User:Kdurr2/sandbox

Setting
The Little Cedar Creek Oil field lies in Conecuh county in southern Alabama, just south of the Conecuh Ridge complex and about 72 miles north of Pensacola, Florida. The bulk of the formation was deposited during the Oxfordian part of the late Jurassic epoch. The formation is a result of the rifting of the Gulf of Mexico System which was preceded by the breakup of the super-continent Pangaea in the late Triassic. The rifting of the Gulf of Mexico can be summarized by three main events, with the first being the deposition of salt beginning about 160 million years ago. Following that, the Earth's crust began to thin and stretch as seafloor spreading grew about 150 million years ago. About 7 million years later, seafloor spreading dominated the system and salt dome formations began to take shape. There was also a high amount of faulting in the area, especially as you travel towards the middle of the system from the coastline. On the northern part of the basin, you will find a carbonate ramp which a backbone of the Little Cedar Creek oil field. The depositional setting of the field comes down to an up-dip microbial nearshore environment which is pointed towards the northeast. The current total acreage is approximately 20-24 thousand acres, with one drilling unit being 160 acres.

Looking deeper into the Gulf of Mexico basin, there are many graben-horst formations that dominate the cross section. Regarding the Little Cedar Creek Oil Field, there are four main "paleo-highs" which heavily influenced the deposition of the field. The four paleo-highs are: the Choctaw Ridge, Conecuh Ridge, Wiggins Arch, and Baldwin High. In the late paleozoic, during the convergence of the African and North American plates, the Choctaw and Conecuh Ridge complexes formed as products from the Appalachian tectonic events. The other two paleo-highs, the Wiggins Arch and Baldwin High, formed as a result of the rifting process in the Gulf of Mexico.

Structure
The structure of the oil field reflects the carbonate ramp model. This formation is the result of transgression and regression phases which dominated the system before, during, and even after the Oxfordian age. Due to the depositions being parallel to the shore, the carbonate ramp model is useful to explore carbonate reservoirs because of the lateral relationship of facies. The bulk of the formation is the up-dip coastal environment of limestone, addressed above, which is the Smackover Formation. The Smackover Formation is not associated with any reefs, and spans about 1000 feet in vertical height. Much of the formation consists of ooid grainstones and thrombolitic limestones. The overall structure of the formation results in a dual reservoir system, with two permeable zones being separated by a high density seal rock. At the bottom of the deposition, the Norphlet formation serves as the foundation. Above it, the first permeable zone, an oil filled microbial reef reservoir, sits between a source rock and seal rock. Above the seal lies the second permeable zone, which is an oil filled grainstone reservoir near the top of the Smackover Formation. The average depth of the oil column is about 11000 feet, with the column spanning 800-900 feet vertically.

Summary of petroleum system:

Source Rock: Lime mudstone to wackestone

Reservoir Rock: Subtidal clotted peloidal thrumbolite boundstone and fossiliferous, ooid grainstone to packestone

Seal Rock:  Anhydrites, shale, tight sandstones

Stratigraphy
At the base of the formation, just above the Norphlet, the Lower Smackover Formation provides the source rock which is a lime mudstone to wackestone. Next, the reservoir rocks generally consist of sub-tidal clotted peloidal thrumbolite boundstones and fossiliferous, ooid grainstones to packestones. The overall seal is a result of the Haynesville/Buckner formations at the end of the Oxfordian, which consist of shales, anhydrites, and tight sandstones prohibiting any flow through them. While the Gulf of Mexico Basin has a high amount of faulting, the faulting in the northern region is solely in the Jurassic salt deposits below the Norphlet zone, which is the base of the Little Cedar Creek oil field. Throughout the whole formation, there are no faults present. The "red bed" sandstones making up the Norphlet measure around 500 feet in height, while the carbonate dominated Smackover Formation spans about 1000 feet. The Buckner formation on top measures 100-200 feet, mostly made of the Anhydrites addressed earlier. These features suggest that there was most likely an arid climate which persisted from the Triassic to Jurassic.

Looking specifically into the formation, the rock layers of the Smackover Formation can be broken down into six main parts. With respect to the figure on the right, the layers can be addressed via the following:

Red (1) - Transgressive subtidal lime mudstone and dolostone to wackestone

Green (2) - Sub-tidal clotted peloidal thrumbolite boundstone

Blue (3) - Sub-tidal microbially influenced packestone to lime mudstone

Grey (4) - Deeper water to subtidal lime mudstone

Orange (5) - Shallow subtidal nearshore fossiliferous, peloidal, and ooid grainstones to wackestones

Pink (6) - Peritidal lime mudstone and dolostone to wackestone along with a tidal channel floatstone from the Buckner interface

On average, the porosity of these rocks, excluding the high density seals, lie between 15 and 25 percent.

Drilling and Production History
The first well in the Little Cedar Creek oil field was drilled in 1994 by Hunt Oil Company. This well was approximately 12,100 feet deep and produced 108 barrels of oil per day, while also supplying 50 thousand standard cubic feet of gas per day. This well was the only well in the field for the next 6 years, until Midroc Operating Company drilled 70 wells into the formation. With a high success rate, the production grew to over 100 wells, with over 120 wells drilled in total. With the current state of the oil field nearing the end of primary recovery, portions of the reservoir have been put on enhanced oil recovery. This is the process of injecting fluid into the formation via injector wells in an attempt to increase and restore the formation pressure and boost the oil displacement. These efforts have seen the production numbers rise in neighboring wells. Overall, the formation pressures range from 200-300 psi throughout Little Cedar Creek oil field. Since 2005, Little Cedar Creek has been the top producing oil field in the state, and through March 2014, it is estimated that over 13 million barrels of oil and 2.3 billion standard cubic feet of gas have been amassed. The total reserves are thought to be over 80 million barrels of oil and 30 billion standard cubic feet of gas.