摘要
由于地质构造复杂,表层结构变化剧烈,羌塘盆地一直未能获得令人满意的高信噪比二维地震资料.因此,采用可控震源和井炮激发在北羌塘凹陷与中央隆起带之间的托纳木—笙根地区开展了420 km的高密度高覆盖宽线地震采集试验.可控震源激发参数:振动台次3台1次、扫描频率6~84 Hz、驱动幅度70%、扫描长度18 s.井炮激发参数:单井高速层下7 m激发,最浅井深18 m,药量18 kg;组合方式激发为2口井×15 m×12 kg或3口井×12 m×8 kg.2串检波器沿测线线性图形为最佳接收因素.井炮激发的覆盖次数介于360~960次之间,观测系统为4L3S、3L3S和2S3L;可控震源激发的覆盖次数介于960~1920次之间,观测系统为4L3S、3L3S和2S3L;炮间距介于30~120 m之间.试验结果:(1)采用井炮和可控震源激发的"高密度-高覆盖-宽线"采集技术,首次在羌塘盆地托纳木—笙根地区获得了一批质量优良的、可用于地质构造解释的地震剖面;(2)尽管可控震源单炮记录无法与井炮相比,但其高密度高覆盖采集技术能获得质量优于或等同于井炮的地震资料;(3)羌塘盆地托纳木—笙根地区适合于采用可控震源和井炮联合的宽线采集方案,可控震源覆盖次数1000次左右,井炮覆盖次数360次左右,观测系统3S3L或者2S3L即可.
The satisfactory high signal-noise ratio 2D seismic data could not be acquired in Qiangtang basin because that the geological structure is complicated,the surface and near-surface lithology and structure varies roughly and dramatically. So a series of high density,high fold and wide line profiling tests excited by vibroseis and explosive source along seismic profile with 420 kilometers long have been conducted recently in Tuonamu region,which located from north Qiang Tang depression to central uplift belts. The optimum exciting condition of explosive source is that shot position is at 7 meters below high speed layer in single-hole with 18 meters or above depths,18 kilogram charge sizes,or multiple shot with two holes( each hole is 15-meters depth) and 12 kilogram charge sizes,or three holes( each hole is 12 meters depth) and 8 kilogram charge sizes. Two geophone strings arranged inline direction with liner type is the optimum receiving parameters suitable for the feature of Qiangtang basin. The optimum exciting parameter of general vibroseis is as follows: the vibration pattern is of three vibroseises vibrating for one time,sweep frequency ranges from 6 Hz to 84 Hz,drive level is 70%,sweep length is 18 s. The layout chart with borehole explosive shot designed as 4L3 S or 3L3 S or 3L2 S,and its fold ranging from 360 to 960 times. The layout chart with vibroseis shot arranged as 4L3 S or 3L3 S or 3L2 S,and its fold ranging from960 to 1920 times. The shot point interval range from 30 to 120 meters. The following conclusion can be drawn from test:( 1) A number of good quality seismic sections that can be used for geological structure interpretation are acquired in Tuonamu region of Qiang Tang basin for the first time.( 2) Although shot record of vibroseis is not as good as that of borehole explosive,by using high density and high fold acquisition technique,the quality of sections obtained by vibroseis maybe equal to or superior to that of borehole explosive.( 3) The wide line profiling acquisition technique with a combination of vibroseis and borehole explosive shot is much more suitable to Tuonamu region of Qiang Tang basin,both layout chart of vibroseis and borehole explosive shot can be arranged as 3S3 L or2S3L,with a maximum fold of 1000 times and 360 times at each CMP relatively.
引文
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