Page 398 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 374

[ ] Practical Wellsite Operations
3.3.7

Run in with the next bit and wait above the top of cement. Check
the surface samples. Once the cement has developed enough strength
to drill through, continue drilling ahead.
In severe cases, an Expandable Slotted Liner™ from Petroline
could be considered. This is set in place across the enlarged zone, an
expander plug is pulled through it to expand it, and it is cemented
in place.

3.3.7. Making Connections to Minimize Wellbore Instability and Losses

Surge and swab pressures can be seriously detrimental to your
wellbore. A surge pressure occurs when a temporary increase in pres-
sure is exerted on the formation; a swab pressure occurs when a tem-
porary decrease occurs.
These pressure fluctuations are especially damaging in naturally
fractured formations but can also destabilize nonfractured shales. It is
often not recognized that how you stop the pumps is almost as impor-
tant as how you start them up.
Starting the pumps. Kick in one pump at a few strokes a minute
(say about 10-15% of your normal drilling flow rate). Watch for stand-
pipe pressure and returns—you should see some pressure first then
flow starting. Once you have pressure and returns, kick in the second
pump to the same speed. Let the pressure stabilize. Smoothly increase
pump speed over about 20-30 seconds to the desired flow rate (more
slowly in critical hole sections).
Stopping the pumps. Do not wind both pump controls right away
to zero unless you are stopping the pumps for a potential kick. Reduce
flow rate first to around 75%. Wait until you see a decrease in flow on
the flo-sho (note approximately how long this takes), then come down
to 50%. Wait as long as you had to wait the first time, then reduce flow
rate down to 25%. Wait the same time again then shut off completely.

Significant surge pressures can be created by running in too fast or
starting up the pumps too quickly. The amount of pressure increase on
a connection will depend on how fast the pumps are started up, depth
(i.e., inertia of the weight of mud in the annulus), mud density, mud
gel strength, mud rheology, and hydraulic diameter (which is related to

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