井控与构造约束条件下的网格层析速度建模技术及应用

地震勘探的关键是速度分析,常用的叠前深度偏移速度建模技术为网格层析反演,但当研究区断层较为发育时,网格层析跨越断层进行,速度更新导致断层两侧速度描述不准确,从而产生断层阴影构造假象,对解释及井位部署产生影响。为此,从井震标定和精细构造解释入手,首先建立测井速度与地震层速度的关系,根据层位标定结果在时间域利用VSP速度及测井速度校正沿层层速度;然后将校正后的时间域层速度变换到深度域,将得到的结果作为叠前深度偏移的初始速度;再采用层控、断控高精度网格层析技术进行速度建模,利用深度域解释的层位和断层控制断层两侧速度的准确性;最后采用小网格层析技术提高垂向速度分析的精度,对断层两侧速度进行准确刻画。实际资料处理结果表明利用井控与构造约束条件下的网格层析速度建模技术建立的速度模型符合实际情况,叠前深度偏移结果可以较好地消除断层引起的下部构造假象。

Seismic wave velocity modelling through grid tomography inversion constrained by well logging and structural modeling

Seismic velocity analysis is important for geophysical exploration.Grid tomography inversion is a common technique to estimate the velocity of seismic waves in geological formations.If faults are abundant in the domain under investigation,and the tomography is carried out in a direction transverse to the faults,the seismic wave velocity on the two sides of the faults cannot be described with sufficient accuracy.This phenomenon is known as“fault shadowing”and can have a great impact on the interpretation,and ultimately on the locations chosen for well deployment.In this work,on the basis of seismic calibration of well logs and fine-structure interpretation,a relationship between well logging velocity and seismic interval velocity was established.Accordingly,VSP and logging velocities were used to correct the estimated velocities along the horizon in the time domain.Then,these velocities in the time domain were transformed into depth domain information,so as to serve as the initial velocity field in the pre-stack depth migration.Subsequently,high-precision grid tomography—entailing formation-controlled and fault-controlled techniques—was carried out to obtain the velocity.The information on the faults and that on the horizons obtained in the depth domain were used to invert the velocities on both sides of the faults.Meanwhile,the small-grid tomography technique was also used to improve the vertical accuracy of the velocity field.By this technique,the velocity on both sides of the faults could be accurately described.Results obtained by processing actual data showed that the velocity model obtained by the aforementioned technique was accurate,and the pre-stack depth migration can eliminate the fault shadowing phenomenon effectively.