A Novel Method to Determine Relative Permeability and Capillary Pressure from Corefloods Application to CO2 Storage
Authors: Hemmati Nassim , Borazjani Sara , Genolet Luis , Behr Aron , Zeinijahromi Abbas , Badalyan Alexander , Mahani Hassan , Mohd Shafian Siti Rohaida , Bedrikovetsky Pavel 
Published: October 2022

Abstract

Introduction
In order to account for dissolution of CO2 in water, the core must be initially saturated by carbonized water, which have been in equilibrium with CO2. To account for evaporation of water in CO2, the injected CO2 must be put in contact with water until thermodynamic equilibrium. To account for both, reservoir water with CO2 is put in the tank until the thermodynamic equilibrium is established.

Objectives
Steady-state coreflood test is a widely accepted industrial method to determine relative permeability (Kr), but the capillary pressure (Pc) must be known from other sources (porous plate, mercury injection, and centrifuge tests). Significant difference between the capillary pressure determined from corefloods and by other methods is widely presented in the literature.
We developed a novel coreflood method for simultaneous determination of relative permeability (Kr) and capillary pressure (Pc) − steady-state-transient test (SSTT). The main idea is to use the stabilized data of the steady-state method along with the transient data of the pressure drop. Therefore in the SSTT, the transient data on the pressure drop across the core, between the steady-states, are used instead of the traditionally utilized Pc-curve.
The aim of this work is the development of laboratory procedure and mathematical method of the lab data treatment for SSTT.

Methods
We run the following SSTT for two Berea cores:
– Preliminary mathematical modelling of SSTT to determine optimal test parameters (flow rate, injected water fractions, sampling volumes and frequencies) and type curves for measured pressure drop and water-cut; – Performing water-oil injections with water cuts 0.02, 0.05, 0.1, 0.25, 0.5, 0.75, 0.9, 0.95, 0.98, and 1.00; – Approximation of the measured transient pressure-drop data by the type curves to regularise the inverse problem of Kr and Pc calculations; – Kr and Pc calculations by the inverse modelling.
To approximate the scattered, raw transient pressure-drop data, we determine the type curves within the stabilization-time interval. The S-shape pressure-drop curves are observed for low water fractions in the injected fluid; the exponential form is observed at high water fraction values.

Results and Conclusions
After determination of Kr and Pc curves from the steady-state and transient pressure-drop data by the inverse solver, we compared the measured and modelled values of transient water-cut. High agreement was observed for two Berea corefloods: R2 varies from 0.88 to 0.99. Besides, the matched modelling lines for pressure-drop and saturation are located within the respective error bars in both tests.
We also applied the SSTT method developed to treat the published steady-state data of 3 gas-water and 3 oil-water tests, where steady-state saturation profiles were determined by X-ray CT. The close match validates the SSTT.

Novelty
For the first time, a lab method for simultaneous determination of Kr and Pc from coreflood for gas-water and oil-water fluids has been developed and validated.