Geohazard studies – Shallow gas Interpreted seismic data – Amplitude Anomaly workflow for ArcGIS

1. Geohazard studies – Shallow gas
Interpreted seismic data – Amplitude Anomaly workflow for ArcGIS

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Fugro Survey AS performs…
-geophysical surveys in Norwegian waters
-about 30 site and route survey surveys per year
Fugro Survey AS

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•Site survey interpretation
•Why site surveys?
•Why interpretation?
•Seismic interpretation for site surveys
•Shallow gas warning levels
•Mapping amplitude anomalies
•Interpreted data in the geodatabase
•Demo visualizing data in 3D
Contents

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Site survey interpretation
Fugro Survey – Geohazard studies

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Why site surveys?
“Site surveys are performed to minimise the risk of harm to personnel and equipment, and to protect the natural environment. The objective of any site survey is to identify all possible constraints and hazards from man-made, natural and geological features which may affect the operational or environmental integrity of a proposed drilling operation…”
OGP Guidelines for the conduct of offshore drilling hazard site surveys, 2011

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Why site surveys?
Features to be assessed by a marine site survey
OGP Guidelines for the conduct of offshore drilling hazard site surveys, 2011
= most common features on the NCS

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Equipment used
Source: Sidescan Sonar (SSS)
Function: Identify seabed features
Frequency: 100 – 500 kHz
Penetration: -
Source: Sub-bottom Profiler (Pinger)
Function: Identify very shallow soils
Frequency: 1.4 – 4.5 kHz
Penetration: 10 - 30 m
Source: Echo Sounder - Multibeam (MBES)
Function: Ascertain water depth
Frequency: 200 kHz
Penetration: -
Source: Magnetometer
Function: Identify magnetic objects (wrecks, pipelines, debris, UXO, etc.)
Frequency:
Penetration: -
Source: Seabed Sampling and CPT
Function: Seabed sampling and core penetration tests
Frequency: -
Penetration: -
Source: 2D High Resolution Seismic (2DHR)
Function: Identify deep soils annd drilling hazards
Frequency: 0.05 – 0.25 kHz
Penetration: 1500 m
Source: Sub-bottom Profiler (Mini Sleeve Gun / Mini Air Gun)
Function: Identify intermediate soils
Frequency: 0.4 – 3 kHz
Penetration: 60 – 100 m
Source: Remotely Operated Vehicle (ROV)
Function: Video and still photos of seabed
Frequency: -
Penetration: -

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Why interpretation?
Data are plain facts or measurement results. It is not enough to have data.
Data in themselves are fairly useless.
But when these data are processed and interpreted to determine there true meaning, they become useful and can be called information.
Reference: Data, information and knowledge: Have we got it right? - M. Boisot and A. Canals, UOC Working Paper Series WP04-002 (2004).
Data
Processing
Interpretation
Report Writing & Charting
Information
A survey is much more than just “data” – we produce information!

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Why interpretation?
Site Survey
Interpretation
2DHR Seismic Side Scan Sonar
3D Seismic
Infrastructure Data Archive Data Well Data Geotechnical Data
(CPT)
Sub-bottom Profiles
(HMP/MAG)
Bathymetry (MBE)
Groundtruthing
(Photo, Video, Grab Sampling,
Gravity Coring)

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Seismic interpretation for site surveys
Purpose of 2DHR interpretation for a site survey …
•Prognosis of Stratigraphy and Lithology
•Identification of potential drilling constraints and geohazards at the sub-seabed levels
… down to about 1000 m below seabed.

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Seismic interpretation for site surveys
500 m
500 m
1 km
Shallow Gas
Shallow Gas
2DHR interpretation is
supplemented by 3D Data

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Shallow gas warning levels
•Distance to amplitude anomalies
•Structural / stratigraphical traps
•Geological setting (e.g. up dip position, potential migration paths, lithology)
•Experience from neighboring wells and regional understanding
•Comparability between planned well location and neighboring wells
•Relationship between shallow gas and amplitude anomalies
The level of warning is determined from following factors:
No shallow gas is expected at the planned well location.
No seismic indications for the presence of shallow gas have been identified at or near the planned well location.
No warning
Shallow gas cannot be excluded at the planned well location.
Seismic indications for the presence of shallow gas have been identified at or near the planned well location. However, alternative interpretations are possible. The implementation of sufficient mitigation measures is recommended.
Slight warning
Shallow gas is expected at the planned well location.
Strong seismic indications for the presence of shallow gas have been identified at or near the planned well location. Alternative interpretations are unlikely. A relocation of the planned well is recommended.
Serious warning
A three level scale is used to describe a shallow gas hazard. These warning levels assess the probability of occurrence of shallow gas at a particular planned well location.

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Mapping amplitude anomalies
1.Amplitude anomalies are grouped into intervals based on stratigraphy and interpretation.
2.Maximum amplitude values within these intervals are calculated using tools in IHS Kingdom Suite.
3.A threshold value is defined for each interval to separate anomalous high amplitudes.
4.Areas with amplitudes above the threshold value (= anomalies) are mapped.
Amplitude Anomaly
Top/Base of Geological Units

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Mapping amplitude anomalies

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Amplitude anomlay workflow for ArcGIS
Fugro Survey – Geohazard studies

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Data managed in a geodatabase
Well locations
Survey program
Tracklines /
Navigation
Seabed features
Seismic
interpretation
Shallow soil
Bathymetry
Sonar Mosaic
Geotechnical data
Seabed Survey Data Model (SSDM)
GIS Server

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Create a workflow
•To be used for all interpreted seismic data
•To standardize the information populated in the database
•Easy to use
Requirements for the workflow
•Need to populate the Seabed Survey Data Model (SSDM) feature classes and attributes
•Data is to be used in figures for the report and in presentations
•Data is to be used in charts
•Data is to be used in Web Map applications
•Need to be able to search and filter the data based on location and attributes
•Data is to be visualized in 3D
Interpreted seismic data in the geodatabase

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3D Seismic
VatABS - XY Time Grid
Contour
Amplitude GeoTif
3D anomalies with attribues and TWT as Z
Add Time from grid to Z value of anomaly polygon
xABS - XY Amplitude Grid
(absolute values)
Kingdom / Geos
ArcGIS and Tools / Processing & Charting
Site Survey Database (SSDM)
Workflow
Create Polygon from Contour for each level
Merge AAT, and calculate SSDM attributes
Amplitude Anomaly table (AAT)
Geo / Interpretation
2D anomalies with attribues and TWT as Z
2D Seismic
VatABS Amplitude and Time
Create lines and points for each level
Raster Datasets

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Input
•ASCII files exported from Kingdom (interpretation software)
•XYZ files with Amplitude and TWT
•Information from the interpretation (xls spread sheet)

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Workflow – a set of tools

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•Acoustic features point
•Acoustic features line
•Acoustic features polygon
•Raster datasets
•Attributes in the database populated
Output

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Anomaly summary map

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Figures for report

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Data example figures for presentations

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Web map application

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Steps for creating 3D Web Scenes in ArcScene
•Symbolize vector data with 3D symbology
•Create line features with xyz for point features that should be shown vertically
•Drape raster and vector layers that do not have z- values on bathymetry and horizons
•Create bookmarks of features to be shown
Export ArcScene file to WebScene
Extensions
•3D Analyst
•Seismic Explorer from Geocap
2D High Resolution seismic with 3D cube
Sidescan Sonar draped on bathymetry with seabed features
Visualization of data in 3D in a web browser

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Demo

28. Marit Aakerholt
Senior GIS Consultant, Geo Services
Mobile: +47 917 37 412
E-mail: m.aakerholt@fugro.no / Website: www.fugro-survey.no
Address: Karenslyst Alle 2, N-0278 Oslo / P.O. Box 490 Skøyen, N-0213 Oslo, Norway
Trade Register / VAT: Nr 937 107 978
Dr. Björn Bohling
Chief Geologist, Geo Services
Mobile: +47 950 40 667
E-mail: b.bohling@fugro.no / Website: www.fugro-survey.no
Address: Karenslyst Alle 2, N-0278 Oslo / P.O. Box 490 Skøyen, N-0213 Oslo, Norway
Trade Register / VAT: Nr 937 107 978