For 8 months, the client’s drilling operation had been at a standstill due to a difficult sidetrack that was required on an 8200mMD deep horizontal well. The client needed a window to be milled on the horizontal well that had a non-standard 8 ⅝” casing with an inclination of 89°. Difficult geological formations of the horizontal wellbore presented many risks due to its challenging trajectory.
Job Profile
During drilling there were partial circulation losses at 5905mMD. The LWT recorded up to 5918mMD, which was in correlation to the surface samples obtained, however it did not verify entry into the reservoir, and this is the reason why the geologists continued to drill. At a depth of 6063mMD total losses occurred.
Once the annular space reached a pressure of 240psi, the well had to be shutdown. This was a result of bad cementing on the 8 5/8” casing. When they increased the density of the mud from 1.05g/cm3 to 1.60g/cm3 a circulation loss was detected. The client was able to successfully remove the MWD equipment and rerun a controlled BHA up to 6020mMD.
The well was out of control because an equilibrium could not be achieved. This was due to density increases, which resulted in a return loss when the gas diminished. After reviewing the LWT and electrical logging, the reservoir entrance was confirmed to be from 5860mMD, which put the client 203m inside the reservoir. This explained the circulation losses during cementing and confirmed that there was almost no cementing behind the 8 5/8” liner.
The first attempt to remedy the situation was to pump a 10m3 plug with the aim of pressurizing 5m3 area between the formation and the 8 5/8″ casing. This operation left the DP4 tubing trapped inside the 8 5/8″ liner.
Attempts to reopen the well included two failed maneuvers with Back-off Spear + DP5″LH and a Taper Tap LH, which left the pipe stuck again.
Solution
A different approach had to be used for this application because a cement plug was not a viable option in this environment. The PathBreaker™ Hydraulic Whipstock provided a unique inflatable design that allowed the anchor to be set without any need for cementing a plug at 4855mMD.
The hydraulic anchor system had no issue being set in this difficult well and successfully completed the window milling at the desired depth. A positive and negative pressure test was performed to confirm the theory that gas entered through the shoe. A deviating bucket with a hydraulic anchor (PathBreaker™) was lowered to 4849mMD and a window was opened, thus closing the old stage.
Alternative whipstock tools estimated window milling to take 10 hours, but the PathBreaker™ Hydraulic Whipstock was designed for pure efficiency and only took 5 hours. Thanks to years of development and building off of SPT’s extensive whipstock orientation experience, SPT has been able to deliver a superior product for the whipstock industry. Due to its clever hydraulic anchor system with multi-profile expandible design, it was able to sidetrack without cementing a plug, which ended up being paramount in the success of sidetracking this horizontal well.
The PathBreaker™ was oriented using Schlumberger’s MWD system. A custom designed circulation valve was produced and included in the Bottom Hole Assembly (BHA).
Key Notes
- The stage since its inception took approximately 473 days to complete.
- The Stockholm Precision Tools (SPT) PathBreaker™ whipstock intervention took 24 hours to complete
- Drilling 9 5/8″ from 4404mMD to 6063mMD was done with oil-based mud with density 1.53-1.55g / cm3 and it was later extended to 10 1/8″.
- The first severe circulation losses occurred at 5905mMD and subsequently at 5955mMD and 6063mMD.
- The first LWT logging at 5918mMD, did not identify the entrance to the reservoir.
- The cementation of the first section from 6020mMD – 3621mMD was done with total losses, so it was not cemented.
- The first change of oil base mud per water base is made from 1.05 g / cm3 to 3620 mMD before drilling the Tie Back seal.
- The top of the reservoir according to correlation between geophysical records was found at 5860mMD and not at 6040m as the project initially said.
- The TLC record shows the poor cementing of the liner 8 5/8″.
- The pumped cement plug for remediation left the pipe clamped at 5571mMD.
- Operations pending left-hand pipe were stopped on June 7 and resumed after 206 days on December 30, 2018.
Conclusion
SPT and Schlumberger were able to successfully complete this difficult job where others had failed. They saved the client millions of dollars by reopening the well for operation. The PathBreaker™ high-performance tungsten carbide triple mill system allowed for unparalleled speed in sidetracking this well. The client has been able to reopen operation and continue drilling from their previous 8-month hiatus.
