Geology & Pay Zones

As a mineral owner, you own the rights for subsurface minerals at all depths (unless otherwise stipulated in the mineral deed). This is important, because at different depths there are different geological zones, or formations, that may contain valuable resources. If the characteristics of these zones are favorable, multiple wells may be drilled on the same mineral acres in order to exploit hydrocarbon-rich zones at different depths.

Porosity & Permeability

Prior to the shale revolution of the past 15 years, drilling for oil and gas was a much riskier venture. Traditional, vertically drilled wells were not suited for exploiting shale formations, whose low permeability and porosity kept their massive reserves from being accessed. The tightness of the rock prevented the hydrocarbons contained within from escaping to the surface for extraction.

Porosity is a physical characteristic that measures the amount of pore space, or open space, in a rock or substance. Permeability is a physical characteristic that measures the connectivity between these pores. When there is abundant pore space with significant connectivity between those pores, liquid like heated hydrocarbons can flow freely through the rock.

Conventional vs. Unconventional Reservoirs

In conventional reservoirs, hydrocarbons are trapped in a source rock that has high porosity and permeability, like sandstone or limestone. The embedded hydrocarbons migrate upwards as increased heat and pressure below the surface percolate the organic material. Eventually, they are trapped beneath a cap rock. This impermeable layer of rock acts as a container that traps the hydrocarbons in a pocket, or reservoir, underneath.

By contrast, an unconventional reservoir holds hydrocarbons in rock that has low permeability and porosity, like shale. Oil and gas cannot flow freely through the rock, so stimulation must occur to allow these resources to flow. This is where hydraulic fracturing comes into play. During this process, a mixture of sand, water, and chemicals is injected into the shale formation at strategic points to induce fractures, or cracks, in the rock. This fracturing allows oil and gas to escape that would otherwise be impossible to access.

Directional Drilling

In the illustration above, you will notice that the wellbore entering the unconventional reservoir turns at a 90° angle. This is because of a technology called directional drilling. Directional drilling involves drilling vertically downward until a desired zone or formation is reached, then turning the wellbore and drilling horizontally in another direction.

By using directional drilling and hydraulic fracturing to unlock the resources contained in its massive shale basins, the United States became a top producer of oil and gas in a short period of time.

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