Hello:
I have a 2D hydraulic fracturing model, where the fracture is located in the middle of the porous elastic reservoir. At the middle of the fracture, there is one node where the fluid is being injected. The fluid is going into the fracture in the positive and negative x-directions. The meshed model picture is attached.
I have also attached the inp file of my model.
I have three steps in my model.
Step1: Geostatic
Step2: Soils (where I inject the fluid)
Step3: Soild (where I inject the fluid at the same flowrate, but with proppants)
However, for now, in step 3, I am not injecting proppants, only the fluid. Therefore, all the results are just being propagated from step 2 to step 3. Therefore, there should be no “bumps” to pore pressure changes or flowrate. I have attached pictures of the pore pressure and flowrate at the injection node with time.
Somehow, when step 3 starts, the model starts acting abnormally! There is sudden decrease in pressure. The fracture width goes down at the beginning of step 3. The flowrate goes exponentially up at the beginning of step 3. I have no idea what is it that is causing all of this! In step 2, everything makes sense. In step 3, everything goes wild!
The inp file is attached, along with the pictures! Could one of you please tell me why this is happening?
Thank you.
Have you checked the pressure distribution by the end of Step 2 in the 2D grid? is it normal?
also check the pressure distribution during Step 3 and try to find any abnormality behaviour.
If you inject fluid in the fracture, the pressure should increase in the fracture first then pressure increment propagate toward the adjacent matrix cells. otherwise there is problem in the model properties. also check how the fracture is connected to your 2D model.
Hello Faisal:
Thanks for the reply!
I checked the pore pressure distribution. In my model, since there is no leakoff from fracture to reservoir, the pore pressure inside the reservoir stays the same throughout step 2 and step 3.
However, I suspect about the amplitude I am utilizing along with the keyword *cflow.
I am still not sure how amplitude works, after reading the documentation. When I use step time, and type the following:
*Amplitude, name=Amp-1, time=TOTAL TIME
0.,0.,50.,-1.
*Cflow, amplitude=Amp-1
inlet_Node, , 3.0e-07
Does this mean that between 0s to 50s, the flowrate will linearly increase from 0 m3/s to 3.0e-7 m3/s?
If I make this into "time=STEP TIME", how will it differ from total time?
Can I just directly type like this for the amplitude for the flowrate function?
*Amplitude, name=Amp-1, time=TOTAL TIME
0.,0.,50.,-3.0e-7
This will indicate that I want to, for the first 50 seconds, gradually and linearly increase the flowrate from 0 m3/s to 3.0e-7 m3/s.
I am still a little confused about the amplitude function. If you could help me with this, that would be great. I think my problem might be related to this amplitude of the flowrate, and this is affecting the pore pressure, gap flow volume rate, and fracture width opening variables for my model.
Thank you once again!