Gas chimneys are one of the most intriguing manifestations of the focused fluid flows in sedimentary basins. To predict natural and human-induced fluid leakage, it is essential to understand the mechanism of how fluid flow localizes into conductive chimneys and the chimney dynamics. This work predicts conditions and parameters for chimney formation in two fields in the SW Barents Sea, the Tornerose field and the Snøhvit field in the Hammerfest Basin. The work is based on two types of models, basin modeling and hydro-mechanical modeling of chimney formation. Multi-layer basin models were used to produce the initial conditions for the hydro-mechanical modeling of the relatively fast chimneys propagation process. Using hydro-mechanical models, we determined the thermal, structural, and petrophysical features of the gas chimney formation for the Tornerose field and the Snøhvit field. Our hydro-mechanical model treats the propagation of chimneys through lithological boundaries with strong contrasts. The model reproduces chimneys identified by seismic imaging without pre-defining their locations or geometry. The chimney locations were determined by the steepness of the interface between the reservoir and the caprock, the reservoir thickness, and the compaction length of the strata. We demonstrate that chimneys are highly-permeable leakage pathways. The width and propagation speed of a single chimney strongly depends on the viscosity and permeability of the rock. For the chimneys of the Snøhvit field, the predicted time of formation is about 13 to 40 years for an about 2 km high chimney.

Key Words: numerical modelling, elasto-plastic analytical solutions, shear bands, geomechanics. The correct analysis of wellbore stability in unconventional reservoirs receives much interest from the industry as shale rock and tar sands demonstrate perceptible plastic behavior which influences the estimation of rock failure. To tackle this problem the 3D finite element code has been developed for computing the stress-strain state in the elastoplastic medium near a borehole. The accuracy of the results, obtained due to the application of the finite element technique, can be affected by various numerical effects. Since the theory of plasticity assumes infinitesimal load increments, errors associated with finite increments are almost inevitable. The accuracy of the numerical solution can be verified by comparing the numerical results with the analytical solutions. Elasto-plastic analytical solutions [1], [2] stand out among others because they are the only ones among many others, mentioned in the cited monographs, that consider analytical solutions under conditions of non-hydrostatic loading. In this study, the numerical and analytical solutions were verified and relative errors were calculated for different loading paths. It turned out, for example, that Galin’s analytical solution works well not only in the field of its applicability, but also outside of it, despite different errors. This work discusses questions related to the influence of the increment of the applied load on the structure of a stationary elasto-plastic solution, including in the case of the formation of zones of localized plastic deformation. The issue of the appearance of shear bands zones is also considered: these bands develop directly around the hole under certain boundary conditions or gradually grow out of the zones of elliptical plastic deformation. The first, third and fifth authors acknowledge support of research by Geosteering technologies company within the scope of Geonaft project sponsored by Skolkovo foundation, Russia. The second and fourth authors acknowledge support of research by Government of Russian Federation under grant 2019-220-07-9139. REFERENCES [1] Detournay, E. (1986). An approximate statical solution of the elastoplastic interface for the problem of Galin with a cohesive-frictional material. International Journal of Solids and Structures, 22(12), 1435–1454. [2] Galin, L.A. (1946). Plane elastoplastic problem. Applied Mathematics and Mechanics, 10 (3), 365–386.

Microseismicity and acoustic emission (AE) studies are a part of earthquake science. Compared to ordinary earthquakes, microseismic events are characterized by higher frequencies, lower magnitudes, shorter duration, and more complex source mechanisms. The researchers associate the induced seismicity with different processes: borehole breakouts, tunnel excavations, hydraulic fracturing, wastewater injection, and stimulation of geothermal reservoirs.Acoustic emission represents elastic waves generated spontaneously due to the formation of microfractures when the rock is undergoing a sufficiently high load. AE can be used to obtain continuous data at various stages of the deformation process: from distributed plastic failure to localized macroscopic failure. The spatial distribution of AE events indicates the location of fractures, and the source mechanism provides information about the failure mode: a tensile fracture, a shear fracture, or a combination of both.This work shows the results of an experimental study of borehole breakouts in sandstones. We measured AE during the deformation experiments and applied the moment tensor analysis to microseismic waveforms. We used a continuum mechanics model of Minakov and Yarushina [2021] to relate the laboratory AE data to the deformation processes. The comparison of the failure patterns and corresponding seismic responses obtained in laboratory and simulations, allows to classify the deformation regimes in real rocks based on seismic observables.EG, MB, SS, and VS gratefully acknowledge support from the Ministry of Science and Higher Education of the Russian Federation under agreement No. 075-15-2020-119 within the framework of the development program for a world-class Research Center. References:Minakov, A., Yarushina, V., Elastoplastic source model for microseismicity and acoustic emission, Geophysical Journal International, Volume 227, Issue 1, October 2021, Pages 33–53, https://doi.org/10.1093/gji/ggab207