Research Items (7)
Regionally, the Nenana and Tanana basins are located in a crustal deformation zone characterized by complex interactions between regional crustal scale dextral strike-slip faults, active northeast-striking sinistral faults, and the active fold-and-thrust belt growing the Alaska Range. A detailed knowledge of the crustal architecture of these two basins is crucial for investigating the interplay between the intra-plate stress field and the development of regional structural features in Interior Alaska. Although the geology and structures along the northern and southern margins of the Nenana and Tanana basins have been studied extensively in the past, the present-day crustal structure and internal geometries of both basins are poorly understood. We investigated the modern-day crustal architecture of the Nenana and Tanana basins using existing seismic reflection, aeromagnetic and gravity anomaly data and demonstrated that the basement of both basins shows strong crustal heterogeneity. The Tanana basin is a relatively shallow (up to 2 km) asymmetrical foreland basin with its southern, deeper side controlled by the northern foothills of the central Alaska Range. NE-trending strike-slip faults within the Tanana basin are interpreted as a zone of clockwise crustal block rotation. The Nenana basin has a fundamentally different geometry and is a deep (up to 8 km), narrow transtensional pull-apart basin that is deforming along the left-lateral Minto Fault.
The Nenana basin of interior Alaska forms a segment of the diffuse plate boundary between the Bering and North American plates and is located within a complex zone of crustal-scale strike-slip deformation that accommodates compressional stresses due to oblique plate convergence to the south. The basin is currently the focus of new oil and gas exploration. Integration of seismic reflection and well data, fracture data and apatite fission track analyses with regional data improves our understanding of the tectonic development of this continental strike-slip basin.The Nenana basin formed during the Late Paleocene as a 13-km-wide half-graben, affected by regional intraplate magmatism and localized crustal thinning across the Minto fault in south-central Alaska. The basin was uplifted and exhumed along this faulted margin in Early Eocene through to Late Oligocene time in response to oblique subduction along the southern Alaska margin. This event resulted in the removal of up to 1.5 km of Late Paleocene strata ...
The northeastern Brooks Range of northern Alaska is an active, north-directed fold-and-thrust belt that is advancing on the Barrow arch and the north-facing passive margin of the Arctic Basin. Density logs, leak-off tests, and mud-weight profiles from 57 wells from the northeastern North Slope were used to determine the magnitude of the present-day in situ stresses and document significant regional lateral and vertical variations in relative stress magnitude. Preliminary analysis of the in situ stress magnitudes indicates two distinct stress regimes across this region of Alaska. Areas adjacent to the eastern Barrow arch exhibit both strike-slip and normal stress regimes. This in situ stress regime is consistent with fault patterns in the subsurface and with north-south extension along the Barrow arch and the northern Alaska margin. To the south in and near the northeastern Brooks Range thrust front, in situ stress magnitudes indicate that an active thrust-fault regime is present at depths up to 6000 ft (1829 m). This is consistent with the fold-and-thrust structures in surface exposures and in the subsurface. However, at depths greater than 6000 ft (1829 m), the relative in situ stress magnitudes indicate a change to a strike-slip regime. This observation is consistent with the few earthquake focal mechanisms in the area and suggests deep north-northeast-oriented strike-slip faults may underlie the western margin of the northeastern Brooks Range. Copyright © 2017. The American Association of Petroleum Geologists. All rights reserved.
Naturally fractured, unmineable coal seam reservoirs are attractive targets for geological sequestration of carbon dioxide (CO2) because of their high CO2 adsorption capacity and possible cost offsets from enhanced coal bed methane production. In this study, we have investigated the CO2 sequestration and coal bed methane (CH4) production potential of the subbituminous to high-volatile C bituminous Healy Creek Formation coals through preliminary sensitivity analyses, experimental design methods, and fluid flow simulations. The sensitivity analyses indicate that the total volumes of CO2 sequestered and CH4 produced from the Healy Creek coals are mostly sensitive to bottom-hole injection pressure, coal matrix porosity, fracture porosity, fracture permeability, coal compressibility, and coal volumetric strain. The results of the Plackett–Burman experimental design were used to further generate proxy models for probabilistic reservoir forecasts. The probabilistic estimates for the mature, subbituminous to high-volatile C bituminous Healy Creek coals in the entire Nenana Basin indicate that it is possible to sequester between 0.41 trillion cubic feet (TCF) (P10) and 0.05 TCF (P90) of CO2 while producing between 0.36 TCF (P10) and 0.05 TCF (P90) of CH4 at the end of 44-year forecast. Fluid flow scenarios show that CO2 sequestration through a primary reservoir depletion method is the most effective way to inject CO2 in the coals of the Nenana Basin. Including a horizontal well instead of the vertical well resulted in relatively high average gas production rates and subsequent total cumulative gas production. The CO2 buoyancy scenario suggests that the effect of CO2 buoyancy and the nature of caprock should be considered in identifying potential geologic sites for CO2 sequestration.
- Mar 2014