Huseyin Denli

Multiparameter material model and source signature full waveform inversion

We present a time domain full wavefield inversion algorithm to perform the simultaneous inversion of all the source signatures and the multiple parameters representing the material model. The algorithm is based on the inexact Gauss-Newton method with an alternation strategy. To improve the computational efficiency, we use the simultaneous source encoding method presented by Krebs et al. (2009). The wave equation is discretized in space with the discontinuous Galerkin (DG) method and in time with Runge-Kutta (RK) time stepping. Two realistic inversion experiments illustrate the algorithmic performance.

Elastic-wave sensitivity analysis for seismic monitoring

Effective and reliable reservoir monitoring is critically important for optimizing oil/gas production and ensuring safe geological carbon sequestration. It requires an optimal seismic sensor deployment that uses a minimum number of sensors to record the most significant information resulting from reservoir property changes. The monitoring survey has typically been designed using conventional seismic-wavefield illumination analyses. However, seismic-wavefield illumination cannot alone yield an optimum seismic acquisition for effectively monitoring reservoir property changes. We introduce a new approach for designing optimal seismic monitoring surveys by analyzing sensitivities of elastic wavefields with respect to reservoir property changes. The method is based on differentiating the elastic-wave equation with respect to geophysical parameters. The resulting equations are solved using a finitedifference scheme. Numerical studies demonstrate that seismic survey designs based on elastic-wave sensitivity analysis can be very different than those based on elastic-wavefield illuminations under the same optimal criteria. Sensitivity analyses can also be used to investigate whether a VSP or a surface seismic survey is more effective for monitoring Por S-wave speed changes in a target region.

Introduction to PDE-Constrained Optimization in the Oil and Gas Industry

This article is an expanded version of a tutorial on applications of PDE-constrained optimization in the oil and gas industry that was given at the Frontiers in PDE-Constrained Optimization workshop. (The workshop was held at the Institute for Mathematics and its Applications June 6–10, 2016.) We begin with an overview of the oil and gas supply chain that highlights the importance of PDE-constrained optimization. Next, we take an in-depth look at two key applications: full-wavefield inversion and reservoir history matching. For each application, we introduce a PDE model, derive the gradient of the objective function using the adjoint-state method, and present simple numerical results. We conclude with a discussion of key challenges.

Full-Wavefield Inversion: An Extreme-Scale PDE-Constrained Optimization Problem

Full-wavefield inversion is a geophysical method aimed at estimating the mechanical properties of the earth subsurface. This parameter estimation problem is solved iteratively using optimization techniques aimed at minimizing some measure of misfit between computer-simulated data and real data measured in a seismic survey. This PDE-constrained optimization problem poses many challenges due to the extreme size of the surveys considered. Practical issues related to the physical fidelity and numerical accuracy of the forward problem are presented. Also, issues related to the inverse problem such as the limitations of the optimization methods employed, and the many heuristic strategies used to obtain a solution are discussed. The goal of this paper is to demonstrate some of the progress achieved over the last decades while highlighting the many areas where further investigation could bring this method to full technical maturity. It is our hope that this paper, together with other contributions in this book, will motivate a new generation of researchers to contribute to this broad and challenging research area.

Double-difference tomography of microseismic data for monitoring carbon sequestration

Summary More than 2000 microseismic events have been recorded since early 2008 using a cemented geophone string for monitoring CO2 injection at the Aneth oil field in Utah. The double-difference seismic tomography method has recently been developed for improving earthquake locations and imaging the seismic velocity structure. The method uses both the absolute and differential arrival times to invert the velocity distribution and the source locations simultaneously, leading to an improved precision for microseismic event location. We explore the use of doubledifference tomography for obtaining high-precision locations of microseismic events and improved resolution of velocity structure at the Aneth oil field.