sonic logging present

By group 4 membersSONIC LOGGING

Show relative measurement of formation capacity to transmit

INTRODUCTION

Can be used :

Factor that

effecting sonic

logging

Fluid content

porosity

Rock matri

x

Usually sonic loging is used in shallow are because

fictitious reflections

Lower variation

Wave propagation technique as applied in seismic survey

Transducer – produce sound waves by oscillating motion in rock formation

In elastic medium , there are two types of medium. hard medium = propagate fast soft medium = propagate slow

BASIC PRINCIPLE OF SONIC LOGGING

Measurable

properties

velocity

frequency

amplitude

Snell’s law : acoustic signal behaves at the velocity boundary separating the borehole and the formation.

It also explains on how the waves travel and bounce back to the receiver.

As we all know snell’s law is used when it comes to 2 diff erent isotropic media but it also can be used within diff erent media such as in the rock itself.

Acoustic logging tools are designed to measure one or more of these properties, with velocity (slowness) being the most common.

The waveform recorded at the logging tool’s receivers is a composite signal containing diff erent energy modes, each with a diff erent frequency, velocity, and amplitude.

For borehole logging, the modes of primary interest are, in order of arrival

compressionalStoneleyshear

The particles do travel everywhere following the waves but it only vibrates in its loci.

One way to classify acoustic waves is via direction of particle displacement with respect to the direction of wave propagation :

longitudinal(compressional) transverse (shear)

Acoustic energy mode present in borehole are: Normal (pseudo-Rayleigh)Tube (Stoneley) waves

Factor affecting velocity of waves

cementation

Clay contetn

t

Overburden pressure

lithology

The basic principle of the acoustic logging tool (operating principle of the tool)

• Sonic logging is a well logging tool that provides a formation’s interval transit time, designated as t, which is a measure of a formation’s capacity to transmit seismic waves.

• Geologically, this capacity varies with lithology and rock textures, most notably decreasing with an increasing eff ective porosity.

• A sonic log can be used to calculate the porosity of a formation if the seismic velocity of the rock matrix are known.

BASIC RESPONSE

Acoustic theory and wave propagation• The principles of borehole acoustic logging (and

surface seismic methods) are based on the theory of wave propagation in an elastic medium.

• The oscillating motion generated by a sound source (transducer) in an elastic medium (rock formation) is called an elastic wave or acoustic wave (also called head or body waves).

• The waveform recorded at the logging tool’s receivers is a composite signal containing diff erent energy modes, each with a diff erent frequency, velocity, and amplitude.

BASIC RESPONSE OF ACOUSTIC LOGGING TOOL

PROPERTIES FROM BASIC RESPONSE

The Wyllie Time Average Equation: Can be written in terms of velocity or Δt Empirically determined For clean and consolidated sandstones Uniformly distributed small pores

CALCULATION OF POROSITY FROM SONIC LOG

For uncompacted formations:

This is when adjacent shale beds have Δt values greater than 100μs/ft resulting in overestimation

The Raymer-Hunt equation: Based on field observation Yields slightly greater porosity in the 5 to 25% range Does not require compaction correction

ADVANTAGES AND DISADVANTAGES

The sonic measurement is one of the purest of log measurements.

It requires very few assumptions and is largely unbiased by models relative to nuclear and induction tools.

The concept of the technique has not changed profoundly since 1935, when Conrad Schlumberger written the fi rst patent for sonic logging as we know it today.

However, advances in technology and our increased understanding of sonic waveforms in the borehole, largely through computer based modeling, have increased the applications of sonic logging far beyond those imagined in the early decades of exploration technology development in the 20th century.

CONCLUSION