Short Courses and Conferences

# Second International Workshop on Induced Polarization in Near-Surface Geophysics

### October 31 - November 2, 2011

#### Call for Papers

Papers are being solicited for presentation at the Workshop. Submission deadline for abstracts is **September 19, 2011**.

Papers bearing on the following areas will be considered:

- Day 1 :: Session 1
*Chairs: Lee Slater/Andrew Binley*- Pore scale physics
- Influence of microstructure
- Theory and experiments

- Day 1 :: Session 2
*Chairs: Andre Revil/Konstantin Titov*- Pore scale physics
- Influence of the pore water and surface chemistry
- Theory and experiments

- Day 2 :: Session 3
*Chairs: Andrew Binley/Lee Slater*- Field scale measurements, observations, and theory

- Day 2 :: Session 4
*Chair: Andreas Kemna*- 1D to 4D tomography and data inversion

- Day 3 :: Session 5
*Chairs: Ken Williams and Estella Atekwana*- Influence of biological activity on low frequency electrical signals

- Day 3 :: Session 6
*Chair: Ernst Niederleithinger*- Latest developments in laboratory and field equipments

#### Instructions for Abstract Submission

Title, authors, 5 to 20 lines of abstract. Add the email address of the presenter. Underline the name of the presenter. Add the name of the session and your preference: oral communication/poster. Example:

Time-lapse 3D inversion of complex conductivity data using an active time constrained (ATC) approach

M. Karaoulis (1), A. Revil (1), A., D.D. Werkema (2), B. Minsley (3),

W.F. Woodruff (1), and A. Kemna (4)

(1) Colorado School of Mines, Dept. of Geophysics, Golden, CO, USA

(2) U.S. EPA, ORD, NERL, ESD, CMB, Las Vegas, Nevada, USA .

(3) USGS, Federal Center, Lakewood, 10, 80225-0046, CO.

(4) University of Bonn, Nussallee 8, 53115, Bonn, Germany.

E-mail of the contact: Karaoulis Marios [karaouli@geo.auth.gr]

Session 4. Preference: Oral

Complex conductivity (magnitude and phase) is measured using a network of electrodes located at the ground surface or in boreholes. This method yields important information related to the distribution of permeability and contaminants in the shallow subsurface. We propose a new time-lapse 3D modeling and inversion algorithm to image the evolution of complex conductivity distributions. We discretize the subsurface using hexahedronal cells. Each cell is assigned a complex resistivity or conductivity value. Using the finite-element approach, we model the in-phase and out-of-phase (quadrature) electrical potentials on the 3D grid, which are then transformed into apparent complex resistivity. Inhomogeneous Dirichlet boundary conditions are used at the boundary of the domain. The calculation of the Jacobian matrix is based on the adjoint technique. The aim of time-lapse inversion is to determine the change in the complex resistivity of each cell in the model as a function of time. Each model along the time axis is called a reference space model. This approach can be simplified into an inverse problem that seeks the optimum of several reference space models using the approximation that the material properties vary linearly in time between two subsequent reference models. Regularizations in both space domain and time domain effectively reduce inversion artifacts and improve the stability of the inversion problem. In addition, the use of the time-lapse equations allows the simultaneous inversion of data obtained at different times in just one inversion step (4D inversion). The new inversion algorithm is demonstrated on synthetic time-lapse data resulting from the simulation of a salt tracer test in an heterogeneous random material. If applied to multi-frequency time-lapse data, it will also allow determining the spatio-temporal evolution of complex conductivity characteristics, for instance in terms of Cole-Cole model parameters.

Abstracts must be submitted electronically as a computer file in Microsoft Word ".doc" format. Please point your Internet browser to:

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