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Integration and Evaluation of Four Geochemical Methods for Regional Onshore Petroleum Exploration in the Mackenzie Delta, Northwest Territories, Canada

Seneshen, David; Fontana, John
Vista Geoscience, Golden, CO.

A regional geochemical orientation survey was conducted over the Tuk Tertiary oil field (10-25 MMBO), Tuk Cretaceous gas field (280 BCF) and the Mayogiak Devonian oil field (4 MMBO) in the Mackenzie Delta of the Northwest Territories, Canada. The orientation survey evaluated four analytical methods to determine which, if any, could provide surface expressions of the oil & gas fields through thick permafrost (100 to 600 m). The most effective method(s) could then be used to focus cost-prohibitive seismic surveys and drilling over onshore parts of the vast Mackenzie Delta. Lake sediment and soil core samples were collected at 500 to 1,000 meter intervals on 2-kilometer spaced lines over an approximate area of 150 square kilometers. Lake sediments and soil cores were analyzed for headspace- and blender-extractable C1-C6 alkanes by flame ionization detection gas chromatography (GC-FID). Soil cores were also analyzed for acid-extractable C1-C6 alkanes (GC-FID) and C6-C36 aromatic hydrocarbons by Synchronous Scanned Fluorescence (SSF).

All methods tested provided surface indications of the oil & gas fields. Thermogenic (C2-C6) hydrocarbons are anomalous in lake sediments and soil cores over and adjacent to the oil & gas fields. Acid-extractable C2-C6 hydrocarbons in soil cores provide the best discrimination between background and productive areas. Headspace C2-C6 hydrocarbons in lake sediments show more coherent anomalies over the Tuk and Mayogiak oil & gas fields than do blender-extracted gases. Three-ring aromatic hydrocarbons are anomalous in soil cores directly over the Tuk oil & gas fields.

The main conclusion from the geochemical orientation study over the Tuk and Mayogiak fields is that hydrocarbon analysis soil cores and lake sediments provides statistically significant thermogenic hydrocarbon anomalies over oil and gas fields at wide-spaced sample intervals, despite the thick permafrost in this region. Regional geochemical surveys for similar sized fields in the Mackenzie Delta should therefore involve the collection of lake sediments at 500 to 1,000 meter intervals for headspace C1-C6 hydrocarbon analysis. Lake sediments are the preferred sample medium because they can be collected at greater frequency and lower cost than soil cores. Anomalous areas should be followed up with closer-spaced (~200 meter) soil core samples for acid-extractable C1-C6 alkanes by flame ionization gas chromatography (GC-FID) and C6-C36 aromatics by SSF.

 

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012