Wednesday, September 14, 2011

Tuscaloosa Marine Shale: Frac Risks - Lithology

One of the known risks with the TMS play is lithological and mineralogical content of the shale for the purpose of hydraulic fracturing.  High calcareous and silica content are desired to provide for rock brittleness.  Of importance when trying to assess the rock properties of the TMS is the transition to the lithological unit known as the Pilot Lime in the deep Tuscaloosa Trend.  This interval, original named the Bain Marker by Chevron in the 70's, is a very calcareous rich zone located in the basal portion of the TMS.  The Pilot Lime is easily recognized on the gamma ray log. 

At Port Hudson Field, the casing shoe is set in this interval prior to drilling through the normally pressured Tuscaloosa sands.  During my Amoco days in the Tuscaloosa, we used a device called a "calcimeter" to measure the calcium carbonate percentage from the cuttings to determine when the Pilot Lime was penetrated.  Very high percentages of calcium carbonate occur in this interval.  A "more marine" environment will likely present better rock properties for hydraulic fracturing.

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