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This is the most important subject of this school– The practices used by most groups are completely inappropriate– The serious problems experienced are self-inflicted, and
unnecessary
This section will cover:What is required for safe tripping
PracticesBHA requirements
BackreamingIs it good or bad ?Why do you see what you do ?How to do it safely (and when to do it)
Tripping & Backreaming Practices• Back-reaming or pumping out should be avoided
whenever possible in high-angle wells– The ability to trip out without pumping or backreaming is a
critical objective– Choosing any practice or equipment that forces you to
backream to trip out makes a mockery of risk-management• Because back-reaming and/or pumping out are the single-most
dangerous operation in any ER well– Maximum risk of stuck pipe, and of destabilizing the wellbore– It is also time consuming, and destructive on BHA equipment
– Engineers :• It’s not just a matter of circulating more … it’s a design issue too
What we will cover in this section:• Part 1 – What is happening downhole• Part 2 – How to enable tripping on elevators• Part 3 – Tripping procedures• Part 4 – Backreaming procedures
What happens downhole when tripping in a deviated well ?– Firstly, assume that the hole is NOT 100% clean
– Even with a thorough clean-up– Even with Rotary Steering Tools !
– The BHA does NOT pull cuttings up the hole– Cuttings flow around the BHA, until they become too compressed– BHA design is critical to “flow around” ability– Has significant implications for how to manage tight hole
The dirt must be able to flow through the bit & BHA• Just like mud, we have a serious problem when the dirt can’t get past the BHA• Consider ketchup / sauce poured through a kitchen funnel
• What are the downsides/risks associated with Backreaming?– Stuck pipe– BHA equipment failures due to vibration– Key seating– Lost returns (if packoffs exceed fracture gradient)– Self-inflicted wellbore stability problems
• Interpretation of “wellbore stability” problems changes entirely if the wellbore has been “Hammered”– Often, the presence of cavings after packoffs is perceived as
the very cause of the packoffs• K&M contend that it is more likely the packoff created the cavings
due to the hammer effect• Evidence of this is “wellbore stability” problems often go away when
tripping practices are modified (due to avoidance of packoffs)
• Part 2 – How to enable tripping on elevatorsMany operators say “don’t back-ream unless you have to …”But experienced ER people “know” that no-matter what the
procedures say, that’s the only way they can get out of the hole
The ability to trip regularly on elevators is possible – But simply circulating more isn’t the answer
• Unless the BHA components are addressed as a high priority ….– Conventional tripping may be impossible despite best practices– It only takes one component to make a BHA un-trippable
• No matter how much circulation is done
– This makes a mockery of every risk management precaution we make, if this isn’t addressed as the highest priority
THIS IS THE SINGLE BIGGEST THING YOU CAN DO TO REDUCE (OR INCREASE) RISK IN YOUR PROJECT
Trip #1 (5 Blade, 14.5in2 JSA)No problems, very similar to behavior on first well (similar bit)Minor 20-30k “peak” over pull in places (fairly slick on average)Average FF = 0.16 – 0.18
Trip #2 (9 Blade, 12.5in2 JSA)Long and troublesome trip with several intermediate circulation points required due to 50-60 k overpull in several locationsAverage FF = 0.19-0.20
Trip #3 (8 Blade, 20.9in2 JSA)Very smooth trip with the fewest number of tight spots of all the trips out. “Peak” overpull of <15k.Average FF = 0.16-0.18
Cleaning-up for a trip– This process does leave cuttings in the hole– The hole doesn’t have to be completely clean. – The goal is to have trouble free trips.
1. Pull out of hole without rotation or circulation• Trip speed is important … controls speed of dirt flow
through the stabilizers & bit• Tighter BHAs require slower speeds
2. Monitor P/U weight while tripping out of hole• Compare real-time to theoretical drag trends (“roadmaps”)• Must have a road-map to know what “normal” is
• Circulate & rotate at > 120 rpm for 30 minutes– Goal is to verify cuttings dune, so as not to waste time if otherwise– Conveyor belt must be on, if cuttings are to be moved
• POH carefully without rotation or circulation watching for the tight spot to recur
– If the tight spot has moved up hole, then obstruction was cuttings– Continue cleaning the hole up, per standard clean-up procedures
• If the tight spot has NOT moved up hole, then genuine tight hole is likely (key seat, ledge, swelling formation, etc.)– Circulating or backreaming may be used with caution – Must avoid pack-off while circulating or backreaming out of the hole
• Risk of stuck pipe• Pressure damage to wellbore below pack-off• Don’t want to lose returns
– Hole cleaning get’s really messy if we can’t circulate !
Pipe Stretch Implications- Vertical: Pick-up weight = Rotating wt = Slack-off wt- High angle: Weights are very different ….so what ?
Consider what’s actually happening downhole when the weight indicator changes when you kick the rotary on …- BHA immediately sucks up the hole, with missing force load
- typical stretch is 1’ per 1000’ MD (ie, 12’ at 12000’ MD)- If you rotate with any tension remaining …
- I think I’m stuck, will just make sure about that before I call somebody !
Backreaming Procedure• Think of backreaming as drilling backwards
• Be patient - Backreaming must be done slowly- 10 min/stand sounds slow, but is equivalent to ROP of 600 ft/hr- Acceptable speed is very sensitive to angle when above 70o
- Dune will move slowly, especially if using low RPM- Pack-off will occur if pickup speed is too fast
• Torque is primary tool to monitor pulling speed • If rig systems allow, consider pumping at drilling flowrate &
rotate at 120+ rpm (for larger hole sizes)- This will help disperse cuttings dune above BHA- However, hard on top drive & may cause casing wear- Alternative is low RPM while up-reaming, then high RPM down-reaming,
before final pick up to rack stand (without rotation– repeat cycle if tight)
• Always clean up hole immediately after finish of backreaming -- never just pull out of the hole– Applies for cased hole as well as open hole– This explains the industries “typical” experience that once backreaming
starts, it can’t be stopped (in reality, all we need to do in order to return to tripping on elevators is erode the due away from the top of the BHA)
• Take special care coming into a casing shoe– Large OD rathole/washout accumulates cuttings– Consider extra circulation with rotation before proceeding
Underreamer Considerations• Backreamed 8 1/2”x9 7/8” with RWD in string• Memory resistivity shows rugous and washed out hole after backreaming• Multiple packoffs and subsequent instability ensued on trip in