鄂尔多斯盆地太原组致密灰岩天然气成藏地质特征与勘探潜力

doi:10.13745/j.esf.sf.2022.8.24

摘要/Abstract

摘要：

2021年鄂尔多斯盆地榆探*H在太原组灰岩完钻喜获日产超50万m³的高产工业气流,勘探取得重大突破,同时还有700余口探井在太原组灰岩见到明显的含气显示,展示了盆地太原组灰岩良好的潜力,对于重新认识盆地太原组灰岩勘探领域具有极其重大的地质意义。对该区烃源岩特征、沉积环境、储集特征及成藏组合等进行综合研究表明:(1)太原组灰岩为陆表海碳酸盐沉积,发育生屑滩、生物丘有利沉积相带,沉积大面积分布的生屑粉晶灰岩、藻黏结灰岩,经准同生期短暂的大气淡水淋滤后,可形成有利储层;(2)太原组灰岩发育多类型储集空间,溶孔、亚微米级及纳米级晶间微孔、微裂缝等叠置组合发育,构成立体网络储集空间,平面上,横山—靖边—志丹生屑粉晶灰岩储层发育,厚4~10 m,佳县—子洲—清涧地区藻黏结灰岩储层发育,厚2~6 m;(3)发育“三明治”成藏模式,灰岩储层夹在主力煤系烃源岩之间,生成的天然气通过断裂、裂缝进入灰岩储层聚集,形成岩性气藏,横山—靖边地区的生屑滩和子洲—清涧的生物丘是太原组灰岩有利勘探区,面积约为1.5万km²,有望形成天然气增储上产的现实领域。

关键词: 鄂尔多斯盆地, 太原组, 灰岩, 生物碎屑粉晶灰岩, 藻黏结灰岩, 成藏模式, 源内致密灰岩气

Abstract:

In 2021, a high-yield daily output of more than 5.0×10⁵ m³ industrial gas was obtained in well Yutan*H, signifying a major breakthrough in natural gas exploration in the limestone reservoir of Taiyuan Formation, Ordos Basin. Now, more than 700 exploratory wells have good gas shows in the reservoir, showing excellent exploration potential, which is of great significance for further studying the geological characteristics of the limestone of Taiyuan Formation. Based on comprehensive analysis of the source rock characteristics, sedimentary environment, reservoir characteristics and hydrocarbon accumulation assemblage in the area, we show that: (1) The limestone of Taiyuan Formation is an epicontinental carbonate deposit, in which favorable sedimentary facies belt composed of bioclastic beach and biological mound is developed, and the widespread bioclastic silty limestone and algal-rich limestone can form favorable reservoirs after short-term leaching by atmospheric freshwater in penecontemporaneous period. (2) The limestone of Taiyuan Formation develops several types of reservoir space, where solution pores, submicron to nano intergranular micropores and microfractures superimpose to form a three-dimensional reservoir space; meanwhile across the region, 4-10 m thick bioclastic silty limestone reservoir develops in the Hengshan-Jingbian-Zhidan area, and 2-6 m thick algal-rich limestone reservoir develops in the Jiaxian-Zizhou-Qingjian area. (3) The hydrocarbon accumulation mode has a “sandwich-like” structure, where the limestone reservoir is sandwiched between main coaly source rocks, and the generated natural gas enters limestone reservoir through faults and fractures to accumulate and form a lithologic gas reservoir. With a combined area of 1.5×10⁴ km², the bioclastic beach in Hengshan-Jingbian area and the biological mound in Zizhou-Qingjian area are the favorable exploration targets for the limestone of Taiyuan Formation, which is expected to bring the increase of natural gas reserve and production.

Key words: Ordos Basin, Taiyuan formation, limestone, bioclastic silty limestone, algal-rich limestone, hydrocarbon accumulation mode, tight limestone gas in source

中图分类号:

TE13

付金华. 鄂尔多斯盆地太原组致密灰岩天然气成藏地质特征与勘探潜力[J]. 地学前缘, 2023, 30(1): 20-29.

FU Jinhua. Accumulation characteristics and exploration potential of tight limestone gas in the Taiyuan Formation of the Ordos Basin[J]. Earth Science Frontiers, 2023, 30(1): 20-29.

图/表 14

图1 鄂尔多斯盆地太原组灰岩分布图

Fig.1 Distribution map of limestone of Taiyuan formation in Ordos Basin

图2 鄂尔多斯盆地二叠系太原组地层综合柱状图

Fig.2 Stratigraphic histogram of the Permian Taiyuan formation in Ordos Basin

图3 鄂尔多斯盆地太原组灰岩岩石学特征 a—浅灰色颗粒灰岩,3 408.10 m,太原组斜道段;b—泥晶化生屑质球粒灰岩,单偏光,3 408.10 m太原组斜道段;c—生屑铸模孔,扫描电镜,3 408.10 m,太原组斜道段;d—灰褐色花斑状微生物凝块灰岩,3 035.78 m,太原组斜道段;e—微生物凝块灰岩,发育残余格架孔,3 035.78 m,太原组斜道段;f—残余格架孔,见方解石胶结物,3 035.78 m,太原组斜道段。

Fig.3 Distribution map of limestone of Taiyuan formation in Ordos Basin

图4 鄂尔多斯盆地太原组沉积微相图

Fig.4 Sedimentary microfacies map of Taiyuan formation in Ordos Basin

图5 (a)Jin26井沉积柱状图; (b)ZT1H井沉积柱状图

Fig.5 (a) Sedimentary histogram of well jin26; (b) Sedimentary histogram of well ZT1H

图6 鄂尔多斯盆地太原组灰岩储层特征 a—褐灰色藻黏结灰岩,ZT1H导眼井,2 487.70 m,太原组;b—褐灰色生屑粉晶灰岩,T65井,3 247.74 m,太原组;c—灰黑色生屑泥晶灰岩,S217,2 085.55 m,太原组;d—生屑泥晶灰岩,生物碎屑发育,M28井,2 166.93 m,太原组;e—藻格架溶孔,藻黏结灰岩,Y36井,3 034.4 m,太原组;f—晶间孔及晶间溶孔,T58井,3 414.16 m,太原组;g—残余有孔虫体腔孔及溶孔,Z3井,2 348.65 m,太原组;h—构造网状缝,被方解石和泥质充填,ZT1H,2 492.12 m,太原组;i—溶蚀缝发育,被方解石和泥质充填,T58井,3 413.18 m,太原组。

Fig.6 limestone reservoir characteristics of Taiyuan formation in Ordos Basin

图7 盆地太原组灰岩储层孔隙度分布直方图

Fig.7 Porosity histogram of limestone reservoir of Taiyuan formation in Ordos Basin

图8 盆地太原组灰岩储层渗透率分布直方图

Fig.8 Permeability histogram of limestone reservoir of Taiyuan formation in Ordos Basin

图9 太原组灰岩储层压汞曲线特征

Fig.9 Characteristics of mercury intrusion curve in limestone reservoir of Taiyuan formation

图10 鄂尔多斯盆地太原组灰岩中典型的岩溶角砾照片 a—褐灰色角砾灰岩,微裂缝发育,被泥质全充填,T65井,3 250.2 m,斜道段;b—灰褐色角砾泥晶灰岩,溶蚀缝发育,溶蚀孔被方解石、泥质半-全充填,T58,3 413.2 m,斜道段;c—褐灰色角砾灰岩,溶蚀孔缝发育,溶蚀孔被方解石、泥质半-全充填,J21,3 405.2 m,斜道段。

Fig.10 Typical karst breccia in limestone of Taiyuan formation, Ordos Basin

图11 盆地太原组灰岩有机质镜下特征 a—Qi71,斜道段,2 857.00 m,泥质灰岩,TOC:6.07% S1+S2:2.14 mg/g;b—Mi154,毛儿沟段,2 451.76 m,泥质灰岩,TOC:3.82%,S1+S2:0.75 mg/g;c—Mi154,庙沟段,2 457.66 m,藻纹层灰岩,TOC:2.37%,S1+S2:1.04 mg/g,D—Yu93,东大窑段,2 466.90 m, 泥晶灰岩,TOC:1.36%,S1+S2:0.1 mg/g。

Fig.11 Microscopic characteristics of organic matter in limestone of Taiyuan Formation in the basin

图12 鄂尔多斯盆地东部太原组灰岩断裂系统宏观微观特征 a—小型断裂,高角度缝,招贤剖面;b—共轭剪切裂缝,成家庄剖面;c—共轭剪切裂缝,Jin26井;d—横山北地区断裂系统。

Fig.12 Macro and micro characteristics of limestone fracture system of Taiyuan formation in Ordos Basin

图13 盆地太原组灰岩天然气成藏模式图

Fig.13 Natural gas accumulation model map of Taiyuan limestone in Ordos Basin

图14 洲*井太原组灰岩生产曲线

Fig.14 Production curve of Zhou * well in Taiyuan limestone

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