So how big are these terminal decline rates actually?

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Significantly higher than expected terminal decline rates are seen in the Niobrara, 25 to 35%, resulting in a much faster drop in production. A topic that we’ll be paying some attention to in the coming weeks, also when looking at other basins.

In this particular case, for wells that started production between 2011 and 2015, we see that the decline rate starts to accelerate the production curves downward as lower production levels are reached. That doesn’t bode well for long-term recovery estimates.

The example discussed shows horizontal wells in Weld County that started production since 2012. The only wells selected are those that fell below a production rate of 40 bo/d before November 2015.

 

 

The top graph shows the average flow rate of all the 1,354 horizontal wells that met these criteria, versus time (the number of months after they fell below 40 bo/d).

The graph on the bottom plots the average terminal decline rate of all these wells.

 

Ignoring some of the inherent bias of this selection, we focused on the results up to month 20 or so. You can see that a relatively steady state has been reached after 24 months. Between 24 months, and 36 months, which contains data for all these wells, you will find an average annual decline rate between 25 and 30%.

This seems a very high terminal decline rate, possibly more than is commonly assumed when making ultimate recovery estimates.