# Reservoir Simulation - Probabilistics

This module enables user to perform probabilistics analysis on one or more variables at once. At least one variable is required to perform this analysis. The number of cases can be changed with minimum of 1 and maximum of 300 cases.

There are four distribution types with different inputs required:

1. Constant: Value
2. Uniform: Minimum and maximum value
3. Triangular: Minimum, peak, and maximum value
4. Normal: Minimum (p90), maximum (p10), mean value and standard deviation

"View Summary" button can be used to see the summary of p90, p50, p10, mean and standard deviation of the variables in numbers. One can also export the summary and/or the simulated results by clicking the "Export" button.

## Definition of P10, P50, P90

First cases are ordered/ranked by cumulative production at end of history.

• Dry gas and wet gas are ranked by cumulative gas production at end of history.
• Black oils, volatile oils, near-critical fluids and gas condensates are ranked by cumulative oil production at end of history.

In the software we have chosen to define p10 case as the 10th percentile best-case scenario. In a similar manner, p90 is the 90th percentile best case and p50 is the average.

Why do we do it like this?

We want the p10 case of gas to match the p10 case of water (and oil when relevant).

If we assumed a normal distribution at every point and used the rates to calculate the standard deviation for every point to define the p10 case in for each plot, then the p10 stems of gas, water and oil would have no physical connection between them. This would not make sense.

However, a normal distribution on every point (or a flowing confidence interval) provides a lot of insight as well. The colored area is meant to visualize this:

• the middle of the dark area is the average,
• edges of the dark area are one standard deviation outside,
• edges of the light-colored area are two standard deviations outside.

What does this mean: if you run a new case with inputs inside the boundaries you have set, there is a ~95% probability that the simulation will exist within the entire colored area (roughly estimated as we do not account for covariances)

Summary: p10, p50 and p90 cases are the same physical simulations in every plot. Colored areas are the 1- and 2-sigmas confidence interval for a new simulation.