Formation Evaluation - Mud logging, Core logging and wireline logging

Group 9 Members: Luke, Tom, Sid, Nhan and Richard


by Tom Sturman & Luke Stoeckel, with edits by Richard Yeomans

In order to gain an accurate representation of the Earth's subsurface, data is the key. This is especially important when companies are exploring for exploitable resources (such as hydrocarbons) with targets to reach and share holders to please. This creates the necessity for many data sources to be used in conjunction with each other so as accurately as possible estimate, model and simulate the production stages of a venture. With this in mind the correlation between geophysical data, core samples and real-time drilling data, and the generation of useful information from this data, is critical in evaluating the productivity and longevity of a hydrocarbon field.

Core taken from the well during the drilling stage can be used as a physical representation of the subsurface formations. Laboratory tests can be run on physical specimens to determine its properties such as absolute porosity, effective porosity and permeability; while physical characteristics such as grain size, lithology, grain shape, sorting and the presence of any biological/vegetation matter can also be logged visually. Another important technique in data collection is geophysical logging which is used to provide a continuous, depth related record of geophysical parameters down hole. These parameters are used to help characterize the reservoir by qualitative and quantitative measurements and assessments of the lithological and petrophysical properties. Some of these tests and logs include; calliper logs, temperature logs, spontaneous potential logs, gamma ray logs, resistivity logs, induction logs, sonic logs, density logs, photoelectric logs and neutron logs.

In this Wiki we illustrate the importance of correlating geophysical data and core logs to locate the presence of hydrocarbon accumulations within in a well, whilst also creating a more accurate reservoir characterisation. With the correlations it is possible to find the same reservoir units in other wells by similar readings in the wire line logs.


by Tom Sturman, with edits by Luke Stoeckel, Richard Yeomans

The term “Formation Evaluation” can be defined as being the analysis of a formation, and determination of its ability to produce petroleum. By using a variety of data sources with information taken from within a formation, hydrocarbons are able to be detected and quantified. The most common data sources used are; geophysical (or wireline) logs, core samples and mud logs which are interpreted from the rock cuttings brought up by the drilling fluid. Each source has their own advantages and disadvantages which can provide us with different information. No single data source is able to provide all the information needed, thus in order to determine as much information as possible about a well, multiple data sources need to be utilized and correlated. It is the combined knowledge from each log that helps give the most accurate description of the reservoir rock and its properties. Additionally, geophysical logs can be subdivided into three categories; mechanical, spontaneous and induced (Table 1, below).

Use the links in Table 1 to obtain more infomation on the specific log:

Log type
Formation parameter measured
Hole diameter

Borehole temperature

SP (Spontaneous Potential)
Spontaneous electric currents

Gamma ray
Natural radioactivity

Resistance to electrical current

Conductivity of electrical current

Velocity of sound propagation

Reaction to gamma ray bombardment

Reaction to gamma ray bombardment

Reaction to neutron bombardment
[Table 1: Wireline log types and categories]

Hoisting a MWD Tool into Oil Rig

In the video below you can see the MWD/LWD tool being raised onto the drilling rig before being lowered into the hole for measurement purposes. As you can see the device is not insignificant at all! It is around 11 meters long containing all the reqired equipments, however it should be noted that most of that length are its powering batteries.


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