Learning Forum

[Faysal Ahammad]

Hi everyone. I want to do oil/gas wellbore integrity analysis. The steps include in the analysis are given below:

Step 1. The model is loaded with horizontal (?? & ?ℎ) and vertical (??) in-situ stresses.

Step 2. The borehole is drilled, and a fluid weight is applied to the rock formation.

Step 3. The casing is added to the borehole with the fluid weight being applied to the inner and outer surfaces of the casing and the borehole.

Step 4. This step represents the completion of the wellbore and has two parts:

a. The cement slurry is pumped into the well. A hydrostatic pressure caused by the cement slurry is applied to the outer surface of the casing and the borehole while the inner casing surface has the fluid weight pressure.

b. Cement hydrates and hardens. The cement elements are added to the model with framework stress, pore pressure, and zero shrinkage assuming the cement is fully bonded to the rock formation and outer casing surface. The hardened cement is inserted with zero deformation but with framework stress in all three principal directions equivalent to the hydrostatic pressure. The fluid weight pressure is still applied to the inner surface of the casing.

Step 5. The wellbore is producing. The fluid weight pressure is removed from the inner surface of the casing and replaced with the production pressure referenced as the “Internal Casing Production Pressure".

 

Can somebody please give me an idea how to deal with it? Do I have to create separate model for each of the step and transfer the data from one step to another? or can I do that using multiple load steps?

 

The final geometry will look like the following:

[Ashish Khemka]

Hi,

 

I may not be able to provide an accurate solution for your requirement but my thinking is that:

For Step 1: You can define initial stress using external data module in a static analysis.

For Step 2: I am not sure how you drill out the borehole? Do you want to change geometry after step 1? If yes then Do step 1, see if you can export deformed model to Explicit analysis and then if you can export deformed model (with material eroded) from explicit analysis to a new static analysis. Apply fluid weight as pressure or force.

If the borehole is already modeled then define second step of multi load step analysis with pressure/ force application to model fluid weight.

For step 3: You can have a part already modeled in step 1 but with no contact activated and activate the same in step 3.

For step 4: Apply all the pressure as you think might be needed.

For step 5: Removed the fluid weight modeled as pressure/ force.

Regards,

Ashish Khemka