A Systematic Approach for Upscaling of the EOR Results from Lab-Scale to Well-Scale in Liquid-Rich Shale Plays
Authors: Akita Emmanuel , Moghanloo Rouzbeh G. , Davudov Davud , Tinni Ali 
Published: March 2018

This paper examines a priori equation to describe recovery factors of EOR processes in oil shale plays. The existing studies imply promising future for implementing gas cyclic injection through hydraulically fractured wells completed in shale plays; the EOR agent (a mixture of HC gas or CO2) is injected and after a soaking period, the well is put back on production. However, translation of lab-scale EOR results to field-scale is yet to be resolved. Dynamic penetration volume (DPV) controls the amount of contacted oil by the EOR agent (fluid-fluid interface), slowly grows with time and limits the recovery efficiency in the pilot-scale. The main idea proposed in this paper is developing a systematic approach to upscale the EOR recovery in lab-scale to pilot-scale.

We use a combination of modeling, theoretical, and experimental work to investigate potential recovery loss in well-scale compared to recovery measured in the lab-scale. In our formulation, the recovery in pilot-scale is defined as the product of recovery in lab-scale by field factor. Recovery in lab-scale is a function of pressure drawdown during production (choke effect). Choke-size controls how fast the mixture of gas and vaporized oil components will be produced back after soaking time.

Field factor entails two parameters that control how much of in-situ liquid hydrocarbon can potentially interact with EOR agent; basically, field factor is evaluated as a fraction of reservoir volume prescribed within inter-well spacing accessible to the EOR agent when injection process begins. Field factor is calculated as a product of fraction of stimulated reservoir volume (SRV) accessible to EOR agent (DPV/SRV) at any given time by fraction of reservoir volume stimulated during fracturing; SRV is controlled by the efficiency of fracturing treatment. The pore connectivity loss can occur because of the physical closure of flow path at the fracture-matrix interface and/or two-phase blockage. The limiting two phase phenomena can potentially prevent the injected gas from getting into pore space because of capillary forces.

Our results suggest that recovery in the pilot-scale can be significantly reduced owing to pore connectivity loss (a factor of two). The pore connectivity is reduced as pore pressure decreases and effective stress increases. We evaluate change of fluid conductivity under stress and differentiate contribution of pore connectivity loss and pore shrinkage. We also introduce the concept of the Biot number, which lumps together all parameters unaccounted for on the field scale, and thus helps to use similar equations at different scales, providing a systematic approach. Moreover, our results suggest that chokes size effect observed in the experiments can be explained by loss of pore connectivity. We also observe that total recovery is a function of the diffusivity coefficient, and is not significantly altered by varying ratios of fracture to matrix volumes.

For the first time, an equation is presented to upscale the EOR results obtained in lab-scale to pilot-scale. The outcome is expected to help operators with the pilot-test performance evaluations.