Seismic Characteristics Research Articles

Pore and Microfracture Characterization in Tight Gas Sandstone Reservoirs with a New Rock-Physics-Based Seismic Attribute

Pores and microfractures provide storage spaces and migration pathways for gas accumulation in tight sandstones with low porosity and permeability, acting as one of the controlling factors of gas production. The development of a rational rock physics model is essential for better understanding the elastic responses of tight sandstone with complex pore structures. Accordingly, seismic characterization of pores and microfractures based on the rock physics model provides valuable information in predicting high-quality tight gas sandstone reservoirs. This paper proposes a rock-physics-based approach to compute the pore–microfracture indicator (PMI) from elastic properties for pore structure evaluation in tight sandstones. The PMI is achieved based on the axis rotation of the elastic parameter space using well-log data. The rotation angle is determined by finding the maximum correlation between the linearized combination of the elastic parameters and the introduced factor associated with total porosity and microfracture porosity. The microfracture porosity is then estimated with an inversion scheme based on the double-porosity model. Finally, the optimized rotation angle is employed to compute the PMI with seismic data. The obtained results are of great benefit in predicting the permeable zones, providing valuable information for sweet spot characterization in tight gas sandstone reservoirs.

ON THE STRESS WAVE IN THE EARTH'S BODY DUE TO DIFFERENTIAL ROTATION OF THE MANTLE AND CORE

Seismic energy generated as a result of elastic deformation of tectonic plates or blocks of rocks is realized by unloading at deformations exceeding the ultimate strength of rocks. The currently generally accepted earthquake source models are essentially local and are not able to establish a connection between seismic activity and some geophysical phenomena on a planetary scale. One of the features of seismicity is the recurrence of strong earthquakes in one place after a certain time interval. The purpose of this work is to study the influence of differential rotation of the solid core and mantle on seismic processes. It has now been established that the rate of rotation of the solid core exceeds the rate of rotation of the mantle. In relative motion, the solid core makes one revolution presumably in 200–400 years. Earlier, based on this, an explanation was proposed for long-period variations in the length of the day. In this paper, on a simple mechanical model, it is shown that the differential rotation of the elastic mantle and the solid core of an ellipsoidal shape generates a stress wave in the Earth's body. The idea of a stress wave is qualitatively new in the physical description of a seismic process. To demonstrate this effect, a solution is given to the problem of deformation of an elastic spherical shell interacting with a dumbbell-shaped solid body rotating in its cavity. When solving the problem, the apparatus of spherical vectors was used. The stress distribution of the spherical layer inside the shell is constructed and the areas of greatest risk are identified. It is shown that taking into account the differential rotation leads to the migration of the zones of greatest risk with a period equal to half the period of a complete rotation of the dumbbell relative to the shell (100–200 years). The results of the work can be useful in studying the relationship between seismicity and planetary rotation regimes.

Comparative study of the simulation ground motion by amplitude scale and spectral matching

Dynamic analysis is more accurate than static analysis in determining a response of structure due to earthquake loads. The limitation of this analysis is the lack of recorded ground motion data of an earthquake for the entire territory of Indonesia. Therefore, according to the Indonesian Code, it is permitted to use seismic data from other locations that have similar seismic characteristics. In application, ground motions need to be modified to match the Indonesia design code. There are two modification methods, which are amplitude scaling and spectral matching. Thus, the purpose of this study is to determine the reliability of these two methods. As the result, the response spectra of the ground motion modified by the spectral matching method present a similar pattern to the target response spectra compared to the amplitude scaling method. Ground motions modified by the spectral matching method generate Peak Ground Acceleration (PGA) values almost the same as the target PGA values. In contrast, the modified motions with amplitude scaling provide diverse PGA values that are not the same as the target PGA. From this study, the utilization of the spectral matching method is recommended in modifying ground motion data for dynamic analysis.

Seismic Fragility Analysis of Equipment Considering the Inelastic Energy Absorption Factor of Weld Anchorage for Seismic Characteristics in Korea

Seismic Fragility Analysis of Equipment Considering the Inelastic Energy Absorption Factor of Weld Anchorage for Seismic Characteristics in Korea

ВЛИЯНИЕ СОДЕРЖИМОГО КАРТ-ОСАДКОНАКОПИТЕЛЕЙ БАЙКАЛЬСКОГО ЦЕЛЛЮЛОЗНО-БУМАЖНОГО КОМБИНАТА НА ОКРУЖАЮЩУЮ СРЕДУ

The problem of the influence of the contents of the sedimentation maps of the Baikal Pulp and Paper Mill on the ecological situation in the Baikal region is considered. Data on the com-position and properties of the contents of the drives are given. The factors threatening Lake Baikal are highlighted. Geographical and seismic characteristics of the locality of the dislocation of objects of environmental danger are given

A physical modelling study of waveform amplification effects of reservoir heterogeneity on time‐lapse seismic attribute analysis

AbstractHydrocarbon depletion causes fluid saturation and pressure changes, resulting in perturbations in reservoir elasticities and, hence, observable time‐lapse (or 4D) seismic responses. Using controlled physical modelling experiments, we aim to evaluate reservoir heterogeneities‐related scattering effects on seismic signatures and assess pore‐fluid substitution impacts on the 4D seismic attributes. Physical modelling experiments reveal that wave propagations in heterogeneous rocks produce substantially magnified 4D attribute differences related to fluid replacements, contrary to seismic features in homogeneous rocks. In particular, reflected waveforms from the gas‐filled scenario exhibit more apparent discontinuities and amplitude variations than water‐ and oil‐saturated scenarios in the heterogeneous regions. It is interesting to see that fluid substitution‐induced 4D seismic differences are observable within the weakly heterogeneous region but significantly strong within the highly heterogeneous region. Although it is expected that substituting oil with water produces weak perturbations in reservoir elasticities, the 4D difference observations between time‐varying records are apparent. This implies that in addition to reservoir heterogeneities‐induced amplifying effects, 4D seismic anomalies are also caused by pore‐fluid changes. Due to mesoscopic rock heterogeneities, seismic responses are complicated, and 4D difference estimates will be amplified strongly and, thus, unable to quantify variations in fluid saturation appropriately. This implies that obvious difference volumes in the underburden regions do not necessarily correspond to significant variations in pore‐fluid. Subsequently, two end‐member rock physics models were applied to predict the widest range of velocity variations and pore‐fluid behaviours. Although mesoscopic heterogeneities cause varying degrees of difficulties for hydrocarbon detection, the deformed waveform‐induced seismic attribute anomalies, which are often greatly amplified, may be beneficial for more accurately identifying reservoir fluids and monitoring their minor variations in practice.

SEISMICITY of the RUSSIAN PART of EAST EUROPEAN PLATFORM and ADJACENT TERRITORIES in 2016–2017

Seismic observations by 46 stationary seismic stations, including seven temporary seismic stations located in the area of Novovoronezh and Kursk nuclear power plants, and by two arrays were carried out on the Russian territory of the East European Platform. A feature of seismicity in 2016–2017 is a manifestation of swarms of weak earthquakes in the northwest in the Leningrad region and the adjacent territory of Finland, as well as earthquakes on the Ukrainian Shield with Мs(est.)=3.8 in Krivoy Rog, where mass explosions are carried out in mines, but earthquakes of moderate magnitude МL=2.6–3.9 also occur (2007, 2013). Weak earthquakes in the peripheral parts (in the southwest, west and northwest) and in zones associated with paleorift structures: in the northeast – with the Kirov-Kazhim and Central Russian aulacogenes continue to be recorded. Weaker natural seismicity with ML≤2.5 was recorded in Karelia and the regions bordering Finland, near the Kandalaksha Bay, near the Khibiny and Lovozero massifs on the Kola Peninsula and in the territory of the Voronezh crystalline massif.

Effect of Frequency Content of Earthquake Ground Motions on Structures with Varying Dimension

An earthquake is a catastrophe which is always a topic of concern for structural designers and civil technocrats. Not only it causes physical damage to the structures but also successful to impart psychological disorder in human minds for long-run. In order to mitigate the devastating effects of earthquake on society, it is eminent to study the dynamic characteristics in detailed manner i.e. to examine how the structure responds owing to the seismic characteristics. The various ground motion characteristic includes time-duration and velocity, frequency content and amplitude, displacement, incremental velocity and incremental displacement, peak ground accelerations (PGAs), etc. Out of these, effect of frequency content and maximum amplitude value of earthquake ground motions on the seismic response of structures is often underestimated. This paper investigates the effect of frequency content and maximum amplitude value on the seismic response of structures which is dominant of all characteristics. The study proceeds with recording time-history of acceleration obtained from conventional unidirectional harmonic shake table. Further, FFT (Fast Fourier Transform) analysis of applied time-history is done and the effect of frequency content and the maximum amplitude value of applied time-history on the seismic responses of structures is investigated and studied. For this, structures with varying dimensions (height, length, and width) are modelled and time-history analysis of structural models has been carried out in SAP2000v19. Seismic responses of analysed structures are represented in the form of fundamental natural frequency, storey displacement, and base shear. It is reported that out of many earthquake indices, frequency content and amplitude of earthquake ground motions are the most dominating. It is reported that the resonance phenomena occurs for the less height structure and thus it shows maximum displacement and base shear responses. Also, as height, length, and width of structure increases; displacement, base shear, and fundamental time-period of structure increases.

Seismic Characterization to Identify Geological Structures and Petroleum Play in Lower Indus Basin, Pakistan

The Cretaceous shale intervals of Talhar and Sembar Formations – distributed in the Lower Indus Basin of Pakistan – are organic-rich shales that can act as shale gas plays. Two-dimensional seismic using synthetic modeling has been carried out in Khewari oil field to identify petroleum plays. This work was completed with the help of eight seismic processed and migrated lines. Based on structural interpretation different geological structures were marked. The seismic character, continuity, and coherency in seismic reflection patterns indicate that the area is under an extensional regime with normal faults pattern associated with horst and graben structure. This structure is favorable for the accumulation of hydrocarbon. The shales of Talhar and Sembar formations are overlying Chilton limestone, which is a proven reservoir. The isopach maps show that Talhar Shales and Sembar Formation are dipping towards the northeast. Precisely to characterize the reflector, a synthetic seismogram was employed to tie well tops and seismic profiles.

Statistical study on the regional characteristics of seismic activity in and around Japan: frequency-magnitude distribution and tidal correlation

AbstractWe propose a statistical analysis method to identify common features of seismic activity that are indistinguishable from most other seismicity, and to find anomalous activity that differs from these common features. Using the hypocenter catalog of earthquakes which occurs in and around Japan during the past 20 years, we apply this method for the parameters of the frequency-magnitude distribution and a parameter that expresses the correlation of seismicity with tides as indices, with a focus on objectively understanding the regional characteristics of seismicity. As a result, we extracted a "typical" probability density distribution of each index value common to the most analysis regions and "anomalous" regions with index-value distributions that differ significantly from the typical distributions. In terms of the frequency-magnitude distribution, most estimated values of indices in the anomalous activity areas can be explained as variations corresponding to the effects of fluids, interplate coupling, and stress fields that control faulting styles that have been pointed out in previous studies. By extracting typical index values for the frequency-magnitude distribution, common features of the frequency-magnitude distribution that depend on the earthquake occurrence interval were identified. Although seismicity showed no clear correlation with tides, the index value for tidal correlation changes to reflect the proportion of earthquakes occurring in a series of periods shorter than the tidal period; it is therefore useful as an index to capture the characteristics of such earthquake occurrence intervals. We also show that the typical probability density distribution of these index values can be represented by existing models or their extensions. By using the proposed models as a reference, it is possible to quantify the degree of anomaly using the same concept as that of the method presented here; hence, such a method should be applicable to monitor seismic activity. Graphical Abstract

Global and local effects of seismic activity in the ionosphere

We considered ionospheric effects of powerful seismic events using total electron content (TEC) maps of the ionosphere (http:// www.aiub.unibe.ch/download/CODE/) for the northern hemisphere, except the polar region, in the winter seasons of 2012— 2018. It is shown that the seismic-ionospheric effect is global, which is superimposed by local effects over the epicenters of individual earthquakes (EQ). Temporal TEC variations near the time of strong EQs at a great distance from their epicenters (global effect) consist of two maxima: the precursor and the «aftershock» maximum. In TEC variations over the EQ epicenter (local effect), only a precursor is usually registered, the amplitude of which at night (on average, ~ 8 %) is about twice as high as during the day. Always (locally and globally) after a positive surge in TEC, its reduced values are observed for several days. The maximum amplitude zone of the seismic-ionospheric effect belongs to the middle latitudes, especially 35...40° N, and within this zone at longitudes near 30° W (Mid-Atlantic ridge) and 140...150° E (Japanese islands and adjacent waters of the Pacific Ocean). Latitudinal amplitude maxima of the seismic-ionospheric effect are in good agreement with the latitudinal maxima of the EQ number in both geographic and geomagnetic coordinate systems. Changes in the EQ number and, consequently, the effect in the ionosphere on geomagnetic coordinates are more ordered, which indicates a significant impact on the seismicity of the same processes at the boundary of the liquid core and lower mantle, which form the Earth’s magnetic field. In addition to seismic belts and zones of mid-ocean ridges, an increase in TEC has been recorded along the so-called lineaments, marking the weakened zones of the Earth’s crust with increased flows of deep gases. The correspondence between the spatial features of seismicity and the seismic-ionospheric effect testifies in favor of the «radon» mechanism of lithosphere-ionosphere coupling and indirectly confirms the role of deep gases in the formation of seismicity planetary features.

Non-linear finite element analysis of seismically excited sloped wall tank

The non-linear seismic behavior of a ground-supported sloped wall tank is analyzed in the present study using a finite element model. A combination of three-node triangular and four-node quadrilateral finite elements is used to discretize the liquid domain. The velocity potential formulation is adopted for the liquid domain with a mixed Eulerian-Lagrangian scheme. By comparing the current numerical results with the existing experimental results, the competency of the present non-linear model is verified. The fundamental sloshing frequencies obtained from the present non-linear model are found closer to the experimental results compared to the linear counterpart. Non-linear seismic characteristics of liquid sloshing inside a ground-supported sloped wall tank are investigated under six different earthquakes categorized as low-, intermediate-, and high-frequency contents. Also, the dynamic impulsive and convective response components of hydrodynamic base shear force and pressure are quantified successfully. The comparison of the non-linear hydrodynamic response with the linear counterpart shows a significant difference in results which reasonably clarifies the limited capabilities of the linear model for response prediction as well as designing sloped wall tanks subjected to seismic excitation. The developed non-linear numerical model in the present study can be utilized for tuning and designing structure-coupled sloped wall TLDs.

County in Southwest Ordos Basin Block 1 Period of Sand Body Distribution Characteristics of Mountains

Huanxian block is one of the key oil and gas exploration and development blocks in Longdong Gas field of Changqing Oilfield Company. The Mesozoic exploration is about to enter the saturation state, and it is urgent to explore new fields. Therefore, the seismic characteristics, reflection structure characteristics and reservoir sand body distribution characteristics of Shan-1 member of Permian Shanxi Formation of Upper Paleozoic in this block are studied comprehensively. By using the data of drilling core, well logging curve and 3D seismic interpretation, the regional small beds are finely divided and correlated, and the unified stratigraphic framework of the area is established. The structural characteristics of the bottom of Shan-1 member of Shanxi Formation are studied, and the distribution characteristics of reservoir sand bodies and effective sand bodies of Shan-1 member are analyzed and studied.

Seismic features and vulnerability of traditional building practices in the Himalayan State, Himachal Pradesh, India

In the present study, widespread field surveys are conducted to identify the traditional building practices prevalent in the Indian state of Himachal Pradesh. The conducted field surveys led to the identification of the Kath-kunni, Thathara, Drystone, and Rammed earthen buildings in the study region. These building practices are studied, classified, and sketched for their siting, architectural and structural features, soil conditions and foundations. The qualitative seismic vulnerability assessment is conducted to highlight earthquake-resilient and vulnerable features of the studied traditional buildings.

Ground Motion Simulations for the 19 January 2020 Jiashi, China, Earthquake Using Stochastic Finite‐Fault Approach

AbstractA 6.0‐magnitude (Mw) earthquake was reported to have occurred in Jiashi County, Xinjiang at 21:27 on 19 January 2020, Beijing time (13:27 UTC). This study applied a stochastic finite‐fault approach based on the dynamic corner frequency (EXSIM) to simulate 23 near‐field stations within a distance of 120 km from the epicenter. The stochastic finite‐fault approach is the simplest and most effective method for simulating high‐frequency ground motions. According to studies and empirical relationships, we estimated a region‐specific parameter (κ0) for use in simulations. In this study, two different slip models, namely, random and inverted slip models, were used to explain their influence on the simulation results. For most stations, the simulated seismic characteristics, such as the peak ground acceleration (PGA), pseudo spectral acceleration ,and Fourier acceleration spectrum, are highly compatible with the observed values in the frequency range (f > 1 Hz), indicating that the stochastic finite‐fault approach is not highly sensitive to input slip distributions and fault dimensions. The simulation results indicated no significance between the two slip models under high‐frequency conditions. Finally, based on the predicted PGA values of 1891 field points selected near the fault, the acceleration field of the Jiashi earthquake is plotted. The results show that the use of the acceleration time history predicted by modified EXSIM is feasible and practical in the high‐frequency band above 1 Hz.

Looking through the Orange Glass – A Novel Perspective on Key Seismic Features and Their Influence on Hydrocarbon Potential within the Orange Basin, South Africa

This work evaluates the hydrocarbon potential of the Orange Basin offshore South Africa by considering key seismic features such as basement, Gravity Slide Systems (GSS), Mass Transport Complexes/Deposits (MTCs/MTDs), contourites, mixed depositional systems, and seafloor morphology. Further, by integrating an updated structural domains classification, we revise the chronostratigraphy of the basin. Two gravity slide systems within the northern and southern parts of the basin are mapped in their entirety and named the Orange-Senqu and Bergoli Deepwater Fold and Thrust Belts (DWFTBs), respectively. In addition to uplift, gravitational collapse, and differential sediment loading, sediment failure is likely also triggered by fluid expulsion from the basement and gas hydrate dissociation. MTCs comprise 70–90% of the Cretaceous succession from the slope seaward. We propose the name ‘crestal deformation surface’(creds) for the top of an MTC. Contourite and mixed depositional systems are described for the first time in the basin. The Sandhaai prospect is a new turbidite-contourite fan play type. Venus and Graff-type analogues, and ‘intra MTC’ plays are also recorded within the basin. Finally, we document a segmented continental slope. Segmentation is attributed to sediment mass failure and deposition, and large-scale erosion driven by bottom currents, giving the slope a graded-to-stepped appearance.

Fossilized silica diagenetic fronts: Implications for palaeoceanographic evolution across the Falkland/Malvinas plateau

A set of newly collected 2D seismic reflection data allows the mapping of two distinct cross-cutting reflectors across the Falkland/Malvinas Plateau. Reflector XR-F/MB in the Falkland/Malvinas Basin appears as a bottom simulating reflector that mimics the geometry of the present seafloor, whereas reflector XR-F/MT in the Falkland/Malvinas Trough is a non-bottom simulating reflector that mimics a shallower reflector representing the Early-Middle Miocene unconformity. The discordant geometry of these two reflectors with respect to the host-stratigraphy is argued to be associated with Opal-A to Opal-CT diagenesis, which is primarily a function of temperature. However, the estimated temperature at the present depth for reflector XR-F/MB lies below the minimum temperature for the onset of silica diagenesis. Based on their geometry and seismic characteristics, the two reflectors are interpreted to be fossilized silica diagenetic fronts, formed under palaeo-thermal conditions different from today. We hypothesize that the erosional action of intensified deep and bottom water masses subsequent to Antarctic glaciations during the Early-Middle Miocene may have driven the fossilization of the diagenetic front in the study area. It is estimated that erosion of a minimum of 270 m of overburden would account for the temperature drop driving the fossilization of the silica diagenetic fron.

Seismic characterization analyses of the Bulgarian Black Sea shelf for assessment of reservoir properties

In the Bulgarian Black Sea shelf, several gas fields have been discovered in Maastrichtian–Paleocene sediments to date. In this study, amplitude versus offset analysis (AVO) was carried out, and the extended elastic impedance (EEI) was also used, to predict fluid and lithology properties. Thus, in these special cases, AVO (or reflection angle) can significantly de-risk the existing Paleocene prospects and allow to focus on the Miocene–Oligocene successions, where some prospects have also been identified. By examining the variations in angle amplitude (or offset), it is possible to unravel lithology and fluid effects on the top of a reservoir. Seismic modeling is used to determine what type of seismic response, in terms of AVO, to expect at the depth of interest in the study area. There are five classes or types of AVO responses, and in the study area classes 1 and 2 were defined in the Miocene–Oligocene prospects. Brine-filled reservoirs and conglomerates exhibit class 1 AVO response, whereas gas-filled reservoirs show class 2 AVO responses. EEI has the ability to give estimates for elastic parameters, such as Vp/Vs ratio, bulk modulus, shear modulus, Poisson’s ratio and other parameters. In the current study, simultaneous inversion testing was done and, analyzing all the wells together, Poisson’s ratio is the most promising fluid and lithology indicator, showing good separation between water and gas responses, although there is some overlap. Projection of EEI at an angle of 38° through brine points gives a useful separation of brine, 10% gas and 90% gas reservoirs. However, the amplitude of the resulting projection is still low, which may make it difficult to resolve fluid variation once seismic noise has been added.

Fault geometry and slip rates from the Nullarbor and Roe Plains of south‐central Australia: Insights into the spatial and temporal characteristics of intraplate seismicity

AbstractAnalysis of TanDEM‐X and Shuttle Radar Topography Mission (SRTM) data reveals geomorphic evidence for 292 fault‐propagation fold scarps across the Miocene Nullarbor and Pliocene Roe Plains in south‐central Australia. Vertical displacements (VD) are determined using topographic profiling of a subset (n = 48) of the fold traces. Fault dips (mean = 44 +16/−14° at 1σ) are estimated from seismic reflection data; the mean dip is assigned to faults with unknown dip and combined with VD to estimate net displacements (ND) and average net displacements (AD) for each fault. AD exceeds single‐event displacements estimated from fault‐length scaling regressions, indicating the identified faults have hosted multiple earthquakes. Combining AD with (i) faulted surface ages (Nullarbor ~10–5 Ma, Roe ~2.5 Ma), (ii) ages of faulted erosional–depositional features (e.g. relic Late Miocene dune fields and Pliocene paleochannels), and (iii) onset of the neotectonic regime in Australia at ~10 Ma yields average slip rates from <0.1 m Myr−1to >17 m Myr−1(mean = 1.1 m Myr−1). Summation of displacements across faults yields crustal horizontal shortening rates lower than geodetically detectable resolution (≤0.01 mm yr−1) since the Late Miocene. The ca. 10 Myr‐long record of neotectonic faulting on the Nullarbor Plain provides important insights into earthquake spatial–temporal behaviours in a slowly deforming intraplate continental region.

High-Precision Characterization of Seismicity from the 2022 Hunga Tonga-Hunga Ha'apai Volcanic Eruption

AbstractThe earthquake swarm accompanying the January 2022 Hunga Tonga-Hunga Ha'apai (HTHH) volcanic eruption includes a large number of posteruptive moderate-magnitude seismic events and presents a unique opportunity to use remote monitoring methods to characterize and compare seismic activity with other historical caldera-forming eruptions. We compute improved epicentroid locations, magnitudes, and regional moment tensors of seismic events from this earthquake swarm using regional to teleseismic surface-wave cross correlation and waveform modeling. Precise relative locations of 91 seismic events derived from 59,047 intermediate-period Rayleigh- and Love-wave cross-correlation measurements collapse into a small area surrounding the volcano and exhibit a southeastern time-dependent migration. Regional moment tensors and observed waveforms indicate that these events have a similar mechanism and exhibit a strong positive compensated linear vector dipole component. Precise relative magnitudes agree with regional moment tensor moment magnitude (Mw) estimates while also showing that event sizes and frequency increase during the days after the eruption followed by a period of several weeks of less frequent seismicity of a similar size. The combined information from visual observation and early geologic models indicate that the observed seismicity may be the result of a complex series of events that occurred after the explosive eruption on 15 January, possibly involving rapid resupply of the magma chamber shortly after the eruption and additional faulting and instability in the following weeks. In addition, we identify and characterize an Mw 4.5 event five days before the paroxysmal explosion on 15 January, indicating that additional seismic events preceding the main eruption could have been identified with improved local monitoring. Our analysis of the HTHH eruption sequence demonstrates the value of potentially utilizing teleseismic surface-wave cross correlation and waveform modeling methods to assist in the detailed analysis of remote volcanic eruption sequences.