Comparison of Travel-Time Approximations for Unconventional Reservoirs From Santos Basin, Brazil

Abstract

ABSTRACT. The reflection seismic method is extremely important for the hydrocarbon exploration. With more complex geological structures, as the pre-salt from Santos Basin, the reservoir exploration becomes more challenging and the multicomponent seismic investigation improves its mapping and characterization. To obtain multicomponent seismic data of an offshore survey it is necessary to use the OBN (Ocean Bottom Nodes) technology. The converted wave behavior, the large offsets and the difference of datum between source and receptors for layered media, results in strong nonhyperbolic travel-time events. Furthermore, the complexity and peculiarities of some unconventional reservoirs found in the pre-salt also increase the difficulty to perform the velocity analysis. For these reasons, it is necessary to use nonhyperbolic multiparametric travel-time approximations to control the nonhyperbolicity. Here we perform the comparison of nonhyperbolic travel-time approximations of seismic reflection events derived from geological models. The numerical study was considered as an inverse problem and it was treated according to an optimization criterion. The complexity analysis was performed in order to understand the behavior of each approximation concerning the unicity. After the computation of the relative errors between the observed curve and the calculated curve for each nonhyperbolic approximation, it was possible to find out the one with the highest accuracy for the events tested here. Keywords: multicomponent, OBN, nonhyperbolic.RESUMO.Ométodo sísmico de reflexão é extremamente importante para a exploração de hidrocarbonetos. Comestruturas geológicasmais complexas, como o pré-sal da Bacia de Santos, a exploração de reservatórios se tornamais desafiadora e a utilização da sísmica multicomponente promove o mapeamento e caracterização estrutural. Para obter-se dados de sísmica multicomponente em um levantamento offshore é necessário utilizar a tecnologia OBN (Ocean Bottom Nodes ). O comportamento de ondas convertidas, longos afastamentos e diferença de datum entre fonte e receptor pra meios estratificados resultam em uma forte não-hiperbolicidade dos eventos de tempos de trânsito. Além disso, a complexidade e peculiaridades, de alguns reservatórios não convencionais encontrados no pré-sal, também aumentam a dificuldade em realizar a análise de velocidades. Por estes motivos, é necessário usar aproximações não-hiperbólicas multiparamétricas de tempos de trânsito para controlar os efeitos da não-hiperbolicidade. No presente trabalho, foi realizada a comparação de aproximações não-hiperbólicas de tempos de trânsito de eventos sísmicos de reflexão provenientes de modelos geológicos. O estudo numérico foi considerado como um problema inverso e foi tratado de acordo com um critério de otimização. A análise de complexidade foi realizada para compreender o comportamento de cada aproximação com respeito a unicidade. Após computar os erros relativos entre a curva observada e as calculadas com cada aproximação, foi possível descobrir a aproximação que apresentou maior precisão para os testes realizado.Palavras-chave: multicomponente, OBN, não-hiperbólicas.

L2- And L1-Norm Applied to Inversion of Nonhyperbolic Travel-Time

“…The approximation was lately studied concerning its parameter by Li (2003), and after compared with other approximations (Zuniga et al, 2015(Zuniga et al, , 2016b(Zuniga et al, , 2017Zuniga, 2017). As the approximation showed to have a multimodal statistical distribution in previous works, it must be tested with the L1-norm rather than the L2-norm to observe if it could suppress the local minimum region, or at least makes a narrower global minimum region to increase the accuracy during the inversion.…”

Local Search Optimization: A Comparison of Algorithms for Nonhyperbolic Travel-Time Analysis

“…In this work it is used the nonhyperbolic travel-time approximation known as shifted hyperbola proposed by Malovichko [25]. Previous works compared travel-time approximations among them for VTI (Vertical Transverse Isotropy) media [3,17,42], strong heterogeneity [41], and for OBN (Ocean Bottom Nodes) data [40,[43][44]. However, this work aims to compare different optimization algorithms to improve the results obtained with shifted hyperbola equation in previous works.…”

“…Several nonhyperbolic travel-time approximations were developed in last decades essentially for the velocity analysis step [4,7,24,25,28,38], with different characteristics and proposals. These approximations have been tested and compared along the last decade for different situations and conditions, with different kinds of analysis [3,17,[40][41][42][43][44]. Comparison of accuracy of the traveltime approximations, processing time of each approach and objective function analysis are some examples of tests performed so far.…”

Comparison of Global Search Optimization Algorithms to Perform the Velocity Analysis With a Converted Wave Moveout Equation

“…The comparison of nonhyperbolic multiparametric travel-time approximation was performed in many works recently [8,[38][39][40][41][42]. However, none of them considered different optimization algorithms to be tested.…”