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Splitter wellhead & collision risk mitigation
22 August 2018


We are planning to drill adjacent wells within the same conductor pipe with splitter wellhead (2x wells in One CP). The conductor pipe might be angled (with a small angle under 10°).

As per vendor procedure, before drilling the first well (16in) a downhole guide is lowered in the second slot (of the same CP) to reserve the space for the next wells. Those DH guide are similar to big stabilizers with 15.67in OD.

Having the CP inclined imply that the relative position of the DH guide string and the 16in BHA at surface won't probably be the same downhole. The DH guide might lay on the low side or maybe not. This is exactly the uncertainty that increase the risk of  collision when drilling the second well.

Do you have any idea of a process to determine with precision the position of the BHA and the downhole guide relative to each other at the CP shoe depth? pip tag marker in the DH guide string and Azimuthal GR on the Drilling BHA?

The solution is perhaps very different from our proposition. Do you have any other options to solve our question?

Thank you in advance,


Documents uploaded by user:
Downhole guide-BHA position.docx
4 answer(s)
Managing Director
International Consulting & Trading - Europe
Total Posts: 4
Join Date: 09/09/14

Are you aware of the recent publications on improving driller's depth measurement ? There is a method called Driller's Way-point Depth (DwpD) that, depending on the accuracy of the measured parameters, can provide along-hole drill pipe depth to same order of magnitude of accuracy as what open hole wireline can. There have been a couple of papers/presentations at SPE-ISCWSA and SPWLA on this. The methodology is also explained in "Along-hole Depth" ( The important thing is that DwpD also has an ability to provide an associated uncertainty for the measurement made. The key issue in your question is: how accurate do you really need to be ? What amount of along-hole depth uncertainty do you really need in locating the transmitter ? Let me know if you need any help with this.

Harald Bolt
Depth Solutions
General Manager
Total Posts: 15
Join Date: 27/02/16

Hello Mike

Note that I don’t have much experience with splitter WH, but I would suggest what follows, based on experience in some well intercept and re-entries operations.

Your CP being set with 5-8° inclination helps defining relative position of slots in slots with the use of an e-line oriented Camera. Obviously it requires to have your CP full of clear water.

With your DH Guide in place in one slot, RIH an open-ended string with a couple of centralizers down the 2nd slot CP, circulate clear water, then run your e-Camera down the open-ended string. Do not run the e-Camera past the open-ended string, but camera optical nose just out of the re-entry guide. Observe where your open-ended string lies relative to your DH guide.

Your e-Camera optical may be self-orienting to gravity, if not a gravity measuring tool can be coupled to your e-Camera and survey tool Tool Face scribed with a marker on the e-Camera optical.

Based on the relative position observed between your DH guide and Open-Ended String, you will know which direction to high side to nudge your first well not hindering exit of your 2nd well, mitigating your collision risks.

Hope this helps


Deputy Chief engineer
Douson Drilling & production
Total Posts: 1
Join Date: 19/04/19
We are running dummy string in south china sea also, without the downhole splitter. The dummy string is common and mature way in south China sea. see attached. 
Documents uploaded by user:
dummy string.pdf
Drilling Superintendent
Total Posts: 20
Join Date: 31/10/07
in Malaysia we commonly run 2 in 1 system w/o the downhole separator/guide you talked about. What is commonly done here is to run a dummy string (normally flush jnts or skimmed down coupling) run to around the conductor shoe in the spare slot as a separator. The advantage is that it is simpler and also providing the ability to clean the annulus between conductor and the main csng strng to ensure no cement is above the conductor shoe.
This dummy string is later retrieved before drilling in the 2nd slot. As usual you may need a MoU as the separation factor between the wells may not fulfill your required SF. See paper OTC 24908 for further info on systems other than your downhole guide. These are old methods as far as I know not any longer used.
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