horizontal well basics
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Horizontal Well Completions
Objectives To provide a clear, applications oriented view of
horizontal well completions and workovers.
To enable the class participant to design aneffective horizontal well completion.
What data to collect and why it is importantHow to select a candidateWhat computer models to use / Who can helpWhat completion is probable, possible and practicalWhat to expect on production / How to operate itHow to design it.
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Horizontal Wells
First conceived in US and USSR in 1930s First serious attempts in 1950s
First successful completions in 1970s Caught on world-wide in 1980s Now a standard well configuration
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Slide modified from BP
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Uses of Horizontal Wells
increasing reservoir contact water/gas coning control water/steam injection extended reach capability minimizing surface locations, slot saving improving wellbore location
prospecting and gathering reservoir info. drain individual compartments
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Other Uses
Prospecting - as a tool to prove up seismic inan area
Accessing all parts of the field - flank wells afavorite in offshore reservoirs
As a platform for fracturing
As a gathering system - Amoco Canadas BigKahuna
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Favorite Targets
Naturally fractured chalks and shales Water coning problem areas
Field edges
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Best Candidates from a ReservoirPerspective
1. Must still have good volume of reserves,pressure and fluids of value.
2. Permeability values (horizontal and vertical)more a design consideration than a limit.
3. Oil was thought to be a better candidatethan gas because of hydraulic fracturing,
however, horizontal wells with multistagefracturing are a common completion for lowpermeability gas plays.
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Best - non stimulated candidates
No vertical barriers and generally highpermeability reservoirs.
Kv/Kh > 0.1 to 0.5 (opinion) (consider frac if perm is too low)
natural fractures often viewed as good, butwatch effects on the drainage profile and alsobottom water.
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Reservoir Considerations
Will reduced footprint help? (offshore andhigh land cost or political areas)
Will there be improvements in contact withsome dipping beds.
Pay configuration issues: layers boundries anisotrophy
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Permeability Variance
Kh, KH, Kv Barriers
Bed angle (a vertical well can be horizontal tothe bedding plane in some instances
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Directional Permeability
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Permeability Contribution fromVertical and Horizontal Permeability
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Drainage in a Horizontal Well for Casesof Permeability Anisotrophy
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Placement of the Horizontal Above theO/W Contact
Depends on: vertical permeability fluid viscosities pay zone thickness anomolies in the zone depth (?) and formations above the pay zone
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Pay Zone Thickness
no minimum or optimum vertical and horizontal permeability more
critical fractures
incidence of fractures location of fractures
permeability of fractures good or bad? - water???
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Stacked and Opposed
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Compartment Recognition
Geological clues DSTs
Production behavior Hydrocarbon source variances (oilfingerprinting)
Early Recognition - addressed in design Later Recognition - requires a workover
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A two flow period test of reservoirpotential what does it tell?
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Information available fromdownhole gauges and flowtests.Reservoir pressurePerm estimatesDepletionBarriersDamageCompartmentalization
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RecognizingCompartmentalization
Slide from George Tews
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Horizontal Well Expectations
Uncertainty??? can it be drilled? can it be completed? can it be operated/produced? is it really a good candidate? is fracturing needed?
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Horizontal and Lateral Drilling
An introduction to horizontal well drillingtechnology: Goal is to make the engineer/foreman aware of
some problems and solutions available in drillingoperations that can have a major effect oncompletions and production.
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Types of Horizontal Kick-Off designs.Increasing the angle limits weight transfer to the bit.
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Long radius wellsat 2 to 6 o areused forextended reach.
Medium radiuswells at 6 to 8 o
minimize drillingbut lose someextensioncapacity.
Short radius wellsover 8 to 10 o canmiss problemzones above thepay, but are
short.
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Ability to Lift Cuttings
Must reach high enough velocities to carryparticles upward. Problems in horizontals:
limited circulation rate large annular areas = low flow velocity striated flow regimes especially at 30 o to 60 o
difficult in all liquid systems (rate)
difficult in all gas systems (striation)
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Cuttings Beds
Symmetric suspension - constant concentration incross section
Asymmetric suspension - all carried, but more atbottom
Moving bed - like a dune Stationary bed - builds to height dictated by flow rate Boycott settling - explains severe solids drop out in
the 30 to 60 degree range.
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Boycott SettlingGas Rise Rate???
Vertical holes - 1000 ft/hr30 to 60 o deviation - 4000 to 7000 ft/hr
Region of greatest settlingProblems, 30 to 60 degrees theBoycott Region
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Lighter fluids rise to thetop side of the wellbore(striatation) and densefluids and cuttings dropout to the bottom outof the fast movingupper fluids result ispoor hole cleaning andsticking of strings.
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Consequences of Poor Hole Cleaning
Bridging - sticking pipe Failure to run to bottom
Debris in perfs Emulsions and scale seeds left in the well? Cave-ins? - probably not
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Where are the casing set points inthis example?
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BUT, is it stable as the hole approaches horizontal? Rememberthat hole stability is lowest in the bend area.
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Drilling Fluid Operating Window
Mud density must be higher than the porepressure to keep fluids from entering the well.
Mud density must control tendency of shale to
spall particles into wellbore Mud density must be less than the formation
fracture (extension) gradient corrected forfriction pressures while circulating. The pressureexerted by the fluid at any depth is a function of its density plus the friction pressure in thecirculating path back to the surface.
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Drilling Wellbore Stability
Issues - during drilling, completion andproduction
Destabilizing Mechanism support pressure too low (spalling) support pressure too high (fracturing) Rx with drilling fluids (sloughing, swelling) formation stress unloading
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A model of wellbore stability (most stressed regions in blue) of a horizontal wellbore.
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y ( g )
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Broad Based Conclusion
Most Important Failure Factors pore pressure prediction weak, fissible beddling planes
low support pressures time dependent loss of strength
Open holes best in stable formations
(carbonates, clastics) Most instability problems in the shales
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So, how far do you drill?
Consider edge boundries Consider drilling costs (usually low in lateral)
Consider vertical perm
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Effect of length and horizontal permeabilityon PI in horizontal wells
1000
100
10
P . I .
( M s c
f d / p s
i )
100 1000 10000 100000 1000000
Drilled length x Kh
71970001.ppt3/14/2009 38George E. King EngineeringGEKEngineering.com
Hariot-Watt Horizontal Study
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71970002.ppt
10000
1000
100
1010 100 1000 10000 100000 1000000
Length x (KvKh)^0.5
Effect of horizontal well factors on PIA fieldB fieldC fieldD fieldF fieldG fieldI fieldJ fieldN field
P . I . ( M s c
f d /
m ( p ) )
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Hariot-Watt Horizontal Study
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Undulation Problems Within theHorizontal Well
50423007
How long a well can you effectively complete and produce?Depends on shape, angle, path and fluids.
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Improving Artificial Lift for Horizontal Wellsby Using Rat Hole on Short Radius
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Production Index Factors
(a comparison to horizontal well performance)
Theoritical PIFs may range from 1 to 8. Actual PIFs range from 1 to about 4 or 5. Causes:
reservoir not homogeneous reservoir estimates too generous completion design was an after-thought
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Horizontal Well PIFs(1300 well study)
Reservoir Type PIF Average (Mean)------------------- --------------------------Conventional Reservoirs 4Heavy Oil Reservoirs 7Fractured Reservoirs 12All reservoirs comb. 5PIF = Prod. Improvement Factor: comparison of
horizontal to vertical prod of wells at the samelocation.
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Lower Than Expected Production?
1. Low vertical perm. 2. Formation damage 3. Reservoir quality variance 4. Pressure drop along the lateral ?? - few psi
at max, but can be important.
5. Poor initial knowledge and assumptions.
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Pay Thickness Effect
0
1
2
3
4
5
0 500 1000 1500 2000
Horiz Length
P I F
NP = 25'
NP = 50 ft
NP = 75'
NP = 100'
NP=150'
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Effect of Kh/Kv
0
1
2
3
4
5
6
0 500 1000 1500 2000
Horiz Length, ft
P I F
kh/kv=1
kh/kv=5
kh/kv=10
kh/kv=25
kh/kv=50
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Horiz vs Frac
0
200
400
600
800
1000
0 500 1000 1500 2000
horizontal length, ft
X f e q u i v
a l e n
t
kh/kv=1
kh/kv=5
kh/kv=10
kh/kv=25
kh/kv=50
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Horizontal Uses?
Consider them any time a well is designed. Particularly good for:
Coning control, Extending reach, Increasing reservoir contact, Lowering drawdown per unit area, As a platform for multiple fracture stimulation In some water injector projects.