detection and estimation of gas hydrates

8/7/2019 Detection and Estimation of Gas Hydrates

http://slidepdf.com/reader/full/detection-and-estimation-of-gas-hydrates 1/13



Detection and estimation of gas hydrates involves a five

step integrated multidisciplinary approach that included:

(1) reprocessing conventional 3D seismic data at the higherresolution using an amplitude-preserving flow with

prestack time migration,

(2) a detailed stratigraphic evaluation and interpretation to

identify potential hydrate zones,(3) Seismic attribute analysis to further delineate

anomalous zones,

(4) full waveform prestack inversion to characterize

acoustic properties of gas hydrates in 1D (Mallick, 1995)and map in 3D using a hybrid inversion technique (Mallick

et al., 2000),

(5) quantitative estimation of gas hydrate saturation using

rock property models (Figure 1).



Figure 1. Five-step process for gas hydrate detection and estimation using

seismic.



Stratigraphic evaluation

Figure 2. Seismic section with stratigraphic interpretation at Keathley Canyon w ith BSR i nd icated by y ell ow dotted li ne.



Figure 3. BSR defined by the termination of bright sands as indicated by

the negative amplitude that is caused by the free gas in the pore space.



Figure 4. Seismic section of Atwater Valley study area showing hydrate

mound and general stratigraphy.



Figure 5. Seafloor gas hydrate features at Atwater Valley study area.



Rock physics of gas hydrates. The presence of aBSR,

seafloor mounds, amplitude blanking, or other

gas hydrate indicators cannot positively confirmthe existence of hydrates. To better determine

the existence of gas hydrate, and to quantify

actual saturation, elastic property inversion is first

performed using high-quality seismic data. This isfollowed by rock physics inversion to further

transform the elastic properties into gas hydrate

saturation estimates.



Figure 6. Existing microstructural models of gas hydrate bearing sediments.



Figure 7. P-wave velocity versus gas hydrate saturation for the rock physics models

shown in Figure 6. M3 is the best model (model 3 inset) that matches the gas hydrate

saturation at Mallik 2L-38.



Figure 8. S-wave velocity versus gas hydrate saturation for the rock physics models

shown in Figure 6. M3 (model 3 inset) best matches the gas hydrate saturation at Mallik

2L-38.



Figure 9. Prediction of gas hydrate stability zone in the deepwater Gulf of

Mexico. The thermal gradient used is 25°C/km.



Gas hydrate saturati on for At water Valley li ne. Upper panel d is pl ay s the P-im pedance d er ived

from

h

ybr i d i nve

r si

on and the

l ow

er pan

el sh

ow s the

estim

ate

d gas h

ydrate

satu

rati

on.

detection and estimation of gas hydrates

Documents