Some Aspects of Time-to-Depth Conversion for Depth Imaging
Authors: Sidorovskaia Natalia A. , Lockard Emmitt S. , Stafford Rod 
Published: October 2008

Time-to-depth conversion procedures are being used to enhance the structural signature of complex geological features on seismic sections. It is important to separate the effects that arise from actual geological structure from those created by a particular numerical algorithm used to build the depth/velocity model. The accuracy of the numerical model i influenced by the quantity of well control incorporated into the time-to-depth conversion procedure. The velocity models based on different amounts of information coming from seismic signal processing and well-control data are applied to the same dataset. The results are then compared to determine the effects of the mathematical interpolation and calibration procedures in the time-to-depth conversion. The improvement in accuracy of a particular numerical model by incorporating time-depth tables that have been synthetically generated from available well log data is discussed. The fast and effective workflow allows an geoscientist to produce depth-converted maps of large project areas quickly and easily. Some aspects of understanding a compromise between accuracy and computational costs using various depth conversion methods are discussed.

An increase in model accuracy by using more advanced but more computationally intensive depth conversion and velocity extraction techniques may play an important role in reducing prospect risk beneath complex geological structures, such as salt domes. The examples of accuracy increase fo complex geological structure imaging through implementing more advanced algorithms are present. The effectiveness of two workflows is compared for different geological scenarios. The depth model validation through available 3D ray tracing simulation is considered.

Introduction

Seismic data represent the temporal records of acoustic signal on a surface where a receiving system is mount. In the past, the processed seismic data were interpreted in time. Of course, the main goal of seismic exploration is to create the image of undersurface Earth layers in depth that gets really critical fo planning drilling projects. The depth converted seismic data also provide an enhancement of the structural signatures of complex geological structures. Modern seismic processing methods offer different solutions for accomplishing depth-conversion goals from vertical stretch techniques to prestack depth migration.1–5 A choice of depth-conversion workflow depends on many factors, including the required depthconversion accuracy, the quality and type of data available, deadlines, computer time constraints, the complexity of geological site and so on. In the paper we will consider different approaches for depth conversion. We will demonstrate an opportunity of increasing accuracy of the depth-conversion method by optimally incorporating well control and seismic data. We will also address the issues of depth model validation using 3-d ray tracing that helps an geoscientist to identify areas where a particular algorithm introduces unacceptable errors on the depth surfaces, so one should proceed towards using the more advanced velocit analysis technique and depth-conversion workflow to increase the model accuracy.