Question

To prevent the souring of crude oil, ________ is added to oil well injection water to encourage ________ instead of ________.

A) oxygen / aerobic respiration / sulfate reduction
B) sulfate / sulfate reduction / fermentation
C) sulfate / sulfate reduction / nitrate reduction
D) nitrate / nitrate reduction / sulfate reduction

Answer 1

The addition of nitrate to injection water in oil fields is a strategy to promote nitrate reduction over sulfate reduction, preventing the souring of crude oil.

Step-by-step explanation:

To prevent the souring of crude oil, nitrate is added to oil well injection water to encourage nitrate reduction instead of sulfate reduction.

The correct answer is D) nitrate / nitrate reduction / sulfate reduction. When oil fields are water-flooded to enhance oil recovery, sulfate from the injection water can serve as an electron acceptor for sulfate-reducing bacteria, leading to the production of hydrogen sulfide, which is a toxic and corrosive compound that causes the souring of crude oil.

Adding nitrate to the injection water promotes the growth of nitrate-reducing bacteria, which outcompete the sulfate-reducing bacteria, thus preventing the generation of hydrogen sulfide.