基于热弹性理论的天然气水合物和游离气饱和度估算
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摘要
目前大多通过双相介质理论的纵波速度来估计水合物和游离气的饱和度。含水合物的地层具有低导热和高纵波速度等特性,以热弹性理论为基础,建立天然气水合物和游离气饱和度与纵波速度之间的关系,就可以估算出天然气水合物和游离气的饱和度。首先给出了热弹性理论估算水合物和游离气饱和度的方法;然后利用ODP164航次实际地震资料估算了布莱克海台地区的水合物和游离气的饱和度。纵波速度通过约束宽带反演方法得到,天然气水合物和游离气饱和度的估算采用迭代正演模拟法。同时,对影响饱和度的因素进行了分析, 认为地层孔隙度是影响水合物和游离气饱和度的关键因素。对水合物而言,若假定的地层孔隙度比实际孔隙度高,则反演得到的饱和度就偏高;反之,饱和度偏低。对游离气来说,若假定的地层孔隙度比实际孔隙度高,则反演得到的饱和度就偏低;反之则偏高。
Compressional wave velocity based on Two-Phase theory is used to estimate gas hydrate and free gas saturation. However, the effects of thermodynamics properties are often ignored. The hydrated sediments have low heat conductivity and high compressional wave velocity compared to those of the surrounding unhydrated sediments. So gas hydrate saturation can be obtained from compressional wave velocity based on thermoelasticity. Interval velocities obtained with sonic log at Leg 164 sites and seismic data from broadband constrained inversion have been applied to quantify amounts of gas hydrate and free gas based on thermoelasticity. It is referred that porosity is the main factor to affects saturation directly. When porosity of sediment is higher than actual porosity, gas hydrate saturation obtained from velocity is also higher; while porosity of sediment is lower, its saturation obtained from velocity is also lower. However, free gas saturation is contrary to gas hydrate. When porosity of sediment is higher, free gas saturation is lower; while porosity of sediment is lower, its saturation is higher.
Compressional wave velocity based on Two-Phase theory is used to estimate gas hydrate and free gas saturation. However, the effects of thermodynamics properties are often ignored. The hydrated sediments have low heat conductivity and high compressional wave velocity compared to those of the surrounding unhydrated sediments. So gas hydrate saturation can be obtained from compressional wave velocity based on thermoelasticity. Interval velocities obtained with sonic log at Leg 164 sites and seismic data from broadband constrained inversion have been applied to quantify amounts of gas hydrate and free gas based on thermoelasticity. It is referred that porosity is the main factor to affects saturation directly. When porosity of sediment is higher than actual porosity, gas hydrate saturation obtained from velocity is also higher; while porosity of sediment is lower, its saturation obtained from velocity is also lower. However, free gas saturation is contrary to gas hydrate. When porosity of sediment is higher, free gas saturation is lower; while porosity of sediment is lower, its saturation is higher.
引文
1 Tinivella U. A method for estimating gas hydrate and free gas concentrations in marine sediments[J]. Bolle-ttino di Geofisica Teoricaed Applicata, 1999, 40 (1): 19-30
2 Domenico S N. Effect of brine-gas mixture on velocity in an unconsolidated sand reservoir [J]. Geophysics, 1976, 41(5):882-894
3 Lee M W, Hutchinson D R, Collet T S, et al. Seismic velocities for hydrate-bearing sediments using weighed equation[J]. Journal of Geophysical Research, 1996, 101(B9):20347-20358
4 Hyndman R D, Spence G D. A seismic study of methane hydrate marine bottom Simulating reflectors [J]. Journal of Geophysical Research, 1992, 97 (B5): 6 683-6 698
5 Katzman R, Holbrook W S, Paull C K. Combined vertical-incidence and wide-angle seismic study of a gas hydrate zone, Blake Ridge[J]. Journal of Geophysical Research, 1994, 99(B9):17 975-17 995
6 Minshull T A, Singh S C, Westbrook G K. Seismic velocity structure at a gas hydrate reflector, offshore western Colombia, from full waveform inversion [J]. Journal of Geophysical Research, 1994, 99 ( B3 ): 4 715-4 734
7 Carcione J M, Tinivella U. Bottom-simulating reflectors: seismic velocities and AVO effects[J]. Geophysics, 2000, 65(1):54-67
8 Tinivella U, Accaino F. Compressional velocity structure and Poisson's ratio in marine sediments with gas hydrate and free gas by inversion of reflected and refrac ted seismic data (South Shetland Islands, Antarctica) [J]. Marine Geology, 2000, 164 (1-2):13-27
9郭自强．固体中的波[M]．北京:地震出版社,1982． 194-230
10 Amos N．双相介质中波的传播[M]．许云译．北京:石 油工业出版社,1986．86-100
11 Keenan J H, Keyes F G, Hill P G,et al. Steam Ta bles[M]. New York: John Wiley, 1969. 128-140
12 Lu S M, Mc Mechan G A. Estimation of gas hydrate and free gas saturation, concentration, and distribution from seismic data[J]. Geophysics, 2002, 67(2): 582-593
13 Paull C K, Matsumoto R, Wallace P J, et al. Proceedings of the ocean drilling program[J]. Initial Report, College Station, TX(Ocean Drilling Program) , 1996. 1-318
14 Dvorkin J, Prasad M, Sakai A, et al. Elasticity of marine sediments [J]. Geophysical Research Letter, 1999, 26 (12):1 781-1 784
15 Hamilton E L. Variations of density and porosity with depth in deep-sea sediment[J]. Journal of Sedimentary Petrology, 1976, 46(2):280-300
16 Ecker C, Dvorkin J, Nur A. Estimating the amount of gas hydrate and free gas from marine seismic data[J]. Geophysics, 2000, 65 (2): 565-573
17 Lee M W, Hutchinson D R, Agena W F, et al. Seismic character of gas hydrates on the southeastern U S continental margin[J]. Marine Geophysical Research, 1994,16(1):163-184
18 Holbrook W S, Hoskins H, Wood W T,et al. Methane hydrate and free gas on the Blake Ridge from vertical seismic profiling[J]. Science, 1996, 273: 1 840-1 843
2 Domenico S N. Effect of brine-gas mixture on velocity in an unconsolidated sand reservoir [J]. Geophysics, 1976, 41(5):882-894
3 Lee M W, Hutchinson D R, Collet T S, et al. Seismic velocities for hydrate-bearing sediments using weighed equation[J]. Journal of Geophysical Research, 1996, 101(B9):20347-20358
4 Hyndman R D, Spence G D. A seismic study of methane hydrate marine bottom Simulating reflectors [J]. Journal of Geophysical Research, 1992, 97 (B5): 6 683-6 698
5 Katzman R, Holbrook W S, Paull C K. Combined vertical-incidence and wide-angle seismic study of a gas hydrate zone, Blake Ridge[J]. Journal of Geophysical Research, 1994, 99(B9):17 975-17 995
6 Minshull T A, Singh S C, Westbrook G K. Seismic velocity structure at a gas hydrate reflector, offshore western Colombia, from full waveform inversion [J]. Journal of Geophysical Research, 1994, 99 ( B3 ): 4 715-4 734
7 Carcione J M, Tinivella U. Bottom-simulating reflectors: seismic velocities and AVO effects[J]. Geophysics, 2000, 65(1):54-67
8 Tinivella U, Accaino F. Compressional velocity structure and Poisson's ratio in marine sediments with gas hydrate and free gas by inversion of reflected and refrac ted seismic data (South Shetland Islands, Antarctica) [J]. Marine Geology, 2000, 164 (1-2):13-27
9郭自强．固体中的波[M]．北京:地震出版社,1982． 194-230
10 Amos N．双相介质中波的传播[M]．许云译．北京:石 油工业出版社,1986．86-100
11 Keenan J H, Keyes F G, Hill P G,et al. Steam Ta bles[M]. New York: John Wiley, 1969. 128-140
12 Lu S M, Mc Mechan G A. Estimation of gas hydrate and free gas saturation, concentration, and distribution from seismic data[J]. Geophysics, 2002, 67(2): 582-593
13 Paull C K, Matsumoto R, Wallace P J, et al. Proceedings of the ocean drilling program[J]. Initial Report, College Station, TX(Ocean Drilling Program) , 1996. 1-318
14 Dvorkin J, Prasad M, Sakai A, et al. Elasticity of marine sediments [J]. Geophysical Research Letter, 1999, 26 (12):1 781-1 784
15 Hamilton E L. Variations of density and porosity with depth in deep-sea sediment[J]. Journal of Sedimentary Petrology, 1976, 46(2):280-300
16 Ecker C, Dvorkin J, Nur A. Estimating the amount of gas hydrate and free gas from marine seismic data[J]. Geophysics, 2000, 65 (2): 565-573
17 Lee M W, Hutchinson D R, Agena W F, et al. Seismic character of gas hydrates on the southeastern U S continental margin[J]. Marine Geophysical Research, 1994,16(1):163-184
18 Holbrook W S, Hoskins H, Wood W T,et al. Methane hydrate and free gas on the Blake Ridge from vertical seismic profiling[J]. Science, 1996, 273: 1 840-1 843
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