The "geologic recipe" ultimately defines the spatial distribution of reservoir quality and the success of the play. With hundreds of historical well logs from deep Tuscaloosa sand tests, one can already define the sweet spots and spatial distribution of the rock's characteristics. The drill bit follows and confirms.
The key to the geologic formula is:
PRODELTA = INTERBEDDED SILTSTONES/SHALES = BRITTLE = NATURAL FRACTURES = RESISTIVITY & POROSITY = HYDROCARBON ACCUMULATION = ECONOMIC RESULTS
As the "east vs west" debate raged a couple of years ago, a case was made that the TMS-EAST had too much clay. Yes, the TMS-EAST is downdip of the Tuscaloosa delta. These distal, silty deposits are the key piece to the productivity of this reservoir. Throw in some great organics to the "hydrocarbon kitchen" and you have an attractive play. So delta proximity is a positive. What was overlooked was how important the presence of quartz is with regards to the storage capacity and brittleness of the reservoir. The brittleness in this rock has enabled it to form excellent natural fractures. What was also incorrectly perceived and misunderstood is the change in clay/quartz percent as you transgress up the vertical section in the Tuscaloosa A TST (transgressive systems tract). Historically, the TMS has been "lumped" together as 400-1000' of section typically called the Eutaw Formation. When one focuses on the high TOC reservoir target (75-150'), the geologic details are much different. The basal portion of the TMS has much more silt due to it's lower position in the TST. Resistivity is only one variable. Understanding the spatial and vertical variability in porosity is significant.
Lastly, the vast amount of well control and data confirms that the characteristics of this shale are very consistent. Thinning of high TOC TMS gradually occurs north, south, east, and west. This will result in production consistency and enable the operators to predict reserves with accuracy as the play shifts to development mode.
|Note the natural fractures at both 12572' and 15205'.|