Lecture Presentations

PGE368Fall 2003 Semester

November 13 and 18

Principles and Interpretation of Borehole Sonic Measurements

Carlos Torres-Verdn, Ph.D.Assistant Professor

Bulk Density Logging

Neutron Logging

Sonic Logging

Electrical Resistivity of Rocks

Electrical Resistivity Tools:Induction and Laterolog

Course Plan, II

Saturation

Invasion

Active NuclearLogging

Porosity

GasLithology

Invasion

CoreData

Objectives:

To understand the physical principles behind the operation of sonic logging tools,

To understand the principles behind the interpretation of sonic logs, and

To understand the limitations of sonic borehole measurements.

Complementary Reading Assignment:

1. Bassiouni, Z., 1994, Theory, Measurement, and Interpretation of Well Logs, Chapter 3: Acoustic Properties of Rocks.

APPLICATIONS:

Mechanical Property Analysis

Formation Evaluation

Geophysical Prospecting (Seismic Exploration)

Stress and Strain

Stress and Strain

Mechanical Properties and Petrophysics

Units and Conversions

P and S WAVES

BASIC PRINCIPLES

250 cm 200 150 100 50 0 cm

80 cm

80 cm

40 cm30 cm 20 cm

60 cm

5 cm 2 cm 0 cm

INDUCTION LOG

LATEROLOG

NEUTRONGAMMA RAY

DENSITY

SONICMICRO RESISTIVITY

MICROLOGDIPMETER

DEPTH OF INVESTIGATION

RES

OLU

TIO

NRESISTIVITY

RADIOACTIVITY

RESISTIVITY

ACOUSTIC

Logging Tools

Traditional Monopole Tool

Single Transmitter-Single Receiver Tool

Single Transmitter-Dual Receiver Tool

EARLIER TOOLSSingle Transmitter Dual Receiver

EARLIER TOOLSDual Transmitter Dual Receiver(Borehole Compensation)

Synthetic Compensation

Monopole in a Fast Formation

Different Waves, Different Velocities

MONOPOLE WAVEFORM

BOREHOLE WAVES

HARD FORMATION, MONOPOLE EXCITATION

SOFT FORMATION, MONOPOLE EXCITATION

CYCLE SKIPPING

Typical Ranges of Velocities

P-WAVE VELOCITIES OF GASES

P- and S-WAVE VELOCITIES OF SEDIMENTARY ROCKS

Typical Ranges of Velocities

Relationship with Depth

Relationship with Pressure

Formation Over-Pressure

Influence of Saturating Fluids

Influence of Gas and Water Saturation

Qualitative Summary

DIPOLE FLEXURAL WAVE

Sonic Porosity

1. The porosity from the sonic slowness is different from that of

the density or neutron tools.

2. Sonic porosity reacts to primary porosity only, i.e. it does not

see the fractures or vugs.

3. The difference between the sonic porosity and the neutron-

density porosity gives a Secondary Porosity Index (SPI) which

is an indication of how much of this type of porosity there is in

the rock.

Intuitive Model

tlog = t f + 1 ( )t ma

= tlog t mat f t ma

This is very simple with the inputs of a matrix slowness and a fluid slowness

The basic equation for sonic porosity is the Wyllie Time Average Formula (strictly speaking, an empirical formula):

Sonic Porosity

Theory and Measurements

Compaction Effects

Sonic Porosity

=Ctlogtma

tlogC is a constant usually taken as 0.67

There is another possibility for transforming slowness to porosity, called Raymer Gardner HuntThis formula tries to take into account some irregularities seen in the fieldthe basic equation is

a simplified version used on the CSU and Maxis is

1t c

=1( )2t ma

+

tf

Synthetic Seismogram (cont.)

Applications Well Tie & Correlation Allow to correlate log

data with surface seismic data

Surface Seismic

Acoustic ImpedanceSynthetic

Seismogram

BOREHOLE DIPOLE SOURCE

SOFT FORMATION, DIPOLE EXCITATION

DIPOLE WAVEFORMS: Fast Formation

DIPOLE SONICARRAY TOOL

EXAMPLE:Ultra Slow Compressional Wave

EXAMPLE:Ultra Slow Dipole Shear Response

STONELEY PERMEABILITY

FRACTURE EVALUATION

LOGGING FOR MECHANICAL PROPERTIES

CROSS-DIPOLE:In-Situ Stress

In-Situ Stress

SANDING MODEL DIAGRAM

ACKNOWLEDGEMENTSBaker Atlas

Schlumberger