7 research outputs found
The Role of Fault-Zone Architectural Elements on Pore Pressure Propagation and Induced Seismicity
We used hydrogeologic models to assess how faultâzone properties promote or inhibit the downward propagation of fluid overpressures from a basal reservoir injection well (150 m from fault zone, Q = 5000 m3/day) into the underlying crystalline basement rocks. We varied the permeability of the faultâzone architectural components and a crystalline basement weathered layer as part of a numerical sensitivity study. Realistic conduitâbarrier style fault zones effectively transmit elevated pore pressures associated with 4 years of continuous injection to depths of approximately 2.5 km within the crystalline basement while compartmentalizing fluid flow within the injection reservoir. The presence of a laterally continuous, relatively lowâpermeability altered/weathered basement horizon (kaltered layer = 0.1 Ă kbasement) can limit the penetration depth of the pressure front to approximately 500 m. On the other hand, the presence of a discontinuous altered/weathered horizon that partially confines the injection reservoir without blocking the fault fluid conduit promotes downward propagation of pressures. Permeability enhancement via hydromechanical failure was found to increase the depth of earlyâtime pressure front migration by a factor of 1.3 to 1.85. Dynamic permeability models may help explain seismicity at depths of greater than 10 km such as is observed within the Permian Basin, NM
Imaging shallow gas migration pathways in a mudâvolcano province using an autonomous underwater vehicle (Malta Plateau, Mediterranean Sea)
Data acquired by an autonomous underwater vehicle (AUV) towing a source (1600â3500 Hz) and a horizontal array of hydrophones have been analysed to image discrete, isolated or even a small cluster of scatterers within the sediment, to determine shallow migration paths of hydrocarbons in a mud volcano system of the Malta Plateau. An algorithm based on a semblance function was applied to the acoustic data to highlight scatterers rather than interface reflections. The resulting scatterer map, obtained along the AUV track, generated a pseudoâthreeâdimensional coverage of the study area, with a horizontal and vertical resolution of roughly 3â5 m and 5â10 m, respectively. This map was combined with highâresolution bathymetric and backscattering seafloor maps obtained from previous explorations. This integrated dataset provides new evidence for the role of fault zones as a preferential path for gas/fluid migration and reveals the intermittent activity of seeping gas. The data show, in particular, that gas bubble slugs, i.e. discontinuous gas columns, rise through PlioâQuaternary sediments along a complex system of conduits terminating at the surface into quiescent mud volcanoes. The gas flux is facilitated by the regional stress field that results in dilatant conditions on the mapped fault zones