Do Oil Wells Re-Charge Themselves?

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. _Recharging of Oil & Gas Fields

RigzoneOf course we all understand the concept of "repressurising 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. _Rigzone Gas Injection

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 (here and here for example) 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 FormationThis image 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 image 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.

An Infinite Supply of Hydrocarbons: Coal and Kerogen Beyond the Stars

Relatively complex, carbon-containing molecules are found in comets and on nearby planets, thought to have been made elsewhere in our Solar System.

But a report in Nature suggests even larger molecules may be forged near young stars and flung outwards. _BBC

Wired.uk.co

Researchers at the University of Hong Kong observed stars at different evolutionary phases and found that they are able to produce complex organic compounds and eject them into space, filling the regions between stars. The compounds are so complex that their chemical structures resemble the makeup of coal and petroleum, the study's lead author Sun Kwok, of the University of Hong Kong, said.

..."Coal and kerogen are products of life and it took a long time for them to form," Kwok said. "How do stars make such complicated organics under seemingly unfavorable conditions and [do] it so rapidly?" _CBS

If scientists can detect the signatures of complex hydrocarbons within the clouds of interstellar dust, then it is clear that the quantities of such materials in the universe must be truly immense.

There is reason to believe that a significant amount of hydrocarbon was incorporated into the deep planetary structures of the Earth in the earliest stages of planetary formation. Theorists such as Thomas Gold, and Sergey and Alexey Marakushev have maintained that much of the oil & gas that is produced commercially, came from this pre-biotic hydrocarbon.

Other bodies in our solar system, such as Titan, possess oceans of hydrocarbon -- clearly not of biological origin. In fact, as we are discovering, complex hydrocarbons appear to be ubiquitous wherever one looks in the universe.

The Deep Carbon Observatory of the Carnegie Institution for Science is engaged in the study of the deep Earth carbon cycle, and hopes to learn more about the different forms of carbon which cycle through the deep planet and up into the crust.

The true story of the origin and extent of our world's hydrocarbons has not yet been written -- much less understood. It is far too early for humans to claim to know the limits of their planet's resources.

Deep Earth Hydrocarbons of Abiotic Origin

Scientists at Lawrence Livermore National Laboratory used supercomputers to simulate what would happen to carbon and hydrogen atoms buried 40 to 95 miles beneath the Earth’s crust, where they would be subjected to prodigious pressures and temperatures.

They found at temperatures greater than 2,240 degrees F and pressures 50,000 times greater than those at the Earth’s surface, methane molecules can fuse to form hydrocarbons with multiple carbon atoms. Interactions with metal or carbon sped up the fusion process, the researchers said. These conditions are present about 70 miles down, according to an LLNL news release. _PopSci

PO
A team of scientists and engineers from UC Davis, Lawrence Livermore Labs, and Shell Projects and Technology have created sophisticated simulations which demonstrate that methane can be polymerised to multi-carbon chains under conditions similar to those in the deep crust and mantle of Earth. (Published in PNAS)

...hydrocarbons of purely chemical deep crustal or mantle origin (abiogenic) could occur in some geologic settings, such as rifts or subduction zones said Galli, a senior author on the study.

"Our simulation study shows that methane molecules fuse to form larger hydrocarbon molecules when exposed to the very high temperatures and pressures of the Earth's upper mantle," Galli said. "We don't say that higher hydrocarbons actually occur under the realistic 'dirty' Earth mantle conditions, but we say that the pressures and temperatures alone are right for it to happen.

Galli and colleagues used the Mako computer cluster in Berkeley and computers at Lawrence Livermore to simulate the behavior of carbon and hydrogen atoms at the enormous pressures and temperatures found 40 to 95 miles deep inside the Earth. They used sophisticated techniques based on first principles and the computer software system Qbox, developed at UC Davis.

They found that hydrocarbons with multiple carbon atoms can form from methane, (a molecule with only one carbon and four hydrogen atoms) at temperatures greater than 1,500 K (2,240 degrees Fahrenheit) and pressures 50,000 times those at the Earth's surface (conditions found about 70 miles below the surface). _PO

More information in an earlier AFE posting

Abundant Hydrocarbons Buried Underground: Out of Sight Out of Mind

Oil&GasGeology_via_BitToothEnergy
Bit Tooth Energy blog takes a fascinating look at petroleum creation and deposition at various depth, using the Eagle Ford shale play as an example.

As a rough rule of thumb down to 15,000 ft the hydrocarbon is more likely to be oil, (which is thus referred to as the Oil Window) and below that it is more likely to be gas. That is only a rough rule of thumb, and one must remember that over time there has been a lot of uplifting and eroding, so that 15,000 ft isn’t necessarily what it used to be.

And the Eagle Ford shale is a fairly good example of this. If we use the EIA map of the play you can see that in the North, where the reservoir is about 6,000 ft deep the hydrocarbon is oil, while further South, where the deposit is down at around 14,000 ft then the hydrocarbon is dry gas. And in between it is what is known as a wet gas.

...You may note that the condensate from the wells in the wet gas zone have produced around 2.3 million barrels, while there has only been about 1.6 million barrels of crude produced. It is also worth noting that while the natural gas coming from the formation has been twice the equivalent volume of oil, the market for natural gas, at the moment is still down at around $4.6 per kcf, which using the Apache conversion, would give it a price of around $27.60 a barrel of oil equivalent. On the other hand the condensate is a light high quality product, and West Texas Intermediate crude is running at the moment at around $88.30 a barrel. _BitToothEnergy

The Bit Tooth article above talks about petroleum as coming from 500 million years of algal deposition in sediment, and conversion at depth -- heat and pressure -- to petroleum. The deeper the sediment, the more likely to be converted to gas, according to the source.

Now, if you look at the timelines provided above, you should note that photosynthetic organisms have been converting massive quantities of CO2 into organic carbon for over 3 billion years. The graphic below provides the mirror image of that process -- the production of atmospheric O2 juxtaposed by the evolutionary time of origin for various photosynthetic organisms.

Oxygen is a waste product of photosynthesis, and organic carbon is the main product. Rapid production of oxygen should correspond to a rapid production of organic carbon -- which was then buried in sediments. Whether this organic carbon became coal, kerogen, bitumen, petroleum, or other hydrocarbon resource, would depend upon where it ended up in the Earth's crust, or perhaps, mantle.

Recent science suggests that short chain hydrocarbons in the mantle are capable of surviving for significant periods of time at high pressure and temperature, perhaps later to migrate into the crust. These mantle hydrocarbons may have been subducted into the mantle via oceanic crust, or may be generated abiotically within the mantle itself.

The important thing to understand, is that massive quantities of organic carbons have been buried in the Earth for over 3 billion years. They no doubt exist in a wide variety of forms, from minimally altered to partially transformed to fully transformed, etc. Some of this carbon was no doubt oxidised to CO2 in the mantle and released into the atmosphere for recycling. Some of it no doubt seeped into the biosphere and was metabolised by microbes.

It is highly unlikely that humans have even begun to account for most of this missing organic carbon. Most of it will not be economically recoverable in any form. But we will not actually know that until we look for it, and find it.

Can Hydrocarbons Survive in the Hot, Pressured, Mantle?

The mantle is a dense, hot layer of semisolid rock approximately 2,900 kilometers thick. The mantle, which contains more iron, magnesium and calcium than the crust, is hotter and denser because temperature and pressure inside Earth increase with depth. Because of the firestorm-like temperatures and crushing pressure in Earth’s mantle, molecules behave very differently than they do on the surface. _Source

Earth's hydrocarbons are typically formed when organic matter is trapped in sediments on the bottom of Earth's oceans, seas, lakes, swamps, and bogs. Over a period of time, exposed to varying temperatures, pressures, and anaerobic conditions, the organic matter is transformed into hydrocarbons such as natural gas, peat, coal, and oil of various types.

Sediments trapped in oceanic crust (as opposed to continental crust) are subducted into the Earth's mantle after dozens of millions of years -- and exposed to very high pressures and temperatures. Many geologists had presumed that any hydrocarbons that had not migrated out of these subducted sediments, would be destroyed in the oxidising environment of the mantle. But a variety of research over the past several years suggests that not only can hydrocarbons survive the heat and pressure of the upper mantle -- new short-chain hydrocarbons may actually be created within the mantle.

... conventional geochemists argued that hydrocarbons could not possibly reside in Earthʼs mantle. They reasoned that at the mantleʼs depth—which begins between 7 and 70 kilometers below Earthʼs surface and extends down to 2,850 kilometers deep—hydrocarbons would react with other elements and oxidize into carbon dioxide. (Oil and gas wells are drilled between 5 and 10 kilometers deep.) However, more recent research using advanced high-pressure thermodynamics has shown that the pressure and temperature conditions of the mantle would allow hydrocarbon molecules to form and survive at depths of 100 to 300 kilometers. Because of the mantleʼs vast size, its hydrocarbon reserves could be much larger than those in Earthʼs crust. _PDFLivermoreLabPDF

“The notion that hydrocarbons generated in the mantle migrate into the Earth's crust and contribute to oil-and-gas reservoirs was promoted in Russia and Ukraine many years ago. The synthesis and stability of the compounds studied here as well as heavier hydrocarbons over the full range of conditions within the Earth's mantle now need to be explored. In addition, the extent to which this 'reduced' carbon survives migration into the crust needs to be established (as in, without being oxidized to CO2). These and related questions demonstrate the need for a new experimental and theoretical program to study the fate of carbon in the deep Earth,” the expert adds. _Softpedia

Now for the first time, scientists have found that ethane and heavier hydrocarbons can be synthesized under the pressure-temperature conditions of the upper mantle -the layer of Earth under the crust and on top of the core. The research was conducted by scientists at the Carnegie Institution's Geophysical Laboratory, with colleagues from Russia and Sweden, and is published in the July 26, advanced on-line issue of Nature Geoscience. _Geology.com

So far there is no strong evidence that large quantities of economically important hydrocarbons are being generated within the mantle, with subsequent migration up into the crust -- where humans can access them. But it seems quite likely that new gaseous hydrocarbons do migrate from the mantle into the crust -- in some quantities -- and contribute to gas deposits of various types, including methane clathrates.

What is more interesting to me than the abiotic generation of hydrocarbons is the fate of billion year old hydrocarbons of biological origin which find their way into the upper mantle through geologic upheaval. No doubt some of this hydrocarbon will survive as medium chain alkanes, although I suspect most will end up as methane or ethane. Some will get caught up in volcanic activity and be converted to CO2 -- or get ejected into the atmosphere or ocean as CH4. But what is the proportion of each product? How much will end up in a typical oil & gas "trap" in the crust where they can be economically extracted?

We will learn more about that over time. But between the abiotic gases and the truly ancient hydrocarbons that have survived the eons, it is likely that there is far more hydrocarbon in the deep Earth than geologists typically allow themselves to dream.

More: A rare, optimistic view of energy from the NYTimes