9-borehole Seismic_lw.pdf

Log Evaluation and QA/QC Seminar Borehole Seismic

Lukas Wihardjo Apr-2014

What is a VSP?

A VSP or Vertical Seismic Profile is the process of recording seismic data in a wellbore environment. The geophones are vertical in the earth versus horizontal along it as in surface seismic.

SEISMIC SIGNAL IN THE BOREHOLE

Seismic Signal in the Borehole Time • Downgoing direct arrival

• Reflected upgoing primary • Downgoing multiple • Reflected upgoing multiple

Depth

Vertical Seismic Profile • Time-Depth • Seismic Reflections Time

Depth

One-Way Time vs. Two Way Time Surface Seismic

TWT = OWT + TT

VSP

Time TWT

TT

Reflecti on

TWT

TT

OWT

Depth

Transit

Reflection

Time (TT)

Time (OWT)

Borehole Multiples

Upgoing Multiples

Borehole Multiples Downgoing Multiple

Borehole Multiples All Multiples

Tube Wave Energy Source

Tube waves are generated when surface waves from the source come in contact with the borehole fluid and become a guided wave traveling up and down the borehole. As the tube wave travels vertically in the borehole it pushes the wall horizontally.

When the geophones are properly clamped to the borehole wall most of the tube wave energy will be seen in the horizontal geophones.

At changes in the borehole dimensions some of the tube wave energy will be reflected back to the surface. This will also occur when the energy reaches the bottom of the hole.

Tube Waves Raw Data

Vertical Channel

Y

X

Tube wave

HODOGM

Horizontal Channel

Depth

One-Way Time

Y

X

HODOGM

Tube wave

Surface Seismic Comparison VSP Data

Surface Seismic Offset

Depth

BOREHOLE SURVEY TYPES

Borehole Seismic History Checkshot

Single Trace

2-D Lateral Coverage

Geometry of surveys

CHECKSHOT

ZERO OFFSET

WALKABOVE

OFFSET

HORIZONTAL

WALKAWAY

3D VSP

SALT PROX

Checkshot Surveys CHECKSHOT Depth (m)

Source

Depth Model

Surface Seismic

Geophones

Acoustic Impedance

Formation Travel Times Formation Velocities

Synthetic Seismogram

Depth-Velocity Model Inputs

Time (s)

Surface Seismic Correlation Wavelet Processing

Zero Offset VSP Source Depth (m)

ZERO OFFSET

Depth Model

Surface Seismic

Surface Seismic Correlation

Geophones

Over-pressure Zone Prediction Corridor Stack

Multiple Pattern Identification

Time (s)

Wavelet Processing Formation Velocities

Vertical Incident VSP Sources Depth (m)

WALKABOVE

Depth Model

Surface Seismic

Surface Seismic Correlation

Geophones

Lateral Coverage Beneath Well VSP Image

Multiple Pattern Identification

Time (s)

Fault and Dip Identification Formation Velocities

Offset VSP Source Depth (m)

OFFSET

Depth Model

Surface Seismic

Surface Seismic Correlation

Geophones

Fault and Dip Identification

Time (s)

VSP Image

Salt Proximity Identification Shear Wave Analysis Surface Seismic Survey Design

Imaging Walkaway Source Depth (m)

WALKAWAY

Surface Seismic Geophones

Surface Seismic Correlation Fault and Dip Identification

Depth Model VSP Image

Shear Wave Analysis Surface Seismic Survey Design

AVO Walkaway AVO WALKAWAY

Source Positions P-Wave

S-Wave

True Seismic Amplitude With Changing Offset

P-P and P-SV Analysis Anisotropy velocity model Reflector

Q factor analysis

Salt Proximity Survey Provides Accurate Salt Face Image 2D, 2.5D and 3D Imaging Solutions

3D VSP 3-DVSP VSP 3D

Well 1

Well 1

Well 2

3D-VSP Depth Migration

Surface seismic 3D PSDM

Well 2

Very High SubSurface Imaging Resolution Exploration and Development Applications Detailed Preplanning and 3D Modeling Required