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An interpretive (structural and stratigraphic) study of the two,-dimensional seismic, data of East Nasiriya area (30 km to the south east of Nasiriya oil field within Thi-Qar province, southeastern Iraq) was carried out using Petrel 2017 program. The study area has an importance due to its location between many oil fields, but still without exploration of oil wells. Twenty five seismic lines were used, date back to different types of seismic surveys conducted in the region at different time periods. Also, the seismic velocity surveys of the nearest wells to oil fields, such as Nasiriya-1 and Subba-8, in addition to their sonic and density logs were used. A synthetic seismogram with a good matching with the seismic section was achieved to ensure the identification of the reflectors and reflectivity type (peak or trough) and follow up each one through the whole area of interest. Top Zubair reflector was picked using the composite line to link the seismic sections with each other after enhancing the ties between seismic lines. Time and depth maps were made using velocity maps created from the velocity model. The seismic, interpretation, in the area showed the existence of certain stratigraphic, features, in the ,studied reflector. Some distribution mounds and sand lenses were observed in the study area, which are continuous in more than two-dimensional seismic line in the area. These activity elements provide a reasonable explanation for the distribution of hydrocarbons in the area of study.

This research includes structure interpretation of the Yamama Formation (Lower Cretaceous) and the Naokelekan Formation (Jurassic) using 2D seismic reflection data of the Tuba oil field region, Basrah, southern Iraq. The two reflectors (Yamama and Naokelekan) were defined and picked as peak and tough depending on the 2D seismic reflection interpretation process, based on the synthetic seismogram and well log data. In order to obtain structural settings, these horizons were followed over all the regions. Two-way travel-time maps, depth maps, and velocity maps have been produced for top Yamama and top Naokelekan formations. The study concluded that certain longitudinal enclosures reflect anticlines in the east and west of the study area representing Zubair and Rumaila fold confined between them a fold consist of two domes represents Tuba fold with the same trending of Zubair and Rumaila structures. The study confirmed the importance of this field as a reservoir of the accumulation of hydrocarbons.

This research deals with a 2D seismic structural and stratigraphic interpretation of Khan Al-Baghdadi area which is located in the western part of Iraq in Anbar governorate. Two main seismic reflectors are identified within the Silurian and Ordovician; these are the Hot_shale_1 within Akkas Formation and the Top Khabour Formation, which were deposited during the Paleozoic, based on synthetic seismogram of Akk_3 well near the study area. Time, depth, and velocity maps show the presence of two anticline structures trending east-west and located on the west side of the study area. The first is the Tulul structure (here denoted as A) and the second is denoted as B. Also, the maps show the increase in time towards the eastern side of the study area. The general slope of the reflectors is towards the southeast and the increase in the thickness of formations is gradually to the southwest and the northwest sides of the study area. The direct hydrocarbon indicator (DHI) was identified as sand lenses and flat spots on the studied reflectors, when applying seismic attributes like the instantaneous phase and the instantaneous Frequency), which give indicators of potential hydrocarbon accumulations. The primary reservoir in the study area is sandstone within the Khabour Formation, while the source and seal rocks are in the Hot_shale within Akkas Formation. They are interpreted to be present throughout Akkas Field, as gas-condensate accumulations, 100 km to the west of the study area and demonstrate the viability of the Paleozoic petroleum system in the Western Desert of Iraq.

In this paper, a simple numerical model is presented for analyzing arbitrarily shaped alluvial valleys subjected to propagating obliquely incident plane SH-waves. A time-domain half-plane boundary ...

[The applications of MPGA‐DTW utilized for division and correlation of stratigraphic sequence in this study is based on multiple wireline logs. The integrated results of the sequence boundaries searched by the MPGA were consistent with the sequence boundaries revealed by commonly used approaches based on geophysical data and spectral trend attribute analyses (wavelet transform, maximum entropy spectrum, time‐frequency analyses, and integrated prediction error filter). This study reveal that the combination of MPGA‐DTW may be a powerful tool for intelligent sequence stratigraphy division and correlation. , Abstract The division and correlation of sequence stratigraphy are one of the essential steps in petroleum exploration. To comprehensively utilize the sequence stratigraphic information implied in multiple wireline well logs and improve the accuracy and reliability of sequence stratigraphic division, based on the edge detection, optimal partition, and natural evolution theories, and realizes the information fusion (formed one ‘chromosome’) of multiple wireline well logs (named as ‘genes’) which can reflect the feature information of sequence stratigraphy by using multipopulation genetic algorithm (MPGA) based on Fisher algorithm, in this study, geophysical data (wireline well logs and 3D seismic data) were used for spectral trend attribute analyses (wavelet transform, maximum entropy spectrum, time‐frequency analyses, and integrated prediction error filter). Since the seismic reflection characteristics of K1q were difficult to identify and considering subjective factors in conventional methods, a MPGA was also used to intelligently identify the sequence stratigraphy framework of the Lower Cretaceous Qingshuihe (K1q) Formation. Since the MPGA is an optimization algorithm, the code was run 10 times for accuracy with changes in the dividing layers. The optimal parameters in the process of data fusion (gene combination process) are selected. The sequence boundaries (SBs) searched by the MPGA matched those of the spectral trend attribute analyses, confirming that the MPGA was an effective, fast, and user‐friendly tool for defining the main SBs. MPGA can provide an optimal layering scheme (‘elite population’) through simultaneous searching at multiple depth ranges (‘multipopulation’), recording the optimal SBs (‘elite individuals’) of each population and making the results more convinced. Although simulation solutions may not be unique, the MPGA still provides us a chance to gain some insights into the details of the stratigraphy. Based on this intelligent identification, the maximum flooding surface, two first flooding surfaces (FFS), and three SBs were defined in K1q. The cyclic patterns (prograding, aggrading, and retrograding) were identified. They showed the relationship between accommodation space (related to tectonic subsidence of the Chemo paleo‐uplift) and sediment supply. In addition, dynamic time warping (DWT) technique was used for sequence discrimination and correlation on the integrated prediction error filter analyses curve. A massive pebbly sandstone set, named ‘bottom sandstone,’ was identified in the lowstand system tract of SQ1 (K1q1), constrained by SB1 and FFS1, which was a favourable hydrocarbon exploration target.]

This paper presents a rigorous but pragmatic and data driven approach to the science of making seismic-to-well ties. This pragmatic approach is consistent with the interpreter’s desire to correlate geology to seismic information by the use of the convolution model, together with least squares matching techniques and statistical measures of fit and accuracy to match the seismic data to the well data. Three wells available on the field provided a chance to estimate the wavelet (both in terms of shape and timing) directly from the seismic and also to ascertain the level of confidence that should be placed in the wavelet. The reflections were interpreted clearly as hard sand at H1000 and soft sand at H4000. A synthetic seismogram was constructed and matched to a real seismic trace and features from the well are correlated to the seismic data. The prime concept in constructing the synthetic is the convolution model, which represents a seismic reflection signal as a sequence of interfering reflection pulses of different amplitudes and polarity but all of the same shape. This pulse shape is the seismic wavelet which is formally, the reflection waveform returned by an isolated reflector of unit strength at the target depth. The wavelets are near zero phase. The goal and the idea behind these seismic-to-well ties was to obtain information on the sediments, calibration of seismic processing parameters, correlation of formation tops and seismic reflectors, and the derivation of a wavelet for seismic inversion among others. Three seismic-to-well ties were done using three partial angle stacks and basically two formation tops were correlated. Keywords: seismic, well logs, tie, synthetics, angle stacks, correlation

The risk of anthropogenic earthquakes created by fluid injection and completion of horizontal wells is managed using maps of recent seismicity and by creating buffer zones around previously mapped faults. In Madison and Fayette Counties, Ohio, faults were identified in 1969 using analogue paper-recorded seismic reflection technology. These faults were located primarily by mapping a prominent “Conasauga reflector” from a shale within the subsurface Cambrian section. The faults were associated with an apparent abrupt increase of the regional dip to the east. The appearance of these faults on subsequent structural maps guides regulation of horizontal drilling activity in Ohio. A time-migrated, nominal 60-fold, mini-hole-sourced, seismic section using a digital recorder with 24-bit sigma delta technology was acquired over what was reported to be the best constrained of these faults; it revealed no detectable fault or significant change in the regional dip. A synthetic seismogram derived from a sonic log acquired at a nearby well enabled identification of a seismic facies change that was likely mistaken for faulting using the earlier technology. Regulations should consider acquisition parameters and vintage of seismic surveys used to identify faults for induced seismicity risk management.

A study was conducted to use low-frequency amplitudes obtained through spectral decomposition as a direct hydrocarbon indicator within the geologically and seismically challenging area. An offshore data set from the Gulf of Thailand with well-known geology and good well control for both water and hydrocarbon bearing zones were used in this study. The rocks physics reveals similar P-impedance for gas and water-wet sands. Moreover, organic shales have similar Poisson’s ratio as of gas saturated zones. This makes differentiation of fluids and lithologies through post-stack seismic inversion and AVO analysis difficult. Reservoir wedge modelling, spectral decomposition of the synthetic and field data and analyses were conducted to understand the spectral decomposition response to thickness variation and reservoir fluids. Spectral decomposition was also applied on partial angle stacks (near, mid and far). Gas sands show bright amplitudes at low frequencies (from 10 to 15 Hz). However, spectral decomposition of the synthetic seismogram of the organic shales indicates that it consists of only relatively higher frequencies (greater than 25 Hz). Therefore, low-frequency amplitudes of spectral decomposition may help to identify hydrocarbon saturated zones.

To investigate the sediment structures within the Tangshan earthquake region in North China, we developed an effective and inexpensive method for reliably detecting the thickness of Quaternary sediments by using converted waves from local, small earthquakes recorded by a dense seismic array. From January to March 2017, we deployed 145 three-component seismographs with inter-station distances ranging between 1 and 4 km throughout the Tangshan earthquake region. Tens of local events with magnitudes between ML 0.1 and ML 2.4 were adequately recorded by the Tangshan dense seismic array and were accurately relocated. A synthetic seismogram analysis clearly showed that the travel-time differences between direct S and Sp converted waves or between direct P and Ps converted waves were almost linearly correlated with the sediment thicknesses, providing tight constraints on the basement depth. With this method, we generated a sediment thickness map of the Tangshan earthquake region. Overall, the measurements from the local converted wave method are consistent with those of previous microtremor horizontal-to-vertical spectral ratio studies. The sediment thicknesses indicate that the subsurface sedimentary structure throughout the Tangshan earthquake region has experienced significant transformations over time, partially controlled by the NE–SW-trending Tangshan Fault. The obtained sediment thickness map provides beneficial information for ensuring the safe construction of infrastructure in Tangshan city and can serve as an important model for simulating earthquake strong ground motions in the Tangshan earthquake region. Our study suggests that the proposed simple and efficient method of using converted waves could be applied to other populous plains or basins with high seismic activity and could be used to determine the general characteristics of the sediment structures in a given study area.

SUMMARY The plane-wave reflection coefficient (PRC) plays a remarkable role in conventional amplitude variation with offset (AVO) analysis and inversion. Compared with the widely exploited PRC that breaks down at the near- and supercritical incidence angles, the spherical-wave reflection coefficient (SRC) can overcome the influence of wide-angle reflection and give an accurate description of the actual seismic wave reflection phenomenon based on spherical-wave fronts. However, SRC is not widely used in AVO inversion due to its nonlinearity and computational complexity. In our study, the characteristics of frequency–depth-dependent monochromatic SRC are discussed and a novel three-parameter SRC is derived. Compared with the conventional six-parameter SRC, the novel three-parameter SRC improves the stability of spherical-wave AVO inversion. In addition, the concept of SRC within the Fresnel zone is proposed, and the accuracy of SRC within the Fresnel zone in the deep subsurface is tested. Finally, a nonlinear spherical-wave AVO inversion method for elastic media is proposed, which can make full use of all frequency components of wavelet. The robustness of the proposed method is verified by the application on synthetic seismogram with white Gaussian noise. The feasibility and practicability of this method are verified by comparing the spherical-wave AVO inversion results with the filtered well logs at the known well location.

The offshore part of the Nile Delta is considered one of the most prolific provinces for gas production and for future petroleum exploration. Amplitude Variation with Offset (AVO) analysis supported by composite logs considered as one of the best-advanced techniques enables the interpreter to understand the seismic data. It is used to generate a new view of the output results, especially for the identification of gas zones as gas channels by using pre-stack AVO attributes that based on the intercept product gradient (A*B) and the Scaled Poisson’s Ratio Change. Free gas, regardless of the percentage show obvious AVO anomaly. Well log data, including gamma-ray, resistivity, and Vp sonic logs are used in the seismic data to well tie and in the generation of the synthetic seismogram. Seismic data conditioning processes with check-shot correction is performed to improve the resolution of the reflection events and signal to noise ratio. AVO attributes technique, as a direct hydrocarbon indicator, including AVO gradient analysis and AVO crossplot separate the gas levels in the sand-shale sequences. The identified gas-bearing zones consistent with well log data responses. As the main conclusion, we show the visual evidence for the gas-bearing zones by interpreting different AVO responses due to the changes in fluid and rock types.

Seismic design for high-rise buildings is challenging particularly in areas of moderate seismic activity where acceleration records of past events are not available and the long period effect of distant earthquakes needs to be incorporated. The New Administrative Capital of Egypt is built in an area of low-to-moderate seismicity, with a known active fault system and it is historically proved that strong earthquakes in the Mediterranean have damaging effects on Northern Egypt. In this work, we have utilized the neo-deterministic seismic hazard approach a modern approach that can incorporate all information, from geology, tectonics, geodesy, rupture process, and seismicity, to produce site-specific seismic hazard assessment. Both, local and distant earthquakes, have been incorporated to produce a synthetic seismogram (displacement, velocity, and acceleration) and spectral accelerations to be used by the structural designers. The response spectra equivalent to the peak values of acceleration (PGA), at 50th, 84th, and 95th percentiles, are obtained by selecting at each period of the spectrum the scenario that may contribute to the level of hazard at each site. The results obtained estimated the PGA median value (50th percentile) is about 0.16 g, which is comparable to 0.15 g PGA of the Egyptian building code for zone II where the site is located. The 84th and 95th percentile of seismic response spectra are also calculated to provide further input for the performance-based design. The PGA value for 84th and 95th percentile equals 0.23 and 0.28 g, respectively.

The extensive application of pre-stack depth migration has produced huge volumes of seismic data, which allows for the possibility of developing seismic inversions of reservoir properties from seismic data in the depth domain. It is difficult to estimate seismic wavelets directly from seismic data due to the nonstationarity of the data in the depth domain. We conduct a velocity transformation of seismic data to make the seismic data stationary and then apply the ridge regression method to estimate a constant seismic wavelet. The estimated constant seismic wavelet is constructed as a set of space-variant seismic wavelets dominated by velocities at different spatial locations. Incorporating the weighted superposition principle, a synthetic seismogram is generated by directly employing the space-variant seismic wavelets in the depth domain. An inversion workflow based on the model-driven method is developed in the depth domain by incorporating the nonlinear conjugate gradient algorithm, which avoids additional data conversions between the time and depth domains. The impedance inversions of the synthetic and field seismic data in the depth domain show good results, which demonstrates that seismic inversion in the depth domain is feasible. The approach provides an alternative for forward numerical analyses and elastic property inversions of depth-domain seismic data. It is advantageous for further studies concerning the stability, accuracy, and efficiency of seismic inversions in the depth domain.

The reflection coefficient solved by using the traditional impedance inversion method cannot reflect low-frequency information sufficiently and its continuity and resolution are limited, so the quality and resolution of impedance inversion are impacted seriously. In this paper, the advantages of rich low-frequency signals were discussed with the theoretical synthetic seismogram and wavelet simulation as the fulcrum. Then, the low-frequency sparse double-constrained reflection coefficient method was introduced to modify the sparse optimization item, and thus a new method was formed. Finally, based on the broadband data and non-broadband data of the actual work area, the reflection coefficient and impedance inversion solved by the traditional basis-pursuit reflection coefficient inversion were compared and then the calculation results of low-frequency sparse double-constrained reflection coefficient inversion were compared to verify the effect of the modified method. And the following research results were obtained. First, the broadband data with rich low-frequency information is less affected by the side lobe, and its seismic data resolution is higher, which is more favorable for the improvement of inversion accuracy and resolution. Second, in the new method, the L2 norm low-frequency model is added on the basis of the BPDN basis-pursuit denoising problem to constrain the residual, so as to realize the direct solution of the reflection coefficient with low-frequency information. Third, the reflection coefficient and wave impedance solved by using the new method have better continuity and resolution than those solved by using the traditional method and they are in good agreement with the well data. In conclusion, the new method achieves higher resolution on the impedance inversion of broadband data and non-broadband data and the accuracy of impedance inversion is increased, so it has higher application values in predicting the distribution of thin reservoirs. Keywords: Compressed sensing, Low-frequency information, Impedance inversion, Broadband, Low-frequency constraint, Reflection coefficient, High resolution, South China Sea area

Marine vertical cable seismic (VCS) is a promising survey technique for submarine complex structure imaging and reservoir monitoring, which uses vertical arrays of hydrophones deployed near the seafloor to record seismic wavefields in a quiet environment. Recently, we developed a new type of distributed VCS system for exploration and development of natural gas hydrates preserved in shallow sediments under the seafloor. Using this system and air-gun sources, we accomplished a 3D VCS yield data acquisition for gas hydrates exploration in the Shenhu area, South China Sea. In view of the characteristics of VCS geometry, we implement reverse time migration (RTM) on a common receiver gather to obtain high-resolution images of marine sediments. Due to the unique acquisition method, it is asymmetrical for the reflection path between the sources and the receivers in the VCS survey. Therefore, we apply accurate velocity analysis to common scatter point (CSP) gathers generated from common receiver gathers instead of the conventional velocity analysis based on common depth point gathers. RTM with this reliable velocity model results in high-resolution images of submarine hydrate-bearing sediments in deep water conditions. The RTM imaging section clearly shows the bottom simulating reflector (BSR) and also the reflection characteristics of the hydrate-bearing sediments filled with consolidated hydrates. Moreover, its resolution is relative to that of acoustic logging curves from the nearby borehole, and this imaging section is well consistent with the synthetic seismogram trace generated by the logging data. All these results reveal that VCS is a great potential technology for exploration and production of marine natural gas hydrates.

The variations of elastic parameters and attenuation of rock under deformation are of great importance for a number of geophysical problems. Here, we estimate elastic parameters and their evolution...

In the past, several destructive earthquakes have occurred in the North African Atlas Mountain ranges located along the Africa–Eurasia plate boundary. Although the region is rich with impressive archaeological sites, including those in modern Tunisia, few comprehensive archaeoseismological studies have been conducted. Historic sources account at least three damaging earthquakes in the Kairouan area in central Tunisia between AD 859 and 1041. Little is known about which faults triggered these earthquakes or the size of these events. The water supply of the city of Kairouan depended on a 32-km-long aqueduct with a large bridge (now partially collapsed) at the confluence of the de Mouta and Cherichira rivers. The original bridge of Roman construction was retrofitted twice during the Aghlabid period (AD 800–903) and probably in AD 995 during the Fatimid period. The ruined section of the bridge shows damage which might be related to the AD 859 earthquake shaking. Here, we present a detailed study of the history, the status and the damage of the Cherichira aqueduct bridge using previous historic accounts and written works, a 3D laser scan model, local geological and seismological characteristics, and include results of radiocarbon dating and a timeline of events. In addition to earthquake ground motions, we consider severe flash floods on the bridge as a potential cause of the damage. We estimate the severity of such flash floods and develop a model with 18 earthquake scenarios on local reverse and strike-slip faults with magnitudes between MW 6.1 and 7.2. While a few damage patterns might be indicative of flooding, most damage can be attributed to earthquakes. It is highly probable that the earthquake in AD 859 caused enough damage to the Aghlabid bridge to render it dysfunctional; however, to resolve the question of whether another earthquake in AD 911 or 1041 caused the complete destruction of the previously retrofitted aqueduct by the Fatimids requires dating of additional sections of the bridge., Universität zu Köln (1017)

The Bohemian Massif exposes structures and metamorphic rocks remnant from the Variscan Orogeny in Central Europe and is bordered by the Franconian Fault System (FFS) to the west. Across the FFS, possible presence of Variscan units and structures are buried by Permo-Mesozoic sedimentary rocks. We integrate existing DEKORP 2D seismic reflection, well and surface geological data with the newly acquired FRANKEN 2D seismic survey to investigate the possible westward continuation of Variscan tectonostratigraphic units and structures, and their influence on latest to post-Variscan basin development. Subsurface Permo-Mesozoic stratigraphy is obtained from available wells and are tied to seismic reflection profiles using a synthetic seismogram calculated from density and velocity logs. Below the sedimentary cover, three main basement units are identified using seismic facies descriptions that are compared with seismic reflection characteristics of exposed Variscan units east of the FFS. Our results show that Upper Paleozoic low-grade metasedimentary rocks and possible Variscan nappes are bounded and transported by Variscan shear zones to ca. 65 km west of the FFS. Basement seismic facies in the footwall of the Variscan shear zones are interpreted as Saxothuringian basement. We show that the location of normal fault-bounded latest to post-Variscan Upper Carboniferous-Permian basins are controlled by the geometry of underlying Variscan shear zones. Some of these Upper Carboniferous-Permian normal faults reactivated as steep reverse faults during the regional Upper Cretaceous inversion. Our results also highlight that reverse reactivation of normal faults gradually decreases west of the FFS.

Lithofacies are very influential in the transmission of fluids within the reservoir. The objective of this study is to use geostatistical techniques of sequential indicator simulation (SISIM) a variogram-based algorithm (VBA), single normal equation simulation (SNESIM) and filter-based simulation (FILTERSIM) of multiple-point geostatistics (MPG) in developing realistic facies model. A reservoir sand package “Reservoir-E” was correlated across five wells in the field. Synthetic seismogram of well HT-1 was generated, and Horizon E picked on seismic section to produce time and depth surfaces of the reservoir. The conditional if statement to generate lithofacies was applied on the extracted volume of shale data within “Reservoir-E,” and the data were inputted in Stanford Geostatistics Modeling Software for facies modeling. The first realization from SISIM was converted to a training image used for MPG. Visually, the MPG algorithm of SNESIM and FILTERSIM produced realization that is substantially better and more realistic than the VBA of SISIM. The magnitude of correlation coefficients of algorithms was carried out using the mean and variance of realizations, the results revealed mean and variance magnitude of correlation coefficients between SISIM and SNESIM with 0.8933 and 0.9637, SISIM and FILTERSIM with 0.8639 and 0.5097 and SNESIM and FILTERSIM with 0.9717 and 0.8603. The results revealed a very good mean and variance magnitude of correlation coefficients between SISIM and SNESIM; good between SISIM and FILTERSIM; and very good mean and variance correlation coefficient between SNESIM and FILTERSIM. The qualitative interpretation of the model built with SNESIM and FILTERSIM clearly detects lithofacies in the field which makes them a better algorithm in facies modeling.

As a most important step in geological interpretation, stratigraphic correlation plays important roles in reservoir estimation and geologic modeling. A variety of datasets are used for stratigraphic correlation, such as well-logging data and seismic data, which are collected by different kinds of sensors. However, much uncertainty will be generated in the traditional course of stratigraphic correlation, because the complex underground geological structures cannot be comprehensively depicted by single dataset. Therefore, in this paper, we propose a visualization system to present and reduce the uncertainty in stratigraphic correlation based on the fusion analysis of multi-source datasets. First, a synthetic seismogram is modeled for each drilling well and a traditional time-depth conversion is conducted to match the seismic data and logging data. Then, an uncertainty model is proposed to quantify the depth difference between seismic horizons and stratigraphic structures extracted from different datasets. Furthermore, a set of visual designs are integrated into an uncertainty visualization system, enabling users to conduct intuitive uncertainty exploration and supervised optimization of stratigraphic correlation. Case studies based on real-world datasets and interviews with domain experts have demonstrated the effectiveness of our system in analyzing the uncertainty of stratigraphic correlation and refining the results of geological interpretation.

Adequate analyses of seismic and petrophysical data help to minimize drilling risk and maximize well and reservoir productivity. Reservoir characterization was carried out to provide information and improve understanding of the geological and petrophysical parameters, and hence improve decision making regarding the development of the field under study. Wireline logs obtained from three wells as well as a 3D Seismic data coverage of G-field in the Niger Delta were evaluated using the petrel software. Suites of gamma and deep resistivity logs aided the delineation and correlation of the sandstone unit, while the top was tied to the seismic data using synthetic seismogram to determine seismic characters. Well correlation enabled the delineation of reservoir sand across the wells. The quality of the reservoir was determined from petrophysical averages, in which the reservoir has an average thickness of 72 m, average porosity of 0.31, average net to gross of 0.75, average V-shale of 0.25, and average water saturation of 0.19, respectively. Listric normal faults were mapped across the field. The models reveal lateral and horizontal variations in reservoir properties which capture subsurface heterogeneity and anisotropy across the reservoir sand, and also possible sweet-spot zones were identified. These are diagnostic of areas for future exploitation and recovery of hydrocarbon. Seismic attributes analysis was done to predict variation in lithofacies across the sandstone body.

Resolution of seismic data is critical to reservoir prediction and the near surface underground structure . Low resolution of seismic data is caused by many factors, such as the surface environment, shielding layer and sand body. To widen the frequency bandwidth and improve the resolution of the post-stack seismic reflection profiles, we analyze the characteristics of amplitude-spectrum of the post-stack profiles and design frequency expanding inverse filter based on the logging data for data fusion , including the loss of longitudinal frequency information and the variation of transverse frequency. This method creates broadband synthetic seismogram by using a wide bandwidth seismic wavelet and a series of reflection coefficients calculated from acoustic logging and density logging data. By analyzing the synthetic seismogram of widening frequency band with borehole seismic traces, the loss regularity of vertical frequency signal generated by low-pass filter of formation is restored. Additionally, to compare borehole seismic traces with arbitrary cross-well trace, the filtering effect about transverse variation of formation is obtained. The successful application of the inverse filter in terms of data fusion to acquire a new profile with better resolution called the seismic-logging profile, demonstrated that the proposed data fusion method has the advantage of being efficient in compensating the high frequency components of seismic section.

Aimed at the serious mismatch between the synthetic seismogram and the real data of the Sinian Dengying Formation and the Lower Cambrian Qiongzhusi Formation in the GS1 well area, Sichuan Basin, four aspects of internal multiples identification and suppression were studied. Firstly, a forward modeling method of internal multiple based on reflectivity method was developed. Through eight means such as post-stack and pre-stack forward modeling of internal multiple, and combined with VSP data, it was demonstrated that well-seismic mismatching in this area is mainly caused by the internal multiples. Secondly, the simulation results of internal multiple forward modeling using the stripping method combined with the internal multiple periodicity analysis showed that four groups of overburden layers with velocity inversion were the main sources of the internal multiples. Thirdly, by identifying internal multiples accurately and using suppression technology based on pattern recognition, an effective and replicable suppression scheme suitable for these formations was established, overcoming the difficulty of the small speed difference between internal multiple and primary reflection wave which makes the current methods ineffective. Fourthly, an evaluation index of internal multiple intensity was proposed, and the internal multiple intensity distribution diagram of the fourth member of Dengying Formation (Deng-4 Member) in Gaoshiti-Moxi area was compiled. This scheme greatly improved the well-seismic match, and the strata sedimentary features are clearer on the new seismic profiles with higher lateral resolution, with which smaller faults and geological anomalies can be identified and a series of the bead reflections in the Dengying Formation are first discovered. The coincidence rate of reservoir prediction based on seismic waveform classification was increased from 60% to 90%, and that of hydrocarbon detection based on dual phase medium theory was increased from 70% to 100%. Key words: internal multiple, reflectivity method forward modeling, well-seismic match, velocity inversion, seismic waveform classification, hydrocarbon detection, Sichuan Basin, Sinian Dengying Formation

In December 2017, a triplet earthquake sequence of Mw 5.8–6.1 occurred near Hojedk, southeast Iran. The sequence was not destructive, but occurred in a highly seismically active region that previously experienced the 1981–1998 Sirch-Golbaf earthquake sequence and destructive 2003 Mw 6.6 Bam earthquake. We apply a waveform inversion method based on the modeling of regional seismic broadband data to derive the point source and kinematic rupture parameters of the triplet and its five significant aftershocks. The choice of an earthquake source model with a reduced number of parameters and a sequential inversion process with several iterations result in unique and stable earthquake source solutions. Within the inversion process, we combine the modeling of low- and high-frequency seismological data to retrieve the moment tensor and the kinematic source parameters. Synthetic seismogram and spectra are generated for an accurate regional velocity model. Our results suggest that the triplet ruptured a segmented fault system, with centroid locations aligned along a single lineament. Estimation of rupture directivity suggests the activation of SE-NW structure. In conclusion, we suggest that the triplet was associated with the failure of one or more aligned blind thrust faults, oriented SE-NW and dipping to the NE, in a restraining bend between strike-slip faults in a region that is a part of the greater system of the present continental shortening in Iran.

The recent discovery of gravitational waves (GWs) and their potential for cosmic observations prompted the design of the future third-generation GW interferometers, able to extend the observation distance for sources up to the frontier of the Universe. In particular, the European detector Einstein Telescope (ET) has been proposed to reach peak strain sensitivities of about 3×10−25 Hz−1/2 in the 100 Hz frequency region and to extend the detection band down to 1 Hz. In the bandwidth [1,10] Hz, the seismic ambient noise is expected to represent the major perturbation to interferometric measurements, and the site that will host the future detectors must fulfill stringent requirements on seismic disturbances. In this article, we conduct a seismological study at the Italian ET candidate site, the dismissed mine of Sos Enattos in Sardinia. In the range between few mHz to hundreds of mHz, out of the detection bandwidth for ET, the seismic noise is compatible with the new low-noise model (Peterson, 1993); in the [0.1,1] Hz bandwidth, we found that seismic noise is correlated with sea wave height in the northwestern Mediterranean Sea. In the [1,10] Hz frequency band, noise is mainly due to anthropic activities; within the mine tunnels (≃100 m underground), its spectrum is compliant with the requirements of the ET design. Noise amplitude decay with depth is consistent with a dominance of Rayleigh waves, as suggested by synthetic seismograms calculated for a realistic velocity structure obtained from the inversion of phase- and group-velocity dispersion data from array recording of a mine blasting. Further investigations are planned for a quantitative assessment of the principal noise sources and their spatiotemporal variations.

3D data have several advantages that include creation of seismic sections in any desired azimuth for display and extraction of multiple seismic attributes. Horizontal viewing of 3D seismic is another advantage that resolves small-scale depositional features better in plan view. Stratal attribute slices are extensively used as a tool to map channel/fan complexes with their associated diverse facies. Horizontal-view seismic is also useful for sequence stratigraphy interpretation (SSSI) to build tectono-stratigraphic frameworks for petroleum system modeling.

Modeling is a computational process to determine the seismic response of a given geologic model and can be 1D, 2D and 3D and structural or stratigraphic. Synthetic seismogram is the most elementary and common example of one-dimensional (1D) modelled seismic response of the earth. Field of application, benefits and limitations of forward modeling are briefly stated with examples.

Seismic interpretation conveys the geologic meaning of seismic data by extracting subsurface information from it and can be of different kinds, such as structural, stratigraphic and seismic stratigraphy. It depends on the geologic objectives linked to the phase of exploration and on the type of available data, its grid density and its quality. The workflow for each category is described and the shortcomings highlighted.

Amplitude versus offset (AVO) analysis integration to well log analysis is considered one of the advanced techniques to improve the understanding of facies and fluid analysis. Generating AVO attributes are one solution to give an accurate result in facies and fluid characterization. This study is focused on a field of Northern Malay basin, which is associated with a fluvial-deltaic environment, where this system has high heterogeneity, whether it is vertically or horizontally. This research is aimed to demonstrate an application of the scale of quality factor of P-wave (SQp) and the scale of quality factor of S-wave (SQs) AVO attributes for facies and fluid types separation in field scale. These methods are supposed to be more sensitive to predict the hydrocarbons and give less ambiguity. SQp and SQs are the new AVO attributes, which derived from AVO analysis and created according to the intercept product (A) and gradient (B). These new attributes have also been compared to the common method, which is the Scaled Poisson&rsquo, s Ratio attribute. By comparing with the Scaled Poisson&rsquo, s Ratio attribute, SQp and SQs attributes are more accurate in determining facies and hydrocarbon. SQp and SQs AVO attributes are integrated with well log data and considered as the best technique to determine facies and fluid distribution. They are interpreted by using angle-stack seismic data based on amplitude contrast on interfaces. Well log data, e.g., density and sonic logs, are used to generate synthetic seismogram and well tie requirements. The volume of shale, volume of coal, porosity, and water saturation logs are used to identify facies and fluid in well log scale. This analysis includes AVO gradient analysis and AVO cross plot to identify the fluid class. Gassmann&rsquo, s fluid substitution modeling is also generated in the well logs and AVO synthetics for in situ, pure brine, and pure gas cases. The application of the SQp and SQs attributes successfully interpreted facies and fluids distributions in the Northern Malay Basin.

A lot of seismic phenomena with small magnitude has been taking place in the Ladoga lake region (northwestern Russia). One of them is the earthquake which was recorded on the 31st of July, 2010 followed by the swarm of microearthquakes near Nikonovsky cape. There is only one station in the region that is why it is difficult to process the data. In this work, we propose a new approach to construct synthetic seismograms of the main event with minimum data. Also this approach applies us to calculate parameters of the source. The approximate magnitude of the main event is $$M_L=-0.8$$ . For swarm events, we have magnitude values from $$-\,1.0$$ to $$-\,2.6$$ . The data of swarm events (microearthquakes) is used to test the technique of constructing synthetic seismograms. The approach we propose is based on Green’s function method with using two temporal $$\delta$$ -sequences (the Lorentzian function and the continuous Dirichlet kernel). A comparison of synthetic and real seismograms shows that the Lorentzian function is better to describe small local events, and the continuous Dirichlet kernel is more appropriate for earthquakes. This approach can be generalized to various problems of different nature.

Highlights • Physical properties obtained from core and log data at the Danube deep sea fan are reported. • Core-log-seismic integration defines stratigraphic framework at the S2 channel. • All data suggest no gas hydrate is present at drill sites within uncertainties of methods employed. Abstract Drilling, coring, and geophysical logging were performed with the MARUM-MeBo200 seafloor drilling rig to investigate gas hydrate occurrences of the Danube deep sea fan, off Romania, Black Sea. Three sites within a channel-levee complex were investigated. Geophysical log data of P-wave velocity, electrical resistivity, and spectral gamma ray are combined with core-derived physical properties of porosity, magnetic susceptibility, and bulk density. Core- and log physical property data are used to define a time-depth conversion by synthetic seismogram modeling, which is then used to interpret the seismic data. Individual polarity reversed reflectors within the stratigraphic column drilled are linked to reduction in P-wave velocity and bulk density. Those reflectors (and associated reflection packages) are accompanied by distinct and systematic changes in sediment porosity, magnetic susceptibility, and electrical resistivity. Overall, the sediments at drill site GeoB22605 (MeBo-17) represent the younger (upper) levee sequence of the channel, that has been eroded at drill site GeoB22603 (MeBo-16). Splicing seismic data across the channel from the East (MeBo-16) to the West (MeBo-17) demonstrates the continuation of reflectors underneath the channel. The upper ∼50 m below seafloor (mbsf) at site MeBo-16 do not stratigraphically belong to the same sequence of the (deeper) levee-deposits. Above the marked erosional unconformity, sediments at Site MeBo-16 are likely derived by a mixture of repeated slump-events (identified as seismically transparent units) interbedded with hemi-pelagic sedimentation. Similarly, sediments within the upper ∼20 mbsf at Site MeBo-17 are not stratigraphically the same levee-deposits, but are derived by a mixture of slump-events (also seen in the marked seafloor amphitheatre architecture of a large failure complex extending further upslope) and hemi-pelagic sedimentation. All observations combined show that the seismically observed stratigraphic pattern represents a reflectivity sequence mostly driven by variations in density (porosity) and correspondingly by changes in P-wave velocity and electrical resistivity. All observations from the geophysical log- and core, as well as geochemical data do show no evidence for the presence of any significant gas hydrates within the drilled/cored sequences.

Summary Deep reflection seismic interpretation is challenging due to the heterogeneity of the crystalline crust. Statistical approaches are suggested as a potentially powerful tool for deep seismic interpretation as the reflection wavefield can represent at least the spatial velocity heterogeneity of the geology. The lateral correlation length is an essential parameter of the von Karman stochastic model which is considered as a proper description of the heterogeneity of crustal velocity. To estimate the lateral correlation length, it is crucial to obtain accurate autocorrelation function from limited data sets. We introduce an innovative algorithm to estimate lateral correlation length from deep seismic reflection data. First, the power spectrum is obtained through autoregressive spectral estimation. Then inverse Fourier transform is applied to the power spectrum to obtain the autocorrelation function. Moreover, average multitrace one-dimension autocorrelation is used to replace the two-dimension autocorrelation function. A synthetic seismogram is used to verify the resolution of our method. The geological meaning of different seismic reflection patterns was discussed after applying our method to deep seismic reflection field data. The result shows that lateral correlation can identify Moho discontinuity, crustal reflections, and some structure in sedimentary strata

International audience; 3-D frequency-domain full waveform inversion (FWI) is applied on North Sea wide-azimuth ocean-bottom cable data at low frequencies (≤10 Hz) to jointly update vertical wave speed, density and quality factor Q in the viscoacoustic VTI approximation. We assess whether density and Q should be viewed as proxy to absorb artefacts resulting from approximate wave physics or are valuable for interpretation in the presence of soft sediments and gas cloud. FWI is performed in the frequency domain to account for attenuation easily. Multiparameter frequency-domain FWI is efficiently performed with a few discrete frequencies following a multiscale frequency continuation. However, grouping a few frequencies during each multiscale step is necessary to mitigate acquisition footprint and match dispersive shallow guided waves. Q and density absorb a significant part of the acquisition footprint hence cleaning the velocity model from this pollution. Low Q perturbations correlate with low-velocity zones associated with soft sediments and gas cloud. However, the amplitudes of the Q perturbations show significant variations when the inversion tuning is modified. This dispersion in the Q reconstructions is however not passed on the velocity parameter suggesting that cross-talks between first-order kinematic and second-order dynamic parameters are limited. The density model shows a good match with a well log at shallow depths. Moreover, the impedance built a posteriori from the FWI velocity and density models shows a well-focused image with however local differences with the velocity model near the sea bed where density might have absorbed elastic effects. The FWI models are finally assessed against time-domain synthetic seismogram modelling performed with the same frequency-domain modelling engine used for FWI.

A new stochastic seismic inversion method based on the local gradual deformation method is proposed, which can incorporate seismic data, well data, geology and their spatial correlations into the inversion process. Geological information, such as sedimentary facies and structures, could provide significant a priori information to constrain an inversion and arrive at reasonable solutions. The local a priori conditional cumulative distributions at each node of model to be inverted are first established by indicator cokriging, which integrates well data as hard data and geological information as soft data. Probability field simulation is used to simulate different realizations consistent with the spatial correlations and local conditional cumulative distributions. The corresponding probability field is generated by the fast Fourier transform moving average method. Then, optimization is performed to match the seismic data via an improved local gradual deformation method. Two improved strategies are proposed to be suitable for seismic inversion. The first strategy is that we select and update local areas of bad fitting between synthetic seismic data and real seismic data. The second one is that we divide each seismic trace into several parts and obtain the optimal parameters for each part individually. The applications to a synthetic example and a real case study demonstrate that our approach can effectively find fine-scale acoustic impedance models and provide uncertainty estimations.

Numerical 3D high-resolution models of subsurface petroelastic properties are key tools for exploration and production stages. Stochastic seismic inversion techniques are often used to infer the spatial distribution of the properties of interest by integrating simultaneously seismic reflection and well-log data also allowing accessing the spatial uncertainty of the retrieved models. In frontier exploration areas, the available data set is often composed exclusively of seismic reflection data due to the lack of drilled wells and are therefore of high uncertainty. In these cases, subsurface models are usually retrieved by deterministic seismic inversion methodologies based exclusively on the existing seismic reflection data and an a priori elastic model. The resulting models are smooth representations of the real complex geology and do not allow assessing the uncertainty. To overcome these limitations, we have developed a geostatistical framework that allows inverting seismic reflection data without the need of experimental data (i.e., well-log data) within the inversion area. This iterative geostatistical seismic inversion methodology simultaneously integrates the available seismic reflection data and information from geologic analogs (nearby wells and/or analog fields) allowing retrieving acoustic impedance models. The model parameter space is perturbed by a stochastic sequential simulation methodology that handles the nonstationary probability distribution function. Convergence from iteration to iteration is ensured by a genetic algorithm driven by the trace-by-trace mismatch between real and synthetic seismic reflection data. The method was successfully applied to a frontier basin offshore southwest Europe, where no well has been drilled yet. Geologic information about the expected impedance distribution was retrieved from nearby wells and integrated within the inversion procedure. The resulting acoustic impedance models are geologically consistent with the available information and data, and the match between the inverted and the real seismic data ranges from 85% to 90% in some regions.

The Moho discontinuity is one of the fundamental boundaries on Earth, separating the crust from the upper mantle. Arrival times of seismic reflection and refraction data are used to estimate the depth of the Moho, but the nature of the Moho remains illusive. We present a synthetic seismogram modelling study for a suite of possible velocity models of the oceanic lower crust and Moho transition zone (MTZ). For modelling, we have used a 45-km long multichannel streamer (MCS) geometry, to get insight about waveforms and amplitudes of seismic phases like the crustal refraction (Pg), Moho reflection (PmP) and mantle refraction (Pn), and the interactions between these phases. We find that the nature of PmP reflection not only depends on the velocity structure of the MTZ but also on the velocity structure of the lower crust and upper mantle. The triplication resulting from these three seismic arrivals and its lateral extent mainly depend on the velocity structure in the lower crust. Apart from the velocity in the crust, the critical distance for the PmP arrival depends on the velocity gradient in the MTZ. The amplitude versus offset analysis of the wide-angle PmP arrivals indicates that there are two broad high amplitude peaks for the MTZ thickness less than or equal to the dominant seismic wavelength and only one large narrow peak for a thicker MTZ. Consequently, strong PmP arrivals for a thick MTZ lie in a narrow offset range around the critical offset whereas they lie over a large offset range for a sharp Moho. We also have modelled the synthetic seismograms for velocity structures from the Oman and the Bay of Islands ophiolites. Our modelling results indicate that the quantitative analysis of amplitudes and waveforms of ultra-long offset MCS data could provide detailed information about the lower crust and MTZ.

The Foulden Maar is a terrestrial monogenetic volcanic crater found within the latest Oligocene–Late Miocene Waipiata Volcanic Field on the South Island of New Zealand. A geophysical characterisati...

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.

Based on the time-lapse seismic data of CO2-EOR project in Gao89 area of Shengli Oilfield in China, this paper carries out the calibration of time-lapse seismic data and the analysis of amplitude differences before and during CO2 injection. From well-log based forward model, we applied Hertz-Mindlin formula and combined it with Gassmann's equation to predict the P-wave velocity, S-wave velocity and density logs at different effective pressure and CO2 fluid saturation. Then we made time-lapse synthetic seismogram to calibrate time lapse seismic data and analyzed amplitude differences from forward model. Our study shows that the effective pressure is the dominant factor for the changes of elastic parameters and seismic amplitudes at the early time of CO2 injection because the reservoir pressure was much lower than that of in-situ pressure. The deficit of reservoir pressure was caused by oil producing. In addition, CO2 saturation also affects the elastic parameters of reservoir and seismic amplitude. Finally, we calibrated the RMS amplitude of time-lapse seismic data at CO2 injection layers and caprocks in Gao89 CO2 injection area. The difference of time-lapse seismic amplitudes reflects low pressure zone of reservoir which is also the migration path and the distribution of CO2.

The InSight mission will land a single seismic station on Mars in November 2018, and the resultant seismicity catalog will be a key component for studies aiming to understand the interior structure of the planet. Here, we present a preliminary version of the web services that will be used to distribute the event and station metadata in practice, employing synthetic seismograms generated for Mars using a catalog of expected seismicity. Our seismicity catalog consists of 120 events with double-couple source mechanisms only. We also provide Green’s functions databases for a total of 16 structural models, which are constructed to reflect one-dimensional thin (30 km) and thick (80 km) Martian crust with varying seismic wave speeds and densities, combined with two different profiles for temperature and composition for the mantle. Both the Green’s functions databases and the precomputed seismograms are accessible online. These new utilities allow the researchers to either download the precomputed synthetic waveforms directly, or produce customized data sets using any desired source mechanism and event distribution via our servers.

Normal-mode summation is the most rapidly used method in calculating synthetic seismograms. However, normal-mode summation is mostly applied to point sources. For earthquakes triggered by faults extending for as long as several 100 km, the seismic waves are usually simulated by point source summation. In this paper, we attempt to follow a different route, i.e., directly calculate the excitation of each mode, and use normal-mode summation to obtain the seismogram. Furthermore, we assume the finite source to be a “line source” and numerically calculate the transverse component of synthetic seismograms for vertical strike-slip faults. Finally, we analyze the features in the Love waves excited by finite faults.

Seismic resolution enhancement has a key role in seismic interpretation, especially in reservoir characterization and geologic interpretation. Exploration seismology has a limitation in temporal resolution and thin-layer detection, so any effort to improve the resolution of available data is valuable. Seismic deconvolution is one of the main steps in seismic processing and is intensively used for enhancing the vertical resolution. In this procedure, the seismic wavelet is compressed in order to decrease wavelet interferences and improve temporal resolution. In the common method of seismic deconvolution — i.e., Wiener deconvolution — the seismic wavelet is estimated by using the early part of autocorrelation of traces. Assuming the reflection series is a random function, the smoothed version of the amplitude spectrum of traces can be considered as the amplitude spectrum of the seismic wavelet. The wavelet spectrum can be properly reconstructed by the linear combination of a number of Ricker wavelets with different peak frequencies. The authors aim to introduce a novel method for resolution improvement based on fitting and finding main Ricker components of the source-wavelet spectrum. This attempt is classified under the group of the separable nonlinear least squares (SNLS), the objective function of which is a combination of linear and nonlinear functions. A variable projection method is applied to recognize the optimum peak frequency of Ricker wavelets involved in the wavelet spectrum. Our synthetic tests indicate that the SNLS algorithm is able to achieve a very close approximation of dominant Ricker components of the source spectrum. Considering the minimum phase assumption of the wavelet, the phase spectrum is also computed by Hilbert transform of the estimated amplitude spectrum. Once the amplitude and phase information are available, the deconvolution operator can be designed. Our synthetic and real tests indicate that, in comparison with Wiener deconvolution, spectral modeling based on dominant Ricker components (SMDRC) has improved the deconvolution outputs.

Faults are the most important geological structures that need to be detected in any modern underground coal mining project. Even a fault with a throw of a few metres can create safety issues and lead to costly delays in mine production. While seismic surveys are usually successful at locating faults with throws greater than 5-10 m, reliable techniques for resolving more subtle faults, dykes and other minor features are yet to be developed. In seismic data, there are two types of seismic energy signatures that can be used for subsurface imaging: specular reflections and diffractions. Specular reflections are created by relatively smooth surfaces between layers of differing impedance contrasts such as at coal-rock interfaces. Specular reflections are used in conventional seismic reflection surveys. Diffractions are generated by local discontinuities caused by surface roughness, faults, dykes and fractures. In this paper, we describe the use of a moving average error filter which, along with a process of reflection event flattening for accommodation of dips and undulations of coal seam reflections, can be used to effectively extract diffraction signals from post-stack reflection seismic data. By identifying diffractions, small faults and other minor features that are elusive using conventional seismic reflection processing can be detected, suggesting that diffraction imaging may be a superior method to seismic reflection imaging. Both synthetic and real (2D and 3D) coal seismic data are used to illustrate the feasibility of diffraction imaging for small fault detection. It is demonstrated from synthetic examples that the extracted diffractions can be used to detect faults with a throw of 1 m while a real data example shows that it is possible to detect igneous dykes with widths of just 4 m.

Raw seismic data show the subsurface reflectors among the rock layers, while the acoustic-impedance section shows the layers. Therefore, acoustic impedance is closer to reality and more accurate than the raw seismic section. Also, acoustic-impedance sections are convertible to other reservoir characteristic sections such as porosity and permeatability, which provide data about these mentioned characteristics. Seismic inversion can be used as a reliable method for quantitative estimation of reservoir properties and to obtain quantified values of acoustic impedance from seismic data, well-logging data, and interpreted horizons. The primary aim of this research is to provide a reservoir acoustic-impedance model in one of the oil fields in southwestern Iran. Six 2D seismic sections obtained in the form of poststack seismic data and the results of the analysis of well logs obtained from two wells (A-1 and A-12) were interpreted in the study area. According to the results, the model-based inversion of seismic data, which is highly dependent on the initial model, produced good results compared to other methods. Regarding the results of inversion sections, it is recognized that the acoustic impedance of the reservoir and two well locations show small values, confirming good-quality reservoir on the Ghar Formation. Eventually, with the study of the obtained acoustic-impedance model, it is recognized that the lowest value of acoustic impedance in the region was related to the common-depth point of the 3370 location, so it can be used for future study.

Crustal-scale imaging by the full-waveform inversion (FWI) of long-offset seismic data is inherently difficult because the large number of wavelengths propagating through the crust makes the inversion prone to cycle-skipping. Therefore, efficient crustal-scale FWI requires an accurate starting model and a stable workflow minimizing the nonlinearity of the inversion. Here, we attempt to reprocess a challenging 2D ocean-bottom seismometer (OBS) dataset from the eastern Nankai Trough. The starting model is built by first-arrival traveltime tomography (FAT), which is FWI-assisted for tracking cycle skipping. We iteratively refine the picked traveltimes and then reiterate the FAT until the traveltime residuals remain below the cycle-skipping limit. Subsequently, we apply Laplace-Fourier FWI, in which progressive relaxation of time damping is nested within frequency continuation to hierarchically inject more data into the inversion. These two multiscale levels are complemented by a layer-stripping approach implemented through offset continuation. The reliability of the FWI velocity model is assessed by means of source wavelet estimation, synthetic seismogram modeling, ray-tracing modeling, dynamic warping and checkerboard tests. Although the visco-acoustic approximation is used for wave modeling, the synthetic seismograms reproduce most of the complexity of the data with a high traveltime accuracy. The revised FWI scheme produces a high-resolution velocity model of the entire crust that can be jointly interpreted with migrated images derived from multichannel seismic data. This study opens a new perspective on the design of OBS crustal-scale experiments amenable to FWI; however, a further assessment of the optimal OBS spacing is required for reliable FWI.