Exploration with Wireline Logs

The information from wireline logs is used to enhance two principle

objectives in the exploration program:

Rock & Reservoir Properties Hydrocarbon Evaluation

a. Environment of Deposition a. Correlation

b. Lithology & Mineralogy b. Structure

c. Radioactivity c. Permeability Traps

d. Porosity Type d. Porosity Type

e. Fluid Properties & Distribution e. Salinity Traps

f. Formation Pressure

g. Temperature

h. Rock Strength & Elastic Properties

There are several complicating factors which must be dealt with in order to

arrive at acceptable values for those formation and hydrocarbon variables.

The three most common factors are:

• The borehole is a dynamic system. The mud system will

penetrate the rocks surrounding borehole, and the borehole wall

is affected by the drilling process and time (time difference

between drilling and the wireline logging runs).

• Matrix and Pore Fluids affect certain tools differently.

• Tool Depth of Investigation is relatively shallow.

Classification of Wireline Logging Tools

1. Lithology Logs - These logs are designed to:

a. Identify permeable formations

b. Determine boundaries between permeable and non-permeable

formations

c. Provide lithology data for correlation with other wells

d. Provide a degree of certainty for quantifying the formation

lithology.

Examples of lithology logs are:

Spontaneous Potential

Gamma Ray

2. Porosity Logs - These logs are designed to:

a. Provide accurate lithologic and porosity determination

b. Provide data to distinguish between oil and gas

c. Provide porosity data for water saturation determination.

Examples of porosity logs are:

Sonic/Acoustic

Neutron

Formation Density

3. Saturation (Resistivity) Logs - These logs are designed to:

a. Determine the thickness of a formation

b. Provide an accurate value for true formation resistivity

c. Provide information for correlation purposes

d. Provide a quick indication of formation pressure, hydrocarbon

content and producibility.

Examples of saturation logs are:

Normal and Lateral Devices

Laterologs

Induction Logs

There are a number of auxiliary wireline services which can provide

additional information to augment the interpretation of formation

characteristics. These include: 1) caliper logs, 2) directional logs, 3)

dipmeter logs, 4) sidewall coring, and 4) formation testers.

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