Micro-modeling for Enhanced Small Scale Porosity-Permeability Relationships

Abstract

Accurate modeling of vertical and horizontal permeability in oil sands is difficult due to the lack of representative permeability data. Core plug data could be used to model permeability through the inference of a porosity-permeability relationship. The drawbacks of this approach include: variability and uncertainty in the porosity-permeability scatter plot as a result of sparse sampling, and biased core plug data taken preferentially from sandy or homogeneous intervals. A two-step process can be used where core photographs and core plug data are used to assess small scale permeability followed by upscaling to a representative geomodeling cell size. This paper expands on a methodology that utilizes core photographs to infer porosity-permeability relationships. This methodology is robust because there is abundant core photograph data available compared to core plug permeability samples and the bias due to preferential sampling can be avoided. The proposed methodology entails building micro-scale models with 0.5 mm cells conditional to 5 cm×5 cm sample images extracted from core photographs. The micro-models are sand/shale indicator models with realistic permeability values (k sand≈7 000 mD, k shale≈0.5 mD). The spatial structure of the micro-model controls the resulting porosity-permeability relationships that are obtained from upscaling. Previously, these models were generated with sequential indicator simulation (SIS). However, SIS may not capture the spatial structure of the complex facies architecture observed in core photographs. Models based on multiple point statistics and object based techniques are proposed to enhance realism. Micro-models are upscaled to the scale of the log data (5 cm in this case) with a steady-state flow simulation to determine the porosity-permeability relationship. The porosity-permeability relationships for geomodeling, or flow simulation, can be determined with subsequent mini-modeling and further upscaling. The resulting porosity-permeability relationship can be used to populate reservoir models and enhance traditional core data. Wells from the Nexen Inc. Long Lake Phase 1 site in the Alberta Athabasca oil sands region are used to demonstrate the methodology.