柴达木盆地东坪地区基岩风化壳特征

摘要/Abstract

摘要：

柴达木盆地阿尔金山前斜坡带发现了规模分布的东坪基岩气田,其基岩风化壳的作用成为关注的问题。依据元素分析、X-射线衍射分析、岩心薄片观察,常规测井响应和成像测井响应特征,识别出东坪地区基岩风化壳发育不同结构层,且不同结构层的储集特征有很大差异。研究表明,基岩风化壳结构可划分为土壤层、完全风化层和半风化层,而半风化层又可进一步分为溶蚀带和崩解带;其中土壤层厚度0~2 m,完全风化层厚度4~15 m,溶蚀带厚度36.5~164 m,崩解带厚度300~1 000 m。基岩半风化层是储层发育带,其中溶蚀带储集物性好于崩解带,溶蚀带发育较多的溶蚀孔洞和溶蚀加宽的网状裂缝,孔隙度范围2%~16%;而崩解带发育弱溶蚀构造缝和节理缝,孔隙度范围2%~8%。东坪地区大规模发育基岩风化壳为柴达木盆地远离烃源岩灶的斜坡地区寻找油气提供了借鉴依据。

关键词: 风化壳, 基岩风化结构, 基岩风化储层, 柴达木盆地

Abstract:

Large-scale distributed gas fields are discovered in frontal slope of the Altun Mountain in Qaidam Basin and the role of the basement weathering crust becomes the concerns. Basing on element analysis, X-ray diffraction analysis, cores and slices observation, conventional logging and image logging, structures of the basement weathering crust are identified and each structure owns different reservoir properties. The result shows that the structure of the basement weathering crust of Dongping area in Qaidam Basin can be divided into three layers, soil layer, completely weathered layer and semi-weathered layer which can be further divided into two zones, dissolution weathered zone and fracture weathered zone. The thickness of soil layer is 0-2 m. The thickness of completely weathered layer is 4-15 m. The thickness of dissolution weathered zone is 36.5-164 m. The thickness of fracture weathered zone is 300-1,000 m. The semi-weathered layer is the reservoir of the basement weathering crust. The reservoir property of the dissolution weathered zone is better than that of fracture weathered zone. The dissolution weathered zone with porosity range from 2%-16% develops dissolved pores and map fractures with high degree of dissolution, and the fracture weathered zone with porosity range from 2%-8% develops tectonic fractures and joint fractures with low degree of dissolution. Large-scale development of the basement weathering crust in Dongping area provides the basis for finding hydrocarbon in the slope area of Qaidam Bain far from the source rock.

Key words: weathering crust, basement weathering crust structure, basement weathering crust reservoir, Qaidam Basin

中图分类号:

TE122.2

伍劲, 高先志, 马达德, 张永庶, 周伟, 牛花朋, 孔红喜, 王波. 柴达木盆地东坪地区基岩风化壳特征[J]. 现代地质, 2017, 31(01): 129-141.

WU Jin, GAO Xianzhi, MA Dade, ZHANG Yongshu, ZHOU Wei, NIU Huapeng, KONG Hongxi, WANG Bo. Characteristics of the Basement Weathering Crust in Dongping Area, Qaidam Basin[J]. Geoscience, 2017, 31(01): 129-141.

图/表 15

图1 东坪地区工区位置

Fig.1 Location map of Dongping area

图2 东坪地区基岩岩类分布

Fig.2 Lithological distribution of the basement in Dongping

图3 东坪地区基岩岩石学特征

Fig.3 Petrologic characteristics of the basement rock in Dongping area

图4 东坪地区基岩风化结构划分

Fig.4 Basement rock weathering crust division of Dongping area

图5 坪1H-2-3井基岩风化壳顶部岩心特征

Fig.5 Characteristics of the basement core of the top weathering crust in well Ping1H-2-3

图6 东坪地区基岩风化壳完全风化层岩心和薄片矿物蚀变特征

Fig.6 Characteristics of cores and mineral alteration of the completely weathered layer in Dongping area

图7 东坪地区基岩风化壳半风化层溶蚀带的矿物蚀变和孔缝特征

Fig.7 Characteristics of mineral alteration and reservoir space of the dissolution weathered zone in Dongping area

图8 东坪地区基岩风化壳半风化层崩解带的矿物蚀变和溶蚀孔缝特征

Fig.8 Characteristics of mineral alteration and reservoir space of the fracture weathered zone in Dongping area

图9 东坪105井片麻岩氧化物含量与风化指数随深度的变化

Fig.9 Variation of the oxide percent contents and weathering indices for the gneiss with depth in Dongping 105 well

图10 东坪风化壳取心段X-射线衍射分析的全岩(a)与黏土(b)矿物成分含量直方图

Fig.10 Histograms of mineral percent contents of bulk rock(a) and clay(b) by X-ray diffraction analysis for weathering crust in Dongping

图11 东坪地区基岩风化壳储集空间岩心和显微照片

Fig.11 Reservoir space in cores and slices of basement weathering crust in Dongping

表1 东坪地区基岩风化壳物性测井解释统计

Table 1 Log interpretation of physical property of basement weathering crust in Dongping

风化壳结构	东坪1井区片麻岩风化壳				东坪3井区花岗岩风化壳
风化壳结构	AC/(μs/m)	基质孔隙度/%	裂缝孔隙度/%		AC/(μs/m)		基质孔隙度/%		裂缝孔隙度/%
完全风化层	$175 ~ 233 200$	<0.2	<0.1	$7 ~ 146 37$		<0.2		<0.1
半风化层溶蚀带	$181 ~ 217 195$	$2.14 ~ 11.14 4.35$	$0.17 ~ 5.57 1.87$	$37 ~ 599 180$		$1.3 ~ 7.63 3.96$		$0.05 ~ 2.45 1.27$
半风化层崩解带	$171 ~ 210 190$	$1.9 ~ 6.14 2.97$	$0.05 ~ 2.86 1.12$	$45 ~ 413 199$		$0.45 ~ 4.9 3.39$		$0.05 ~ 1.91 0.84$

表1 东坪地区基岩风化壳物性测井解释统计

Table 1 Log interpretation of physical property of basement weathering crust in Dongping

风化壳结构	东坪1井区片麻岩风化壳				东坪3井区花岗岩风化壳
风化壳结构	AC/(μs/m)	基质孔隙度/%	裂缝孔隙度/%		AC/(μs/m)		基质孔隙度/%		裂缝孔隙度/%
完全风化层	$175 ~ 233 200$	<0.2	<0.1	$7 ~ 146 37$		<0.2		<0.1
半风化层溶蚀带	$181 ~ 217 195$	$2.14 ~ 11.14 4.35$	$0.17 ~ 5.57 1.87$	$37 ~ 599 180$		$1.3 ~ 7.63 3.96$		$0.05 ~ 2.45 1.27$
半风化层崩解带	$171 ~ 210 190$	$1.9 ~ 6.14 2.97$	$0.05 ~ 2.86 1.12$	$45 ~ 413 199$		$0.45 ~ 4.9 3.39$		$0.05 ~ 1.91 0.84$

图12 坪1H-2-3井基岩风化壳结构常规测井曲线特征

Fig.12 Conventional logging response of the basement weathering crust in well Ping1H-2-3

图13 东坪9井基岩风化壳储层成像测井响应特征

Fig.13 Image logging response of the basement weathering crust in well Dongping 9

图14 东坪地区基岩风化壳发育模式

Fig.14 Weathering crust model of the basement in Dongping area

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