Plugging Wells With Hydrated Bentonite

Brian F. Towler University of WyomingDenver SPE Section, December 17, 2008

Outline

• Introduction• Advantages of Bentonite Plugs• Previous Work• Experimental Procedure• Experimental Results• Conclusions

Permanent abandonment well schematic

Temporary abandonment well schematic

Advantages of Bentonite Plugs

• Heals itself if disturbed• Immune to seismic events,

deformation of casing, salt intrusion etc.

• Workover Rig often not required• Cheaper

Previous Work

• James (1984-96) Wyoming OGC• Wheaton et.al. (1994) Montana BOM• Ogden and Ruff (1989-1992) CSU• Towler and Ehlers (1997)• Englehardt et al. (2001) Chevron• Clark and Salsbury (2003) Chevron• Idaliu et al. (2004) Chevron

Gulf of Mexico History

Annual number of wells permanently and temporarily plugged and abandoned in the

GOM (1947–2006)

Average P&A aggregate cost per well ($1000/well), 2002–2007

Field Trials in California

• Performed in Coalinga, California by Chevron Environmental Management Company in 2001

• Well included primary producers, waterflood producers/injectors, and steamflood producers

• Three generalized abandonment designs

• 19 total wells

Case 1

• No Freshwater• 25 ft plug at

surface• 100 ft plug at

top of perforations or liner top

• 11 wells

Case 2

• Freshwater present

• Cement in annulus covers freshwater

• 100’ bentonite needs to cover freshwater interface, 4 wells

Case 3• Freshwater

present• Cement in

annulus does not cover freshwater

• Cavity shot is required

• Completed in two phases

• 4 wells

Field Results

• All 19 of the plugs met California’s Department of Conservations Division of Oil, Gas and Geothermal Resources (DOGGR) approval

• Hydrating time of bentonite was observed to be affected by water temperature

• Bridging observed with bentonite nodules

Field Trial in Australia

• Barrow Island field, Windalia Reservoir

• Single trial in 2002• Planned to apply it to a 100 well

abandonment program.

Plugging cost comparison (Australia)

Some Problems

• In oil and gas wells with standing water column granulated bentonite can swell and bridge off when it hits the water column, creating a plug at the wrong location.

• Integrity and strength in Saline Water is unproven

• Temperature Effects unproven

Bentonite bars

• We have developed compressed cylindrical bullet shaped bentonite bars as a plugging product, designed to overcome the bridging problem.

• Salinity and Temperature effects being investigated in lab.

DROP DIRECTION

8.25” LENGTH

2.7

5”

8.25” LENGTH

4”

1.2

5” H

OLE

DROP DIRECTION

Characteristics• Material: Sodium Bentonite• Granulation: 5/16-3/8”• Binding Agent- Water Soluble • Forming under high pressure• Length of the Bars: 8.25” (29.55 mm)• Diameter: - 2.75”( 69.8 mm)- No hole; Weight: approx: 2 kg - 3.5” ( ¾” dia. axial hole) - 4.00 ” dia.

- 4.00” ( 1” dia. axial hole); Weight: approx: 3.6 kg. Other options at request

Pressure Containment

• Important question to answer. • What pressure differential can

the bentonite plug withstand?

Theory: Towler and Ehlers (1997)

• Where• H = height of bentonite plug• D = diameter of plug

• Kb = friction factor

• γb = SG of Bentonite

• ρw = density of water

][24 2

HLD

H

D

HLKP bww

bwwb

Hence Plot

D

H

D

HLVersusHLP bw

wbww

224][

Towler and Ehlers Results

Towler and Ehlers Results

• Friction Factor, Kb = 0.8

Density of Bentonite

• Brunton (1988): the density of bentonite particles is 2.457 g/cc

• Clark and Salsbury (2003): compressed bentonite nodules as 2.05-2.2 g/cc.

• Englehardt et al. (2001) hydrated bentonite density: 1.75 g/cc.

• Towler and Ehlers (1997) hydrated bentonite1.616 g/cc

Density of Bentonite

• Our Results:• Compressed: 2.31 g/cc• Hydrated: 1.489-1.846 g/cc

(depends on moisture content)

Experimental setup

Diam 6”

PIPE ID

3 BENTONITE PLUGS

Diam 2.75” / 8.25” LONG

Conclusions

• Compressed bentonite bars have shown a friction factor for hydrated bentonite plugs in steel casing of 1.886.

• This compares with previously measured values 0.8 for hydrated bentonite pellets in steel.

Conclusions

• The friction factor is function of the moisture content of the hydrated bentonite contributing to scatter in the friction factor plot.

• Expansion of the bullets (or bars) of 85% to 300% was observed when hydrated.

Conclusions

• The density of the hydrated plugs varied from 1.489 to 1.846 g/cc depending on the moisture content.

• It is expected that these bars will be effective for sealing pressures in the plugging and abandonment of oil and gas wells.