Impact of Relative Permeability Hysteresis on Water-Alternating-Gas WAG Injectivity: Modeling and Experimental Study

Abstract

Gas injection is a proven enhanced oil recovery (EOR) process, representing the leading EOR-technique in the United States. In recent years, gas EOR technologies are expanding to more challenging (deeper and tighter) reservoirs. In gas injection, there are two basic techniques – continuous gas flooding and water-alternating-gas (WAG) injection. The WAG injection promises improved sweep efficiency, with water being used for mobility control and stabilizing displacement fronts, but suffers from injectivity loss due in part to gas trapping. This injectivity loss can have a major impact on project economics. In this work, we study the modeling of relative permeability hysteresis and its impact on WAG injectivity under both immiscible and miscible conditions.Core flooding experiments are also performed and simulated to understand and quantify the WAG injectivity. Our study showed that the most significant impact of gas relative permeability hysteresis on WAG injectivity lies in the water injectivity reduction following gas flooding. Experimental results confirmed the reduced water injectivity, and this effect can be modeled and sufficiently captured by the gas relative permeability hysteresis.

State of the Art on Relative Permeability Hysteresis in Porous Media: Petroleum Engineering Application

“…(1) Decrease in injection capacity [72,76,77] The hysteresis effect of phase permeability can lead to an increase in injection well pressure, especially during water injection after gas displacement. Once the pressure reaches a certain level, it may result in the inability to inject water and gas.…”

“…At the front edge of the CO 2 slug, gas continues to displace the wetting phase during drainage, while at the rear edge, water displaces gas during imbibition, leading to gas phase fragmentation and subsequent trapping. As the slug migrates upwards, some CO 2 is trapped as residual immobile phase in pore spaces, effectively isolating CO 2 in the rock until the immobile gas dissolves over geological time [11,73,74,76,77,[85][86][87].…”

Compositional Modeling to Analyze the Effect of CH4 on Coupled Carbon Storage and Enhanced Oil Recovery Process

“…Although conventional two-phase hysteresis models assume the reversibility of permeability during the drainage process following the previous imbibition cycle, this assumption is invalid for three-phase fluid flow because the relative permeability of gas is lower when displacing a water-oil mixture than when displacing oil only [29]. The three-phase hysteresis model proposed by Larsen and Skauge [30] is adopted in the present study and has shown better matching to experimental data than the two-phase model [31,32].…”