Development of an Evaluation Matrix of Geological Control Factors for Production-Induced Seismicity in North German Gas Fields

Production-induced seismicity occurs only in some gas fields in Northern Germany, not in the majority of the fields. Why this is the case will be investigated in DGMK project 825, which aims at a semi-quantitative analysis of the geological control factors for production-induced seismicity in North German carboniferous, rotliegend and permian gas fields.
Preliminary studies with numerical models suggest that a number of geological factors must interact for induced seismicity to occur. This working hypothesis will be tested by means of an evaluation matrix that surveys these parameters for each gas field and subsequently validated with geomechanical model calculations. It is expected that this data-driven analysis will result in a better understanding of the actual controlling factors and a process understanding-based explanation for the selective occurrence of production-induced seismicity in the North German gas reservoirs. The semi-quantitative approach is also seen as an important intermediate step towards detailed, geomechanical-numerical 3D modelling of individual reservoirs, which is currently limited by, among other things, uncertainties in parameterisation and in the characterisation of the initial stress state.

The findings from the above preliminary study will be applied to 20-25 carbon, rotliegend and permian gas fields in northern Germany. In particular, it will be investigated whether fields with production-induced seismicity actually have a combination of geological factors that, according to the modelling results, favours fault reactivation or whether missing seismicity correlates with an attenuating parameter combination.
For this purpose, a catalogue of possible control parameters will be compiled for each field in collaboration with the individual cooperation partners, such as the depth and thickness of the reservoir, the position of the fault, and pore pressure reduction. The results will be classified in a matrix with the anonymised field names and the respective parameter assessment by means of a ++/+/o/-/- - evaluation.
The results of the evaluation of the individual fields with regard to the control factors for the occurrence or absence of induced seismicity will be used in a second project phase to validate the geomechanical modelling concept, i.e. on the basis of 3D models with parameter variations in the strike of the fault it will be checked whether the parameter combination resulting from the evaluation matrix actually has an amplifying or attenuating effect on the reactivation potential of the fault or whether modifications of the modelling approach are required to improve its prognostic capability.

The research report was published