--> Are You Leaving Liquids Behind? Diamondoid Analysis to the Rescue!

AAPG Annual Convention and Exhibition

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Are You Leaving Liquids Behind? Diamondoid Analysis to the Rescue!

Abstract

Diamondoids, nanometer-size, hydrogen-terminated diamonds, are structurally and thermally stable petroleum compounds. They become progressively concentrated during oil cracking i.e., the thermal conversion of oil to gas and pyrobitumen. Our results indicate that diamondoid analysis can be used to modify flowback schedules in order to maximize liquids production. Twenty-nine produced oil samples were analyzed and studied using diamondoid and biomarker ratios. The samples chosen are all Niobrara-sourced, produced either from the Niobrara or Codell, and are from the same basin yet vary substantially in their thermal maturity and gas-to-oil ratios. Diamondoid concentrations indicate that some of the oils have been extensively cracked, in one case with up to 90% indicative of the wet gas window of thermal maturity. On the other hand, many of the oils show no indication of cracking and biomarker ratios suggest Mid-Late Oil Window levels of maturity. In addition to providing information on thermal maturity and oil cracking in an unconventional reservoir, it appears that diamondoid ratios, in particular the ratio of the more volatile adamantanes to the less volatile diamantanes, can provide for the optimization of production rates. A relative enrichment of adamantanes in the produced oils correlate to fractionation due to production and/or migration. Production flowback histories were utilized to help interpret the cause of fractionation. This unique data set shows fractionation patterns associated with a loss of the heavy ends due to both overly aggressive flowback practices and migration. Our results indicate that this approach can have significant business impact, by suggesting modification to flowback schedules that potentially maximize liquids production.