Page 13 - Well Logging and Formation Evaluation

Basics 3

quently used are proven reserves, developed reserves, scope for recov-
ery reserves, probable reserves, and possible reserves.
• Remaining reserves = that part of the reserves that has not yet been
produced
• Cumulative production = that part of the reserves that has already been
produced
• UR = ultimate recovery; the total volume of reserves that will be pro-
duced prior to abandonment of the field
• NPV = net present value; the future economic value of the field, taking
into account all future present value costs and revenues
• RF = recovery factor; the reserves as a proportion of the STOIIP
(or GIIP)
• B o = oil volume factor; the factor used to convert reservoir volumes of
oil to surface (stock tank) conditions. Likewise B g for gas.

In order to produce the hydrocarbons, wells are needed and a develop-
ment strategy needs to be constructed. This strategy will typically be pre-
sented in a document called the field development plan (FDP), which
contains a summary of current knowledge about the field and the plans
for future development.
Once an FDP has been approved, the drilling campaign will consist of
well proposals, in which the costs, well trajectory, geological prognosis,
and data-gathering requirements are specified. The petrophysicist plays a
part in the preparation of the well proposal in specifying which logs need
to be acquired in the various hole sections.

1.2 BASIC LOG TYPES

Below is a list of the main types of logs that may be run, and why they
are run.

1.2.1 Logging While Drilling (LWD)

Traditionally, petrophysicists were concerned only with wireline
logging, that is, the data acquired by running tools on a cable from a winch
after the hole had been drilled. However, advances in drilling/logging
technology have allowed the acquisition of log data via tools placed in
the actual drilling assembly. These tools may transmit data to the surface
on a real-time basis or store the data in a downhole memory from which
it may be downloaded when the assembly is brought back to the surface.