Models of Talik, Permafrost and Gas Hydrate Histories—Beaufort Mackenzie Basin, Canada

Models of talik, permafrost and gas hydrate (GH) histories below shallow lakes are investigated and compared to models of Beaufort Mackenzie Basin (BMB) GH occurrences to describe lacustrine inundation effects, which are compared against factors controlling the variations among Mackenzie Delta (MD) permafrost, GH and talik occurrence. Models using a 2–4 °C boundary temperature range indicate that geological setting, specifically underlying lithology and porosity, are the primary controls in talik formation below lakes. Below a lake of any size, where the underlying lithology is sandy it is practically impossible to produce a pervasive talik or to completely degrade significant GH accumulations in response to the boundary condition thermal effects alone. Models predict that talik formation is, in such cases, restricted to the upper few tens of meters below the lake. Permafrost degradation appears common where porosities are <40% and water bottom temperatures reach 2–4 °C, in both marine and lacustrine settings. Where porosities are higher a thin GH stability zone can persist, even where deep taliks have formed

Methane Gas Hydrate Stability Models on Continental Shelves in Response to Glacio-Eustatic Sea Level Variations: Examples from Canadian Oceanic Margins

We model numerically regions of the Canadian continental shelves during successive glacio-eustatic cycles to illustrate past, current and future marine gas hydrate (GH) stability and instability. These models indicated that the marine GH resource has dynamic features and the formation age and resource volumes depend on the dynamics of the ocean-atmosphere system as it responds to both natural (glacial-interglacial) and anthropogenic (climate change) forcing. Our models focus on the interval beginning three million years ago (i.e., Late Pliocene-Holocene). They continue through the current interglacial and they are projected to its anticipated natural end. During the current interglacial the gas hydrate stability zone (GHSZ) thickness in each region responded uniquely as a function of changes in water depth and sea bottom temperature influenced by ocean currents. In general, the GHSZ in the deeper parts of the Pacific and Atlantic margins (≥1316 m) thinned primarily due to increased water bottom temperatures. The GHSZ is highly variable in the shallower settings on the same margins (~400–500 m). On the Pacific Margin shallow GH dissociated completely prior to nine thousand years ago but the effects of subsequent sea level rise reestablished a persistent, thin GHSZ. On the Atlantic Margin Scotian Shelf the warm Gulf Stream caused GHSZ to disappear completely, whereas in shallow water depths offshore Labrador the combination of the cool Labrador Current and sea level rise increased the GHSZ. If future ocean bottom temperatures remain constant, these general characteristics will persist until the current interglacial ends. If the sea bottom warms, possibly in response to global climate change, there could be a significant reduction to complete loss of GH stability, especially on the shallow parts of the continental shelf. The interglacial GH thinning rates constrain rates at which carbon can be transferred between the GH reservoir and the atmosphere-ocean system. Marine GH can destabilize much more quickly than sub-permafrost terrestrial GHs and this combined with the immense marine GH reservoir suggests that GH have the potential to affect the climate-ocean system. Our models show that GH stability reacts quickly to water column pressure effects but slowly to sea bottom temperature changes. Therefore it is likely that marine GH destabilization was rapid and progressive in response to the pressure effects of glacial eustatic sea level fall. This suggests against a catastrophic GH auto-cyclic control on glacial-interglacial climate intervals. It is computationally possible but, unfortunately in no way verifiably, to analyze the interactions and impacts that marine GHs had prior to the current interglacial because of uncertainties in temperature and pressure history constraints. Thus we have the capability, but no confidence that we can contribute currently to questions regarding the relationships among climate, glacio-eustatic sea level fluctuations and marine GH stability without improved local temperature and water column histories. We infer that the possibility for a GH control on climate or oceanic cycles is speculative, but qualitatively contrary to our model results

An assessment of tight oil resource potential in Upper Cretaceous Cardium Formation, Western Canada Sedimentary Basin

The Cardium Formation “halo oil” occurs either in the fringe of, or between, existing conventional discrete sandstone reservoirs. It is commonly associated with conventional oil and gas pools in stratigraphic traps. This paper uses a geological model-based simulation approach to assess Cardium “halo oil” resource potential. The geological model-based approach consists of a geological model, a resource model and a stochastic modeling procedure that extracts essential information regarding the richness and spatial characteristics of oil resources from various data sources using statistical methods. It integrates them with the geological and resource models, respectively, to estimate the resource potential. This approach predicts not only the resource potential, but also the resource spatial distribution and the exploration risk. These outcomes provide critical information for exploration decision-making. Cardium “halo-oil” assessment results indicate a mean total oil in-place (conventional and unconventional) of 4.6×109 m3 and a mean undiscovered “halo oil” in-place of 2.9×109 m3. Using current technology and economic constraints the undiscovered recoverable “halo oil” in this tight formation is 0.11×109 m3. This represents <4% of the remaining in-place oil resource, but it accounts for 38% of the total recoverable Cardium oil. A comparison with resource estimates obtained using a well-performance approach that is based on production data extrapolations from stimulated horizontal wells suggests that the mean recoverable estimate obtained using the two different approaches are similar, suggesting that the geological model-based approach provides a reliable oil resource potential estimate. Key words: unconventional, Halo oil pool, stochastic simulation, resource assessmen

ONSET AND STABILITY OF GAS HYDRATES UNDER PERMAFROST IN AN ENVIRONMENT OF SURFACE CLIMATIC CHANGE - PAST AND FUTURE

Modeling of the onset of permafrost formation and succeeding gas hydrate formation in the changing surface temperature environment has been done for the Beaufort-Mackenzie Basin (BMB). Numerical 1D modeling is constrained by deep heat flow from deep well bottom hole temperatures, deep conductivity, present permafrost thickness and thickness of Type I gas hydrates. Latent heat effects were applied to the model for the entire ice bearing permafrost and Type I hydrate intervals. Modeling for a set of surface temperature forcing during the glacial-interglacial history including the last 14 Myr, the detailed Holocene temperature history and a consideration of future warming due to a doubling of atmospheric CO2 was performed. Two scenarios of gas formation were considered; case 1: formation of gas hydrate from gas entrapped under deep geological seals and case 2: formation of gas hydrate from gas in a free pore space simultaneously with permafrost formation. In case 1, gas hydrates could have formed at a depth of about 0.9 km only some 1 Myr ago. In case 2, the first gas hydrate formed in the depth range of 290 – 300 m shortly after 6 Myr ago when the GST dropped from -4.5 °C to -5.5. °C. The gas hydrate layer started to expand both downward and upward subsequently. More detailed modeling of the more recent glacial–interglacial history and extending into the future was done for both BMB onshore and offshore models. These models show that the gas hydrate zone, while thinning will persist under the thick body of BMB permafrost through the current interglacial warming and into the future even with a doubling of atmospheric CO2.Non UBCUnreviewe

Definition and characterization of petroleum compositional families in Williston Basin, North America using principal component analysis

Summarization: Petroleum hydrocarbons in the gasoline range (GRH) and saturate (SFH- >210 °C boiling point) fractions carry information that is often obscured by compositional diversity and multiple processes working simultaneously. Multivariate statistical methods can enhance the analysis and interpretation of compositional data from these fractions, especially in conjunction with independent geological information. In the present study, Principal Component Analysis (PCA) was applied to the GRH and SFH data for 171 oil samples from the Williston Basin. These oils were previously classified using polycyclic terpane and sterane biomarker traits. Our results indicate that only Family A oils can be uniquely classified using PCA. Families B, C and D oils show GRH and SFH characteristic compositions consistent with biomarker-defined families, but these characteristics are insufficient for independent classification. However, the PCA analyses of the GRH and SFH compositional traits proves to be a useful technique in recognizing the effect of mixing of oils derived from different sources.Presented on: Organic Geochemistr