What Does Oil Initially in Place Mean?
Let me explain what oil initially in place, or OIIP, really means. It's the initial estimate of the total crude oil in a reservoir. You need to understand that OIIP isn't the same as oil reserves—OIIP covers everything potentially there, not just what you can actually pull out. To calculate it, engineers look at the rock's porosity around the oil, the possible water saturation levels, and the net volume of the reservoir rock. They get these numbers from test drills conducted around the site.
Understanding Oil Initially in Place (OIIP)
You might hear oil initially in place referred to simply as oil in place, or OIP. There are a few related terms you should know. Stock tank oil initially in place, STOIIP, is the same calculation but specifies the volume at surface temperature and pressure, not the compressed volume under geological pressure in the reservoir. Original gas in place, OGIP, applies the same to natural gas reservoirs. And hydrocarbons initially in place, HCIIP, is the broad term for estimating either oil or gas in a potential site.
The Importance of Oil Initially in Place (OIIP)
When I talk about why OIIP matters, it's because it's a core factor in figuring out the economics of developing an oil field. OIIP gives you a sense of a reservoir's potential—it's the starting point for any drilling decision. It estimates the total barrels under your leases. If all that oil were recoverable, you'd just drill from the largest to the smallest while controlling costs. But in practice, only part of the OIIP comes out, and the formation's traits affect those costs.
So, analyzing OIIP leads to evaluating how much is recoverable with today's tech. That recoverable estimate helps decide if current prices justify drilling. For instance, if you can only get 50% out, you might classify it as probable reserves and wait. Use the saved capital for a better-producing site instead. But if oil prices rise, that same reservoir could become viable. That's why companies continually reassess their holdings and OIIP against market prices to plan where and when to drill.
