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.
STATIC AND SEISMIC MODELLING OF A TURBIDITE CHANNEL COMPLEX (PAB FORMATION PAKISTAN) AUTHORS T. EUZEN S. ROHAIS A. BOURGEOIS P. NIVLET O. LERAT R. DESCHAMPS E. ALBOUY and R. ESCHARD Adress Institut Français du Pétrole 1 et 4 Avenue de Bois-Préau 92852 Rueil-Malmaison Cedex France Introduction: Deep offshore prospects and the improvement of oil recovery are currently topics of major importance of the petroleum industry. Reservoir characterisation using seismic imaging and interpretation tools is often used to improve the understanding of deepwater reservoirs. However the 3D lithoseismic analysis and interpretation of turbidite complexes requires good a priori knowledge of both
The main controls on petroleum accumulations in sedimentary basins include source rock distribution, thermal maturity, migration pathways, as well as structural and stratigraphic traps. While shale plays and conventional reservoirs are endmembers governed by contrasted geological processes, unconventional hybrid systems represent a continuum between them and share common characteristics with both. The Montney Formation provides a well-documented example of such a play, where petroleum distribution is controlled by a combination of downdip increase of thermal maturity, fluid migration influenced by lateral and vertical permeability variations, and pressure compartmentalization. In this paper, we integrate publicly available data from thousands of wells within a well-defined stratigraphic framework, to illustrate these regional and local controls on petroleum distribution in the Montney hybrid play. We demonstrate that produced gas compositional mapping is a powerful tool that complements comparatively sparse data from core or cuttings-based organic geochemistry and petrography methods, to provide an unparalleled level of detail of petroleum distribution at various scales. Coupling this compositional mapping with reservoir pressure data and published faults reveals a strong control of the structural framework on petroleum migration routes. The main targets of horizontal drilling in the Montney play are carrier beds that were charged by up-dip migrating petroleum and experienced further thermal maturation during the burial history. The relative contribution of different source rocks to this petroleum system remains speculative and further investigation is needed to solve this conundrum.
Abstract Thick Spathian deposits of the Lower Triassic Montney Formation are preserved in northeastern British Columbia and west-central Alberta, where they hold massive amounts of unconventional resources. Understanding the internal architecture of these marine deposits at basin-scale can provide a framework to better predict the distribution of source-rocks, reservoirs and seals within this petroleum system and to investigate their control on hydrocarbon generation and migration pathways. Ultimately, this high resolution stratigraphic framework can be used to investigate the impact of geological heterogeneities on well performance at the regional scale. In northeastern British Columbia, the Spathian deposits consist mainly of offshore and offshore transition sediments forming a wedge prograding from northeast to southwest. This wedge is punctuated by major marine flooding surfaces bounding parasequence sets that can be correlated regionally owing to their characteristic gamma ray logs signature and to the high density of well and core control. The regional correlation of these parasequence sets, based on over 1450 wells, reveals well-defined clinoform morphologies characterized by topset, foreset and bottomset geometries along a proximal-distal depositional profile. The facies analysis and the characteristic dimensions of these morphologies are consistent with deposition in a predominantly siliciclastic shoreface to shelf setting and marks a significant contrast to the ramp setting of hybrid clastic-carbonate lithologies which prevailed during the Griesbachian to Smithian. The stratigraphic architecture is analogous to “subaqueous shelf-prism clinoforms” that have been described on numerous present-day and ancient continental shelves. Subaqueous shelf-prism clinoforms typically display a sigmoidal shape in the dip direction and along-shore-elongated depositional thick in plan-view. This geometry results from the interaction of clastic sediment input with shelf hydrodynamic processes such as storm generated waves and sediment gravity flows, as well as nearshore and offshore bottom currents. Consequently, the topset, foreset and bottomset of these clinoforms are characterized by different depositional facies that can be predicted and mapped at basin-scale, over hundreds of kilometres. In the Spathian depositional system of Western Canada, clinoform bottomset facies are mainly a product of suspension deposition, hemipelagic sedimentation and mineral precipitation. These facies form the main source-rock intervals within the Montney Formation, due to anoxic conditions and lower sedimentation rates resulting in better preservation of organic matter. Clinoform foresets result from traction transport processes of coarser siliciclastics and higher sedimentation rates, forming thick, mostly organic-lean intervals with better reservoir quality. Foreset deposits form the thickest part of the Spathian parasequence sets and are the main targets of horizontal drilling and multistage fracturing. Clinoform topsets mainly consist of shoreface to offshore transition deposits and are poorly preserved due to the erosion under the top Montney unconformity. The distribution of the depositional thick in map view and along a strike-oriented regional cross-section suggest that these deposits were influenced by major structural elements at basin scale. The regional flooding surfaces bounding the parasequence sets might form extensive permeability barriers that potentially control up-dip migration of hydrocarbons within the Montney petroleum system.
Abstract Trace metal elements (TMEs) are commonly used to reconstruct the environmental conditions present during the deposition of organic-rich sediments. For example, TME concentrations controlled by changes in primary productivity and redox conditions are widely used in paleoenvironmental studies. Recently, these proxies have undergone a resurgence of interest and are commonly used in large-scale (10–1000 km) studies. However, applying these geochemical proxies at basin scale while ignoring variations in sedimentation rates (SR) may lead to misinterpretation of paleoenvironmental conditions. Here, we show how SR can affect the geochemical records and may lead to incorrect interpretations of TME evolution. Accounting for SR, we computed the authigenic fraction accumulation rates of key TMEs in the Upper Montney Formation and Doig Phosphate (Triassic, western Canada), and we correct the concentration of these elements in the Vaca-Muerta Formation (Jurassic–Cretaceous, Argentina). Our SR-corrected TME proxies require a different interpretation of paleoenvironmental conditions (e.g., primary productivity, basin restriction) compared to conventional TME results and highlight that elementary enrichments commonly interpreted as indicative of anoxic depositional environments may reflect low SR and the formation of condensed intervals. This work also introduces a new workflow to account for SR in paleoenvironmental studies at basin scale and over long time periods.
This study focuses on the Lower–Middle Triassic Montney, Sunset Prairie, Doig and Halfway formations from the foreland basin of the Canadian Cordillera (Alberta and British Columbia). Based on core and outcrop descriptions, the correlation of 400 wells, and on mineralogical analyses, this study interprets the basin-scale, 3D-stratigraphic architecture of these formations and discusses the controls on its evolution. Well correlation highlights four sequences (1–4) interpreted to occur in two second-order cycles (A and B). In this work, the Early Triassic Montney Formation and the early Middle Triassic Sunset Prairie Formation are interpreted to consist of three third-order sequences (1–3) related to the first second-order cycle (cycle A). The Middle Triassic Doig and Halfway formations are interpreted to consist of a fourth sequence (4) related to a second second-order cycle (cycle B). Integration of the stratigraphic surfaces with previously published biostratigraphic analyses emphasizes a major time gap of c. 2 myr between these two cycles, interpreted to record a major reorganization of the basin. Mineralogical analyses suggest that during cycle A, sediments were delivered from the east (Canadian Shield); whereas in cycle B, additional sources from the west (proto-Canadian Cordillera) occurred. This study shows that the stratigraphic architecture evolution was affected by the structural heritage of the basin and continental geodynamic evolution. This study provides a large-scale understanding on the controls of the stratigraphic architecture of the Lower and Middle Triassic strata, suggesting local and regional controls on the reservoir extension and unconventional play configuration within these strata.
Abstract The facies associations of the overflow deposits associated with turbidite channels were studied in the outcrops of the Maastrichtian Pab Sandstone, in SW Pakistan. In this area, a basin-floor fan was preserved from the platform to the deep basin setting. In the mid-fan setting, a channel complex crops out in three dimensions, and consists of a dozen channels and their overflow deposits, including levees, crevasse lobes and spill-over lobes. The overbank deposits can be directly in contact with the channel-fill, but, in many cases, matrix-supported debris-flow deposits made lenses close to the channel base. Heterolithic drapes of thin-bedded turbidite deposits were also preserved along the channel margins. A three-dimensional (3D) static model describing the heterogeneity distribution within the turbiditic channel complex was compiled using both stochastic and deterministic approaches in a site where two channels were laterally connected by overbank deposits. Petro-acoustic properties derived from a subsurface database were then assigned to the facies to perform seismic simulations. The synthetic seismic simulations showed that the channel base can easily be misinterpreted compared to the geological model. Dynamic modelling, such as well test and streamline simulations, was also performed using the model to assess the transition between the channel and overbank deposits from a dynamic point of view. As a result of the streamline simulations, the overbank deposits connecting the channel homogenized the pressure regime in the reservoir. However, the sweeping efficiency of water injection can be affected by the heterogeneity distribution along the channel margins. A significant volume of oil could also be by-passed because of the occurrence of early water breakthrough through the spill-over lobes, or because the flow slowed down when it reached the heterogeneity along the channel margin.
