What is a “well test”?

A well test or a drill stem test (DST) is when a well is control flowed from the deep reservoir to the surface under a predetermined programme of varying rates and pressures. Gas is flowed to surface to ascertain an initial flowing potential of the well, the reservoir begins to slowly lose pressure and the well is then closed or “shut-in”. The reservoir pressure slowly returns to normal as the gas accumulation replenishes what was extracted. This is repeated over a number of different flowing periods and shut-in periods. The flow rates allow a calculation of the deliverability of the wells and the reservoir whilst the changes in pressure allow a calculation of the size and shape of the gas accumulation.