Replies to This Discussion

Permalink Reply by Billy Jack Rockefeller on March 3, 2011 at 1:51am

Depends on what geologic formation, current depth, permeability and porosity of the rock, etc.  TOC is just a base marker for whether or not a rock can expel gas or oil.  Just remember, usually, the higher the TOC, the more gas or oil a rock can expel.

• ▶ Reply

Permalink Reply by JK Fowler on March 3, 2011 at 3:15am

To answer your question more directly, "prospective" (apparently and economically producible) gas shale TOC (total organic carbon or total organic content, terms that are usually considered synonymous) should ideally be over 2%, with 5% about the max that will be encountered in a typical gas shale.  The presence of TOC often dictates the porosity of the shale, as most of the shale's porosity is contained within the microscopic pore space of the organic matter itself.  The depth of the formation doesn't really determine TOC content nor does permeability.  TOC is solely determined by the amount of organic matter that is deposited with the original grains that make up the mud in a basin; this mud is later converted by heat and the weight of overburden into shale.   TOC will become a mixture of free carbon and kerogen under the heat and pressure encountered in the shale formation.  Depending on the length of time the kerogen is "cooked", it will first generate oil, then condensate, and then gas. 

• ▶ Reply