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Permalink Reply by Kangoo on May 31, 2013 at 4:50am

Black oil is an industry term for oil with a low GOR. GOR stands for Gas Oil Ratio, meaning black oil has little natural gas dissolved in it (which is the case for 'volatile oil').

The black oil window is the area to the west of the 'volatile oil window', which is to the west of the condensate window and the condensate window is to the west of the dry gas window. The condensate window is currently the most active one because well productivity appears best and product prices are better than in the dry gas window (where well results appear good, but natural gas price is low). An example for a county in the condensate window would be Harrison for example.

 

 

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Permalink Reply by Jack Straw on May 31, 2013 at 5:42am

There are a continuum of hydrocarbons that can be present in the subsurface, depending upon the type of organic material originally present and the burial history of the rocks containing that organic material (the history of temperatures and pressures).

 

The simplest hydrocarbon is Methane (natural gas); which contains only one Carbon atom in each molecule.

Next in complexity come the group of hydrocarbons referred to as Natural Gas liquids; such as Ethane, Propane, Butane (molecules with ever increasing numbers of Carbon atoms in each molecule).

Next comes Condensate; Natural Gasoline.

Next comes Oil.

 

A basic explanation:

When rocks containing organic material are buried, increasing temperatures and pressures first produce biogenic methane (biogenic natural gas).

With increasing temperatures and pressures, Oil is next produced.

With increasing temperatures and pressures, the Oil begins to be broken down (cracked) into smaller molecules (condensates and natural gas liquids).

With increasing temperatures and pressures, thermogenic methane (thermogenic Natural Gas) is produced.

When temperatures and pressures reach a certain point, nothing but thermogenic Natural Gas exists.

An end point is when the temperatures and pressures reach a point where all the hydrocarbons are “overcooked” and only the element Carbon is present; all hydrocarbons have been destroyed.

 

Now getting to your question:

 

All depending upon burial history:

In particular rocks in the subsurface you can find only:

Natural Gas (and natural gas alone); this is referred to as Dry Gas – and the physical area where this is the case is referred to as the Dry Gas Window.

In particular rocks in the subsurface you can find a combination of Dry Gas and Natural Gas Liquids; this is referred to as Wet Gas – and the area where this is the case is referred to as the Wet Gas Window.

In particular rocks in the subsurface you can find a combination of Dry Gas and Natural Gas Liquids and Oil –the area where this is the case is referred to as the Oil Window or (Black Oil Window).

 

In the Marcellus and in the Utica, the “Oil Window” not only contains Oil but also tends to contain significant quantities of Natural Gas Liquids and Natural Gas.

 

Usage of the term Black Oil is not always consistent, it can simply mean Oil.

Or, as Kangoo noted, it can be refer to an Oil that has a relatively small amount of Natural Gas present.

 

In the subsurface, where Oil and Natural Gas are present, pressures are such that the Natural Gas is found in solution within the Oil. As pressures are reduced when this Oil/Gas mixture approaches the surface, the Natural Gas comes out of solution. Also, as a gas, the Natural Gas is highly compressible and expands in volume as the pressures decrease.

 

JS

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