High side pretesting provides 20x greater permeabilities in Vietnam

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-184773-MS.