Ground surface monitoring method for carbon dioxide flooding storage engineering site

Abstract

The invention relates to the field of environment monitoring, in particular to a carbon leakage earth surface monitoring method for a carbon dioxide flooding storage engineering field, which comprises the following steps: S1, acquiring the distribution of injection production wells in a to-be-detected area, and selecting different point positions for monitoring; s2, estimating the diffusion rate of soil CO2 gas into free air, calculating soil gas flux data, and collecting soil moisture and temperature data; s3, the carbon dioxide flux of the corresponding area is obtained, and the surface concentration of carbon dioxide at different point positions is obtained through an infrared gas analyzer; s4, determining whether carbon dioxide leakage exists in the region or not according to the surface concentrations of the carbon dioxide at the different point locations; wherein the method for selecting different point locations in the step 1 is to select 2-4 point locations with the longest accumulated injection time in an engineering field for detection, and the linear relation between the selected point locations and the injection time is Y (t) = 0.08 t + 0.5. According to the monitoring method, earth surface sampling monitoring is selected, large-range encryption point distribution is achieved, cost is low, the geological structure cannot be damaged, cost is reduced, and safety is improved.

Description

Technical Field

[0001] The invention belongs to the field of environmental monitoring, and in particular relates to a surface monitoring method at a carbon dioxide flooding and oil storage project site. Background Art

[0002] Carbon dioxide enhanced oil recovery technology is a method to improve oil field recovery, and it can also permanently store carbon dioxide underground and reduce greenhouse gas emissions. However, geological leakage or surface leakage may occur during carbon dioxide recovery, posing potential risks to the environment and human health. Carbon capture utilization and storage technology (CCUS) is regarded as an indispensable part of the global climate change challenge. Through the carbon dioxide recovery and storage mechanism, it can effectively improve oil recovery while effectively storing carbon dioxide underground. It is the combination of greenhouse gas emission reduction and rational resource utilization, and an effective win-win method for both. The goal of CO2 storage is to store it safely in geological formations for a long time, but CO2 stored in geological formations may face the challenges of seepage and leakage. Slow leakage of CO2 may gradually occur along geological faults and cracks. If it is not controlled, it may evolve into large-scale high-speed CO2 leakage, resulting in damage to the integrity of the wellbore or pipeline. Large-scale carbon dioxide leakage may have a serious impact on the ecological environment. If leakage occurs, it will have adverse effects on climate change, groundwater environment, ecological environment and human health.

[0003] The main causes of CO2 storage leakage are: (1) geological structure leakage (including leakage from fault zones, rock formation permeability, and wellbore defects); (2) hydrogeological leakage (including groundwater flow carrying CO2 outside the storage layer and saltwater layer interaction causing CO2 leakage); (3) microbial activity (underground microorganisms affect the storage state of CO2 through metabolism); (4) human activity impact (including the construction of storage facilities that may disturb the formation, increase the risk of leakage, and abandoned wellbores may become a channel for CO2 leakage); (5) natural aging (including the change of the rock in the storage layer over time, affecting the storage efficiency, and the movement of the earth's crust may cause the movement and deformation of the storage layer, thereby affecting the storage effect); therefore, it is necessary to continuously monitor the storage facilities, timely detect potential leakage problems, and take corresponding measures to repair and reinforce them to ensure CO2 storage. Therefore, by monitoring CO2 leakage, potential environmental risks can be discovered and prevented in a timely manner to ensure the sustainable development of the ecological environment.

[0004] Existing technologies have limited ability to monitor surface carbon dioxide leakage in a timely manner, making it difficult to achieve full coverage and high-density monitoring. Moreover, there are certain limitations in monitoring accuracy and sensitivity, and it is impossible to effectively identify and locate the source and scale of surface carbon dioxide leakage. In addition, the cost and complexity of monitoring technology are also one of the current challenges. The high cost and complex operation limit the promotion and application of monitoring technology. The existence of these problems makes it difficult for current monitoring technology to meet the needs of surface carbon dioxide leakage monitoring, and it is necessary to seek more advanced and reliable solutions.

[0005] Therefore, there is an urgent need for a reliable, convenient, and highly sensitive method for monitoring geological leaks and surface leaks. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention discloses a surface monitoring method for a carbon dioxide flooding and oil storage project site, characterized in that the method comprises:

[0007] S1. Obtain the distribution of injection and production wells in the area to be tested and select different points for monitoring;

[0008] S2. measuring the rate of increase of gas in the air chamber according to the different points, estimating the rate at which soil gas diffuses into free air, calculating soil gas flux data, and collecting soil moisture and temperature data;

[0009] S3, obtaining the carbon dioxide flux of the corresponding area according to the soil gas flux data measured at different points, and obtaining the surface concentration of carbon dioxide at different points by an infrared gas analyzer;

[0010] S4. Determine whether there is a carbon dioxide leak in the area according to the surface concentration of carbon dioxide at different points;

[0011] Among them, the method of selecting different points in S1 is to select 2-4 points with the longest cumulative injection time at the engineering site for testing;

[0012] The linear relationship between the selected point and the injection time is Y(t)=0.08t+0.5, where Y(t) is the distance from the injection port (km) and t is the injection time (a).

[0013] In the present invention, the monitoring method provided by the inventor uses a specific method for selecting points, and selects points according to the injection time of the injection well.

[0014] According to the present invention, the distribution of injection and production wells in S1 is obtained according to the distribution of oil wells at the oil recovery site.

[0015] According to the present invention, the S3 specific method includes:

[0016] S31, estimate the rate of diffusion of soil gas into free air based on the gas concentration gradient driving the gas diffusion, the gas mole fraction, the atmospheric pressure, the temperature, and the soil moisture;

[0017] S32, calculating soil carbon dioxide flux data using a gas flux calculation equation based on the rate at which soil gas diffuses into free air;

[0018] S33. Determine the surface concentration of carbon dioxide at different points according to the soil carbon dioxide flux data at different points.

[0019] According to the present invention, the monitoring method takes 60-120 minutes.

[0020] According to the present invention, the method of determining whether there is a carbon dioxide leak in the area according to the surface concentration of carbon dioxide at different points in S4 includes:

[0021] Static comparison within the site to confirm the carbon dioxide concentration at different points for comparison;

[0022] Based on the changes over time, the carbon dioxide concentrations at the same point in different seasons are compared.

[0023] According to the present invention, the concentration of carbon dioxide in the site is compared with that in the surrounding environment to determine whether there is a leak. The specific method includes:

[0024] If the calculated carbon dioxide flux is greater than the carbon dioxide concentration in the surrounding environment, it is determined that there is a leak;

[0025] If the calculated carbon dioxide flux is less than or equal to the carbon dioxide concentration in the surrounding environment, it is determined that there is no leakage.

[0026] In the present invention, the surrounding environment is a range that can be routinely determined by those skilled in the art.

[0027] According to the present invention, the concentration of carbon dioxide contained in the environment at different distances in the site is compared with that in the same area to determine whether there is a leak. The specific method includes:

[0028] If the calculated carbon dioxide flux is greater than the carbon dioxide concentration in the environment at different distances, it is determined that there is a leak;

[0029] If the calculated carbon dioxide flux is less than or equal to the carbon dioxide concentration in the environment at different distances, it is determined that there is no leakage;

[0030] Among them, the points are selected at different distances in the same area at an interval of 2km.

[0031] According to one embodiment of the present invention, the derivation model used is:

[0032] The volume of the air chamber above the soil v(m 3 ) and soil surface area s(m 2 ), CO2 gas outflow rate f c (mol·m -2 ·s -1 ) and water evaporation flux rate f w (mol·m -2 ·s -1 ).

[0033] The mass balance equations for CO2, water vapor, and air are expressed as:

[0034] storage = flux in-flux out

[0035] The CO2 gas mass balance equation is:

[0036]

[0037] The mass balance equation for H2O is:

[0038]

[0039] The air mass balance equation is:

[0040]

[0041] Where: is the number density of CO2 in the chamber, is the number density of water vapor in the air chamber, ρ c is the number density of the air in the chamber, in mol·m -3 ; in, is the number density of dry air in the chamber. c is the CO2 mole fraction inside the measurement chamber (mol / mol), w c It is used to measure the mole fraction of water vapor inside the chamber (mol / mol).

[0042] f c Defined as the gas mole fraction gradient and conductivity coefficient at the soil-air cell interface:

[0043] f c =ρ c g(c s -c c )

[0044] In the formula, ρ c is the mole fraction of gas exchange between the soil surface and the air chamber (mol·mol -1 ), g is the CO2 gas conductivity (m·s-1 ), is the air density (mol·m -3 ).

[0045] In this experiment, the above formula can be transformed into:

[0046]

[0047] Where: F c is the soil CO2 gas emission flux (μmol·m -2 ·s -1 ), V is the volume (cm 3 ), P0 is the initial pressure (kPa), W0 is the initial water vapor mole fraction (mmol·mol -1 ), S is the soil surface area (cm 2 ), T0 is the initial air temperature (℃), is the initial rate of change of CO2 mole fraction after water correction (μmol·mol-1·s -1 ).

[0048] After the mixture is stabilized, the data is fitted according to the empirical equation, which is in the form of:

[0049] C'(t)=C' x +Ae -at

[0050] Where: C'(t) represents the instantaneous value of CO2 mole fraction after moisture correction, C' x is a parameter that defines the asymptote, and its unit is micromoles of CO2 per mole of air (μmol / mol); a is the curvature parameter of the fitting equation (s -1 )

[0051] Beneficial effects:

[0052] The monitoring method provided by the present invention selects surface sampling monitoring, encrypts points over a large area, has low cost, does not damage the geological structure, reduces cost, and improves safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a flow chart of a method for monitoring geological leakage and surface leakage during CO2 flooding and storage;

[0054] Figure 2 It is a distribution map of injection and production wells in an oilfield flooding demonstration site provided by an embodiment;

[0055] Figure 3 is a graph of soil gas flux, moisture content, and carbon dioxide flux data of an embodiment;

[0056] Figure 4 is a fitting function diagram of an embodiment;

[0057] Figure 5 It is a schematic diagram of a leakage monitoring device for a carbon dioxide flooding and oil storage project provided in an embodiment;

[0058] Figure 6 3 is a comparison chart of carbon dioxide concentration at different measurement points provided in the embodiment. DETAILED DESCRIPTION

[0059] The technical scheme of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. Obviously, the embodiments described herein are only some embodiments of the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments implemented by ordinary technicians in this field without making creative improvements belong to the protection scope of the present invention.

[0060] Example

[0061] When monitoring carbon leakage from CO2 flooding in oil fields, numerical simulation software is used to analyze the CO2 migration in 5, 15, 30, and 70 years, and different sampling points are selected for monitoring, taking into account the distribution of injection wells and production wells on site. Figure 2 As shown, through surface testing at different sampling points, we can fully understand the impact of carbon dioxide flooding on underground reservoirs, as well as the migration and distribution of CO2 in underground reservoirs, ensuring that comprehensive and accurate monitoring data are obtained.

[0062] In the early stage of measurement, select appropriate measurement sites according to the distribution of carbon dioxide formations. The distribution of wellbores in the oilfield flooding demonstration area is as shown in the following figure. Figure 2 As shown in the figure, AO is the CO2 injection well of the oil field, and 001-015 are CO2 production wells. Among them, injection wells A and B have a cumulative injection practice of about 5 years, and the injection time of other injection wells is shorter and the injection volume is less. Therefore, this on-site detection focuses on injection wells A and B. In order to ensure the accuracy and scientificity of the measurement, the field test is carried out around points A and B to ensure that the surface flux of CO2 in the entire oil recovery demonstration area can be evaluated. At the same time, a control experiment is carried out at a distance of about 10 kilometers from the oil recovery demonstration area.

[0063] Data measurements were taken at the site at two different times, with a 6-month interval between the two measurements. The results are shown in Table 1.

[0064] Table 1

[0065]

[0066] Data detection was carried out near the injection well in the experimental demonstration area. The measurement time was 14400s, and a total of 14400 data were obtained. The soil gas flux, moisture content and carbon dioxide flux data are shown in the attached figure. Figure 3 As shown in the figure, it can be seen that during the measurement process, the gas flow rate is 0.765L / min, the flow rate is relatively stable, and the change trends of the moisture content in the gas are close to that of the carbon dioxide content, and gradually tend to be stable with the change of time.

[0067] Using the experimental data collected on site, it can be seen that the empirical formula fitting of soil surface carbon dioxide flux is consistent with the change trend of concentration, R 2 It approaches 1, and the fitting parameters are shown in Table 2. The fitted function model can well explain the variability of the measurement data. The difference between the fitting value and the detection value is very small, and the measurement method is reliable.

[0068] Table 2

[0069]

[0070]

[0071] Figure 6 3 is a comparison chart of carbon dioxide concentrations at different measuring points provided in the embodiment. It can be seen from the figure that through data fitting, the carbon dioxide concentration around the injection wells in the carbon dioxide enhanced oil recovery demonstration area is relatively high compared with the concentration around the production wells. The injection wells are generally higher than the surrounding production wells by about 18%, and the change trends of the injection well data and the corresponding production well data are synchronized as a whole.

[0072] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A surface monitoring method for a carbon dioxide flooding and oil storage project site, characterized in that: The method comprises: S1. Obtain the distribution of injection and production wells in the area to be tested and select different points for monitoring; S2. measuring the rate of increase of gas in the air chamber according to the different points, estimating the rate at which soil gas diffuses into free air, calculating soil gas flux data, and collecting soil moisture and temperature data; S3, obtaining the carbon dioxide flux of the corresponding area according to the soil gas flux data measured at different points, and obtaining the surface concentration of carbon dioxide at different points by an infrared gas analyzer; S4. Determine whether there is a carbon dioxide leak in the area according to the surface concentration of carbon dioxide at different points; Among them, the method of selecting different points in S1 is to select 2-4 points with the longest cumulative injection time at the engineering site for testing; The linear relationship between the selected point and the injection time is Y(t)=0.08t+0.5, where Y(t) is the distance from the injection port (km) and t is the injection time (a).

2. The method according to claim 1, characterized in that The distribution of injection and production wells in S1 is obtained according to the distribution of oil wells at the oil recovery site.

3. The method according to claim 1, characterized in that The S3 specific method includes: S31, estimate the rate of diffusion of soil gas into free air based on the gas concentration gradient driving the gas diffusion, the gas mole fraction, the atmospheric pressure, the temperature, and the soil moisture; S32, calculating soil carbon dioxide flux data using a gas flux calculation equation based on the rate at which soil gas diffuses into free air; S33. Determine the surface concentration of carbon dioxide at different points according to the soil carbon dioxide flux data at different points.

4. The method according to claim 1, characterized in that: The monitoring method lasts for 60-120 minutes.

5. The method according to claim 1, characterized in that In S4, according to the surface concentration of carbon dioxide at different points, it is determined whether there is carbon dioxide leakage in the area, and the specific method includes: Static comparison within the site to confirm the carbon dioxide concentration at different points for comparison; Based on the changes over time, the carbon dioxide concentrations at the same point in different seasons are compared.

6. The method according to claim 5, characterized in that The concentration of carbon dioxide in the site is compared with that in the surrounding environment to determine whether there is a leak. The specific method includes: If the calculated carbon dioxide flux is greater than the carbon dioxide concentration in the surrounding environment, it is determined that there is a leak; If the calculated carbon dioxide flux is less than or equal to the carbon dioxide concentration in the surrounding environment, it is determined that there is no leakage.

7. The method according to claim 5, characterized in that The concentration of carbon dioxide in the site is compared with that in the environment at different distances in the same area to determine whether there is a leak. The specific method includes: If the calculated carbon dioxide flux is greater than the carbon dioxide concentration in the environment at different distances, it is determined that there is a leak; If the calculated carbon dioxide flux is less than or equal to the carbon dioxide concentration in the environment at different distances, it is determined that there is no leakage; Among them, the points are selected at different distances in the same area at an interval of 2km.

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