化学刺激法提高花岗岩类岩石裂隙渗透性的实验研究

doi:10.13745/j.esf.sf.2019.12.2

摘要/Abstract

摘要：

增强型地热系统(EGS)用于通过人工形成地热储层的方法从深部低渗透性岩体中开采地热能;国际上常采用水力压裂辅以化学刺激的方法改造EGS 储层以提高其渗透率。本文以采自青海共和盆地的花岗闪长岩样品为对象,选用3种不同化学刺激剂(氢氧化钠、盐酸和土酸),在3组不同注入流速条件下开展了系统化学刺激实验。结果表明:注入盐酸和土酸后样品渗透率均有提高,且采用土酸时渗透率提高幅度明显大于盐酸;但注入氢氧化钠后,样品渗透率反而降低。在3类化学刺激剂中,土酸对长石类矿物的溶蚀能力最强,而氢氧化钠溶液对石英的溶蚀能力最强,但氢氧化钠溶液在溶解岩石样品裂隙表面矿物后极易形成非定形态二氧化硅或非定形态铝硅酸盐蚀变矿物并阻塞裂隙,反而对化学刺激效果造成负面影响。总体来看,土酸是青海共和盆地干热岩体的最佳化学刺激剂。在中等注入速度(3 mL·min^-1)条件下,土酸对岩石样品的溶蚀程度就可达到最高;在此基础上进一步降低流速,则可能使溶解组分更易从液相中沉淀而充填于样品裂隙,导致样品渗透率有所下降。

关键词: 干热岩, 增强型地热系统, 化学刺激, 土酸, 渗透率

Abstract:

Enhanced geothermal system (EGS) has been used to extract heat from deep hot dry rock with low permeability by creating an artificial geothermal reservoir. Hydraulic fracturing, along with chemical stimulation, was usually adopted to improve the permeability of a target EGS reservoir. In this study, we collected granodiorite samples from the Gonghe basin of Qinghai Province and subjected them to a systematic chemical stimulation test by use of three chemical agents (sodium hydroxide, hydrochloric acid and mud acid) at three different injection rates. The results show that the permeability of the rock samples increased upon injection of hydrochloric acid or mud acid, with the latter bringing larger increases; whereas the application of sodium hydroxide solution reduced the permeability. Among the three chemical agents, mud acid exhibited the strongest ability of dissolving feldspar minerals in granodiorite; in contrast, quartz was eroded most severely by sodium hydroxide solution. Nevertheless, during the chemical stimulation test using sodium hydroxide solution, we saw amorphous silica or aluminosilicates precipitation due to excess dissolution of the primary minerals on the fracture surface; and precipitation resulted in micro-fracture filling which definitely had a negative effect on improving permeability. Thus, in general, mud acid is the best chemical agent for the target hot dry rock in this study. At a moderate injection rate (3 mL·min^-1), mud acid can most effectively erode granodiorite samples and remarkably enhance sample permeability. Lowering injection rates, however, could cause secondary mineral precipitation and fracture filling therefore lowering sample permeability.

Key words: hot dry rock, enhanced geothermal system, chemical stimulation, mud acid, permeability

中图分类号:

郭清海, 何曈, 庄亚芹, 骆进, 张灿海. 化学刺激法提高花岗岩类岩石裂隙渗透性的实验研究[J]. 地学前缘, 2020, 27(1): 159-169.

GUO Qinghai, HE Tong, ZHUANG Yaqin, LUO Jin, ZHANG Canhai. Expansion of fracture network in granites via chemical stimulation: a laboratory study[J]. Earth Science Frontiers, 2020, 27(1): 159-169.

图/表 12

图1 岩心流动仪实物图和结构示意图

Fig.1 Photograph (Left) and schematic description (Right) of the core flow apparatus used in this study

图2 3种不同注射率下注入空白溶液时岩样渗透率的变化

Fig.2 Permeability change of rock samples upon blank solution injection at three injection rates

图3 3种不同注射率下注入盐酸时岩样渗透率的变化

Fig.3 Permeability change of rock samples upon hydrochloric acid injection at three injection

图4 3种不同注射率下注入土酸时岩样渗透率的变化

Fig.4 Permeability change of rock samples upon blank solution injection at three injection rates

图5 三种不同注射率下注入氢氧化钠溶液时岩样渗透率的变化

Fig.5 Permeability change of rock samples upon injection of sodium hydroxide solution at three injection rates

表1 化学刺激实验不同阶段岩样的渗透率变化

Table 1 Permeability change of rock samples in different stages of chemical stimulation test

实验条件			岩心裂隙渗透率/(10^-4μm²)
			注前置液		注中置液			注后置液
			k_1-avg		k_2-avg / k_2-max			k_3-avg
	1	2.60		3.85		/	4.65		4.37	1.68
10% HCl	3	7.61		11.09		/	14.53		9.51	1.25
	5	3.01		4.13		/	5.56		4.76	1.56
	1	0.48		1.76		/	3.31		3.41	7.15
10% HCl+0.5% HF	3	1.67		21.7		/	90.95		18.93	11.34
	5	2.98		16.61		/	27.47		21.16	7.11
	1	5.87		3.55		/	4.90		1.24	0.21
10% NaOH	3	6.18		1.74		/	2.82		0.30	0.05
	5	9.76		0.84		/	1.59		0.08	0.01

图6 注入不同化学刺激剂后岩石样品裂隙表面溶蚀全貌(SEM分析) a—注入盐酸后裂隙表面全貌; b—注入土酸后裂隙表面全貌; c—注入氢氧化钠后裂隙表面全貌。

Fig.6 SEM images of the fracture surfaces of rock samples treated by various chemical agents, showing the overall erosion. (a) After hydrochloric acid injection; (b) After mud acid injection; and (c) After injection of sodium hydroxide solution.

图7 注入不同化学刺激剂后裂隙表面矿物的XRD分析

Fig.7 XRD patterns of the minerals on the fracture surfaces of rock samples treated by various chemical agents

图8 注入不同化学刺激剂后岩石样品中石英的溶蚀(SEM-EDX分析) a—注入盐酸后石英未溶蚀;b—注入土酸后石英未溶蚀;c—注入氢氧化钠后石英溶蚀呈蜂窝状。

Fig.8 Erosion of quartz in the rock samples treated by various chemical agents according to the SEM-EDX analysis

图9 注入不同化学刺激剂后岩石样品中长石的溶蚀(SEM-EDX分析) a—注入盐酸后长石溶解程度低,表面有微小的溶蚀坑洞;b—注入土酸后长石溶蚀严重,沿解理溶蚀,呈沟壑状;c—注入氢氧化钠后长石溶解程度低,表面有微小的溶蚀坑洞。

Fig.9 Erosion of feldspar minerals in the rock samples treated by various chemical agents according to SEM-EDX analysis

表2 化学刺激实验后液相pH和其中主要化学组分的质量浓度

Table2 PHs and major constituent concentrations of the liquid phase after chemical stimulation test

实验条件	注入流速 /(mL·min^-1)	pH	化学组分质量浓度/(mg·L^-1)
实验条件	注入流速 /(mL·min^-1)	pH	K	Na	Ca	Mg	Al	Fe	Si	Cl	F
	1	-0.42	220.3	384.3	334.4	265.4	265.4	603.9	57.8	106.5	n.d.
10% HCl	3	-0.43	179.5	358.7	291.3	194.1	182.3	404.9	47.4	107.2	n.d.
	5	-0.42	98.5	352.2	255.2	127.6	103.2	457.8	46.1	105.1	n.d.
	1	-0.37	195.7	614.8	434.6	122.3	396.1	277.1	373.7	103.5	5.1
10% HCl+0.5% HF	3	-0.37	277.1	665.4	464.1	172.5	414.7	308.0	770.0	102.8	4.9
	5	-0.37	266.4	654.2	393.2	156.3	445.8	303.5	438.6	103.2	5.0
	1	14.04	144.7	1 217.6	127.5	13.7	13.0	n.d.	47.4	n.d.	n.d.
10% NaOH	3	14.04	143.9	742.7	103.8	13.8	3.5	n.d.	31.1	n.d.	n.d.
	5	14.05	154.0	1 216.0	195.9	25.4	4.2	n.d.	52.9	n.d.	n.d.

图10 化学刺激实验后液相中化学组分质量浓度的变化

Fig.10 Concentration variations of liquid phase constituents after chemical stimulation test

参考文献 18

[1]	郑克棪, 陈梓慧. 中国干热岩开发: 任重而道远[J]. 中外能源, 2017, 22(2):21-25.
[2]	汪集旸, 胡圣标, 庞忠和, 等. 中国大陆干热岩地热资源潜力评估[J]. 科技导报, 2012 (32):25-31.
[3]	TESTER J W, ANDERSON B, BATCHELOR A, et al. The future of geothermal energy:impact of enhanced geothermal systems (EGS) on the United States in the 21st century[C]. Cambridge : Massachusetts Institute of Technology, 2006.
[4]	HOFMANN H, BABADAGLI T, ZIMMERMANN G. Hot water generation for oil sands processing from enhanced geothermal systems: process simulation for different hydraulic fracturing scenarios[J]. Applied Energy, 2014, 113:524-547. DOI URL
[5]	郭亮亮, 张延军, 胡忠君, 等. 增强型地热系统压裂和开采方案研究[C]// 2015年全国工程地质学术年会论文集. 长春: 中国地质学会, 2015.
[6]	雷宏武. 增强型地热系统(EGS)中热能开发力学耦合水热过程分析[D]. 长春: 吉林大学, 2014.
[7]	BROWN D W, DUCHANE D V. Scientific progress on the Fenton Hill HDR project since 1983[J]. Geothermics, 1999, 28(4/5):591-601. DOI URL
[8]	郭剑, 陈继良, 曹文炅, 等. 增强型地热系统研究综述[J]. 电力建设, 2014, 35(4):10-24.
[9]	SANDRINE P, LAURRENT A, FRANCOIS-D.V. Review on chemical stimulation techniques in oil industry and applications to geothermal systems[C]. Basel: Deep Heat Mining Association, 2007.
[10]	ZIMMERMANN G, BLÖCHER G, REINICKE A, et al. Rock specific hydraulic fracturing and matrix acidizing to enhance a geothermal system: concepts and field results[J]. Tectonophysics, 2011, 503(1):146-154. DOI URL
[11]	CORREIA H, SIGURDSSON O, SANJUAN B, et al. Stimulation test of a high-enthalpy geothermal well by cold water injection[J]. Geothermal Resources Council Transactions, 2000, 24:129-136.
[12]	PORTIER S, VUATAZ F-D, NAMI P, et al. Chemical stimulation techniques for geothermal wells: experiments on the three-well EGS system at Soultz-sous-Forêts, France[J]. Geothermics, 2009, 38(4):349-359. DOI URL
[13]	BREEDE K, DZEBISASHVILI K, LIU X, et al. A systematic review of enhanced (or engineered) geothermal systems: past, present and future[J]. Geothermal Energy, 2013, 1(1):4. DOI URL
[14]	王敏黛, 郭清海, 严维德, 等. 青海共和盆地中低温地热流体发电[J]. 地球科学: 中国地质大学学报, 2014(9):1317-1322.
[15]	DAVIES D, FABER R, NITTERS G, et al. A novel procedure to increase well response to matrix acidising treatments[J]. SPE Advanced Technology Series, 1994, 2(1):5-14. DOI URL
[16]	PERTHUIS H, TOUBOUL E, PIOT B. Acid reactions and damage removal in sandstones: a model for selecting the acid formulation[C]. Houston: Society of Petroleum Engineers, 1989.
[17]	NASR-EI-DIN H A. Surfactant:use in acid stimulation[M]. Cambridge: Cambridge University Press, 2000.
[18]	康燕. 长岩心流动实验评价酸液酸化效果[J]. 大庆石油地质与开发, 2005, 24(3):77-78.