The Oil Drum

You asked why they are injecting 40% more water than they they are producing oil.

There are several possible reasons, but the most likely is what is known as Oil Formation Volume Factor (FVF for short, mathematical symbol capital B subscript little O). Basically, oil takes up more space in the reservoir than it does on the surface. The main reason for this is that oil in the reservoir contains large amounts of dissolved gas - possibly 1000 or 2000 cubic feet of gas per barrel of oil (say up to 300 cubic metres of gas per cubic metre of oil).

The gas molecules are small and fit in between the oil molecules, but oil with gas in solution is less dense and the oil simply takes up more space. Add to that the fact that the oil is up to 100 degrees Kelvin hotter at depth, so bigger, and then take off a little volume to allow for the high pressure downstairs, and you end up with Bo = 1.4; so for every barrel of oil you produce at surface you need to inject 1.4 barrels to replace what you are taking out.

1.4 is a very typical oil FVF - it can vary from 1.15 or so up to maybe 1.6 or 1.7, depending on a number of factors, principally the quantity of dissolved gas.

It is good reservoir management practice to inject one barrel of something for every barrel you produce. Here Aramco are producing oil, so they are balancing reservoir-conditions production by injecting 40% more water than they are producing oil at surface. I don't know what they are doing with the gas - they may be injecting it as well, in which case they are either over-injecting (and increasing reservoir pressure), or maybe compensating for an FVF of more than the 1.4 I mentioned.

When water starts to come through, the rate of water injection may be required to balance oil PLUS water production, so injection may have to increase further. Some of that extra 40% might be replacing that smll amount of water that they're getting already.

I don't know much about the history of Ghawar, so I don't know whether Haradh is far enough below initial pressure to need repressuring. So maybe they're overinjecting deliberately. Or maybe they've sized the WI plant extra big just in case of early water production, and they're taking advantage of it to overinject. With something that size you'd have to overinject like crazy before you did any harm.

4% is an acceptable inital watercut for an infill well, which this isn't, really. Probably means the water isn't quite where they thought it was. IIRC Ghawar is mainly reservoired in the Arab D Limestone, so a bit of water might easily cause scaling. It will be interesting to see if those expensive branched wells really make any difference to oil recovery in the long run.

My son does not work as an oilfield geologists
or in production of oil in any way. He is in
training, or more correctly testing, of Saudi
operators and electronic maintenance. He
primarily in the northern part of the country
but he often gets sent to other fields to
qualify operators. He is part of the
"Saudiaziation of Aramco" that they have been
trying to do for the last 25 years. As you
probably know Saudi hopes to replace all
Western workers with Saudis. But my son seems
to think this will be impossible because of
Wasta. He says people never get promoted
because of their ability to perform but Wasta
rules everything. Those who get promoted have
Wasta and they get promoted even if they cannot
do squat. Those who do not have Wasta never get
anywhere regardless of how qualified they are.
http://www.freenewmexican.com/news/10507.html

I had to work with him to get him even
interestedin peak oil. But I gave him my copy
of "Twilight in the Desert" and now he asks
questions everywhere he goes. (He said when he
finished the book that seven other people were
already in line to read it.) At any rate the
next time he posts me anything concerning Saudi
oil I will post it.