3D Seismic Model Research Articles

3D seismic modeling in geothermal reservoirs with a distribution of steam patch sizes, permeabilities and saturations, including ductility of the rock frame

Abstract Seismic propagation in the upper part of the crust, where geothermal reservoirs are located, shows generally strong velocity dispersion and attenuation due to varying permeability and saturation conditions and is affected by the brittleness and/or ductility of the rocks, including zones of partial melting. From the elastic-plastic aspect, the seismic properties (seismic velocity, quality factor and density) depend on effective pressure and temperature. We describe the related effects with a Burgers mechanical element for the shear modulus of the dry-rock frame. The Arrhenius equation combined to the octahedral stress criterion define the Burgers viscosity responsible of the brittle-ductile behaviour. The effects of permeability, partial saturation, varying porosity and mineral composition on the seismic properties is described by a generalization of the White mesoscopic-loss model to the case of a distribution of heterogeneities of those properties. White model involves the wave-induced fluid flow attenuation mechanism, by which seismic waves propagating through small-scale heterogeneities, induce pressure gradients between regions of dissimilar properties, where part of the energy of the fast P-wave is converted to slow P (Biot)-wave. We consider a range of variations of the radius and size of the patches and thin layers whose probability density function is defined by different distributions. The White models used here are that of spherical patches (for partial saturation) and thin layers (for permeability heterogeneities). The complex bulk modulus of the composite medium is obtained with the Voigt-Reuss-Hill average. Effective pressure effects are taken into account by using exponential functions. We then solve the 3D equation of motion in the space-time domain, by approximating the White complex bulk modulus with that of a set of Zener elements connected in series. The Burgers and generalized Zener models allows us to solve the equations with a direct grid method by the introduction of memory variables. The algorithm uses the Fourier pseudospectral method to compute the spatial derivatives. It is tested against an analytical solution obtained with the correspondence principle. We consider two main cases, namely the same rock frame (uniform porosity and permeability) saturated with water and a distribution of steam patches, and water-saturated background medium with thin layers of dissimilar permeability. Our model indicates how seismic properties change with the geothermal reservoir temperature and pressure, showing that both seismic velocity and attenuation can be used as a diagnostic tool to estimate the in situ conditions.

Seismo-stratigraphic model of "La Bandita" area in the Palermo Plain (Sicily, Italy) through HVSR inversion constrained by stratigraphic data

Ambient noise Horizontal-to-Vertical Spectral Ratio (HVSR) technique is commonly used approach to obtain 1D models of the shear-wave velocity in the shallow surface of an investigated area. However, obtained models can have a wide margin of uncertainty if inversions have not been appropriately constrained by detailed stratigraphic information. An application of HVSR inversion constrained by lithostratigraphic data is presented in order to verify the effectiveness of this technique for purposes of geological and geophysical reconstruction of a sedimentary basin in a densely urbanized area. This is often the case of seismic microzonation studies, in which almost all the information derives from near surface stratigraphic drillings, since other geophysical methods are logistically difficult to carry out. In our work, we used stratigraphic constraints derived from 93 superficial bore-holes whose depth rarely exceeds 30 m. In an area called La Bandita, located in Palermo Plain (Sicily, Italy), a geophysical survey was performed by means of 55 microtremor recordings. Part of these was distributed randomly, while others very close to the available stratigraphic perforations. The reconstruction of the stratigraphy in the studied area has been obtained by a review of the main stratigraphic sequences and by a consequent stratigraphic three-dimensional modelling. HVSR curves have been interpreted taking care the thicknesses of the near surface successions derived by the stratigraphic 3-D model. The results, in terms of vertical profiles of the shear-wave velocity, have been interpolated to obtain a 3D seismic model. This has been used to extract basic information to identify and reconstruct the seismic bedrock and the main geological boundaries that were not directly identifiable by means of only stratigraphic logs. It results that the bedrock is affected by a fault system that generated adjacent depressions where Quaternary successions deposited.

Создание геологической 3D сейсмолитофациальной модели одиночных рифов пинаклового типа

Создание геологической 3D сейсмолитофациальной модели одиночных рифов пинаклового типа

Integration of reflection seismic data into the documentation during the construction of the Brenner Base Tunnel

AbstractThe 64 km long Brenner Base Tunnel will be the longest railway tunnel in the world when complete. As part of this mega project, an exploratory tunnel is currently under construction with a tunnel boring machine (∅ 8 m). Even though a geological model along the tunnel route was generated beforehand from the results of geological field mapping and deep drilling campaigns from the surface, some uncertainties persist due to the high overburden of up to 1,300 m. In particular, several fault systems intersect the tunnel route, but their position and orientation is uncertain. The excavation work is being documented with geological and geotechnical data, continuously updating the current geological model. Continuous seismic prediction measurements are integrated into this revision process. The aim is the detection, location and characterization of (sub‐)perpendicular to (sub‐)parallel fault zones ahead and to the side of the tunnel, based on the principle of body wave propagation. In a case study of a seismic campaign, the smooth integration of the acquisition into the regular advance is presented and the obtained 3D seismic models are compared to the geological documentation of the site geologists. It will be shown how the seismic analysis gives an added value for the advance and how it benefits the geological forecast for the forthcoming main tunnels.

Joining statistics and geophysics for assessment and uncertainty quantification of three‐dimensional seismic Earth models

Seismic inversions produce seismic models, which are 3‐dimensional (3D) images of wave velocity of the entire planet retrieved by fitting seismic measurements made on records of past earthquakes or other seismic events. Computing power of the TeraFlop era, along with the dataflow from new, very dense, seismic arrays, has led to a new generation of 3D seismic Earth models with an unprecedented level of resolution.Here we compare two recent models of western United States from the Dynamic North America (DNA) seismic imaging effort. The two models only differ in the wave propagation that was used for their inversion: one is based on ray theory (RT), and the other on finite frequency (FF). We evaluate the two models using an independent numerical method and statistical tests. We show that they differ in how they produce seismic signals from a subset of earthquakes that were used in the original inversion and were recorded on the US array. This is especially true for measurements done in the Yellowstone area which has a large negative seismic anomaly. This result is of importance for seismologists who have been debating on the practical benefit of using FF in ill‐posed Earth inversions. Model evaluation, such as the one reported here, represents an opportunity for collaboration between geophysical and statistical communities. More opportunities should arise with the upcoming Exascale era, which will provide enough computational power to explore together several sources of errors in models with thousands of parameters, opening the way of uncertainty quantification of seismic models.

Assessment of the Limitations on the Seismic Detectability of Injected CO2 within a Deep Geological Reservoir

Aquistore is a deep saline CO2 storage research and demonstration project located near Estevan, Saskatchewan where CO2 is transported via pipeline and injected into a sandstone reservoir ∼3200 m below the surface. A pre-injection time-lapse analysis performed on two sparse 3D seismic datasets was used to characterise the background time-lapse signal-to-noise level at the storage site. The time-lapse analysis revealed that the lowest global nRMS was 0.07 which was taken to represent the level above which CO2 would be detectable in the reservoir. We investigate the conditions under which the injected CO2 can be detected above the defined minimum noise level through Gassmann fluid substitution and 3D seismic forward modelling. Additionally, Wave Unix was used to simulate the seismic response of the reservoir due to the injected CO2 by generating the synthetic surface reflection seismic data from an explosive surface P-wave source. We generated noise-free synthetic seismograms for the baseline model as well as for the 2-phase fluid replacement of brine with CO2 for CO2 concentrations up to 100% within the target zone – the monitors. The baseline and monitor traces from the 3D seismic survey at Aquistore are used as the noise traces in this study, and were added to their respective baseline and monitor synthetic traces. The nRMS within the reservoir was then computed for the noisy baseline and various noisy monitor surveys and was used in the assessment of the limitation to the detection of the injected CO2 in the reservoir under the background noise level at the site. We are able to conclude that the time-lapse repeatability will not limit the ability to monitor the CO2 induced changes in the reservoir at the Aquistore storage site.

Monitoring Results after 36 Ktonnes of Deep CO2 Injection at the Aquistore CO2 Storage Site, Saskatchewan, Canada

The Aquistore CO2 Storage Site is located in southeastern Saskatchewan, Canada. CO2 is injected into a brine-filled sandstone formation at ∼3200 m depth immediately above the Precambrian basement. Sustained injection rates of 400-600 tonnes/day were achieved at the site starting in the fall of 2015 with a total of 88 ktonnes having been injected by the end of September, 2016. Seismic monitoring methods have been employed to track the subsurface CO2 plume and to record any injection-induced seismicity. Passive seismic monitoring is being conducted using two orthogonal arrays of short-period geophones, 3 broadband seismographs, and an array of downhole geophones. No significant injection-related seismicity (Mw > -1) has been detected during the first 17 months of CO2 injection. The first post-injection time-lapse 3D seismic surveys (surface and VSP) were conducted at the site in February, 2016. The VSP data were acquired with a distributed acoustic sensing system using a 2750 m casing-conveyed optical fibre cable in the observation well. 3D seismic modelling of fluid flow simulations in conjunction with seismic repeatability estimates obtained from field data indicate that the time-lapse VSP should be capable of imaging the CO2 plume after a total injection of ∼30 ktonnes. In addition, this first monitor survey tests the ability of surface seismic data acquired with a sparse permanent array to detect or image the CO2 plume after limited injection. Time-lapse logging is being conducted on a regular basis to provide in situ measurement of the change in seismic velocity associated with changes in CO2 saturation.

A memory-efficient staining algorithm in 3D seismic modelling and imaging

The staining algorithm has been proven to generate high signal-to-noise ratio (S/N) images in poorly illuminated areas in two-dimensional cases. In the staining algorithm, the stained wavefield relevant to the target area and the regular source wavefield forward propagate synchronously. Cross-correlating these two wavefields with the backward propagated receiver wavefield separately, we obtain two images: the local image of the target area and the conventional reverse time migration (RTM) image. This imaging process costs massive computer memory for wavefield storage, especially in large scale three-dimensional cases. To make the staining algorithm applicable to three-dimensional RTM, we develop a method to implement the staining algorithm in three-dimensional acoustic modelling in a standard staggered grid finite difference (FD) scheme. The implementation is adaptive to the order of spatial accuracy of the FD operator. The method can be applied to elastic, electromagnetic, and other wave equations. Taking the memory requirement into account, we adopt a random boundary condition (RBC) to backward extrapolate the receiver wavefield and reconstruct it by reverse propagation using the final wavefield snapshot only. Meanwhile, we forward simulate the stained wavefield and source wavefield simultaneously using the nearly perfectly matched layer (NPML) boundary condition. Experiments on a complex geologic model indicate that the RBC-NPML collaborative strategy not only minimizes the memory consumption but also guarantees high quality imaging results. We apply the staining algorithm to three-dimensional RTM via the proposed strategy. Numerical results show that our staining algorithm can produce high S/N images in the target areas with other structures effectively muted.

Development of a first 3D crustal velocity model for the region of Bogotá, Colombia

Knowledge regarding the characteristics of soils in Bogotá basin has been possible to get through previous microzonation studies. However, there is still insufficient knowledge of the crustal velocity structure of the region. Bogotá is located in a region prone to a significant seismic hazard. Historically, the city has been affected by strong earthquakes, reaching moment magnitudes greater than or equal to 7. Furthermore, the city was built on a lacustrine basin, with soft soils of considerable depth that may strongly amplify the ground motion during an earthquake. In this article, we describe the development of a first crustal structure and material properties model for the region of Bogotá, Colombia, covering an area of about 130 km by 102 km. This effort aims at constructing a realistic 3D seismic velocity model using geological and geotechnical information from several sources. Major geological units have been identified and mapped into the model. The Inverse Distance Weighted (IDW) interpolation was used to create continuous surfaces delimiting the geological units. Seismic-wave properties are assigned to any point in the domain using a location-based approach. We expect this model to be useful for a wide range of applications, including dynamic ground motion simulations and fault system modeling.

Geologically driven 3D modelling of physical rock properties in support of interpreting the seismic response of the Lalor volcanogenic massive sulphide deposit, Snow Lake, Manitoba, Canada

Abstract 3D lithofacies and physical rock property models were generated to interpret 3D seismic data acquired over the Lalor volcanogenic massive sulphide deposit, Manitoba, Canada. The lithofacies model revealed that strong seismic reflectivity is associated with ore–host rock and mafic–felsic lithofacies contacts, including their hydrothermally altered equivalents. Different physical rock property models were subjected to 3D seismic forward modelling using the SOFI3D finite difference code. Seismic synthetics from discrete and interpolated models in which kriging of P-wave velocity and density was conditioned by curvilinear grids conformable to the 3D-modelled geological structure showed a much better match to the seismic data in comparison with those generated by kriging in Cartesian space. Synthetics from these curvilinear grid models corroborate the origin of seismic reflectors, as qualitatively inferred from the lithofacies model. Seismic synthetics generated from physical rock property models in which physical rock properties were augmented by densely sampled secondary variables, such as FeO percentage, enhanced lateral continuity of seismic reflectivity, although these co-kriged petrophysical models were not more accurate than their kriged equivalents. The physical rock property modelling methodology was also useful for testing the utility of passive interferometric seismic surveys, as this highlighted the limitations of the discrete physical rock property model.

Hypocenter Relocation of Earthquake Swarm in West Halmahera, North Molucca Region, Indonesia by using Double-Difference Method and 3D Seismic Velocity Structure

The earthquake swarm events sequence occurred in west Halmahera, north Molucca, Indonesia for the period of October 2015 to February 2016 as reported by Meteorological, Climatological, and Geophysical Agency (BMKG) of Indonesia. There were tenths swarm events with Magnitude larger than four in the region during the period. In this study, we used the earthquake catalog data compiled by BMKG to improve the location of swarms event in west Halmahera, north Molucca, Indonesia. We relocated 86 swarm events by applying teleseismic double-difference method and 3D seismic velocity model. The focus depth of swarm events mainly concentrated at depth of 5 to 12 km at south-east of Jailolo volcano. Our preliminary interpretation the earthquake swarms may be related to the stress change around the deep magma region of the volcano.

Configuration of the Moho discontinuity beneath the Japanese Islands derived from three-dimensional seismic tomography

Abstract The Mohorovicic discontinuity (Moho) is defined on the basis of an abrupt increase in seismic velocity in the lithosphere which has been observed using seismic refraction and receiver function analysis methods worldwide. Moho depth varies regionally and remains a fundamental parameter of crustal structure. We present a new method of mapping the Moho using a 3D seismic tomography model. Since the tomographic method cannot locate discontinuities, we treat the Moho as a zone of high velocity gradient. Maximum lower crust/minimum upper mantle P-wave velocities in Japan are known to be 7.0 km/s and 7.5 km/s, respectively. We map the residual between isovelocity surfaces of 7.0 km/s and 7.5 km/s to find areas where the residual is small, the separation between the surfaces is narrow, and the velocity gradient is high. The Moho is best constrained where the isovelocity surfaces are close together, and under much of Japan, they are 10 km apart. We chose an isovelocity surface of 7.2 km/s as a representative Moho ‘proxy’ in these areas. Our resulting ‘Moho’ map under Japan compares favorably with existing regional Moho models that were obtained from controlled-source seismic investigations. The ‘Moho’ varies from shallow (25–30 km) to deep (> 30 km), and this variability relates to the structural evolution of the Japanese islands: the opening of the Sea of Japan back-arc, ongoing arc-arc collisions at the Hidaka and Izu collision zones, ongoing back-arc extension in Kyushu, and a possible failed back-arc extensional event of Mesozoic age. It is apparent that the Moho is less well-constrained in areas where the crustal structure has been modified by magmatic activity or thickened due to arc-arc collision.

Aftershocks of the 2014 South Napa, California, Earthquake: Complex Faulting on Secondary Faults

Abstract We investigate the aftershock sequence of the 2014 M w 6.0 South Napa, California, earthquake. Low‐magnitude aftershocks missing from the network catalog are detected by applying a matched‐filter approach to continuous seismic data, with the catalog earthquakes serving as the waveform templates. We measure precise differential arrival times between events, which we use for double‐difference event relocation in a 3D seismic velocity model. Most aftershocks are deeper than the mainshock slip, and most occur on the west of the mapped surface rupture. Although the mainshock coseismic and postseismic slip appears to have occurred on the near‐vertical, strike‐slip West Napa fault, many of the aftershocks occur in a complex zone of secondary faulting. Earthquake locations in the main aftershock zone, near the mainshock hypocenter, delineate multiple dipping secondary faults. Composite focal mechanisms indicate strike‐slip and oblique‐reverse faulting on the secondary features. The secondary faults were moved toward failure by Coulomb stress changes from the mainshock slip. Clusters of aftershocks north and south of the main aftershock zone exhibit vertical strike‐slip faulting more consistent with the West Napa fault. The northern aftershocks correspond to the area of the largest mainshock coseismic slip, whereas the main aftershock zone is adjacent to the fault area that has primarily slipped postseismically. Unlike most creeping faults, the zone of postseismic slip does not appear to contain embedded stick‐slip patches that would have produced on‐fault aftershocks. The lack of stick‐slip patches along this portion of the fault may contribute to the low productivity of the South Napa aftershock sequence.

Improved Basin Structures in Southern California Obtained Through Full‐3D Seismic Waveform Tomography (F3DT)

A realistic 3D seismic velocity model plays an important role in wave‐propagation simulations for estimating ground motions from damaging earthquakes. In addition, the 3D velocity variations associated with sedimentary basins are particularly important. Recent updates on the Community Velocity Model (CVM) for southern California made through crustal‐scale full‐3D seismic waveform tomography (F3DT) have improved the basin structures substantially. The basin structures in the updated 3D velocity model CVM‐S4.26 exhibit high correlation with surface geology, independent gravity measurements, and 2D controlled source tomography profiles. The improvements in basin structures are reflected in the much‐improved fits between synthetic and observed waveforms that are sensitive to basin structures. Seismic‐hazard analysis based on either empirical approaches or numerical simulations can potentially benefit from the improvements in basin structures in CVM‐S4.26.

Frequency-space domain acoustic wave simulation with the BiCGstab (ℓ) iterative method

The vast computational cost and memory requirements of LU decomposition are major obstacles to 3D seismic modelling in the frequency-space domain. BiCGstab (l) is an effective bi-conjugate gradient method to solve the giant sparse linear equations, but the convergence rate is extremely low when the threshold value is set small enough. The BiCGstab (l) iterative method was introduced into 3D numerical simulation to overcome these problems in this paper. Numerical examples have shown that the precision of the BiCGstab (l) iterative method meets the demand of seismic modelling and the result is equivalent to that of LU decomposition. The computational cost and memory resource demands of the BiCGstab (l) iterative method are superior to that of LU decomposition. It is an effective method of 3D seismic modelling in the frequency-space domain.

High-resolution 3D seismic model of the crustal and uppermost mantle structure in Poland

In the area of Poland a contact between the Precambrian and Phanerozoic Europe and the Carpathians has a complicated structure and a complex P-wave velocity of the sedimentary cover, crystalline crust, Moho depth and the uppermost mantle. The geometry of the uppermost several kilometers of sediments is relatively well recognized from over 100,000 boreholes. The vertical seismic profiling (VSP) from 1188 boreholes provided detailed velocity data for regional tectonic units and for stratigraphic successions from Permian to the Tertiary and Quaternary deposits. These data, however, do not provide information about the velocity and basement depth in the central part of the Trans-European suture zone (TESZ) and in the Carpathians. So, the data set is supplemented by 2D velocity models from 32 deep seismic sounding refraction profiles which also provide information about the crust and uppermost mantle. Together with the results of other methods: vertical seismic profiling, magnetotelluric, allow for the creation of a detailed, high-resolution 3D model for the entire Earth's crust and the uppermost mantle down to a depth of 60 km. The thinnest sedimentary cover in the Mazury–Belarus anteclise is only 0.3 to 1 km thick, which increases to 7 to 8 km along the East European Craton (EEC) margin, and 9 to 12 km in the TESZ. The Variscan domain is characterized by a 1–4 km thick sedimentary cover, while the Carpathians are characterized by very thick sedimentary layers, up to about 20 km. The crystalline crust is differentiated and has a layered structure. The crust beneath the West European Platform (WEP; Variscan domain) is characterized by P-wave velocities of 5.8–6.6 km/s. The upper and middle crusts beneath the EEC are characterized by velocities of 6.1–6.6 km/s, and are underlain by a high velocity lower crust with a velocity of about 7 km/s. A general decrease in velocity is observed from the older to the younger tectonic domains. The TESZ is associated with a steep dip in the Moho depth, from 30–35 km in the Paleozoic Platform to 42–52 km in the Precambrian craton. The new model confirms the Moho depth derived from previous compilations. In the TESZ the lower crust has a very high seismic velocity (> 7.0 km/s) which correlates to the high P-wave velocity (about 8.4 km/s) in the uppermost mantle beneath the Polish Basin. The Cratonic area is generally characterized by high P-wave velocities (> 8.2 km/s), while the Phanerozoic area is characterized by velocities of ~ 8.0 km/s. In the TESZ very high velocities of 8.3–8.4 km/s are observed, and the southwestern limitation of this area coincides with a high velocity lower crust, and could be continued to the NW toward the Elbe line. The influence of the structure for teleseismic tomography time residuals of seismic waves traveling through the 3D seismic model was analyzed. Lithological candidates for the crust and uppermost mantle of the EEC and WEP were suggested by comparison to laboratory data. The presented 3D seismic model may make more reliable studies on global dynamics, and geotectonic correlations, particularly for sedimentary basins in the Polish Lowlands, the napped flysch sediment series in the Carpathians, the basement shape, the southwestern edge of the EEC, a high-velocity lower crust and the high-velocity uppermost mantle in the TESZ. Finally, the new 3D velocity model of the crust shows a heterogeneous structure and offers a starting point for the numerical modeling of deeper structures by allowing for a correction of the crustal effects in studies of the mantle heterogeneities.

Numerical earthquake model of the 20 April 2015 southern Ryukyu subduction zone M6.4 event and its impact on seismic hazard assessment

The M6.4 earthquake that took place on the 20 April 2015 off the shore of eastern Taiwan was the largest event in the vicinity of Taiwan during 2015. The mainshock was located in the southern Ryukyu subduction zone, which is the interface between the Philippine Sea Plate and the Eurasian Plate. People in Taipei experienced strong ground shaking for more than 40 s, even though the epicenter was located more than 150 km away. In order to understand the origin of ground motions from this earthquake and how it caused such strong shaking in Taipei, a numerical earthquake model is analyzed, including models of source rupture and wave propagation. First, a joint source inversion was performed using teleseismic body wave and local ground motion data. Source inversion results show that a large slip occurred near the hypocenter, which rapidly released seismic energy in the first 2 s. Then, the rupture propagated toward the shallow fault plane. A large amount of seismic energy was released during this rupture stage that slipped for more than 8 s before the end of the rupture. The estimated stress drop is 2.48 MPa, which is consistent with values for subduction zone earthquakes. Forward simulation using this inverted source rupture model and a 3D seismic velocity model based on the spectral-element method was then performed. Results indicate that the strong ground motion in Taipei resulted from two factors: (1) the Taipei basin amplification effect and (2) the specific source radiation pattern. The results of this numerical earthquake model imply that future subduction zone events that occur in offshore eastern Taiwan are likely to cause relatively strong ground shaking in northern Taiwan, especially in the Taipei metropolitan area.

A 3DQPAttenuation Model for All of New Zealand

Online Material: Table of New Zealand-wide Q P and V P with resolution estimate; figure showing nonparametric curve fit Q P ( V P ). Over the last 13 years, we have developed 3D seismic attenuation models for many parts of New Zealand through individual regional studies using local earthquake data, often collected using regional temporary seismic networks. Most of New Zealand is seismically active, as illustrated by Figure 1a, which shows the distribution of earthquakes of magnitude≥4.5 for the 2001–2011 period. These earthquakes illustrate how convergence between the Pacific and Australian plates is accommodated in very different ways along the New Zealand plate boundary, from subduction of the Pacific plate under the Australian plate at the Hikurangi subduction zone in the North Island and northern South Island, to continental convergence in the central South Island, to steep subduction of the Australian plate beneath the Pacific plate in Fiordland in southwestern South Island. Figure 1. (a) Tectonic setting of the New Zealand region, showing earthquake epicenters for events of magnitude≥4.5 from the period 2001–2011; the 2 km bathymetry contour is shown offshore. The dashed box shows the extent of the defining New Zealand-wide grid, and the narrower box (solid lines) indicates the area shown in Figure 3. (b) Stations used in the QP inversions and areas of individual studies: A, northeastern North Island (Eberhart-Phillips and Chadwick, 2002); B, southern North Island (Eberhart-Phillips et al. , 2005); C, central–southern South Island (Eberhart-Phillips, Chadwick, et al. , 2008); D, central North Island (Eberhart-Phillips, Reyners, et al. , 2008); E, northern South Island (Eberhart-Phillips et al. , 2014). The locations of previous regional studies of 3D seismic attenuation are shown in Figure 1b. From north to south, these are Eberhart-Phillips …

Microseismic geomechanics of hydraulic-fracture networks: Insights into mechanisms of microseismic sources

Microseismic interpretation of hydraulic fracturing requires an understanding of the mechanism of the microseismic sources. Quantitative geomechanical models can predict microseismicity for quantitative comparison with field data and can be used to reconcile 3D seismic earth models, fracture engineering, and fracture monitoring. Because microseismicity represents only one component of the geomechanical response to hydraulic fracturing, a microseismic geomechanics framework can provide insights into the connection with the fracture network. During hydraulic fracturing, microseismicity can be induced by both fluid pressure and stress mechanisms, resulting in wet events directly associated with the fracture network and remote dry events. Accurate interpretation of the hydraulic-fracture characteristics requires distinguishing identification of dry microseismicity not in hydraulic connection with the stimulated fracture network. Predictive microseismic geomechanical models also can be used to infer the primary, conductive hydraulic-fracture networks and to run scenario testing to improve engineering design.

Quantitative Seismic Monitoring of a Saline Aquifer: A Feasibility Study for the CO2 Injection (The Pilot Site Ketzin, Germany)

Abstract Carbon dioxide (CO2) storage requires a proven monitoring methodology. In this study we investigate whether seismic methods are able to quantitatively detect relatively small amounts of CO2 (20-60 kilotons) injected into a saline aquifer. The 3D time-lapse (4D) seismic data were acquired at Ketzin. 85-95% injected CO2 could be imaged quantitatively. Nevertheless this estimate contains considerable uncertainties. Results of 4D seismic forward modeling at four wells penetrating the reservoir prove this quantitative interpretation supporting the conclusion that the 4D seismic method is a suitable technique to monitor even relatively small amounts of injected CO2 quantitatively.