According to the principle that gas diffuses freely through the rock sample under concentration gradient, hydrocarbon gas is filled at one end and nitrogen gas is filled at the other end in the diffusion chamber at both ends of the rock sample. Under the condition of constant temperature and pressure, the concentration of each component gas changes with time. The diffusion coefficient of hydrocarbon gas in rock samples can be obtained by measuring the concentration of each component gas in two diffusion chambers at different times.
Instruments and equipment
See the device schematic diagram 72.5438+0 for the measuring device of hydrocarbon gas diffusion coefficient in rock matrix pores, including:
There is a cavity of 20 ~ 40 cm3 container on the two plugs of the core holder, which is directly open to the rock sample and called diffusion chamber.
Hot box (150 0.5)℃.
Pressure gauge 1.0MPa, accuracy 0.4.
The differential pressure sensor is 20kPa with an accuracy of 0.0 1kPa.
Fig. 72.2 1 Schematic diagram of measuring device for hydrocarbon gas diffusion coefficient in rocks
Gas chromatograph.
The nominal pressure of high-pressure metering pump is greater than 10MPa.
The vacuum degree of the vacuum pump is less than 6× 10-2Pa.
Reagents and materials
The purity of methane, ethane, propane, butane and pentane is more than 99.9%.
Natural gas.
The purity of nitrogen is more than 98.0%.
Epoxy resin can resist high temperature 150 ~ 200℃.
Sodium chloride.
Anhydrous calcium chloride
Magnesium chloride hexahydrate.
Rock sample preparation
1) dry sample preparation. Rock sample preparation, oil washing and drying (see 4.3.2, 4.5 and 4.6 in SY/T 5336-88). According to the requirements of vertical permeability analysis, drill a rock sample with a length of 0.5 ~ 2.5 cm. Muddy rock samples that are easily dispersed in water and difficult to drill can be made into small-diameter columnar or square rock samples by hand, and then cemented in metal casing with epoxy resin, and aged at room temperature for more than 12h.
2) Preparation of saturated water rock samples. Saturate the prepared dry samples according to the requirements of 6. 1.2 in SY/T 5336-88 to simulate formation water. The simulated formation water should be prepared according to the formation water data. When there is no formation water data, standard saline water (containing 70g sodium chloride, 6g anhydrous calcium chloride and 4g magnesium chloride hexahydrate in each liter of water) can be used instead.
Analytical method
Load the rock sample into the core holder and increase the confining pressure to above 3MPa. Set the test temperature of the incubator according to the high molding temperature and keep it constant for 2 ~ 2.5h When measuring the diffusion coefficient of hydrocarbon gas in the dry sample, start the vacuum pump to vacuum the core holder and the corresponding pipeline1~1.5h.: Do not pause while measuring saturated water and rock samples. Nitrogen and hydrocarbon gas are introduced into two diffusion chambers respectively, and the two diffusion pressures are simultaneously raised to 0.65438±0 MPa；; When the pressure difference is less than 0. 1kPa, disconnect the air source. When determining the diffusion coefficient of hydrocarbon gas in dry samples, samples should be taken every 0.5 ~ 6h. When determining saturated water rock samples, take gas every 2 ~ 12h, and sample and analyze according to GB 104 10.2. Each rock sample shall be tested at least 12h, and at least 5 gas samples shall be taken from each end. The temperature of the incubator was lowered to room temperature, and the gases in the two diffusion chambers were released, thus ending the test.
data reduction
According to GB 104 10.2, the gas concentrations of each component in the two diffusion chambers were calculated.
According to Fick's second law, the diffusion coefficient of hydrocarbon gas in rock samples is calculated.
Investigation and analysis technology of resources and environment in the fourth volume of rock mineral analysis
These include:
Investigation and analysis technology of resources and environment in the fourth volume of rock mineral analysis
According to the formula (72. 1 19):
Investigation and analysis technology of resources and environment in the fourth volume of rock mineral analysis
Ln (δ Ф 0/δ Ф I) has a linear relationship with ti, and the slope S is obtained by least square fitting. According to s, the diffusion coefficient of hydrocarbon gas in rock samples can be obtained:
Investigation and analysis technology of resources and environment in the fourth volume of rock mineral analysis
Where: d is the diffusion coefficient of hydrocarbon gas in the rock sample, cm2s-1; δ Ф 0 is the concentration difference of hydrocarbon gas in two diffusion chambers at the initial moment,%; Δ Ф i is the concentration difference of hydrocarbon gas in two diffusion chambers at time i,%; Ti is I time, s; T0 is the initial time, s; Ф i1is the concentration of hydrocarbon gas in the hydrocarbon diffusion chamber at the first moment,%; Ф I2 is the concentration of hydrocarbon gas in the nitrogen diffusion chamber at the first moment,%; A is the cross-sectional area of the rock sample, and cm2l is the length of the rock sample, cm; V 1, V2 are the volumes of hydrocarbon diffusion chamber and nitrogen diffusion chamber respectively, and cm3e is the intermediate variable, cm-2; S is the slope, s- 1.