please help me with an injection well

[javimalu]

Please I need your help. We have a Disposal Well, for seven years was injected into the well.
I have two question:
1.-how to calculate the current reservoir pressure (after 7 years of injection)
2 .- It may be that the pressure in the reservoir reaches such a high value that will produce the return of water injected into the well?

Thanks a lot!!!

[vinomarky]

You can get an estimate from a falloff plot.
Simply, stop injecting and plot WHP decline with SQRT time - extrapolate like you would a Horner plot
If you well cannot support a full column of fluid then you either need a BHP guage, OR (if you can tolerate less accuracy) take a number of sonalogs down the annulus with time (calculating level of fluid) to infer declining pressure - gives a coarse reading but may get you in the ballpark.

Note: In my experience the results you get from injectors can be difficult to draw definitive conclusions from - Depending upon whether you are in a developed pattern or not and how tight, the late time pressure can sometimes appear to simply asymptote to the injection pressures of surrounding injectors..... you may need to use a leap of faith and use mid-time slope to infer reservoir pressure..... It's certainly worth a look though, and as with most things while the absolute values may be suspect, by taking a number of these readings over time the trend is often more informative.

Good luck

[javimalu]

Thanks buddy! but I had a little problem ... when I stopped the injection, the hydrostatic pressure was less than pressure of the sand, so there was a back flow. Know any case similar to what happened to me?

[vinomarky]

I'm not sure what to say here.... either I'm missing something fundamental, or you are ;-)

Unless the injection well goes on vacuum straight away, you expect the well to have the potential to flow back initially.... the 'trick' is to close a valve on surface to prevent it flowing back, and to have a pressure gauge upstream of this valve to record the falloff.