大容量气枪震源子波激发特性分析
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摘要
大容量气枪水库激发作为陆地震源的可行性与有效性已经得到成功验证.为进一步提高气枪震源激发效果,本文通过水库气枪激发试验对单枪容量为2000 in~3的气枪震源激发子波特征及规律进行了研究.依据近场水听器和远场短周期地震仪记录数据,分析气枪震源沉放深度、工作压力等不同激发条件对压力脉冲和气泡脉冲的影响.有助于人们根据不同尺度地下结构探测对震源激发信号的要求,调整气枪激发参数和激发环境,获得最佳激发效果.试验结果表明:(1)沉放深度对压力脉冲波形影响较小,其优势频率不随沉放深度而改变;(2)随着沉放深度从5 m增加到11 m,气泡脉冲的优势频率由5 Hz增加至7 Hz,其最大振幅亦近线性递增;(3)工作压力越大,激发压力脉冲能量越强,而对气泡脉冲的影响主要体现在主频降低.适合远距离深穿透地下结构探测的低频信号主要来自大容量气枪所激发气泡的反复振荡,由于气枪振荡过程非常复杂,本文通过较为简洁的数学和物理模型进行了解释.
Large volume air-gun excited in a reservoir has been demonstrated successfully as an effective and feasible seismic source.In order to improve its efficiency further, the excitation characters of a 2000 in~3 air-gun were studied in a field experiment in a reservoir.Based on the records from near-field hydrophones and far-field seismographs, the dependence of the signature on the gun parameters including gun depth and firing pressure was analyzed.The results showed that;(1) pressure pulses were little affected by gun depth, its dominant frequency changed little with gun depth;(2) the dominant frequency of bubble pulses changed from 5Hz to 7Hz when the gun depth changed from 5m to 11m;(3) the energy of pressure pulses increased with firing pressure, but the dominant frequency of bubble pulses decreased.Low frequency signal fit for subsurface exploration in large scale is mainly created by the bubble oscillation, because of its complexity, a succinct Mathematical and Physical model was applied to explain the process.
Large volume air-gun excited in a reservoir has been demonstrated successfully as an effective and feasible seismic source.In order to improve its efficiency further, the excitation characters of a 2000 in~3 air-gun were studied in a field experiment in a reservoir.Based on the records from near-field hydrophones and far-field seismographs, the dependence of the signature on the gun parameters including gun depth and firing pressure was analyzed.The results showed that;(1) pressure pulses were little affected by gun depth, its dominant frequency changed little with gun depth;(2) the dominant frequency of bubble pulses changed from 5Hz to 7Hz when the gun depth changed from 5m to 11m;(3) the energy of pressure pulses increased with firing pressure, but the dominant frequency of bubble pulses decreased.Low frequency signal fit for subsurface exploration in large scale is mainly created by the bubble oscillation, because of its complexity, a succinct Mathematical and Physical model was applied to explain the process.
引文
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[12] Dragoset B. Introduction to air guns and air-gun arrays. The LeadingEdge, 2000, 19(8) : 892～897
[13] Mayne W H, Quay R G. Seismic signatures of large air guns. Geophysics, 1971, 36(6) : 1162～1173
[14] 丘学林,陈■,朱日祥等.大容量气枪震源在海陆联测中的应用:南海北部试验结果分析.科学通报,2007,52(4) :463～469Qiu X L, Chen Y, Zhu R X, et al. The application of large volume airgun sources to the onshore-offshore seismic surveys: Implication from the experimental results in northern South China Sea. Chinese Science Bulletin (in Chinese), 2007, 52(4) : 463～469
[15] 赵明辉,丘学林,夏少红等.大容量气枪震源及其波形特征.地球物理学报,2008,51(2) :558～565Zhao M H, Qiu X L, Xia S H, et al. Large volume air-gun sources and its seismic waveform characters. Chinese J. Geophys. (in Chinese), 2008, 51(2) : 558～565
[16] Ziolkowski A. A method for calculating the output pressure waveform from an air gun. Geophys. J. Roy. Astr. Soc., 1970, 21:137～161
[17] Ziolkowski A. Measurement of air-gun bubble oscillations.Geophysics, 1998, 63(6) : 2009～2024
[18] Johnson D T. Understanding air-gun bubble behavior. Geophysics, 1994, 59(11) : 1729～1734
[19] Keller J B, Kolodner I I. Damping of underwater explosion bubble oscillation. J. Applied Physics, 1956, 27(10) :1152～1161
[2] Lutter W J, Fuis G S, Thurber C H, et al. Tomographic images of the upper crust from the Los Angeles basin to the Mojave Desert, California: Results from the Los Angeles Region Seismic Experiment. Journal of Geophysical Research, 1999, 104(B11) : 25543～25565
[3] Okaya D, Henrys S, Stem T. Double-side onshore-offshore seismic imaging of a plate boundary: “super gathers” across South Island, New Zealand. Tectonophysics, 2002, 255: 247～263
[4] Stern T, Okaya D, Scherwath M. Structure and strength of a continental transform from onshore-offshore seismic profiling of South Island, New Zealand. Earth Planets & Space, 2002, 54:1011～1019
[5] Van Avendonk H J A, Holbrook W S, Okaya D, et al. Continental crust under compression: a seismic refraction study of South Island Geophysical Transect, South Island, New Zealand. J. Geophys. Res. , 2004, 109, B06302
[6] 赵明辉,丘学林,夏戡原等.南海东北部海陆联测地震数据处理及初步结果.热带海洋学报,2004,23(1) :58～63Zhao M H, Qiu X L, Xia K Y, et al. Onshore-offshore seismic data processing and preliminary results in NE South China Sea. Journal of Tropical Oceanography (in Chinese), 2004, 23(1) : 58～63
[7] 丘学林,陈■,朱日祥等.大容量气枪震源在海陆联测中的应用:南海北部试验结果分析.科学通报,2007,52(4) :463～469Qiu X L, Chen Y, Zhu R X, et al. The application of large volume airgun sources to the onshore-offshore seismic surveys: Implication from the experimental results in northern South China Sea. Chinese Science Bulletin (in Chinese), 2007, 52(4) : 463～469
[8] 陈■,张先康,丘学林等.陆地人工激发地震波的一种新方法.科学通报,2007,52:1317～1321Chen Y, Zhang X K, Qiu X L, et al. A new method to generate seismic wave on land. Chinese Science Bulletin (in Chinese), 2007, 52: 1317～1321
[9] Chen Y, Liu L B, Ge H K, et al. Using an airgun array in a land reservoir as the seismic source for seismotectonic studies in northern China: experiments and preliminary results. Geophysical Prospecting, 2008, 56 : 601～612
[10] 林建民,王宝善,葛洪魁等.大容量气枪震源特征及深部介质中传播的震相分析.地球物理学报,2008,51:206～212Lin J M, Wang B S, Ge H K, et al. Study on airgun source characteristics and seismic phase analysis. Chinese J. Geophys. (in Chinese), 2008, 51:206～212
[11] Langhammer J, Landro M. Tempreture effects on airgun signatures. Geophysical Prospecting, 1993, 41:737～750
[12] Dragoset B. Introduction to air guns and air-gun arrays. The LeadingEdge, 2000, 19(8) : 892～897
[13] Mayne W H, Quay R G. Seismic signatures of large air guns. Geophysics, 1971, 36(6) : 1162～1173
[14] 丘学林,陈■,朱日祥等.大容量气枪震源在海陆联测中的应用:南海北部试验结果分析.科学通报,2007,52(4) :463～469Qiu X L, Chen Y, Zhu R X, et al. The application of large volume airgun sources to the onshore-offshore seismic surveys: Implication from the experimental results in northern South China Sea. Chinese Science Bulletin (in Chinese), 2007, 52(4) : 463～469
[15] 赵明辉,丘学林,夏少红等.大容量气枪震源及其波形特征.地球物理学报,2008,51(2) :558～565Zhao M H, Qiu X L, Xia S H, et al. Large volume air-gun sources and its seismic waveform characters. Chinese J. Geophys. (in Chinese), 2008, 51(2) : 558～565
[16] Ziolkowski A. A method for calculating the output pressure waveform from an air gun. Geophys. J. Roy. Astr. Soc., 1970, 21:137～161
[17] Ziolkowski A. Measurement of air-gun bubble oscillations.Geophysics, 1998, 63(6) : 2009～2024
[18] Johnson D T. Understanding air-gun bubble behavior. Geophysics, 1994, 59(11) : 1729～1734
[19] Keller J B, Kolodner I I. Damping of underwater explosion bubble oscillation. J. Applied Physics, 1956, 27(10) :1152～1161
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