Page 160 - Hydrocarbon Exploration and Production Second Edition

Reservoir Description 147

Figure 6.36 Principle of wireline logging.

secondary objective it should normally remain subordinate to well integrity
considerations. In practical terms this means that logging operations will be
curtailed in development wells if hole conditions deteriorate. This need not rule out
further data acquisition, as logging through casing options still exist.
Figure 6.36 depicts the basic setup of a wireline logging operation. A sonde is
lowered downhole after the drill string has been removed. The sonde is connected
via an insulated and reinforced electrical cable to a winch unit at the surface. At a
speed of about 600 m/h the cable is spooled upward and the sonde continuously
records formation properties like natural GR radiation, formation resistivity or
formation density. The measured data are electrically transmitted through the cable
and are recorded and processed in a sophisticated logging unit at the surface.
Offshore, this unit will be located in a cabin, whilst on land it is truck mounted.
Today, the important acquisition and processing software is carried to the well site
by the logging engineer in a laptop. The data acquisition can be observed in real
time by the client using a secure Internet site. In some cases, specialist tools can be
run and processed ‘remotely’ by offsite experts at logging company headquarters.
A vast variety of logging tools are in existence and Section 6.4 will cover only
those which enable the evaluation of essential reservoir parameters, specifically net
reservoir thickness, lithology, porosity and hydrocarbon saturation.