Hi, everyone
I try to use negative discharge at flowknots to simulate production well behavior in geothermal study. I notice that there are weird effective minimum principal stress distribution at production points so I do the simple simulation like below.
Model (with one joint as fracture):
Here is only neagative dishcharge rate (as production, -10 ton/hour) at center and no injection. There is positive stress (tension) near production points compared to initial condition. Greater stresses occur at distances from the production point.The larger eff. min. principal stresses are more likely caused by reduced pore pressure.
Initial stress:
End 30 days simulation:
My question is about why there is tensile stress occurs near production points and how to explain it ?
I assume you have matrix flow on in this example. If you look at the displacements, you see inward movement, suggesting compression. However the stiff fluid is exiting the system so the stresses become more tensile. You can explore this further by running a fluid-only analysis. You will see no displacements, but the stress still becomes more tensile (assuming you have a non-zero fluid bulk modulus).
Hi, @jhazzard. Thanks for your reply. You’re right! I have matrix flow in this simulation.
If I don’t want the tensile to happen in simulation, what can I do? In reality, I believe that tensile failure due to production is nearly impossible. Is the only solution to turn off matrix flow or reduce production discharge rate?
The way to solve this is to take more mechanical steps per fluid step. Then the mechanical compression will more accurately balance the change in stress due to the fluid pressure change.
OR, make the fluid modulus lower, but then you will get a less accurate transient response for the fluid flow.
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Thanks a lot for your kind support! I will try these methods in my simulation.
