Estimating pore-space gas hydrate saturations from well log acoustic data (original) (raw)
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Estimation of gas hydrate and free gas saturation, concentration, and distribution from seismic data
Gas hydrates contain a major untapped source of energy and are of potential economic importance. The theoretical models to estimate gas hydrate saturation from seismic data predict significantly different acoustic/ elastic properties of sediments containing gas hydrate; we do not know which to use. Thus, we develop a new approach based on empirical relations. The water-filled porosity is calibrated (using well-log data) to acoustic impedance twice: one calibration where gas hydrate is present and the other where free gas is present. The water-filled porosity is used in a combination of Archie equations (with corresponding parameters for either gas hydrate or free gas) to estimate gas hydrate or free gas saturations. The method is applied to single-channel seismic data and well logs from Ocean Drilling Program leg 164 from
Can We Estimate the Amount of Gas Hydrates by Seismic Methods
Annals of The New York Academy of Sciences, 2000
Abstract: Elastic wave velocity is the key parameter in determining the quantity of gas hydrate in sediment. Using data acquired in permafrost, elastic responses of gas hydrate bearing sediment are examined in detail by fitting observed elastic wave velocities of VSP and logging data with computed velocities based on two opposing gas hydrate bearing models. It is concluded that observed elastic wave velocity best fits a model of gas hydrate disseminated in pore space, without assuming cementation on grain boundaries in model simulations. This conclusion is important in the sense that shear wave velocity is crucial in determining gas hydrate bearing model and estimating gas hydrate saturation rate in pore space. The current case is the first example in model determination by reliable elastic wave velocity observed in the field.
Journal of Applied Geophysics, 2004
We estimate the concentration of gas hydrate at the Mallik 2L-38 research site using P- and S-wave velocities obtained from well logging and vertical seismic profiles (VSP). The theoretical velocities are obtained from a generalization of Gassmann's modulus to three phases (rock frame, gas hydrate and fluid). The dry-rock moduli are estimated from the log profiles, in sections where the rock is assumed to be fully saturated with water. We obtain hydrate concentrations up to 75%, average values of 37% and 21% from the VSP P- and S-wave velocities, respectively, and 60% and 57% from the sonic-log P- and S-wave velocities, respectively. The above averages are similar to estimations obtained from hydrate dissociation modeling and Archie methods. The estimations based on the P-wave velocities are more reliable than those based on the S-wave velocities.