Investigation of the controlling rock petrophysical factors on water phase trapping damage in tight gas reservoirs

Abstract

This paper presents an investigation into the effect of rock physical parameters on water phase trapping (WPT) damage in tight gas reservoirs. The investigation involved water imbibition and drainage experiments that were performed to simulate the WPT formation process. Gas permeability was measured before and after WPT, and an empirical formula was used to determine water film thickness in order to examine the influence of WPT on effective gas flow channel. Results showed that the average water saturation of 15 tight core samples increased from 19.41% to 44.76% during water imbibition and declined to 38.72% after drainage. Increments in water saturation caused a degree of damage to gas permeability in the 36.03%‐78.10% range with an average value of 59.31%. Comparative analysis showed that the dominant factors affecting WPT were average pore throat radius followed by rock permeability and porosity. Meanwhile, calculations showed that water film thickness in the 21.22‐38.18 nm range correlated to a reduced effective gas flow channel of 20.20‐45.15 nm caused by WPT, which suggests that tight rocks with smaller pore throats may be particularly sensitive to WPT damage. The relative size of the water film filling the pore throat, trapping gas, and reducing the effective gas flow channel together with the size of the pore throat itself were found to be the most common damage mechanisms of WPT and have proven to be fundamentally beneficial in understanding the controlling factors of these damage mechanisms.

Three‐dimensional Lattice Boltzmann simulation of gas‐water transport in tight sandstone porous media: Influence of microscopic surface forces

“…Tight sandstone has strong hydrophilicity and high irreducible water saturation in tight gas reservoirs. When the water and gas phases coexist in tight porous materials, a water film with a certain thickness and stable adsorption is usually presented on the walls of the porous media, which affects the mass transfer of the gas . In micropores and nanopores, the throat structure for gas‐water two‐phase seepage in tight sandstone causes the solid‐liquid microscopic surface forces between the solid rock wall and fluid water phase to be stronger than the gas‐solid interfacial force for single‐phase gas seepage.…”