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Tutorial: Injectivity simulations

An injectivity simulation calculates wellhead pressures at different steady-state mass flowrates for a well injection. The result is called an injectivity curve; usually this is used to predict predict the pump pressure required to inject at a given mass flowrate. For more on injectivity simulations see here.

Pumped or free-flowing wells

This tutorial covers pumped injection wells, where for all mass flowrates the fluid has to be pumped into the well, the wellhead pressure is positive and the fluid is liquid throughout the well. Note that a pumped well can become free-flowing at low mass flowrates; you can see this in the injectivity simulation by the wellhead pressure becoming close to zero.

Free-flowing wells can (perhaps only at low mass flowrates) accept fluid without pumping and have a wellhead pressure close to zero, see this tutorial.

Running a TestData injectivity simulation

This TestData injectivity simulation uses the measured injectivity curve Test rate data - 1. Assume CO2 is 5,000 ppm and NaCl is 0 ppm (both in total fluid) at the deepest feedzone.

  1. In the sample database, open a new injectivity simulation for .

  2. Enter these values:

    Note:

    • Select an Injection test type of TestData, then load the measured injectivity curve from the Measured Injectivity Test dropdown list. You can then click the Injection Test Rates tab to see the measured injectivity curve data.

    • Ensure there is a tick under Reservoir pressure so WellSim will calculate this.

  3. Preprocess, run and save the new simulation:

    • WellSim calculates the linear injectivity factor (0.115 barg/t/hr) and the reservoir pressure (207.53 barg).

    • To stop the run, click .

    • If you get the error Solution did not converge see here.

Interpreting an injectivity simulation

  1. Go to measured injectivity curves, tag Test rate data - 1, click Graph, click Apply to 2nd worksheet.

  2. Go to injectivity simulations, tag TestData - from test rate data - 1.

  3. Click MultipleGraph. If necessary, change the graph to:

Red line: Pressure at the deepest feedzone:

Black line: Pressure at the wellhead.

Blue line: The measured injection curve, Test rate data - 1, used for the injectivity simulation.

Running a TopDown injectivity simulation

This uses the TopDown injection simulation Td 110 barg 860 t/hr. Also, assume reservoir pressure is 207 barg (the value calculated by the above injectivity simulation), CO2 is 5,000 ppm and NaCl is 0 ppm (in total fluid) as above.

  1. In the sample database, open a new injectivity simulation for .

  2. Enter these values:

  3. Preprocess, run and save the new simulation.

Note

  1. WellSim calculates the linear injectivity factor, 0.119 bar/t/hr. This is very close to 0.118 bar/t/hr, which is the 'actual' value calculated by the output simulation From better TD 100 t/hr see here.

  2. This is surprising, because the data used for the injection simulation Td 110 barg 860 t/hr is probably not very accurate.

  3. What has happened is that the reservoir pressure we assumed above (207 barg) is also in error compared to the 'actual' value of 200 barg used in the output simulation From better TD 100 t/hr. And the two errors have cancelled each other out.

  4. If you rerun the above injectivity simulation and enter a reservoir pressure of 200 barg then it calculates the linear injectivity factor to be 0.127 bar/t/hr, suitably in error.