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

A method for determining an amount of different cation exchange sites occupied by crude oil in a rock core sample, at a non-preserved state of the rock core sample, the method comprising:

• providing a rock core sample in a non-preserved state;
• 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, wherein the second organic solvent is the last injected;
• displacing the second organic solvent with a formation brine to adsorb a plurality of exchangeable cations onto the different cation exchange sites of the rock core sample;
• displacing an excess of cations from the formation brine present in a plurality of interstitial pore spaces of the rock core sample by using a third organic solvent;
• displacing the plurality of exchangeable cations adsorbed onto the different cation exchange sites of the rock core sample with a first injection fluid until completion of extraction;
• displacing the first injection fluid with the formation brine such that the cations present in the formation brine adsorb onto the cation exchange sites;
• injecting a reservoir crude oil into the rock core sample until reaching irreducible water saturation and equilibrium between formation brine, the reservoir crude oil, and the cation exchange sites, such that rock core sample includes a plurality of indigenous exchangeable cations adsorbed onto the cation exchange sites, a plurality of cation exchange sites occupied by a crude oil, and one or more fluids occupying pore spaces in the rock core sample;
• displacing the reservoir crude oil in the rock core sample with formation brine until oil ceases production;
• displacing an excess of cations present in a plurality of interstitial pore spaces of the rock core sample by using a fourth organic solvent;
• 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;
• calculating an amount of indigenous exchangeable cations adsorbed onto the cation exchange sites and a total amount of the exchangeable cations adsorbed onto the cation exchange sites;
• and
• calculating the amount of the different cation exchange sites occupied by crude oil based on the amount of indigenous exchangeable cations adsorbed onto the cation exchange sites and the total amount of the exchangeable cations adsorbed onto the cation exchange sites.

A method for determining a wettability of different cation exchange sites of a rock sample, at a non-preserved state of the rock core sample, the method comprising:

• providing a rock core sample in a non-preserved state;
• 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, wherein the second organic solvent is the last injected;
• displacing the second organic solvent with a formation brine to adsorb a plurality of exchangeable cations onto the different cation exchange sites of the rock core sample;
• displacing an excess of cations from the formation brine present in a plurality of interstitial pore spaces of the rock core sample by using a third organic solvent;
• displacing the plurality of exchangeable cations adsorbed onto the different cation exchange sites of the rock core sample with a first injection fluid until completion of extraction;
• displacing the first injection fluid with the formation brine such that the cations present in the formation brine adsorb onto the cation exchange sites;
• injecting a reservoir crude oil into the rock core sample until reaching irreducible water saturation and equilibrium between formation brine, the reservoir crude oil, and the cation exchange sites, such that rock core sample includes a plurality of indigenous exchangeable cations adsorbed onto the cation exchange sites, a plurality of cation exchange sites occupied by a crude oil, and one or more fluids occupying pore spaces in the rock core sample;
• displacing the reservoir crude oil in the rock core sample with formation brine until oil ceases production;
• displacing an excess of cations present in a plurality of interstitial pore spaces of the rock core sample by using a fourth organic solvent;
• 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;
• calculating an amount of indigenous exchangeable cations adsorbed onto the cation exchange sites and a total amount of the exchangeable cations adsorbed onto the cation exchange sites;
• and
• calculating the wettability of the different cation exchange sites based on the amount of indigenous exchangeable cations adsorbed onto the cation exchange sites and the total amount of the exchangeable cations adsorbed onto the cation exchange sites.