- journal_title：Geophysics
- Contributor：Richard C. Nolen-Hoeksema
- Publisher：Society of Exploration Geophysicists
- Date：2000-
- Format：text/html
- Language：en
- Identifier：10.1190/1.1444826
- journal_abbrev：Geophysics
- issn：0016-8033
- volume：65
- issue：5
- firstpage：1355
- section：TUTORIALS
Gassmann's equations relate the low-frequency drained and undrained elastic-wave response to fluids. This tutorial explores how different modulus–porosity relationships affect predictions of the low-frequency elastic-wave response to fluids based on Gassmann's equations. I take different modulus–porosity relations and substitute them into Gassmann's equations through the framework moduli. The results illustrate the range of responses to fluids and can be summarized in a nomograph of the effective fluid coefficient, which quantifies the change in the pore-space modulus (∂ Kpore / Kpore) in response to a change in fluid modulus (∂ Kfluid / Kfluid). Two ratios control the effective fluid coefficient: the ratio of the fluid modulus to the solid-grain modulus (Kfluid / Ksolid) and the ratio of the Biot coefficient to porosity (αK/ϕ). The effective fluid coefficient nomograph is a convenient tool for estimating how low-frequency elastic-wave properties will respond to changes in reservoir fluids.