North Slope Borough, Alaska

Horizontal wells only: 481 of the 538 wells in these cohorts. Average daily production per well, drawn against the cohort’s cumulative production per well on a log rate scale, for wells grouped by when they first produced. Includes every well of the cohort that is old enough at each month. Wells that are shut in or have stopped producing count as zero, so the average reflects the full cohort, not just survivors. Rates are calendar-day (volume ÷ days in month). The cumulative axis accumulates those same monthly averages at the average month length. Months not yet fully reported are excluded. The 2010-2014 curve draws those years as one group. The chart opens on average daily rate against months on production; the view control switches to rate against cumulative production per well (the log-rate form described above) or to cumulative production per well against months. Every view draws the same cohorts from the same production history. Each cohort with a dashed curve is solid through the last month all of its wells sit inside fully reported data. Past it the dashed curve carries the same wells forward, on our forecast where a well’s own record ends, for up to five years. A dashed curve runs as far as at least nine in ten of its wells are accounted for. A cohort with no dashed curve is drawn only through the months where at least 30% of its wells are old enough for the month to be fully reported. A well that is old enough but shut in still counts, as zero. The measured months are what these wells reported. In the forward months each well counts its own reported figure for each month it has one, our forecast for each month it has only that, and zero for the rest. The forward average counts every well of the cohort. The drawn forecast runs up to five years past the measured months. Line thickness tracks how many wells each curve is drawn from.