First of all, unless you get a perfect cement job almost every
sidetrack can be considered "open hole". Read these notes with that
The higher the angle, the softer the formation the more chance of
success. Low angle, hard formation; you will need a very big bend
implying high dogleg severity as it kicks off. Anticipate this if
Pick your spot carefully. Go to the logs and find the best
formation and ROP. If possible pick a big dogleg and sidetrack the
opposite way. If the old hole builds and turns left then drop and
turn right. Obvious really but well planning doesn’t always see it
that way. Be prepared to fight for a better spot if you can see
one. Do it right and you only need to do it once.
Sidetracking easiest on low side but low/left, low/right usually
not too difficult. Going for all turn without a drop is only
possible in soft formations and not recommended. Turn and build
almost impossible except with a perfect cement job and they are
Open Hole Sidetrack - Two schools of thought – The reamers and the
time drillers. Reamers pick a spot to side-track well down a stand
then pick up, set a tool-face and ream slowly down to that spot.
Then pick up again, not so far and ream down again and so on
reducing the reamed section progressively concentrating the effort
on one spot till they are sure they have a ledge. Then comes the
crunch when you set gently down on the ledge and watch how things
react, hopefully side-tracking fairly swiftly.
Reaming is useless where you have a high down drag and therefore a
lot of compression in the string. It is impossible to be certain
you are stopping at the exact same spot every time since the string
may still be on the move even though you have stopped slacking off.
Same problem on a semi with heave and tide adding to the
I am more of the time drilling school. Start above the side-track
point, set a toolface and time drill. Obvious, yes? Well, a little
more than that. Time drilling means you can see immediately you get
a ledge of formation through small changes in differential
pressure, toolface and possibly WOB. The cuttings stream also
relates to what you are doing with the bit at a point and not just
over a section. Time drilling allows you to take advantage if, with
a little luck, you get an edge early. You are not trapped in a
programme. You can react to subtle changes as they occur, slowing
things down or speeding them up as appropriate. Nothing wrong with
a combination of techniques. Spend some time polishing a section to
aid sliding before settling down to time drilling.
And by time drilling I mean t…i……m……..e drilling. Patience is
essential especially at low angle in hard formation. Rule of thumb
– Time drill at 1/10 previous ROP. Sidetracking
from semis on several occasions the tide has gone out faster than I
have been time drilling (Important to keep track of the tide when
drilling this slowly on a semi). Patience and consistency –
slacking off a foot and waiting an hour is not time drilling at one
foot an hour. Mark the pipe and keep the driller on schedule. The
hardest part of the job is overcoming other people's impatience;
the company man, the toolpusher, the driller. Many a sidetrack has
been lost through pushing ahead too soon and slipping off the ledge
back into soft cement or the open hole. You need to have moved the
hole by at least half a diameter before you have a reliable ledge
that you can begin to push on. Assuming a consistent 4°/100 dogleg
then in 8½" hole you have to drill 32' to get that much
displacement and in 12¼" a half diameter takes 38'. This takes time
at say 5'/hr. Warn everyone before you start.
Proceed cautiously and look for every clue that the bit is digging
– slight reactive torque (toolface drifting left), a little
differential pressure (let it drill off), a little WOB (let that
drill off too), till you are confident that you have engaged
Track the cuttings and check for yourself the percentage of
cement/formation. Take samples off the top screen as well. Loggers
have a habit of taking only the fines and this can give an
excessive percentage of cement since it shows up more in the fines.
I have had geologists and loggers insist that we had 80% cement
when great chunks of clay have been bouncing off the top
Jump the Plug – If you find you have plenty of good quality hard
cement to dress off surrounded by softer formation it is sometimes
possible to "jump the plug", an involuntary sidetrack while
dressing off cement. Be conscious of this and track the cutting
stream to take advantage of this possibility. It can save a lot of
time. Good things do sometimes happen.
Cement Plugs –
Sidetracking, for the use of.
Where possible the best
place to set a cement plug is on bottom. If this means pumping a
few extra barrels of cement to reach kick off point then this is
much simpler and better than spotting a pill. This can depend on
the length of stinger available. Cementing up round the drillpipe
is not a good idea and anyway leads to contaminated cement.
Either a bridge plug or spot a weighted hi-vis pill below the
planned setting depth.
Temperature is very important – MWD should be able to supply – tell
the cementer though he has probably checked with the mud
API density for class G cement is 15.8ppg (1.9SG) – This can be
pushed to 16.8 ppg (2.0SG) with thinners which can help early
strength but needs batch mixing.
Pump enough to compensate for contamination – the problem of
contamination increases in deeper and smaller hole and in oil-based
mud. 25% excess at least or 100’ extra.
Use highest possible flow rates – turbulent flow in spacers if
possible. But remember you can shake a very thin tubing stinger to
pieces by pumping too hard.
Use a diverter tool at the end of the stinger to at least direct
the flow sideways and if possible up the annulus.
Check setting times – Don’t tag till at least 8 hours and 12-24 is
Open hole sidetrack with
GeoPilot – Notes from the G-P running procedures.
Several successful open hole sidetracks have been performed in
Determine the sidetrack
point primarily based on drillability and secondarily on
Time drill at a setting between 150 left and 150 right of highside.
Monitor the ABI and determine ROP for time drilling.
Previous open hole sidetracks have taken from 2.5 to 18 hours,
sometime It can be more, it’s depending of the
If you don’t be patient during side track
Your goldfish may die.
- A strange dog might bite you on the street.
- A friend may punch you.
- Your computer may catch fire.
- Your loved one may leave you.
Anyways it will be bad...