Lecture 11

Question 1

Why is “sweet” crude oil preferable?

Answer 1

The lower sulfur content makes it easier and safer to refine, reducing the total cost of production.

Question 2

What percentage of sulfur in crude oil (wt/wt) is the cut off for it to be considered “sour”

Answer 2

> 0.5% Sulfur is considered sour.

Question 3

What are two non-biological mechanisms for reservoirs to have a high sulfur content?

Answer 3

1. Decomposition of sulfur containing compounds under high temperatures
2. Dissolution of pyrite FeS₂

Question 4

At what level of biodegradation are Phenanthrenes and dibenzothiophenes most prominently found? pg 1

Answer 4

Wenger scale: Severe
Peters and Moldowan scale: 6-10

Question 5

What is the main product generated from microbial souring?

Answer 5

H₂S
pg 1

Question 6

Why can the use of sea water injection cause souring?

Answer 6

It is a source of SO₄^2- which can be reduced by microbes into H₂S

Question 7

What are four souring associated problems?

Answer 7

1. Health and safety (H₂S)
2. Lower quality crude
3. Microbial influence corrosion
4. Reservoir plugging by metal sulfide minerals and biomass

Question 8

What are five souring control strategies?

Answer 8

1. Sulfate filtration
2. H₂S stripping
3. biocides
4. nitrite (NO₂^-) inhibition of SRM
5. nitrate (NO₃^-) or nitrite reduction.

pg 2

Question 9

What does PWRI stand for, and what is meant by “the zone of influence”?

Answer 9

PWRI = Produced Water Re-Injection
the zone of influence is the area in the reservoir where the injected water enters. It is here that the water has the highest chemical and biological influence.

Question 10

What are the seven phylum level lineages of SRM?

Answer 10

Deltaproteobacteria, Nitrospirae, Clostridia, Thermodesulfobiaceae, Thermodesulfobacteria, Euryarchaeota, and Crenarchaeota
pg1

Question 11

What is the name of the gene which is used as a marker for sulfur reduction?

Answer 11

dsrAB or dissimilatory sulfite reductase

Question 12

In the reduction of Sulfate to Sulfide how many electrons are transferred due to the action of the dissimilatory sulfite reductase?

Answer 12

6 electrons (SO₃^2- —–> H₂S)

Question 13

Is the reaction pathway of catalyzed by sulfite reductases part of the dissimilative or assimilative sulfate reduction?

Answer 13

Dissimilative sulfate reduction
pg 1

Question 14

Group the seven SRM lineages into mesophiles, thermophiles and hyperthermophiles.

Answer 14

mesophiles: Deltaproteobacteria
thermophiles: G+ Clostridia
hyperthermophiles: Nitrospirae, Thermodesulfobiaceae, Thermodesulfobacteria, Euryarchaeota, and Creanarchaeota.

Question 15

What water temperature supports SRM?

Answer 15

5 - 75 C with the optimal temperature being 30 C

Question 16

How do Clostridia endospores affect reservoir souring?

Answer 16

It is believed that their endospores will survive extremely hot and deep environments but will then germinate upon reservoir cooling where they will begin sulfate reduction

Question 17

Name 4 steps during which sulfate reduction can occur in the anaerobic metabolism of oil organics.

Answer 17

-H₂
- oil organics to acetate
- reduced compounds (lactate) to acetate
- acetate to CO₂

pg 2

Question 18

What does NIWR stand for?

Answer 18

Near Injection Wellbore Region