patrick.net

Old oil and gas fields do get refilled quite frequently. Liquid and gaseous hydrocarbon have lower density than rocks, so they get pushed up due to displacement; it's the same reason why we get out-gassing of methane on Mars, volcano eruptions on earth (due to methane ejection, melted rocks / lava wouldn't explode upward by themselves as they are liquids and solids, not compressible like gas such as methane), methane ice crystals at the bottom of the ocean (accummulated out-gassing from ocean floor) and sometimes massive methane bubbles in the sea that sink ships, as well as the oozing out of petroleum in Pennsylvania and Texas. In parts of Pennsylvania and upstate NY, it was well known that water from private water wells filling the bathtub could often lead to lighting a fire on top of the water due to the dissolved methane coming out of the water as the water temperature rises in the tub (compared to temperature under ground in the water well), long before the shale drilling technology.

The reason why "petroleum reserve" has always been about 30 years since petroleum found industrial use in the 19th century (instead of being pollutant ruining good farm land as they oozed out of ground on their own), is because finding cheap tapping point costs money (capital intensive in the initial geological searching/prospecting process; you wouldn't want to sink millions of dollars into the ground only to find someone else can drill nearby for less than you do and then sell oil/gas cheaper than you can). So when there is about 30yrs of worth of finds waiting to be tapped, the industry slows down / cancels the search/prospecting prrograms. That's why oil drilling / finding equipment companies like Schlumberger are highly cyclical. Due to the refilling process mentioned above, an existing well often produce more than initially estimated volume, so eventually leading to oil price depression, further depressing investment in prospecting . . . which after a few years of course leads to higher prices due to dwindling "reserves." Then as oil prices go up on rumors of "running out of oil!" more money is put into oil prospecting and drilling of new wells. The cycle starts again.

The overall situation is a little like "housing shortage": not because of the world running out of houses or "Peak Houses," but because empty houses unused for long would deteriorate (and builder wouldn't be able to pay interest and tax on empty houses) so houses are only built when there is (expected) sustainable market demand. All the regulations only make the suppliers all the more cautious and less competitive with each other when it comes to new builds.