Current models used to forecast production in unconventional oil and gas formations are often not producing valid results. When traditional decline curve analysis models are used in shale formations, Arps b-values greater than 1 are commonly obtained, and these values yield infinite cumulative production, which is non-physical.. Additional methods have been developed to prevent the unrealistic values produced, like truncating hyperbolic declines with exponential declines when a minimum production rate is reached. Truncating a hyperbolic decline with an exponential decline solves some of the problems associated with decline curve analysis, but it is not an ideal solution. The exponential decline rate used is arbitrary, and the value picked greatly effects the results of the forecast. A new empirical model has been developed and used as an alternative to traditional decline curve analysis with the Arps equation. The new model is based on the concept of logistic growth models. Logistic growth models were originally developed in the 1830s by Belgian mathematician, Pierre Verhulst, to model population growth. The new logistic model for production forecasting in ultra-tight reservoirs uses the concept of a carrying capacity. The carrying capacity provides the maximum recoverable oil or gas from a single well, and it causes all forecasts produced with this model to be within a reasonable range of known volumetrically available oil. Additionally the carrying capacity causes the production rate forecast to eventually terminate as the cumulative production approaches the carrying capacity. The new model provides a more realistic method for forecasting reserves in unconventional formations than the traditional Arps model. The typical problems encountered when using conventional decline curve analysis are not present when using the logistic model. Predictions of the future are always difficult and often subject to factors such as operating conditions, which can never be predicted. The logistic growth model is well established, robust, and flexible. It provides a method to forecast reserves, which has been shown to accurately trend to existing production data and provide a realistic forecast based on known hydrocarbon volumes. / text

The Eagle Ford is a well-known source rock for both sandstone (Woodbine) and carbonate (Austin and Buda) hydrocarbon reservoirs in East and South Texas. Recent discoveries have demonstrated that source rocks, such as the Eagle Ford, are capable of producing significant volumes of gas and oil. At the same time, variations in well producibility indicate that these rocks, like conventional reservoirs, display considerable geological heterogeneity. Yet, only limited research has been published on the subsurface stratigraphy and character of Eagle Ford facies. Understanding the types, controls, and distribution of these heterogeneities requires in-depth rock-based studies. In order to characterize Eagle Ford facies, 27 cores from 13 counties were investigated for rock textures, fabrics, sedimentary structures, and fossil assemblages. These studies were supported by light and electron microscopy as well as analysis of elemental chemistry and mineralogy. Regional subsurface stratigraphic correlations and facies distributions were defined using wireline logs calibrated from core studies. In South Texas, the Eagle Ford Formation was deposited during a second-order transgressive/regressive cycle on the flooded, oxygen-restricted Comanche Shelf. Nine depositional facies consisting predominately of organic-rich, fine-grained (5.0 % TOC) to coarser-grained (3.05 % TOC) fabrics were identified. Facies developed in low-energy environments episodically interrupted by higher-energy, event sedimentation (current winnowing, cohesive and non-cohesive density flows, and turbidity flows). Locally, these rocks show evidence of early diagenetic recrystallization of calcite. Concurrent water anoxia and organic matter preservation persisted locally into later Austin deposition, resulting in formation of a three-fold division of the Cenomanian-Coniacian Eagle Ford Formation. Common facies of lower and upper Eagle Ford members include (1) unlaminated, fissile, clay- and silica-rich, organic-rich mudrocks, (2) laminated, calcareous, organic-rich mudrocks, and (3) laminated, foraminifera- and peloid-rich, organic-rich packstones. The transitional Eagle Ford member consists of highly-cyclic (1) ripple-laminated, organic-rich wackestone (cycle base) and (2) burrowed, organic-lean lime wackestones (cycle top). Transitional Eagle Ford facies developed in oxygen-restricted, basinal depositional environments as distal equivalents to burrowed, foraminiferal lime wackestones of the Austin Formation. Facies complexities in the Eagle Ford stem from complicated and interrelated processes of sediment production and distribution, diagenesis, and water column chemistry. Integrated core studies shed light on both controls of facies formation and their spatial distribution. These findings provide a framework for upscaling the fine-scale, heterogeneous character of shelfal Eagle Ford mudrocks; thus allowing development of predictive models into the distribution of key reservoir properties in the subsurface. / text

This dissertation presents contributions to the understanding of the dynamic nature of permeability of Indonesian coal. It is the first-of-its-kind study, first presenting a comparison of experimental results with those obtained using existing analytical permeability models, and then modifying the existing anisotropic model for application to the unique physical structure of Indonesian coal. The first problem addressed in this dissertation was establishing the pressure-dependentpermeability of coal in a laboratory environment replicating in situ conditions for two coal types from the Sanga Sanga basin of Kalimantan, Indonesia. The change in permeability with depletion and the corresponding volumetric strain of coal were measured in the laboratory under uniaxial strain condition (zero lateral strain). Two gases, helium and methane, were used as the flowing fluids during experimental work. The results showed that, decreasing pore pressure resulted in significant decrease in horizontal stress and increased permeability. The permeability increase at low reservoir pressure was significant, a positive finding for Indonesian coals. Using the measured volumetric changes with variations in pressure, the cleat compressibility for the two coal types was estimated. In a separate effort, volumetric strain as a result of desorption of gases was measured using sister samples under unconstrained condition, in absence of the stress effect. Sorptioninduced strain processes were modeled using the Langmuir-type model to acquire the two important shrinkage parameters. All parameters calculated using the experimental data were used for the modeling exercise. The second component of this dissertation is the permeability variation modeling to enable projecting long-term gas production in the Sanga Sanga basin. For this, two commonly used isotropic permeability models were selected. These models, developed primarily for the San Juan coal, were unable to match the measured permeability data. This was believed to be due to the inappropriate geometry used to represent Indonesian coal, where butt cleats are believed to be absent. This was followed by application of the most recent model, incorporating partial anisotropy in coal. This consideration improved the modeling results although there clearly was room for improvement. The final challenge addressed in this dissertation was to consider the coal geometry appropriate for Indonesian coal, stack of sheets as opposed to a bundle of matchsticks. In order to incorporate the structural anisotropy for the stack of sheets geometry, two input parameters were modified, based on geo-mechanical anisotropy. After applying these to the modified model, the permeability modeling results were compared with the experimental data. The matches improved significantly. Finally, the effect of maximum horizontal stress on permeability of coal was estimated by using high and low maximum horizontal stress values and constant vertical and minimum horizontal stresses. The effect of maximum horizontal stress on permeability was found to be significant under uniaxial strain condition for both coals.

L’exploitation des ressources naturelles non conventionnelles en substitution du pétrole est un des défis du 21e siècle. La transformation microbiologique in situ de ces ressources en méthane est une des voies les plus prometteuses développées aujourd’hui mais son application reste à démontrer. Mes objectifs ont été de démontrer l'existence d'une conversion microbiologique en méthane de la matière organique (MO) de schistes immatures et de la quantifier pour extrapoler la production potentielle de méthane à l’échelle d’un bassin sédimentaire. Une méthode de détection et de suivi des consortia méthanogènes des schistes cartons en microcosmes, par une combinaison de PCR quantitative, GC-FID et pyrolyse Rock-Eval, a été mise au point et validée. Elle a été appliquée à l’étude de la distribution spatiale des méthanogènes dans les schistes cartons du bassin de Paris et à la démonstration de la méthanisation de la MO de ces roches. Les résultats montrent comme attendu la conversion des fractions solubles de la MO (bitume) par un consortium méthanogène isolé des schistes, mais également la transformation d’une fraction plus complexe (kérogène). L’absence de corrélation stricte entre la lithologie et la présence de méthanogènes actifs rend l’extrapolation au niveau du bassin plus difficile, mais la localisation des méthanogènes à la fois dans et hors les zones riches en MO constitue un avantage certain dans l'optique d'une exploitation économique de ces ressources. Ces travaux démontrent un potentiel élevé de production microbiologique de méthane dans le bassin de Paris et ouvrent la voie vers des études de faisabilité et rentabilité économique à l’échelle d’un site de production. / The exploitation of natural unconventional resources in substitution for petroleum is one of the challenges of the 21st century. In situ microbial transformation of these resources in methane is one of the most promising pathway currently developed, although its application needs to be demonstrated. My objectives were to demonstrate the existence of a microbial conversion into methane of the organic matter (OM) of immature shales, and to quantify it in order to extrapolate the potential for methane production of the rocks at the sedimentary basin scale. A method of detection and monitoring of methanogenic consortia from paper shales in microcosms, combining quantitative PCR, GC-FID and Rock-Eval pyrolysis, was developed and validated. It was used to study the spatial distribution of methanogens in paper shales of the Paris Basin and to demonstrate the methanization of the OM of these rocks. The results show the conversion of the soluble fractions of the OM (bitumen) by methanogenic consortia isolated from shales, but also the transformation of a more complex fraction (kerogen). No strict correlation was established between lithology and presence of active methanogens, which makes the extrapolation of methane production to the basin scale more difficult. However, the localization of methanogens in both OM-rich and OM-poor zones constitute an advantage in the perspective of an economic exploitation of these resources. This work demonstrates a great potential for microbial methane production in the Paris Basin and paves the way to studies of economic feasibility and profitability on the scale of a production site.

Oil is the world’s largest primary energy source. It dominates the transportation sector which underpins the world economy. Yet, oil is a nonrenewable resource, destined not to last forever. In the mid-2000s global conventional oil production stagnated, leading to rising oil prices and fears of permanent oil scarcity. These fears, together with the high prices, receded with the unforeseen emergence of a new supply source: tight oil. This licentiate thesis investigates unconventional tight oil production and its impacts on world oil supply in terms of resource availability and oil market dynamics, and in turn briefly discusses some possible wider economic, political and environmental implications of these impacts. The thesis is based on three papers. The first investigates the usefulness of bottom-up modelling by a retrospective study of past oil projections. The second looks at how unconventional tight oil production can be modelled on the well level using decline curve analysis. The third derives typical production parameters for conventional offshore oil fields, a growing segment of conventional production and a useful comparison to tight oil. The results show that tight oil production has increased resource availability significantly, as well as introduced a fast responding marginal supply source operating on market principles rather than political ones. The emergence of tight oil production has altered OPEC’s strategic options and led to a period of lower and less volatile oil prices. However, this condition of world oil supply can only last as long as the unconventional resource base allows, and, at the same time, total fossil fuel consumption will have to fall to limit climate change. It is concluded that this breathing space with lower oil prices could be used as an opportunity to develop and implement policy for an efficient managed decline of global oil use in order to achieve the dual goals of increased human economic welfare and limited climate change, and in the process preempt any future oil supply shortage. Unconventional tight oil production can both help and hinder in this endeavor. Accurate models and analyses of oil production dynamics and impacts are therefore crucial when maneuvering towards this preferred future.