This is the final entry to the three part series regarding the comparison of the Midland and Delaware sub-basins in the Greater Permian Basin. The previous entries have discussed the evolution, deposition, and stratigraphy of both of the sub-basins. This is fundamental information needed to understand Permian Basin oil production and development. But finally, here it is, what everyone really wants to know…what is this booming region producing? This post will discuss the two major contributing reservoirs in each sub-basin.
The Greater Permian Basin has been drilled since the 1920s with a peak in production in the early 70s. It produced approximately 17 percent of the US oil production in 2002 and is estimated to contain 22 percent of the oil reserves (Energy Information Administration, 2003). In recent years, companies have started drilling deeper, exploring new production zones, and drilling horizontally. This is different from the years past where shallow vertical drilling was dominant. Another shift in production has involved the change in focus from conventional resources to unconventional driven plays following the advances in shale gas recovery technologies. New technology has enhanced operating efficiencies and producing rates increasing average lateral length, average frac stages, and amount of total proppant.
Figure 1: The first figure is showing the cummulative oil production in the Permian Basin and the surrounding basins. The second figure is showing the cummulative gas production in the Permian Basin and the surrounding basins. Source: DI 2.0
The Delaware Basin
The Delaware Basin is a multi-stacked play prospect, where almost every well can potentially draw production from different zones. This sub-basin is a more horizontally mature area than the Midland Basin, and thus serves as the foundation for horizontal development in the Greater Permian Basin. Its production is best split into two areas, a northern and southern area. The northern area is known for is advancements in horizontal development while the southern area is associated with vertical wells. The prospective zones for production are located within the Bone Springs and Wolfcamp formations, often referred to as the WolfBone play.
The Bone Spring formation is the most drilled area as well as the most prolific zone in the Delaware Basin (figure 2). Production has rapidly increased since 2008 with the development in horizontal drilling. The hydrocarbon mix is fairly homogeneous throughout the play. Prospected zones to target within the Bone Spring formation vary from the northern and southern region. While both the 2nd and 3rd Bone Spring sands are targeted in the northern region of the Delaware Basin, only the 3rd sand is of interest to most operators in the southern area. “Hot Spots” include: 1) the state line’s Culberson and Eddy counties 2) central Eddy and Lea counties, and 3) west Texas’s Ward County.
Figure 2: Production vs Time in the Delaware Basin colored by reservoir. You can see the Bone Spring formation (in brown) is the most contributing reservoir. Source: DI Analytics in Spotfire
The Wolfcamp formation is present throughout the entire Greater Permian Basin. While the more mature lower Wolfcamp formation is gas prone, the oily upper Wolfcamp is the target of most operators. The hydrocarbon mix is fairly similar to the Bone Spring formation with 60% crude, 20% wet gas, and 20% dry gas. In the past, horizontal wells were dominant in the Delaware’s Wolfcamp play in the north and commingled vertical wells were located in the southern area. However, there has recently been a rise in the amount of horizontal wells in the southern area pursuing the upper Wolfcamp. The hot area for this play is in the western portion of Ward County with other popular regions in the rest of Ward, Loving, and eastern Reeves County.
Figure 3: Well Count vs Time colored by wellbore type in the Delaware Basin. Notice the increase in the amount of horizontal wells. Source: DI Analytics in Spotfire
The Midland Basin
The Midland Basin, like the Delaware Basin, is a multi-stacked play with a long history of vertical exploration dating to the 1940s. Traditionally, the target zone for operators was primarily the Spraberry with only one frac stage. Technology advancements in increased drilling depth and the ability to complete multiple frac’ing stages have influenced operations to look further down to the Wolfcamp formation as well. Both the Spraberry and Wolfcamp formations are fairly consistent throughout the entire sub-basin and are the primary subject for production. This commingled zone is known as the WolfBerry play.
The Spraberry is ranked as one of the largest oil reserves in the US, but when first discovered in 1948, could not be economically produced if fractures in the formation were not present. However, in more recent years it was found that the reservoir was more naturally fractured than once thought and became the core for vertical wells drilled in the Midland Basin. With the new technology of hydraulic frac’ing to stimulate the oil migration of a once “too tight” play, production from the Spraberry has allowed operators to tap into the thick area of pay zones. The Texas Railroad Commission (RRC) recognized the Spraberry trend area as the highest producing Permian Basin oil field since 1993 with just less than 600,000,000 barrels of cumulative oil production (figure 4).
Figure 4: Cummulative Oil Production vs Field. You can see the Sprayberry formation is the largest contributer to the Permian Basin cummulative oil production. Source: Texas Railroad Commission
While the Spraberry was the first formation explored in the Midland Basin, the addition of the Wolfcamp formation, that forms the commingled WolfBerry, has made this play very popular. The thickness of the Spraberry was a major reason the area was so productive, but when you add on the thickness and consistency of the Wolfcamp as well, the possibility of horizontal development adds a large element in the interest of the Midland Basin. The southern portion of the sub-basin has played host to the majority of the horizontal drilling, although higher formation pressures in the central and northern region are driving the operations north.
Figure 5: Well Count vs Time colored by wellbore type in the Midland Basin. Notice the increase in the amount of horizontal wells. Source: DI Analytics in Spotfire
Nearly three quarters of the recent increase in crude oil production from the Permian Basin is from the Spraberry, Wolfcamp, and Bone Spring formations. Drilling activity in the basin had steadily risen until the end of 2014. The RRC reported more than doubling the drilling permits issued from 2005 to 2012 and a significant increase in million barrels of crude oil produced (figure 6). Even now, when rig counts are at a low, the Permian Basin has more working rigs than any other region in the nation. This all leads to the conclusion that The Greater Permian Basin is the nation’s most prolific oil producing area and will be for a while.
Figure 6: New drilling permits from 2005-2012 and Crude Oil Production from 2005-2012 Source: Texas Railroad Commission
Part 2: Stratigraphy
The prequel to this blog post (Part 1: Evolution and Deposition) discussed how the Greater Permian Basin (GPB) formed and was divided into several sub-basins. It continued to uncover why the Midland Basin and the Delaware Basin were different based on variances in sedimentary depositions and tectonics. This post will discuss how the two dominant sub-basins in the GPB differ according to stratigraphy. Understanding the stratigraphy of the Midland Basin and the Delaware Basin will be crucial in linking reservoir quality and production that will be discussed in the next and final post of this series.
The Greater Permian Basin contains early Guadalupian, Leonardian, Wolfcampian, and Pennsylvanian aged strata. While the Wolfcamp formation is present in both the Midland Basin and the Delaware Basin, and is very similar in both sub-basins, stratigraphic nomenclature of the Permian aged strata is entirely different. Cyclic changes in sea level during the Permian time period created a juxtaposition of depositional environments that are reflected in the strata in the two sub-basins (figures 1 & 2). The Spraberry and Bone Spring formations (located in the Midland and Delaware sub-basins, respectively) are time correlative but have different compositions. We will focus on the similarities and differences of the stratigraphy and lithology of Leonardian and Wolfcampian aged formations in the Midland and the Delaware sub-basins of the Greater Permian Basin.
Figure 1: Differences in stratigraphic nomenclature between the Midland and Delaware Basins Source: Permian Basin Easy to Oversimplify, Hard to Overlook by Liam Kelly et al
Figure 2: Cyclic changes in sea level created a juxtaposition of depositional environments between the Midland Basin and the Delaware Basin Source: Permian Cyclic Strata, Northern Midland and Delaware Basins, West Texas and Southeastern New Mexico by Burr A Silver and Robert G Todd
THE MIDLAND BASIN
The Midland Basin’s stratigraphy is widely characterized as a “multilayer” cake with different geologic zones comprising the layers in this analogy. These stacked plays along with high fracture rates are the primary reasons the Midland Basin has great future potential for hydrocarbon recovery. The two stratigraphic sections that make up the Leonardian and Wolfcampian are the Spraberry (along with the Dean) and the Wolfcamp formations. These names are commonly combined and referred to as the “Wolfberry”.
Spraberry & Dean
The Spraberry and Dean formations are a series of Leonardian aged shales with interbedded sands that were associated with channel systems and submarine fans. Fine sandstone, calcareous mudstone, and coarse siltstone comprise the Spraberry and are characterized by having very low porosity and matrix permeability. These qualities, along with a natural fracturing tendency, provide migration paths and a trap for hydrocarbons. The Spraberry formation is divided into upper and lower sandy units with the Dean formation stratigraphically under the lower Spraberry. These sub-units are differentiated by lithology. The upper and lower Spraberry units are fine grained silty sandstone with intermitted silty shale. These are separated by a package composed of mainly black shales and dark carbonates with a sandstone package in the center. The Dean formation, similar to the Spraberry sands, is a sandstone with thin intermitted beds of dense limestone and black shale. The average depth of the top of the Spraberry formation is approximately 6,800 feet across the entire sub-basin. The entire section from the top of the Spraberry to the base of the Dean varies in thickness between 1,200 and 1,870 feet.
The Wolfcamp formation has been widely used as the marker of Permian time period, however recent research has concluded that based on dating condonts (extinct chordates that resemble eels), the base of the Wolfcamp formation is actually upper Pennsylvanian in time. For the easy of clarity in this discussion, we will consider the Wolfcamp formation to be entirely Wolfcampian in age. It is generally a two-lithology based system of mostly shale with interbedded limestone. Minor layers of calcareous sandstone are present. This formation is separated into four units (A, B, C, and D) with slight lithology changes between the sub-units. The Wolfcamp formation is the deepest in the center of the basin, measuring approximately 12,000 feet deep, whereas towards the edges of the basin, it is found at a much shallower depths varying from 4,000 to 7,000 feet (figure 3).
Figure 3: Vertical depth map of the top of the Wolfcamp formation throughout the Midland Basin Source: The “New” Horizontal Permian Basin by Joseph Bachmann et al
THE DELAWARE BASIN
The Delaware Basin stratigraphy, especially Leonardian aged strata, is different from the Midland Basin. Where the Midland has the Spraberry and Dean formation, the Delaware has the Bone Spring and Avalon formations. Similarly, both sub-basins have common Wolfcamp formations that are very analogous. Just like the Midland, these two stratigraphic plays have been combined to be dubbed the “Wolfbone”. The deeper Delaware Basin is also a multi-stacked play area similar to the Midland.
Bone Spring & Avalon
The Bone Spring formation is Leonardian in age and is divided into the 1st, 2nd, and 3rd Bone Spring, each containing a package of carbonate followed by a package of sand. This cyclic sedimentation is due to the change in sea level as mentioned above, where the carbonate is formed when sea level was at a high and sands when the sea level was at a low. Above the 1st Bone Spring carbonate, there are the upper and lower Avalon shales as well as the Avalon carbonate that splits the two shales. The Avalon carbonate is interbedded with dark and carbonaceous shaly siltstones that act as a permeability barrier to vertical flow. Sand strata in the Bone Spring formation were deposited as submarine fan systems. The carbonates are composed of dark and dense carbonaceous wackestone and mudstone that establish an important source rock. The sand intervals of the Bone Spring are composed of dark, thinly bedded, calcareous shales and siltstones. The entire Bone Spring and Avalon formations (often just called the Bone Spring) average in thickness from 2,500 feet to 3,500 feet. The thickest region of the formation occurs in the eastern portion of the Delaware Basin before it quickly disappears into the Central Basin Platform (figure 4).
Figure 4: Vertical depth map of the top of the Bone Spring formation throughout the Delaware Basin Source: The “New” Horizontal Permian Basin by Joseph Bachmann et al
The Wolfcamp formation in the Delaware Basin is an ideal heterogenetic resource of hydrocarbons. While the lithology of the Delaware Wolfcamp is analogous to the Midland Wolfcamp, characterized by interbedded shale and limestone, some differences do occur. In fact, the same Wolfcamp formation in the northwestern section of the Delaware basin is different from the rest of the basin’s Wolfcamp. In the northwestern portion of the basin, the Wolfcamp’s carbonates are light colored dolostones. In contrast, the rest of the basin’s Wolfcampian strata are dark colored lime packstones, wackestones, and mudstones. The depths and thickness of the Delaware Wolfcamp also differ from the Midland Wolfcamp. It has an average thickness of 2,000 feet but can locally exceed 6,000 feet in the western portion of the basin. The top of the Wolfcamp in the Delaware Basin lies on an average depth ranging from 10,000 to 12,000 feet.
STILL TO COME…
We have now covered why and how the Midland and Delaware sub-basins are similar and different. These fundamental understandings are going to be important for the third and final part of this blog series where I will discuss how this all ties into reservoir quality and production of these two hot plays. Again, stay tuned…
Part 1: Evolution and Deposition
This will be the first of a three part series where I will discuss the Permian Basin as well as the similarities and differences in the Midland Basin and the Delaware Basin. This first discussion will cover the evolution and deposition while the following will cover stratigraphy, reservoir quality, and production of this basin.
The Greater Permian Basin (GPB) is one of the largest and most structurally complex regions in North America. This sedimentary basin is comprised of several sub-basins and platforms. It covers an area about 250 miles wide and 300 miles long in 52 counties in west Texas and southeast New Mexico. That’s more than 75,000 square miles! Though it contains one of the world’s thickest deposits of Permian aged rocks, it was actually named after the period of geologic time (Permian: 299 million to 251 million years ago) where the basin reached its maximum depth of 29,000 feet.
The evolution of the basin can be attributed to three distinct phases: (1) mass deposition (2) continental collision (3) basin filling. Before the Permian Basin was formed, this region was a broad marine area called the Tobosa Basin. During the Cambrian to Mississippian periods (541 to 323 million years ago), massive amounts of clastic sediments were deposited in this area causing it to form a depression. What we define as the basin today began forming in late Mississippian and early Pennsylvanian (323 to 299 million years ago) when the supercontinents Laurasia and Gondwana collided to form Pangea causing faulting and uplift. While the area was covered by a seaway (figure 1), episodes of faulting, uplift, and erosion (associated with the Marathon-Ouachita Orogeny) as well as different rates of subsidence caused structural deformations in the larger Tobosa Basin that divided it into sub-basins and platforms.
Figure 1: Paleographic time sequence, from youngest to oldest, of the evolution of the Greater Permian Basin, Source: DI 2.0 Paleo Layer
The final process that created the GPB was the filling of the sub-basins with sediments. The Midland Basin, Central Basin Platform, and the Delaware basin are the three main components of the GPB that we know today. Other sections of the GPB include: the Northwest Shelf, Marfa Bain, Ozona Arch, Hovey Channel, Val Verde Basin, and Eastern Shelf.
Figure 2: Structural differences between the Delaware Basin, Central Platform, and Midland Basin, source: Kelly et al. “Permian Basin – Easy to Oversimplify, Hard to Overlook”
The Midland and Delaware sub-basins share mutual characteristics such as age and lithology, but depths, nomenclature, and development vary throughout the GPB. The sub-basins rapidly subsided, while the platform remained at a higher elevation. This resulted in areas having very different water depths and depositional environments. The basins accumulated terrigenous clastics that are associated with deep water environments, whereas coarse grains associated with shallow reef environments were deposited along the platform. Differences in sedimentary depositions and tectonics initiated stratigraphic discontinuities between the two sub-basins.
The Midland Basin
The eastern Midland Basin accumulated large amounts of clastic sediments from the Ouachita orogenic belt during the Pennsylvanian (323 to 299 million years ago). As these sediments were deposited, they formed a thick subaqueous deltaic system that consumed the basin from east to west. During the Permian period, the delta system was covered with floodplains and was nearly filled by the Middle Permian.
The Delaware Basin
The western area of the GPB, the Delaware Basin, was a structural and topographical low that provided an inlet for marine water during most of the Permian. Minor sedimentation was received from the low coastal plains that surrounded the basin. While the Midland Basin was almost full of sediment by the Middle Permian, the Delaware became host to reefs built by sponges, algae, and microbial organisms. These organisms, along with the deep water inputs supplied by the Hovey Channel (figure 3), promoted carbonate buildups that formed a higher elevation area which separated the shallow water and deep water deposits.
Figure 3: Permian Map: The Hovey Channel supplied the Delaware Basin with deep water sediment, while the Midland Basin was restricted by carbonate reefs of the Central Platform, source: http://www.vyey.com/assets/permian-basin
Depth also had an important impact on the way sediments were deposited in the basin. The Delaware Basin is approximately 2,000 feet deeper than the Midland Basin (figure 4), thus causing the sediments to experience nearly twice as much pressure during burial. This is a leading factor in the stratigraphic discontinuities between the two sub-basins.
Figure 4: Depth map of the Delaware Basin, Central Platform, and Midland Basin, source: http://www.searchanddiscovery.com/pdfz/documents/2012/10412fairhurst/ndx_fairhurst.pdf.html
Still To Come…
Hopefully you now have a better understand of how the Greater Permian Basin, as a whole, evolved into the structure that we know it to be today as well as the relationships between the Midland and Delaware sub-basins. I will next discuss the stratigraphic differences between the two sub-basins and will later discuss how this is all related to the hydrocarbon production of these two popular plays. Stay tuned…
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