Gas-saturated Rocks Research Articles

A squirt-flow model in isotropic porous rocks containing wedge-shaped cracks and its interpretation for laboratory measurements

We present an analytic model of wedge-shaped crack connected with stiff pore space for wave dispersion and attenuation in isotropic porous rocks using the wave-induced fluid flow (WIFF) mechanism. This model addresses squirt flow, a significant factor influencing wave propagation behavior across seismic, sonic, and even ultrasonic frequencies. Our model bridges the gap between existing models, demonstrating consistency with Gassmann’s model at low frequencies and Mavko-Jizba’s model at high frequencies. Employing a hybrid-dimensional approach, we derive a simple formula for the modified fluid modulus to enable calculation of elastic moduli for saturated rocks. The model predicts dispersion and attenuation behaviors at low, intermediate and high frequencies, and accounts for differences in liquid- and gas-saturated rocks. Comparisons with existing disk-shaped models and laboratory measurements showcase the potential advantage of wedge-shaped model for describing seismic dispersion. Validation is achieved through good agreement with published measurements of four rock samples. This model can readily integrate with classic WIFF theories, like Biot’s poroelasticity, extending its applicability across a broader frequency range.

THE ORIGIN OF ICE MOUNDS NEAR THE ERKATA-YAKHA RIVER, YAMAL PENINSULA, FROM THE RELATIONSHIP BETWEEN δD AND δ18О ISOTOPE RATIOS

Ice mounds are widespread cryogenic landforms that occur during freezing of water-saturated sediments and in ice segregation or ice injection with the formation of ice cores. Complex mechanisms of occurrence of these landforms have their own characteristics depending on the type of enclosing sediments, water and gas saturation, freezing rate, and other factors. Ice formation processes are often accompanied by explosions of the central part with the occurrence of negative landforms. In response to the widespread occurrence of perennially frozen gas-saturated rocks, these processes are accompanied by gas emissions, gas inflammation. and other, less intense gas shows. It is quite difficult in these conditions to determine the causes of the catastrophic phenomenon, to reconstruct the dynamics of the process, and to understand the role of gas-saturated fluids. In this paper, an attempt has been made to determine the ice formation conditions using isotopic techniques. The isotopic composition of ice can reflect the conditions of ice formation at the time of occurrence of ice mounds and its related possibility of participation of gas-saturated fluids from deep-lying gas-bearing horizons [Buddo et al., 2023, 2024]. The composition of stable isotopes δD and δ18O was determined for three ice mounds in the south of the Yamal Peninsula, where there were catastrophic explosions of ice mounds with the formation of large craters. The results of the study made it possible to reconstruct the conditions of ice mound occurrence and to determine different ice formation modes.

Tortuosity of pore channels in tight rocks as a key parameter in fluid flow ability

Tortuosity is a significant parameter in porous materials analysis. Not only, when it comes to rocks or soils but also cellular materials, alloys or cells, the multiple definitions exist for tortuosity and several purposes. Geometrical tortuosity describes the pore network paths; on the other hand thermal, diffusional, electrical and hydraulic tortuosity refers to the transport processes in the pore network. Computed X-ray tomography (CT) is the best solution in tortuosity estimation, thanks to the 3D images. In particular, computed X-ray tomography, together with mercury porosimetry (MICP), pulse- and pressure-decay permeability methods (PDP), as well as electrical parameter measurements (EPM), links and expands the information about the tortuosity into the greater meaning. The geological material was composed of tight, low-porosity and low-permeability gas-saturated rocks cored from the present depth of deposition below 3000 m, containing different lithologies, as sandstones, mudstones, limestones, and dolomites. The research presents the novel approach in the identification and analysis of the main pore channels based on 3D CT images. Algorithm of the central axis identifies and analyzes the whole main flow path and calculates tortuosity. High correlation was observed between the tortuosity and Swanson parameter from mercury porosimetry data. Moreover, the high correlation was detected between the tortuosity and saturation exponent from electrical parameter measurement in analyzed tight low-porosity and low-permeability deposits. Multilinear regression (MLR) allows estimating absolute permeability taking CT, MICP and EPM parameters into consideration. Combination of these parameters in one equation with high determination coefficient gives credence in estimating preliminary absolute permeability (PDP) based on the data which is executed as standard core analysis (MICP and EPM) and data from the non-invasive method (CT).

Simplified scaling relations for the depth-dependence and IFT reduction of fluid imbibition in gas-saturated reservoir rocks

Imbibition of water into fractured unconventional reservoirs is a significant factor contributing to the large volumes of permanently lost water by hydraulic fracturing. The lost water partitions at the fracture-matrix interface thereby restricting gas flow into the fractures. Thus, minimizing the large water footprint during the fracturing process is very attractive for water conservation and gas production. A key step towards achieving this goal is quantifying uncertainties needed to reliably predict water imbibition and to evaluate the success of efforts aimed at minimizing it. In this contribution, we present new scaling relations for water imbibition in gas-saturated rocks that account for the depth-dependence of fluid properties and chemical alteration of IFT through the use of a surfactant. We then propose a new method for quantifying uncertainties relating to rock properties, two-phase fluid properties, and the driving force for imbibition. We applied the proposed approach to analyze glass-bead pack and shale experiments involving water imbibition into air-filled pores, and validated our model predictions against published values from X-ray CT images and transient permeability measurements. Our work provides a methodology for quantifying the uncertainties pertaining to water imbibition, thereby enabling optimization of post-fracturing interventions aimed at minimizing water loss in deep unconventional shale gas reservoirs.

The method for driving preparatory roadway in gas-saturated rocks prone to gas-dynamic phenomena

The method for driving preparatory roadway in gas-saturated rocks prone to gas-dynamic phenomena

Weighted geometric mean model for determining thermal conductivity of reservoir rocks: Current problems with applicability and the model modification

Thermal conductivity is one of the fundamental physical parameters of rocks used in all fields of Earth science related to heat transfer in formations. Theoretical modeling of thermal conductivity plays a significant role when it is impossible to carry out measurements on rock samples or when it is necessary to account for variations in bulk thermal conductivity caused by natural or technological factors. Among many theoretical models for determining the thermal conductivity of reservoir rocks, the weighted geometric mean model or so-called Lichtenecker model is the most popular. We demonstrate that the model systematically underestimates the predicted thermal conductivity relative to the experimental results obtained from the thermal conductivity measurements on 20 collections of 1765 samples represented by sandstones, limestone dolomites, limestones, siltstones, and argillites in various saturation states. The underestimation value depends on lithology, porosity, and pore fluid and can reach 53% for high porous (27.6% of porosity) gas-saturated rocks: the average value of the underestimation is 20.5% for dried samples, 14.4% for kerosene-saturated, and 8.6% for water-saturated collections. It means that the applicability of the weighted geometric mean model for determining the thermal conductivity of reservoir rocks creates a serious risk of essential errors in the predicted data that requires revision and improvement of the theoretical model. It is shown that using the correction factor in the weighted geometric mean model resolves the problem leading to an average absolute relative deviation of less than 0.45% for dried and kerosene-saturated samples and less than 0.3% for water-saturated samples. We presented the technique for estimations of the factor for different rock types with corresponding results, and studied its relation with the pore space geometry of carbonate rocks using Effective Medium Theory. Interrelations were studied between the correction factor, rock types, pore fluid, and pore space characteristic - aspect ratio. The suggested improvement technique can be used in numerical calculations after modifying the corresponding option of thermo-hydrodynamic simulators or in theoretical calculations to decrease the uncertainty in bulk thermal conductivity and increase the reliability of calculation results.

An Exact Expression for the Effective Bulk Modulus for Acoustic Wave Propagation in Cylindrical Patchy-Saturation Rocks

Abstract Hydrocarbon reservoirs often contain partially gas-saturated rocks that have attracted the attention of exploration geophysicists and geologists for many years. Wave-induced fluid flow (WIFF) is an effective mechanism to quantify seismic wave dispersion and attenuation in partially gas-saturated rocks. In this study, we focus on the local fluid flow induced by variations in fluids in different regions and present a new model that describes seismic wave propagation in partially gas-saturated rocks, namely, the cylindrical patchy-saturation model. Because the seismic wave velocity and attenuation oscillate at high frequencies, it is not ideal for studying dispersion and attenuation caused by WIFF. To avoid the high-frequency oscillation in the cylindrical patchy-saturated model, we use an approximation to the Newman function instead of the full Newman function to calculate the effective bulk modulus. We then calculate the P-wave velocity and attenuation of the proposed model and interpret the lab-measured data. The proposed model is an alternative patchy-saturation model that can explain the problem of high-frequency oscillation and low-frequency attenuation.

Optimization of safe gas core retrieval using multivariate numerical simulation, based on different pore rheology and rock lamination

High gas compressibility, facies lamination, and presence of sub-lateral microfractures make shale gas reservoir rocks very sensitive to changing outer pressure and lead to severe damage of the whole core when it is recovered to surface. The approaches currently used for safe core retrieval do not adequately account for gas shale features, therefore, they are not capable of reliable modeling of this process. The article presents an extension of the recently developed optimization of the core tripping algorithm to shale gas formations featuring significant improvements. One, we show the lead role of strong inter-relation between gas flow and rock deformation process in the optimization of the core lifting process and propose a new decompression model of gas saturated shale rocks. Two, we introduce the dynamic permeability concept for shale gases, which considers individual behavior of the pores in organic matter, inorganic matrix, and microcracks. Three, we propose ways for calculation of the stress-strain state in cylindrical domain by applying numerical and semi-analytical solutions. Four, we introduce an interface failure mechanism for lamination rocks. Finally, we discuss the influence of different void types on decompression and dependence of the optimal schedule on microfracturing properties. Eventually, the article outlines several significant conclusions. In the fractured region, the degassing slows down due to crack closure near to the outer core boundary. The interface failure is an overlooked mechanism of rock failure. Frequent and long stoppages are required for preventing interface crack extension.

All-Time Modeling of Co-Current Spontaneous Water Imbibition Into Gas-Saturated Rocks Using a Novel Transition Time

Abstract Spontaneous imbibition (SI) into a porous medium is an important transport phenomenon in petroleum reservoir engineering. The study of spontaneous water imbibition is critical to predict the production performance in these reservoirs developed by waterflooding, especially in the fractured gas reservoirs with active aquifers. While some studies have been reported to characterize spontaneous water imbibition into gas-saturated rocks, they are either limited or inaccurate due to the fact that the existing models have specific assumptions that cannot be applied in other time intervals. To this end, we proposed a novel transition imbibition time t* and developed an all-time (including both early- and later-time SI) model to match the experimental SI data. Furthermore, we proposed a novel model to estimate capillary pressures at different water saturations and to characterize the water saturation profile in capillary-dominated stage. Comparison with the existing capillary pressure estimation models was performed to test the differences. The results demonstrated that the all-time model could fit the experimental imbibition data of the entire SI process satisfactorily. The new saturation model established in this paper can be well fitted with the water saturation profile measured by the X-ray computer tomography (CT) scanners. The results and findings from this work may be of great significance in many areas related to SI, particularly in the development of naturally fractured gas reservoirs with active aquifers.

The influence of fluid type on elastic wave velocity and attenuation in volcanic rocks

Volcano-seismic signatures are the convolution of source and path effects. The source signature provides important information about the dynamic rock deformation and fluid resonance processes within the volcano, but path effects are the result of the volcanic plumbing, the edifice physical conditions, and the complex geological structure. Complicating the inversion of seismic data further, is the influence of fluid properties. Here, we use ultrasonic experiments to understand the effect of variable fluid viscosity and bulk modulus on P-wave attenuation and velocity for volcanic rocks from White Island volcano (Whakaari), New Zealand.Our experimental conditions for high-porosity ash tuff and low-porosity lava resemble shallow and deep volcano facies respectively. P-wave velocity, Vp, and quality factor, Qp, increase with the viscosity and bulk modulus of the saturating fluid and decrease with porosity and fracture volume. Tuffs are highly sensitive to saturating fluid, with variations in Vp of up to 67% and Qp of 383%. Vp and Qp in fractured lavas are slightly less sensitive to fluids (24% and 296% respectively), but Vp can be used to identify lithology for these tuff vs. lavas. Comparison of the experimental data with rock physics models suggests that squirt flow is the dominant attenuation mechanism for viscosities greater than that of water, while scattering losses may be important in gas saturated rocks. Our results have significant implications for the interpretation of seismic tomography studies and for volcano hazard monitoring based on the characteristics of detected seismicity.

Geosystems of gas-saturated permafrost

The object of this study is the geosystems of gas-saturated permafrost. Currently, the theoretical basis for examination of gas component in permafrost is practically not developed. At the same time, the theoretical and practical significance of this problem has rapidly increased in recent years. This is due to gas emissions during drilling of wells in frozen rocks, the identification of significant greenhouse gas emissions in the Arctic, the detection of previously unknown processes in the permafrost zone – the formation of craters due to gas emissions.The main method applied in the article is the analysis of research materials. The synthesis of the results was carried out on the basis of the geosystem approach. The authors are first to demonstrate that gas-saturated zones in seasonally and permafrost rocks have all the attributes of geosystems: localization in space, boundaries, morphology, individual structure and properties, development history, life cycle, hierarchy. Five types of geosystem were determined: active layer; genetic type; confined to geological structures; secondary, associated with the decomposition of gas hydrates in vivo; technogenic (due to thermal or mechanical effects on hydrated and gas saturated frozen rocks). The artcile describes promising directions in studying gas-saturated geosystems of permafrost zone, as well as  the advanced research methods.

ОСОБЛИВОСТІ ОЦІНКИ РЕСУРСІВ ГАЗУ НЕТРАДИЦІЙНИХ КОЛЕКТОРІВ ЗА ДАНИМИ ГЕОФІЗИЧНИХ ДОСЛІДЖЕНЬ СВЕРДЛОВИН

Possibilities of estimation of shale gas resource and gas of tight reservoirs with the use of the well-logging data on the example of typical gascondensate field in the southern side of the Dnieper-Donetsk Depression are considered. The peculiarity of such works at this stage of studying the prospects of unconventional hydrocarbon resources in Ukraine is the shortage of factual material regarding special geochemical analysis of the core from perspective intervals of well sections. Emphasis is placed on the application of data from the standard set of well-logging methods. Using the method of Q. Passy, the content of organic carbon (TOC) in the rocks within the intervals of drilled wells was estimated. The characteristics of the lithological composition of rocks and the gas saturation of the traditional type of reservoirs were taken into account in the well-logging data. In the absence of available core data on thermal maturity of the rocks within the identified promising thicknesses, gas resources were estimated in several scenarios. The peculiarities of the well-logging data interpretation in the case of cross sections of wells of gas-saturated rocks with capacitance characteristics below the limit are given. Dependencies of the type "porosity - permeability", "porosity - residual water saturation" should be used to establish a lower porosity and gas saturation limit for tight reservoirs. At the end of the article, recommendations for calculating of gas resources in non-conventional reservoirs are provided.

Wave-velocity dispersion and rock microstructure

Porosity, fluid type and rock texture significantly affect acoustic wave propagation, since velocity dispersion and attenuation in fluid saturated rocks are mainly caused by wave-induced local fluid flow between microcracks and intergranular pores. We analyze P-wave velocity dispersion as a function of porosity to obtain information about the rock microstructure. The P-wave velocities in water-saturated rocks are predicted from measurements in gas-saturated rocks, using the Gassmann fluid substitution equation (the relaxed state). The dispersion is estimated from the difference between this predicted velocity and the measured one, where the latter corresponds to the unrelaxed state. We evaluate the wave dispersion as a function of porosity for 112 carbonates, 128 sandstones and 56 volcanic rocks, including our measurements for 86 tight rocks, showing that dispersion increases with porosity in the low porosity range, but decreases in the high porosity range. The dispersion peak occurs at a porosity of approximately 15%. Double-porosity poroelasticity modeling based on the local fluid-flow mechanism confirms this behavior. The microcrack radius has a peak in the porosity range 15–19% for all the lithologies from our collection, while the behavior of microcrack porosity is less evident. The dispersion peak may reveal the characteristics of lithological units, in particular porosity, fluid type and rock microstructure.

Exploring the Beetaloo: will Australia's first viable shale play be sourced by billion year old gas?

Origin Energy completed exploration campaigns in 2015 and 2016 in the Beetaloo Sub-basin of the Greater McArthur Basin in the Northern Territory, drilling three vertical wells and one horizontal well. These wells have provided a wealth of technical data to assist in the characterisation of the primary source rock reservoirs or ‘shale gas’ plays in the Basin – the Velkerri Formation Play and the Kyalla Formation Play. In this paper we demonstrate the presence of thick, gas saturated and over-pressured source rocks across the sub-basin. In addition to the drilling campaign, the multi-stage hydraulic fracture stimulation of the Amungee NW-1H horizontal well was completed in 2016 – this operation was unique as it represents the first horizontal stimulation operation in the Beetaloo Sub-basin and the longest ‘plug and perf’ type horizontal completion in Australia. Data from the extended production test of the Amungee NW-1H are critical from a technical and, potentially, economic and political perspective. In addition to the technical work program, Origin has undertaken preliminary environmental baseline studies and substantial stakeholder engagement. Ensuring environmental baseline data are available is key to demonstrating that onshore gas developments can be undertaken without adverse environmental outcomes, and also for gaining social acceptance. However, data and facts alone are not sufficient to build community confidence. Origin has engaged extensively with pastoralists, local communities and Traditional Owners to build direct relationships and partnerships that encourage acceptance of the gas industry’s ability to coexist and deliver mutual benefits to the businesses and communities of the Barkly region and the Northern Territory more broadly.

The methods to identify compacted saturated hydrocarbon rocks (on the example of southern Dnieper-Donets basin margin

Formulation of the problem. The article focuses on the study of one variety of unconventional sources of saturated hydrocarbon compacted rocks. It is known that in the last 5-7 years Ukraine started to pay close attention to the issue of unconventional hydrocarbons. The vector of additional prospecting industry refocused on existing fields of implementation and the involvement of new, advanced technologies. Following the example of countries that have successfully extracted gas and oil from compacted rocks we can say with confidence that the chosen direction is the most relevant and promising for our country. The purpose of the article. To survey the results of Pereschepynskii-Ulyanivskii deposits, and considering the research results of leading countries to show the feasibility study of compacted deep saturated hydrocarbon species within Dnieper-Donets basin. Methods. In writing this article the authors used the experience of domestic and foreign authors as well as their own research data. Results. In the early 70's XX century the US has carried out exploration work during which four large pools of compacted rocks were revealed. Due to the rapid growth of steel production the USA became a world leader with almost 40% of gas accounted for non-traditional sources (25% - gas condensed explosive rocks). Basic research methods are: analysis of material exploration, geological and geophysical surveys; industrial logging operations; tectonic and stratigraphic knowledge of the region; petrophysical features of rocks; preliminary, operational, detailed studies of core and sludge wells; the reinterpretation of GDS and other materials. For example, the survey results of Pereschepynskii and Ulyanovskii deposits located in the southern area alongside Dnieper-Donets depression (PPD) suggest that prospective compacted rock strata are associated with traditional anticlinal traps and are in direct contact with intervals of productive strata. The area has prospects for industrial flow of gas from reservoir compaction. The highest probability to find hydrocarbons in compacted rocks can be expected with rhythmic siltstone layering. In their further study gas-saturated rocks should be considered comprehensively. Scientific novelty and practical significance. Earlier studies of dense sand strata in siltstone of Pereschepynskii and Ulyanivskii areas were not considered as potential sources of hydrocarbons. We can assume that most likely carbon deposits should be considered regionally. Distribution of hydrocarbons was traced both horizontally and vertically. It is possible that in the future there will be increase in the number of carbon productive horizons in the deposits. Upon confirmation of carbon saturation in the thick compacted rocks they can be considered and recommended as a potential source of siltstone gas.

An Experimental Study of Velocity-Saturation Relationships in Volcanic Rocks

In this paper, experiments are carried out under different pressures and water saturations using core samples of volcanic rocks from the Junggar Basin in China to understand how water saturation affects P- and S-wave velocities. The results show that water saturated rocks exhibit significantly higher P- and S-wave velocities than gas saturated rocks. In addition, the P- and S-wave velocity ratio declines with increasing water saturation. Furthermore, a P- and S-wave velocity ratio vs. resistivity cross plot is created to identify gas reservoirs in the volcanic rocks in the Junggar Basin.

A modified rock physics model for analysis of seismic signatures of low gas-saturated rocks

In seismic applications, the bulk modulus of porous media saturated with liquid and gas phases is often estimated using Gassmann's fluid substitution formula, in which the effective bulk modulus of the two-phase fluid is the Reuss average of the gas and liquid bulk moduli. This averaging procedure, referred to as Wood's approximation, holds if the liquid and gas phases are homogeneously distributed within the pore space down to sizes well below the seismic wavelength and if the phase transfer processes between liquid and gas domains induced by the pressure variations of the seismic wave are negligible over the timescale of the wave period. Using existing theoretical results and low-frequency acoustic measurements in bubbly liquids, we argue that the latter assumption of “frozen” phases, valid for large enough frequencies, is likely to fail in the seismic frequency range where lower effective bulk modulus and velocity, together with dispersion and attenuation effects, are expected. We provide a simple method, which extends to reservoir fluids a classical result by Landau and Lifshitz valid for pure fluids, to compute the effective bulk modulus of thermodynamically equilibrated liquid and gas phases. For low gas saturation, this modulus is significantly lower than its Wood's counterpart, especially at the crossing of bubble point conditions. A seismic reflector associated to a phase transition between a monophasic and a two-phase fluid thus will appear. We discuss the consequences of these results for various seismic applications including fizz water discrimination and hydrocarbon reservoir depletion and CO2 geological storage monitoring.

A technique for improving pseudo-synthetic seismograms generated from neutron logs in gas-saturated clastic rocks

In clastic and carbonate rock sequences, the neutron and sonic log curves usually deflect in a similar fashion. Moreover, in some cases the two curves can be overlain and they generally appear to mimic each other, with variations between them only in the amplitudes of the two curves. This descriptive correlation is the basis of direct cross-plot techniques used to convert a neutron log into a pseudo-sonic log, which can then be combined with a density log to create a pseudo-synthetic seismogram. Unfortunately, the seismograms produced in this way may not match the standard synthetic seismograms produced from the sonic and density logs if the ?gas effect? is not taken into account. In order to correct for the gas effect, the inter-log correlations between the compensated neutron log (CNL) and the borehole-compensated (BHC) sonic log curves from a well in Taiwan were carefully examined. Then, we developed a technique for transforming the CNL log into a pseudo-BHC log by splicing together several continuous sandstone intervals in which the gas effect could be identified from the scattered data on the cross-plot of neutron porosity versus sonic interval transit time. Based upon our results, application of the new composite transform method yields a pseudo-synthetic seismogram that better matches the standard synthetic seismogram (made from the sonic and density logs) according to frequency, amplitude and polarity. This gas correction technique may be particularly useful in oil and gas exploratory and development areas where neutron logs are more prevalent than sonic logs or where sonic logs are scarce.

Ultrasonic moduli for fluid-saturated rocks: Mavko-Jizba relations rederived and generalized

Mavko and Jizba propose a quantitative model for squirt dispersion of elastic-wave velocities between seismic and ultrasonic frequencies in granular rocks. Their central results are the expressions for the so-called unrelaxed frame bulk and shear moduli computed under an assumption that the stiff pores are drained (or dry) but the soft pores are filled with fluid. Mavko-Jizba expressions are limited to liquid-saturated rocks but become inaccurate when the fluid-bulk modulus is small (e.g., for gas-saturated rocks). We have derived new expressions for unrelaxed moduli of fluid-saturated porous rocks using Sayers-Kachanov discontinuity formalism. The derived expressions generalize the established Mavko-Jizba relations to gas-saturated rocks, reduce to Mavko-Jizba results when the pore fluid is liquid, and yield dry moduli when fluid-bulk modulus tends to zero. We tested this by comparing our model and the model of Mavko and Jizba against laboratory measurements on a sample of Westerly granite.

Multiple resolution seismic attenuation imaging at Mt. Vesuvius

A three-dimensional S wave attenuation tomography of Mt. Vesuvius has been obtained with multiple measurements of coda-normalized S-wave spectra of local small magnitude earthquakes. We used 6609 waveforms, relative to 826 volcano-tectonic earthquakes, located close to the crater axis in a depth range between 1 and 4km (below the sea level), recorded at seven 3-component digital seismic stations. We adopted a two-point ray-tracing; rays were traced in an high resolution 3-D velocity model. The spatial resolution achieved in the attenuation tomography is comparable with that of the velocity tomography (we resolve 300m side cubic cells). We statistically tested that the results are almost independent from the radiation pattern. We also applied an improvement of the ordinary spectral-slope method to both P- and S-waves, assuming that the differences between the theoretical and the experimental high frequency spectral-slope are only due to the attenuation effects. Consequently we could check the coda-normalization method also comparing the S attenuation image with the P attenuation image. The images were obtained inverting the spectral data with a multiple resolution approach. Results have shown the general coincidence of low attenuation with high velocity zones. The joint interpretation of velocity and attenuation images allows us to interpret the low attenuation zone intruding toward the surface until a depth of 500m below the sea level as related to the residual part of solidified magma from the last eruption. In the depth range between −700 and −2300 images are consistent with the presence of multiple acquifer layers. No evidence of magma patches greater than the minimum cell dimension (300m) has been found. A shallow P wave attenuation anomaly (beneath the southern flank of the volcano) is consitent with the presence of gas saturated rocks. The zone characterized by the maximum seismic energy release cohincides with a high attenuation and low velocity volume, interpreted as a cracked medium.