Permeability Evolution of Porous Sandstone in the Initial Period of Oil Production: Comparison of Well Test and Coreflooding Data

Abstract

Permeability prediction in hydrocarbon production is an important task. The decrease in permeability due to depletion leads to an increase in the time of oil or gas production. Permeability models usually are obtained by various methods, including coreflooding and the field testing of wells. The results of previous studies have shown that permeability has a power-law or exponential dependence on effective pressure; however, the difficulty in predicting permeability is associated with hysteresis, the causes of which remain not fully understood. To model permeability, as well as explain the causes of hysteresis, some authors have used mechanical reservoir models. Studies have shown that these models cannot be applied with small fluctuations in effective pressures in the initial period of hydrocarbon production. In this work, based on the analysis of well test data, we came to the conclusion that in the initial period of production under constant thermobaric conditions, the permeability of a slightly clayey terrigenous reservoir depends on the amount of fluid produced. A model has been obtained that describes the change in permeability in the initial period of oil production. Core samples were flooded to confirm the model. Coreflooding showed high convergence of the model obtained from well test data. With computed tomography (CT) and scanning electron microscope (SEM), the properties and structure of the core were studied, and it was found that the main reason for the decrease in the permeability of slightly clayey rocks in the initial period of production is the migration of natural colloids.