Subsurface Mapping

Introduction

Introduction

Objectives of subsurface mapping

Methods Before you start

Objectives

Most of the Earth’s structure and stratigraphy are hidden

Structure/stratigraphy may host features of economic or academic importance

Need to be able to map/interpret the subsurface

Objectives

Petroleum industry Explore for and develop oil and

natural gas reserves Mining

Explore for and develop minerals and other economic deposits

Groundwater Explore for and develop

groundwater

Objectives Waste disposal

Find suitable repositories for waste

Environmental remediation Geotechnical engineering

Locate and map the distribution of layers with specific properties

Academic studies Structure, stratigraphy

Etc.

Objectives

This course: focus on petroleum

Why? Methods applicable to other

fields Best datasets

Objectives

Develop the most reasonable subsurface interpretation(s) for the area being studied, even in areas where the data are sparse or absent Integration of different types of data

Interpretations used to direct future exploration & development

Methods Wireline logs Core, cuttings (“samples”) Seismic data (2-D, 3-D) Potential field data (gravity,

aeromag) Ground-penetrating radar Engineering data (fluids,

pressures, etc.) Previous reports Etc.

http://sofia.usgs.gov/publications/wri/94-4010/upperflaq.html

Geophysical logs used in groundwater studies

http://www.geoprobe.com/products/tools/geotechnical/cptpro_log.htm

Geotechnical borehole logs

Air Guns

Streamer Tail buoy

Marine seismic vessels typically tow arrays of air guns and streamers containing hydrophones a few meters below the surface of the water.

Messinian Salt – Mediterranean SeaMessinian Salt – Mediterranean Sea

Courtesy TGS-Nopec

Salt

Vibroseis Operations - AlgeriaVibroseis Operations - Algeria

Courtesy François Gauthier

•Dip panels

Waiting on 84wy314

Courtesy Anadarko

Mapping Faults Using Dip Panels in Thrust Mapping Faults Using Dip Panels in Thrust RegimesRegimes

Seismic Cube

Slicing and Dicing to Extract Geologic InformationSlicing and Dicing to Extract Geologic Information

Timeslices

Methods

Previous reports Paper copies of data (analog) Digital data: computer-based

interpretations

Methods

Caveat: Without understanding what you’re doing, you’ll get a wrong answer.

Working with computers, you’ll get a wrong answer at light speed (but it may be good-looking!).

Methods

Interpretations (maps, etc.) are working hypotheses, never “final” May need to update, revise as

new data become available Easier with digital data

Applies to ANY branch of (Earth) Science!!!

Collect Data

Interpret Data

Drill

Collect Data

Interpret Data

Drill

Collect pertinent data and reports

Build Database

Scan through data(quality, phase,

geology)

Scan through data(quality, phase,

geology)

Tie well and seismicdata (vsp, synthetics,

tops, paleo, etc.)

Tie well and seismicdata (vsp, synthetics,

tops, paleo, etc.)

Pick Horizons & Faults

Pick Horizons & Faults

Mapping&

Analysis

Mapping &Analysis

(I ntegration)

ReservoirProperty

Prediction

ReservoirProperty

Prediction

Output to Simulator

Output to Simulator

Output to SimulatorDrilling

Collect pertinent data and reports

Build Database

Collect pertinent data and reports

Build Database

Scan through data(quality, phase,

geology)

Scan through data(quality, phase,

geology)

Scan through data(quality, phase,

geology)

Scan through data(quality, phase,

geology)

Tie well and seismicdata (vsp, synthetics,

tops, paleo, etc.)

Tie well and seismicdata (vsp, synthetics,

tops, paleo, etc.)

Tie well and seismicdata (vsp, synthetics,

tops, paleo, etc.)

Tie well and seismicdata (vsp, synthetics,

tops, paleo, etc.)

Pick Horizons & Faults

Pick Horizons & Faults

Pick Horizons & Faults

Pick Horizons & Faults

Mapping&

Analysis

Mapping &Analysis

(I ntegration)

Mapping&

Analysis

Mapping &Analysis

(I ntegration)

ReservoirProperty

Prediction

ReservoirProperty

Prediction

ReservoirProperty

Prediction

ReservoirProperty

Prediction

Output to Simulator

Output to SimulatorOutput to Simulator

Output to Simulator

Output to SimulatorDrillingOutput to SimulatorDrilling

Before you start…

Need clear definition of objectives Structure? Stratigraphy?

Exploration? Development? Etc. Without knowing where you’re going,

you’re unlikely to get there…

Before you start…

Need good understanding of structural geology, stratigraphy and other related fields The more geology one knows, the more

reasonable the resulting interpretation Need good understanding of

physical basis for any geophysical methods being used

Prestack Depth Migration ExampleSubsalt – Offshore GOM

Before you start…

Use correct mapping techniques and methods Prepare reasonable subsurface maps

and cross-sections “Maps and cross-sections are the

primary vehicles used to organize, interpret and present available subsurface information”

Digital products (e.g., volumes) becoming more common

http://www.kgs.ku.edu/Workshops/IVF2000/nissan-ivf/tocnav640.html

Geocellular model:Each cube is assigned initial

properties (porosity, permeability, fluid saturation etc.)

3D display of georeferenced scanned images of collar locations, geological cross-sections, integrated with drillholes displaying assay concentrations, and magnetic and gravity modeled bodies.

www.rockware.com

Before you start…

Need to define fault behaviour in 3-D Faults may have important affects on

location, movement of fluids Show location of faults on maps, but

also map fault surfaces May need to do structural

reconstruction to validate accuracy of fault interpretations

A 2-D expression of a fault

Twiss and Moores, 1992

Faults are 3-D features

Fault visualization (Hart et al., 2001)

0m i 2 .5m i

0km 2.5kmFault visualization (Sagan and Hart, in press)

Courtesy Midland Valley

Before you start… All subsurface data need to be used

to develop a reasonable and accurate subsurface interpretation Geologic (including paleontologic),

geophysical, engineering Attention to resolution, accuracy of

each type Integration of different types of data

results in more robust interpretation

Before you start… Need to document the work done.

Lots of data likely to be collected and/or generated – document in a format that may be referenced, used, revised

People working on project may change, may want to “revisit” work many years after it is done

Electronic media (PowerPoint files, hypertext documents, etc.) good vehicles – especially when working with digital data

Really great stuff Fred, but how did you generate it?

Ummm….

Summary

Subsurface mapping of important economic & fundamental importance

Push towards digital, computer-based interpretation

Need to understand fundamentals – geology, geophysics

Integration of different types of data results in more robust interpretation