The Impact of Capillary Condensation on the Hydrocarbon Storage and Mobility

Abstract

Description: Gas behavior is important for many reservoirs, yet challenging to characterize due to limited understandings on the nanophysics governing the mechanisms of storage and mobility. For Duverney shale in particular, the over-pressurized liquid rich behavior revealed by well test data is dramatically different from the relatively better understood dry gas shale. Conventional two-component gas-in-place (GIP) model, i.e., free gas plus surface adsorbed gas, under-predicts storage. This project introduces capillary condensation in nano-scale pores as the third component to the conventional GIP model. The microstructure of organic porosity from a Duvernay sample is visualized using focused ion beam - electron scanning microscope (FIB-SEM). Distributions of pores and pore throats are reconstructed from FIB-SEM using an artificial intelligence-based image processing technique. Direct numerical modeling on imaging data using computational fluid dynamics (CFD) characterizes hydrocarbon transport through organic porosity network, while capillary condensation conditions are dynamically applied. GIP contribution from capillary condensation and its blockage effect on mobility are quantified.

Applications: In addition to its critical role in all gas reservoirs, capillary condensation is also important to any organic shale plays where fundamental understanding on gas drive and gas diffusivity are necessary for both asset evaluation and reservoir engineering purposes.

Results and Conclusions: New GIP model with capillary condensation component predicted an increase of nearly 300% in gas reserve, comparing with the storage calculated using the conventional free gas plus adsorption model. In the meanwhile, capillary condensation blocks the smallest pore throat, hence has an adverse effect on gas mobility. For the analyzed rock sample in unstimulated reservoir, absolute gas permeability can drop by 40% at one specific capillary condensation condition when 5% of the pore space are controlled by throats condensated with liquid gas. Reservoir engineering considerations is discussed.

Technical Contributions: This work is the first time that capillary condensation has been considered in GIP estimate of an active shale play. It further illustrates the image-based computational framework to evaluate micro-physics for reservoir characterization that are difficult to study experimentally.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018