On-Site Hydraulic Characterization Tests

Abstract

Deep saline aquifers are target for carbon sequestration since these geological structures abound in many areas worldwide. Hydraulic characterization tests are focused on site feasibility assessment to inject CO2 in an efficient and safely manner. For this, it is necessary to carry out both laboratory and field tests to determine hydraulic properties and operating parameters such as permeability and injectivity in the reservoir, and the trapping degree of the structural complex. CO2 injection experiences usually come from projects conducted in aquifers composed by sandstones and similar rocks, unlike those carried out in carbonates that are quite limited. Sometimes carbonates are porous mediums, but in other cases, primary permeability is really poor being the fluid transmissivity mainly through the fracture network. Moreover, geochemical reactivity produced by the acidification of the mixture of CO2 and resident brine plays a key role in these cases. This chapter address the innovative on-site hydraulic characterization tests conducted in the deep saline aquifer of Hontomin Technology Development Plant (Spain), which is composed of naturally fractured carbonates with low primary permeability. The impacts of artificial brine and CO2 migration through the fracture network are described, analyzed and discussed, considering that produces hydrodynamic, mechanical and geochemical effects different from those caused by the injection in mediums with a high matrix permeability.