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提出了一种2．5维井间地震透射波走时层析成像方法。考虑实际钻井轨迹的三维空间展布和井间地震射线对三维模型覆盖次数的严重不足,建立了2．5维井间速度模型。结合钻井、测井等获得的地层资料,把模型离散成2．5维水平梯形棱柱单元,每个单元慢度用其左右边界处的离散慢度值的线性函数表示。根据Fermat原理,提出了基于这种2．5维离散模型的三维射线追踪算法,并用预条件共轭梯度优化算法解层析反演问题。该方法适于井孔偏斜的情况,能很好地描述地层起伏和速度的变化,方便地使用先验信息进行建模和约束,提高了层析成像结果的可靠性和分辨率。对理论合成资料和实际采集资料皆取得了良好的应用效果。
A 2.5-D crosswell seismic transmission time-history tomography method is proposed. Considering the serious shortage of three-dimensional model and the three-dimensional space distribution of actual drilling trajectory and the cross-well seismic ray coverage, a 2.5-m crosswell velocity model was established. Combined with the formation data obtained by drilling and logging, the model is discretized into 2.5-D horizontal trapezoid prismatic units, and the slowness of each unit is expressed as a linear function of the discrete slowness values at the left and right boundaries. According to the Fermat principle, a three-dimensional ray tracing algorithm based on this 2.5-D discrete model is proposed, and the preconditioned conjugate gradient optimization algorithm is used to solve the inversed tomography inversion problem. This method is suitable for wellbore deflection and can well describe the variation of formation fluctuation and velocity. It is convenient to use the prior information for modeling and constraint, and improves the reliability and resolution of tomographic results. The theory of synthetic data and the actual data collected have achieved good results.