Thermal maturation in the Ellef Ringnes Island and surrounding area, Sverdrup Basin

Determining thermal maturity studies in the Ellef Ringnes Island area was c omplicated by numerous factors such as the presence of cavings, bitumen sta ining, and igneous intrusions. Cavings are a problem in certain intervals i n Hoodoo H-37, Dome Bay P-36, and Helicopter J-12. Bitumen staining resulti ng in suppression of reflectance has occurred in the lower part of the Jame son Bay shales in flue M-40. Thick sills resulted in increase of Po to 40%, whereas thin sills had a minimal impact on reflectance increase. Other fea tures observed include overpressuring caused by hydrocarbon generation in t he Schei Point source rocks as well as in the Jameson and Ringnes shales, a nd a "kinky" Po profile caused by the presence of low-permeability gas-bear ing 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-1 2 to 0.23 log %Ro/km in Sirius K-28, but most ape between 0.12 and 0.15 log %Ro/km. Geothermal gradients range from 16.5 degrees C/km in Hoodoo H-37 t o 37.8 degrees C/km in Sirius K-28, with the majority being close to 20 deg rees C/km. The Tmax: values range from 436-445 degrees C in the Jameson Bay but reach 453 degrees 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 degrees 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 paramete rs in this arenaceous formation. The Ringnes shales have Tmax of 430-434 de grees C with corresponding HI of 209-244. The Schei Point Group shales, con sidered to be the main source rocks in the area, have Tmax of 441-443 degre es C. The underlying Blind Fiord has Tmax of 454 degrees C, in good agreeme nt with a TAI of 3 reported in the literature. Igneous sills have increased Tmax to 468-507 degrees C in Helicopter J-12 and to 479 degrees C in Louis e O-25. Anomalously high Tmax values in Hoodoo Dome N-52 have been attribut ed to the presence of salt domes and to the "warping up" effect in strata a djacent to and also deeper by the flanks of the dome. Hot fluid circulation s in areas near the intrusives and high inertinite kerogen have also contri buted to elevated Tmax values. In areas that have not been intruded Ro incr eases from 0.36% in Eureka Sound to 0.43% in the Christopher and to 0.50% i n the Isachsen. Coals in the latter formation have been oxidized therefore, Po is slightly higher. Reflectance increases from 0.42-0.48% in Deer Bay t o 0.67% in the Ringnes, reaching 0.70% in the Jameson Bay shales. The Barro w 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. T he presence of oil and gas in a number of fields can be explained by the va riations in thermal maturity.