Lecture 12

Question 1

What are the two main sites in the oil industry where sulfur souring occurs most?

Answer 1

1. Within oil reservoirs, especially during secondary production when seawater is injected
2. In curde oil storage tanks

Question 2

What is the concentration of SO₄^2- in seawater?

Answer 2

25-30 mM

Question 3

What are three things water flooding can cause?

Answer 3

• Introduce nutrients (electron donors/ acceptors, N, P)
• Introduce microbes (SRM)
• Cool the NIWR which may activate SRM endospores and increase microbial activity.

Question 4

What are thermal viability shells?

Answer 4

A means through which the extent of souring in a well can be predicted using a known temperature and pressure.

Question 5

Name two metabolic inhibitors of SRMs and describe how they work.

Answer 5

1. Nitrite - sulfite analog which inhibits dissimilarity sulfite reductase.
2. Molybdate - sulfate analog which is converted by ATP sulfurylase to adenosine phosphomolybdate, the hydrolysis of which depletes ATP reserves.

pg 3

Question 6

Name four biocides of SRM and describe how they work.

Answer 6

1. Glutaraldehyde (Glut) - aldehyde groups cross-link amino acid groups in proteins and nucleic acids.
2. Benzalkonium chloride (BAC) a long alkyl chain solubilizes cytoplasmic membranes to cause cell lysis.
3. Cocodiamine has an even longer alkyl chain than BAC, causing cell lysis.
4. Tetrakis hydroxymethyl phosphonium sulfate (THPS) denatures proteins, damages membranes, interrupt proton flux and ATP generation, inhibits SR.

pg 3

Question 7

What are the three ways nitrate addition reduces souring?

Answer 7

1. Stimulate NRMs which out compete SRMs for organic electron donors such as volatile fatty acids and hydrocarbons.
2. Nitrite is an intermediate in dissimilatory nitrate reduction which inhibits sulfite reductase.
3. Some nitrate reducers will oxidize sulfide which remove H₂S

Question 8

Write out the pathway of dissimilarity nitrate reduction.

Answer 8

pg 2

Question 9

Which is the better electron acceptor, nitrate or sulfate?

Answer 9

Nitrate is a better electron acceptor than nitrate, allowing it to biocompetitively exclude SRMs by NRMs.

Question 10

Can Aromatoleum sp. strain ToN1 biocompetitively exclude Desulfobacula toluolica Tol2 or Desulfococcus biacutus?

Answer 10

It can only biocompetitively exclude Desulfobacula toluolica because both of their key substrates are Toluene. It cannot biocompetitively exclude Desulfococcus biacutus because this SRM’s substrate is Acetone.

Question 11

What do oNRM and soNRM have in common?

Answer 11

1. They both involve the reduction of nitrate.
2. They both involve the depletion of oil organics, though with soRNM this is indirectly.

pg 3

Question 12

What are the denitrification and DNRA nitrate reduction steps? What kinds of microorganisms use these systems?

Answer 12

Denitrification:

• Pseudomonas spp (oNRB)
• Sulfurimonas spp (soNRB)

DNRA:

• Deferribacter spp (oNRB)
• Sulfurospirillum spp (soNRB)

Question 13

To what state can Arcobacter sp. strain FWKOB reduce nitrate to?

Answer 13

Arcobacter sp can only reduce NO₃^- to NO₂^-

Question 14

Which system has more oxidative power, denitrification or DNRA?

Answer 14

DNRA (8 electron transfer) > denitrification (5 electron transfer)

Question 15

What does DNRA stand for?

Answer 15

dissimilatory nitrate reduction to ammonia