羌塘盆地托拉木-笙根地区地震采集技术试验

Acquisition technique test of seismic survey in Tuolamu-Shenggen region,Qiangtang Basin

由于地下构造复杂,表层结构变化剧烈,羌塘盆地一直未能获得令人满意的二维地震资料.从提高资料信噪比入手,近几年在羌塘盆地开展了532 km二维地震采集技术攻关试验：①运用小折射、微测井和地质雷达等技术进行精细表层结构调查,确保在潜水面、高速层或冻土层之下激发;②运用盒子波技术进行干扰波调查,准确获取各种干扰波的速度、传播方向、相对能量、频率、波长及信噪比等信息;③开展了不同井深、不同炸药药量、不同覆盖次数、不同检波器组合图型以及单井与组合井等的对比试验,确定最佳激发/接收参数;④进行“两炮两线”和“三炮三线”的宽线剖面试验,提高覆盖次数,压制干扰波,提高资料信噪比.试验结果证明：单井激发（18 m以上井深）、16～20 kg炸药药量、50 m以下道距、240次覆盖、“X”型检波器组合图型为最佳激发/接收参数,而“两炮两线”（240次覆盖）宽线剖面在羌塘盆地获得了当前质量最好的地震剖面.

The satisfactory 2Dseismic data cannot be obtained in Qiangtang Basin since that the structure is complicated,the surface and near surface lithology and structure varies roughly and dramatical-ly.In order to improve the S/N of the seismic data,a series of tests along seismic profiles with 532km long have been conducted recently:①the surface and near surface structure is investigated precisely by means of LVL refraction,uphole surveys and ground penetrating radar,so as to make sure the shooting location must be below the water table,or high velocity layer,or frozen ground layer; ②by means of box wave technique,the data of velocity,propagation direction,frequency,wavelength,relative energy of noise and S/N of raw records can be precisely obtained;③in order to determine the optimum shooting and receiving parameters,the comparative tests of different hole depth,charge size,trace group interval,fold, and geophone array map as well as comparison between single-hole shooting and array shooting have been conducted;④'two shots and two lines receiving'and'three shots and three lines receiving' wide line profiling survey tests have been taken on the purpose of increasing folds and S/N and suppressing interference.Testing results indicate that single-hole with depth of 18 mor above,16~ 20kg charge sizes,trace group interval of under 50 m,240 folds wide line profiling and'X'type geophone array map are the optimum shooting and receiving parameters suitable for the characteristics of Qiangtang Basin.Meanwhile,the quality of 2Dseismic profiles obtained by'two shots and two lines receiving'is superior to other profiles.