Small changes – big fix

Introduction

A well has been successfully drilled to TD, but the first attempt to run liner failed @ 3359 m MD.

Customer requested to investigate and find out the immediate and root causes of failed run and propose the solution. We have evaluated T&D model precisely based on digital data from surface sensors. After determine the mechanism of liner stuck, we noticed some misinterpretations in preliminary model created by Drilling Contractor.

For instance, it was assumed and confirmed later that rig hookload sensor readings must have been corrected for its internal bias (when you observe enormously different FF on pick-up and slack-off with no good reason to expect this). It resulted in building too optimistic drag model, which didn’t highlight the risk of insufficient weight delivery to the shoe to overcome the ledge.

Customer challenge

To deliver success of the next attempt client reasonably decided to change few inputs in the lack of time and resources. During the mind storm session, we proposed better BHA design by rearranging HWDP and adding 500 m DP 4.5”, replace tubing 2-7/8” with 2-3/8” to reduce weight of liner, which should reduce friction forces too.

Case Study Results

Several small changes were applied to the second liner run attempt. We will not lie if claim that the total cost of those changes for Client were insignificant.

What has been done:

• Placing 500 m 4.5” DP on top of liner and all available at rig site HWDP 4” and 3.5” to push bucking limits further
• Tubing changed for a lighter one to reduce side and friction forces
• 100 rigid centralizers used instead of bow-springs to eliminate any running forces through tight spots

Liner was successfully set @ planned depth.

Customer Value

Now Client understands the root cause of the first attempt failed rather than blaming well-known geology factor.

He also knows that he has enough resources to improve the liner running process by optimizing BHA and centralization design.

It is still a question to discuss the tubing size as hole cleaning suffers with smaller 2-3/8”.

It becomes clear that increasing the horizontal length, so desired by Client Geology Department, will require more specific technological approach.