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

Side Scan Sonar 2DHR Seismic

3D Seismic

Infrastructure Data Well Data Archive 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

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