Sedimentologic and lithostratigraphic properties and reservoir characterization of the Winnipeg Formation, Southern Saskatchewan

The Winnipeg Formation is a Late Ordovician siliciclastic unit that occurs in subsurface of SE Saskatchewan. Deposition of the formation took place on the northern shelf of the sub-circular intracratonic Williston Basin. In the study area, the formation consists of two members: a lower sandstone-dominated Black Island Member and an upper shale-dominated Icebox Member. Core and well-log data from twenty-one wells, along with a detailed petrographic study of rock samples from the cores, have been collected, described, integrated, and interpreted. Textural properties, sedimentary structures, temporal stacking nature of the various lithofacies, and spatial correlation of the logged sections are significant tools used for deciphering the depositional environment, reservoir properties, and cyclostratigraphic analysis of the studied rocks. Ten lithofacies (eight quartz arenite and quartz wacke sandstones, one siltstone, and one shale) are recognized and interpreted as beach to lower offshore accumulations. The sandstone lithofacies are discriminated based on their textural and structural properties, e.g., grain size, bioturbation index (BI), hydrodynamic sedimentary structures, and matrix content. Well correlations show that the basin was somewhat funnel-shaped, with the central axis deepening southward, whereas uplifted flanks to the north and east define the direction of the shallower basin margins. The vertical succession of the Winnipeg Formation is defined by shallow marine, high-energy sandstone of the Black Island Member overlain by relatively deep shelf shales of the Icebox Member. This stratigraphic succession underscores that deposition of the formation in the study area is characterized by a deepening-upward pattern. The Black Island Member's sandstone contains rhythmic units. Despite the overall deepening of the basin, the rhythmic units of the sandstone member underscore flooding events followed by progradation. These are parasequences within the transgressive systems tract. The transgression culminated during the deposition of the shales of the Icebox Member. The unconformity between Icebox and Yeoman Fm. defines the sea level drop and erosion of the uppermost beds (Roughlock Member) of the Winnipeg Formation. This regressive phase is represented by an erosional gap. Toward down south in North Dakota, there is a third member of the formation (Roughlock Member), which may represent the regressive phase of the T-R cycle. Subsurface mapping shows variations in the thickness in three zones. Zone-1 constitutes most of the mapped area, and the isopach map shows that the formation thickens approximately 140m towards the southeast of the province. Zone-2 occurs west of Zone-1 and shows a relatively thinner distribution approximately 60m of the formation. This zone shows a northeast-southwest trend possibly controlled by high paleotopographic features. In Zone-3, the formation gets thicker, approximately 80m west of Zone-2. Depth structure map and 3D mapping show the basin was shallower towards the north, northeast, and northwest and deeper towards the south. The porosity interval map shows the thickness of the porous interval increasing southeastward. The reservoir properties of Black Island Member are classified as quartz arenite, lithic arenite, two types of quartz wacke, feldspathic greywacke, and two types of mudrocks. Among the different well cores studied, the combined quartz arenite lithofacies constitute about 47% of the member, whereas the wacke and the mudrock lithofacies constitute 44% and 9%, respectively. Isopach maps of the various lithofacies indicate that the quartz arenites occur south to southeast, quartz wackes from southwest to southeast, and mudrocks toward the southeast of the studied area. Furthermore, the porosity of the quartz arenites ranges between ~22% and ~29%, whereas that of the wacke sandstone varies from ~8% to ~11%; these are affected by the different diagenetic processes. Thus, the sandstone lithofacies (the arenites and the wackes), which form a total thickness of about 91% of the member, are envisaged to constitute fair to excellent reservoirs.

Name thesis:degree_name

Master of Science (MSc)

Level thesis:degree_level

Master's

Discipline thesis:degree_discipline

Geology

Grantor dc:publisher

Faculty of Graduate Studies and Research, University of Regina

Year dc:date.issued

2023

Author dc:creator

• Iqbal, Naveed

Advisor dc:contributor.advisor

• Salad Hersi, Osman

Committee members dc:contributor.committeemember

• Qing, Hairuo
• Ghafur, Ala

Language dc:language.iso

en

DOI

https://doi.org/10.82465/4210

OAI identifier oai:identifier

oai:uregina.scholaris.ca:10294/16466