Geology

The Brookshire Dome is located within the Gulf Coast geological province, which extends 700 miles from the Rio Grande to Florida. Approximately 450 miles of the trend is within Texas. This is one of the most prolific oil and gas producing provinces in the world.

The Gulf Coast is a homocline with regional dip into the Gulf of Mexico. A thick sequence of Cenozoic sediments exceeding, in places, 20,000 feet were deposited across a flat coastal plain. Alternating transgressive and down warping resulted in a series of structurally and stratigraphically important seaward-marching continental/marine "hingeline" trends.

The provenance of Gulf Coast oils are the thick marine shale sections, just seaward of these "hingelines", the cleaner reservoir rocks are in close proximity to these generative shale’s. The result is a series of productive "fairways". These are designated by stratigraphic nomenclature, i.e. the Wilcox, Wilcox-Yegua, Jackson-Yegua, Frio-Vicksburg, Marginulina-Frio and Miocene trends, to name a few.

Accumulation along these trends is controlled by both structure and stratigraphy. Sedimentary downloading and consequent deformation has resulted in a series of normal (down-to-the-coast) fault systems. These growth faults are associated spatially with prominent anticlinal structures in the down-thrown blocks that have formed some of the most prolific Gulf Coast fields. Within these fields, secondary faulting and diverse depositional processes have combined to produce a variety of complicated structural and stratigraphic traps.

Of at least equal importance as hydrocarbon habitat are the various salt domes for which the Gulf Coast is noted. It was, in fact the discovery at Spindletop Salt Dome, in 1901 that opened the modern age of petroleum exploration and production.

Salt domes are pillars of salt which have risen from depth in response to sedimentary deposition and difference in the specific gravities of the salt and overlying (surrounding) sediments. This salt flowage varies extensively from dome to dome; some domes have surface expression, others are deep-seated. Domal shape may vary from straight-sided to mushroom topped with salt "overhangs" which mask the sequence of underlying sands.

In general, salt domes are classified as either "shallow" or "deep" piercement (shallow being those that extend within 2500' of the surface). Salt Domes are associated with prolific oil and gas fields.