Thermal Maturation in the Ellef Ringnes Island and Surrounding Area, Sverdrup Basin

Abstract

Determining thermal maturity studies in the Ellef Ringnes Island area was complicated by numerous factors, such as the presence of cavings, bitumen staining, and igneous intrusions. Cavings are a problem in certain intervals in Hoodoo H-37, Dome Bay P-36, and Helicopter J-12. Bitumen staining resulting in suppression of reflectance has occurred in the lower part of the Jameson Bay shales in Elve M-40. Thick sills resulted in increase of Ro to 4.0%, whereas thin sills had a minimal impact on reflectance increase. Other features observed include overpressuring caused by hydrocarbon generation in the Schei Point source rocks as well as in the Jameson and Ringnes shales, and a “kinky” Ro profile caused by the presence of low-permeability gas-bearing reservoirs in the Heiberg sandstones in Jackson Bay G-16A. The presence of sapropelic coals with HI up to 329 mg HC/gTOC in Heiberg sandstones in Elve M-40 containing Botryococcus algae should also be noted. Calculated maturation gradients vary from 0.95 log°Ro/km in Helicopter J-12 to 0.23 log %Ro/km in Sirius K-28, but most are between 0.12 and O.l5 log %Ro/km. Geothermal gradients range from 16.5°C/km in Hoodoo H-37 to 37.8°C/km in Sirius K-28, with the majority being close to 20°C/km. The Tmax values range from 436–445°C in the Jameson Bay but reach 453°C at the base of the formation in Sirius K-28. Total organic carbon in Jameson Bay is 1.3–3.3 wt% and HI usually varies from 49–181 mg HC/gTOC, although a value of 374 was measured in Hoodoo Dome H-37. Tmax is also elevated in the Isachsen sandstones (444–445°C”. These values correspond to 0.83–0.90%Ro; however, measured Ro is much lower (0.45–0.50%Ro) pointing to a poor relationship between the two maturity parameters in this arenaceous formation. The Ringnes shales have Tmax of 430–434°C with corresponding HI of 209–244. The Schei Point Group shales, considered to be the main source rocks in the area, have Tmax of 441–443°C The underlying Blind Fiord has Tmax of 454°C, in good agreement with a TAI of 3 reported in the literature. Igneous sills have increased Tmax to 468–507°C in Helicopter J-12 and to 479°C in Louise 0–25. Anomalously high Tmax values in Hoodoo Dome N-52 have been attributed to the presence of salt domes and to the “warping up” effect in strata adjacent to and also deeper by the flanks of the dome. Hot fluid circulations in areas near the intrusives and high inertinite kerogen have also contributed to elevated Tmax values. In areas that have not been intruded, Ro increases from 0.36% in Eureka Sound to 0.43% in the Christopher and to 0.50% in the Isachsen. Coals in the latter formation have been oxidized, therefore, Ro is slightly higher. Reflectance increases from 0.42–0.48% in Deer Bay to 0.67% in the Ringnes, reaching 0.70% in the Jameson Bay shales. The Barrow shales have Ro of 0.7–0.95% increasing to >1.20% in the Pat Bay shales. The Schei Point shales are in the mature stage of hydrocarbon generation. The presence of oil and gas in a number of fields can be explained by the variations in thermal maturity.