Pump out into wellbore during Pressure/sampling

09 April 2009 Hi colleagues,

At a recent DWOP we facilitated, we got to discussing the operational aspects of pressure measurement / sampling in the tight gas reservoir the client is targetting.

We expect having to pump out into the wellbore until we have clean gas ..

The concern expressed was that, with a water-based mud system, any gas would not go into solution (as it would with a synthetic OBM).. and that the subsequent "bubble" migration would cause well-control problems .. or, at the very least, necessitate a wiper trip before running the liner.

The well is border-line HTHP. It is vertical in about 320m water depth.

Please could members share their experiences in similar situations, especially for us to get a better understanding if our concerns are valid .. and what solutions you implemented.

We are aware of the potential volumetric expansion on gas, of the "bubble migrates" .. and are interested in things like :
.. what is the largest volumes you have pumped into the wellbore .. what was the limiting factor in your case
.. if you didn't know the pressures, and hence the amount of over-balance that you had, then how did you work out how much you could pump into the wellbore ..
.. what else did you have to consider ?
.. what other options did you consider ? (eg cased hole pressure measurement; use of FEWD Formation-Pressure-whilst-drilling tools .. remember this is a very tight gas sand)


Thanks and best wishes

Dave Taylor
MD, Relentless Pursuit of Perfection Ltd

4 Answer(s)

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