Assessing the Geomechanical Effects of CO2 Injection in a Depleted Gas Field in Poland by Field Scale Modelling

Orlic, B. (TNO, Earth, Environmental and Life Sciences) | Mazurowski, M. (Polish Oil & Gas Company) | Papiernik, B. (AGH University of Science &Technology) | Nagy, S. (AGH University of Science &Technology)



A field scale geomechanical model was developed in an early phase of the feasibility study considering geological CO2 storage in a depleted gas field in Poland. Geomechanical model of the gas field was adequate to evaluate the induced stress changes, the geomechanical effects on the top seal and induced surface deformation. The estimated geomechanical effects on the top seal are weak and do not pose a risk for the containment. The effects on the regional sub-vertical faults intersecting the reservoir are not expected to cause fault destabilization, except in the case of partial re-pressurization of non-connected neighbouring compartments. However, the reliability of fault stability assessment is low due to the lack of seismic data that would have made detailed mapping of faults at field scale possible. Our future work will include updating the existing model with a more detailed fault interpretation and dynamic reservoir simulation results when they become available.

1 Introduction

Gas extraction and CO2 injection into depleted hydrocarbon reservoirs will change the state of stress in the reservoir and the surrounding rock. As a result of induced stress changes natural fracture systems and faults can be reactivated, and new fractures formed. Open and connected fracture systems in the mechanically damaged seal pose the risk for loss of containment of injected CO2. Besides the effects on the containment, stress changes due to withdrawal and injection of fluids into the subsurface will induce deformation of the storage reservoir (compaction/expansion), surrounding rock (various deformation modes) and ground surface (subsidence/ uplift). Sudden slip on pre-existing faults can lead to induced micro-seismic and (felt) seismic events.

In this paper we describe a geomechanical modelling study carried out to evaluate the geomechanical effects associated with gas extraction and possible future CO2 injection in a depleted gas field in Poland. The study area is located in southwestern Poland on the Fore-Sudetic Monocline (Fig. 1). The two largest fields located in the study area are the Załeęcze and the Ouchlów gas fields. In this paper we report preliminary results of 3D field-scale geomechanical modelling of the Załęcze gas reservoir.