Texas Gulf Coast Basin

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Introduction

The Texas Gulf Coast Basin is a very large basin located in south Texas. It stretches along the gulf coast from the border of Texas and Mexico all the way to the border of Texas and Louisiana. Mostly consisting of the land in the Gulf Coastal Plain. This basin has a very large variety of formations due to the amount of land and unique history this area has.

This image shows the location of the Texas Gulf coast basin along the coastline of Texas while showing other basins nearby.

The history of the Texas Gulf Coast Basin is remarkable. The Greta sandstone compositional makeup helps to tell us if there is any trace of oil. The Greta sandstone was found in the Frio formation which is within the Texas Gulf Coast Basin. The Frio formation is one of the major Tertiary Progradational wedges of the Texas gulf coast basin.[1] During the upper cretaceous time period the Eagle Ford shale was thought to be created. The Eagle Ford shale is more brittle and simpler to excite by hydraulic fracturing as a result of the high carbonate concentration and therefore reduced clay percentage. [2]


Primary Geologic Risks and Uncertainties

There is always a risk when looking to acquire new potential drilling sights and operations. Even the slightest miscalculation could set a chain of events leading to the destruction of the area. Due to the basin's location, there are many natural hazards. The first of which would have to be rattlesnakes and other wildlife. Rattlesnakes are very common in the regions of south Texas. Drilling workers must always be aware of where rattlesnakes could be hiding on a working site and how to manage them if they appear due to the presence of more than 10 distinct species in the region. Other animals include bees, scorpions, wild pigs and deer. Deer and wild pigs pose a threat to drivers since they can cause accidents. Drivers must be wary of wildlife on the road ahead when transporting drilling equipment in the early morning or late afternoon.[3]


Petroleum Elements

Source Rock

The size of the basin contributes to the many different types of source rocks within the basin. In one of reservoirs there have been studies to show that during the Cretaceous period, greta sandstone was created which is now layered under the parts of the Texas gulf coast. The Lower Tertiary Wilcox Group's mudstones, claystones, and coal intervals have been recognized as the Greta sand's primary parent rocks. Early Eocene sedimentation and burial of the source rock intervals drove the maturation of these source rocks.The greta sandstone above found in the Frio reservoir. Additionally, it can be shown that the potassium concentrations in the pore fluids from the younger, actively sinking regions of the basin are close to the kaolinite and illite stability field's edge along the coast. The Eagle ford shale is within the boundary of the Texas gulf coast basin and between the Austin Chalk above and the Buda Limestone below, the formation is situated. For both the productive Austin Chalk play and the vast East Texas oil field, it is regarded as the "source rock," or the initial source of hydrocarbons.[2]

Seal and Trap

Structural, stratigraphic, or structural and stratigraphic combinations of traps can be found in the Frio Formation. Combination traps in fluvial, deltaic, barrier-bar, shelf, or strandplain systems with faulted, rollover anticlines and stratigraphic traps are also frequent. Fluvial systems updip from the main growth faults frequently include stratigraphic traps, and shales supply the seals. Where fluvial and splay sands embedded in the more mud-rich floodplain sequences cross anticlinal structures, hydrocarbons are observed to be generated. Faulting and stratigraphic issues generally hamper the production from such massive, low-relief structures. There is also some stratigraphic trapping. [1]

Hydrocarbon Migration

In the Frio formation located in the Texas Gulf Coast basin the migration of hydrocarbons were found to occur when having compacted water move up along the fault planes the temperature will also be declining. Due to the temperature decrease, the hydrocarbons continuously are becoming separated from the solution forming small globules. The movement of the globules would be slowed by the capillary inherent in the fine grained rocks. Before the compacted water can move to fault zones it must traverse the under compacted shale's pore spaces due to the poor drainage caused by the immense amount of high pressure.[1]

Reservoir

Shows the permitted and approved oil wells along the Eagle Ford Shale in 2013

There are many different formations that reside in the Texas Gulf Coast Basin. One of them being the Frio formation. The Frio formation was thought to have been created in the Oligocene epoch due to the chemical makeup researchers have found. The traces of Greta sandstone have been found within the Frio Formation and others as well. Another being the Eagle Ford Shale. The Eagle ford shale is a hydrocarbon-producing deposit that is quite significant. It has the capacity to produce more oil and gas than other conventional shale plays. In south Texas, it has a substantially greater carbonate shale content—upwards of 70%. As it flows to the northwest, it gets shallower and contains more shale.[4] There are multiple reservoir that lie inside the Texas gulf coast basin. One of them being within the Frio formation.The prime source rocks are believed to be taken from the shallower area of the shale. Which is then led to be believed that there would have to be movement of hydrocarbons horizontally and vertically.[1]


Engineering Aspects

Shows the basic Eagle Ford type log used

Rosetta Resources has a lease from the Gates Ranch lease. Rosetta has has drilled about 62 horizontal Eagle Ford wells on the ranch. That being only over a small period of land within the Basin. Due to the compositional make up of the eagle ford shale, it was found that the most efficient drill was the horizontal eagle ford well.[5]


Potential Petroleum Projection

The field produced over 1.1 billion barrels of oil and condensate and 4.8 trillion cubic feet of natural gas up until December 2014. Around 1.3 million barrels of oil and condensate and 4.9 billion cubic feet of natural gas were produced on a daily average in 2014. It is also expected to have as long as thirty years of its life left. Eagle Ford wells cost between 6.5 and 12 million dollars to complete and drill. It is found that those wells will be profitable in as little as 3 years.[6] From my research if you want to maximize the portfolio I believe that you would wish to operate around or near the eagle ford shale due to its immense and enormous growth in recent history. Over time it may reach its life expectancy but that means you would have to capitalize very soon. If you were to wait too long then the chance of maximizing profit and extraction, you may be too late.[7]


References

 Buursink, M.L., Doolan, C.A., Enomoto, C.B., Craddock, W.H., Coleman, J.L., Jr., Brownfield, M.E., Gaswirth, S.B., Klett, T.R., Le, P.A., Leathers-Miller, H.M., Marra, K.R., Mercier, T.J., Pearson, O.N., Pitman, J.K., Schenk, C.J., Tennyson, M.E., Whidden, K.J., and Woodall, C.A., 2018, Assessment of undiscovered conventional oil and gas resources in the downdip Paleogene formations, U.S. Gulf Coast, 2017: U.S. Geological Survey Fact Sheet 2018–3019

Kincade, Sean C.. “The Occurrence of the Greta Sandstone, Frio Formation (Late Oligocene), Texas Gulf Coastal Plain.” (2018).

External Links

[7]https://pubs.geoscienceworld.org/books/book/2138/chapter-abstract/116629682/The-Eagle-Ford-Shale-Field-in-the-Gulf-Coast-Basin?redirectedFrom=fulltext

[8]https://www.bizjournals.com/sanantonio/news/2019/12/17/south-texas-drilling-permit-roundup-corpus-driller.html

[9]https://www.shaleexperts.com/plays/eagle-ford-shale/Overview

[10]https://pubs.usgs.gov/of/2013/1257/pdf/of2013-1257.pdf

[2]https://www.universalroyaltyco.com/resources/history-eagle-ford-shale/#:~:text=The%20Eagle%20Ford%20Shale%20is,as%20high%20as%2070%20percent.

[5]https://www.oilandgaslawyerblog.com/drilling-in-the-eagle-ford-sha/

[1]txu-oclc-9267250.pdf (155.0Mb)

[3]https://www.talonlpe.com/blog/natural-hazards-present-during-environmental-drilling-projects-in-texas

[6]https://www.aei.org/carpe-diem/texas-and-eagle-ford-shale-oil-facts/#:~:text=Eagle%20Ford%20wells%20now%20cost,in%20three%20years%20on%20average.