Abstract
This paper discusses risks of fresh water injection in the terrigenous reservoir of the Verkhnechonsky producing horizon where interstitial space is fully or completely filled with halite (naturally occurring salinization).
Strata of salinized sandstone are believed to be a potential "super" reservoir since when fresh water is injected in the layer it washes out salts and induces a manifold increase in the effective porosity and permeability. Such flooding may accelerate water breakthrough into the producing wells, creating water absorption zones and changing the displacement front. All that reduces sweep efficiency and, with that, oil recovery.
The work has focused on flow experiments with core samples to assess the dynamics of change in the permeability and porosity of the rock and arrived at important conclusions on the characteristics of desalination process. A mathematical model of multi-phase filtration has been built to account for the interaction of water with the reservoir salt which brings about changes in the reservoir properties of the porous medium and rheology of injected water. Numerical experiments have been conducted to study the impact of desalination on viscous displacement of oil.
The paper offers systematic information about the injection experiments with salinized core samples from the Verkhnechonsky formation. It offers a description of the mathematical model of filtration of oil, gas and mineralized water which serves as the basis for hydrodynamic simulation at different levels (from core models to a full-scale model of the Verkhnechonsky horizon).
The results obtained give insight into key factors that accompany dissolution of reservoir salt in the injected fresh water, as well as their effect on the efficiency of water-flooding of salinized reservoirs.
The study will be of interest for specialists at oil companies which have in their portfolio oil fields with subsalt and inter-salt oil deposits.
