There have been numerous reports in recent times, of oil and gas fields not running out at the expected time, but instead showing a higher content of hydrocarbons after they had already produced more than the initially estimated amount. This has been seen in the Middle East, in the deep gas wells of Oklahoma, on the Gulf of Mexico coast, and in other places. It is this apparent refilling during production that has been responsible for the series of gross underestimate of reserves that have been published time and again, the most memorable being the one in the early seventies that firmly predicted the end of oil and gas globally by 1987, a prediction which produced an energy crisis and with that a huge shift in the wealth of nations. Refilling is an item of the greatest economic significance, and also a key to understanding what the sources of all this petroleum had been. It is also of practical engineering importance, since we may be able to exercise some control over the refilling process

Of course we all understand the concept of “re-pressurising oil fields” using gas injection and other means.

As the oil or natural gas in a formation is produced, the hydrocarbons remaining in the reservoir may become trapped because the pressure in the formation has lessened, making production either slow dramatically or stop altogether.

…gas injection is used on a well to enhance waning pressure within the formation. Systematically spread throughout the field, gas-injection wells are used to inject gas and effectively sweep the formation for remaining petroleum, boosting production…. gas injection can serve as an economical way to dispose of uneconomical gas production on an oil reservoir. While in the past, low levels of natural gas that were produced from oil fields were flared or burned off, that practice is discouraged in some countries and against the law in others.

…Gas Injection, Gas Lift & Gas Miscible Process

Although the terms are sometimes interchanged, gas injection and gas lift are two separate processes that are used to increase production. While gas injection is a secondary production method, gas lift is a type of artificial lift.

Artificial lift is another way to increase production from a well by increasing pressure within the reservoir. The main types of artificial lift include gas lift and pumping systems, such as beam pumps, hydraulic pumps and electric submersible pumps.

While gas injection is achieved by injecting gas through its own injection well, gas lift occurs through the production wells. In gas lift, compressed gas is injected down the casing tubing annulus of a production well, entering the well at numerous entry points called gas-lift valves. As the gas enters the tubing at these different stages, it forms bubbles, lightens the fluids and lowers the pressure, thus increasing the production rate of the well.

Furthermore, a type of EOR employed on a well in the tertiary production process, a gas miscible process can be used to increase production. The difference in this recovery method is that the gases introduced into the reservoir are not naturally occurring. In a gas miscible process, carbon dioxide, nitrogen and LPG are injected into the reservoir. 

Most of the oil in existing wells remains underground, waiting for people to become smart enough to retrieve it. Better enhanced oil recovery techniques will inevitably be developed to extract more and more of the residual hydrocarbon – until it is no longer economical to do so. Then the remaining oil will wait for further developments.

Thomas Gold argues that oil wells are charged and re-charged with new oil & gas from below. He claimed that most new hydrocarbons are generated deep in the crust, rising into geological traps at several different depths for particular parts of the crust. That is the abiogenic theory of hydrocarbon production, which is supported by astronomical data and by lab data simulating conditions in the deep crust and upper mantle.

Rapid charging of oil fields – such as is suggested here – would require deeper secondary reservoirs under pressure, feeding into the primary reservoirs as they are depleted.

There is another way in which oil & gas fields are re-charged – via the biogenic production of oil & gas. But biogenic production via geologic heat and pressure is generally a much slower method of re-charging than Gold’s abiogenic method. But it inevitably occurs all the same. Biogenic oil is a renewable resource, but it is renewable on a different time scale than humans generally use.

And yet, there is a way in which biogenic oil can “rapidly” recharge a depleted oil field. In the case of multiple communicating oil reservoirs at different depths, heat, and pressure, a deeper biogenic reservoir could re-fill a more superficial reservoir at variable rates, depending upon a number of factors. Oil & gas migrate upwardly, when given the opportunity. In this case, instead of “turtles all the way down,” it is “oil & gas reservoirs all the way down.”

Biogenic Oil Formation

This illustrates the conventional idea of biogenic formation of oil. Imagine it taking place over and over again, during the 3 billion + years that photosynthetic life has been converting CO2 into various biological carbon polymers, layer stacked upon layer etc etc … . .\

Abiogenic Hydrocarbons Forming in the Mantle

This illustrates the likely abiogenic formation of hydrocarbons in the upper mantle. These hydrocarbons then can migrate upward into the crust, and become trapped under impermeable minerals. Abiogenic hydrocarbons almost certainly mix with biogenic hydrocarbons.

Abiogenic hydrocarbons are also modified in various ways by deep crust microbial populations. In other words, the predominately short-chain abiogenic hydrocarbons from the mantle can be converted to longer chain hydrocarbons on the way up.

Finally, there is the ocean crustal tectonic activity which feeds a constant supply of partially processed organic material to the deep crust and mantle via constant subduction of ocean crust beneath continental crust. This is a slow but steady pipeline which supplies feedstock for production of oil & gas on a constant basis. The Earth’s huge gas hydrate resource likely owes a great deal to this tectonic process.