低速带吸收补偿提高地震资料分辨率

地震波在近地表疏松介质中传播时，会产生强烈的吸收效应，降低了地震记录的分辨率。在大港油田进行了近地表吸收结构调查现场试验，尝试通过品质因子Q补偿消除低速带吸收对地震资料分辨率的影响。首先利用上行波微测井确定低速带的厚度和速度，再利用双井微测井观测和估算低速带的Q因子。具体步骤为：布设2口水平间隔为6 m的激发井和接收井，接收井井深3 m，与该地区低速带厚度相当，井口和井底分别埋置一个检波器。在激发井的16 m和20 m深度分别进行震源激发，在接收井的井口和井底接收直达波地震信号。利用谱比法对地震波的衰减进行了分析，在100~400 Hz频带范围内，地震衰减呈现明显的非线性特征，显示了Q对频率的依赖性。通过对衰减曲线进行非线性拟合，估算了频率依赖的Q因子，再采用反Q滤波消除了低速带吸收对地震数据分辨率的影响。

Enhancing seismic resolution via compensation for the weathering layer absorption

Seismic waves suffer from strong absorption when they travel through the weathering layer, which consequently decreases seismic resolution. We conducted a field experiment to compensate for the weathering layer absorption in Dagang oilfield of China. We first established the thickness and velocity of the weathering layer using uphole seismic survey, then measured its absorption using a cross-hole seismic survey. Two boreholes, separated by 6 m, were drilled, one for the sources, the other one for the receivers. The depth of the receiver hole was 3 m, equal to the thickness of the weathering layer. Two shots were fired under the weathering layer from the depths of 16 m and 20 m in the source hole, and the direct waves were recorded at the surface and the bottom of the weathering layer in the receiver hole. We analyzed the seismic attenuation via the log spectral ratio, and the nonlinear attenuation was well observed in the frequency band of 100 Hz to 400 Hz. We estimated the frequency dependent Q by nonlinearly fitting to seismic attenuation, and applied inverse Q filtering to remove the effect of the weathering layer absorption on seismic resolution.