Page 453 - KAPPA - Ecrin v4.30 tutorials

Ecrin v4.30 - Doc v4.30.01 - © KAPPA 1988-2013 Rubis Guided Session #7 • RubGS07 - 7/19
We need now to initialize the fluid column: click on the initial state button , the initial state
definition dialog will appear:
Fig. D01.3 • Initial state definition dialog
In this multiphase context we will specify the depth of the Gas-Oil Contact (GOC) as well as a
‘Reference Initial Pressure’ at a ‘Reference Depth’ in the initial fluid column. In this case we
want to initialize the fluid as a saturated gas cap overlying a condensate zone: to achieve so,
specify a reference initial pressure of 1300 psia at a reference depth of 6100 ft, and set also
the GOC at the same 6100 ft depth. Click on ‘OK’ to validate the initial state setup.
A few more explanations may be useful at this stage to precise what we actually did in this
quick initialization input: if a GOC is defined with its reference pressure point, Rubis will derive
the mixture composition of the corresponding fluid such that the gas-cap and the underlying oil
are in equilibrium at the contact. From the GOC input, phase compositions are adjusted to
ensure thermodynamic equilibrium in the initial fluid column:
- If the saturation pressure is not specified in the ‘Saturation pressure’ tab the
saturation pressure is considered constant below the GOC while the fluid is
considered at saturation in the gas cap. This result in a constant composition in the
oil zone and in a varying one in the saturated gas cap. Figure D01.4 (left pane)
illustrates the corresponding pressure profiles in a column in a general three phase
context – this situation corresponds to the input we just made.
- If the saturation profile is defined in the ‘Saturation pressure’ tab, the compositions
are adjusted in consequence and the saturation pressure is ‘forced’ at the GOC. If
the prescribed saturation pressure is larger than the reference pressure at the GOC,
it is lowered to the reference pressure and recomputed downward by adjusting the
oil composition. The resulting oil zone will hence be saturated and its composition
computed with an iterative process in the column. Figure D01.4 (right pane)
illustrates the corresponding pressure profiles in that case.