Cased-Hole Logging Environment - Cased-Hole Log Analysis and Reservoir Performance Monitoring - page 10

The cable itself is at all times subject to an extrusion force, since the portion
inside the riser experiences wellhead pressure, while the portion outside the riser
experiences atmospheric pressure. The upward force is thus the difference in pres-
sure multiplied by the cross-sectional area of the cable itself. Sometimes this upward
force can be surprisingly large and tools will not go down the well unless
“ballasted” with additional weights.
Question #2.1
Tubing head pressure is 4,986 psi. The logging cable OD is 7/32 in. The tool weighs
20 lb and is 16 ft long.
(a) Calculate the upward force on the cable.
(b) If weights are available, each 4 ft long and weighing 26 lb, how many are
needed to make the tool go down the well?
(c) In that case, how long a riser is required?
(d) If the top of the BOP is 10 ft above ground level, the grease-seal equipment
measures 10 ft, and the sheave assembly requires 6 ft of clearance, how tall
must the workover rig be in order to log this well?
It is also important to plan the arrangement of the Christmas tree—the objective
being to be able to log the well without disturbing the dynamic behavior of the pro-
duction or injection process. Sometimes this consideration is forgotten in the plan-
ning with the result that the only way to get production logging tools into and out of
the well is by shutting in the well. This is undesirable, since a well may take hours
or days to reach equilibrium again after being shut in. Figure 2.2 illustrates an ideal
Christmas-tree setup. Note the numbered items in the fi gure:
#1 Valve on the riser side of the production line
#2 Valve on the production line
#3 Valve on the well side of the production line
#4 Pressure gauge on the riser
#5 Bleed-off valve on the riser
Question #2.2
(a) What happens if item # 1 is missing?
(b) What happens if item #3 is missing?
(c) Why are items #4 and #5 needed?
The Borehole Environment
In many of the problems that arise in completed wells, quantitative analysis will
require detailed knowledge of fl ow rates, casing and tubing sizes and weights, as
well as the types of fl ow that are occurring. For example, in the analysis of