A novel integrated workflow based on Nuclear Magnetic Resonance (NMR) Factor Analysis (FA) is developed to evaluate organic shale reservoirs. Current organic shale formation evaluation techniques cannot distinguish immobile hydrocarbons from producible hydrocarbons. The new workflow aims to quantify producible hydrocarbons and characterize shale reservoir quality.
The new approach incorporates NMR factor analysis technique with NMR and spectroscopy data to focus on the characterization of organic shale by: 1) identifying fluid types with associated pore size distribution; 2) computing pore fluid volumes to quantify producible hydrocarbon in place; and 3) fluid facies classification to evaluate reservoir quality and identify the sweet spot.
Understanding fluid types and volumetrics in shale reservoirs is the key to evaluate reservoir quality and estimate hydrocarbon production. The integrated workflow separates fluid hydrocarbon from kerogen with NMR and advanced spectroscopy data. In addition, it differentiates the formation fluid into individual pore fluids, including bound hydrocarbon, clay-bound water, irreducible water (capillary-bound), irreducible oil (capillary-bound), free water and producible hydrocarbon. The workflow also provides the porosity of each pore fluid and quantifies producible hydrocarbon, which is one of the most important influencing factors of shale reservoir production. The reservoir quality of fluid facies from NMR factor analysis is characterized using pore fluid porosities. Zones with high producible hydrocarbon porosity and no free water is classified to have the best reservoir quality for production.
The results from the novel workflow successfully characterize the reservoir quality and producibility, and mark the sweet spot of organic shale reservoirs.