Guidelines for the study of subsidence triggered by hydrocarbon production

This study was carried out by the SEADOG Research Center at Politecnico di Torino (Italy). The purpose of this work was to evaluate which complexity degree would be required to reliably approach a subsidence study for different scenarios. The study was based on sensitivity analyses which were performed using a series of 3D synthetic numerical models of which the structural characteristics and geological and mechanical properties were based on available public data of onshore and offshore hydrocarbon fields in Italy. An array of simulations, both one-way and two-way coupled, were carried out to assess the magnitude and extension of subsidence potentially induced by hydrocarbon production. The results allowed the calculation of subsidence indices defined as the rate of compaction propagation (i.e., the ratio between the maximum surface displacement and the maximum reservoir compaction) and as the rate of volume loss (i.e. the ratio between the volume of the subsidence bowl or cone and the volume variation of the reservoir). These indices together with the degree of the underground systems’ heterogeneity led to the definition of the Intact Rock Qualitative Subsidence Index (IRQSI), upon which the needed complexity degree of a subsidence study can be discerned

Calculation of lithology-specific p-wave velocity relations from sonic well logs for the po-plain area and the northern adriatic sea

One of the most useful petrophysical parameters in hydrocarbon reservoir studies is the velocity of the seismic waves propagating in the Earth’s subsurface. Seismic velocities have multiple applications in geophysical exploration, well log interpretation and petrophysical and geomechanical characterization. In this study we used publicly available well data (VIDEPI database) covering the Po Plain and the northern Adriatic areas to calculate the P-wave sonic velocity from the analysis of well profiles (1:1000 scale). Data were collected from 134 wells located inside the region of interest that included sonic log registrations. From each of the wells the cuttings interpretation log, the available spontaneous potential or gamma ray logs and the sonic log were digitized from existing profiles whereas the hydrocarbon-bearing-marker (resistivity log readings) and the geological formation log were constructed. The lithological and the geological formation logs were used to analyse the regional stratigraphy while the resistivity log was used to identify and exclude the hydrocarbon bearing intervals affecting the sonic log readings. The various lithologies reported on the well profiles were combined to characterize 9 main lithological groups (6 clastic, 1 marly, 2 carbonatic). For each group a linear regression was applied to extract the relation of velocity versus depth. The results show a gradual velocity increase with depth for most of the lithologies, while limestones and dolomites present constant velocities independently of the depth. Furthermore, at approximately 3.5-4 km the velocities of all lithologies tend to stabilise at a value that remains relatively constant even for larger depths. The results of this study can prove helpful for the construction and calibration of velocity models and for the calculation of dynamic geomechanical parameters (e.g. Young’s modulus), which are crucial for the mechanical characterization of the rock during geomechanical studies

Combustion Instability Involving Vortex Shedding in Hybrid Rocket Motors

Hybrid rocket motors usually have an aft-mixing chamber in order to improve combustion efficiency. The presence of a sudden expansion at the exit of the fuel port determines the formation of vortices, whose vigourous burning may drive acoustic waves in the chamber. The shedding of vortices itself is then affected by the flow fluctuations, producing a well-known feedback loop. A reduced-order model, introduced by Matveev and Culick in 2003, is here used to analyze this phenomenon. It is assumed that vortex burning is localized in space and time, and a kicked oscillator model is utilized. A one-dimensional model proposed by the authors is used to determine the values of the eingenacoustic modes and corresponding damping coefficients. Numerical results are compared to experimental data

Integrated InSAR-GPS Monitoring of an Underground Gas Storage (UGS) Field: The Minerbio Pilot Test

In 2014 the Italian Oil & Gas Safety Authority published technical guidelines (Italian Guidelines for monitoring the seismicity, ground deformation and pore pressure) to regulate the monitoring of all existing and future underground activities on the Italian territory. The guidelines suggested that ground deformation monitoring of underground activities was carried out by integrating InSAR and continuous GPS techniques to detect possible surface deformation phenomena linked to the monitored activities during the considered time interval, and to provide information of their space-time variations with respect to the background conditions. The guidelines application on underground gas storage (UGS) was tested on the Minerbio gas field under the supervision of the National Institute of Geophysics and Volcanology (INGV). At the time of the pilot test, Minerbio had a high-quality record of about 15 years of InSAR data and 10 years of CGPS data (from the MINE station). The presented case study shows how the Minerbio ground deformation monitoring system was implemented during the testing phase. The time series of MINE, sited in 2008 in a peripheral area of the field, show that it measures seasonal oscillations in the North-planar component and a certain seasonality in the East-planar component: considering such results, the InSAR data were used to identify a proper site for a second CGPS station with the aim to integrate the results of MINE. The new station MIN2 was placed in 2019 in the center of the field, near the vertical and East-planar InSAR amplitude peaks. The correlation analysis between the CGPS signals and the cumulative curve of UGS volumes of the Minerbio field indicates a strong correlation in the North-planar component for the MINE station and a strong correlation in the East-planar and vertical components for the MIN2 station. According with ILG target, such results indicate that: (i) MIN2 effectively integrates the MINE results by detecting the peak of UGS-related, vertical and East-planar oscillations, (ii) the current geometric configuration of the two-station CGPS system effectively integrates the InSAR information by giving information on the spatial distribution of the North-planar component of ground deformation, and (iii) the integrated InSAR-CGPS monitoring system provides a complete picture of the distribution of UGS-related ground deformations on the Minerbio field

Defining the influence area of uplift and subsidence from underground gas storage in anticline structural traps: Insights from InSAR cross-correlation

We investigate the relationship between Underground Gas Storage (UGS) operations and ground deformation of three UGS fields in the Po Plain basin, Italy, hosted in Pliocene clastic deposits within anticline structural traps. Sentinel-1 InSAR data from 2015 to 2021 were analyzed to quantify seasonal uplift and subsidence patterns associated with the cyclic injection and withdrawal of gas. The methodology evaluates correlations between UGS activity and the seasonal amplitude of vertical displacement using cross-correlation parameters R and K, which measure the shape (R) and scale (K) similarity between vertical displacement time series and gas volume fluctuations. Results show that, with the UGS injection/withdrawal plan implemented until 2021, seasonal displacement peaks occur within gas field boundaries and diminish outward. Along the major axis of the anticline traps, UGS-related vertical displacements cease before reaching the field boundary, while transversally, they extend up to approximately 0.5 km beyond. Frequency distributions of seasonal amplitude, R and K values were used to define threshold values for R and K, enabling a quantitative identification of the effective UGS influence area, with GNSS data providing additional constraints. Our findings highlight the influence of structural trap geometry and bounding faults in shaping surface subsidence and uplift patterns. These findings underscore the need for advanced monitoring technologies and a comprehensive understanding of subsurface geology to an effective management of UGS operations. As global demand for gas storage increases, integrating geomechanical modeling with ground deformation monitoring will enhance risk assessment, ensure operational safety, and optimize gas storage strategies. The proposed methodology provides valuable insights for monitoring induced ground deformation, offering a framework for sustainable and effective UGS management