Analysis of Counter-Current Interaction Between Matrix and Fracture for Gas-Water Systems

Abstract

Counter current matrix-fracture interaction is a commonly encountered process in production of geothermal fluids. In this paper we address different aspects of this phenomenon.
The rate of imbibition transfer and the development of residual gas phase under low (20oC) and high temperatures (90 oC) were examined experimentally. Cylindrical Berea sandstone and Indiana limestone samples with different shape factors were obtained by cutting the plugs 1, 2.5, and 5 cm in diameter and 2.5, 5, and 10 cm in length. All sides were coated with epoxy except one end. Static imbibition experiments were conducted on vertically and laterally situated samples where the matrix-fracture interaction took place upward and lateral (horizontal) directions, respectively. Brine and air were used as wetting and non-wetting phases, respectively.
The experimental scheme followed was useful in identification of the development of residual gas saturation for fully counter-current matrix-fracture interaction. We investigated and clarified to what degrees the rock/fluid properties (wettability and matrix shape factor) and existing conditions (temperature, causing lowered surface tension and brine viscosity, and gravity) become effective on the residual gas saturation. Finally, critical matrix and fluid properties were correlated to the residual gas saturation and recovery rate.