In Saudi Arabia water is used to boost oil pressure and recoverable oil.  What is the advantage of using Nitrogen?  The results seem impressive.  According to Fig. 1, production increased by some 800,000 b/day.
Cantarell Nitrogen Injection Project (pdf)
The above considerations, along with other technical and economical studies led Pemex to conclude that pressure maintenance by nitrogen injection was required to maximize the economic value of Cantarell fields. Among gas injection technologies, nitrogen was selected by considering availability, cost, handling infrastructure, environmental, safety, and reservoir issues.

Nitrogen?  The results seem impressive.

What I though was impressive was how the Nitrogen used represented a large %age of total Nitrogen gas produced.

2-3 years ago a web page was claiming %40 (or was it 60%) of production was used.