Page 19 - Well Logging and Formation Evaluation

Basics 9

to the annulus. The toolstring is then run in farther to the deepest logging
point, and logging commences. The reason the SES is not installed when
the toolstring is at the surface is partly to save time while running in (and
allowing rotation), and also to avoid the wireline extending beyond the
last casing shoe in the annulus. If the openhole section is longer than the
cased hole section, the logging will need to be performed in more than
one stage, with the SES being retrieved and repositioned in the string.
Pipe-conveyed logging is expensive in terms of rig time and is typically
used nowadays only where it is not possible to acquire the data via LWD.
Most contractors now offer a means to convert an operation to pipe-
conveyed logging if a toolstring, run into the hole on conventional wireline,
becomes stuck in the hole. This is usually termed “logging while fishing.”

1.3 LOGGING CONTRACTS

Typically, an oil company will set up logging contracts with one or more
contractors for the provision of logging services. Usually some kind of
tendering process is used to ensure competitive bidding among various
companies able to provide such services. Elements that exist in common
contracts include the following:

• Depth charge: This relates to the deepest depth that a particular tool will
be run in the hole.
• Survey charge: This relates to the interval that a particular tool is actu-
ally logged in the hole.
• Station charge: For tools such as formation pressure sampling tools and
sidewall samples, this is a charge per station measurement. Usually the
contract will make certain specifications regarding when such a charge
may be dropped (e.g., if no useful data are recovered).
• Tool rental: Usually a daily charge for the tools to be on the rig on
standby prior to or during a logging job
• Logging unit rental charge: Usually a monthly charge for the logging
unit (winch, tool shed, and computers) while it is on the rig
• Base rental: There may be a monthly charge to have a pool of tools
available for a client. For LWD tools, this may supersede the tool rental,
depth, and survey charges.
• Engineer charge: Usually a day rate for any engineers, specialists, or
assistants present for the logging job
• In-hole charge: Some LWD contracts specify an hourly charge while
tools are actually being run in the hole.