What’s the plan if the sidetrack fails?, page-69

"So then the question is - how likely if differential sticking on wireline which will push us to sample on pipe again? If we’re unfortunate to have a zone with high permeability and lower pressure than our main reservoirs then it could very well happen again. If the root cause is mud design and filter cake building up then it’s also possibly still likely."

The factors controlling diff sticking are permeability in the rock and mud weight (and fluid loss).

"I’m just surprised that they seem to be doing so much damage to the tools on pipe. This method is used to log horizontal wells where you’d think scraping along the side of the well would be a lot worse."

On wireline gravity drives the tool down the hole. If you hit a ledge youre never going to have more than weight of tool plus part of cable weight pushing against the ledge. On wireline the winchman will get an early warning that the tool is hanging up by a drop in cable tension. The winchman will also have hi and low limits set on his winch so if weight drops below or goes above set values the winch will automatically shut down if winchman doesnt respond. On drill pipe youve got the weight of the tool PLUS a dirty great drill string pushing down on the tool. If you hit a ledge at speed its like driving a car into a brick wall. You get no warning on the winch tension display.....youre relying on the driller to respond quickly to his Martin Decker weight indicator.

"I’d also be suprised if there wasn’t a contingency plan to complete all sampling on wireline, regardless of whether we experience differential sticking of the cable. So long as the tool itself isn’t getting stuck - why would they not just run in over the cable with the fishing tool to free the cable at the location of differential sticking (not run all the way down to connect to the tool). Then rope up with the wireline to the next station once the cable is free and keep doing this from the bottom up? The sticking is obviously not bad enough to affect things while the wireline cable is moving."

At first glance your plan sounds logical but there are practical reasons why it wouldn't work. The main problem would be repeatedly latching and unlatching the overshot drill string from the tool downhole. There are also other practical reason why this plan either wouldnt work or would entail excessive amounts of time to get to work.

Realistically the options are as follows:

- Go in on wireline.
- If cable showing early signs of sticking then abandon and go to TLC or run liner.
- if cable gets stuck conduct a logging while fishing operation.
- if tool gets stuck. Fish and then run liner.