scholarly journals An Investigation of Seismic Velocity Variation through a Tectonic Boundaries-Case Study in Central Iraq

2021 ◽  
pp. 2614-2626
Author(s):  
Ahmed S. AL-Banna ◽  
Hassan E. Al-Assady
Keyword(s):  
High Velocity ◽  
Seismic Velocity ◽  
Velocity Model ◽  
Seismic Inversion ◽  
Velocity Variation ◽  
Time Model ◽  
3D Velocity Model ◽  
Western Side ◽  
Well Data ◽  
Seismic Lines

      A 3D velocity model was created by using stacking velocity of 9 seismic lines and average velocity of 6 wells drilled in Iraq. The model was achieved by creating a time model to 25 surfaces with an interval time between each two successive surfaces of about 100 msec.  The summation time of all surfaces reached about 2400 msec, that was adopted according to West Kifl-1 well, which penetrated to a depth of 6000 m, representing the deepest well in the study area. The seismic lines and well data were converted to build a 3D cube time model and the velocity was spread on the model. The seismic inversion modeling of the elastic properties of the horizon and well data was applied to achieve a corrected velocity cube. Then, the velocity cube was converted to a time model and, finally, a corrected 3D depth model was obtained. This model shows that the western side of the study area, which is a part of the stable shelf, is characterized by relatively low thickness and high velocity layers. While the eastern side of the study area, which is a part of the Mesopotamian, is characterized by high thickness and low velocity of the Cretaceous succession. The Abu Jir fault is considered as a boundary between the stable and unstable shelves in Iraq, situated at the extreme west part of the study area. The area of relatively high velocity gradient is considered as the limit of the western side of the Mesopotamian basin. This area extends from Najaf-Karbala axis in the west to the Euphrates River in the east. It is found that the 3D stacking velocity model can be used to obtain good results concerning the tectonic boundary.  

scholarly journals Travel Time Tomography to Delineate 3-D Regional Seismic Velocity Structure in the Banyumas Basin, Central Java, Indonesia, Using Dense Borehole Seismographic Stations

2021 ◽  
Vol 9 ◽  
Author(s):  
Hidayat Hidayat ◽  
Andri Dian Nugraha ◽  
Awali Priyono ◽  
Marjiyono Marjiyono ◽  
Januar H. Setiawan ◽  
...  
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Velocity Model ◽  
Crustal Layer ◽  
Central Java ◽  
Resolution Element ◽  
Passive Seismic ◽  
Dextral Strike Slip Fault ◽  
Southern Central ◽  
Well Data

The Banyumas Basin is a tertiary sedimentary basin located in southern Central Java, Indonesia. Due to the presence of volcanic deposits, 2-D seismic reflection methods cannot provide a good estimation of the sediment thickness and the subsurface geology structure in this area. In this study, the passive seismic tomography (PST) method was applied to image the 3-D subsurface Vp, Vs, and Vp/Vs ratio. We used 70 seismograph borehole stations with a recording duration of 177 days. A total of 354 events with 9, 370 P and 9, 368 S phases were used as input for tomographic inversion. The checkshot data of a 4, 400-meter deep exploration well (Jati-1) located within the seismic network were used to constrain the shallow crustal layer of the initial 1-D velocity model. The model resolution of the tomographic inversions was assessed using the checkerboard resolution test (CRT), the diagonal resolution element (DRE), and the derivative weight sum (DWS). Using the obtained Vp, Vs, and Vp/Vs ratio, we were able to sharpen details of the geological structures within the basin from previous geological studies, and a fault could be well-imaged at a depth of 4 km. We interpreted this as the main dextral strike-slip fault that controls the pull apart process of the Banyumas Basin. The thickness of the sediment layers, as well as its layering, were also could be well determined. We found prominent features of the velocity contrast that aligned very well with the boundary between the Halang and Rambatan formations as observed in the Jati-1 well data. Furthermore, an anticline structure, which is a potential structural trap for the petroleum system in the Banyumas Basin, was also well imaged. This was made possible due to the dense borehole seismographic stations which were deployed in the study area.

scholarly journals Seismic velocity estimation: A deep recurrent neural-network approach

Geophysics ◽  
2019 ◽  
Vol 85 (1) ◽  
pp. U21-U29
Author(s):  
Gabriel Fabien-Ouellet ◽  
Rahul Sarkar
Keyword(s):  
Neural Network ◽  
Neural Networks ◽  
Recurrent Neural Networks ◽  
Model Building ◽  
Seismic Velocity ◽  
Velocity Model ◽  
Velocity Estimation ◽  
Interval Velocity ◽  
Velocity Model Building ◽  
3D Velocity Model

Applying deep learning to 3D velocity model building remains a challenge due to the sheer volume of data required to train large-scale artificial neural networks. Moreover, little is known about what types of network architectures are appropriate for such a complex task. To ease the development of a deep-learning approach for seismic velocity estimation, we have evaluated a simplified surrogate problem — the estimation of the root-mean-square (rms) and interval velocity in time from common-midpoint gathers — for 1D layered velocity models. We have developed a deep neural network, whose design was inspired by the information flow found in semblance analysis. The network replaces semblance estimation by a representation built with a deep convolutional neural network, and then it performs velocity estimation automatically with recurrent neural networks. The network is trained with synthetic data to identify primary reflection events, rms velocity, and interval velocity. For a synthetic test set containing 1D layered models, we find that rms and interval velocity are accurately estimated, with an error of less than [Formula: see text] for the rms velocity. We apply the neural network to a real 2D marine survey and obtain accurate rms velocity predictions leading to a coherent stacked section, in addition to an estimation of the interval velocity that reproduces the main structures in the stacked section. Our results provide strong evidence that neural networks can estimate velocity from seismic data and that good performance can be achieved on real data even if the training is based on synthetics. The findings for the 1D problem suggest that deep convolutional encoders and recurrent neural networks are promising components of more complex networks that can perform 2D and 3D velocity model building.

CSEM-regularized seismic velocity inversion: A multiscale, hierarchical workflow for subsalt imaging

Geophysics ◽  
2018 ◽  
Vol 83 (5) ◽  
pp. B241-B252 ◽  
Author(s):  
Daniele Colombo ◽  
Diego Rovetta ◽  
Ersan Turkoglu
Keyword(s):  
Seismic Velocity ◽  
Fundamental Problem ◽  
Velocity Model ◽  
Seismic Inversion ◽  
Velocity Fields ◽  
Coupling Mechanism ◽  
Correct Result ◽  
Velocity Analysis ◽  
Velocity Inversion ◽  
Velocity Models

Seismic imaging in salt geology is complicated by highly contrasted velocity fields and irregular salt geometries, which cause complex seismic wavefield scattering. Although the imaging challenges can be addressed by advanced imaging algorithms, a fundamental problem remains in the determination of robust velocity fields in high-noise conditions. Conventional migration velocity analysis is often ineffective, and even the most advanced methods for depth-domain velocity analysis, such as full-waveform inversion, require starting from a good initial estimate of the velocity model to converge to a correct result. Nonseismic methods, such as electromagnetics, can help guide the generation of robust velocity models to be used for further processing. Using the multiphysics data acquired in the deepwater section of the Red Sea, we apply a controlled-source electromagnetic (CSEM) resistivity-regularized seismic velocity inversion for enhancing the velocity model in a complex area dominated by nappe-style salt tectonics. The integration is achieved by a rigorous approach of multiscaled inversions looping over model dimensions (1D first, followed by 3D), variable offsets and increasing frequencies, data-driven and interpretation-supported approaches, leading to a hierarchical inversion guided by a parameter sensitivity analysis. The final step of the integration consists of the inversion of seismic traveltimes subject to CSEM model constraints in which a common-structure coupling mechanism is used. Minimization is performed over the seismic data residuals and cross-gradient objective functions without inverting for the resistivity model, which is used as a reference for the seismic inversion (hierarchical approach). Results are demonstrated through depth imaging in which the velocity model derived through CSEM-regularized hierarchical inversion outperforms the results of a seismic-only derived velocity model.

scholarly journals Dip‐moveout processing for depth‐variable velocity

Geophysics ◽  
1994 ◽  
Vol 59 (4) ◽  
pp. 610-622 ◽  
Author(s):  
Craig Artley ◽  
Dave Hale
Keyword(s):  
Vertical Velocity ◽  
Seismic Data ◽  
Seismic Velocity ◽  
Velocity Model ◽  
Velocity Variation ◽  
System Of Nonlinear Equations ◽  
Newton Raphson ◽  
Zero Offset ◽  
Improved Accuracy ◽  
Raphson Iteration

In dip‐moveout (DMO) processing, the seismic velocity is often assumed to be constant. While several approximate techniques for handling vertical velocity variation have recently become available, here we propose a method for computing the kinematically exact DMO correction when velocity is an arbitrary function of the depth. While not known in advance, the raypath from source to receiver and the corresponding zero‐offset raypath satisfy several relationships, which are used to form a system of nonlinear equations. By simultaneously solving the equations via Newton‐Raphson iteration, we determine the mapping that transforms nonzero‐offset data to zero‐offset. Unlike previous schemes that approximately handle vertical velocity variation, this method makes no assumptions about the offset, dip, velocity function, or hyperbolic moveout. Tests using both synthetic and recorded seismic data demonstrate the effectiveness of this variablevelocity DMO. These tests show this method accurately handles vertical velocity variation, while use of constant‐velocity DMO can lead to significant errors. Comparing this technique to a formulation that approximately handles velocity variation, however, suggests that the improved accuracy of the exact technique may not be justified because of uncertainty in the velocity model and increased cost. While improved accuracy alone may not justify the use of this method in 2-D, its flexibility may in other cases. Changes could be made to handle 3-D DMO, DMO for mode‐converted waves, DMO in anisotropic media, or prestack divergence correction.

Effects of near surface lithology on velocity modelling and time–depth relationships in the Cooper–Eromanga–Lake Eyre Basin

2018 ◽  
Vol 58 (1) ◽  
pp. 321
Author(s):  
Anna Manka ◽  
Glen Buick ◽  
Rob Menpes ◽  
Luke Gardiner ◽  
Cameron Jones ◽  
...  
Keyword(s):  
Seismic Velocity ◽  
Velocity Model ◽  
Petroleum Exploration ◽  
Success Rates ◽  
Near Surface ◽  
Depth Prediction ◽  
Western Flank ◽  
3D Velocity Model ◽  
The Time Domain ◽  
Eromanga Basin

Structural closures on the western flank of the Patchawarra Trough in the Cooper–Eromanga Basin are truly low relief; drilling opportunities regularly target hydrocarbon columns of similar magnitude to the uncertainty of depth prediction. Improving the accuracy and precision of depth prediction will reduce risk for drilling opportunities, and improve drilling success rates. A detailed study of the near surface geology (surface to ~500 m depth) of the western flank of the Patchawarra Trough has been undertaken to better understand the effect of observed geological variations of the near surface on depth prediction at deeper target levels. The stratigraphic interval investigated includes the top of the Eromanga Basin and the entire Lake Eyre Basin, which is sparingly studied and routinely overlooked in the statics and velocity modelling process. This study analysed recently acquired cased-hole sonic logs in conjunction with gamma logs and mudlog data to map out the observed geological variations, and construct a 3D velocity model of the near surface. Variations of layer thickness and seismic velocity were input into Monte Carlo simulations to investigate sensitivities of each formation on two-way travel time and depth prediction. This investigation has found that velocity variations of the Weathered Winton Formation, and thickness variations of the Namba Clastics have the greatest impact on imaging of structures at depth. Independently, these have the potential to completely conceal or create structures in the time domain. Continued efforts in improved understanding of the near surface will subsequently lead to enhanced imaging of structures, which can then be used in the mapping of structural closures in petroleum exploration and development.

Pitfalls in the seismic interpretation of fault shadow events — Vicksburg formation of south Texas

2015 ◽  
Vol 3 (1) ◽  
pp. SB17-SB22 ◽  
Author(s):  
Richard C. Bain
Keyword(s):  
Seismic Data ◽  
Seismic Velocity ◽  
Velocity Model ◽  
South Texas ◽  
Velocity Anomaly ◽  
3D Velocity Model ◽  
Production Wells ◽  
Hidalgo County ◽  
Velocity Changes ◽  
Depositional Units

Reliance on prestack time-migrated seismic data to define structural highs without incorporating all subsurface data and without taking into account the regional and local lateral depositional trends may result in dry holes or poorly positioned production wells due to local velocity changes, which are usually caused by some depositional or structural phenomenon. Tying check-shot control to depositional units may reveal those phenomena and permit assumptions to be made about velocities in areas beyond check-shot control points. We discovered a significant gas accumulation in an area surrounded by dry holes and marginal wells in the Vicksburg Formation in McAllen Ranch Field, Hidalgo County, Texas, by treating a seismic velocity anomaly as a geologic problem and by simple application of arithmetic and geometry to a 3D velocity model. Due to the effects of the anomaly, seismic data displayed in time gave no indication of the existence of a 325 ha (800 ac), 150 BCFG anticlinal structure. A subsurface model that accounted for the velocity anomaly was able to predict its extent and severity by readily identifiable thickness changes in the anomalous units. The resulting discovery yielded a sevenfold increase in field production within a two-year time span.

scholarly journals 2D Seismic Reflection Study for Zubair Formation in East Nasiriya area, Southern Iraq

2021 ◽  
pp. 3952-3961
Author(s):  
Mohammed S. Faisal ◽  
Kamal K. Ali
Keyword(s):  
Seismic Velocity ◽  
Velocity Model ◽  
Oil Field ◽  
Oil Fields ◽  
Two Dimensional ◽  
Seismic Line ◽  
Seismic Section ◽  
Area Of Interest ◽  
Seismic Sections ◽  
Seismic Lines

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.

scholarly journals Application of Double Difference Tomography Method to Determine The 3D Seismic Wave Velocity Structure of GoLF Geothermal Field

2018 ◽  
Vol 16 (1) ◽  
pp. 27
Author(s):  
Kana N. Naamin ◽  
David P. Sahara ◽  
Andri D. Nugraha ◽  
Irvan Ramadhan
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Correlation Method ◽  
Velocity Model ◽  
Geothermal Field ◽  
Double Difference ◽  
Seismic Wave Velocity ◽  
Recording Time ◽  
3D Velocity Model ◽  
Geophysical Surveys

GoLF geothermal eld is located in South Solok Regency, 150 km SE of Padang city, West Sumatra.Geology, geochemistry and geophysical surveys had been conducted since 2008. Geophysical survey which had been performed including microseismic and magnetotelluric surveys. Seismic velocity structure modelling need to be conducted in order to characterize geothermal reservoir.This study uses microseismic data recorded from 36 seismometers which installed in two time recording time ranges; from September 2010 to April 2011 and from September 2012 to December 2013, with microseismic events recorded respectively 135 and 2692 events. To maximize the result of picking waveform, the data is processed using the Master Event Cross Correlation method to update the catalog data and get more accurate arrival time. Furthermore, the author used TomoDD software to produce hypocenter relocation and the 3D velocity structure under GoLF's geothermal reservoir. The results of the 3D velocity model can be used to determine the structure and phase of the fluid under GoLF geothermal field.

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