The Lower Cretaceous Upper Mannville Formation in West- Central Alberta has been intensively penetrated by wells targeting deeper reservoirs during the last decades. Production and well log data in this area suggest that significant volumes of gas are still present in both conventional and tight reservoirs of this formation. The Upper Mannville reservoirs in West-Central Alberta consist of fluvial sandstones filling incised valleys. The valley infills are made up of arkosic sandstones with a complex mineralogy. The matrix of these sandstones is made up of various amounts of quartz, feldspars, clay minerals and rock fragments. They were subjected to a complex diagenetic history and the resulting paragenesis influenced the present reservoir properties. Consequently, heterogeneities in the petrophysical properties result in significant exploration risks and production issues. We present in this paper results of a diagenetic study, performed within a well constrained stratigraphic framework, that aims at understanding the impact of mineralogy and diagenesis on reservoir quality evolution. Seventy one core samples from eight wells were collected to perform a petrographic analysis, and to propose a paragenetic sequence. Four main diagenetic events were identified that occurred during burial: - clay coating around the grains; - compaction/dissolution of matrix grains; - quartz and feldspars dissolution that initiated smectite-illite transformation and kaolinisation; - carbonate cementation in the remaining pore space. Clay minerals content and carbonate cementation are the main factors that altered the reservoir quality of these sandstones. The Smectite-Illite transformation was initiated after potassium was released in the formation fluids due to K-feldspars dissolution. This transformation proportionally increased with temperature during burial. Carbonate cementation occured during the uplift phase of the basin, intensively plugging the pore space where the clay content is reduced. Additional SEM and XRD analyses allowed characterizing and quantifying more accurately the different mineralogical phases occluding the porous network. The characterization of both mineralogy and petrophysical properties gives useful keys to locate the diagenetic phases laterally and vertically, and to predict the petrophysical properties distribution.

Impact of mineralogy and diagenesis on reservoir quality of the Lower Cretaceous Upper Mannville formation (Alberta, Canada) / R. Deschamps, E. Kohler, M. Gasparrini, O. Durand, T. Euzen, F. Nader. - In: OIL & GAS SCIENCE AND TECHNOLOGY. - ISSN 1294-4475. - 67:1(2012), pp. 31-58.

Impact of mineralogy and diagenesis on reservoir quality of the Lower Cretaceous Upper Mannville formation (Alberta, Canada)

M. Gasparrini
Writing – Original Draft Preparation
;
2012

Abstract

The Lower Cretaceous Upper Mannville Formation in West- Central Alberta has been intensively penetrated by wells targeting deeper reservoirs during the last decades. Production and well log data in this area suggest that significant volumes of gas are still present in both conventional and tight reservoirs of this formation. The Upper Mannville reservoirs in West-Central Alberta consist of fluvial sandstones filling incised valleys. The valley infills are made up of arkosic sandstones with a complex mineralogy. The matrix of these sandstones is made up of various amounts of quartz, feldspars, clay minerals and rock fragments. They were subjected to a complex diagenetic history and the resulting paragenesis influenced the present reservoir properties. Consequently, heterogeneities in the petrophysical properties result in significant exploration risks and production issues. We present in this paper results of a diagenetic study, performed within a well constrained stratigraphic framework, that aims at understanding the impact of mineralogy and diagenesis on reservoir quality evolution. Seventy one core samples from eight wells were collected to perform a petrographic analysis, and to propose a paragenetic sequence. Four main diagenetic events were identified that occurred during burial: - clay coating around the grains; - compaction/dissolution of matrix grains; - quartz and feldspars dissolution that initiated smectite-illite transformation and kaolinisation; - carbonate cementation in the remaining pore space. Clay minerals content and carbonate cementation are the main factors that altered the reservoir quality of these sandstones. The Smectite-Illite transformation was initiated after potassium was released in the formation fluids due to K-feldspars dissolution. This transformation proportionally increased with temperature during burial. Carbonate cementation occured during the uplift phase of the basin, intensively plugging the pore space where the clay content is reduced. Additional SEM and XRD analyses allowed characterizing and quantifying more accurately the different mineralogical phases occluding the porous network. The characterization of both mineralogy and petrophysical properties gives useful keys to locate the diagenetic phases laterally and vertically, and to predict the petrophysical properties distribution.
La Formation Mannville Supérieur du Crétacé Inférieur d’Ouest-Central Alberta a été intensivement forée les précédentes décennies par des puits visant des réservoirs plus profonds. Cependant, les données de production dans ce secteur suggèrent que des volumes significatifs de gaz soient présents dans les réservoirs tant conventionnels que non conventionnels (“tight reservoirs”) de cette formation. Les réservoirs de la Formation Mannville Supérieur d’Ouest-Central Alberta sont constitués de grès fluviatiles remplissant des vallées incisées. Ces grès présentent une minéralogie complexe, avec des quantités variables de quartz, de feldspaths, de minéraux argileux et des fragments de roche. Ils ont été soumis à une histoire diagénétique complexe et la paragenèse qui en résulte a eu un impact sur leurs propriétés réservoirs. Par conséquent, les hétérogénéités dans les propriétés réservoirs induisent des risques significatifs en termes d’exploration et de production de ces réservoirs. Nous présentons dans cet article les résultats de l’étude diagénétique, effectuée dans un cadre stratigraphique bien contraint, visant à comprendre l’impact de la minéralogie et de la diagenèse sur l’évolution de la qualité des réservoirs. Soixante et onze échantillons prélevés sur huit puits ont permis de réaliser une analyse pétrographique et proposer une séquence paragénétique. Quatre événements diagénétiques principaux ont été identifiés et sont liés à l’enfouissement du bassin : – coating d’argile autour des grains; – compaction/dissolution de grains matriciels; – dissolution partielle des grains de quartz et de feldspaths, qui ont initiés la transformation smectite-illite et kaolinisation; – cimentation carbonatée dans l’espace poreux restant. Les transformations de minéraux argileux et la cimentation carbonatée sont les facteurs principaux qui ont affecté la porosité et la perméabilité de ces grès. La transformation Smectite-Illite a été amorcée après que le potassium issu de la dissolution des feldspaths ait été libéré dans le fluide de formation. Cette transformation augmente proportionnellement avec l’enfouissement et la température. Une intense cimentation carbonatée est survenue pendant la phase de soulèvement du bassin, colmatant de façon très significative l’espace poreux là où la teneur en argile était réduite. Des analyses au Microscope Électronique à Balayage et des analyses de DRX ont permis de caractériser et d’évaluer quantitativement les différentes phases diagénétiques responsables de l’évolution de l’espace poreux. La caractérisation de la minéralogie et de l’évolution des propriétés pétrophysiques des réservoirs apportent des clés utiles pour localiser les différentes phases diagénétiques temporellement et spatialement, afin de prédire la distribution de propriétés pétrophysiques.
pyrite formation; origin; basin; sandstones; carbonate; evolution; sequence; foreland; burial; geochemistry
Settore GEO/02 - Geologia Stratigrafica e Sedimentologica
2012
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/722335
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