IN-SITU CHEMICAL ANALYSIS OF HYDROCARBONS AT A NANOPORE SCALE, CRETACEOUS NIOBRARA FORMATION, DENVER BASIN, COLORADO (Invited Presentation)

Understanding the controls on pore network evolution in unconventional reservoirs remains a research focus nearly a decade into the “shale boom”. Most operators recognize that these controls are related to both mineral diagenesis and the emplacement of hydrocarbons. Because crude oil is a mixture of molecules with varying size, polarity, and thermal stabilities, it flows through porous media in a complex manner. In particular, the emplacement of large asphaltene molecules into just a few of the narrow pore throats characteristic of unconventional reservoirs may dramatically alter the efficacy of the total pore network, impacting flow of even the most mobile hydrocarbons. However, petroleum industry- standard techniques for analyzing hydrocarbon chemistry (SARA, pyrolysis, etc.) extract the hydrocarbons from the rock, and likewise, most standard porosity/permeability tests clean the sample of the hydrocarbons before analysis. No standard analyses allow for simultaneous investigation of the spatial distribution of porosity-compromising hydrocarbons and the pores themselves, or chemical characterization of hydrocarbons at the pore scale.

Developments in near-field microscopy have resulted in a novel method to chemically characterize hydrocarbons at the pore scale without extracting them, thus preserving spatial relationships. Nano-spectroscopic data from infrared scattering-scanning near-field optical microscopy demonstrates submicron spatial variability in hydrocarbon functional groups and mechanical properties in the Niobrara Formation, a prolific unconventional resource in Colorado’s Denver Basin. With additional investigation, it is anticipated that this approach will demonstrate correlativity between the distribution of pore-compromising hydrocarbons and other reservoir properties such as mineralogy, pore geometry, and pore-throat size with tens-of-nanometers resolution.