Options for hot water energy recovery 1

[PetroBob]

I've been asked to generate innovative options for recovering energy from hot frac flowback water (on wellpad). Water flowrate is dropping exponentially from initial startup, but flowrate will spike back up again when new wells are brought online. Ie there is huge variability in flow. We don't have many uses for heat on-pad (ie heat integration). There is a need to cool the water.

Can folks suggest some current industry practise options for energy reuse? In this or any other industry.

Technical info as follows:
Initial water temperature: 130C / 266F
Initial water pressure: 125 barg / 1800 psig
Required final water temperature: 60C / 140F
Required final water pressure: atmospheric
Initial water flow rate from 1 well on day 1: 4000 m3/d / 734 gpm
Water flow rate at day 5 from 1 well: 800 m3/d
Total flow from 3 wells on day 11, as 3rd well is brought online: 5000 m3/d

Apologies for the simple question; it's outside my area of expertise so I'd be interested in what solutions to investigate, to avoid re-inventing the wheel.

 

[LittleInch]

First off figure out if you can use the water direct in any turbine or process equipment or do you need to use heat exchangers. For this sort of temperature to generate electricity, which is probably your key potential effect, you need a substance with a lower boiling point than water to cool your water, but create vapour with sufficient pressure to drive a decent sized turbine. It will then need cooling itself to regenerate....

The current practice is to instal a cooler as all this additional kit costs much more than any savingin energy or price you get for the electricity. Unless you needed heat at this temperatures for your process the numbers rarely add up correctly.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[sshep]

This starts out as about 20k pph of atmospheric steam equivalent if you recover the heat by flashing, and 800hp of hydraulic power from the pressure. If you can't use the low level heat (such as to run a adsorptive chilling cycle, or a regenerator tower), there might still be a way to harvest the hydraulic power. The short duration of the good heat and power is working against you, but it is good to see you giving it some thought.

best wishes always,
sshep

 

[turb1]

I know of one application such as you describe using an ORC (organic rankine cycle) to generate power from wellhead water/steam return. The problem with this solution is that at such a low temperature the total efficiency will be very low (5% or so) and therefore the economics are not very good as already mentioned. The prices for these types of applications are coming down, but they also won't meet most typical oilfield specifications either.

A hydro turbine is promising with the pressure you list although I've never seen one in this application. Also if you have steam generation nearby that lets down pipeline natural gas you may be able to use the waste heat as a pre-heat for the natural gas let-down and install a turbine to recover the pressure let down. I have looked at this application for one oil field, the issue there was the location of steam generation which was spread out over the field so the gas was not let down in a single location.