Danping Cao

Joint Inversion of 3D Seismic, VSP And Crosswell Seismic Data

Inversion of 3D seismic data is a strongly ill-posed problem. The inversion resolution is limited by the bandwidth of the seismic data used. A good choice to get accurate result is the joint inversion with all the available information. Based on the Bayesian theorem, the VSP and crosswell seismic data is injected into the inversion process according to the joint probability distribution. The joint inversion theory is built and the inversion stage is complete. Model test shows that the joint inversion method possessed the different frequency bandwidth information of VSP and crosswell data, the inversion result is more accurate and the resolution is higher. The joint inversion method of 3D seismic data, VSP and crosswell seismic data is feasible with different field data. The impedance inversion result is more reasonable and can match better with the logging data.

A computational method for full waveform inversion of crosswell seismic data using automatic differentiation

Abstract Full waveform inversion (FWI) is a model-based data-fitting technique that has been widely used to estimate model parameters in Geophysics. In this work, we propose an efficient computational approach to solve the FWI of crosswell seismic data. The FWI problem is mathematically formulated as a partial differential equation (PDE)-constrained optimization problem, which is numerically solved using a gradient-based optimization method. The efficiency and accuracy of FWI are mainly determined by the three main components: forward modeling, gradient calculation and model update which usually involves the gradient-based optimization algorithm. Given the large number of iterations needed by FWI, an accurate gradient is critical for the success of FWI, as it will not only speed up the convergence but also increase the accuracy of the solution. However computing the gradient still remains a challenging task even after the adjoint PDE has been derived. Automatic differentiation (AD) tools have been proved very effective in a variety of application areas including Geoscience. In this work we investigated the feasibility of integrating TAPENADE, a powerful AD tool into FWI, so that the FWI workflow is simplified to allow us to focus on the forward modeling and the model updating. In this paper we choose the limited-memory Broyden–Fletcher–Goldfarb–Shanno (L-BFGS) method due to its robustness and fast convergence. Numerical experiments have been conducted to demonstrate the effectiveness, efficiency and robustness of the new computational approach for FWI.

An Adjoint-Based Hybrid Computational Method for Crosswell Seismic Inversion

Waveform tomography, or full waveform inversion (FWI), is in general better than ray tomography; however, a reliable initial model is usually required to ensure success. Here, the authors designed a cascade-like hybrid tomography technology to solve the crosswell seismic inversion problem. The new method is a combination of several widely used tomography technologies, implemented in a sequence, where the cheaper method is used as the initial model feeder for the more expensive method. They start with the Radon-transform-based back-projection method; then the Linear Iterative Reconstruction method, such as selective internal radiation therapy, is adopted to update this initial model; which is further improved by the nonlinear, Gradient-based Eikonal Equation Tomography method. Finally, the velocity model reconstructed from the previous multiple ray tomography methods is used as the initial model for the FWI.

Impedance Inversion Method Constrained with Crosswell Seismic Data

Summary Impedance inversion of surface seismic data is an inherently non-unique problem. The conventional seismic inversion resolution is limited to characterize the subsurface reservoirs because of the narrow frequency bandwidth. The high frequency components of crosswell seismic data are rich enough to connect the surface seismic data and the logging curve. Based on the sparse spike inversion assumption, the crosswell seismic data is introduced into the surface seismic impedance inversion flow. The objective function of impedance inversion method is built constrained with the crosswell seismic data and well logging data. The field data inversion result shows that the crosswell seismic data constrained inversion method can improve the resolution of the conventional well-logging constrained inversion method. It is a new way to solve the geology problems with kinds of geophysical data.