I would like to share experience about washout drill pipe. We observed pressure gradually dropped from 4,100 psi to 3,600 psi (500 psi pressure loss) with same pumping rate 250 GPM. There was no mud weight or mud properties change at that time. Then, we tried to switch to another pump but the same problem still occurred so there must be something wrong down hole or surface.
When we observed pressure loss, we stopped rotating, just only circulating, and figured out where the washout was.
Note: It’s a good practice not to rotate while we are losing pressure because we can snap drill pipe easily due to washout.
At this stage, when we saw the pressure loss, we needed to know where pressure loss occurred.
1. Check surface equipment: Closed IBOP, pressure up surface equipment with mud pump to 3000 psi and held for 5 mins. Everything was OK, no pressure loss. Therefore, there was nothing wrong with surface line and It should be down hole.
2. Check MWD signal: You may not see the change in signal so you need to recycle pump to ensure whether signal was good or not. We found that the signal generated by tool was weaken at the same flow rate of 240 GPM. This indication showed us that washout location was above MWD tool.
We were pretty sure that we had washout drill pipe downhole and we decided to pull out of hole to find washout. This was what we found. Internal washout at pin end of drill pipe resulted in pressure loss.
We laid down washout drill pipes and made up TDS and attempted to circulate with 240 GPM to see if pressure continued dropping. Pressure came back close to where it should be. Everything was OK then we ran back in hole to continue drilling operation. Please remember that if you pull many stands of drill pipe before you see washout when you make up TDS and circulate pressure may not be like what you previously have.
Note: You can calculate depth of washout via this topic, Depth of Washout
If you have any experience regarding this issue, please feel free to share with us.