Rock Core Cation Exchange Site Wettability Analysis

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Solution Overview

Problem

Conventional methods for determining cation exchange capacity and wettability in rock samples are not representative of in-situ reservoir conditions, leading to inaccurate measurements and impacting enhanced oil recovery efforts.

Innovation Solution

A method involving coreflooding steps to displace native components, inject formation brine and crude oil, and use organic solvents to determine the properties of cation exchange sites, including the amount of indigenous and total exchangeable cations, and calculate wettability, allowing for differentiation between different cation exchange sites.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the rock sample is cleaned to remove any oil in the rock sample, then the cation exchange capacity can be measured, but the measurement is not representative of in-situ reservoir conditions

Engineering Contradiction:

Improvecation exchange capacity measurementVSAvoidreservoir representativeness

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The method performs preliminary coreflooding steps to establish equilibrium between formation brine, reservoir crude oil, and cation exchange sites before measurement. This preliminary action ensures that the rock sample maintains its in-situ reservoir conditions (with oil adsorbed on cation exchange sites) while still allowing for accurate measurement of cation exchange capacity and identification of exchangeable cations.

Inventive Principle:

Principle #10Preliminary action

2Quantity of substance

If the rock sample is ground to fine particles, then more cation exchange sites are exposed, but the cation exchange capacity is overestimated

Engineering Contradiction:

Improveexposed cation exchange sitesVSAvoidcation exchange capacity

Core Design Contradiction:

Quantity of substanceVSMeasurement precision

Solution Approach 1:

The method uses coreflooding techniques that selectively expose and measure cation exchange sites in situ without requiring extensive grinding of the rock sample. By injecting formation brine and reservoir crude oil through the core sample, the method locally interacts with cation exchange sites at their natural state, avoiding the overestimation that occurs when excessive grinding exposes additional sites not present in the reservoir.

Inventive Principle:

Principle #3Local quality

3Measurement precision

If conventional wettability measurement methods are used, then general wettability can be determined, but the wettability of different cation exchange sites cannot be determined

Engineering Contradiction:

Improvegeneral wettabilityVSAvoidsite-specific wettability

Core Design Contradiction:

Measurement precisionVSDifficulty of detecting and measuring

Solution Approach 1:

The method segments the cation exchange sites based on their affinity for different cations (e.g., calcium-preferred sites, sodium-preferred sites) and determines the wettability of each segment separately. By using selective cation exchange and coreflooding techniques, the method identifies which specific cation exchange sites are occupied by crude oil versus formation brine, providing site-specific wettability information that conventional methods cannot provide.

Inventive Principle:

Principle #1Segmentation

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach provides accurate determination of cation exchange site properties, enabling more effective enhanced oil recovery operations by accounting for the specific characteristics of each site, improving the design of EOR processes.

Implementation Method 1

displacing the second organic solvent with a formation brine to adsorb a plurality of exchangeable cations onto the cation exchange sites of the rock core sample

Methodology Applied

Scientific EffectIon exchange: Ion Exchange

Implementation Method 2

displacing all native components out of the pore space of the rock core sample by alternately injecting a first organic solvent and a second organic solvent

Methodology Applied

Scientific EffectAdsorption: Adsorption

Implementation Method 3

displacing the plurality of indigenous cations adsorbed onto the cation exchange sites of the rock core sample with a second injection fluid until completion of extraction

Methodology Applied

Scientific EffectDesorption: Desorption

Data Source

PatentUS11555812B2Methods of determining cation exchange sites occupied by crude oil and the wettability of cation exchange sites in rock core samples in a non-preserved state

Publication Date: 2023.01.17 SAUDI ARABIAN OIL CO

AI summary

A method for determining properties of different cation exchange sites in a rock core sample at a non-preserved state may include displacing all native components out of the rock core sample before subjecting the rock core sample to coreflooding steps to determine a total amount of exchangeable cations adsorbed onto the cation exchange sites; injecting formation brine and then a reservoir crude oil into the rock core sample such that the rock core sample includes indigenous exchangeable cations adsorbed onto the cation exchange sites, cation exchange sites occupied by a crude oil, and one or more fluids; subjecting the rock core sample to coreflooding steps to displace the indigenous exchangeable cations, the crude oil, and the one or more fluids; determining an amount of indigenous exchangeable cations adsorbed onto the cation exchange sites; and determining at least one property of different cation exchange sites.