Bacteria Damage

• Sulfate Reducing Bacteria

– corrosion

– H2S evolution

• Polymer destruction

• Bacterial colony removal

Bacterial Types and Basic Problems

• Aerobic - lives only w/ oxygen • Anerobic - lives w/o oxygen • Facultative - w/ or w/o, but always has a

preferential environment for faster growth • Problems Caused

– Consumes and degrades polymer – Causes formation damage and corrosion – SRBs may sour reservoir – Corrosion, often severe, generated under colonies

on the pipe wall.

Bacterial Populations

• Planktonic or Free Floating - easy to kill, not that plentiful – Simple treatment with batch biocide is usually

adequate.

• Sessile (attached colonies) – 100,000 x free floating populations, – very difficult to kill, – live in densely matted layers – protected by slime layer (glycocalic mass) – highly accelerated corrosion underneath the layer

because of low pH from bacterial waste.

Bacterial Sources

• Some small populations dormant in reservoir? Probably.

• drinking water < 1000 cells/cc

• sea water - high populations of SRBs, > 1000 cells/cc

• brackish waters - very high populations, >>10,000 cells/cc

• river/pond - moderate to high populations

• concentrated brines - very low concentrations to none in highly concentrated brines. High salinity kills most bacteria (Saturated salt water as a food preservative)

• acids - very low to almost none

Bacterial Corrosion

Bacterial Corrosion on Rods

Source - unknown

Severe Bacterial Corrosion on Tubulars

Bacteria Coating from Gulf of Suez Field

Bacterial deposits on injection tubing. Pitting under the bacterial colony can be severe. Anaerobic

SRB’s - sours the well/reservoir Iron Fixers - slime and sludge Slime Formers - formation damage

Bacteria Attack on Polymer

• The polymer in any fracturing fluid, most viscous kill pills and some water based muds is at risk from bacteria attack.

• Bacteria can degrade and destroy the usefulness of thousands of barrels of fracture fluid in a few hours.

• These fluids must be treated with biocides on a regular basis until used.

Bacterial Control in Injected Liquids

• Bactericides - (same as acid) kills free floating, little effect on sessile colonies.

• Bleaches and Chlorine - (3% to 8%) killd free floating bacteria.

• Chlorine dioxide, very good but consumed rapidly.

• High concentrations of salt in waters and concentrated acids have almost no bacteria.

Bacterial Removal from a Well • Acids - kills free floating, little effect on most sessile (attached) colonies • Bactericides - (same as acid) kills free floating, little effect on sessile colonies • Bleaches and Chlorine - (3% to 8%) like swimming pool shock - strips slime

layer, dissolves cell wall, can’t remove some biomass. Watch corrosion! (There are no long term inhibitors for chlorine on steel and some steels, like stainless – in most sand control screens - are very susceptible to attack by chlorides).

• Bleach, followed by acid - good removal history. – Start with a few barrels of inhibited HCl acid preflush – 5% to 7-1/2% with mutual

solvent. – Follow with a bleach flush (test first on the steel in the well) – Follow with a few barrels of inhibited HCl acid – 5% to 7-1/2% – Flush out of the well and inhibitor treat if needed.

• Chlorine dioxide treatment is very effective and does not require and acid. Also less reactive with many steels..

• Brushes and scrapers – good, but rig required.

Bacterial Removal from a Reservoir

• Deep removal of bacteria from a reservoir is very difficult. Some studies with nitrate materials have shown success.

• Prevention is difficult unless continuous and active bacterial control is maintained at every injection facility and point.