High-frequency (20 MHz) NMR and Modified Rock-Eval Pyrolysis Methods as an Integrated Approach to Examine Producibility in Kerogen-Rich Source-Reservoirs

Carvajal-Ortiz, Humberto (Core Laboratories) | Gentzis, Thomas (Core Laboratories) | Xie, Harry (Core Laboratories)

OnePetro 

Abstract

The geochemical and petrophysical complexity of source-reservoirs in Liquid-Rich Unconventional plays (LRU) urges for the implementation of alternative analytical protocols for initial play assessment. In this study, samples from selected source-reservoirs in the USA and the UK were analyzed by high frequency-nuclear magnetic resonance (HF-NMR relaxometry), followed by hydrous pyrolysis, and modified Rock-Eval pyrolysis methods (multi-heating rate methods, MHR). The analytical protocol here presented attempts to better qualify and quantify different petroleum fractions (mobile, heavy hydrocarbons, viscous, solid bitumen), and thus provide valuable and refined information about producibility of target intervals during appraisal stages.

Modified Rock-Eval Pyrolysis (MHR). Briefly, the pyrolysis oven program had four temperature ramps (at 50 °C/min) and isothermal plateaus (maintained isothermal for 15 minutes) at 200°C, 250°C, 300°C and 350°C, with a fifth and last ramp of 25°C/minute to 650°C. HF-NMR Relaxometry Hydrogen NMR measurements were made with a special 22MHz spectrometer from MR Cores equipped with a 30-mm diameter probe. The T2 data were acquired using the CPMG sequence with an echo time spacing of TE=0.07 ms. The T1 data were acquired using an inversion-recovery sequence. Selected samples (Kimmeridge Clay, Green River Shale) were subjected to hydrous pyrolysis experiments. Crushed rock chips (2-4 g, 1-3mm top size) were loaded into mini-reactor vessels (25-35 mL internal volumes). Rock chips were covered with deionized water and the reactor was placed in a gas chromatograph oven at the chosen temperature, generally for 72h.

Initial results show how the hydrocarbon fractions interpreted from NMR regions are in good agreement with those from MHR pyrolysis analysis in terms of hydrocarbon mobility/producibility. Results from hydrous pyrolysis experiments show that an exception to this general agreement between NMR and MHR estimates occurs for the Kimmeridge Clay samples, where MHR shows an increase of > 90% in producible hydrocarbon yields vs. minimal to no presence of mobile hydrocarbons in NMR T1-T2 maps. Ongoing experiments will clarify the role of pore structure and networks in these discrepancies of producible oil estimates when comparing pyrolysis with NMR-based techniques. This multi-step, multidisciplinary approach provides an opportunity to use it as a screening analysis to identify zones of higher OIP and predict fluids mobility prior to drilling. The novelty of our study is the integration of laboratory-derived analytical data (HF H-NMR, MHR and Hydrous Pyrolysis, organic petrography) to assess the proportion of the OIP that is producible prior to drilling or completions.

  Country: North America > United States (0.66)
  Industry: Energy > Oil & Gas > Upstream (1.00)
  Technology: Information Technology (0.46)