Geomechanics of Geological CO2 Storage and Underground Natural Gas Storage

Zeit:	14. Juni 2012
Referent*in:	Dr. Bogdan Orlic TNO, Geological Survey of the Netherlands
Veranstaltungsort:	Pfaffenwaldring 61, Raum U1.003 (MML), Universität Stuttgart
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CO2 injection into depleted hydrocarbon reservoirs and saline aquifers, or Underground Gas Storage (UGS), will change the state of stress in a reservoir-seal system due to poro-mechanical, thermal and possibly chemical effects. As a result of induced stress changes top seals can be mechanically damaged, pre-existing sealing faults and fractures can be re-activated, or new fracture systems can be created, allowing fluid migration out of the storage complex. Besides the effects on the containment, CO2 injection could also induce ground movement, which can be either aseismic - in the form of ground surface uplift, or (micro-)seismic - caused by a sudden slip on pre-existing discontinuities or faults.

Geomechanical studies are conducted to investigate the feasibility of candidate sites for geological CO2 storage and to define operational guidelines for safe CO2 injection. TNO has been involved in all feasibility studies of geological CO2 storage in depleted gas fields and aquifers in the Netherlands as well as in the many feasibility studies and actual demonstration and industrial-scale CO2 injection projects abroad (e.g. CO2 storage in the Utsira formation in the Norwegian sector of the North Sea, Snohvit in the Barents Sea and the In Salah CO2 storage project in Algeria).

The objective of geomechanical studies is to evaluate the impact of induced stress changes, resulting from past hydrocarbon extraction and future CO2 injection, or cyclic injection and extraction of natural gas, on the reservoir rock, top seals and faults. This is typically achieved by assessing: (i) The mechanical integrity and the potential for induced hydro-fracturing of the reservoir rock and top seals; (ii) The mechanical integrity and the potential for re-activation of faults, as fault slip can make previously sealing faults conductive and induce seismic events at the injection site; (iii) The induced ground/seabed deformation.

A workflow for assessment of the geomechanical effects of CO2 injection and storage was developed and refined through conducting several feasibility studies. Examples from different studies of CO2 storage in depleted hydrocarbon reservoirs, and natural gas storage, will be used to illustrate the use of workflow in evaluating the geomechanical impact of depletion and injection.