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[Mr.white]

I want to simulate the process of formation water diffusing from one stratum to another and observe the fractionation of 13C. Initially, I used existing data to simulate the gas-water equilibrium process in two strata, and then used the equilibrated solutions to simulate the diffusion. However, I only used two solutions, so why does the simulation result show a solution 0? Or how should I simulate to observe the fractionation of 13C?
SOLUTION 1
    temp      200
    pH        6.471
    pe        3.572
    redox     pe
    units     mol/kgw
    density   1
    C(4)      0.009327
    Ca        0.005786
    Cl        0.3141
    K         0.06401
    Mg        0.01214
    N         0.001229
    Na        0.2533
    S         0.01325
    [13C1]    0.001041
    [C1]      0.001039
    [C2]      0.0008692
    [C3]      0.0003758
    -water    1 # kg
SOLUTION 2
    temp      180
    pH        7.221
    pe        3.266
    redox     pe
    units     mol/kgw
    density   1
    C         0.01929
    Ca        0.06332
    Cl        2.922
    K         0.1089
    Mg        0.1934
    N         0.001061
    Na        1.706
    S         0.3848
    [13C1]    9.924e-006
    [C1]      0.0008876
    [C2]      0.0007525
    [C3]      0.0003254
    -water    1 # kg
TRANSPORT
    -cells                 2
    -time_step             3153600000000 # seconds
    -flow_direction        diffusion_only
    -boundary_conditions   constant closed
    -lengths               2*500
    -print_cells           1
    -punch_cells           1
END

[dlparkhurst]

You need a solution 0 to be the constant concentration boundary. My guess is that solution 1 is replicated to be solution 0, but you should define it explicitlyr.

Normally, you would define solution 0 to be the solution in one formation, and then, most simply, another solution for the cells of the diffusion column. I would use a few more cells, say 5, initially for the column. I would also start with a short column and short time scale to see that the diffusion is occurring as you expect.

As I recall [C1], [C2], and [C3] are 12C methane, ethane, and propane. You would also need 13C versions of each one, including [13C1], which you have included. The SOLUTION_SPECIES definitions for these species should include the diffusion coefficient definitions. The 13C versions would have slightly different diffusion coefficients than the 12C versions. You haven't included this data block, so I cannot repeat your calculation.