涠西探区井-震速度误差分析和速度模型建立及应用

Well-seismic Velocity Error Analysis and Velocity Model Establishment and Application in Weixi Exploration Area

在地震勘探的井位论证中钻前准确地预测速度是一项至关重要的工作。获取地层速度的方式有不同的方法 :井孔速度、地震密点速度(预探井附近多个位置处理速度谱上拾取的叠加速度)。一般情况下会用预探井位附近的地震密点速度来求取时深关系用于钻前预测,而在涠西探区复杂断块的应用中发现地震密点速度要比井孔VSP速度偏大导致预测深度偏深,也就是说预测的误差会更大。不能使用地震密点速度进行钻前预测。为此由已钻井VSP速度和层位约束建立三维速度模型,从速度模型中提取预探井点速度来开展时深转换。而实际钻井表明:对于涠西探区复杂断块构造,用速度模型提取的井速度比预探井点处地震密点速度更接近实际钻井速度,预测误差在允许范围内。针对地质地震特点复杂地区要使用适合该地区的速度进行预测,尽可能减少预测误差,降低勘探风险。

It is very important to predict the velocity accurately before drilling in the well location demonstration of seismic exploration.There are different ways to get formation velocity:borehole velocity,seismic dense point velocity(the stack velocity picked up from velocity spectrum processed at multiple locations near the pre-exploration well.In general,the time-depth relationship can be obtained by using the seismic dense point velocity near the pre-exploration well location for pre-drilling prediction.However,in the application of complex fault block in Weixi exploration area,it is found that the seismic density point velocity is greater than the wellbore VSP velocity,which leads to a greater prediction depth,which means the prediction error will be larger.It is not possible to use seismic dense point velocity for predrilling prediction.For this reason,a 3D velocity model is established based on VSP velocity and horizon constraints,and the velocity of pre-exploration well point is extracted from the velocity model to carry out time-depth conversion.The actual drilling shows that for the complex fault block structure in Weixi exploration area,the well velocity extracted by model is closer to that of actual drilling,and the prediction error is within the allowable range.For areas with complex geological and seismic characteristics,the velocity suitable for the area should be used for prediction,so as to minimize the prediction error and reduce the exploration risk.