Sampling an oil composition and determining minimum miscibility pressure of an oil composition with a fluid

1. A method of determining a minimum miscibility pressure of a fluid with an oil composition, the method comprising:

placing a fluid into a pressure chamber at a first pressure, the pressure chamber comprising a plurality of capillary tubes each having one end disposed in an oil composition in the pressure chamber and with each of the capillary tubes having a different diameter, wherein the fluid comprises at least one of a gas, a liquid, and a supercritical fluid, wherein the oil composition comprises a plurality of compounds each having a different molecular weight;

measuring a height of the oil composition in each of the capillary tubes;

repeating the measuring for at least one cycle using a second pressure different than the first pressure, wherein the first and second pressure are selected such that a majority of a desired molecular weight fraction of the oil composition remains immiscible with the fluid; and

determining the minimum miscibility pressure of the desired molecular weight fraction of the oil composition with the fluid by extrapolating the pressure at a height of a fluid-fluid interface between the desired molecular weight fraction and the fluid in the capillary tubes of zero independently for each of the capillary tubes from the two or more measurements of the height of the fluid-fluid interface between the desired molecular weight fraction and the fluid in each of the capillary tubes and averaging the at least two extrapolated pressures.

2. The method of claim 1 , further comprising equilibrating pressure within the pressure chamber prior to measuring the height of the fluid-fluid interface between the desired molecular weight fraction and the fluid.

3. The method of claim 1 , wherein the second end of the capillary tubes is disposed in the fluid in the pressure chamber.

4. The method of claim 1 , further comprising equilibrating temperature within the pressure chamber prior to measuring the height of the fluid-fluid interface between the desired molecular weight fraction and the fluid.

5. The method of claim 1 , wherein the height of the fluid-fluid interface between the desired molecular weight fraction and the fluid in at least one of the capillary tubes is the distance between the surface of the oil composition in the pressure chamber and the surface of the fluid-fluid interface between the desired molecular weight fraction and the fluid in the capillary tube.

6. The method of claim 1 , wherein the fluid comprises at least one of carbon dioxide, nitrogen, methane, ethane, propane, hydrogen sulfide, n-butane, iso-butane, natural gas, natural gas liquids, and produced gas.

7. The method of claim 1 , wherein the oil composition comprises crude oil or a crude oil fraction.

8. The method of claim 1 , wherein the oil composition comprises a live oil sample.

9. The method of claim 1 , wherein the oil composition comprises a plurality of compounds comprising at least one desired compound, further comprising selecting the first and second pressure such that each cause at least 5-99 wt % of the oil composition to become miscible with or substantially soluble in the fluid, such that the desired compound remains substantially immiscible with the fluid at the first and second pressure, such that the determined minimum miscibility pressure is approximately the minimum miscibility pressure of the fluid with the desired compound.

10. The method of claim 1 , wherein the oil composition comprises a plurality of compounds comprising at least one desired compound, further comprising selecting the first and second pressure such that each cause no more than 0-95 wt % of the oil composition to become miscible with or substantially soluble in the fluid, such that the desired compound remains substantially immiscible with the fluid at the first and second pressure, such that the determined minimum miscibility pressure is approximately the minimum miscibility pressure of the fluid with the desired compound.

11. The method of claim 1 , further comprising performing a flooding treatment of a subterranean formation comprising therein a petroleum composition that is the same as or substantially resembles the oil composition, wherein the flooding treatment is performed using the fluid at a pressure that is equal to or above the determined minimum miscibility pressure.

12. The method of claim 11 , further comprising performing the method of determining the minimum miscibility pressure using as the oil composition a sample produced from the subterranean formation after the flooding treatment has begun.

13. A method of flooding a subterranean formation with a fluid, the method comprising:

obtaining or providing a maximum pressure for a subterranean formation;

performing the method of claim 1 using as the oil composition a sample from the subterranean formation or that substantially resembles a sample from the subterranean formation;

adjusting the composition of the fluid and repeating the performance of the method, until at least one fluid composition is determined that has a lower minimum miscibility pressure with the oil composition than the maximum pressure for the subterranean formation; and

performing a flooding treatment of the subterranean formation using the fluid at a pressure that is equal to or above the determined minimum miscibility pressure and below the maximum pressure for the subterranean formation.

14. A method of determining a minimum miscibility pressure of a fluid with an oil composition, the method comprising:

placing a fluid into a pressure chamber at a first pressure, the pressure chamber comprising a plurality of capillary tubes each having one end disposed in an oil composition in the pressure chamber and with each of the capillary tubes having a different diameter, wherein the fluid comprises at least one of a gas, a liquid, and a supercritical fluid, wherein the oil composition comprises one or more desired compounds;

measuring a height of the oil composition in each of the capillary tubes;

repeating the measuring for at least one cycle using a second pressure different than the first pressure, wherein the first and second pressure are selected such that each cause at least about 5 wt % to about 99 wt % of the oil composition to become miscible with or substantially soluble in the fluid, such that the one or more desired compounds remain substantially immiscible with the fluid at the first and second pressure; and

determining the minimum miscibility pressure of the one or more desired compounds with the fluid by extrapolating the pressure at a fluid-fluid interface between the one or more desired compounds and the fluid in the capillary tubes of zero independently for each of the capillary tubes from the two or more measurements of the height of fluid-fluid interface between the one or more desired compounds and the fluid in each of the capillary tubes and averaging the at least two extrapolated pressures.

15. A method of determining a minimum miscibility pressure of a fluid with an oil composition, the method comprising:

placing a fluid into a pressure chamber at a first pressure, the pressure chamber comprising a plurality of capillary tubes each having one end disposed in an oil composition in the pressure chamber and with each of the capillary tubes having a different diameter, wherein the fluid comprises at least one of a gas, a liquid, and a supercritical fluid, wherein the oil composition comprises one or more desired compounds;

measuring a height of the oil composition in each of the capillary tubes;

repeating the measuring for at least one cycle using a second pressure different than the first pressure, wherein the first and second pressure are selected such that each cause no more than about 0 wt % to about 95 wt % of the oil composition to become miscible with or substantially soluble in the fluid, such that the one or more desired compounds remain substantially immiscible with the fluid at the first and second pressure; and

determining the minimum miscibility pressure of the one or more desired compounds of the oil composition with the fluid by extrapolating the pressure at a height of a fluid-fluid interface between the one or more desired compounds and the fluid in the capillary tubes of zero independently for each of the capillary tubes from the two or more measurements of the height of the fluid-fluid interface between the one or more desired compounds and the fluid in each of the capillary tubes and averaging the at least two extrapolated pressures.