7/29/2019 1 - Well Clean Up

http://slidepdf.com/reader/full/1-well-clean-up 1/12

1

SShheellll EP LEP LeeaarrnniinnggCopyright2001 SIEP B.V

Well Clean Up

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Why clean up the well?

z Solids initially suspended in the completion fluid will settle undergravity end up sitting in top of any barriers in the well - top packer can effect function of moving equipment such as sliding sleeves, safety

valves, dynamic seal assemblies etc.

z Solids can prevent the release of anchor latches and retrievablepackers

z During completion operations solids in the completion fluid cancause problems solids on top of wireline plug could prevent recovery Plug flow paths Obstruct seal bores

7/29/2019 1 - Well Clean Up

http://slidepdf.com/reader/full/1-well-clean-up 2/12

2

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Elements of hole clean up

zRemoval of solids

zMud displacement

zChemical clean up of Oil Based Muds

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Removal of Solids

zRemoval of all drilling solids, prior to mud displacementand chemical clean-up, important for two reasons : removal of drilling solids from a deviated wellbore better

performed with drilling fluid.

base fluid and clean-up chemicals will not remove solid debrisfrom the wellbore.

z Efficient hole cleaning is directly dependent on theability of mud to suspend the drill cuttings and carrythem to the surface.

7/29/2019 1 - Well Clean Up

http://slidepdf.com/reader/full/1-well-clean-up 3/12

3

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Factors effecting solids removal

z Annular velocity.

z Hole inclination because of its effect on cuttings beds.

z Mud rheology.

z Sweeps.

z Pipe rotation and reciprocation to counteract settling tendency.

z Wellboregeometry.

z Particle size, shape and density.

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Significance of hole inclination

An equilibrium thickness is reached where the rate of bed formation is equal tothe rate of bed erosion. As the flow rate is increased, the bedis de-stabilisedand more cuttings are forced into the flow stream.

50-90 deg

At low flow rates the bed thickness increases with hole angle, reaching amaximum at hole angles within this range.Critical range of hole angles where hole cleaning is more difficult due to thegravity forces causing the cuttings beds to slide downwards against the flow.With no flow rate the cuttings beds tend to avalanche down the wellbore, which

can result in packing off around drill strings.

40-50 deg

cuttings move towards the low side of the annulus resulting in the formation of a cuttings bed.

>10 deg

Similar to that in a vertical wells - no tendency for cuttings to form a bed.0-10 deg

Transport MechanismHole Inclination

7/29/2019 1 - Well Clean Up

http://slidepdf.com/reader/full/1-well-clean-up 4/12

4

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Sweeps

z Use of high-viscosity sweeps to improve cuttings removal is

common practice. Hi-vis pills most effective in vertical and low angle wells can be effective in high angle wells if cuttings moved into flow stream need to be disturbed by rotation / reciprocation whilst the hi-vis pill is

passing

z Turbulent (lov Vis) sweeps can help if flow rate is high andvolume of the sweep is large  Turbulence can erode existing cuttings beds

if the volume of the sweep is insufficient, cuttings only transported shortdistance before settling back to the low side of the hole

problem can sometimes be overcome by tandem pills (turbulent sweepthen viscous pill).

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Pipe Rotation and Reciprocation

z pipe rotation good in high inclination wells: mechanically disturbs cuttings beds, moving solids back into the mud

flow stream for removal. particularly useful in laminar flow, with viscous fluids - particles on the

low side of the hole are moved into the higher flow velocity regions particles can settle and be re-deposited quite quickly if viscosity and gel

strengths are insufficient

7/29/2019 1 - Well Clean Up

http://slidepdf.com/reader/full/1-well-clean-up 5/12

5

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Displacement to Completion Fluid

zMud Conditioning prior to displacement

zUse of Displacement Pills

zCentralisation of drillstring

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Displacement pill s for OBM

Pill will act like a piston and will displace the wholemud out of the hole. It will help remove solids that haveaccumulated on the low side of the hole, particularly atadverse angles.

100-150bbl

100 bblPush Pill

Used to thin the mud and prevent gelled mud fromsticking to the casing wall. Pill should be treated with 1-2 ppb emulsifier to ensure no solids settlement when

mixed with any gelled mud sticking to the casing wall.

50-100 bbl30 bblBase Oil

Comments

High Mud

Weight or 

High

Deviation

Low Mud

Weight &

Low

Deviation

Fluid

• The composition of the push pill should be 3 ppb XC polymer +3 - 5%surfactant in seawater. Aim for YP of approx. 50.

• The displacement flow rate should be such that the base oil is in turbulent

flow and the push pill is in laminar flow.

7/29/2019 1 - Well Clean Up

http://slidepdf.com/reader/full/1-well-clean-up 6/12

6

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Pipe Stand Off 

z Without centralisation stand-off of most sizes of drillpipe, in adeviated hole section, is below 50%

z Pipe stand-off has impact on: flow rate required to initiate fluid movement critical flow rate for turbulence upper limit of laminar flow in order to avoid by-passing fluid.

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Chemical and Mechanical Clean Up

z Aim is to displace oil based drilling fluid from the wellbore leaving the casing‘water wet’, before displacing the well to the completion fluid (inhibitedseawater or brine).

z At end of drilling process, well is usually left full of oily mud

z Mud generally consists of an oily base fluid with water, clay (for viscosity) andbarite / dolomite (for density)

z Emulsifiers - oil wetting agents - in oil phase ensure all surfaces (tubulars,barite, formation) are oil wet, any water is encapsulated as microscopicdroplets.

z When displacing the well to water, not only does the oily mud requiredisplacing, but also the casing surfaces need to be changed from oil wet towater wet.

7/29/2019 1 - Well Clean Up

http://slidepdf.com/reader/full/1-well-clean-up 7/12

7

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Removal of Oil

z Water alone will not remove oily mud.

z oily mud is best removed by pumping: solvents, to dissolve any oily residues; surfactants (surface active agents), to change the casing surface from oil

wet to water wet, i.e. counteracting the emulsifiers in the oily mud.

z Chemical pills ideally pumped at maximum pump rate togenerate turbulent flow.

z reasonably long contact times for each pill is required – often asmuch as 10 minutes

z The well is then displaced to inhibited freshwater, seawater orbrine, depending on the completion requirements.

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Surfactants

7/29/2019 1 - Well Clean Up

http://slidepdf.com/reader/full/1-well-clean-up 8/12

8

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Mechanical Tools

zMechanical tool strings aide chemicals during theclean-up process

z generally of a scraper, a brush or a combination of both

zHistorically used conventional drilling equipment

zMore recently, purpose designed equipment on market

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Mechanical Clean-Up Tools

360 deg Scraper

WellborePatroller

7/29/2019 1 - Well Clean Up

http://slidepdf.com/reader/full/1-well-clean-up 9/12

9

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

How Clean is the Well?

z Success of the well clean-up operation generally assessed by measuring thepercent solids content of fluids returning from the well

z  Turbidity meters sometimes used as secondary confirmation of havingachieved a clean well

z Neither measurement gives an accurate measure of how clean the well isdown hole – they merely measure the cleanliness of the water returning atsurface

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Solids Centrifuge

7/29/2019 1 - Well Clean Up

http://slidepdf.com/reader/full/1-well-clean-up 10/12

10

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Filtration

z Usual technique to remove suspended solids from brines andcompletion fluids.

z Filtration technology changed considerably from the 1980's

z increased awareness of the importance of both the content andsize distribution of suspended solids in workover and completionfluids led to the introduction of more sophisticated filtrationequipment.

z In preparation for brine filtration it is of paramount importancethat all-surface and subsurface equipment (tanks, lines, pumpsand downhole tubulars) are scrupulously cleaned to preventbrine contamination.

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Filtration Systems

7/29/2019 1 - Well Clean Up

http://slidepdf.com/reader/full/1-well-clean-up 11/12

11

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Filter Cartr idges

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

DE Filtration Unit

7/29/2019 1 - Well Clean Up

http://slidepdf.com/reader/full/1-well-clean-up 12/12

   C  o  p  y  r   i  g   h   t   2   0   0   1   S   I   E   P    B .   V

SShheellll EP LEP Leeaarrnniinngg

Filtration considerations