Pretesting with MDT oriented to high side demonstrates 20x greater permeability compared to low side pretests, proving formation fluid gradient
In an offshore Vietnam well, pressure tests conducted on the low side of the wellbore with XPT were invalid because of low mobility and supercharging.
In deviated wells the weight of the drill pipe is borne on the low side of the wellbore. Suspended cuttings are ground into the pore spaces by the rotating drill-string. Further damage is done as the drill pipe scours the sealing mudcake from the wellbore wall, thereby allowing repeated invasion of drilling fluids on the low side. Sampling from the high side of the wellbore results in faster clean-up due to improved permeability and less filtrate invasion.
On the subsequent run, a 170ft long MDT sampling string was oriented probe-up by Tool Taxis in order to sample from the undamaged high side of the wellbore.
The permeability on the high side of the wellbore was 20x greater than the low side. This allowed the operator to prove hydrocarbon content from pressure gradient alone. On the same run the operator successfully took 12 samples in low permeability reservoirs (~5mD) with an average clean up time of less than an hour.
Further details of this operation can be found in SPE paper SPE-184773-MS.
Petromac wheels orient the probe to the high side resulting in higher pretest success rate and improved permeabilities.
The operator expected the reservoir to be low permeability, which was confirmed by the XPT pressure tests. It was not possible to prove hydrocarbon from gradients in many zones. Permeability indicated that sampling would not be possible on the MDT run.
Petromac Tool Taxis were run on the MDT sampling string to orient the MDT probe up in 12.25” hole. All zones of interest were in-gauge, and as such the large hole kit was not required (hole 13.5”).
The operator obtained high quality pretests which proved the formation fluid gradient and was able to take 12 high quality samples.
Holefinder system facilitates wireline logging in an ‘impossible well’ in Iraq
Near Vertical ‘Impossible Well’ Logged in Iraq
An operator in Iraq was combating major issues with wellbore ledges in a well with only 6 deg deviation. After two wireline runs which were held up at shallow depth, the operator undertook a wiper trip, only to experience similar problems again on the 3rd attempt. The decision was made to run a TLC operation, however this was also unsuccessful.
In all a total of 5 days of rig time had been lost trying to pass a 20” washout with associated ledge.
Frustrated with the lack of results from conventional wireline and TLC, the operator sought the expertise of Petromac to log this critical well. A total of 6 descents were made with Petromac Wireline Express – all seamlessly conveyed to TD.
Without a holefinder, wireline toolstrings are easily held up by ledges and washouts.
Using the Wireline Express holefinder, the toolstring does not loose any momentum as it slides over wellbore obstructions.
In ‘vertical’ wellbores large ledges will persistently holdup toolstrings, even on TLC operations.
Petromac Tool Taxis ensure that the angled holefinder is always oriented upwards, allowing the toolstring to slide seamlessly over ledges.
A well which could not be logged on TLC was subsequently logged using the Petromac holefinder system (6 successful runs in hole).