Standard Assessment
The entry-level asset evaluation with Ariane for Oil & Gas corresponds to standard industry practice for prospect assessment. You provide uncertainty distributions for gross rock volume (GRV), reservoir and fluid parameters for the calculation of success volumes of stock tank oil initially in place (STOIIP) and gas initially in place (GIIP). In parallel, you estimate the chance of success (COS) for the asset.
- GRV-depth or Area-depth & thickness;
- Reservoir and fluid parameters;
- Independent COS.
The following fluid parameters to any standard assessment are direct inputs, i.e., a straight result of the assessor’s decision.
- Oil versus gas prospects – in most cases an ON/OFF switch for economic value;
- Column heights – one of the most influencing parameters for in-place volumes (for sure the most uncertain);
- Fluid properties – Gas oil ratio (GOR) and oil density are closely linked but independently described (even though correlated).
This methodology is widely used and accepted, but we believe that it bears severe limitations. Whereas for the GRV and reservoir parameters, many established workflows allow to generate a probabilistic view on the uncertainty variables used in the assessment, the estimation of uncertainty distributions for fluid parameter is much less straight-forward and more subjective. With additional target that issue with additional process-based assessment levels.
Charge & Seal
The process of fill, spill & leak are integrated based on assumptions of charge and seal.
- Charge phase, volumes and properties.
- Seal integrity
- Seal capacity (top and lateral seal)
What you get in addition to a Standard assessment:
- Column heights
- Trap spill and leak volumes;
- Frequency – e.g., out of 10,000 Monte Carlo iterations, how often do I get liquid (mostly oil) versus vapor (mostly gas) versus two phases?
The frequency results can optionally be used as a model-dependent estimation of COS (seal failure due to overpressure exceeding leak-off pressure, fluid type).
PVT
The trap phase and trap fluid parameters (GOR, CGR, densities) are calculated based on trap pressure and temperature conditions and a PVT model. In those calculations, we reason both in oil and gas (components) but also in liquid and vapor (phases).
Also, see how Ariane Charge & Seal assessments compares to basin and petroleum systems modelling workflows.