HR: 15:50h
AN: S34A-02 INVITED     [Abstracts]
TI: Fluid Induced Microseismicity: A Possible Triggering Mechanism And Analysis For Reservoir Characterization
AU: * Rothert, E
EM: rothert@geophysik.fu-berlin.de
AU: Shapiro, S A
EM: shapiro@geophysik.fu-berlin.de
AB: The attention to the microseismic monitoring during operation of geothermal or hydrocarbon reservoirs has grown considerably over the last several years. The observation of microseismicity occurring during borehole fluid injections or extractions has a large potential in characterizing reservoirs in terms of their hydraulic properties as far as several kilometers from boreholes. An approach for the interpretation of microseismic data was proposed to provide in-situ estimates of hydraulic diffusivity or permeability characterizing a geothermal or hydrocarbon reservoirs on the large spatial scale (of the order of 10³ m). We call this approach "Seismicity Based Reservoir Characterization" (SBRC). It considers microseismicity triggered by a pore pressure relaxation process at critically stressed locations in rocks. The approach uses a spatio-temporal analysis of fluid-injection induced microseismicity to reconstruct scalar values as well as the tensor of hydraulic diffusivity and to estimate the tensor of permeability for the seismically active volume. The method provides a possibility to invert for hydraulic diffusivity distributions in fluid-saturated rocks. Estimates of hydraulic diffusivity tensors on large spatial scales as well as imaging of its distributions in space resulting from this concept can be of significant importance for industrial applications and understanding of physical properties of geological structures.
Here we introduce the fundamental concepts for the interpretation of microseismic data and show numerical verifications of the method. We propose an approach for the numerical modeling of microseismicity. We focus on the verification of the SBRC inversion algorithms using synthetic data. The results of numerical modeling show that in spite of the apparent simplicity of this approach it reproduces significant features of microseismicity observed in reality. The structure and temporal evolution of microseismicity clouds depends on hydraulic properties of rocks as well as on the statistics and spatial distribution of their criticality. The inversion algorithms have been successfully validated. We consider this as an indication that our description of the main physical features of the triggering phenomenon are adequate. The pore pressure relaxation process seems to be an important mechanism for triggering microearthquakes in fluid-saturated rocks.
We also show the application of the SBRC approach to various data sets. Data examples of Hot Dry Rock experiments in crystalline rocks (Fenton Hill and Soultz sous Forˆts) are presented as well as the analysis of microseismicity obtained during fluid injections in sedimentary environment. We show that it seems to be promising to apply the diffusion-process-based approach even for hydraulic fracturing experiments.
DE: 0910 Data processing
DE: 5114 Permeability and porosity
DE: 5199 General or miscellaneous
SC: Seismology [S]
MN: 2005 Joint Assembly