Geochemistry and Origin of Diagenetic Fluids and Paleohydrology of Paleozoic Carbonates in Southwestern Ontario, Canada

This study presents integrated petrography, stable carbon and oxygen isotopes, strontium isotopes and rare earth elements (REE) geochemistry as well as fluid inclusion microthermometry of diagenetic minerals from the Paleozoic carbonates succession of southwestern Ontario, Canada. These data provide new insights into the nature of fluids affecting these rocks and their spatial and temporal relationships. Fractures in the Paleozoic succession had an important role in reservoir enhancement, channelling of diagenetic fluids and migration of hydrocarbons. The spatial patterns, extent of dolomitization and dolomite petrography indicate that different hydrologic systems were responsible for dolomitization in each of the stratigraphic intervals considered. Fine-crystalline Devonian and Silurian dolomite formed in early stages of diagenesis whereas coarse-crystalline fracture-related Ordovician dolomite formed in later stages of diagenesis in burial environment and in the presence of hydrothermal fluids. The distinct δ18 Ofluid , δ 13 C, ΣREE values, and REESN patterns of dolomite from each age interval suggest compartmentalization of diagenetic fluids. The δ18 Ofluid and 87 Sr/ 86 Sr ratios indicate diagenetic fluids in each strata originated from coeval seawater and evolved through water/rock interaction. The more positive δ 18 Ofluid calculated from dolomite δ18 O values and the high salinity of Ordovician and Silurian brines and less radiogenic 87 Sr/86 Sr ratios of Ordovician dolomite relative to those of coeval seawater indicate mixing of Ordovician and Silurian connate waters with 18 O-enriched fluids influenced by dissolution of Silurian evaporites. The significantly higher dolomite Th values (75 to 120°C) from Devonian to Ordovician units relative to inferred maximum burial temperature (60 to 90°C) of these strata suggest involvement of hydrothermal fluids in the precipitation and/or recrystallization of dolomite. The presence of hydrocarbon-bearing fluid inclusions with high T h values (\u3e80°C) in late-stage calcite cements from Devonian to Ordovician and their negative δ 13 C values (approaching -32[per thousand]VPDB) implies that hydrothermal diagenetic fluids carried hydrocarbons. A thermal anomaly along the mid-continent rift during Devonian to Mississippian (Alleghanian orogeny) time likely was the source of excess heat in the Michigan Basin. The potential thermal buoyancy of hot brines was the driving force for migration of hydrothermal fluids from the center of the basin towards its margin through regional aquifers and network of fractures

CO2-Enhanced Oil Recovery Mechanism in Canadian Bakken Shale

The recovery factor in unconventional reservoirs is typically 5–10%, with extensive hydraulic fracturing and infill drilling to maintain the production rate. Concurrently, the rush towards decarbonization is opening up new possibilities for CO2 utilization, enhanced oil recovery (EOR) being one example. CO2-EOR in unconventional reservoirs presents an opportunity for both financial gain through improved recovery factors, as well as reducing the carbon footprint of the produced oil. In this work, we examine the CO2-EOR potential in 4 organic-rich shale samples from the Canadian Bakken Formation. A number of characterization tests alongside CO2 extraction experiments were performed to gain insight into the controlling factors of CO2-EOR in these ultra-tight formations. The results show CO2 can penetrate the tight rock matrix and recover a substantial amount of hydrocarbon. Concentration gradient driven diffusion is the dominant form of recovery

High rates of organic carbon burial in submarine deltas maintained on geological timescales

Burial of terrestrial organic carbon in marine sediments can draw down atmospheric CO2 levels on Earth over geologic timescales (≥105 yr). The largest sinks of organic carbon burial in present-day oceans lie in deltas, which are composed of three-dimensional sigmoidal sedimentary packages called clinothems, dipping from land to sea. Analysis of modern delta clinothems, however, provides only a snapshot of the temporal and spatial characteristics of these complex systems, making long-term organic carbon burial efficiency difficult to constrain. Here we determine the stratigraphy of an exhumed delta clinothem preserved in Upper Cretaceous (~75 million years ago) deposits in the Magallanes Basin, Chile, using field measurements and aerial photos, which was then combined with measurement of total organic carbon to create a comprehensive organic carbon budget. We show that the clinothem buried 93 ± 19 Mt terrestrial-rich organic carbon over a duration of 0.1–0.9 Myr. When normalized to the clinothem surface area, this represents an annual burial of 2.3–15.7 t km−2 yr−1 organic carbon, which is on the same order of magnitude as modern-day burial rates in clinothems such as the Amazon delta. This study demonstrates that deltas have been and will probably be substantial terrestrial organic carbon sinks over geologic timescales, a long-standing idea that had yet to be quantified

Organic carbon measurements on rock samples collected in Cerro Cazador, Chile

This dataset includes organic carbon measurements on rock samples collected upper Cretaceous deposits found in Cerro Cazador (Magallanes Basin, Patagonia, Southern Chile) in March 2020. The dataset was collected during the Chile Slope System geologic field trip that took place between February and March 2020, and led by Steve Hubbard, Brian Romans and Lisa Stright. Samples were collected along a 525-m geologic section using hammers and shovels