The Eagle Ford play in south Texas is currently one of the hottest plays in the United States. In 2012, the average Eagle Ford rig count (269 rigs) was 15% of the total US rig count. Assessment of Eagle Ford oil and gas resources and their associated uncertainties in the early stages is critical for optimal development. The objective of our research was to assess Eagle Ford shale oil and gas reserves, contingent resources, and prospective resources.Probabilistic decline curves using Markov Chain Monte Carlo (MCMC) were used to forecast reserves and resources. The Eagle Ford play from the Sligo Shelf Margin to the San Marcos Arch was divided into 8 different production regions based on geology, fluid type, and well performance. We used the Duong model switching to the Arps model with b = 0.3 at the minimum decline rate to model the linear flow to boundary-dominated flow behavior often observed in shale plays. Cumulative production after 20 years predicted from Monte Carlo simulation combined with reservoir simulation was used as prior information in the Bayesian decline-curve methodology. Probabilistic type decline curves for oil and gas were then generated for all production regions. Individual-well reserves and resources estimates were aggregated probabilistically within each production region and arithmetically between production regions.The total oil reserves and resources range from a P 90 of 5.3 to P 10 of 28.7 billion barrels of oil (BBO), with a P 50 of 11.7 BBO; the total gas reserves and resources range from a P 90 of 53.4 to P 10 of 313.5 trillion cubic feet (TCF), with a P 50 of 121.7 TCF. These reserves and resources estimates are much higher than the U.S. Energy Information Administration's 2011 recoverable resource estimates of 3.35 BBO and 21 TCF. The results of this study provide a critical update of the reserves and resources estimates and their associated uncertainties for the Eagle Ford shale formation of South Texas.

Most estimates of the resource endowment [original gas in place (OGIP)] reported for world unconventional gas start with Rogner's top-down study (Rogner 1997). That global estimate is most likely quite conservative because the oil and gas industry has discovered enormous volumes of shale gas around the world since the 1990s. The data from these new reservoirs add substantially to our understanding of the unconventional resource base. Furthermore, the uncertainty of Rogner's assessment was not quantified. Thus, considering the uncertainty, a new assessment of original unconventional gas in place worldwide is needed.The objective of this project was to estimate the probabilistic distributions of original volumes of gas trapped in coalbed, tightsand, and shale reservoirs worldwide. To accomplish this objective, we reviewed published assessments of coal and conventional and unconventional resources and established the quantitative relationship between unconventional gas [coalbed methane (CBM), tight-sands gas, and shale gas] and the conventional hydrocarbon (coal, conventional gas, and oil) resource endowments for North America. Then, we used this relationship to extrapolate original unconventional gas in place worldwide. Our assessment of the world resource endowment established an unconventional OGIP of 83,400 Tcf (P10) to 184,200 Tcf (P90), which is 2.6 to 5.7 times greater than Rogner's estimate of 32,600 Tcf.Our regional assessments of unconventional OGIP should help industry better target its efforts to rapidly accelerate the development of unconventional gas resources worldwide. The methodology used to assess the distribution of each type of unconventional OGIP may be used to estimate unconventional gas resources at the country or basin level, given knowledge of the coal in place and technically recoverable resources of conventional hydrocarbons.Review of Rogner's Assessment Methods. Rogner (1997) estimated global CBM resources by use of the distribution of coal resources and estimated values for coalbed gas content. On the bassis of Kuuskraa et al. (1992), Rogner reported that the worldwide coalbed gas resources range from 2,980 to 9,260 Tcf (85 to 262 Â 10 12 m 3 ). However, only the top 12 coal resource countries were included in the assessment. Although this initial work focused on these major coal-bearing areas, many other countries, such as Spain, Hungary, and France, have smaller but significant coal reserves and, by extension, coalbed gas resources. Thus, more countries should be included to improve Rogner's estimates.Rogner's methodology for estimating world shale-gas resources, which he states is quite speculative, assumed that shale-oil occurrence outside the US contains the US gas-in-place value of 17.7 Tcf/Gt. However, it is difficult to estimate shale-oil resources, and it is not certain that the two even correlate. Consequently, we believe an improved region-level shale-gas OGIP assessment methodology is required.Tight-sands-gas reservoirs are present in every petroleum province. In Rogner (1997...

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Arrival of Laramide uplift sediments to the Texas Gulf Coastal Plain and northwestern Gulf of Mexico during the early Paleogene is recorded in strata of the Wilcox Group as a significant increase in sediment accumulation and with the appearance of 65-52 Ma detrital zircons that correspond with the timing of late Laramide uplift. New U-Pb dating of detrital zircons by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) for samples obtained from the Lower Paleocene Tehuacana Member through the Lower Eocene Queen City Formation in east-central Texas identifies the Hooper Formation of the Wilcox Group as the oldest stratigraphic unit to contain 65-52 Ma ages. Late appearance of 65-52 Ma detrital zircons in the Hooper Formation is correlated with unroofed Laramide magmatic intrusions or nearly syndepositional volcaniclastic sources; whereas older detrital zircons are inferred to be derived primarily from sedimentary cover and basement rocks exposed during uplift of Laramide blocks. Potential source region and Gulf Coastal Plain detrital zircon data support a relatively similar paleodrainage area and sediment sources for eastcentral Texas Tehuacana Member to Carrizo Formation and central Louisiana Wilcox Group data, and for east-central Texas Queen City Formation and central Louisiana middle-upper Claiborne Group data. South Texas Wilcox Group data contrast with data from these samples and support a different paleodrainage area and sediment sources for the south Texas region. We propose that headwaters sourced from southeastern Wyoming to the southern Rocky Mountain region delivered sediments to east-central Texas and central Louisiana during the Paleocene to Middle Eocene. Pronounced Mesoproterozoic and Neoproterozoic detrital zircons in the lower Claiborne Group of east-central Texas and the middle-upper Claiborne Group of central Louisiana are attributed to new or unroofed recycled sediments with Grenvillian age detrital zircons incorporated from the Ouachita region and other proximal locations in the preexisting paleodrainage area. The inferred paleodrainage area for east-central Texas and central Louisiana includes most of the Rocky Mountain Laramide uplift blocks, has a southern boundary separating it from a south Texas paleodrainage, and an eastern boundary roughly coincident with the Mississippi embayment, which separates it from Appalachian Mountains drainages.