Abstract

The geologic controls on reservoir properties and potential hydrocarbon (volatile, low-molecular-weight liquid and gas) resources of the Cretaceous Shaftesbury Formation in northeastern British Columbia have been investigated. Maturity varies from the oil to dry gas window (Tmax = 429–486°C), with increasing maturity and depth of burial toward the south. The Tmax, in degrees Celsius, is the oven temperature at the peak generation of S2 during pyrolysis. Total organic carbon (TOC) content ranges between 0.64 and 8.0 wt. %, with an average of 2.2 wt. %. The TOC content distribution mirrors the trends in maturity, with lower TOC content in areas of high maturity. Kerogen is characterized as either type II-III or type III. The quartz content ranges between 33 and 66%, with higher quartz content in areas with lower TOC content and greater maturities. Porosity ranges between 4.5 and 14.6%, with higher porosities observed within shallower wells, low quartz content, or maturities, or a combination of all three. The porosity is reduced in high-maturity samples by mechanical compaction and silica cementation. Total gas capacities range between 4.5 and 24.8 cm3/g, and gas-in-place (GIP) estimates are between 0.98 and 3.39 bcf/(section × meter). The calculated hydrocarbon generation is less than 3.6 bcf/(section × meter), with light liquid generation between 3.7 and 516.2 MMBO.

Present-day depths and organic maturity have strong influences on the hydrocarbon capacity more so than TOC content. Deeper, higher maturity samples in the south have the largest total gas capacity and GIP estimates (0.98–3.39 bcf/[section × meter]). Maturity is within the dry gas window in the southern one-third of the study area. Highest volumes of light liquid hydrocarbons are found within the less mature northern part of the study area.

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