User:ColeTrain1009/sandbox

Location


The area that emcompasses the Tuscaloosa Maine Shale takes up approximately 8 million acres. The area stretches from the far western Louisiana border parishes of Beauregard and Vernon through the middle of the state into the southwestern corner of Mississippi and the far east parishes of St. Tammany and Washington.

Geological Setting
The TMS is sandwiched in between the Upper and Lower Tuscaloosa sands. The Tuscaloosa Group is comprised of three units. The lower Tuscaloosa represents a transgressive stage of the depositional cycle and consists of an arenaceous and argillaceous lower unit. The marine shale forms the middle Tuscaloosa unit and represents the inundated phase of the depositional cycle. It is the same age as the Eagle Ford Shale. It has a base depth of -10,500 to -14,000, and a thickness from 230-500 ft. It has a zone of interest that with a high log resistivity of 5 ohms at the base of the shale section. it varies in thickness from 0-325ft over the area and can be found at the shallowest depth of 10,000 ft in the area.

Formation & Contents
The Tuscaloosa Group ranges from Cenomanian to Coniacian in age with the most recent evidence suggesting that the TMS was deposited in the Turonian.

The marine shale unit consists of dark gray, silty, micaceous, fossiliferous, calcareous, laminated clay- stone interbedded with dark gray, silty, micaceous, fossiliferous, glauconitic, calcareous siltstone and very fine-grained sandstone. Late Cenomanian plank- tonic foraminiferal assemblages have been recovered from the marine shale beds immediately overlying the lower Tuscaloosa Formation.

The most likely source rocks for oils in Tuscaloosa sands are the downdip marine Tuscaloosa claystones.

The total organic carbon has the highest values (up to 4.6 wt%) above the boundary between LT and TMS, whereas the upper interval of the Marine Shale is characterized by lower TOC values accompanied by a decrease in resistivity.

The producing section of the TMS averages 1.65 wt% TOC and 48% total clays.

Self-sourced hydrocarbons in the Cenomanian– Turonian shale of the Tuscaloosa Marine Shale include black and volatile oils in the shallower, paleoshelf areas where vitrinite reflectance is less than 1.1 percent Ro and wet gas and condensate in the deeper paleoslope areas where vitrinite reflectance is 1.1 percent Ro to about 1.3 percent Ro.

Potential Troubles & Current Issues
In a resistivity study done by the University of Louisiana-Lafayette, they found that the last unit of the Tuscaloosa Group shows gamma-ray values typical to sandstone facies, an occurrence being a potential concern when hydraulically fracturing the overlying TMS due to their aquiferous character. However, the shale interval above the Tuscaloosa sandstone presenting high gamma-ray values could be a potential frac barrier.

They also found that the mineralogical content varies greatly well to well, with two X-ray diffraction tests at different wells showing substantial differences in calcite concentrations.

A presentation by the The Tuscaloosa Marine Shale Laboratory in 2018 summarized many drilling troubles operators have faced in the past:

Drilling the lower section of the TMS has been troublesome due to an area called the “rubble zone”: large pieces of rock that slough off, difficulty in running centralizers: drag from the centralizers in such unstable wellbore, post-fracture casing deformation: the casing deformation appears to get worse with attempts to perform the cleanout work.