天然气水合物藏多层联合开采数值模拟研究

doi:10.13809/j.cnki.cn32-1825/te.2023.03.015

摘要/Abstract

摘要：

海域天然气水合物藏往往伴随着大量游离气的存在，而储层的低渗透性限制了不同层系的气水流动，利用储层中的水合物分解气和游离气是提升水合物藏产气效率的关键。基于中国南海神狐海域的实际地质数据，使用TOUGH+HYDRATE模拟器，建立3种不同水合物储层垂直井联合开采的数值模型，分析了产气、产水、温度、压力场和水合物饱和度的空间变化，进而提出天然气水合物的优化降压开采策略。结果表明：降压开采过程中，气和水不断向开采井汇集，井周围的温度压力迅速下降；持续降压开采10 a，随着产气速率的减小，产水速率不断增大，三层联合开采方式的累计产气量最高可达4.59×10⁶ m³，其累计产水量为8.31×10⁵ m³；水合物的分解由降压的压力梯度控制，井周围的水合物优先分解，下伏层水的流动会加快储层水合物的分解。

关键词: 天然气水合物, 产气效率, 联合开采, 数值模型, 神狐海域

Abstract:

Offshore natural gas hydrate reservoirs are often accompanied by a large amount of free gas. However, the low permeability of the reservoir limits the flow of gas and water in different layers. Therefore, the fully exploitation of the hydrate-dissociation gas and free gas in the reservoir is the key to improve gas production efficiency. Based on the actual geological data in the Shenhu area of the South China Sea, the TOUGH+HYDRATE code is used to establish the numerical model of the combined exploitation of three different hydrate reservoirs with vertical wells. The spatial changes of gas production, water production, temperature, pressure field and hydrate saturation are analyzed, and then the optimized depressurization production strategy of natural gas hydrate is put forward. The results show that during the depressurization production, gas and water are continuously collected to the production well, and the temperature and pressure around the well drop rapidly. After continuous production for ten years, the water production rate continues to increase with the decrease of gas production rate. The cumulative gas production of three-layer combined mining method is up to 4.59×10⁶ m³, and the cumulative water production is 8.31×10⁵ m³. Hydrate dissociation is controlled by the depressurized gradient, hydrates around the well are preferentially dissociated, and the flow of underlying water will accelerate the dissociation of reservoir hydrates.

Key words: natural gas hydrate, gas production efficiency, combined exploitation, numerical model, Shenhu area

中图分类号:

TE53

杨作亚,武晓敏. 天然气水合物藏多层联合开采数值模拟研究[J]. 油气藏评价与开发, 2023, 13(3): 393-402.

YANG Zuoya,WU Xiaomin. Numerical simulation study on multi-layer combined exploitation of natural gas hydrate reservoirs[J]. Petroleum Reservoir Evaluation and Development, 2023, 13(3): 393-402.

图/表 13

图1

表1

图2

表2

图3

图4

图5

图6

图7

表3

图8

图9

表4

参考文献 22

[1]	YIN Z Y, LINGA P. Methane hydrates: A future clean energy resource[J]. Chinese Journal of Chemical Engineering, 2019, 27(9): 2026-2036. doi: 10.1016/j.cjche.2019.01.005
[2]	ZHANG R W, LU J A, WEN P F, et al. Distribution of gas hydrate reservoir in the first production test region of the Shenhu area, South China Sea[J]. China Geology, 2018, 1(4): 493-504. doi: 10.31035/cg2018049
[3]	邹才能, 赵群, 丛连铸, 等. 中国页岩气开发进展、潜力及前景[J]. 天然气工业, 2021, 41(1): 1-14.
	ZOU Caineng, ZHAO Qun, CONG Lianzhu, et al. Development progress, potential and prospect of shale gas in China[J]. Natural Gas, 2021, 41(1): 1-14.
[4]	REN X, GUO Z Y, NING F L, et al. Permeability of hydrate-bearing sediments[J]. Earth-Science Reviews, 2020, 202:103100. doi: 10.1016/j.earscirev.2020.103100
[5]	YIN Z Y, MORIDIS G, TAN H K, et al. Numerical analysis of experimental studies of methane hydrate formation in a sandy porous medium[J]. Applied Energy, 2018, 220: 681-704. doi: 10.1016/j.apenergy.2018.03.075
[6]	刘树根, 焦堃, 张金川, 等. 深层页岩气储层孔隙特征研究进展——以四川盆地下古生界海相页岩层系为例[J]. 天然气工业, 2021, 41(1): 29-41.
	LIU Shugen, JIAO Kun, ZHANG Jinchuan, et al. Research progress on the pore characteristics of deep shale gas reservoirs: An example from the Lower Paleozoic marine shale in the Sichuan Basin[J]. Natural Gas Industry, 2021, 41(1): 29-41.
[7]	FENG J C, WANG Y, LI X S, et al. Production behaviors and heat transfer characteristics of methane hydrate dissociation by depressurization in conjunction with warm water stimulation with dual horizontal wells[J]. Energy, 2015, 79(1): 315-324. doi: 10.1016/j.energy.2014.11.018
[8]	WANG Y, FENG J C, LI X S, et al. Experimental investigation of optimization of well spacing for gas recovery from methane hydrate reservoir in sandy sediment by heat stimulation[J]. Applied Energy, 2017, 207(1): 562-572. doi: 10.1016/j.apenergy.2017.06.068
[9]	郭建春, 赵志红, 路千里, 等. 深层页岩缝网压裂关键力学理论研究进展[J]. 天然气工业, 2021, 41(1): 102-117.
	GUO Jianchun, ZHAO Zhihong, LU Qianli, et al. Research progress in key mechanical theories of deep shale network fracturing[J]. Natural Gas Industry, 2021, 41(1): 102-117.
[10]	YIN Z Y, MORIDIS G J, CHONG Z R, et al. Numerical analysis of experimental studies of methane hydrate dissociation induced by depressurization in a sandy porous medium[J]. Applied Energy, 2018, 230: 444-459. doi: 10.1016/j.apenergy.2018.08.115
[11]	QIN X W, LU J A, LU H L, et al. Coexistence of natural gas hydrate, free gas and water in the gas hydrate system in the Shenhu Area, South China Sea[J]. China Geology, 2020, 3(2): 210-220. doi: 10.31035/cg2020038
[12]	BOSWELL R, SCHODERBEK D, COLLETT T S, et al. The Iġnik Sikumi Field experiment, Alaska North Slope: Design, operations, and implications for CO₂-CH₄ exchange in gas hydrate reservoirs[J]. Energy & Fuels, 2017, 31(1): 140-153. doi: 10.1021/acs.energyfuels.6b01909
[13]	周守为, 陈伟, 李清平, 等. 深水浅层非成岩天然气水合物固态流化试采技术研究及进展[J]. 中国海上油气, 2017, 29(4): 1-8.
	ZHOU Shouwei, CHEN Wei, LI Qingping, et al. Research on the solid fluidization well testing and production for shallow non-diagenetic natural gas hydrate in deep water area[J]. China offshore oil and gas, 2017, 29(4): 1-8.
[14]	HANCOCK S H, COLLETT T S, DALLIMORE S R, et al. Overview of thermal-stimulation production-test results for the JAPEX/JNOC/GSC et al. Mallik 5L-38 gas hydrate production research well[C]// Paper presented at the 2002 Mallik International Symposium on Gas Hydrate Production Research Well Program, Makuhari, Japan, December 2003.
[15]	DALLIMORE S R, WRIGHT J F, NIXON F M, et al. Geologic and porous media factors affecting the 2007 production response characteristics of the JOGMEC/NRCan/Aurora Mallik gas hydrate production research well[C]// Paper ICGH-5829 presented at the proceedings of the 6th International Conference on Gas Hydrates, Vancouver, Canada, July 2008.
[16]	RUTQVIST J, MORIDIS G J, GROVER T, et al. Geomechanical response of permafrost-associated hydrate deposits to depressurization-induced gas production[J]. Journal of Petroleum Science and Engineering, 2009, 67(1-2): 1-12. doi: 10.1016/j.petrol.2009.02.013
[17]	KURIHARA M, FUNATSU K. Analysis of Production Data for 2007/2008 Mallik gas hydrate production tests in Canada[C]// Paper SPE-132155-MS presented at the International Oil and Gas Conference and Exhibition in China, Beijing, China, June 2010.
[18]	LI J F, YE J L, QIN X W, et al. The first offshore natural gas hydrate production test in South China Sea[J]. China Geology, 2018, 1(1): 5-16. doi: 10.31035/cg2018003
[19]	YE J L, QIN X W, XIE W W, et al. The second natural gas hydrate production test in the South China Sea[J]. China Geology, 2020, 3(2): 197-209. doi: 10.31035/cg2020043
[20]	KURIHARA M, SATO A, FUNATSU K, et al. Analysis of formation pressure test results in the Mount Elbert methane hydrate reservoir through numerical simulation[J]. Marine and Petroleum Geology, 2011, 28(2): 502-516. doi: 10.1016/j.marpetgeo.2010.01.007
[21]	苏正, 何勇, 吴能友. 南海北部神狐海域天然气水合物热激发开采潜力的数值模拟分析[J]. 热带海洋学报, 2012, 31(5): 74-82. doi: 10.11978/j.issn.1009-5470.2012.05.011
	SU Zheng, HE Yong, WU Nengyou. Numerical simulation on production potential of hydrate deposits by thermal stimulation[J]. Journal of Tropical Oceanography. 2012, 31(5): 74-82. doi: 10.11978/j.issn.1009-5470.2012.05.011
[22]	BOSWELL R, MYSHAKIN E M, MORIDIS G J, et al. India National Gas Hydrate Program Expedition 02 summary of scientific results: Numerical simulation of reservoir response to depressurization[J]. Marine and Petroleum Geology, 2019, 108: 154-166. doi: 10.1016/j.marpetgeo.2018.09.026

参数	数值
非稳定水合物层底部初始压力/MPa	15.50
非稳定水合物层底部初始温度/°C	16.59
初始孔隙度及各相饱和度/%	水饱和度S_A=100.0,φ=35（上盖层）
	S_H=34.0,S_A=66.0,φ=35（水合物层Ⅰ）
	S_H=31.0,S_A=61.2,S_G=7.8,φ=33（水合物层Ⅱ）
	S_A=92.2,S_G=7.8,φ=32（游离气层）
	S_A=100.0,φ=32（下盖层）
CH₄/%	100
地温梯度/（°C/m）	0.044 3
孔隙水盐度/%	3.05
本征渗透率k/10^-3 μm²	2.9（上盖层&水合物层Ⅰ）
	1.5（水合物层Ⅱ）
	7.4（游离气层&下盖层）
开采井内渗透率/10^-3 μm²	1
湿热导率k_ΘRW/[W/（m·K）]	1.7
干热导率k_ΘRD/[W/（m·K）]	1.0
毛细压力模型^[20]	p_cap=-p₀[（S）^-1/λ-1]^1-λ
毛细压力模型^[20]	S=（S_A-S_irA）/（S_mxA-S_irA）
残余水饱和度S_irA/%	30
毛细管系数λ	0.45
静水压力p₀/Pa	10⁵
相对渗透率模型^[20]	k_rA=（S_A）ⁿ,k_rG=（S_G）ⁿ^G
	S_A=（S_A-S_irA）/（1-S_irA）
	S_G=（S_G-S_irG）/（1-S_irA）
水相相对渗透率衰减因子n	3.572
气相相对渗透率衰减因子nG	3.572
残余气饱和度S_irG/%	3

案例	井位置	深度范围/m	长度/m
方案1	稳定水合物层+ 非稳定水合物层	1 495~1 545	50
方案2	非稳定水合物层+游离气层	1 530~1 572	42
方案3	稳定水合物层+ 非稳定水合物层+游离气层	1 495~1 572	77

案例	累计产气量/10⁴ m³	单位井长产气量/10⁴ m³	累计产水量/10⁴ m³	单位井长产水量/m³
方案1	220	44	22	4 300
方案2	397	94	61	14 500
方案3	459	60	83	10 800

案例	本征渗透率/ 10^-3 μm²	累计产气量/ 10⁴ m³	日均产气量/ m³
方案3	1.5	459	1 258
方案4	15.0	716	1 962
方案5	100.0	1 585	4 343