Estimation of porosity and gas hydrate saturation by inverting 2D seismic data using Very Fast Simulated Annealing in the Krishna Godavari offshore basin, India

Marine seismic data and well‐log measurements at the Blake Ridge offshore South Carolina show that prominent seismic bottom‐simulating reflectors (BSRs) are caused by sediment layers with gas hydrate overlying sediments with free gas. We apply a theoretical rock‐physics model to 2-D Blake Ridge marine seismic data to determine gas‐hydrate and free‐gas saturation. High‐porosity marine sediment is modeled as a granular system where the elastic wave velocities are linked to porosity; effective pressure; mineralogy; elastic properties of the pore‐filling material; and water, gas, and gas‐hydrate saturation of the pore space. To apply this model to seismic data, we first obtain interval velocity using stacking velocity analysis. Next, all input parameters to the rock‐physics model, except porosity and water, gas, and gas hydrate saturation, are estimated from geologic information. To estimate porosity and saturation from interval velocity, we first assume that the entire sediment does not contain gas hydrate or free gas. Then we use the rock‐physics model to calculate porosity directly from the interval velocity. Such porosity profiles appear to have anomalies where gas hydrate and free gas are present (as compared to typical profiles expected and obtained in sediment without gas hydrate or gas). Porosity is underestimated in the hydrate region and is overestimated in the free‐gas region. We calculate the porosity residuals by subtracting a typical porosity profile (without gas hydrate and gas) from that with anomalies. Next we use the rock‐physics model to eliminate these anomalies by introducing gas‐hydrate or gas saturation. As a result, we obtain the desired 2-D saturation map. The maximum gas‐hydrate saturation thus obtained is between 13% and 18% of the pore space (depending on the version of the model used). These saturation values are consistent with those measured in the Blake Ridge wells (away from the seismic line), which are about 12%. Free‐gas saturation varies between 1% and 2%. The saturation estimates are extremely sensitive to the input velocity values. Therefore, accurate velocity determination is crucial for correct reservoir characterization.

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Application of very fast simulated annealing and differential evolution in the search for FO-CRS wavefield attributes

Geophysics ◽

10.1190/geo2018-0193.1 ◽

2019 ◽

Vol 84 (5) ◽

pp. O81-O92

Author(s):

German Garabito ◽

João Carlos R. Cruz

Keyword(s):

Global Optimization ◽

Simulated Annealing ◽

Differential Evolution ◽

Seismic Data ◽

Optimization Algorithms ◽

Two Dimensions ◽

Seismic Section ◽

Data Set ◽

Computational Costs ◽

Very Fast Simulated Annealing

The finite-offset common-reflection-surface (FO-CRS) stack method can be used to simulate any common-offset (CO) seismic section by stacking prestack seismic data along the surfaces defined by the paraxial hyperbolic traveltime approximation. In two dimensions, the FO-CRS stacking operator depends on five kinematic wavefield attributes for every time sample of the target CO section. The main problem with this method is identifying a computationally efficient data-driven search strategy for accurately determining the best set of FO-CRS attributes that produce the optimal coherence measure of the seismic signal in the prestack data. Identifying a global optimization algorithm with the best performance is a challenge when solving this optimization problem. This is because the objective function is multimodal and involves a large volume of data, which leads to high computational costs. We introduced a comparative and competitive study through the application of two global optimization algorithms that simultaneously search the FO-CRS attributes from the prestack seismic data, very fast simulated annealing (VFSA) and the differential evolution (DE). By applying this FO-CRS stack to the Marmousi synthetic seismic data set, we have compared the performances of the two optimization algorithms with regard to their efficiency and effectiveness in estimating the five FO-CRS attributes. To analyze the robustness of the two algorithms, we apply them to real land seismic data and show their ability to find the near-optimal attributes and to improve reflection events in noisy data with a very low fold. We reveal that VFSA is efficient in reaching the optimal coherence value with the lowest computational costs, and that DE is effective and reliable in reaching the optimal coherence for determining the best five searched-for attributes. Regardless of the differences, the FO-CRS stack produces enhanced and regularized high-quality CO sections using both global optimization methods.

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Using Very Fast Simulated Annealing in the Weighted AB Semblance method

Brazilian Journal of Geophysics ◽

10.22564/rbgf.v37i4.2020 ◽

2019 ◽

Vol 37 (4) ◽

Author(s):

Marcelo Souza ◽

Milton Porsani

Keyword(s):

Simulated Annealing ◽

Seismic Data ◽

Real Data ◽

Velocity Spectrum ◽

Velocity Analysis ◽

Inversion Algorithm ◽

Coherence Measure ◽

Reflection Seismic ◽

Very Fast Simulated Annealing ◽

Velocity Spectra

ABSTRACTThe conventional velocity analysis does not consider AVO effects in reflection seismic data. These conditions lead to obtaining of inadequate velocity fields, making it difficult to execute other steps in seismic processing. To overcome this problem, researchers developed the Weighted AB semblance method, a coherence measure which deals with AVO effects in velocity spectra. It is based on the application of two sigmoid weighting functions to AB semblance, which depend on four coefficients. The values of these coefficients directly influence the resolution of the resulting velocity spectrum. In this work, we apply the inversion algorithm Very Fast Simulated Annealing (VFSA) to obtain these values. Numerical experiments show that VFSA is a quite effective method, obtaining correct coefficient values and allowing the generation of the velocity spectrum with an excellent resolution for both synthetic and real data. Results also proved that Weighted AB semblance is an optimal coherence measure to be used in velocity spectrum, because it is insensitive to AVO effects and reversal polarity and presents considerably a better resolution than conventional semblance.Keywords: velocity analysis, AVO, high-resolution velocity spectra RESUMOA análise de velocidades convencional não considera efeitos de AVO em dados sísmicos de reflexão. Essas condições levam à obtenção de campos de velocidades inadequados, dificultando a execução de outras etapas do processamento sísmico. Para superar esse problema, pesquisadores desenvolveram o método AB semblance Ponderado, uma medida de coerência que lida com efeitos de AVO em espectros de velocidades. Ela ´e baseada na aplicação de duas funções sigmoides à AB semblance, que depende de quatro coeficientes. Os valores desses coeficientes influenciam diretamente a resolução do espectro de velocidade resultante. Nesse trabalho, n´os aplicamos o algoritmo de inversão Very Fast Simulated Annealing (VFSA) para obter esses valores. Experimentos numéricos mostram que VFSA é um método bastante eficaz, obtendo valores corretos dos coeficientes e permitindo a geração do espectro de velocidade com uma excelente resolução tanto para dados sintéticos quanto para dados reais. Resultados também provam que o AB semblance Ponderado ´e uma medida de coerência ótima para ser usada no espectro de velocidade, porque ela é insensível aos efeitos de AVO e apresenta resolução consideravelmente melhor do que a semblance convencional.Palavras-chave: análise de velocidades, AVO, espectro de velocidades de alta resolução.

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Estimation of gas‐hydrate saturation using multicomponent seismic data

10.1190/1.2147985 ◽

2005 ◽

Cited By ~ 1

Author(s):

Dhananjay Kumar ◽

Mrinal K. Sen ◽

Nathan L. Bangs

Keyword(s):

Gas Hydrate ◽

Seismic Data ◽

Multicomponent Seismic ◽

Hydrate Saturation

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Gas hydrate saturation from seismic data constrained by log data in the Krishna-Godavari Basin

Journal of Petroleum Exploration and Production Technology ◽

10.1007/s13202-015-0170-1 ◽

2015 ◽

Vol 6 (1) ◽

pp. 13-23 ◽

Cited By ~ 4

Author(s):

Uma Shankar

Keyword(s):

Gas Hydrate ◽

Seismic Data ◽

Log Data ◽

Hydrate Saturation ◽

Godavari Basin

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Fractal-based stochastic inversion of poststack seismic data using very fast simulated annealing

Journal of Geophysics and Engineering ◽

10.1088/1742-2132/6/4/009 ◽

2009 ◽

Vol 6 (4) ◽

pp. 412-425 ◽

Cited By ~ 19

Author(s):

R P Srivastava ◽

M K Sen

Keyword(s):

Simulated Annealing ◽

Seismic Data ◽

Stochastic Inversion ◽

Very Fast Simulated Annealing

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GAS HYDRATE SATURATION ESTIMATED FROM ACOUSTIC IMPEDANCE IN THE ANDAMAN SEA, INDIA

Marine Geology & Quaternary Geology ◽

10.3724/sp.j.1140.2013.02163 ◽

2014 ◽

Vol 33 (2) ◽

pp. 163-168

Author(s):

Xiujuan WANG ◽

Jiliang WANG ◽

Wei LI ◽

Nittala Satyavani ◽

Kalachand Sain

Keyword(s):

Gas Hydrate ◽

Acoustic Impedance ◽

Andaman Sea ◽

Hydrate Saturation

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Wave Propagation Characteristics in Gas Hydrate-Bearing Sediments and Estimation of Hydrate Saturation

Energies ◽

10.3390/en14040804 ◽

2021 ◽

Vol 14 (4) ◽

pp. 804

Author(s):

Lin Liu ◽

Xiumei Zhang ◽

Xiuming Wang

Keyword(s):

Gas Hydrate ◽

Clay Content ◽

Clean Energy ◽

Compressional Wave ◽

Physical Parameters ◽

Well Log ◽

Log Data ◽

Phase Velocities ◽

Hydrate Saturation ◽

Hydrate Bearing Sediments

Natural gas hydrate is a new clean energy source in the 21st century, which has become a research point of the exploration and development technology. Acoustic well logs are one of the most important assets in gas hydrate studies. In this paper, an improved Carcione–Leclaire model is proposed by introducing the expressions of frame bulk modulus, shear modulus and friction coefficient between solid phases. On this basis, the sensitivities of the velocities and attenuations of the first kind of compressional (P1) and shear (S1) waves to relevant physical parameters are explored. In particular, we perform numerical modeling to investigate the effects of frequency, gas hydrate saturation and clay on the phase velocities and attenuations of the above five waves. The analyses demonstrate that, the velocities and attenuations of P1 and S1 are more sensitive to gas hydrate saturation than other parameters. The larger the gas hydrate saturation, the more reliable P1 velocity. Besides, the attenuations of P1 and S1 are more sensitive than velocity to gas hydrate saturation. Further, P1 and S1 are almost nondispersive while their phase velocities increase with the increase of gas hydrate saturation. The second compressional (P2) and shear (S2) waves and the third kind of compressional wave (P3) are dispersive in the seismic band, and the attenuations of them are significant. Moreover, in the case of clay in the solid grain frame, gas hydrate-bearing sediments exhibit lower P1 and S1 velocities. Clay decreases the attenuation of P1, and the attenuations of S1, P2, S2 and P3 exhibit little effect on clay content. We compared the velocity of P1 predicted by the model with the well log data from the Ocean Drilling Program (ODP) Leg 164 Site 995B to verify the applicability of the model. The results of the model agree well with the well log data. Finally, we estimate the hydrate layer at ODP Leg 204 Site 1247B is about 100–130 m below the seafloor, the saturation is between 0–27%, and the average saturation is 7.2%.

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