四川盆地元坝气田长兴组古原油的运移方向与聚集特征

doi:10.13745/j.esf.sf.2023.2.22

摘要/Abstract

摘要：

元坝气田的长兴组天然气主要为原油裂解气。研究古原油的运移方向与聚集特征,对于分析从古油藏到现今气藏的演化过程以及揭示现今气-水界面的分布特征,从而指导元坝气田及邻区的天然气勘探与开发具有重要意义。本文利用流体包裹体确定了古原油的充注时间,恢复了原油充注期的储层顶面构造形态,并以此为基础模拟了古原油的运移路径;然后利用储层沥青的烷基二苯并噻吩类分子标志物示踪了古原油的运移方向;最后分析了古原油的聚集特征与油气藏的演化过程。结果表明:(1)长兴组储层发育较多的沥青包裹体,与之伴生的盐水包裹体的均一温度为110~130 ℃,结合地层埋藏史和温度演化史确定的古原油充注的时间为晚三叠世到早侏罗世;(2)古原油充注期的长兴组顶面形态继承了长兴组沉积期的顶面形态,台地边缘的礁滩处于相对高部位,而礁后滩处于相对低部位;(3)数值模拟显示古原油从台地边缘斜坡向台地边缘的礁滩圈闭侧向运移,储层沥青的烷基二苯并噻吩比值也沿着运移方向逐渐降低,表明古原油具有侧向运移特点;(4)位于相对高部位的台地边缘礁滩圈闭的古原油充满度高,而位于相对低部位的礁后滩圈闭的古原油充满度低。综合来看,元坝气田的古原油具有近源充注、在相对高部位的台地边缘礁滩圈闭聚集的特征;对经历高热演化的古油藏而言,烷基二苯并噻吩类化合物在古原油的运移方向示踪方面具有一定潜力。

关键词: 烷基二苯并噻吩, 固体沥青, 古原油运移方向, 长兴组, 元坝气田, 四川盆地

Abstract:

The natural gas in the Permian Changxing Formation (P₂ch) in the Yuanba gas field is mainly derived from oil cracking. Study on the migration direction and accumulation characteristics of paleo-oil can provide valuable insights into the reservoir evolution and fluid contact distribution in the P₂ch reservoirs to guide natural gas prospecting and exploration in the region. In this paper, the paleo-oil charging period was first determined using fluid inclusions data, and the reservoir cap structure during oil charging was restored. Based on the reservoir cap structure the oil migration pathway was simulated, and the oil migration direction was traced using alkyl dibenzothiophene markers from solid reservoir bitumen. Finally, the paleo-oil accumulation characteristics and oil/gas reservoir evolution in the P₂ch reservoirs were analyzed. The main findings were (1) bitumen inclusions were widespread, and the associated brine inclusions had a homogenization temperature of 110-130 ℃. Combined with the burial history and thermal evolution data, the estimated paleo-oil charging period spaned from the Late Triassic to Early Jurassic. (2) The reservoir cap structure during reservoir deposition was retained during paleo-oil charging. (3) Paleo-oil migrated laterally from the platform margin slope to the reef-shoal traps, while the alkyl dibenzothiophene ratio for solid reservoir bitumen also gradually decreased along the migration direction consistent with lateral oil migration. (4) The degree of paleo-oil filling was higher in reef-shoal traps in the platform margin compared to lower positions. On the whole, the paleo-oil in the Yuanba gas field was characterized by near-source charging and oil accumulation in reef-shoal traps in the elevated platform margin. For paleo-reservoirs that had undergone high temperature thermal evolution, alkyl dibenzothiophenes may be used to trace the paleo-oil migration direction.

Key words: alkyl dibenzothiophene, solid bitumen, migration direction of paleo-oil, Changxing Formation, Yuanba gas field, Sichuan Basin

中图分类号:

P618.13

李平平, 魏广鲁, 徐祖新, 李毕松, 彭雨晴, 邹华耀. 四川盆地元坝气田长兴组古原油的运移方向与聚集特征[J]. 地学前缘, 2023, 30(6): 277-288.

LI Pingping, WEI Guanglu, XU Zuxin, LI Bisong, PENG Yuqing, ZOU Huayao. Migration direction and accumulation characteristics of paleo-oil in the Changxing Formation in Yuanba Gas Field, Sichuan Basin[J]. Earth Science Frontiers, 2023, 30(6): 277-288.

图/表 11

图1 川北地区的构造单元、元坝气田的位置(a)及综合地层柱状图(b)(a据文献[19,25]修改)

Fig.1 Structural units in the northern Sichuan, location of the Yuanba gas field and general stratigraphic column. Modified after [19,25].

图2 元坝气田长兴组顶面构造图、礁滩圈闭与气藏的分布(据文献[21]修改)

Fig.2 Top structural map, reef shoal traps and gas reservoir distribution of the Changxing Formation in the Yuanba gas field. Modified after [21].

图3 四川盆地北部吴家坪组(a)和大隆组烃源岩厚度图(b)(a据文献[19,30]修改;b据文献[30]修改)

Fig.3 Thickness map of source rocks of the Wujiaping Formation (a) and Dalong Formation (b) in the northern Sichuan Basin. a modified after [19,30];b modified after [30].

图4 元坝气田长兴组储层流体包裹体镜下特征 a,b—分别为单偏光和荧光(×500)下,元坝271井,6 337.75 m,长兴组,白云石晶粒中见呈星散状分布的沥青包裹体;c,d—分别为单偏光光和荧光(×500)下,元坝9井,长兴组,7 065.41 m,残余生屑粉细晶白云岩内孔洞充填的亮晶方解石中见微弱白色荧光的气体包裹体、无荧光的盐水包裹体、无荧光黑色的沥青包裹体和含沥青气相烃包裹体;e,f—分别为单偏光和荧光(×100)下,元坝2井,长兴组,6 587.62 m,溶孔生屑白云岩溶洞充填亮晶方解石晶体中见少量发浅黄色、蓝白色荧光油包裹体和大量不发荧光的黑色沥青包裹体。

Fig.4 Microscopic characteristics of fluid inclusions in the Changxing Formation of the Yuanba gas field.

图5 元坝气田长兴组储层流体包裹体均一温度(a)与原油充注时间(b)(b图底图引自文献[21])

Fig.5 Homogenization temperature of fluid inclusions (a) and charging time of paleo-oil (b) in Changxing Formation of the Yuanba gas field. b adapted from [21].

图6 元坝气田长兴组飞仙关组沉积末期(a)和原油充注期早侏罗世(b)顶部构造图

Fig.6 Top structural map of the Changxing Formation at the deposition of the Late Feixianguan Formation (a) and paleo-oil charing in the Early Jurassic (b) in the Yuanba gas field.

图7 元坝气田长兴组模拟古原油二次运移路径与聚集区

Fig.7 Secondary migration pathways and accumulation areas of simulated paleo-oil in the Changxing Formation of the Yuanba gas field.

表1 元坝气田长兴组固体沥青样品芳烃和含氮化合物分析结果

Table 1 Analysis results of aromatic hydrocarbons and nitrogenous compounds in solid bitumen samples of the Changxing Formation in the Yuanba gas field

编号	井位	深度/m	分子标志物比值
			4-/1-	2,4-/1,4-	4,6-/1,4-	4-/1-	1,8-/2,4-	1,8-/2,5	[a]/[c]
			MDBT	DMDBT	DMDBT	MDBF	DMC	DMC	[a]/[c]
1	元坝102	6 725.40	4.68	1.06	1.62	0.51	4.89	4.11	3.19
2	元坝11	6 773.50	4.06	0.87	1.36	0.35	8.79	5.53	8.98
3	元坝104	6 710.20	2.78	0.75	1.05	0.21	3.23	2.90	1.73
4	元坝204	6 548.50	5.30	1.08	1.71	0.28	4.16	4.52	2.39
5	元坝205	6 459.38	4.27	0.92	1.49	0.32	5.38	3.71	5.51
6	元坝2	6 580.50	4.17	0.87	1.46	0.29	3.69	3.59	2.04
7	元坝27	6 301.60	7.06	1.09	1.64	0.17	2.31	2.26	2.77
8	元坝27	6 294.02	4.60	1.19	1.70	0.25	3.24	2.78	2.22
9	元坝271	6 324.10	2.67	0.99	0.98	0.30	—	—	—
10	元坝271	6 328.01	3.15	0.84	1.20	0.28	0.61	4.26	—
11	元坝271	6 339.90	3.21	0.74	1.20	0.39	—	—	—
12	元坝12	6 692.45	4.55	0.86	1.44	0.34	4.31	3.38	—
13	元坝16	6 966.72	2.47	1.05	0.84	0.36	2.42	2.99	2.48
14	元坝224	6 635.46	4.70	0.88	1.45	0.35	4.21	4.57	3.55
15	元坝224	6 638.40	4.25	0.91	1.46	0.38	—	—	—
16	元坝224	6 648.87	6.23	1.06	1.54	0.03	1.62	2.41	—
17	元坝273	6 827.35	4.12	0.89	1.54	0.33	3.86	3.88	3.92
18	元坝28	6 807.10	4.01	0.70	1.39	0.38	6.51	2.58	2.71
19	元坝29	6 640.00	3.94	0.82	1.33	0.37	5.64	4.76	2.96
20	元坝9	6 907.87	5.10	0.88	1.59	0.66	4.43	2.00	—
21	元坝9	6 908.47	3.12	0.74	1.20	0.45	6.40	4.97	—

图8 元坝气田长兴组古油藏充注期咔唑类(a)和二苯并噻吩类(b)分子标志物示踪与模拟运移结果

Fig.8 The simulated and traced migration pathway by carbazole (a) and dibenzothiophene molecular markers (b) in the Changxing paleo-oil reservoir of the Yuanba gas field.

图9 元坝气田长兴组古油藏生储盖配置关系与充注过程(剖面线见图2)

Fig.9 Relationship of source-reservoir-cap assemblage and charging process of the Changxing Formation paleo-oil reservoir in the Yuanba gas field (section line is shown in Fig.2)

图10 元坝气田长兴组元坝2井(a),元坝123井(b)、元坝224井(c)和元坝102井(d)沥青与古油层分布(a和b据文献[20]修改,元坝102井沥青含量基于6 710~6 850 m深度的系统岩屑薄片分析得出)

Fig.10 Distribution of bitumen and paleo-oil layers in the wells Yuanba 2 (a), Yuanba 123 (b), Yuanba 224 (c) and well Yuanba 102 (d) of the Changxing Formation in the Yuanba gas field (a and b adapted from [20], and the bitumen content of Well Yuanba 102 is based on the systematic cuttings analysis of 6710-6850 m)

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