Evaluation method for gas injection energy supplement effect

Abstract

The invention belongs to the field of oil and gas field development engineering, and particularly relates to a method for evaluating a gas injection energy supplementing effect. According to the evaluation method for the gas injection and energy supplementation effect, through simulation of different gas injection media, gas injection time, gas injection speed and different types of reservoirs, the gas drive effect of a gas reservoir in the gas injection and energy supplementation process is systematically evaluated, the change rule of gas injection and energy supplementation for improving the recovery ratio under different conditions is determined, and the recovery efficiency is improved. And a basis is provided for efficient development and scientific decision-making of gas reservoirs.

Description

Technical Field

[0001] The present invention belongs to the field of oil and gas field development engineering, and particularly relates to a method for evaluating the effect of gas injection for energy replenishment. Background Art

[0002] The output of Puguang Gas Field accounts for 30% of Sinopec's natural gas output and 95.6% of Zhongyuan Oilfield's natural gas output. Puguang Gas Field is also a gas reservoir with relatively large discovered natural gas reserves in China. The continuous stable production of the gas field plays an important role in realizing the stable supply of domestic natural gas. Affected by factors such as water invasion and sulfur deposition, the natural gas output of Puguang Gas Field has begun to decline. The main directions for continuous stable production are to improve the recovery rate in old areas and roll out additional reserves and build production in new formations. Among them, there is a large room for improvement in the recovery rate of old areas, but problems such as water control, sulfur treatment, and lack of new production enhancement technologies need to be overcome.

[0003] Gas injection in high-sulfur gas reservoirs is a new direction for exploring enhanced recovery technologies in recent years. The annual emission of tail gas (i.e., flue gas) from Puguang purification plant reaches 15 million tons, among which N2 is 10.7 million tons and CO2 is 2 million tons. It can provide gas sources for exploring new gas injection energy replenishment, water control, and sulfur control technologies and is conducive to reducing carbon emissions. To carry out research on steam injection energy replenishment in gas fields, simulation and effect evaluation of gas injection for energy replenishment in gas reservoirs are indispensable, otherwise it is difficult to achieve efficient development and scientific decision-making of gas reservoirs. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for evaluating the effect of gas injection for energy replenishment, so as to provide a basis for the efficient development and scientific decision-making of gas reservoirs.

[0005] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0006] A method for evaluating the effect of gas injection for energy replenishment includes the following evaluation steps for different gas injection media, different gas injection times, different gas injection rates, and different types of reservoirs:

[0007] Evaluation of gas injection media:

[0008] (1) Saturate a core model with formation gas and age it, then inject the gas injection medium into the core model for displacement experiments, and calculate the degree of natural gas recovery.

[0009] (2) Repeat step (1) to determine the degree of natural gas recovery of different gas injection media, and optimize the gas injection media.

[0010] Evaluation of gas injection time:

[0011] (a) Saturate a core model with formation gas and age it. After the original formation pressure or the original formation pressure is depleted to the design pressure, conduct displacement experiments according to the designed flow rate and gas injection medium, and calculate the degree of natural gas recovery.

[0012] (b) Repeat step (a) to determine the gas production degree under different pressure conditions and optimize the gas injection timing.

[0013] Gas injection rate evaluation:

[0014] (Ⅰ) Saturate the core model with formation gas and age it, conduct a displacement experiment at the designed injection rate, and calculate the gas production degree.

[0015] (Ⅱ) Repeat step (Ⅰ) to determine the gas production degree under different injection rates and optimize the gas injection rate.

[0016] Evaluation of different types of reservoirs:

[0017] (i) Select a core model that meets the requirements of the reservoir type, saturate the core model with formation gas and age it, conduct a displacement experiment under the designed injection conditions, and calculate the gas production degree.

[0018] (ii) Repeat step (i) to determine the gas production degree of the core model of other types of reservoirs or the parallel core model formed by the parallel connection of core models of different types of reservoirs, and evaluate the gas injection energy supplement effect of different types of core models.

[0019] The evaluation method for the gas injection energy supplement effect provided by the present invention systematically evaluates the gas drive effect during the gas injection energy supplement process of the gas reservoir through the simulation of different gas injection media, gas injection timing, gas injection rate, and gas injection of core models of different types of reservoirs, clarifies the variation law of the enhanced oil recovery by gas injection energy supplement under different conditions, and provides a basis for the efficient development and scientific decision-making of the gas reservoir.

[0020] Preferably, in step (2), the different gas injection media include carbon dioxide, nitrogen, and flue gas.

[0021] Preferably, the core models involved in the evaluation of different types of reservoirs include single cores and parallel cores formed by the parallel connection of core models of different types of reservoirs.

[0022] Preferably, the different types of reservoirs include Class I reservoirs and Class II reservoirs; the parallel core model includes a parallel core formed by the parallel connection of Class I reservoir cores and Class II reservoir cores. Among them, the classification of Class I reservoir cores and Class II reservoir cores refers to the petroleum and natural gas industry standard "SY / T 5388-2000 Classification Method for Carbonate Rock Reservoirs". The porosity of the Class I reservoir core selected for the experiment is 9.98%, and the permeability is 8.864×10 -3 μm 2 , and the porosity of the Class II reservoir core is 5.23%, and the permeability is 2.897×10 -3 μm 2 .

[0023] Preferably, in step (1), step (a), step (Ⅰ), and step (i), the displacement experiment ends when the injected gas volume reaches more than 1.2 times the pore volume of the core model or the gas component composition at the production end no longer changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 FIG. is a schematic diagram of a physical simulation device for evaluating the effect of gas injection for energy replenishment used in the present invention;

[0025] Figure 2 FIG. is a graph of the recovery rate of gas drive experiments with different injection media;

[0026] Figure 3 FIG. is a graph of the recovery rate of gas drive experiments with different injection pressures;

[0027] Figure 4 FIG. is a graph of the recovery rate of gas drive experiments with different injection rates;

[0028] Figure 5 FIG. is a graph of the recovery rate of gas drive experiments for core samples of Class I reservoirs and Class II reservoirs;

[0029] Figure 6 FIG. is a graph of the recovery rate of gas drive experiments for parallel cores of Class I reservoirs and Class II reservoirs;

[0030] Among them, 1 - first injection pump; 2 - first needle valve; 3 - first piston container; 4 - first pressure gauge; 5 - check valve; 6 - first six-way valve; 7 - second six-way valve; 8 - long core model; 9 - pressure and saturation detection component; 10 - second injection pump; 11 - second needle valve; 12 - second piston container; 13 - second pressure gauge; 14 - third needle valve; 15 - back pressure valve; 16 - back pressure automatic tracking pump; 17 - fourth needle valve; 18 - third pressure gauge; 19 - fifth needle valve; 20 - buffer container; 21 - gas flow meter; 22 - gas chromatograph; 23 - computer control and visual observation system. DETAILED DESCRIPTION OF THE INVENTION

[0031] To meet the production requirements of improving the recovery rate and maintaining stable production in Puguang Gas Field, the present invention designs a physical simulation device for evaluating the effect of gas injection for energy replenishment and conducts evaluations on the effect of gas injection for energy replenishment, optimization of the timing of gas injection for energy replenishment, optimization of the gas injection rate for energy replenishment, and the influence of reservoir types on gas injection effects based on this device. Using this method, the variation law of improving the recovery rate by gas injection for energy replenishment under different conditions can be clarified, providing a basis for the efficient development and scientific decision-making of gas reservoirs.

[0032] The schematic diagram of the above physical simulation device for evaluating the effect of gas injection for energy replenishment is as shown in Figure 1 FIG., including an injection part, a core group, a production part, and a computer control part.

[0033] The injection section is used to inject gas medium into the core model, including three groups of injection components arranged in parallel. Each injection component includes an injection pipeline and a first injection pump 1, a first needle valve 2, a first piston container 3, a first pressure gauge 4, and a check valve 5 arranged in sequence on the injection pipeline. The three groups of injection components are connected to the core group through a first six-way valve 6. The three piston containers can respectively contain different gas media, such as methane, formation gas, carbon dioxide, etc.

[0034] The core group includes two groups of core components arranged in parallel. Each core component includes a core pipeline and a core holder connected to the core pipeline. The two core pipelines are connected to a second six-way valve 7, and the second six-way valve 7 is connected to the first six-way valve 6. The core holder holds a long core model 8. There are also 6 pressure and saturation detection components 9 and a confining pressure control system on each core holder. The confining pressure control system includes a confining pressure pipeline and a second injection pump 10, a second needle valve 11, a second piston container 12, a second pressure gauge 13, and a third needle valve 14 arranged in sequence on the confining pressure pipeline. A backpressure system is provided downstream of the core holder on the core pipeline. The backpressure system includes a backpressure valve 15 and a backpressure pipeline connected to the backpressure valve 15. A backpressure automatic tracking pump 16 and a fourth needle valve 17 are arranged in sequence on the backpressure pipeline. A third pressure gauge 18 and a fifth needle valve 19 are arranged in sequence on the core pipeline between the core holder and the backpressure valve 15 along the displacement direction.

[0035] The production section includes a production pipeline connected after the backpressure valve. A buffer container 20, a gas flow meter 21, and a gas chromatograph 22 are arranged in sequence on the production pipeline.

[0036] The computer control section includes a computer control and visualization observation system 23 for real-time monitoring of the detection results of the pressure and saturation detection components 9.

[0037] The scheme for evaluating the effect of gas injection for energy replenishment using the above physical simulation device is as follows:

[0038] The first step: Based on the detailed analysis of the geological research understanding and development dynamics of the gas reservoir, the flow and diffusion speed of the gas is relatively large. In order to provide sufficient flow space for gas injection, eliminate interlayer differences and intra-layer differentiation, a long core is used to evaluate the gas injection effect. The long core model selects a core column with a diameter of 25 mm or 38 mm and a length of 5 - 10 cm, and is spliced into a long core according to the Bragg's law. A filter paper is set between the end of the previous core and the front end of the next core to eliminate the end effect. The three groups of saturation electrodes and pressure monitoring components are evenly placed at the gas displacement along-path positions of the long core before thermoplastic sealing of the core. The saturation electrodes are used to monitor the change of irreducible water, and the pressure is used to monitor the range and intensity of gas injection for energy replenishment.

[0039] Step 2: First, put the long core into a heat-sealed plastic sleeve, and then use a hot air glue gun to uniformly heat it. During the heating process, pay attention to the uniform heating of the heat-sealed plastic sleeve to firmly wrap the long core model with the heat-sealed plastic sleeve.

[0040] Step 3: Put the plastic-sealed core model into the clamping system of the model and seal the two ends with end plugs. Connect the components according to Figure 1 Connect each component, evacuate the core model, and the evacuation time shall not be less than 20 hours.

[0041] Step 4: Connect the methane gas source to conduct a leak test on the tightness of the device. After passing the test, heat up the injection pump and the core holder. The injection pump is heated to 60°C, and the core temperature gradually rises to the preset formation temperature.

[0042] Step 5: Use gas to calibrate the pore volume of the model, test the permeability of the spliced core model, and the test method refers to SY / T29172-2012 Core Analysis Method. Check whether the core porosity and permeability meet the designed requirements.

[0043] Step 6: Saturate the core model with formation gas, conduct gas component analysis at the outlet end, and establish a backpressure after the components are consistent with the formation gas components. Let it stand and age for more than 24 hours, check the flow pressure situation, and ensure that the backpressure of the core model in the device reaches the preset value.

[0044] Step 7: Heat up and pressurize the displacement medium designed in the experiment to the preset temperature and pressure, and start the displacement experiment according to the designed flow rate and pressure.

[0045] Step 8: During the experiment, the monitoring end records the pressure along the way and the gas saturation value in real time, and regularly detects the gas component composition at the production end. The experiment ends when the injected gas volume reaches more than 1.2 times the pore volume or the gas component composition at the production end remains stable and no longer changes.

[0046] Step 9: After the temperature of the core model drops to room temperature, reduce the pressure of the core model until the pressure drops to atmospheric pressure.

[0047] Step 10: Use a vacuum pump to evacuate for 20 hours. Refer to SY / T29172-2012 Core Analysis Method, use gas to measure the pore volume and permeability of the model, determine the change range of gas-measured porosity and permeability, and start the next set of experiments.

[0048] When conducting the next set of experiments, steps 6 to 10 can be repeated to complete the gas flooding experiments on cores of different injection media, different timings, different injection speeds, and different types of reservoirs, analyze and process the collected data, so as to complete the effect evaluation of different gas injection energy supplementation schemes and provide experimental data support for the preparation of gas injection energy supplementation schemes.

[0049] The implementation process of the present invention will be described in detail below in conjunction with specific embodiments.

[0050] Example 1

[0051] The evaluation method of the gas injection energy replenishment effect in this example includes the following steps:

[0052] Step 101: According to the requirements of gas reservoir development, select the target formation for gas injection energy replenishment. Drill natural core columns with a diameter of 25 mm or 38 mm and a length of 5 - 10 cm according to the core-taking situation of the formation. Measure the pore permeability parameters of the core, sort the core using the Bragg's law, then seal it with a thermoplastic envelope, and connect the instrument according to the Figure 1 schematic diagram.

[0053] The core used is the natural core from Well Puguang 102 - 1 and 104 - 1. 16 cores with a diameter of 2.50 cm are sorted and spliced according to the Bragg's law to form a long core model with a total length of 101.53 cm, and the harmonic permeability is 2.897×10 -3 μm 2 .

[0054] Step 102: Vacuum the core model, and the vacuum time is not less than 20 hours. Connect the methane gas source to test the airtightness of the device. After passing the test, heat the core model to a temperature of 125 °C.

[0055] Step 103: Use gas to calibrate the pore volume of the model, test the permeability of the spliced core model, and the test method refers to SY / T29172 - 2012 Core Analysis Method. Check whether the core porosity and permeability meet the design requirements.

[0056] Step 104: Saturate the core model with formation gas, conduct gas component analysis at the outlet end until the components are consistent with the formation gas components, then establish a backpressure, and let it stand and age for more than 24 hours. Check the flow pressure situation to ensure that the backpressure of the core model in the device reaches the preset value. The initial backpressure of the experiment is 46 MPa.

[0057] Step 105: Under the condition of the original formation pressure of 46 MPa, rely on natural energy to reduce the pressure for production until 22 MPa (deplete to 22 MPa), and then inject flue gas into the core model for displacement experiments. During the experiment, the monitoring end records the along - path pressure and gas saturation values in real time, and regularly detects the gas component composition at the production end. End the experiment when the injected gas volume reaches more than 1.2 times the pore volume or the gas component composition at the production end remains stable and no longer changes. After the temperature of the core model drops to room temperature, reduce the pressure of the core model. When the pressure reaches atmospheric pressure, use a vacuum pump to vacuum for 20 hours to determine the change range of gas - measured porosity and permeability, and start the next group of experiments.

[0058] Step 106: Conduct gas injection energy supplementation evaluations with carbon dioxide, nitrogen, and flue gas as the injection media in the manner of Steps 104 and 105. The influence of different injection media on the energy supplementation effect is as follows Figure 2 shown. The experimental results indicate that under the same experimental conditions, the ultimate recovery rates for gas injection energy supplementation with carbon dioxide, flue gas, and nitrogen are not significantly different, suggesting that gas drive with gas is similar to piston displacement and that different injection gas media have little influence on the ultimate recovery rate.

[0059] Step 107: Conduct long core CO2 flooding experiments at different pressures during depletion in the manner of Steps 104 and 105 to study the influence of different injection timing on the energy supplementation effect. Four groups of experiments show that: at the original pressure of 46 MPa, the gas production degree for CO2 injection is 78.65%; at 30 MPa for CO2 injection, the gas production degree is 78.11%; at 22 MPa for CO2 injection, the gas production degree is 75.78%; and at 18 MPa for CO2 injection, the gas production degree is 73.72%. Under the same experimental conditions, the earlier the carbon dioxide is injected in the gas field, the better the energy supplementation effect. See Appendix Figure 3 .

[0060] Step 108: All experiments in this group are long core CO2 flooding experiments at a depletion pressure of 22 MPa, and the influence of different injection rates on the energy supplementation effect is carried out in the manner of Steps 104 and 105. Three groups of experiments show that: under the same experimental conditions, the production degree at an injection rate of 0.2935 m / d is 75.78%; at an injection rate of 0.8805 m / d, the production degree is 77.81%; and at an injection rate of 1.4675 m / d, the production degree is 78.10%. As the injection rate increases, the injection-production pressure difference increases, and the increase in energy supplementation for enhanced recovery increases. The faster the gas injection rate, the better the energy supplementation effect. See Appendix Figure 4 .

[0061] Step 109: All experiments in this group are long core CO2 flooding experiments at a depletion pressure of 22 MPa, and the influence of cores of different reservoir types on the energy supplementation effect is carried out in the manner of Steps 104 and 105. Three groups of experiments show that: under the same experimental conditions, the gas production degree for gas injection in type II reservoir cores is 69.73%, and for type I reservoir cores is 75.78%. See Appendix Figure 5During the initial stage of gas injection in the parallel core gas injection and energy replenishment experiment, the core of the Class I reservoir was the dominant channel, and the recovery rate increased rapidly. When 0.66 times the pore volume was injected, the recovery rate reached 70%. Subsequently, the upward trend of the recovery rate during gas injection and energy replenishment was very slow. During the process of gas injection and energy replenishment in the core of the Class II reservoir, the recovery rate has been increasing in a slanting line trend. The interlayer heterogeneity affects the upward trend of the recovery rate improved by gas injection and energy replenishment. However, when the gas injection volume reaches 5.42 times the pore volume, the influence of heterogeneity on the final recovery rate of the medium-high permeability (core of the Class I reservoir) and low-permeability reservoir (core of the Class II reservoir) is less than 0.25 percentage points. See appendix Figure 6 。

[0062] Through the above experimental process, the effects of different injection media, different gas injection and energy replenishment times, different injection rates, and core reservoir types on the recovery rate are clarified, which can provide a basis for the efficient development and scientific decision-making of gas reservoirs.

Claims

1. An evaluation method for the effect of gas injection for energy replenishment, characterized in that, Including the evaluation steps for different gas injection media, different gas injection timings, different gas injection rates, and different types of reservoirs as follows: Evaluation of gas injection media: (1) Saturate the core model with formation gas and age it, then inject the gas injection medium into the core model for displacement experiments and calculate the recovery degree of natural gas; (2) Repeat step (1) to determine the recovery degree of natural gas for different gas injection media, and optimize the gas injection media; Evaluation of gas injection timing: (a) Saturate the core model with formation gas and age it. After the original formation pressure or the pressure is depleted from the original formation pressure to the designed pressure, conduct displacement experiments according to the designed flow rate and gas injection medium, and calculate the recovery degree of natural gas; (b) Repeat step (a) to determine the recovery degree of natural gas under different pressure conditions, and optimize the gas injection timing; Evaluation of gas injection rate: (Ⅰ) Saturate the core model with formation gas and age it, and conduct displacement experiments at the designed injection rate to calculate the recovery degree of natural gas; (Ⅱ) Repeat step (Ⅰ) to determine the recovery degree of natural gas at different injection rates, and optimize the gas injection rate; Evaluation of different types of reservoirs: (i) Select a core model that meets the requirements of the reservoir type, saturate the core model with formation gas and age it, and conduct displacement experiments under the designed injection conditions to calculate the recovery degree of natural gas; (ii) Repeat step (i) to determine the recovery degree of natural gas for the core models of other types of reservoirs or the parallel core models formed by the parallel connection of core models of different types of reservoirs, and evaluate the gas injection energy supplement effect for different types of core models.

2. The evaluation method of the gas injection energy supplement effect according to claim 1, wherein In step (2), the different gas injection media include carbon dioxide, nitrogen, and flue gas.

3. The evaluation method for the air injection energy replenishment effect according to claim 1, wherein The different types of reservoirs include Class I reservoirs and Class II reservoirs; the parallel core model includes a parallel core formed by the parallel connection of Class I reservoir cores and Class II reservoir cores.

4. The evaluation method for the gas injection energy supplement effect according to claim 1, wherein In step (1), step (a), step (Ⅰ), and step (i), the displacement experiment ends when the injected gas volume reaches more than 1.2 times the pore volume of the core model or the gas component composition at the production end no longer changes.

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