An experimental method for supercritical CO2/H2O mixed fluid huff and puff for shale oil development, using an experimental device for supercritical CO2/H2O mixed fluid huff and puff for shale oil development, the experimental device comprising a CO2 storage tank, a water vapor generator, a mixing vessel, and a core holder, wherein the CO2 storage tank is in communication with the mixing vessel via a CO2 delivery pipeline, and the CO2 delivery pipeline is provided with a first booster pump;
- the water vapor generator is in communication with the mixing vessel via a water vapor delivery pipeline, and the water vapor delivery pipeline is provided with a second booster pump;
- a first pressure gauge and a hygronom are connected to an upper end of the mixing vessel, a displacement pump is connected to a lower end of the mixing vessel, and the mixing vessel is connected to a vacuum pump;
- the mixing vessel is connected to an inlet end of the core holder via a mixed fluid delivery pipeline, and the mixed fluid delivery pipeline is provided with a gas flow meter, a third booster pump, an injection valve and a second pressure gauge in sequence;
- the core holder is connected to a hand pump via a confining pressure application pipeline, and the confining pressure application pipeline is provided with a third pressure gauge;
- the inlet end of the core holder is connected to an inlet end of a drying pipe via an oil-gas extraction pipeline, the oil-gas extraction pipeline is provided with a two-way valve, degreasing cotton is provided inside the drying pipe, an outlet end of the drying pipe is connected to a measuring cylinder via a gas extraction pipeline, and the measuring cylinder is disposed upside down in a liquid containing dish, wherein the liquid containing dish and the measuring cylinder are filled with a saturated sodium carbonate solution;
- an outlet end of the core holder is provided with a fourth pressure gauge for observing outlet pressure in real time;
- and
- the mixing vessel, the first pressure gauge, the hygronom, the gas flow meter, the third booster pump, the injection valve, the second pressure gauge, the two-way valve, the core holder and the fourth pressure gauge are all arranged in a thermostat chamber;
- the experimental method comprising the following steps:
- at step (1), measuring the dry weight, length, and diameter of a rock core, and saturating the rock core with a simulated oil;
- and measuring the wet weight of the rock core to calculate the amount of the saturated oil;
- at step (2), carrying out a supercritical CO2/H2O huff and puff experiment:
- at i), preparing a supercritical CO2/H2O mixed fluid of a certain ratio in the mixing vessel;
- at a., establishing a relation formula by the following steps:
- converting relative humidity into molar content of water vapor in gas according to the following formulas:
- relative humidity:
- e
- E
- =
- φ
- (
- 1
- )
- where:
- e—actual water vapor pressure in humid air, Pa
- E—saturated water vapor pressure at the same temperature, Pa
- φ—relative humidity
- conversion formulas:
- φ
- =
- P
- ·
- h
- P
- 0
- (
- 2
- )
- h
- =
- φ
- ·
- P
- 0
- P
- (
- 3
- )
- h
- P
- 0
- =
- φ
- P
- (
- 4
- )
- where:
- φ—relative humidity
- P—gas pressure in the vessel, Pa
- h—molar content of water vapor in gas
- P0—saturated vapor pressure of water at experimental temperature
- at b., turning on the thermostat chamber to make the temperature in the thermostat chamber be constant;
- and turning on the vacuum pump to vacuumize the mixing vessel and the pipelines;
- opening the CO2 storage tank, injecting a certain amount of CO2 gas into the mixing vessel via the first booster pump and the CO2 delivery pipeline, and reading the pressure of the mixing vessel from the first pressure gauge;
- then, turning on the water vapor generator, introducing water vapor into the mixing vessel via the second booster pump and the water vapor delivery pipeline, and recording the pressure and relative humidity of the mixing vessel from the first pressure gauge and the hygronom, respectively;
- with the formula (4), according to the molar content and temperature of water vapor in a mixed fluid designed in an experiment scheme, when the ratio of the relative humidity and the pressure meets requirements of experiment, turning off the water vapor generator to complete the preparation of a mixed fluid with a certain content of water vapor;
- and then recording the pressure of the mixing vessel;
- at ii), putting the oil-saturated rock core of step (1) into the core holder, and applying a confining pressure to the core holder by the hand pump, the confining pressure applied being displayed by the third pressure gauge;
- opening the injection valve, injecting the prepared mixed fluid with a certain molar fraction of water vapor into the core holder by the third booster pump while keeping the pressure of the mixing vessel constant by the displacement pump, keeping the injection pressure, after reaching an experiment pressure, stable for a certain period of time, and recording the volume of injected gas from the gas flow meter;
- and
- at iii), shutting off the injection valve, carrying out shut-in on the core holder, and monitoring the pressure during shut-in in real time by the second pressure gauge and the fourth pressure gauge;
- weighing the initial weight of the degreasing cotton before putting the degreasing cotton into the drying pipe, opening the two-way valve when the shut-in is completed for flowback of liquid and gas, then weighing the weight of the degreasing cotton to measure the amount of produced oil, and measuring the amount of CO2 flowed back by the measuring cylinder;
- and
- obtaining an oil recovery according to the ratio of the measured amount of produced oil to the amount of saturated oil as the measurement result of the experiment.