Page 165 - Introduction to Petroleum Engineering

152 DRILLING

geologist at 10 ft intervals. The geologist also enters detailed descriptions of cuttings
collected at the shale shaker in another column. This column includes notes on oil or
gas shows. Composition of hydrocarbon gas that evolves from the mud is continually
recorded in the last column. The organization and extent of the mud log varies
from company to company. As the first source of data from the subsurface forma-
tions, the mud log is vital for drilling management, hydrocarbon exploration, and
completion designs.
When drilling reaches the target depth, the drilling crew circulates mud until the
hole is clean and then trips the drill pipe out of the hole. The well is ready now for
the next stage of the drilling process.

example 8.4 Drill String

How many stands of drill pipe are needed to prepare a drill string that is
10 000 ft long? A stand is three pipes, and each pipe has a length of 30 ft.
Assume one stand of drill collar and neglect elongation of pipe.
Answer
Length of drill string = 10000 ft = length of drill collar + length of drill pipe
Length of drill collar = 90 ft
So
Length of drill string = 10000 ft = 90 ft + length of drill pipe
Length of drill pipe = 9910ft
One stand of drill pipe = 90 ft
Therefore we need 9910 ft/(90 ft/stand) = 110 1 stands of drill pipe.
.
110 stands of drill pipe would be short, so 111 stands would be needed.

8.3.4 Open‐Hole Logging
After drilling to target depth, the operator needs to make a decision: set production
casing and complete the well or plug and abandon the well. Before making this
decision, the operator gathers more data on the formations exposed by drilling. The
lowest cost data are obtained by logging the well with tools deployed on a wireline
composed of steel cable wrapped around multiple strands of electrically conductive
wire. Logging at this stage of the drilling process is open‐hole logging because there
is no casing in the hole.
When properly interpreted, open‐hole logs show lithology, porosity, and water
saturation in the rock around the hole from bottom to top of the logged interval. The
log also includes the diameter of hole measured by the caliper from bottom to top.
Hole diameter is important for two reasons. First, interpretability of the other logs
rapidly declines if the hole diameter is not constant. And second, the diameter is used
to estimate the amount of cement needed to case or plug the well. More details of log
interpretation are discussed in the next chapter.
The wireline logging contractor arrives on location with a wireline logging truck
and one or two pickup trucks loaded with 10–20 ft long logging tools and lubricator