Developments in Seismic Imaging of the MC118 from 2D, 3D and 4D data

Presented to the GoM-GHRC Annual Meeting – Oxford, MS – Oct 26-27 2010

Antonello Simonetti1, James H. Knapp1, Leonardo Macelloni2, Camelia C. Knapp1, Carol B. Lutken2

1. Department of Earth and Ocean Sciences, University of South Carolina2. Mississippi Mineral Resources Institute and Center for Marine Resources and Environmental Technology, University of Mississippi

SUMMARY TOPICS• WHERE WE WERE:

- Integration and interpretation of TGS 3D data, SSDR 2D Hi-Res data and AUV-Chirp 2D data;

- Pseudo 4D seismic analysis, some insights about the GHSZ of the MC118.

• WHERE WE ARE:

- Recent re-processing of SSDR High Resolution data and correction of the timing problem;

- Western Geco 3D Oil-Ind data.

• WHERE WE ARE HEADING:

- Further interpretations on SSDR High Resolution data;

- 4D seismic analysis using TGS and Western Geco data; - “Marine Hydrate stability and response to oceanographic variability: an integrated modeling and empirical approach” (NASA Proposal)

SEISMIC DATA INTEGRATION

Seafloor Pockmarks and Craters are circular depression of the

seafloor. Generally, they formed by the escape of fluids or gas

into the water column and by violent episodic gas blowout,

respectively.

Seafloor Pockmarks and Craters are located above the Master Faults

which are most likely the main conduits for thermogenic HC.

Time slice from TGS 3D volume

Seafloor Pockmarks and Craters are closely related to

their underlying acoustic anomalies refered as free gas

at the base of GHSZ. The anomalies occur at constant

depth of 160 ms TWTT (~ 150 m b.s.f.)

PSEUDO 4D SEISMIC ANALYSIS

GHSZ INFERRED FROM SEISMIC DATA

- GHSZ shows transience on the scale of the years, basing on Pseudo 4D seismic analysis.

- It exhibits heterogeneity in the subsurface of the Woolsey Mound.

- Shallow GH formation and accumulation appear to be concentrated near faults and fractures.

- BGHSZ observed ~150 m beneath the seafloor.

- Trigger mechanisms of temporary gas hydrates dissociation still remain unclear. They might be a combination of multiple processes (tectonics, upwards stress-failure induced by arising HC, oceanographic variations, or any phenomena which lead to perturbations into the GH stability field).

SUMMARY TOPICS• WHERE WE WERE:

- Integration and seismic interpretation of TGS 3D Oil-Ind data, SSDR 2D Hi-Res data and AUV-Chirp 2D data;

- Pseudo 4D seismic analysis, some insights about the GHSZ of the MC118.

• WHERE WE ARE:

- Recent re-processing of SSDR High Resolution data and correction of the timing problem;

- Western Geco 3D Oil-Ind data.

• WHERE WE ARE HEADING:

- Further interpretations on SSDR High Resolution data;

- Real 4D seismic analysis using TGS and Western Geco data; - “Marine Hydrate stability and response to oceanographic variability: an integrated modeling and empirical approach” (NASA Proposal)

SSDR data re-processing and time correction

SSDR data before the time correction

Sample rate 10 μsec

SSDR data after the time correction

Sample rate 8 μsec

SSDR data re-processing and time correction

WesternGeco

3D Industry Seismic Data

Acquired 2002 (May, Aug, Dec)

10 sec TWTT

Volume extends 1 mi beyond MC118

In-Line & Cross-Line spacing: 12.5 m

TGS

Record Length: 3 sec TWTT

Record Length: 10 sec TWTT

vs WGeco

SUMMARY TOPICS• WHERE WE WERE:

- Integration and seismic interpretation of TGS 3D Oil-Ind data, SSDR 2D Hi-Res data and AUV-Chirp 2D data;

- Pseudo 4D seismic analysis, some insights about the GHSZ of the MC118.

• WHERE WE ARE:

- Recent re-processing of SSDR High Resolution data and correction of the timing problem;

- Western Geco 3D Oil-Ind data.

• WHERE WE ARE HEADING:

- Further interpretations on SSDR High Resolution data;

- Real 4D seismic analysis using TGS and Western Geco; - “Marine Hydrate stability and response to oceanographic variability: an integrated modeling and empirical approach” (NASA Proposal)

Further Interpretations on SSDR data

High-Frequency signal scattering

near fault.

GH accumulation?

4D Seismic Analysis

TGS (2000) WesternGeco (2002)

Detecting temporal changes in seismic anomalies

through amplitude map, residual map etc

NASA Proposal

Potential influence of oceanographic events on hydrate stability

Reconstruct GOM oceanography through remote sensing and modeling

Compare with observations from past MC118 cruises

Forecast future oceanographic events and plan observations on future cruises

CONCLUSIONS - Woolsey Mound at MC118 hosts a very complex scenario for GH, where salt, thermogenic hydrocarbons, faults and fractures play a significant role for the hydrate/carbonate mound evolution.

- A further analytical approach will be addressed to our site in order to understand whether or not the GHSF could be affected even by very short term (months or weeks) variations in oceanographic currents.

- Pseudo 4D seismic analysis reveals a subsurface dynamic systems that seem to change in a short time frame (5 or 6 years). Therefore, they need regular detailed observations multiple surveys through the time. As we have no seismic records since 2006, our suggestion would be to collect a new seismic survey shortly.

- Quantitative estimation of GH saturation can be hardly argued without auxiliary constrains. Geophysical borehole logging into the GHSZ (i.e. resistivity log, density log and sonic log) would provide diagnostic information about the GHSF.

- Gas Hydrates formation, accumulation and dissociation are closely related to deep-seated faults which provide hydrocarbons through the sea floor and into the water column.

ACKNOWLEDGEMENTS

TGS Nopec

WesternGeco

SMT

Lookout Geophysical Company

MMRI & CMRET – University of Mississippi

Funds provided by DOI, MMS, DOE, NTEL, DOC, NOAA-NIUST