Progress of the Atlantis 4C Node Project

1
Progress of the Atlantis 4C Node Project

• Presented by Jeff Kao
• M.S. Geophysics
• Advisor Dr. Robert Tatham

2
Outline

• Objective of research
• Introduction to project
• Methodology
• Overview of research and preliminary progress
• Summary
• Future Work

3
Objective

• Analyze the P-SV converted waves in
  multicomponent data
• Determine velocities for Vp and Vs
• Observe the occurrences of the converted waves
• Use seismically estimated Vp and Vs to describe
  shallow pore-pressure variations

4
Introduction

• Atlantis Field was discovered in 1998 by BP
• Located 300km south of New Orleans in the GOM
• Water depths range between 1300m to 2200m
• Survey deployed 902 OBS 4C nodes

5
Survey Geometry

• Node spacing of 426m
• Shot spacing of 53.7m
• Nodes arranged in a hexagonal sampling technique
• Density of nodes is 6.36 nodes/km2

6
Atlantis Field
Beaudoin et al.
7
Shot and Node Grid Geometry
Beaudoin et al.
8
Methodology

• Begin analysis with one node
• Extract shots along strike of the regional
  geology extending W to E
• Take one shot line near node extending NW to SE
• Analyzing horizontal components
• Observing approx. first 3 seconds of data

9
Methodology

• Extract shots contributing to 1 node to obtain a
  2D swath
• QC polarity of 3C and hydrophone at the direct
  arrival
• Rotate horizontal components to radial and
  transverse
• Velocity analysis to attain Vp and Vs values

10
Map of Nodes
N
11
Line Extending East West
12
X Raw
E
W
13
Y Raw
W
E
14
Z Raw
W
E
15
Shot Line Trending NW to SE
16
Line 21289 X Raw
SE
NW
17
Line 21289 Y Raw
SE
NW
18
Line 21289 Z Raw
SE
NW
19
Preliminary Velocity Analysis
20
X RAW
1352 1514
1904 1326
21
Y RAW
1366 1507
1880 1316
22
Z RAW
1376 1510
1864 1351
23
Summary

• Dealing with water depth of 2050 m
• Direct arrival at normal incidence is 1.3
  seconds
• Observing shallow reflections
• Asymmetric travel time

24
Future Work

• Estimate pore pressure in the deep water
  sediments
• Many opportunities for future students with this
  BP data set