Seismic modeling of complex hydrocarbon traps in shot domain and data processing to obtain stack-migration sections

Bashir Y., Kemerli B.D., Yılmaz T., Saral M., Göknar E.C., Korkmaz E.

Bashir Y., Waheed U.B., Ali S.H., Karaman A., İmren C.

One of the primary challenges faced in seismic exploration is to determine the methodology for analyzing the dispersive wave in various models while maintaining the wave's stability at a low-rank one-step approximation. An optimal signal-to-noise ratio can be achieved by utilizing time-stepping in a low-rank one-step wave extrapolation. It is important to note that the ideal time step should be complex valued. Preserving subsurface diffractions can be quite challenging and demands careful monitoring. To tackle this challenge, we suggest implementing the optimal plane-wave destruction (OPWD) method. To ensure the stability of wave propagation, a fundamental three-layer velocity model is calculated at various time intervals. Afterward, a practical model is used to monitor the movement of the mentioned model. The model being discussed includes a syncline, anticline, distinct edges, and a fault with a steep dip angle. The model is evaluated for the process of simultaneous stepping and marching. Based on the research findings, it is evident that there are variations in the time-stepping between the simple and complex models. These differences align with the Nyquist limit of the sampling interval, as expected. Extending the model beyond the Nyquist limit can cause fluctuations in its stability. OPWD achieved excellent results in diffraction separation and high-resolution imaging on both the synthetic data and real data. The synthetic data included a complex model with anticlines, synclines, sharp edges, and deeper faults. The real data was obtained from the Gulf of Mexico, specifically the Walker Ridges line no. 331. The results suggest that the OPWD method is successful in preserving diffraction in both simulated and actual subsurface environments.

El-Nikhely A., El-Gendy N.H., Bakr A.M., Zawra M.S., Ondrak R., Barakat M.K.

Sandstone channels are one of the best stratigraphic traps for hydrocarbon accumulation, and their depositional and composition make them difficult to detect on ordinary seismic data, especially in structurally affected onshore areas like the Western Desert of Egypt. The Western Desert of Egypt has many hydrocarbon-bearing reservoirs of various compositions like carbonates and sandstones with high production rates, and thus the Western Desert of Egypt is recognized as a hot spot for oil and gas exploration. One of the important reservoirs in the Lower Cretaceous “the Aptian sand” produced around 285 MBBLS cumulative oil of 22° API and still produces 102 BOPD. This reservoir has a channel-type depositional environment, and the dimensions of this channel could be resolved by good quality 3D seismic data in the moderately deep basins as the basins become deeper, the detection of the channel becomes increasingly challenging. This study aims to delineate the geometry of this reservoir and reveal the exposure from the Aptian sand channel in the Alamein area using the seismic attributes analogy on the re-processed 3D seismic data to determine the best drilling location for increasing the production from this reservoir. In this context, the relative acoustic impedance (RAI), iso-frequency components, and sweetness stratigraphic attribute analyses were conducted on the optimized seismic data and attested as important as they resolved the stratigraphic geological mystery in the structurally affected study area. These attribute analyses revealed the exposure from the distinctive meander channel of the Aptian sand for the first time in the study area nearby the producing Alamein field, where this channel was hard to be distinguished by the ordinary seismic interpretation methods and there is no drilled well penetrated the detected channel’s body. Upon the results, the conclusion and recommendation summaries to intensify the efforts to test the productivity of the detected channel to increase the production from this motivating reservoir by drilling a new well targeting the best structural locations of the channel body.

Bashir Y., Mohd Muztaza N., Abbas Babasafari A., Khan M., Mahgoub M., Moussavi Alashloo S.Y., Abdul Latiff A.H.

Abstract Seismic Imaging for the small-scale feature in complex subsurface geology such as Carbonate is not easy to capture because of propagated waves affected by heterogeneous properties of objects in the subsurface. The initial step for machine learning (ML) is to provide enough data which can make our learning algorithm updated and mature. If one has not provided the multiple shapes of diffraction data, then your prediction of ML will be not accurate or even ML not able to detect the pattern of diffraction in the data. After the learning, our machine, the detection of the target is the crucial part that compares with the target and searches the specific signature in the given data. In this paper, we feed it with data in the form of the image and feature. Which can pass through the learning algorithm to predict the target. The idea of ML is to get the difference between your prediction and the target as closely as much possible. Which leads to the better preservation of diffractions amplitude in laterally varying velocity conditions. ML destruction is used for diffraction data separation as the conventional filtering techniques mix the diffraction amplitudes when there are a single or series of diffractions.

Bashir Y., Mohd Muztaza N., Moussavi Alashloo S.Y., Ali S.H., Prasad Ghosh D.

Fractured imaging is an important target for oil and gas exploration, as these images are heterogeneous and have contain low-impedance contrast, which indicate the complexity in a geological structure. These small-scale discontinuities, such as fractures and faults, present themselves in seismic data in the form of diffracted waves. Generally, seismic data contain both reflected and diffracted events because of the physical phenomena in the subsurface and due to the recording system. Seismic diffractions are produced once the acoustic impedance contrast appears, including faults, fractures, channels, rough edges of structures, and karst sections. In this study, a double square root (DSR) equation is used for modeling of the diffraction hyperbola with different velocities and depths of point diffraction to elaborate the diffraction hyperbolic pattern. Further, we study the diffraction separation methods and the effects of the velocity analysis methods (semblance vs. hybrid travel time) for velocity model building for imaging. As a proof of concept, we apply our research work on a steep dipping fault model, which demonstrates the possibility of separating seismic diffractions using dip frequency filtering (DFF) in the frequency–wavenumber (F-K) domain. The imaging is performed using two different velocity models, namely the semblance and hybrid travel time (HTT) analysis methods. The HTT method provides the optimum results for imaging of complex structures and imaging below shadow zones.

Abdel-Fattah M.I., Pigott J.D., El-Sadek M.S.

Sand-lithofacies distributions are a vital component of reservoir characterization and the generation of successful reservoir models. Through the integration of selected seismic attributes with post-stack stochastic seismic inversion reservoir distributions and architectures are accurately delineated for the Upper Cretaceous reservoir (Abu Roash “C”) in the Wadi field of NE Abu-Gharadig Basin, Egypt. Seismic interpretation and 3D structural modeling generate a regionally accurate image of the subsurface of Wadi field revealing a variety of structures: low-relief horsts and grabens, a faulted inversion-related anticline, normal and reverse faults (inverted basin phenomenon). Seismic attributes (second derivative and acoustic P-impedance) indicate that the Abu Roash “C” reservoir is characterized by the presence of two discrete sand-filled channels. The P-impedance attributes derived from post-stack seismic inversion utilized with the distributed petrophysical properties (density) predict the occurrence probability of the distinctive lithofacies in Abu Roash “C” reservoir. As stochastic seismic inversion provided an extensive vertical and lateral information set for the reservoir heterogeneity between wells, it was utilized as the definitive information requirement in generating the lithofacies models. The lithofacies obtained from integrating seismic attributes and inversion are calibrated with facies identified using well logs. The lithofacies model derived from this integrated approach provides an added geologic insight into the stratigraphic architecture and reservoir distribution and lessens exploration/development risk in the Wadi field. The resulting workflow is an effective tool for highlighting potential areas of better quality reservoir development, thereby demonstrating the value of this integrated approach.

Li A., Liu H.

Frequency-domain numerical simulation is the most important foundation of frequency-domain full-waveform inversion and reverse time migration. The accuracy of numerical simulation seriously affects the results of the seismic inversion and image. In this article, we develop an optimized compact finite difference scheme for acoustic wave equation in frequency domain to improve numerical simulation accuracy. For the sake of avoiding the extra memory and computational costs caused by solving the inverse of a pentadiagonal band matrix, we calculate the optimized compact finite difference discrete operator for the Laplace operator in the numerical simulation. Although the optimized compact finite difference scheme has only second-order formal accuracy, it has a spectral-like resolution feature. This method can significantly reduce the numerical dispersion and the numerical anisotropy. We find that the results of the optimized compact finite difference scheme agree well with the analytic solution according to accuracy analysis. Two numerical simulations are done to verify the theoretical analysis of the optimized compact finite difference scheme.

Mohebian R., Riahi M.A., Yousefi O.

Bashir Y., Ghosh D.P., Sum C.W.

Small-scale geological discontinuities are not easy to detect and image in seismic data, as these features represent themselves as diffracted rather than reflected waves. However, the combined reflected and diffracted image contains full wave information and is of great value to an interpreter, for instance enabling the identification of faults, fractures, and surfaces in built-up carbonate. Although diffraction imaging has a resolution below the typical seismic wavelength, if the wavelength is much smaller than the width of the discontinuity then interference effects can be ignored, as they would not play a role in generating the seismic diffractions. In this paper, by means of synthetic examples and real data, the potential of diffraction separation for high-resolution seismic imaging is revealed and choosing the best method for preserving diffraction are discussed. We illustrate the accuracy of separating diffractions using the plane-wave destruction (PWD) and dip frequency filtering (DFF) techniques on data from the Sarawak Basin, a carbonate field. PWD is able to preserve the diffraction more intelligently than DFF, which is proven in the results by the model and real data. The final results illustrate the effectiveness of diffraction separation and possible imaging for high-resolution seismic data of small but significant geological features.

Aksu A.E., Hiscott R.N., Kostylev V.E., Yaltırak C.

High-resolution multibeam mosaics show that the seafloor across the southwestern Marmara Sea is host to remarkably organized near-circular bioherm mounds, which commonly are arranged into large, tightly packed clusters. Grab samples and gravity cores reveal that the bioherms are predominantly composed of very fine-grained, calcareous, silty mud with abundant bioclasts, including centimetre-scale masses of coralline red algae and intact disarticulated mollusc shells (mainly the genera Modiolus and Mytilus). Geometric analysis of multibeam images reveals that the average bioherm is 15.6 m in diameter, occupies ~ 190 m2 of seabed, stands 113 cm above the adjacent seafloor, and its crest is 20.6 m from the crests of neighbouring bioherms. In regions of tightly packed bioherm clusters (referred to as ‘bioherm colonies’) the inter-mound depressions are on average 4.4 m wide and 33 cm deep. Although each bioherm mound is nearly circular, the surrounding inter-mound channels form a more rectilinear mesh of linked pentagonal and hexagonal polygons suggesting densest possible spatial packing of the mounds. Near-neighbour statistics of R = 2.11–2.14 indicate an essentially uniform spacing between the bioherms, which is the expected result for close packing on a plane and full utilization of the available space. The bioherms occur at depths between − 30 m and − 60 m. They are absent above and below these depths. In this part of the southwestern Marmara Sea at the eastern exit of the Strait of Dardanelles, water depth controls important water mass properties such as salinity, nutrient supply and availability of light. Other inferred critical controls are the availability of a suitable hard substrate where Holocene muds are thin or absent, and nutrient supply, potentially including a component from escaping methane-rich pore fluids. Evidence here and elsewhere in the Marmara Sea provisionally dates the onset of bioherm growth and development to the latest Pleistocene–earliest Holocene, after global sealevel rose to the breach depth of the Strait of Dardanelles at ~ 13.8 cal ka.

PAN S., LIU H., ZAVALA C., LIU C., LIANG S., ZHANG Q., BAI Z.

Based on the integrated analysis of seismic, drilling and core data, a large channel-fan system of hyperpycnal flow origin was found in the Qijia-Gulong area of the Nen 1 Member of the Cretaceous Nenjiang Formation in the Songliao Basin. The hyperpycnal flow in this area, which originated from the edge of the basin and then passed the northern delta, formed a complete channel-fan system in the deepwater area. The channel-fan system comprises straight channels and meandering channels extending from north to south over a straight distance of more than 80 km with a width of 100−900 m, and distal fan lobes at the channel tip cover a maximum area of 20 km2. This system, which is dominated by fine-grained deposits, contains massive sandstone, sedimentary structures of flow-water origin, and internal erosion surfaces; it also contains abundant continental organic clasts and exhibits evidence of bed-load and suspended-load transportation mechanisms. The hyperpycnite sequence contains pairs of coarsening-upward lower sequences and fining-upward upper sequences, reflecting the dynamic features of cycles in which floods first strengthen and then weaken. A new sedimentary model has been built for hyperpycnites in the Songliao Basin.

Robertsson J.O., van Manen D., Schmelzbach C., Van Renterghem C., Amundsen L.

© The Authors 2015. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Burschil T., Beilecke T., Krawczyk C.M.

Abstract. High-resolution reflection seismic methods are an established non-destructive tool for engineering tasks. In the near surface, shear-wave reflection seismic measurements usually offer a higher spatial resolution in the same effective signal frequency spectrum than P-wave data, but data quality varies more strongly. To discuss the causes of these differences, we investigated a P-wave and a SH-wave seismic reflection profile measured at the same location on the island of Föhr, Germany and applied seismic reflection processing to the field data as well as finite-difference modelling of the seismic wave field. The simulations calculated were adapted to the acquisition field geometry, comprising 2 m receiver distance (1 m for SH wave) and 4 m shot distance along the 1.5 km long P-wave and 800 m long SH-wave profiles. A Ricker wavelet and the use of absorbing frames were first-order model parameters. The petrophysical parameters to populate the structural models down to 400 m depth were taken from borehole data, VSP (vertical seismic profile) measurements and cross-plot relations. The simulation of the P-wave wave-field was based on interpretation of the P-wave depth section that included a priori information from boreholes and airborne electromagnetics. Velocities for 14 layers in the model were derived from the analysis of five nearby VSPs (vP =1600–2300 m s-1). Synthetic shot data were compared with the field data and seismic sections were created. Major features like direct wave and reflections are imaged. We reproduce the mayor reflectors in the depth section of the field data, e.g. a prominent till layer and several deep reflectors. The SH-wave model was adapted accordingly but only led to minor correlation with the field data and produced a higher signal-to-noise ratio. Therefore, we suggest to consider for future simulations additional features like intrinsic damping, thin layering, or a near-surface weathering layer. These may lead to a better understanding of key parameters determining the data quality of near-surface shear-wave seismic measurements.

Kuteynikova M., Tisato N., Jänicke R., Quintal B.

To better understand the effects of fluid saturation on seismic attenuation, we combined numerical modeling in poroelastic media and laboratory measurements of seismic attenuation in partially saturated Berea sandstone samples. Although in laboratory experiments many physical mechanisms for seismic attenuation take place simultaneously, with numerical modeling we separately studied the effect of a single physical mechanism: wave-induced fluid flow on the mesoscopic scale. Using the finite-element method, we solved Biot’s equations of consolidation by performing a quasistatic creep test on a 3D poroelastic model. This model represents a partially saturated rock sample. We obtained the stress-strain relation, from which we calculated frequency-dependent attenuation. In the laboratory, we measured attenuation in extensional mode for dry and partially water-saturated Berea sandstone samples in the frequency range from 0.1 to 100 Hz. All the measurements were performed at room pressure and temperature conditions. From numerical simulations, we found that attenuation varies significantly with fluid distribution within the model. In addition to binary distributions, we used spatially continuous distributions of fluid saturation for the numerical models. Such continuous saturation distribution was implemented using properties of an effective single-phase fluid. By taking into account the matrix anelasticity, we found that wave-induced fluid flow on the mesoscopic scale due to a continuous distribution of fluid saturation can reproduce seismic attenuation data measured in a partially saturated sample. The matrix anelasticity was the attenuation measured in the room-condition dry sample.

Nejati M., Hashemi H.