MODULE 16-horizontal drilling v1 Flashcards
what percentage of wells drilled are horizontal?
80%
what’s a main reason for horizontal well failure?
poor reasoning and planning
what tool has increased in drilling horizontal wells since the 70’s?
MWD
List the improvements that have made horizontonal drilling feasible?
- Mud motors
- MWD tools
- LWD tools
- Geosteering system
- Downhole Data transmission systems
- top drive drilling rig systems
How has technology improved horizontonal well drilling?
- reducing rig time
- improving directional control
- reducing risk of stuck pipe
Horizontal well applications- list 6
- Thin pay zones
- Naturally fractured reservoirs
- Heavy oil
- Gas reservoirs with low perm(enhance draining), high perm (reduce turbulence)
- gas storage schemes to enhance productivity
- EOR schemes including “water floods, miscible floods and oil sandwiches”
Benefits attributable to horizontal wells?
- Productivity (increased direct contact, linear drainage, reduced pressure gradient at the well bore)
- Development (reduced number of wells/max drainage, penetration of natural fractions, specialized product shemes)
- Heterogeneous reservoirs (can affect flow patterns)
types of heterogeneous reservoirs?
- channel point bars (alternating permeable and non permeable sands)
- braided stream deposits (areas of high perm conglomerates or sands with areas of low perm ss)
What’s preferable for horizontal drilling, thin or thick pay zones and why?
think because when fracturing, it will only target a certain depth
when is the productivity of a horizontal well significantly reduced?
when the vertical perm is less than the horizontal perm
what are some typical ranges of lateral lengths in the WCSB? (most common)
800m, 1000m-1300m, 2500m
What are 5 steps to do prior to planning a horizontal well?
- HC thickness
- IOIP
- Production mechanism(res drive pressure)
- Fracture intensity and directions
- surrounding well history
- Geological characteristics
what is the most immediate concern in hz well planning?
directional control
what is the expected cost ratio if hz wells to vert wells?
2.5 times. This will reduce rapidly and by the 3 or 4th well, you can see costs less than twice.
what percentage of production needs to be achieved to make it economical?
50 %more than a vertical well
what are the 4 well profiles?
long
medium
short
ultra-short
What are 6 ways to determine a well profile choice?
- casing program
- target entry point
- ability to move to surface location
- min build up rate restrictions\
- KOP restriction
- Pay zone thickness
what are the preferable well profiles?
long or medium
Ultra short BUR
45-90/.3m
Short BUR
5-10/m
Medium BUR
8-30/30m
Long BUR
1-6/30m
what determined the build angle in a hz well?
- Torque
- Drag
- Ability to transfer weight on bit
- Hole size
- Hole cleaning ability
how far apart should multilateral KOP’s be?
20-30m
BUR equation
180/(pi*r) *30
RADIUS equation
(30*180/pi)/BUR
steps required for well profile design?
KOP
BUR
Tangent section
TVD uncertainty
what is the greatest single cause of casing wear?
drill string rotation
applications for a long radius profile?
- Intersecting a reservoir displaced from the surface location
Advantages of a long radius profile?
- uses conv drilling equip
- Gives the op ability to rotate BHA
- Develops less torque and dra
- drills longer HZ section
- allows for conventional cores/logging
- Can be cased and completed.
Disadvantages of a long radius profile?
- Greater wall contact, higher true and drag and increased risk of differential sticking
- require top drive use
- needs bigger mud pumps
Medium radius well applications
intersects reservoir where long displacement from surface is not required
Advantages medium well profile
- conventional drilling equipment
- reduced wall contact and decreases torque and drag
- decreases well costs
- Increases hydraulic efficiency
Disadvantages medium well profile
Inability to rotate BHA during build
disallows some completion and logging techniques
Increases bit and motor stress
Restricts some bit type
advantages of short profile
- more precise placement of the HZ section
- Less expensive and drilled from existing well
- Less risk because KOP is below the fluid contacts
Disadvantages of short profile
- needs customized drilling equipment
- no MWD logging, no control over azimuth
- short hz section
- open hole completion only
- no logging or coring services
Benefits of multilateral drilling?
reduced well costs improve economics higher production increased recoverable reserves additional fracture development heavy oil development reduced environment impact
TAML?
technical advancement of multi-laterals
Muti-lateral well classification- Level 1?
Open/Unsupported Junction
Mother bore lateral or slotted liner hung off in either bore
most common
used in medium to short build
Multi-lateral classification- Level 2?
Mother bore cased and cemented: Lateral open hole
pack off slotted liner inside the formation
mother bore cased to below lateral kick off point
Multi-lateral classification- Level 3?
mother well bore is cased and cemented and the lateral drilled as per a level 2 multilateral- is also cased and the casing ties back to the mother well bore with some form of liner hanger.
Multi-lateral classification- Level 4?
Mother-bore & Lateral Cased and Cemented
Both bore cemented at the junction
Multi-Lateral classification- Level 5?
Pressure integrity at the junction
cement not acceptable, packer and tubing used
Multi-lateral classification-Level 6?
Pressure integrity at the Junction
cement not acceptable, achieved with casing
Multi-lateral classification- Level 6s?
Downhole splitter
Large main well bore with 2 smaller lateral bores of equal size
what 2 multi-lateral classification are the preferred systems?
level 3 and level 6
considerations for drilling multi lateral?
- connecting to discrete reservoirs
- to encounter maximum number of natural fractures
- restricting drainage to a particular horizon
- alleviate coning
- reducing problems caused by sands
List the application of multi laterals?
Multiple targets Limited size targets Drainage pattern improvement Heavy Oil production Completion by layer Handle Reservoir Geology Limit water or gas production Injectivity
how much NPT does stuck pipe account for?
50%
What are the most common problems to occur downhole?
fluid related
formation related
key activities associated with stuck pipe prevention
selecting BHA
Drilling
Tripping
when to change your BHA in regards to stuck pipe
Optimize jar placement
Accurately gauge worn bits and stabilizers
Efficient Hole cleaning is impacted by a combination of
mud type
flow rate
solids control
Differential Sticking causes, required action to minimize it happening
High potential to occur
High Risks if happened
Recovery Possible
Geo-pressured formation
Exploration wells
Predominately shale / clay formations
Recognition is essential
Difficult to tell if it is happening when there is high pressure and low volume of gas
Unconsolidated zones
Low potential when: In drilling program fully prepared adherence to procedures Recovery is possible
Key seat sticking
High potential
Requires alertness and skillful drillers
Ream out when detected
Reactive formation
Shallow depths
alleviated by inhibition
recovery cumbersome and costs potential high
Drill string vibration
not a mechanism but a catalyst
makes fragile but stable formations become unstable
fractured / faulted formations
formation is brittle
aggravation by: losses and dril string vibration
early recognition allows recovery potential to be high
mobile formation
usually salt, sometimes shales
tectonically stressed
recognition and preventive measures essential
hole cleaning
in conduction with thole instability, is the main cause of stuck pipe around the world
borehole geometry
difficult to recognize
deep wells, high risks
difficult to recover
often in combination with other mechanisms
cement related
poor cementations
long ratholes
does NOT normally result in permanently stuck pipe
under gauged hole / junk in hole
unnecessary: negligence mis-preparation pushing luck recovery can be difficult and costly requires alertness and skillful drillers
factors contributing to differential sticking
excessive hydrostatic pressure opposite a permeable zone
high filtration rate
high mud solid content
large drill collars in relation to hole size
length of a shut down time opposite a permeable formation
early warning signs of differential sticking
increased torque and increased drag
causes of differential sticking
drilling through depleted reservoirs
formation pressure increases with depth more than the mud hydrostatic pressure and the mud weight is increased too dramatically - exceeding formation pressure
fluid related problems
differential sticking - caused by pressure differential from the well bore to a permeable formation. minimize risk by reducing mud density and monitoring filter cake. Pulling free is unlikely. Reducing mud density and friction is a solution.
Formations problems
include salt sections, lost circulation and sloughing shales which can be handled with the use of good mud additives
describe differential sticking
differential pressures of hydrostatic vs. formation is great and causes the pipe to embed into the filter cake and adds to the problems of release
minimum annular velocity is determined by?
the cuttings slip velocity
when velocity of the fluid(vf) = slip fluid
minimum annular velocity
is Slip velocity independent of fluid velocity?
YES!!
stoke’s law assumptions
assumes perfect sphere
no turbulence
Major effects affecting hole cleaning
annular fluid velocity
inclination
drilling fluid density
drill string rotation
minimum rate in most problematic inclination to continue carrying of the cuttings and reduce bed setting
150 fpm
