The Barnett Shale just keeps on giving. It’s still very early in development; but, there is another oily horizontal opportunity opening up in the Fort Worth Basin (FWB). The Barnett Shale, the grandfather of all shale plays, might be entering its twilight. However, the Marble Falls formation, lying above the Barnett, may be the hot new play pumping life back into the FWB.
Reservoir rocks of the Barnett- Paleozoic TPS are carbonate and clastic rocks that range in age from Ordovician to Permian. Production from rocks of Ordovician, Mississippian, and Early Pennsylvanian is mostly from carbonate reservoirs, whereas production in the Middle Pennsylvanian through Lower Permian is mostly from clastic reservoirs. The Barnett Shale acts as the source rock for hydrocarbons and the system is somewhat comparable to the Mississippi Lime play of Oklahoma, where the Woodford Shale functions as the source rock to the adjacent carbonate and clastic type reservoirs.
The 1995 USGS National Oil and Gas Assessment of undiscovered, technically recoverable oil and gas identified five conventional plays as well one continuous-type (unconventional) Barnett Shale in the Bend Arch-Fort Worth Province. The cumulative mean undiscovered resource for the conventional plays was 381 MMBO, 103.6 MMBNGL, 479 BCF associated gas, and 1,029 BCF non-associated gas. The main concept here is the opportunity for multiple pay targets around the Bend Arch of North Central Texas.
The Marble Falls has great potential to be a prolific tight oil horizontally fractured play. The rock has poor primary porosity and according to Jim Henry, a consulting geologist in the area, the true Marble Falls of the FWB is an impure calcareous rock that contains a large amount of silica in the form of sponge spicules, quartz sand, and shale. Various sources describe the Marble Falls as having multiple facies of spiculitic siltstones and black fissile claystones within the formation. However, I don’t want to go into too much detail on specifics of rock characteristics, but rather get a look how oily the Marble Falls is and where the sweet spots are located. Using Drillinginfo and some data pulled from DI Desktop I have created a couple of maps to highlight these properties.
Then just to take a quick look at the unconventional activity and which operators are jumping on this emerging play early, I have provided a map showing horizontal wellbore permits over the past 5 years targeting the Marble Falls Formation. It will be interesting to see if this conventional reservoir will take off and create the same kind of stir seen up in the Mississippi Lime.
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