Viscoelastic behavior of a Brazilian turbidite reservoir and its relationships to facies attributes

Vásquez, Guilherme; Filho, Ivan de Araújo Simões; Bruhn, Carlos H.L.; Dillon, Lucia

doi:10.1190/1.1815810

Cited by 6 publications

(1 citation statement)

References 3 publications

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“…It were measured the elastic velocities at ultrasonic frequencies on the laboratory by the pulse transmission technique (Vasquez et al, 2000) on a set of limestone and sandstone samples. The samples were saturated with brine to simulate the in situ formation water (65000 ppm of NaCl for the limestone and 240000 ppm for the tight sand).…”

Section: Methodsmentioning

confidence: 99%

Experimental determination of the effective pressure coefficients for Brazilian limestones and sandstones

Vásquez¹,

Vargas²,

Ribeiro³

et al. 2009

Rev. Bras. Geof.

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ABSTRACT. There are numerous efforts to obtain information about saturation and pressure changes due to reservoir production from time-lapse seismic data. In spite of some good examples existing on the literature, there are a lot of approximations behind those studies. Generally, it is assumed that the seismic properties are functions of saturation and differential pressure P d (overburden minus fluid pressure). Actually, the stress that governs the seismic behavior is the effective stress P e f , which is not exactly equal to P d . In fact it is equal to the overburden stress minus n times the fluid pressure. Such coefficient (n) is known as the effective stress coefficient. Sometimes, depending on the circumstances, it might be identified as the Biot-Willis coefficient taking into consideration the bulk modulus of the porous media. In this paper, laboratory results in a tentative to quantify the n values for Brazilian limestones and tight sands will be presented. It is important to point out, that is the first effort to perform this sort of measurements on Brazilian rocks. The results have shown that the mentioned approximations can introduce errors on pressure estimations from time-lapse data even for high porosity rocks.Keywords: effective pressure, porepressure, seismic velocities, Biot-Willis coefficient, 4D seismic. RESUMO.Há vários esforços no sentido de obter informações sobre mudanças de saturação e pressão, devidasà produção dos reservatórios, a partir de dados sísmicos com lapso de tempo. A despeito de alguns bons exemplos existentes na literatura especializada, várias aproximações são feitas para a realização destes estudos. Geralmente,é assumido que as propriedades sísmicas são funções da saturação e da pressão diferencial P d (pressão de soterramento menos pressão de fluido). Na verdade, a tensão que determina o comportamento sísmicoé a tensão efetiva P e f , que nãoé exatamente igual a P d . De fato, estaé igualà tensão de soterramento menos n vezes a pressão de fluido. Tal coeficiente né conhecido como coeficiente de tensão efetiva. Eventualmente, a depender das circunstâncias, este pode ser identificado com o coeficiente de Biot-Willis considerando o módulo de compressão volumétrica do meio poroso. Neste trabalho serão apresentados resultados de medidas em laboratório procurando quantificar os valores de n para calcários e arenitos fechados brasileiros.É importante salientar que esteé o primeiro esforço de realização deste tipo de medidas em rochas brasileiras. Os resultados mostram que as aproximações mencionadas podem introduzir erros nas estimativas de pressão a partir de dados de monitoramento sísmico mesmo para rochas muito porosas.Palavras-chave: pressão efetiva, poro-pressão, velocidades sísmicas, coeficiente de Biot-Willis, sísmica 4D.

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Section: Methodsmentioning

confidence: 99%

Experimental determination of the effective pressure coefficients for Brazilian limestones and sandstones

Vásquez¹,

Vargas²,

Ribeiro³

et al. 2009

Rev. Bras. Geof.

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Experimental efforts to access 4D feasibility and interpretation issues of Brazilian presalt carbonate reservoirs

2019

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Brazilian presalt reservoirs comprise carbonate rocks saturated with light oil with different amounts of [Formula: see text] and excellent productivity. The occurrence of giant-size accumulations with such productivity generates the interest in production monitoring tools, such as time-lapse seismic. However, time-lapse seismic may present several challenges, such as imaging difficulties, repeatability, and detectability of small variations of reservoir properties. In addition, when assessing time-lapse seismic feasibility, the validity of Gassmann’s modeling for complex, heterogeneous carbonate rocks is arguable. Other questions include the pressure variation effects on the seismic properties of competent rocks. The effective stress is a linear combination of confining stress and pore pressure that governs the behavior of physical properties of rocks. Many applications assume that the effective stress for elastic-wave velocity is given by the difference between confining stress and pore pressure, whereas another common approach uses the Biot-Willis coefficient as a weight applied to the pore pressure to estimate the effective stress. Through a series of experiments involving ultrasonic pulse transmission on saturated core plugs in the laboratory, we verified the applicability of Gassmann’s fluid substitution and estimated the empirical effective stress coefficients related to the P- and S-wave velocities for rock samples from two offshore carbonate reservoirs from the presalt section, Santos Basin. We observed that Gassmann’s equation predicts quite well the effects of fluid replacement, and we found that the effective stress coefficient is less than one and not equal to the Biot-Willis coefficient. Moreover, there is a good agreement between the static and dynamic Biot-Willis coefficient, which is a suggestion that the presalt rocks behave as a poroelastic media. These observations suggest that more accurate time-lapse studies require the estimation of the effective stress coefficient for the particular reservoir of interest.

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Effective Pressure Coefficients of Some Brazilian Rocks

Vásquez

Vargas

Leão

et al. 2007

10th International Congress of the Brazilian Geophysical Society &Amp; EXPOGEF 2007, Rio De Janeiro, Brazil, 19-23 November 200

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Viscoelastic behavior of a Brazilian turbidite reservoir and its relationships to facies attributes

Cited by 6 publications

References 3 publications

Experimental determination of the effective pressure coefficients for Brazilian limestones and sandstones

Experimental determination of the effective pressure coefficients for Brazilian limestones and sandstones

Experimental efforts to access 4D feasibility and interpretation issues of Brazilian presalt carbonate reservoirs

Effective Pressure Coefficients of Some Brazilian Rocks

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