Webinar no 1

Generalized Geertsma solution and its application to pressure monitoring for CO2 storage

Presenter: Joonsang Park
Norwegian Geotechnical Institute (NGI), Oslo, Norway
Time: August 2021

Link to the webinar will become available here shortly.

The SENSE project investigates ground deformations that may occur as a result of pressure change in subsurface, and examines different solutions and technologies to measure such deformations.

The well-known, and commonly used Geertsma solution defines the relationship between pressure in the subsurface and ground deformation. However, the Geertsma solution solves for isotropic homogenous materials, while the realistic subsurface is more complex (Figure 1).

In the SENSE project, we have developed a generalized Geertsma solution in order to overcome such limitations in the Geertsma solution.

In this webinar, we will present the generalized Geertsma solution, and discuss its usefulness in the context of CO2 storage monitoring using ground surface deformation. Additionally, we will provide a brief review on Geertsma-type analytical solutions available in the literature. We will also demonstrate how to apply the generalized Geertsma solution to realistic geological models via solving an In-Salah-like model with utilizing the linear superposition theorem.

Figure 2. Schematic description of arbitrarily-distributed pressure anomaly. We assume that the pressure anomaly is discretized into J number of square-cuboid grids, to each of which a value of pressure pj is specified. The vertical displacement at a point (say uz,i) on the surface can be obtained by linearly summing up the contribution from all the pressure grids.
Figure 1. Vertically transverse isotropic (VTI) subsurface model consisting of N layers and subjected to fluid-induced constant pore pressure p(r, z) (darker-shaded) of radius R in an n-th layer. Note r, Vs, Vst, Vp, Vpt, and h are mass density, radial/horizontal and vertical S-wave velocities, radial/horizontal and vertical P-wave velocities, and layer thickness, respectively. Axisymmetric coordinates (r, z) are used and z-positive is upwards.

SENSE is a research project funded under the ERA-NET ACT program. Its primary objective is to demonstrate reliable, cost efficient CO2 storage monitoring using ground surface deformation detection combined with geomechanical modelling and inversion to provide information on pressure distribution and hydraulic behaviour of storage sites. For this purpose, it is crucial to apply an efficient solution to link surface deformation directly and accurately to the fluid pressure change and hydro-mechanical properties in the subsurface.