Continuous Resources Vs Traditional Resources: Geology
1. Continuous Resources Vs Traditional Resources: Geology
2. Continuous Resources Vs Traditional Resources: Technology Changes
3. Continuous Resources Vs Traditional Resources: Energy Return on Energy Invested
4. What Continuous Resources Mean for North America. (not written yet)
My post regarding a shift in Hubbert’s peak stirred the pot a little and brought up a lot of questions that I think are worth answering. It also allowed me to identify knowledge gaps in people who seem to know their stuff regarding energy.
This post is broken into sections.
Step 1 Define continuous resources.
Step 2 Explain what the technological changes mean.
Step 3 Try to relate the energy return on investment to other energy sources. I found that most people who understand energy think they understand the energy return on fracking and oil sands, but their knowledge is about 3 years out of date.
What are they?
Continuous resources are typically large portions of geologic formations in geologic basins. In cases like the Bakken people have known about the formations for years, but they were not considered for development because they were uneconomic to drill or mine. (This site primarily focuses on drilled resources.)
The USGS website is showing its age in identifying the different types of continuous resources, but here is what they have listed:
- Deep Gas
- Shallow biogenic gas
- Heavy Oil/Natural Bitumen
- Shale Gas and Oil (links to oil shale pages)
- Gas Hydrates (links to gas hydrates pages)
- Coalbed Methane (links to Coalbed Methane pages)
For some reason, their page does not appear to include light oil that occurs as continuous resources. However, if you search for formations like the Bakken and Niobrara, you will see them defined as continuous resources, and both have been evaluated by the USGS as such. I think the lack of defining a section for light oil has seriously misled people regarding EROI on shale oil because they think is all mined or at the very least bitumen. This is not the case in what is actively being developed today.
How are continuous resources different from traditional drilling?
Traditional drilling typically relies on the structure of the rock underground to trap oil and gas. Most commonly one of the following geologic structures is responsible trapping oil and gas:
Anticline, fault system, reef system, salt dome, unconformity, pinchout, meteorite impact
If you would like to see other examples of traditional traps check out these links.
All the systems above rely on buoyancy to move oil and gas into a favorable location for drilling. Over millions of years oil and gas being lighter than water move upward and are trapped under a cap of rock that the hydrocarbons cannot ready flow through. Ideally, the oil moves into a sandstone or a very permeable carbonate which makes the oil easy to get out of the ground, and if you are really lucky the field will even be overpressure so the oil will push its self out of the ground and you will not even need to pump it. (The Ghawar Super Field is probably the best example of an overpressure field) The downfall of a trap is that it traps just about everything that is buoyant so oil in a traditional trap is more likely to be contaminated by fluids or gases that drillers do not what to deal with. Acid gas (H2S) is probably the examples. Continuous resources are less likely to contain hazards impurities.
Why is the oil or gas there?
Continuous resources do not depend on traditional traps for accumulating oil. They are often source rocks
In fact continuous resources are often the source rock for many traditional fields. If not for continuous resources traditional traps would not have any hydrocarbons in them. A few percent of the oil and gas contained in continuous resource leaked out over long periods of time (millions of years) and accumulated in traps. (For reference the Bakken has TOC in the teens)
Although not always the case, most continuous resources that are currently being developed are nearly impermeable to fluid flow of any kind. The oil or gas that is in place is bound to the rock and will not move under normal conditions.
Bound to the rock?
Sort of… Fluid does not flow unless it has a reason. In the case of shale, the rock has porosity (places for oil to pool at a microscopic level), but not much permeability (channels for flow) It takes a lot of head (differential pressure) to make fluids move. (Expanded upon in the next section)
Summary: Spelling out what you should take away from the information above.
Continuous resources cover large geographic areas. (Hundreds of thousands of square miles)
Traditional oil fields cover relatively small areas. (Often just a few square miles and are dependent on geologic structure)
Continuous resources are often the source rock for traditional oil fields, and they do not depend on geologic structure.
Changes in technology how to make continuous resources economic for development.
Advantages and disadvantages of continuous resources.