Study on Forward Numerical Simulation and Instantaneous Seismic Attributes of Natural Gas Hydrate in Permafrost Area
-
摘要: 天然气水合物是一种具有巨大潜能的新型能源,研究冻土区天然气水合物的地震响应特征,对我国陆域天然气水合物的勘探和开发具有重要意义。本文运用Kelvin粘弹性介质模型,基于祁连山冻土区的实际地质地层条件,建立理论地质-地球物理模型;采用交错网格有限差分法进行正演数值模拟,并对自激自收地震记录进行波场特征分析和提取瞬时地震属性。研究结果表明:地震波通过天然气水合物地层时,反射振幅能量较弱;在瞬时频率属性剖面可分辨层厚的范围内,瞬时频率随着层厚增加,频率在小幅度衰减;地震波通过含天然气地层时,反射波表现为强反射特征,瞬时频率能量明显增大;瞬时地震属性对波阻抗界面有更好的分辨能力,特别是瞬时相位属性剖面,作用明显。因此,综合分析波场特征与瞬时属性特征可以为陆域天然气水合物的识别、预测提供依据。Abstract: Natural gas hydrate is a new energy source with great potential. Studying the seismic response characteristics of natural gas hydrate in permafrost area is crucial to the exploration and development of natural gas hydrate in China's land area. Based on the Kelvin viscoelastic media model, our work establishes a theoretical geological-geophysical model based on the actual geological and stratigraphic conditions of the Qilian Mountain permafrost, uses the staggered-grid finite difference method to perform forward numerical simulation, and performs wave field characteristic analysis and instantaneous seismic attribute extraction of self-excitation and self-receiving seismic records. The results show that the reflected amplitude energy is weaker when the seismic wave passes through the gas hydrate formation. In the range where the instantaneous frequency attribute profile can distinguish the layer thickness, the instantaneous frequency decreases marginally with the increase of the layer thickness. When seismic waves pass through natural gas-bearing formations, the reflected waves show strong reflection characteristics, and the instantaneous frequency energy increases. The instantaneous seismic attribute has better resolution for the wave-impedance interface, especially the instantaneous phase attribute profile. Therefore, the comprehensive analysis of the instantaneous attribute characteristics can provide a basis for the identification and prediction of terrestrial gas hydrates.
-
表 1 祁连山DK-1、DK-3和DK-4三个井孔含水合物和不含水合物层段速度和密度[18]
Table 1. Velocities and densities of the hydrate segments and segments without hydrate in the holes of DK-1, DK-3, and DK-4
井孔 深度h/m 岩性 平均纵波速度Vp/(m/s) 平均密度ρ/(g/cm3) 含水合物段 不含水合物段 含水合物 不含水合物 含水合物 不含水合物 DK-1 133.90~134.86 92.05~94.75 细砂岩 4728 4204 2.34 2.53 143.35~144.30 49.20~69.70 细砂岩 4676 4171 2.38 2.57 DK-3 139.05~154.45 195.05~196.95 泥岩 2996 2867 2.32 2.43 DK-4 134.40~131.70 151.50~152.45 泥岩 4071 2822 2.25 2.31 165.75~167.25 112.45~115.35 粉砂岩 3823 3356 2.22 2.36 表 2 楔状地质-地球物理模型参数表
Table 2. The parameters of wedge-shaped geological-geophysical model
模型编号 Vp/(m/s) Vs/(m/s) ρ/(g/cm3) Qp Qs 层厚/m 冻土层① 3250 1950 2.31 187.2 139.5 54 稳定沉积物② 4000 2000 2.37 295.6 153.0 100 稳定沉积物③ 4450 2130 2.55 373.7 214.8 - 天然气水合物④ 4750 2330 2.29 431.4 373.7 0~40 -
[1] SLOAN JR E D, KOH C A. Clathrate hydrates of natural gases[M]. CRC press, 2007. [2] KVENVOLDEN K A. Potential effects of gas hydrate on human welfare[J]. Proceedings of the National Academy of Sciences, 1999, 96(7): 3420−3426. doi: 10.1073/pnas.96.7.3420 [3] MAKOGON Y F. Natural gas hydrates–A promising source of energy[J]. Journal of Natural Gas Science and Engineering, 2010, 2(1): 49−59. doi: 10.1016/j.jngse.2009.12.004 [4] 裴发根, 方慧, 杜炳锐, 等. 陆域冻土区天然气水合物勘探研究进展[J]. 物探化探计算技术, 2022,44(6): 751−763. doi: 10.3969/j.issn.1001-1749.2022.06.PEI F G, FANG H, DU B R, et al. Advances in exploration of natural gas hydrate in terrestrial permafrost areas of China[J]. Computing Techniques for Geophysical and Geochemical Exploration, 2022, 44(6): 751−763. (in Chinese). doi: 10.3969/j.issn.1001-1749.2022.06. [5] 黄朋, 潘桂棠, 王立全, 等. 青藏高原天然气水合物资源预测[J]. 地质通报, 2002,21(11): 794−798.HUANG P, PAN G T, WANG L Q, et al. Prospect evaluation of natural gas hydrate resources on the Qinghai-Tibeti plateau[J]. Geological Bulletin of China, 2002, 21(11): 794−798. (in Chinese). [6] 刘怀山, 韩晓丽. 西藏羌塘盆地天然气水合物地球物理特征识别与预测[J]. 西北地质, 2004, 37(4): 33-38.LIU H S, HAN X L. Geophysical recognition and prediction of natural gas hydrates in Qiangtang basin of Tibet[J], Northwestern Geology, 2004, 37(4): 33-38. [7] 赵省民, 邓坚, 李锦平, 等. 漠河多年冻土区天然气水合物的形成条件及成藏潜力研究[J]. 地质学报, 2011, 85(9): 1536-1550.ZHAO X M, DENG J, LI J P, et al. Gas hydrate formation and its accumulation potential in Mohe, permafrost area, China[J], Acta Geologica Sinica, 2011, 85(9): 1536-1550. [8] 祝有海, 张永勤, 文怀军, 等. 青海祁连山冻土区发现天然气水合物[J]. 地质学报, 2009, 83(11): 1762-1771.ZHU Y H, ZHANG Y Q, WEN H J, et al. Gas hydrates in the Qilian mountain permafrost, Qinghai, Northwest China[J], Acta Geologica Sinica, 2011, 85(09): 1536-1550. [9] 方慧, 孙忠军, 徐明才, 等. 冻土区天然气水合物勘查技术研究主要进展与成果[J]. 物探与化探, 2017,41(6): 991−997.FANG H, SUN Z J, XU M C, et al. Main achievements of gas hydrate exploration technology in permafrost regions of China[J]. Geophysical and Geochemical Exploration, 2017, 41(6): 991−997. (in Chinese). [10] 张旭东. 琼东南海域天然气水合物地震反射特征[J]. 物探与化探, 2014, 38(6): 1152-1158.ZHANG X D. The seismic reflection characteristics of gas hydrate in southeast Hainan sea area of the South China Sea[J], Geophysical and Geochemical Exploration, 2014, 38(6): 1152-1158. [11] LEE M W, COLLETT T S. In-situ gas hydrate hydrate saturation estimated from various well logs at the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope[J]. Marine and Petroleum Geology, 2011, 28(2): 439−449. doi: 10.1016/j.marpetgeo.2009.06.007 [12] 韩建光, 于常青, 张晓波, 等. 陆域冻土区天然气水合物多波地震数值模拟研究[J]. 地质学报, 2016, 90(9): 2502-2512.HAN J G, YU C Q, ZHANG X B, et al. Multiwave seismic numerical simulation study on terrestrial gas hydrate in permafrost area[J], Acta Geologica Sinica, 2016, 90(9): 2502-2512. [13] 罗登贵, 刘江平, 金聪, 等. 活断层的地震响应特征与瞬时地震属性[J]. 地球科学, 2017, 42(3): 462-470.LUO D G, LIU J P, JIN C, et al. Instantaneous seismic attributes and response characteristics of active faults[J], Earth Science, 2017, 42(3): 462-470. [14] HASTINGS F D, SCHNEIDER J B, BROSCHAT S L. Application of the perfectly matched layer (PML) absorbing boundary condition to elastic wave propagation[J]. The Journal of the Acoustical Society of America, 1996, 100(5): 3061−3069. doi: 10.1121/1.417118 [15] 祝有海, 张永勤, 文怀军, 等. 祁连山冻土区天然气水合物及其基本特征[J]. 地球学报, 2010, 31(1): 7-16+130.ZHU Y H, ZHANG Y Q, WEN H J, et al. Gas hydrates in the Qilin mountin permafrost and their basic characteristics[J], Acta Geoscientica Sinica, 2010, 31(1): 7-16, 130. [16] 徐明才, 刘建勋, 柴铭涛, 等. 青海木里地区天然气水合物反射地震试验研究[J]. 地质与勘探, 2012, 48(6): 1180-1187.XU M C, LIU J X, CHAI M T, et al. An experimental study of natural gas hydrates in the muli region, Qinghai Province by the seismic reflection method[J], Geology and Exploration, 2012, 48(6): 1180-1187. [17] 吕丽新, 陈永进, 张硕, 等. 冻土区天然气水合物基本特征及国内研究现状[J]. 资源与产业, 2012,14(5): 69−75. doi: 10.3969/j.issn.1673-2464.2012.05.013LV L X, CHEN Y J, ZHANG S, et al. Characteristics and research advances of natural gas hydrate in permafrosts[J]. Resources and Industries, 2012, 14(5): 69−75. (in Chinese). doi: 10.3969/j.issn.1673-2464.2012.05.013 [18] 刘杰, 刘江平, 程飞, 等. 青藏高原冻土区天然气水合物地层的岩石物理分析[J]. 地球物理学进展, 2017, 32(3): 1008-1018.LIU J, LIU J P, CHENG F, et al. Rock physics analysis of the hydrate bearing sediments in the permafrost region of Qinghai-Tibet plateau[J]. Progress in Geophysics, 2017, 32(3): 1008-1018. [19] ALTERMAN Z, KARAL JR F C. Propagation of elastic waves in layered media by finned difference methods[J]. Bulletin of Seismological Society of America, 1968, 58(1): 367−398. [20] 奚先, 姚姚. 二维粘弹性随机介质中的波场特征分析[J]. 地球物理学进展, 2004, 19(3): 608-615.XI X, YAO Y. The analysis of the wave field characteristics in 2D viscoelastic random medium[J], Progress in Geophysics, 2004, 19(3): 608-615. (in Chinese). [21] 李庆忠, 魏继东. 高密度地震采集中组合效应对高频截止频率的影响[J]. 石油地球物理勘探, 2007,42(4): 363−369. doi: 10.3321/j.issn:1000-7210.2007.04.002LI Q Z, WEI J D. Influence of array effect on cutoff frequency of high frequency in high-density seismic acquisition[J]. Oil Geophysical Prospecting, 2007, 42(4): 363−369. (in Chinese). doi: 10.3321/j.issn:1000-7210.2007.04.002 [22] 狄帮让, 裴正林, 夏吉庄, 等. 薄互层油藏模型黏弹性波方程正演模拟研究[J]. 石油地球物理勘探, 2009,44(5): 622−629,527,650. doi: 10.3321/j.issn:1000-7210.2009.05.020DI B R, PEI Z L, XIA J Z, et al. Forward simulation of viscoelastic wave equation n thin-interbedded reservoir model[J]. Oil Geophysical Prospecting, 2009, 44(5): 622−629,527,650. (in Chinese). doi: 10.3321/j.issn:1000-7210.2009.05.020 [23] TANER M T, KOEHLER F, SHERIFF R E. Complex seismic trace analysis[J]. Geophysics, 1979, 44(6): 1041−1063. doi: 10.1190/1.1440994 [24] 程乾生. 希尔伯特变换与信号的包络, 瞬时相位和瞬时频率[J]. 石油地球物理勘探, 1979,14(3): 1−14. [25] MATHENEY M P, NOWACK R L. Seismic attenuation values obtained from instantaneous-frequency matching and spectral ratios[J]. Geophysical Journal International, 1995, 123(1): 1−15. doi: 10.1111/j.1365-246X.1995.tb06658.x -