2014 Rocky Mountain Section AAPG Annual Meeting

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Paleostructural Control of Cretaceous Niobrara Productivity in a Portion of the DJ Basin of Colorado


Subtle thickness changes within the Cretaceous Niobrara are associated with changes in hydrocarbon productivity from the Niobrara in a portion of the DJ Basin of Colorado. Isopachous maps of the Niobrara show thick and thin trends parallel to the Colorado Mineral Belt in Weld and Morgan Counties, in northern Colorado. Locally thinner Niobrara areas are more likely to be economically productive from the Niobrara. Thins also occur where relatively higher resistivity values are measured by electric logs in the Niobrara ‘B’ chalk. Niobrara ‘B’ chalk resistivity is related to productivity in this area. Differences in the basement structure and composition can control local heat flow. Areas of thinner Niobrara may have experienced higher temperatures in the past than thicker areas of Niobrara, maturing source material within the Niobrara to a higher level than nearby thicker and cooler areas. Higher maturity levels increase the gas content within the reservoir and elevate pressure, improving the productivity of Niobrara wells. Microfractures, created by oil expulsion from source material within the Niobrara, enhance porosity and permeability improving productivity. Enhanced porosity in the Niobrara B Chalk due to depositional and diagenetic changes in these thinner areas of Niobrara may also have increased productivity. Careful mapping of the abundant well control within the DJ Basin can aid in a successful exploration program for the Niobrara.