CN105628811A - A kind of supercritical CO2 and CH4 competitive adsorption test device and test method in shale - Google Patents

Abstract

The invention provides a supercritical _CO2 and _CH4 competitive adsorption testing device and testing method in shale. The device includes injection pump system, long core holder, back pressure valve, differential pressure gauge, temperature control system, liquid fraction collector, gas meter and gas chromatograph; the test method includes CH ₄ single-component gas evaluation in shale core Method and Evaluation Method for Supercritical CO ₂ Displacement of CH ₄ Gas in Shale Cores. The present invention satisfies the indoor test detection conditions of supercritical _CO2 displacement shale adsorption _CH4 in shale through the multi-functional long core displacement method, and achieves the purpose of evaluating supercritical _CO2 replacement and adsorption _CH4 efficiency; the present invention adopts The combination of long cores makes the gas injection volume larger, the error is reduced, and the formation conditions are truly restored; the fractured long cores can simulate the process of competing with CH ₄ for adsorption after supercritical CO ₂ fracturing under real shale reservoir conditions; injecting CO ₂ It is in a supercritical state, and the experiment is carried out in a step-by-step pressure reduction method, which can truly simulate the process of formation depletion mining.

Description

A kind of supercritical CO2 and CH4 competitive adsorption test device and test method in shale

technical field

The invention belongs to the technical field of simulation detection experiments, and in particular relates to the simulation and detection technology of the desorption and replacement effect of supercritical carbon dioxide on adsorbed methane gas in shale under high temperature and high pressure, which is used to guide the improvement of reasonable and efficient mining technology of shale gas.

Background technique

The world's shale gas resources are huge. With breakthroughs in North American shale gas exploration and development technology and rapid growth in production, shale gas has been considered as an unconventional natural gas with great mining value. It is very important to understand the development characteristics and development methods of shale gas reservoirs, and to consider how to achieve enhanced shale gas recovery. In shale gas reservoirs, it is generally believed that natural gas occurs in three forms: adsorbed gas, free gas, and dissolved gas. According to the statistics of some scholars, the content of adsorbed gas accounts for 20% to 85%. Strengthening the exploitation of adsorbed gas is particularly important for increasing shale gas production.

According to the successful experience of CO ₂ displacing CH ₄ in coal seams, CO ₂ can successfully displace CH ₄ in coal seams mainly due to the fact that the adsorption capacity of CO ₂ is greater than that of _{CH 4 .} According to the preliminary work, the results show that the adsorption capacity of shale to CO ₂ is significantly stronger than that of CH ₄ . However, there are still very few domestic and foreign laboratory test evaluations on the adsorption of CH ₄ in CO ₂ flooding shale, and most of the experiments that have been carried out cannot meet the conditions of high temperature and high pressure in the formation, especially the actual state of shale that cannot be more completely and comprehensively simulated. , so that the actual production situation cannot be restored, so as to better guide the reasonable and efficient exploitation of shale gas and improve efficiency.

Contents of the invention

The purpose of the present invention is to provide an indoor test detection device and a research method suitable for actual production conditions. The invention evaluates the replacement effect of CO ₂ on the adsorbed gas in shale through the competitive adsorption experiment of supercritical CO ₂ and CH ₄ in shale. The experiment was completed in a multifunctional long core displacement device, which has a reliable principle and a reasonable structure.

The present invention is realized through the following technical solutions:

The invention realizes and discloses a competitive adsorption test device for supercritical CO ₂ and CH ₄ in shale, including: injection pump system, long core holder, back pressure valve, differential pressure gauge, temperature control system, liquid fraction collector , gas meters and gas chromatographs; of which:

The long core holder is composed of a long core outer cylinder, a rubber sleeve and axial connectors at both ends; The device constitutes a closed reaction system;

Injection pump system includes inlet displacement pump, back pressure regulation pump and confining pressure control pump;

The inlet displacement pump communicates with the axial connector at the inlet end through a parallel intermediate container and valve, the back pressure regulating pump communicates with the axial connector at the outlet end through a back pressure valve, and the confining pressure control pump communicates with the axial connector at the outlet end through a valve. The rubber sleeve is connected; a branch of the back pressure valve is also connected with the gas chromatograph through the gas meter.

Each communication pipeline of the device is provided with a differential pressure gauge.

Both the inlet end and the outlet end of the long core holder are provided with differential pressure gauges.

The present invention also provides a test method for competitive adsorption of supercritical CO ₂ and CH ₄ in shale,

The test method adopts the above-mentioned disclosed test device;

The test methods include the CH ₄ single-component gas evaluation method in shale cores and the supercritical CO ₂ replacement CH ₄ gas evaluation method in shale cores:

CH ₄ single-component gas evaluation methods include:

(1) Select small shale rock pillars with a length of 4-6 cm and a diameter of 2.5 cm to measure basic physical properties, arrange the selected short shale cores with fractures in order to form long cores, put them into the core holder and vacuumize ;

(2) Put the long core holder after vacuuming into the oven, set the temperature of the oven to the temperature of the formation to which the shale belongs, set the confining pressure of the holder to the pressure value of the overlying formation of the formation to which the shale belongs, and put it into the airtight Methane gas is fed into the holder system to fully absorb and saturate the methane gas in the shale. The saturation time is 72 hours, and the methane saturation pressure is the pore pressure value of the formation to which the shale belongs;

(3) Close the inlet end of the gripper system, open the outlet end, depressurize the methane gas in the system step by step, and record the depressurization time and gas output at the outlet end, and close the outlet end for 12 hours after depressurization, so that the shale The adsorbed methane gas in the system is fully desorbed, and then the outlet port is opened, and the previous steps of reducing pressure, recording time and gas production volume, and closing/opening the outlet port are repeated until the pressure of methane gas in the system is reduced to the development and abandonment pressure of the gas reservoir to which the shale belongs So far, calculate the cumulative gas output;

_Described supercritical _CO replacement CH gas evaluation method comprises:

(4) Continue to use the CH ₄ single-component gas evaluation method to test rock samples, vacuumize the system, and repeat the above-mentioned experimental operations;

(5) Open the valves at the inlet and outlet of the holder, inject supercritical CO ₂ into the long core at an injection pressure of 35 MPa, and perform chromatographic analysis on the gas at the outlet of the process;

(6) When the gas detected at the outlet is all carbon dioxide, close the valves at the inlet and outlet of the gripper system for 72 hours to fully absorb _CO2 and replace the adsorbed _CH4 gas;

(7) Close the inlet port of the gripper system, open the outlet port, make the mixed gas in the system depressurize by 2MPa, record the depressurization time, and record the output CH gas volume by chromatographic analysis _; the outlet port is closed for 12 hours after depressurization, and the The CO ₂ in the shale is fully adsorbed and replaced with CH ₄ gas, and then the outlet port is opened, and the above steps of pressure reduction, time and gas production record, and closing/opening of the outlet port are repeated until the gas pressure in the system is reduced to the gas reservoir to which the shale belongs Calculate the cumulative output of methane gas up to the development waste pressure;

(8) Comparing the methane gas production at the same pressure drop point in the two groups of experiments, and evaluating the effect of supercritical CO ₂ competitively adsorbing CH ₄ in shale.

The three-axis long core holder about 1 meter long in the test device of the present invention is a key part of the long core displacement device, and is mainly composed of a long core outer cylinder, a rubber sleeve and an axial connector. In this set of devices, the depletion rate of the condensate gas in the rock core is controlled by the pressure drop rate at the outlet end, and the pressure drop rate at the outlet end is controlled by the pressure drop rate of the back pressure valve.

The valve test method is completed by comparing two groups of experiments.

Arrange the short cores in a certain order and combine them with long cores, put them into the core holder, wash, blow dry and vacuumize, then saturate with CH ₄ to the formation conditions, and carry out two groups of experiments at this pressure for 72 hours. The first group of experiments starts from the depletion of formation conditions, and the pressure of each level of depletion is stable for 12 hours to fully desorb, and the corresponding experimental data is recorded at the end of each depletion; the comparative experiment mainly considers the competitive adsorption of CO ₂ to CH ₄ , first through rapid displacement, The CH ₄ in the matrix was completely displaced, and then under the same experimental conditions as the first group, the component content of the produced gas was measured, and the experimental effect was compared with the corresponding test points of the first group.

Compared with existing methods, the present invention has the following beneficial effects:

1) After investigation, it is found that there is currently no experimental test research on the competitive adsorption of supercritical CO ₂ and CH ₄ during the simulated development process under the conditions of simulating real shale reservoir fracturing;

2) By using combined long cores, the gas injection volume is large, the error is reduced, and the formation conditions are truly restored;

3) Long-fractured cores can simulate the competitive adsorption process with CH4 after supercritical CO2 fracturing under real shale reservoir conditions;

4) The injected CO ₂ is in a supercritical state, and the experiment is carried out in a step-by-step pressure reduction method, which can truly simulate the formation depletion mining process.

Description of drawings

Fig. 1 is a schematic diagram of the connection structure of the device of the present invention.

In the figure, 11 is an inlet displacement pump, 12 is a back pressure regulating pump, 13 is a confining pressure control pump, 2 is a long core holder, 21 is a long core outer cylinder, 22 is a rubber sleeve, and 23 is an axial connector , 31 is an intermediate container 1, 32 is an intermediate container 2, 4 is a differential pressure gauge, 5 is a valve, 6 is a back pressure valve, 7 is a gas meter, and 8 is a gas chromatograph.

detailed description

The present invention is specifically described below through the examples, the examples are only used to further illustrate the present invention, and cannot be interpreted as limiting the protection scope of the present invention, some non-essential improvements made by those skilled in the art according to the contents of the present invention And adjustments also belong to the protection scope of the present invention.

Combined with Figure 1.

test device

As shown in Figure 1, the device of the present invention comprises an injection pump system, a long core holder 2, a back pressure valve 6, a differential pressure gauge 4, a temperature control system, a liquid fraction collector, a gas meter 7 and a gas chromatograph 8; The temperature system and the liquid fraction collector are not shown in the figure; where:

The long core holder 2 is composed of a long core outer cylinder 21, a rubber sheath 22 and axial connectors 23 at both ends; the long core outer cylinder 21 is arranged in the rubber sheath 22, and the two ends are connected with the axial connector 23, The rubber sheath 22 and the axial connector 23 form a closed reaction system;

The injection pump system includes an inlet displacement pump 11, a back pressure regulating pump 12 and a confining pressure control pump 13;

The inlet displacement pump 11 communicates with the axial connector 23 at the inlet end through the parallel intermediate containers 31, 32 and valve 5, the back pressure regulating pump 12 communicates with the axial connector 23 at the outlet end through the back pressure valve 6, and the confining pressure control pump 13 communicates with the rubber sheath 22 through the valve 5; a branch of the back pressure valve 6 also communicates with the gas chromatograph 8 through the gas meter 7.

The device of the present invention is provided with a differential pressure gauge 4 in each communication pipeline; a differential pressure gauge 4 is provided at the inlet end and the outlet end of the long core holder 2 .

test experiment

This experiment will be divided into two groups, and the feasibility of the evaluation method will be analyzed through comparison.

Group 1: Evaluation of the production process of CH ₄ single-component gas in shale cores

① Select a shale columnar sample with a length of 4-6 cm and a diameter of 2.5 cm, use the Brazilian splitting method to artificially create fractures on the selected rock samples, and test the porosity and permeability parameters of the rock samples after fractures;

② Calculate the harmonic average permeability of all core columns according to the permeability and length parameters of the rock samples after fracture creation, and select the core column with the closest harmonic average permeability, and record it as the No. 1 core column;

③ Referring to the method in step ②, calculate the new harmonic average permeability from the remaining core columns, and number all the remaining core columns in sequence;

④Put the cores in steps ② and ③ into thermoplastic tubes in series according to the number, and wrap and package the core columns in thermoplastic, so as to splice and form long core experimental samples, put them into the long core holder 2 system, and ensure that the system gas closed, and then evacuate it for 24 hours;

⑤ Put the long core holder 2 into the oven after vacuuming, set the temperature of the oven to 80°C, set the confining pressure of the long core holder 2 to 60MPa, and enter the middle of the airtight long core holder 2 system Container 31 methane gas, so that methane gas can be fully adsorbed and saturated in shale, the saturation time is 72 hours, and the methane saturation pressure is 35MPa;

⑥Close the valve 5 at the inlet end of the long core holder 2 system, open the valve 5 at the outlet end, depressurize the methane gas in the system by 2MPa, and record the depressurization time and gas output at the outlet end, and close the outlet end for 12 hours after depressurization , so that the adsorbed methane gas in the shale is fully desorbed, and then the outlet valve 5 is opened, and the previous steps of reducing the pressure, recording time and gas production volume, and closing/opening the outlet end are repeated until the pressure of the methane gas in the system is reduced to the level of the shale. Calculate the accumulative gas output until the development and abandonment pressure of the gas reservoir;

The second group: Evaluation of the production process of CH ₄ gas in the presence of supercritical CO ₂ replacement in shale cores

① Continue to use the first group of experimental rock samples and experimental devices, vacuumize the system, and repeat the experimental operation of the first group of steps ⑤;

② Open the inlet and outlet valves 5 of the long core holder 2 system, and inject supercritical CO ₂ into the long core at an injection pressure of 35 MPa. Since the fracture permeability is much greater than the matrix permeability, it can be considered that the The contribution of methane all comes from fractures, and this process requires chromatographic analysis of the gas at the outlet;

③When the gas detected by gas chromatography at the outlet end is all carbon dioxide content, it is considered that all the methane in the fracture has been displaced. After the process is over, close the valves at the inlet and outlet ends of the gripper system for 72 hours to fully absorb CO ₂ . And replace the adsorbed CH ₄ gas;

④ Close the valve 5 at the inlet end of the gripper system, open the valve 5 at the outlet end, depressurize the mixed gas in the system by 2MPa, record the depressurization time, and record the amount of methane gas produced by the gas chromatograph 8, and the outlet end is closed after depressurization For 12 hours, let the _CO2 in the shale be fully adsorbed and replaced by _CH4 gas, then open the outlet valve 5, repeat the above step of reducing pressure, recording time and gas output, and closing/opening the outlet until the gas pressure in the system decreases Calculate the accumulative output of methane gas up to the development abandonment pressure of the gas reservoir to which the shale belongs;

⑤Compared the methane gas production at the same pressure drop point in the two groups of experiments, and evaluated the effect of supercritical CO ₂ competitively adsorbing CH ₄ in shale.

Claims (4)

1. a supercritical CO₂With CH in shale₄Competitive adsorption test set, it is characterised in that: comprise injection pump system, long rock core holder, check valve, pressure reduction table, temperature controlling system, liquid distillate collector, gasometer flask and gas chromatograph; Wherein:

Long rock core holder is made up of the axial connector at long cores urceolus, rubber cover and two ends; Long cores urceolus is arranged in rubber cover, two ends are connected with axial connector, and rubber cover forms airtight reactive system with axial connector;

Injection pump system comprises entrance displacement pump, back pressure regulates pump and confined pressure control pump;

Described entrance displacement pump is by intermediate receptacle in parallel, valve and inlet end axial connector UNICOM, and described back pressure regulates pump by check valve and exit end axial connector UNICOM, and described confined pressure controls pump and overlaps UNICOM by valve and rubber; Check valve one branch road is also by gasometer flask and gas chromatograph UNICOM.

2. supercritical CO according to claim 1₂With CH in shale₄Competitive adsorption test set, it is characterised in that: described device each UNICOM pipeline is provided with pressure reduction table.

3. supercritical CO according to claim 1₂With CH in shale₄Competitive adsorption test set, it is characterised in that: described long rock core holder inlet end and exit end are provided with pressure reduction table.

4. a supercritical CO₂With CH in shale₄Competitive adsorption testing method, it is characterised in that:

Described test adopts the test set described in the arbitrary item of claims 1 to 3;

Described testing method comprises CH in shale core₄Supercritical CO in single-component gas evaluation method and shale core₂Displacement CH₄Gas evaluation method:

CH₄Single-component gas evaluation method comprises:

(1) choose length 4��6cm, the little rock pillar of diameter 2.5cm shale, carry out basis physical property measurement, by the selected short rock core of the shale pressing crack in order permutation and combination become long cores, load core holding unit and also vacuumize;

(2) rear long rock core holder will be vacuumized and put into baking oven, setting oven temperature is formation temperature belonging to shale, setting clamper confined pressure is the overlying formation pressure value on stratum belonging to shale, and lead to into methane gas to airtight clamper system, fully absorption is saturated in shale to make methane gas, saturation time is 72 hours, and methane saturation pressure is the Pore Pressure force value on stratum belonging to shale;

(3) clamper system entry end is closed, open exit end, to methane gas step pressure reducing in system, and record step-down time, exit end output tolerance, and exit end closes 12 hours after step-down, make the abundant desorb of adsorbed methane gas in shale, and then open exit end, repeat step-down above, time and output tolerance record, close/open exit end step, till methane gas pressure is reduced to the exploitation abandonment pressure of gas reservoir belonging to shale in system, calculate accumulative output tolerance;

Described supercritical CO₂Displacement CH₄Gas evaluation method comprises:

(4) CH is continued to use₄Single-component gas evaluation method experiment rock sample, vacuumizes system, and repeats above-mentioned experimental implementation;

(5) open clamper inlet end and exit end valve, inject supercritical CO with the injection pressure of 35MPa to long cores₂, and this procedure exit end gas is carried out stratographic analysis;

(6) when the gas that exit end detects out is all carbon dioxide content, close clamper system entry end and exit end valve 72 hours, make CO₂Fully absorption, and replace ADSORPTION STATE CH₄Gas;

(7) close clamper system entry end, open exit end, make mixed gas step-down 2MPa in system, the record step-down time, and by stratographic analysis record output methane tolerance; After step-down, exit end closes 12 hours, makes the CO in shale₂Fully absorption displacement CH₄Gas, and then open exit end, repeat above-mentioned step-down, time and output tolerance record, close/open exit end step, till gaseous tension is reduced to the exploitation abandonment pressure of gas reservoir belonging to shale in system, calculate accumulative output methane tolerance;

(8) contrast the methane yield that two groups are tested same pressure drop point, evaluate supercritical CO₂CH in competitive adsorption shale₄Effect.