*MAFLA - Mississippi,
Alabama & Florida
(Also Applicable to
Upper BDL Core
Photo Courtesy AEEC
Middle BDL Core
Photo Courtesy AEEC
A "HYBRID" UNCONVENTIONAL RESOURCE PLAY THAT IS POORLY UNDERSTOOD
[On May 16, 2012, Steve Walkinshaw served as Presenter for the Lower Smackover Brown Dense Unconventional Oil Trend at Hart Energy's Third Annual DUO (Developing Unconventional Oil) Conference, held in Denver, Colorado. Since the DUO Conference, Steve has reprised the presentation (in a greatly expanded format) before many regional Geological Societies and professional organizations, including the Shreveport Geological Society (SGS), the Lafayette Geological Society (LGS), the New Orleans Geological Society (NOGS), and the Mississippi Geological Society (MGS); as well as the Mississippi Association of Petroleum Landmen (MAPL) and the Emerging Shale Plays USA 2013 and 2014 Conferences, held in Houston, Texas. The following report is taken from Steve Walkinshaw's Brown Dense Limestone presentation.]
The Brown Dense Lime comprises the lower member of the Smackover Limestone, an Upper Jurassic carbonate that is only encountered in the subsurface in the U.S. The Brown Dense Lime is arguably the most prolific source rock in the U.S. Gulf Coast area, and in many areas such as the Mississippi Interior Salt Basin, it accounts for the vast majority of the crude oil produced from Mesozoic reservoirs. To learn more about the Smackover Limestone, please click here. The base of the Brown Dense Lime oil window becomes progressively deeper as one moves east, especially into the southeast Mississippi / South Alabama area, where the oil window extends as deep as 16,000’ or more. Porous reservoirs within the Brown Dense have already produced significant volumes of oil, gas and condensate from the Southeast Mississippi / South Alabama area, with porous carbonates developed along the flanks of the Baldwin High in South Alabama, and porous oil sands encased within the micrite in Southeast Mississippi. Substantial volumes of sour gas and condensate have also been produced from many fields located just downdip from the Mexia-Talco fault system in East Texas, as well as south-central Mississippi. As a rule of thumb, the Brown Dense Limestone is observed to have generated hydrocarbons at burial depths greater than 10,000 feet in the Gulf Coast area. Subsequent uplift and sub-regional variations in temperature gradients and TOC will obviously cause deviations from this rule of thumb; nevertheless, it should be taken into account whenever one is exploring an area where it appears the Brown Dense was never buried to that depth.
The Lower Smackover Brown Dense Limestone (“BDL”) Trend represents a “hybrid” unconventional play, incorporating both conventional and unconventional components. But this trend does not represent a “mining operation”. The tight micritic limestone matrix is not porous and permeable enough to support sustained hydrocarbon production. That being said, in many areas there are lenses of porosity encased within this prolific source rock, and these porosity lenses can be identified using high-resolution seismic data. Such porous reservoirs have already proven to be prolific producers in established areas of the Trend – the so-called “conventional” component. There are large fracture swarms that could represent a substantial “unconventional component”, but ironically, these fracture swarms have not yet been targeted by the “unconventional” players. Vision’s approach would be to use seismic data and existing well control to target the known “sweet” areas of the Trend, while avoiding those areas that are unfractured or contain too much hydrogen sulfide and inert gases.
Despite the drilling of hundreds of Smackover wells in the area over the past 60-70 years, only 30-40 wells, plus or minus, have penetrated the entirety of the Brown Dense Lime in South Arkansas, and even if one expands the radius of investigation to include neighboring North Louisiana, that figure only doubles to around 80-90 wells, even if one includes all of the recent BDL drilling activity. Click here to view a stratigraphic chart and type log exhibit for the South Arkansas / Northwest Louisiana area. In sharp contrast, hundreds of wells drilled in South Mississippi and South Alabama have penetrated the entire Brown Dense Lime interval. This is because the underlying Norphlet Sand was a viable and often prolific drilling target in the Mississippi / Alabama area, providing the incentive for operators to drill deep enough to test both the Smackover and Norphlet. Accordingly, and ironically, the focus of BDL exploration on the South Arkansas / North Louisiana area means that operators in that area are really wildcatting in the classic sense, with minimal Brown Dense Lime well control.
Most researchers who have studied the Brown Dense Lime have subdivided it into three general facies: upper, middle, and lower. The middle and lower facies are generally assumed to have been deposited within an anoxic or oxygen-poor, hypersaline environment, while the upper facies is quite fossiliferous and bioturbated, with numerous shell fragments, especially those of pelecypods; this indicates a less hostile, more oxygenated depositional environment. To view a slabbed core photo taken from an interval that transitions from the upper BDL to the middle BDL, click here. In many areas, the middle and lower facies of the Brown Dense exhibit a cyclical gamma ray curve pattern that is very distinctive; this cyclical log appearance is often described as being associated a with "varved" facies, but that is only correct for certain intervals developed within the lower BDL. The term “varved” refers to the banded calcareous and argillaceous carbonate laminae that are readily observed in diamond cores cut from the lower BDL, while the "varved" (cyclical) gamma ray response observed on the log represents "macro" depositional cycles. To view a core and log exhibit illustrating the varved facies of the lower BDL, please click here.
The depositional environment of the rising Smackover sea during the deposition of the Brown Dense Lime was quite diverse. In the deeper water depths, anoxic conditions, while hostile to life, effectively preserved organic matter transported into the vicinity. However, shallower waters along coastal margins were less hostile to marine life and conducive to the formation of shoals and beach deposits, creating zones of porosity within the Brown Dense. Sediment transported into the area also formed localized porosity lenses. Click here to view an image taken from a 3D survey acquired across such varying BDL / "basement" bathymetry. Atop the Monroe-Sharkey Platform (of Northeast Louisiana and West Mississippi), volcaniclastics such as ash and tuff beds were also deposited within the Brown Dense, and where reworked, may have formed porous reservoirs as well.
On average, total organic content ("TOC") is quite low, but that can be very misleading; organic matter in carbonates tends to concentrate in styolites during the compaction and dewatering process, and the diagenesis that follows burial. Apart from styolites, it appears there were cyclical periods of algal blooms followed by “die-offs” that locally increased TOC content, especially in the area impacted by sediment influx from the ancestral Mississippi River. In fact, it appears the River played a pivotal role in contributing large volumes of organic matter to the Brown Dense Lime, especially in the west-central Mississippi area. For more information regarding factors affecting TOC content in the Brown Dense Limestone, click here.
Vision has analyzed detailed geochemical data recently acquired from 27 key wells located within the oil and wet-gas window of the Brown Dense in west-central and southeast Mississippi. There is a clear correlation between the wells that exhibited the higher levels of average TOC, and the proximity of those wells to the ancestral Mississippi River, which is interpreted to have emptied into the Brown Dense sea in the area just east of the current floodplain, in the west-central Mississippi area. In the vicinity of the ancestral Mississippi River, climactic cycles deposited alternating intervals of clean and argillaceous carbonate within the thick Lower and Middle Brown Dense Lime intervals. NGS logs indicate that higher levels of thorium and uranium, which are readily adsorbed by organic matter transported into the area by the river and other streams, are associated with the darker, more argillaceous layers within the Middle Brown Dense. Thus with some caveats, NGS logs can be used to identify bands of higher organic content within the Brown Dense. An analogous modern relationship can be observed in the present-day thorium concentrations that are elevated in the Mississippi River floodplain. Core analyses and oil saturation plots from wells located as far southeast as Clarke County, Mississippi, demonstrate that even in areas that were located a considerable distance from the River, where the climactic depositional cycles are less apparent, banded layers of high and low residual oil saturations remain discernible. Click here to view an image illustrating these BDL cycles.
Geopressure within the Brown Dense Lime is not uniformly distributed. The tight micritic facies is impermeable and, in most areas, the Brown Dense was not compartmentalized during deposition and burial. Thus the Brown Dense is markedly different than geopressured shales such as the TMS, which were compartmentalized soon after burial and became uniformly microfractured and overpressured as a consequence of the cracking of oil to gas following hydrocarbon generation. Abnormal pressure does exist within certain areas of the Brown Dense Trend, but it is localized and associated more with zones of fractured or primary porosity encased within the Brown Dense, not the interval as a whole.
Another significant challenge for the Brown Dense Lime explorer is the risk that larger fractures within the Brown Dense extend vertically, either (1) upward, high enough to reach and establish "communication" with the overlying Middle and/or Upper Smackover porous facies, or (2) downward, such that the fractures establish communication with the underlying Norphlet sandstone, if it is present. In either case, any pressure drawdown within the Brown Dense fracture system would rapidly introduce large volumes of extraneous brine, overwhelming the production of oil from the Brown Dense. It is also clear that one cannot fracture-stimulate the Brown Dense Lime in an area where such proximal brine-filled porosity exists, for the obvious reason that the frac would only exacerbate the potential for extraneous brine production.
Thus the optimal area for Brown Dense Lime exploration is an area where there is nil porosity development within the overlying Middle and/or Upper Smackover porous facies, and where the underlying Norphlet sandstone is absent. Vision takes this a step further in certain areas, preferring to target areas where the overlying Middle and/or Upper Smackover porous facies has transitioned laterally to an evaporitic facies, further thickening the topseal over the Brown Dense. However, even in such areas the Norphlet may be present. Thus the explorer needs to have a detailed understanding of not just the regional Smackover facies distribution, but also the aerial extent of the Norphlet sandstone.
Like the other "oily" resource plays, storage is the key. In other words, the microfracturing created as a consequence of the source rock in-situ hydrocarbon generation is, in and of itself, not sufficient to provide for the production of oil from the Brown Dense Lime in commercial quantities. There must be additional matrix porosity and permeability present to provide storage (volume); this additional reservoir volume can consist of enhanced fracturing caused by stress (drape over a paleo-structure), or the presence of localized siliciclastics. Because the west central Mississippi area is an area where the Brown Dense Limestone is encountered at a relatively shallow depth, and where sandstones are commonly encountered within the Brown Dense Limestone (an optimal sourcing/entrapment scenario), it would appear that this area represents a potential Bakken-type analog (a siliciclastic lens (the primary storage tank) deposited within a prolific source rock). However, many sand lenses in the updip area are low in porosity and permeability, which presents a challenge for those who would pursue the oil play (which requires, for commercial production rates, much better porosity and permeability that the gas play). Vision has focused its exploration efforts instead within the condensate "window", which is moderate in depth (12,000' to 15,000') and rich in BTU content. The presence of hematite and other iron consituents within the sandstone lenses of the Brown Dense Limestone aids in "scrubbing" a substantial amount of hydrogen sulfide from those reservoirs, and in certain areas of great interest to us, it is clear that certain clay constituents also preserved above-average porosity and permeability by preventing the subsequent formation of diagenetic quartz overgrowths. Thus there are some areas within the trend where above average porosity and permeability harbors exceedingly rich (1,200 BTU) gas and condensate at moderate depths, with nil hydrogen sulfide and very little carbon dioxide. Given the modest lease bonus and royalty terms of the area, and the potentially rich liquids yield, this play makes good economic sense even at $2-$3/MMBTU gas.
The first horizontal well drilled specifically to target a Brown Dense reservoir, the #1 Melvin VLSU, was drilled in 2000 by Spooner Petroleum as contract operator for Hughes-Rawls Corporation, in Vossburg Field in Jasper County, Mississippi (click here to view the log from the Melvin log across the BDL). The reservoir was a moderately pressure-depleted Brown Dense oil sand with approximately 15% porosity. Hughes-Rawls sidetracked a vertical producer and drilled an 815’ lateral into the drawn-down Brown Dense oil sand reservoir. The well is still producing and to date has produced over 740,000 barrels, of which over 444,000 barrels have come from the lateral. One might wonder what this well would have produced had it been drilled into a virgin-pressured reservoir.
The Esenjay #1 Menasco 11-14, which was completed in 1987 in Nancy Field in Clarke County, Mississippi, provides some insight into such potential. It is located just southeast of the Hughes-Rawls well at Vossburg Field (click here to view the Esenjay log across the BDL). Esenjay originally targeted the Upper Smackover when it drilled this well, but stumbled into a porous and permeable Brown Dense sandstone saturated with oil. Without a frac, the Esenjay well was completed flowing 2,346 BOPD + 2.3 million cubic feet of gas per day. This illustrates the "conventional" component of the "Hybrid" BDL Play; consider what a modern lateral completed in such a reservoir would produce on a test of initial potential.
Beginning in 2009/2010, a number of operators in extreme South Arkansas and North Louisiana began drilling horizontal wells through the Brown Dense Lime in an attempt to establish a new unconventional oil resource play. A number of companies also leased large areas of the "river counties" in extreme west central Mississippi (and extreme eastern Louisiana) with a similar intent to test the Brown Dense Lime in that area, despite the fact that in this area the Jurassic was uplifted, tilted (and in many areas, eroded) in early Tertiary time (the Monroe-Sharkey Uplift), and commonly intruded by Tertiary-age igneous dikes and sills. These "late" igneous intrusions are principally confined to the Monroe-Sharkey and Jackson Dome areas, and have insignificant impact upon the hydrocarbon constituency of Smackover reservoirs.
Click here to view a chart of the length of some important Brown Dense Lime lateral wellbores drilled within the past 4-5 years. Drilling problems cut short the ultimate length of several of the planned laterals. At present, the Southwestern Garrett and Whiting Langford wells (drilled recently in Northwest Louisiana) represent the longest laterals drilled to date in the Trend, approximately 6,500’. That having been said, most of the Trend activity since 2013 has focused on the drilling of vertical, not horizontal, Brown Dense wells.
In terms of total proppant load and average proppant load pumped per stage, for what has been reported so far, the Cabot #1 Denny still holds the record, having pumped approximately 3.5 million pounds of proppant, an average of 350,000 pounds per stage. Most operators have reported difficulties in fracking the Brown Dense; Southwestern, for example, has noted problems in attaining frac heights exceeding 200’.
The following represents a brief timeline synopsis of BDL Trend drilling activity.
In 2009, Weiser-Brown drilled a vertical Smackover test well, the #2 ExxonMobil, in Tick Creek Field in Union Parish. It is interesting to note that the #2 ExxonMobil was drilled to test a 2D seismic anomaly within the Brown Dense – a “conventional” target. While drilling within the Middle Brown Dense Lime at a depth of 9,142’, the operator encountered geopressure and was forced to immediately set casing as deep as possible in the wellbore to control the flow of oil and gas from the formation, and the well flowed approximately 600 BOPD from the 42 feet of open-hole interval that remained beneath the casing shoe. As a result of these issues, no open-hole logs were run in the #2 ExxonMobil. The well was subsequently shut in and not turned to sales until late 2012. In Lafayette County in southwestern Arkansas, EOG abandoned its initial Brown Dense pilot hole after testing revealed higher-than-expected concentrations of H2S in the gas produced from the Brown Dense. EOG exited the Trend shortly thereafter, selling its extensive Brown Dense leasehold to Southwestern.
In 2011, Sklar completed a vertical, non-commercial, normally-pressured Brown Dense oil well in Cecil Creek Field in northern Union Parish. This well produced less than 1,500 barrels of oil and was abandoned in September of 2013. Meanwhile, in southwestern Clarke County, Mississippi, Epsilon Energy drilled its 3,600’ Epsilon 27-3H Brown Dense lateral in Hollicar Creek Field, completed in open hole as a non-commercial BDL oil well producing 6-8 barrels oil per day on an average of two days each month.
In 2012, the first Brown Dense laterals drilled in the North Louisiana / South Arkansas area (Brammer Watson-Fullerweider PL #1-12H; Cabot #1 Denny #1-32H; Devon Crossett #1-31H) were completed as non-commercial oil wells (click here to view a core/log exhibit for the Brammer pilot hole). Two vertical wells were also drilled and completed. All of these wells were either non-commercial or abandoned as dry holes. Like EOG, Cabot and Devon effectively exited the play after testing their initial Brown Dense laterals. XTO has also ceased Brown Dense exploratory activity; however, its parent company, ExxonMobil, continues to own a large fee mineral position in the Trend. Southwestern’s first two laterals, the Roberson and Garret wells, initially attracted a lot of industry attention but were ultimately deemed non-commercial.
Southwestern commenced drilling activity in the Ora Field area with the spudding of the BML Properties pilot hole in February 2012. While drilling the initial lateral of the BML well, the operator reported taking a strong “kick” from an interval in the Brown Dense, which necessitated a jump in control mudweight to 15.6 PPG, and subsequently led to stuck pipe; the well was then plugged back and sidetracked, with Southwestern running an intermediate liner to facilitate the high mudweights needed to control the well. Total depth in sidetrack hole was reached in May of 2012 and casing was run to bottom. Following a 19-stage frac, the well officially I.P.’d at 186 BCPD + 1,995 MCFGPD, and was turned to sales in late November 2012.
Southwestern then drilled the #21 Johnson, a vertical Brown Dense test, northeast of the BML lateral. The Johnson well reportedly encountered the same geopressured zone penetrated by the BML lateral. Unfortunately, the frac apparently screened out during the testing of the Brown Dense, and the well is currently shut in. During this time, Cabot permitted three Brown Dense units in the area just northwest of the BML unit.
Shortly after drilling the Johnson well, Southwestern drilled a second vertical test, the Dean 31-22-1, approximately 6 miles east of the BML well. The Dean well also encountered the geopressured zone, and was successfully stimulated with a 3-stage frac across 12 feet of perforations and I.P.’d at a producing rate of 668 MCFGPD plus 112 BCPD. During the testing of this well, Empresa permitted two Brown Dense units in the area north of the Cabot units. At the same time it was drilling the Dean vertical well, Southwestern spudded the Doles 30-22-1H, adjacent to the BML Properties well in Unit “A” of Ora Field. This 6,111’ lateral was stimulated with a 22-stage frac. In late November of 2012, Southwestern turned both the BML Properties lateral and the Doles lateral to sales, reporting their combined production on a commingled unit basis. These represent the first two Brown Dense laterals placed on production in the Northwest Louisiana area. To view a stratigraphic cross-section of the BDL through several of the Southwestern wells, click here.
In February of 2013, Southwestern spudded the Dean 31-22-1 #2 Alternate lateral from the Dean vertical well pad. The well reached total depth and was cased but has not yet been completed. Southwestern then drilled the #22-22-1 Sharp as a vertical test well located approximately midway between the Dean wells at Ora Field and the Weiser-Brown vertical producer at Tick Creek Field. The Sharp vertical well was completed as a gassy oil producer from perforations over a 494’ interval, from 9,174’ to 9,668’. The well I.P.’d at 564 BOPD + 1,089 MCFGPD, and the oil gravity and gas/oil ratio were almost identical to that reported from the Weiser-Brown #2 ExxonMobil initial completion. Keep in mind, however, that the Weiser Brown well produced from only 42’ of open hole, while the Sharp well was perforated selectively across a much greater interval. Also in early 2013, Whiting permitted its first Brown Dense Lime test well, a vertical well named the #1 Hicks FLP 28 in nearby Bull Creek Field. However, the permit for the Hicks well expired. Around the same time, Ankor acquired Cabot’s Brown Dense leasehold and subsequently drilled its first Brown Dense test well, a vertical well named the #1 Tom-Rosa Corp. Ankor cored approximately 400 feet of the Brown Dense in the Tom-Rosa well. Detailed core analysis revealed, among other things, that the tectonic stress responsible for the fractures observed in the cored interval was not attributable to overburden; rather, lateral forces. The Ankor well is currently shut in. Southwestern has subsequently drilled a number of non-commercial vertical BDL wells in the greater Ora Field area. Southwestern also recently drilled and completed the McMahen 19-21 #1-7 well in southwest Columbia County, Arkansas as a non-commercial Brown Dense oil producer. The drilling of these vertical BDL test wells represented Southwestern's unsuccessful attempt to extend the commercial limits of the Ora / Tick Creek Field geopressured Brown Dense Trend along strike to the northwest.
In the middle of neighboring Claiborne Parish, Whiting drilled a vertical BDL test well, the Jackson #23, in Blackburn Field, and has drilled the Langford 4H, a 6,500’ lateral, in Oaks Field to the northeast. The Whiting BDL well in Blackburn Field in Claiborne Parish are on strike with the Wheless #1 Prather, a legacy Brown Dense vertical open-hole completion that was noteworthy for the impressive 450,000 pound open-hole frac effected one month after the initial completion in 1981. Although post-frac flowback rates were dramatically higher, the BDL completion in the Wheless well was abandoned after producing less than 100 million cubic feet of gas and 711 barrels of condensate. In northern Webster Parish, Whiting permitted a BDL lateral, the Garland Brothers #24, in East Dykesville Field and a 1,280-acre Brown Dense unit in North Shongaloo – Red Rock Field. All of the Whiting wells are shut in.
Also In 2013, Dan A. Hughes Company abandoned its 4,100’ Brown Dense lateral in Morehouse Parish, Louisiana, the #1 Plum Creek, after failing to produce commercial volumes of oil, following an 11-stage frac utilizing two million pounds proppant. In Mississippi, Apache (Dove) drilled four Brown Dense test wells, all of which were unsuccessful; Apache has since exited the play.
In August 2014, after conducting a 6-stage frac of the BDL, Southwestern abandoned the only test well drilled on its substantial West Mississippi Brown Dense leasehold, the #1 Lee 26-13, located in Sharkey County, Mississippi. This location places the Lee well on the east flank of the Monroe-Sharkey Platform, near an old Amoco dry hole that encountered scattered oil and gas shows in the Upper and Lower Smackover.
Also in West Mississippi, Conoco-Phillips had amassed a lease position in the updip BDL Trend in Humphreys, Holmes and Yazoo Counties totaling 207,000 gross and 170,000 net acres. Notwithstanding, in 2013 Conoco-Phillips signaled its intent to not drill its first BDL well 100%, but to instead farm out 50% of its working interest in two relatively small areas, which average approximately 5,500 acres each. The farmout requirements include the drilling of a pilot hole and at least a 5,000’ lateral that must be multi-stage fracture-stimulated. To date, Conoco-Phillips has been unsuccessful in attracting interest in its farmout proposal.
To summarize the results of recent Brown Dense Lime Trend drilling, most of the wells were drilled in areas where pre-existing well control indicated the Brown Dense to lack adequate storage and/or permeability; unsurprisingly, these wells failed to encounter porosity and permeability sufficient to produce oil and/or gas at commercial rates, even following substantial fracture stimulation. Several operators have expressed surprise at encountering higher than expected levels of H2S in the gas produced from the Brown Dense, even though nearby legacy Smackover wells had historically produced similar levels of hydrogen sulfide. Understanding the presence and distribution of H2S in the Trend is critical to establishing commercial production and minimizing surface facilities and pipeline costs.
In the greater Ora / Tick Creek Field area of Union Parish, two vertical Brown Dense wells appear to represent commercial completions. Three gassier wells completed to the south are exhibiting rapid decline, and a number of new wells have not yielded commercial flow rates, even after large fracture stimulations.
It would appear that this geologist's concerns regarding the impermeability of the tight micrite of the Brown Dense, stated since 2011, have been validated. In order to sustain commercial oil production from the Brown Dense Lime, additional storage must be present, and in the true oil window, porosity is not enough; the storage must be sufficiently permeable, and that means much more than nanodarcy permeability. It appears that commercial success within the Brown Dense Trend in North Louisiana is increasingly becoming limited to the volatile oil / wet gas window, and especially the geopressured reservoir that has been encountered in the Tick Creek and Ora Field areas. The disappointing results of the recent Apache drilling activity in Mississippi can be best characterized as unsurprising, to those of us familiar with the Trend who remain puzzled by Apache’s choice of location for its four wells. Has the Trend been condemned? Only if your goal is to turn it into a purely unconventional “mining operation”. In that case, you will undoubtedly have your hat handed to you. To paraphrase the recent comments of the CEO of one such Trend player, the Brown Dense can be a “bully”, and if you choose to ignore the basic fundamentals of the play, you will certainly get “beaten up”.
Now that we’ve reviewed what’s been done in the past 5 years, let's address what has not yet been done. Vision recommends concentrating exploratory efforts in those areas where there is additional porosity known to be developed within the Brown Dense. The porosity could consist of porous carbonates, clastic lenses, or enhanced macrofracture swarms. All three of these broad reservoir types are stratigraphically limited and thus compartmentalized, in a regional perspective, within the Brown Dense. The challenge is knowing where and how to explore for them.
If one studies the play from a regional perspective, it is clear that carbonate porosity is present within large areas of the greater Brown Dense Lime Trend. This porosity typically consists of dolomitized pelletal, oncoidal, or algal facies such as those that have produced large volumes of oil and gas at Jay, Blackjack Creek, and Big Escambia Creek Fields in northwest Florida and southeast Alabama. Another example of carbonate porosity development is the 68’ thick zone of porosity encountered in the Exxon #1 Moulder, an Upper Smackover development well drilled in South Atlanta Field in Cass County, Texas (click here to view the log across the BDL in the Moulder well). The porosity is believed to be a leached pelletal deposit developed on the flank of a salt-cored paleohigh. Other similar zones of porosity developed within the BDL in Cass County appear to have been deposited on the submerged flanks of weathered Triassic volcanoes. Analogous intervals of thick Brown Dense porosity have also been observed in neighboring Caddo Parish.
In certain areas of the BDL Trend in Mississippi, thick quartzitic sandstones have been encountered in both the Upper and Lower Smackover. The Upper Smackover sandstones were deposited in a relatively high-energy environment, and are typically gray in color, very calcareous, and moderately porous and permeable. Conversely, sandstones deposited within the Brown Dense Lime were deposited in a low-energy environment by the ancestral Mississippi River. Many wells drilled in those areas encountered remarkably sweet oil, gas and condensate in the sandstones deposited within the Brown Dense (click here to view an example). These sandstone reservoirs can exceed 130’ in thickness and can harbor porosity as high as 22%. Accordingly, these Brown Dense reservoirs are much thicker, porous and permeable than any Brown Dense reservoir that has been encountered to date in the South Arkansas / North Louisiana area. Targeting these sandstones is a straightforward approach to exploiting the “conventional” reservoirs within a hybrid “unconventional” play.
There are areas within the Brown Dense Lime Trend that appear favorable for enhanced macrofracture development. When prospecting for such areas, it is important to remember that the target is a very hard, very brittle carbonate. Along those lines, therefore, one could view the Brown Dense as being very similar to the Austin Chalk. Such hard brittle carbonates become intensely fractured along the downthrown sides of large normal faults and in close proximity to wrench faults, both of which serve to brecciate the carbonate, creating substantial fracture porosity. Contact dolomitization of the fracture walls adds additional vugular porosity and thus, storage. Drape over paleohighs such as localized basement uplifts and the crests of Norphlet seif dunes also generates substantial fracture swarms within the Brown Dense. Click here to view a 3D seismic / log image illustrating an area of optimal drag/shear fracturing.
To summarize: the Brown Dense Limestone is the most prolific source rock in the U.S. Gulf Coast, and has already produced large volumes of oil, gas and condensate from so-called conventional reservoirs encountered in many areas, especially Southeast Mississippi and South Alabama. The Trend must be viewed as a hybrid “unconventional” play, with both conventional and unconventional elements. Despite the recent disappointments, which are readily understood, there remains tremendous potential for the discovery and production of large volumes of hydrocarbons stratigraphically trapped within the Brown Dense Limestone. Adequate storage and permeability are critical for commercial liquids production, and Vision continues to favor the volatile oil / wet gas window of the BDL Trend. There are many Trend areas that appear to harbor sufficient storage, yet remain virtually unexplored, suggesting a bright future for ongoing exploration efforts within the greater Brown Dense Lime Trend.
Steve Walkinshaw, President, Vision Exploration
This report is intended to comprise a brief geological summary of the BDL Trend, and reflects the technical observations and professional opinions of Vision Exploration, LLC; if your company is interested in the Trend, and you would like to learn more about the BDL, or wish to take advantage of our Trend experience and technical expertise, please feel free to contact us.
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