T187 The Changing Landscape of Energy Geology I

Tuesday, 17 October 2023
1:30 PM - 5:30 PM
320

TOTAL NEUTRON SCATTERING EVALUATION OF METHANE BEHAVIOR IN THE NIOBRARA FORMATION AT WET-GAS THERMAL MATURITY CONDITIONS: PERSPECTIVES ON WELL PRESSURE MANAGEMENT

Paper number: T187-2
Program: Technical Sessions
Time: 1:35 PM – 1:50 PM

Authors

Abstract

Within many unconventional source-rock reservoirs at intermediate thermal maturities [e.g., late oil (Ro ~0.9%) to wet gas windows (Ro~1.5%)] the distribution and behavior of methane (CH4) and alkanes (C2-C5) associated with gas condensates in mesopores (diameters 2 to 50 nm) and micropores (diameters <2 nm) are unclear. However, this pore size range may represent a significant portion of available pore volume in the reservoir and are within the size regime where densification effects are known to occur. Hence, understanding petroleum compound (e.g., CH4) distribution within these settings informs our understanding of resource generation, movement, and recoverability, and may aid in developing improved estimates of ultimate recovery. Here, perdeuterated methane (CD4) behavior was investigated in a sample from the Late Cretaceous Niobrara Formation at the late oil/wet gas window using wide Q-range total neutron scattering at reservoir pressures (200 – 750 bar) and temperature (60°C). The Niobrara Formation is an active petroleum-producing formation within the Denver-Julesburg Basin, United States, and is currently producing ~650,000 barrels of oil per day. Neutron scattering data show that larger mesopores (5 to 25 nm) within the Niobrara Formation sample are generally accessible to CD4, e.g., ~80% of 25 nm diameter pores are accessible. In contrast, scattering signals corresponding to small mesopores and all micropores (nominal pore diameters from 0.5 to 5 nm) fluctuate with increased CD4 pressure, inhibiting an accessibility estimation. We interpret these signal fluctuations to signify the creation of organic porosity, likely through deformation of sample organic matter by supercritical CD4, and/or the solvation of CD4. CD4-induced porosity represents a pore volume increase of at least ~8% within the sample. Additionally, densification of CD4 within the sample is clearly indicated by a shift in the CD4 intermolecular scattering peak to higher Q-values compared to bulk CD4. These results provide insight into fluid properties within source-rock reservoirs at intermediate thermal maturity, especially as they relate to pore connectivity, and are discussed with regard to their application in the pressure management of gas condensate wells.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-390236

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