Cathryn,
Just a few thoughts. My father worked with the oil industry first cleaning up discharged waste water and then cleaning it for use in repressuring a field by injecting water into an old well. The process was tricky as to much pressure could fracture the rock and the water would migrated away. To little and it was ineffective. Some field experiences minor quakes as the pressure built up over time.
The information at the time felt that as oil was withdrawn, slippage was slowed as contacts were not as lubricated. The fear with repressuring was that the water would again lubricate the contacts and cause slippage. It seemed to be minor.
He found that along our coast with many quakes it was not uncommon to have a well sheared off where it crossed a fault zone. It seems to me that the tremendous pumping of water has more effect on quakes. The central valley in Cal. has sunk some twenty of thirty feet as the aquafiers settle.
My dad did his work in the 60's and 70's and into the 80's but did not see any correlation to large quakes and the pumping of oil.
This is an interesting question and I wonder if some of the big oil companies have any information on their experiences?
Bob in Woodland Hills