The Val Verde Basin is a marginal foreland basin located in West Texas, just southeast of the Midland Basin. The Val Verde is a sub-basin of the larger Permian Basin and is roughly 24–40 km wide by 240 km long. It is an unconventional system and its sediments were deposited during a long period of flooding during the Middle to Late Cretaceous. This flooding event is referred to as the Western Interior Seaway, and many basins in the Western United States can attribute their oil and gas producing basins to carbonate deposition during this time period.
The Val Verde's structural architecture devolved mainly during the Early Carboniferous to Late Permian period during the Ouachita orogeny. This produced minor structural folding throughout the basin. Today, the Val Verde Basin is a major gas producing system and has recently been recognized for harboring over 5 tcf (trillion cubic feet) of natural gas.
Origin and evolution
The formation of the western interior seaway during the mid to late Cretaceous caused widespread carbonate deposition throughout most of the western United States. During this time period, the seaway flooded the North American mainland and divided the Eastern and Western portions of North America for roughly 60 million years.
~ 105 Ma: Shallow, low energy environment
~ 95 Ma: Period of transgression, moderate - deep water deposits
~ 85 Ma: Continued transgression, moderate - deep water deposits
~ 70 Ma: Retreat of the Western Interior Seaway
Throughout this time period, marine fauna flourished in the warm, shallow water conditions. This led to widespread carbonate deposition throughout the region. Today, many basins throughout the region attribute their source rock and reservoir rock to the sedimentary deposits created during this time. As the seaway transgressed and regressed over time, alternating layers of sandstone and shale were deposited, depending on the depth and overall energy of the environment. This is when the modern-day reservoir rock of the Val Verde basin, the Ozona sequence, was deposited.
The structure of the Val Verde Basin formed as result of tectonic influences for the last ~100 million years.
Major tectonic influences
Syndepositional tectonic events produced the stratigraphic architecture, sandstone distribution and the lithofacies developments within the Val Verde. Although the basin is unconventional, sequence boundaries are marked by systematic shifting of sandstone depocenters in response to episodic thrusting events over time.
Ouachita orogeny:~318-271 Ma
As plate convergence from the Ouachita orogeny began and progressed from the north to the south, offlap and onlap stratigraphic geometries were produced. The orogeny contributed a large amount of sediments from clastic rocks. These were deposited as thick, subaqueous deltaic systems which gradually filled the modern day midland basin over time. The Ouachita Orogeny thrust belt caused regional compression which led to overthrust structures, faulting and folding throughout the region.
Laramide orogeny:~70-80 Ma
The Laramide orogeny was a major tectonic event that caused the most recent and significant deformation in the United States. The Subduction of the Farallon Plate beneath the North American Plate produced compression all across the western portion of the US. Crustal deformation occurred inland from the plate margin and it is mostly related to the deformation of northwestern United States. However this, in combination with Cenozoic rifting produced from the San Andreas fault, crustal folding, faulting and overall deformation have affected the southern regions of the continental US.
Generalized cross section
Ozona sequence
The Ozona formation is part of the larger, unconventional Canyon sandstone system, a tight gas play within the Val Verde basin. Tight reservoirs such as this are characterized by low permeability and low porosity, however the basin is still gas saturated and currently producing today.
Characteristics of the Ozona lithofacies
A description of the lithofacies of the Ozona sequence:
The Ozona is composed of 4 main lithofacies: thick-bedded turbidites, thin-bedded turbidites, mudstone and conglomeratic mudstone Thick and thinly bedded sandstones resemble deposits of mixed sandy and turbidity currents. In the Ozona sequence, the standard Bouma sequence of sedimentary structures properly characterizes the think and thinly bedded turbidites seen here. Some channel-based erosion may occur locally which deposited sediments along with the turbidite deposits