CO2 Enthalpy using ECO2N

[Alison]

We've had a few questions recently about how to deteremine the correct Enthalpy for CO2 using the ECO2N module. I thought I would past the following explanation that Karsten recently sent me:

The best way to obtain CO2 enthalpies is by means of a brief TOUGH2/ ECO2N simulation run. Specify a few grid blocks without any connections between them, assign the desired temperature and pressure conditions to them (with X3=1 to obtain single-phase gas), and perform a run with a single infinitesimal time step, 1.e-9 s, say.

(Compare sample problem *rtab* for ECO2N.) Specify MOP(5)=9 to obtain a full printout of all thermophysical properties. Specific enthalpy will be printed as secondary parameter #5 (see Fig. 3 of TOUGH2 manual).

I suppose your client wants the enthalpy in order to specify CO2 injection. There is a much simpler and better way to specify CO2 injection at prescribed temperature, that does not require worrying about enthalpy. Namely, assign the desired temperature to the injection grid block, and make heat capacity in that grid block "overwhelmingly large," by assigning rock grain density to something like 1.e40 (define a special domain with such density, and attach the injection block to that domain). Then you can leave the enthalpy specification blank for injection (effectively using injection enthalpy zero); the huge heat capacity of the injection block will ensure that all CO2 leaving that block will have the proper temperature.

[Charlie Thornton]

I ran ECO2N with 1 cell at P=4.0e7 and T=30 (based on ECO2N example problem 1) and got the following secondary parameter data:

SECONDARY PARAMETERS

ELEMENT *a   1* ... MASS FRACTIONS: salt in two-component system water-salt is0.000000E+00;		   CO2 in fluid is0.100000E+01
0.100000E+01 0.100000E+01 0.164334E-04 0.898545E+02 0.769940E+06 0.000000E+00 0.000000E+00 0.000000E+00 0.100000E+01 0.000000E+00
0.000000E+00 0.100000E+01 0.000000E+00 0.400000E+07 -.100000E+08 0.960314E+00 0.000000E+00 0.396862E-01 0.000000E+00 0.000000E+00
0.100000E+01 0.215757E+04 0.259849E+05 0.000000E+00 0.000000E+00 0.100000E+01 0.000000E+00 0.300000E+02 0.400000E+07

Here was the input file:

*rtab* ... initialization test for ECO2N (modified for enthalpy demonstration)
ROCKS----1----*----2----*----3----*----4----*----5----*----6----*----7----*----8
SANDS	2  2600.e00	   .35  100.e-15  100.e-15  100.e-15	  2.51	  920.
  4.5e-10
7		   .457	   .30		1.	   .05
7		   .457	   .00	5.1e-5	  1.e7	  .999

MULTI----1----*----2----*----3----*----4----*----5----*----6----*----7----*----8
3	4	3	6
START----1----*----2----*----3----*----4----*----5----*----6----*----7----*----8
----*----1 MOP: 123456789*123456789*1234 ---*----5----*----6----*----7----*----8
PARAM----1----*----2----*----3----*----4----*----5----*----6----*----7----*----8
  1   1	   110 0900000000  4	3
					   -1.
 1.e-9
 1.E-5	 1.E00										
		   60.e5				 0.0				0.01				20.0
SELEC....2....3....4....5....6....7....8....9...10...11...12...13...14...15...16
1											0	0	0	0	0	0	0
	.8		.8
ELEME----1----*----2----*----3----*----4----*----5----*----6----*----7----*----8
a   1	0	1SANDS		1.

CONNE----1----*----2----*----3----*----4----*----5----*----6----*----7----*----8

INCON----1----*----2----*----3----*----4----*----5----*----6----*----7----*----8
a   1
		  40.0e5				 0.0				 1.0				 30.

GENER----1----*----2----*----3----*----4----*----5----*----6----*----7----*----8

ENDCY----1----*----2----*----3----*----4----*----5----*----6----*----7----*----8

I believe that puts the enthalpy at: 0.769940E+06.

We've always kicked around the idea of having more tables and the like in PetraSim - I think this question backs that idea up pretty strongly.

- Charlie