Shale-gas resource plays can be distinguished by gas type and system characteristics. The Newark East gas field, located in the Fort Worth Basin, Texas, is defined by thermogenic gas production from low-porosity and low-permeability Barnett Shale. The Barnett Shale gas system, a self-contained source-reservoir system, has generated large amounts of gas in the key productive areas because of various characteristics and processes, including (1) excellent original organic richness and generation potential; (2) primary and secondary cracking of kerogen and retained oil, respectively; (3) retention of oil for cracking to gas by adsorption; (4) porosity resulting from organic matter decomposition; and (5) brittle mineralogical composition. The calculated total gas in place (GIP) based on estimated ultimate recovery that is based on production profiles and operator estimates is about 204 bcf/section (5.78 × 10 9 m 3 /1.73 × 10 4 m 3 ). We estimate that the Barnett Shale has a total generation potential of about 609 bbl of oil equivalent/ac-ft or the equivalent of 3657 mcf/ac-ft (84.0 m 3 /m 3 ). Assuming a thickness of 350 ft (107 m) and only sufficient hydrogen for partial cracking of retained oil to gas, a total generation potential of 820 bcf/section is estimated. Of this potential, approximately 60% was expelled, and the balance was retained for secondary cracking of oil to gas, if sufficient thermal maturity was reached. Gas storage capacity of the Barnett Shale at typical reservoir pressure, volume, and temperature conditions and 6% porosity shows a maximum storage capacity of 540 mcf/ac-ft or 159 scf/ton.

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Unconventional shale-gas systems: The Mississippian Barnett Shale of north-central Texas as one model for thermogenic shale-gas assessment

The second edition of The Biomarker Guide is a fully updated and expanded version of this essential reference. Now in two volumes, it provides a comprehensive account of the role that biomarker technology plays both in petroleum exploration and in understanding Earth history and processes. Biomarkers and Isotopes in the Environment and Human History details the origins of biomarkers and introduces basic chemical principles relevant to their study. It discusses analytical techniques, and applications of biomarkers to environmental and archaeological problems. The Biomarker Guide is an invaluable resource for geologists, petroleum geochemists, biogeochemists, environmental scientists and archaeologists.

The Biomarker Guide

Rock-Eval pyrolysis is used to rapidly evaluate the petroleum-generative potential and thermal maturity of rocks. Accurate conclusions require programs every 30-60 ft (9-18 m), understanding of interpretive pitfalls, and supporting data, such as visual kerogen, vitrinite reflectance, and elemental analyses. The generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography. Most coals show high S2/S3 (>5) and low HI values (< 300 mg HC/g TOC). Migrated oil and mud additives, which alter Rock-Eval data, can sometimes be removed by special processing. For immature rocks, bimodal S2 peaks and PI values over 0.2 indicate contamination. Pyrolysis downgrades organic-poor, clay-rich rocks, which show lower HI and higher Tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays. Tmax values for small S2 peaks (< 0.2 mg HC/g TOC) are unreliable. Tmax is affected by maturation, organic matter type, contamination, and the mineral matrix. S3 is sensitive to inorganic and adsorbed carbon dioxide, and to instrumentation problems. Acidification of carbonate-rich samples and proper maintenance improves S3 measurement. Constant sample weights (100 mg) are recommended. Below a threshold weight, Tmax increases by up to 10°C, and other parameters decrease. Organic-rich samples, which overload the detector, can be diluted with carbonate. Detector linearity is determined by pyrolyzing various weights of an organic-rich rock.

Guidelines for Evaluating Petroleum Source Rock Using Programmed Pyrolysis

The North Sea is a major continental basin filled with early Paleozoic to Recent sediments. Though graben formation started in the Triassic, the last major period of extension occurred between the Middle Jurassic and the mid-Cretaceous. Following the faulting and graben formation associated with this extension, subsidence within the central North Sea was widespread and uniform and has created a saucershaped sedimentary basin. This was filled successively by chalks, sandstones, and finally, during most of the Tertiary, by shales and mudstones. We examined the subsidence of six wells down the middle and two on the flanks of the Central Graben. In the period of widespread steady subsidence the water-loaded basement depth in the middle increased by 1100–1400 m. On the flanks the basement subsided 600–700 m. We suggest that most of this subsidence results from the thermal relaxation of the lithosphere which was thinned during a Middle Jurassic to mid-Cretaceous stretching of the crust. Assuming a crustal stretching and associated lithospheric thinning of between 50 and 100% in the middle and decreasing on either side, we obtained a good match to the observed amplitude and rate of subsidence. The Middle Jurassic to mid-Cretaceous subsidence which is found within the graben proper we relate to the fault-controlled initial subsidence which occurred during the actual stretching. The measured heat flow is compatible with such a stretching model. Though there is no seismic refraction data across the Central Graben, this model is strongly supported by evidence of a thinner crust under the Viking Graben to the north and the Witchground/Buchan Graben complex to the east. Using the above observations as the basis for a geological interpretation, we examined the thermal maturity and hydrocarbon potential of certain sedimentary horizons in the northern section of the Central Graben. In analyzing the various wells we extended previous work on the compaction correction to handle overpressuring and mixed lithologies in backstripping studies. Further, we expanded these methods to include the variation of thermal conductivity, and calculations of the degree of thermal maturation of the deposited sediments, through time.

Continental stretching: An explanation of the Post-Mid-Cretaceous subsidence of the central North Sea Basin

Organic geochemical proxies of paleoceanographic, paleolimnologic, and paleoclimatic processes

Les etudes fondamentales realisees sur les kerogenes a l'aide de diverses methodes physico-chimiques d'analyse ont permis de mettre au point une methode et un appareillage adaptes a l'exploration petroliere. On expose dans cet article la mise au point de cette methode et on montre, a l'aide des parametres qu'elle permet d'obtenir, ses applications dans le domaine de l'exploration petroliere - reconnaissance des differents types de roche mere et de leur potentiel petrolier; - caracterisation de leur degre d'evolution (zone a huile - zone a gaz). On montre aussi que cette methode convient particulierement bien a l'estimation du rendement en huile des roches bitumineuses et a l'etude de la qualite et du rang des charbons.

Méthode rapide de caractérisation des roches mètres, de leur potentiel pétrolier et de leur degré d'évolution

Concue pour repondre aux besoins de l'exploration petroliere, la methode de pyrolyse Rock-Eval est maintenant largement utilisee. Elle fournit, en effet, et d'une facon rapide, differentes informations sur le contenu organique des roches, telles que le potentiel petrolier des series rencontrees, la nature des kerogenes, leur etat de maturation. En ce qui concerne le materiel, deux nouvelles versions ont ete mises au point a l'Institut Francais du Petrole (IFP) depuis l'apparition en 1977 des premiers appareils Rock-Eval : un Rock-Eval II completement automatise grâce a un microprocesseur et dote, en option, d'un module de dosage du carbone organique; un Rock-Eval III (Oil Show Analyzer) qui se distingue du precedent par le fait qu'il analyse separement le gaz et l'huile et qu'il effectue le dosage du carbone organique a la place du pic S3. En ce qui concerne l'interpretation de la methode, l'experience acquise tant par les applications aux bassins sedimentaires que par les etudes experimentales menees en laboratoire a permis de mieux connaitre les parametres utilises (pics S1, S2, S3, temperature de pyrolyse Tmax) a travers leurs variations et, de la, de mieux discerner les limites d'application de la methode. En ce qui concerne l'application de la methode, la representation verticale des resultats sous forme de logs geochimiques conduit a une interpretation a la fois efficace et pratique. Des abaques et des diagrammes de reference permettent de caracteriser les roches meres (potentiels petroliers, types de matiere organique, degre d'evolution, alterations. . . ) ainsi que les phenomenes de migration. L'etablissement de cartes geochimiques a l'echelle du bassin devient alors possible. Enfin la methode est sortie du domaine de l'exploration petroliere proprement dite pour trouver des applications a l'etude des charbons, des roches bitumineuses, des sediments recents et meme aux techniques du raffinage et de la recuperation secondaire des bruts.

La pyrolyse Rock-Eval et ses applications. Première partie.

Elevation of temperature and pressure during burial of sediments results in a physiochemical transformation of the kerogen, and particularly in changes of elementary composition, infrared spectra, and thermal properties of kerogen. The combined variation of these characters defines an evolution path for each kerogen type (organic matter from similar environments of deposition group along the same evolution path). The degree of evolution of individual samples can be evaluated by using these techniques. An experimental evolution test, using thermogravimetric, infrared, and associated techniques, can reproduce the natural degradation of kerogen during its burial in a sedimentary basin. The test allows the petroleum geologist to make an evaluation of the petroleum potential of a given formation in the buried parts of a sedimentary basin, by using shallow or surface samples and simulating their degradation in the laboratory. The major products generated during the three successive steps of kerogen evolution are carbon dioxide and water; oil; gas. The relative abundance of these products depends on the composition of the original kerogen. Kerogen from a "high" evolution path generates abundant oil, whereas that from a "low" evolution path produces methane at depth, but little or no oil.

Influence of Nature and Diagenesis of Organic Matter in Formation of Petroleum

Presentation, sur 3 series geologiques, de la signification geochimique pouvant etre attribuee aux parametres obtenues par la pyrolyse Rock-Eval effectuee sur des matieres organiques pures ou sur des roches riches en matiere organique

Jean Espitalie

Papers

Méthode rapide de caractérisation des roches mètres, de leur potentiel pétrolier et de leur degré d'évolution

La pyrolyse Rock-Eval et ses applications. Première partie.

Influence of Nature and Diagenesis of Organic Matter in Formation of Petroleum

La pyrolyse Rock-Eval et ses applications. III

Source rock characterization method for petroleum exploration