What is Reservoir Pressure?

Mary McMahon
Mary McMahon

Reservoir pressure is a measurement of the pressure inside an oil and gas deposit. This changes over time in response to geologic processes, as well as human activities like drilling into the reservoir to extract resources. When people provide measurements, they usually include information about the timing of the data collection, as this can be important to understanding the meaning of the measurement. For example, initial reservoir pressure indicates the measurement taken before people began exploiting the resources in the deposit.

An offshore oil platform. When people drill into reservoirs, the natural pressure may push the oil up into the rig.
An offshore oil platform. When people drill into reservoirs, the natural pressure may push the oil up into the rig.

Reservoirs, rather than taking the form of a large bubble under the earth, are usually found in deposits of highly porous or broken rock underground. The pressure inside can vary between pores and cracks, and people usually take a series of measurements so they can come up with a meaningful average. They may also graph the reservoir pressure across an area to show locations of high and low pressure, as this information may be useful when preparing for drilling.

Sometimes, pressure is so high, and a deposit is so close to the surface, that petroleum products bubble up without any outside assistance, forming deposits on the earth's crust. When people drill into reservoirs, the natural pressure may push oil and gas up into the drilling rig, allowing people to extract it more easily. Pockets of very high pressure can become dangerous, as they may create explosions or other safety hazards for workers at the site.

As people pull oil and gas out of a reservoir, the pressure will drop. When the well is closed, reservoir pressure can slowly build back up again. Personnel on site may make note of high and low recordings, as well as measuring pressure after resource extraction ends, to determine how much the pressure fluctuates once they stop drilling. This can be important for people monitoring the health of closed drilling sites, as they want to be sure to catch pressure buildups early so they can address them.

People can use a variety of tools to determine reservoir pressure. Computer systems handle many of the calculations necessary so people no longer need to do the math by hand. Pressure information is useful for everything from fitting equipment properly to estimating how much yield a reservoir may provide. Typically a geological survey team will conduct pressure measurements while collecting other basic data about a prospective drilling site so companies can decide whether they want to move forward with setting up operations.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments

@MrMoody - I remember watching the news coverage about one of the worst oil spills in the Gulf of Mexico a few years back. They were working feverishly to reduce the flow of oil as it was coming out of the pressure tank.

They tried something called “top kill” and other methods which eventually staunched the flow of oil. While I am glad that they solved the problem, I can’t imagine how much wildlife had to die in the process until they figured out a solution. The whole thing was a shame and total embarrassment in my opinion.


@Mammmood - The U.S. Geological survey is always looking for new places to drill for oil. They have advanced computerized equipment that can give precise measurements of the amount of oil pressure and also how much oil can conceivably be retrieved.

Political will is another story. Personally I believe that there are many places in the United States where we have massive oil deposits, but politicians have prohibited exploration of these sites for environmental reasons. I think we can honor environmental concerns and continue to tap the rich store of oil reserves we have in the United States.


@nony - That’s a nice dream. I am afraid those things rarely happen. They do make for good movies though.

Most oil that is explored is scouted out beforehand, using advanced surveying techniques. I have heard of private lands being used for drilling, like in the case of natural gas, but in those cases they have to measure the existing reservoir pressure below the surface before they start drilling.

I don’t think that the “bubble up” scenarios happen too often. In my opinion if pressure were that strong, it might actually be dangerous, like a volcanic explosion. Controlled release of the reservoir fluid is ideal.


My dream is to have an oil gusher in my backyard, just like in the movie “The Beverly Hillbillies.” The oil reservoir pressure will bubble up so strong that oil will gush forth to the surface of my backyard, and the next thing that you know, “black gold” and “Texas tea” will be all over my well manicured lawn.

At that point I won’t care about my lawn’s manicure – I’ll be singing all the way to the bank. The oil company will pay me a handsome some of money, probably in the millions of dollars, for rights to purchase my property outright and set up a drilling spot right in my location.

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