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...

Summary Gas wells in low-permeability formations usually require hydraulic fracturing to be commercially viable. Pressure transient analysis in hydraulically fractured tight gas wells is commonly based on analysis of three flow regimes: bilinear, linear, and pseudoradial. Without the presence of pseudoradial flow, neither reservoir permeability nor fracture half-length can be independently estimated. In practice, as pseudoradial flow is often absent, the resulting estimation is uncertain and unreliable. On the other hand, elliptical flow, which exists between linear flow and pseudoradial flow, is of long duration (typically months to years). We can acquire much rate and pressure data during this flow regime, but no practical well test analysis technique is currently available to interpret these data. This paper presents a new approach to reliably estimate reservoir and hydraulic fracture properties from analysis of pressure data obtained during the elliptical flow period. The method is applicable to estimate fracture half-length, formation permeability, and skin factor independently for both infinite- and finite-conductivity fractures. It is iterative and features rapid convergence. The method can estimate formation permeability when pseudoradial flow does not exist. Coupled with stable deconvolution technology, which converts variable production-rate and pressure measurements into an equivalent constant-rate pressure drawdown test, this method can provide fracture-property estimates from readily available, noisy production data. We present synthetic and field examples to illustrate the procedures and demonstrate the validity and applicability of the proposed approach.