractures (colored cyan). (d) 3-D Volume-rendering of calcite-filled fractures

图6 样品中裂缝三维体积渲染模型
(a)分割体深度6 682.38 m;(b)分割体深度6 723.3 m;(c)分割体深度6 715.0 m;红色箭头为局部发育的孔隙;(a)中亮点代表二维图像下的裂缝中充填的矿物组分如方解石等;(b)中蓝色代表三维动态图像下的裂缝

Fig.6 Three-dimensional volume rendering of fractures for sample
(a) Segment 6 682.38 m. (b) Segment 6 723.3 m. (c) Segment 6 715.0 m. Note the locally distributed pores (red arrow).(a) The bright spots represent mineral components filled in the fractures under the two-dimensional image such as calcite, et al. (b)The blue color represents the cracks in the 3D dynamic image

图7 薄片展示砂岩孔隙结构
(a)粒间孔(红色箭头)粒内孔(蓝色箭头);(b)伊利石颗粒形成的微孔隙(红色箭头);(c)自然裂缝(红色粗线);(d)裂缝(蓝色)

Fig.7 Photomicrographs showing the pore systems of the sandstones
(a) Intergranular pores (red arrow) and intragranular pores (blue arrow). (b) Micropores (red arrow) associated with the illite (IL).(c) Natural fractures (red dashed lines). (d) Fractures are present(blue)

图8 裂缝品质参数相互关系图
(a)裂缝孔隙度与张开度交会图;(b)裂缝密度与孔隙度交会图;(c)裂缝渗透率与孔隙度交会图;(d)裂缝张开度和密度乘积与裂缝渗透率交会图

Fig.8 Crossplots showing the relationships between parameters of fracture
(a) Plot of fracture porosity versus facture aperture. (b) Plot of fracture porosity fracture density.(c) Plot of horizontal permeability versus facture porosity. (d) Plot of horizontal permeability versus fracture aperture multiplied by fracture density

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