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Penetration Test Feedback - Jetting vs Drilling&Cementing
10 February 2013

Hi All,

I am looking for some feedback on the effectiveness of penetration tests.

Our normal procedure is to jet the conductor pipe and have contingency equipment to drill and cement should the jetting fail in the first place. This also in wildcat wells.

It is the first time we drill in this area of the block and there are some (limited) offset data from nearby wells, operated by others.

One of the wells has been reported as having had issues in the jetting, thus determining the jetting route for the future wells.

Our shallow hazard report refers to 'harder' layers some 20m below mud line in one location and ±40m BML in the other.


The decision to be made is the following:

  • jetting
  • penetration test to assess whether to go the jetting or the drilling & cementing route
  • drilling and cementing

The penetration test is acting as an intermediate way to avoid investing already in the first place in the money (and in all the risks) of drilling&cementing. We would run a simple 12¼" BHA, keeping parameters constant in order to determine whether the 'harder layers' really are of any concern.

It is obvious that we could not have the same weight, nor the same bit size of the jetting (26" bit sticking out of the jetting shoe), so the parameters would be different. What we would be after are trends and changes in parameters.

Penetration test would be down to the CP shoe and would be drilled on location.

Any thoughts are welcome.



3 answer(s)
Consultant [retired Shell staff]
Total Posts: 240
Join Date: 02/09/05
As I have written before, pilot holr drilling - RISERLESS - would be my first bet.

For cuttings, I would used water well drilling technology i.e. reverse circulation drilling.

For logs, a pilot bit with a removal insert would allow the logging string to go through the now "hollow" drilling assembly, using it as a mini riser from the rig to the mudline.
Drilling Superintendent
Total Posts: 11
Join Date: 22/10/10
Hi Elisa,

I am currently working on the Repsol Angola B22 project - drop me a mail on <see notes below> - would be good to make contact and discuss a few other issues.

Due to the fact our well is a wild-cat exploration and we have no soil data, our current plan is to commit to drill and cement. The data gathered will then be used to make a decision for the 2nd well (a strategy i know which is also used by some other operators). This approach has also been driven by problems encountered on recent wells in Brazil and Cuba where the wellhead slumped (although poor jetting practises could have also contributed to this). We have also heard similar to what you report with regards to hard layers in the top hole - which is obviously not good for jetting.

Our conductor string will be 7 or 8 joints, which based on experience when cemented, is more than enough, even for long heavy 22" strings.

If planning a penetration test, i would begin to start assessing the actual time that will be saved by jetting due to the time required for the penetration test and effect it will have on your dual ops plan (can you get the BHA out and 22" casing to the seabed before the 26" bit is above the seabed - may not be a major issue depending on water depth and expected ROP in the 26" section). Having both options available also has issues - no fixed plan, different tooling, shoe joints etc. Of course if the penetration is not positive, you will actually lose time compared with committing to drill and cement from the get-go.

You mention drilling the penetration test on location - i assume you mean not at the exact well location? This is not advised due the damage you could do to the soils, even if only drilling a smaller 12 1/4" hole. 

In terms of jetted conductor length required for axial load capacity, there are several SPE papers published on this (search paper 77357).

Did Maersk jet on the previous B23 'Azul' well?

Notes from Dave Taylor(moderator): I have connected both Elisa and Gary directly by email, but have deleted his email address from the site to encourage use of the forum.
Deepwater Engineer Red Sea Project
Saudi Aramco
Total Posts: 1
Join Date: 31/12/12
Hello Elisa,
We face the same concerns in our DW project at the red sea, we performed several penetration test in differents zone, however the conclusion was viable to jet next concern was the lenght to be jetted based on the load from next casing + BOP + Riser bouyed that had to be supported by the soil friction; We took sonic measurement in the investigative hole and make a sinthitic UCS curve, in ideal conditions the undisturbed soil capacity is equal to half of UCS value (acummulated) and we apply a safety factor (10-40%), we made a table with joint from Ml to bottom with the corresponding value of soil capacity + SF until we get the same value of the one calculated with all the weight that would be supported by the soil. that point was the maximum lenght we can jet.
hopefully I gave a good explanation. 
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