Page 166 - Introduction to Petroleum Engineering

THE DRILLING PROCESS 153
segments. While there is a wide assortment of tools available, the most commonly
used are the gamma‐ray tool, formation density tool, neutron density tool, and a
caliper. When these tools are assembled, the total length of the logging string can be
80–120 ft. The lubricator is a pipe of sufficient length and diameter to hold the assem-
bled logging string. The logging crew assembles the lubricator with the cable running
through the stuffing box at its top and then through to its open bottom, attaches the
cable to the top of the logging string, pulls the logging string into the lubricator, and
uses a drill rig hoist to raise the lubricator to flange to the top of the BOP.
With the lubricator attached to the top of the BOP, the logging crew carefully
lowers the tool to the bottom of the well, using the weight indicator for signs of tool
sticking. The length of hanging cable is also measured as it unwinds from the drum
of the wireline truck. One of the first major measurements made with the wireline
string is total depth of the well. This depth is compared to the depth recorded by the
driller based on length of the drill string. With total depth verified and any differ-
ences resolved, the crew slowly raises the tool and records all of the data received
from the tools. Data is not collected on the downward trip but on the upward trip
because the upward trip gives more reliable depth measurements. The time needed
for logging varies from about 6 to 24 hr, depending on the depth range that is
logged and the allowed rising speed of the logging tools. During this time, the dril-
ling crew must be alert for signs of kicks that can occur while logging, especially
on the upward stroke.
In addition to open‐hole logging, operators may use other tests to assess the
exposed formations. Using the drill string, the drill stem test (DST) can measure the
productive capacity of formations. Using wireline, the repeat formation tester (RFT)
can measure pressure in formations and collect small volumes of formation fluids.
Both of these tests can end with a tool stuck in the hole. Indeed, the RFT is called the
“repeat fishing tool” by some field hands.
When open‐hole logging and other tests are done, the operator must decide how
to proceed. Even though a substantial amount of data has been obtained, the risk of a
wrong choice has not been eliminated.

8.3.5 Setting Production Casing
If the operator chooses to abandon the well, the abandonment procedure specified in
the original permit for the well must be followed. This process will involve setting
plugs and pumping cement to seal the well. If, on the other hand, the operator chooses
to case and complete the well, then a crew will set production casing with the drilling
rig following procedures similar to those used for setting surface casing. Whether
plugged or cased, it is time to rig down and move out (RDMO) to the next drilling
location.
Figure 8.10 shows a wellbore diagram for a vertical well. Casing prevents fluid
movement between formations and it prevents collapse of the wellbore. Surface cas-
ing fits inside the conductor pipe and protects freshwater formations. Some wells
have one or more strings of intermediate casing inside the surface casing, each with
a smaller diameter. Intermediate casing protects formations above the target zone.
Intermediate casing may go most of the way to total depth. Production casing has