Investigation of modeling permeable aquifers at the contact zones of basaltic lava flows
Author: Yonathan Hary Hutagalung
Year: 2024
Supervisors: Juliet Ann Newson
Abstract:
The contact zone between basaltic lava flows is often found to be a permeable zone in wells. In the field, these zones are observed to generally have an undulating surface. This research is the first step in an investigation into the effect of this geometry in production or injection scenario using numerical simulator AUTOUGH2. This study developed the modeling workflow and the scripts required to generate the models and plot the results graphically. Thus, actual numerical models were also developed which represent an initial approach to the question of how to investigate the effect of permeable zone geometry on the reservoir.
Model development started with a radial model, proceeds to a two-dimensional rectangular model where the output is compared to the radial model to validate whether it provides a reasonable result. Three dimensional models constructed both porous medium and fractured rock using the MINC module in TOUGH2 was used where the permeable aquifer is enclosed between less permeable rocks.
In the 3D model, the geometry of the permeable layer is different in each model. The aquifer has been designed as a regular grid of mountains and valleys where the peak height and distance between peaks differ for each model. Initially, drone mapping was intended to map exposed and relatively fresh lava surfaces (dating back 13 to 14 million years) for data on possible forms of these contact aquifers. However, due to harsh winter conditions these have been covered by snow and/or the wind has been too strong for the duration of the project. Hence, the aquifer geometry was generated by selecting a high permeability for appropriate blocks using TIM, which is a pre- and post-processor for TOUGH2.
This project has developed a workflow and built initial models which will guide further work investigating the geometry of common permeable zones in basalt. The response to injection from one central well for these models shows that it is possible to see the effects of permeable layer geometry. It appears that the geometry of the aquifer influences the injection pressure, in that greater amplitude and shorter wavelength is related to a decrease in injection pressure. However, one caveat is that the overall volume of the permeable layer was also increased. This was unavoidable due to the coarseness of the model grid and future work needs to take this into account. In addition, more fieldwork is required to produce a more realistic representation showing the possible geometry of the buried lava surfaces that form these permeable aquifers.