They had natural unaided flow back, still did until shut in. The...

They had natural unaided flow back, still did until shut in.

The salinity increased, meaning produced water from the formation was starting to return with the frack water. They have not said how much so other considerations such as if permeability jail are in play is hard to judge.

They know there is hydrocarbons there, but none showed after the plug removed.

All signs point to water blocking the pores where the oil would come out of the rock at a molecular level - surface tension, wettability, osmotic pressure and macro head pressure from the well column all combining to mean that the pressure of the drive to push the oil out of the pores cannot overcome the blocking forces. Water acts like a sticky, viscous fluid in very small pore throats.

Because water is polar and oil is nonpolar, their molecules are not attracted to each other, and are not soluble in each other. eg they will block each other if they need to compete for a very narrow flow path.

“Imbibition into gas shale is made possible by the high capillary suction that a fine-grained, water-wet shale matrix can exert on water. As water is wicked into gas shale, the natural gas in the shale is pushed out. The capillary forces that suck the residual treatment water into the gas shale keep it there.”


Image : Lab test of a water drop on oil laden Marcellus shale.

I believe the purpose intended of the current shut in is to allow the water to be wicked in to the shale, taking it off the surface of the pores so the HC can more easily escape.

Disclaimer : I have no professional experience in these matters, only an unrelated engineering degree and Google.