Petrophysics MSc Course Notes
Dr. Paul Glover
INTRODUCTION TO PETROPHYSICS AND FORMATION
The search or economic accumulations of oil and gas starts with the recognition of likely geological
provinces, progresses to seismic surveying, and the drilling of one or more wild-cat wells.
If one is
lucky, these wells may encounter oil, and if that is the case, measurements made down the hole with
wireline tools are used to assess whether sufficient oil is present, and whether it can be produced.
Clearly, the evaluation of sub-surface formations requires the combined efforts of geologists,
petrophysicists, drilling engineers and even geophysicists. However, it is the geologist and
petrophysicist that has the most influence.
The geologist is interested in the lithology, stratigraphy and depositional environment of the sub-
surface strata penetrated by the drilling bit. The
uses wireline tool responses in a
number of wells to create a large scale image of the sub-surface geology by correlating wireline
responses that are characteristic of a given formation or horizon between formations. This picture is
very useful when carrying out initial reservoir modelling and in the decision where to drill new wells.
carries out much the same process with much more well information,
and adds any extra information that has been gathered to produce a detailed geological model of the
reservoir and related sub-surface formations. This model will be the basis of reservoir modelling, and
all major reservoir management decisions from primary drainage through to enhanced oil recovery and
job is to use all available information to analyze the physical and chemical
properties of the rocks in the sub-surface, and their component minerals, with particular emphasis
given to the amount and distribution of those fluid minerals that we know of as water, oil, and gas.
The petrophysicist will use extensively wireline log data and data from experiments done on cores
extracted from the well, and will occasionally use other sources of information such as engineering
and production logs, as well as mud logging data. Initially, it is the aim of the petrophysicist to
differentiate between oil, gas and water bearing formations, estimate the porosity of the formations
and the approximate amount of hydrocarbons present in each formation. Ultimately, the petrophysicist
also uses laboratory data to estimate how easy it will be to extract the hydrocarbons in place, and to
design reservoir management strategies to optimize long term oil recovery.
There is a large database of information available to both the geologist and the petrophysicist, and as
time passes the amount and variety of information increases. Table 1.1 summarizes a few of the main
measurement that a geologist or petrophysicist will have access to, arranged in approximate
chronological order. It is the responsibility of the wellsite geologist or engineer to ensure that all this