The Strait of Hormuz – the narrow waterway through which between 20% and 25% of the world’s seaborne oil normally passes – has been been effectively closed for just over two months.

As tensions have escalated, Iran has restricted passage through the Strait, while the US has imposed a naval blockade on Iranian shipping, sharply limiting Tehran’s ability to export crude. On May 3, the US president Donald Trump announced Project Freedom, by which US warships would escort vessels from countries not involved in the conflict through the Strait. But some reports have suggested that Iran has since fired on several ships attempting to transit and the waterway remains effectively closed.

The immediate consequences are tankers stranded, prices surging, and Iran rapidly running out of places to store its oil. Analysts now warn that storage could fill within weeks, forcing producers to shut wells altogether.

But the deeper story lies far below the surface. Oil wells are not designed to be switched off and on at will. And when they are, the damage can linger long after the crisis has passed.

To understand why, it helps to ditch the idea of oil fields as underground lakes. In reality, oil sits trapped inside microscopic pores in rock, typically a hundredth of a millimeter wide, held there by pressure, temperature, and a delicate balance between oil, gas and water.

Shutting them down, especially abruptly and for long periods, can alter their internal balance in ways that are difficult, sometimes impossible, to reverse. Production works because the system is in motion. When a well is open, pressure differences drive oil toward the wellbore (a drilled channel connecting the........

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