Water invasion path identification method based on tracer agent

Abstract

The invention provides a tracer agent-based water invasion path identification method, which comprises the following steps of S1, selecting a tracer injection well, injecting a tracer agent into the tracer injection well, and obtaining the tracer agent injection time; s2, multiple wells around the tracer injection well are selected as monitoring wells, and the concentration and time of the tracer appearing in the multiple monitoring wells for the first time are obtained through monitoring; and S3, drawing tracer agent concentration curve graphs of the plurality of monitoring wells according to the concentration and time of the tracer agent appearing in the monitoring wells for the first time, and realizing water invasion path identification between the monitoring wells and the tracer injection wells according to the tracer agent concentration curve graphs. The method is high in precision and accuracy, is not limited by the arrangement of monitoring points, and can obtain comprehensive water invasion path information in a short time.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas field development, and more specifically, to a method for identifying water invasion paths based on tracers. Background Art

[0002] In recent years, conventional, shallow, and relatively easy-to-exploit gas reservoirs have been successively developed, and the focus of development in the industry has shifted to deeper, ultra-deep, shale gas, and tight gas reservoirs, which are more difficult to develop. Such gas reservoirs generally have the characteristics of deep burial, high pressure, strong heterogeneity, complex fracture development, and the widespread existence of edge and bottom water, resulting in the relatively easy occurrence of water invasion in gas reservoirs.

[0003] After water invasion occurs in a gas reservoir, it will bring serious adverse effects to the normal development of the gas reservoir. Its main hazards are manifested in five aspects: ① water production from gas wells, reduction in production capacity, and shortening of the stable production period of the gas reservoir; ② invasion of formation water into the gas reservoir, reduction in the recovery rate of the gas reservoir; ③ water production from gas wells, increase in the flow resistance of the vertical pipe flow, reduction in production, and increase in development difficulty; ④ increase in the workload of water treatment, significantly increasing the development cost; ⑤ increase in production difficulty, affecting the extraction and transportation of natural gas.

[0004] Water invasion not only poses a serious threat to the development of oil and gas fields but may also have an adverse impact on the surrounding environment. Therefore, it is crucial to identify the migration law of groundwater and the water invasion path. Currently, common methods for identifying water invasion paths include statistical analysis methods based on groundwater monitoring data, prediction methods based on numerical simulation of groundwater flow fields, and analysis and identification methods based on geological and geophysical exploration data. However, these methods have some problems in practical applications, such as the low accuracy of the data that can be monitored for groundwater, the immaturity of numerical simulation technology, limited application scope, the need for a large amount of data support, etc. The accuracy and precision are restricted by the layout of monitoring points, and it is impossible to obtain relatively comprehensive water invasion path identification information. Summary of the Invention

[0005] To solve the problems existing in the prior art, the present invention provides a method for identifying water invasion paths based on tracers. This method has high accuracy and precision, is not restricted by the layout of monitoring points, and can obtain relatively comprehensive water invasion path information in a short time.

[0006] To achieve the above object, the present invention provides the following technical solution: A method for identifying water invasion paths based on tracers, comprising the following steps:

[0007] S1 Select an injection tracer well, inject a tracer into the injection tracer well, and obtain the tracer injection time;

[0008] S2 Select multiple wells around the injection tracer well as monitoring wells, and monitor the concentration and time of the first appearance of the tracer in the multiple monitoring wells;

[0009] S3 Draws the tracer concentration curves of multiple monitoring wells respectively according to the concentration and time of the first appearance of the tracer in the monitoring wells, and realizes the identification of the water invasion path between the monitoring wells and the tracer injection well according to the tracer concentration curves.

[0010] Further, in S3, the water invasion direction is determined according to whether the tracer appears in the monitoring well.

[0011] Further, in S3, it is confirmed whether each monitoring well is on the same main channel or there is an obstruction according to whether the tracer appears in the monitoring well.

[0012] Further, in the tracer concentration curve, the peak value of the tracer concentration curve is used to represent the number of main channels and fracture channels between the monitoring well and the tracer injection well.

[0013] Further, the higher the peak value of the tracer concentration curve, the more fracture channels exist between the monitoring well and the tracer injection well.

[0014] Further, in S3, the distances between multiple monitoring wells and the tracer injection well are respectively obtained, as well as the time intervals between the tracer injection time and the appearance time of the tracer in each monitoring well, to obtain the water invasion speed.

[0015] Further, the connectivity between the monitoring well and the tracer injection well is judged according to the water invasion speed.

[0016] Further, the greater the water invasion speed, the stronger the connectivity.

[0017] Further, the tracer is a fluorescent dye, water-soluble sodium iodide, non-ionic polymer or water-soluble salts.

[0018] Further, the injection depth of the tracer in the tracer injection well matches the depth of the monitoring well.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects:

[0020] The present invention provides a method for identifying water invasion paths based on tracers. After adding tracers to the tracer injection well, the tracers can quickly spread in the groundwater system and move together with the water flow. By monitoring the situation of the tracers in the monitoring wells, the water flow path can be accurately determined, without being restricted by the layout of the monitoring points; at the same time, the concentration changes of the tracers monitored in the monitoring wells are represented by the tracer concentration curves, so as to track the movement of the water, and the water invasion path can be identified in time, and more comprehensive water invasion path information can be obtained in a short time, so as to take measures to deal with water damage; and the present invention only needs to add tracers to the water body, and then monitor the movement and concentration changes of the tracers through sampling and analysis, without the need for complex equipment and technology, and is easy to operate.

[0021] In the present invention, the tracer belongs to a non-toxic material, and the added dosage is very small, having little impact on the water environment, no destructiveness to the groundwater system, and not disturbing the natural flow of water.

[0022] The method of the present invention can be applied to various groundwater environments and geological conditions. Whether it is a rock formation, soil or aquifer, this method can effectively identify the movement path of water. Therefore, it also has broad application prospects in the fields of groundwater resource management, environmental protection, water source protection area planning, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow chart of the method for identifying the water intrusion path based on a tracer of the present invention.

[0024] Figure 2 is a graph of the tracer concentration of monitoring well KeS241.

[0025] Figure 3 is a graph of the tracer concentration of monitoring well KeS241-2.

[0026] Figure 4 is a graph of the tracer test results of the overall block. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0028] The present invention provides a method for identifying the water intrusion path based on a tracer, comprising the following steps:

[0029] Step 1: Select a well as the tracer injection well, inject the tracer and record the injection time.

[0030] Step 2: Select several wells around the tracer injection well as monitoring wells, and measure and record the distances between the monitoring wells and the tracer injection well respectively.

[0031] Step 3: Measure and record the concentration and time when the tracer first appears in each monitoring well, and record the time interval between the tracer injection time and the time when the tracer first appears.

[0032] Step 4: Calculate the water intrusion speed using the well distance and the time interval in Step 3.

[0033] Step 5: Draw the tracer concentration curves of the monitoring wells based on the tracer concentrations recorded in Step 3; Drawing the tracer concentration curves of the monitoring wells can fully reflect the strength of the connectivity between the wells. The length of the tracer retention time indicates the number of fracture channels between the wells, and the length of the time interval between the measured tracer and the injected tracer clearly reflects the speed of water invasion. Furthermore, the connectivity between the wells, the fracture development, and the water invasion path are determined, thus providing a direction for better solving the water invasion problem.

[0034] Step 6: Analyze the connectivity and fracture development between the monitoring wells and the tracer injection wells based on the concentration curves drawn in Step 5 and the water invasion speed generated in Step 4, and finally draw a conclusion.

[0035] Preferably, when selecting the tracer injection well, the well spacing, well pattern layout, and the depth and position of the injection well should be selected according to the geological conditions and reservoir characteristics to ensure that the tracer can effectively spread and accumulate in the monitoring wells in the target area. The tracer usually needs to be injected into a position close to the target layer in the tracer injection well to observe and study the tracer concentration in the monitoring well. The depth of the tracer injection into the tracer injection well should be matched and similar to the depth of the monitoring well. At the same time, characteristics such as the permeability and thickness of the reservoir will also affect the well selection. If the reservoir has high permeability, a shallower injection well depth can be selected for the tracer. For reservoirs with lower permeability, a deeper injection well depth can be selected to ensure that the tracer can diffuse to the target layer.

[0036] Preferably, the tracer proposed in the present invention is mainly a tracer that is pollution-free to the water environment. The preferred tracer types are fluorescent dyes, water-soluble sodium iodide, non-ionic polymers (such as polyethylene glycol, etc.), and water-soluble salts. These types of tracers are generally considered to have no pollution risk to the environment, but relevant regulations and standards need to be followed during use.

[0037] Example 1:

[0038] Refer to Figure 1 , and the present invention will be further described below in conjunction with the drawings and specific embodiments. The specific content is as follows:

[0039] Step 1: Select the tracer injection well, inject the tracer and record the injection time

[0040] Select two wells, KeS241-J1 and KeS241-4, in a certain block as the tracer injection wells, and inject tracers of models JWST-1 and JWST-3 on April 22, 2022 and June 2, 2022 respectively.

[0041] Step 2: Select the monitoring wells and measure and record the distances between the monitoring wells and the tracer injection wells respectively

[0042] For the tracer well KeS241-J1, four wells around it, namely KeS241, KeS241-2, KeS241-4, and KeS24-5, were selected as monitoring wells; for the tracer well KeS241-4, the same number of wells around it, namely KeS241-J1, KeS241, KeS241-2, and KeS24-5, were selected as monitoring wells. The detailed results of the distances between the monitoring wells and the tracer wells were measured and recorded as shown in Table 1.

[0043] Step 3: Measure and record the concentration and time when the tracer first appears in each monitoring well, and record the time interval between the time of injecting the tracer and the time when the tracer first appears.

[0044] (1) After injecting the tracer, observe the monitoring wells. The concentration and time when the tracer first appears in each monitoring well were recorded.

[0045] For the tracer well KeS241-J1, the tracers were first detected in two wells, KeS24 and KeS241-2, on May 11, 2022, and June 14, 2022, respectively. The concentration in the KeS24 well was 4.3 μg / L, and the concentration in the KeS241-2 well was 5.6 μg / L. For the tracer well KeS241-4, only the KeS241-2 well first detected a tracer with a concentration of 2.6 μg / L on July 20, 2022.

[0046] (2) The number of time intervals between the time of injecting the tracer and the time when the tracer first appears was recorded.

[0047] For the tracer well KeS241-J1, the time intervals between the first appearance of the tracer in the two monitoring wells, KeS24 and KeS241-2, were 19 days and 53 days, respectively. For the tracer well KeS241-4, the time interval between the first appearance of the tracer in the KeS241-2 monitoring well was 49 days.

[0048] The above detailed results are shown in Table 1.

[0049] Table 1 Statistical Table of Tracer Tests

[0050]

[0051]

[0052] Step 4: Measure and record the tracer concentration in each monitoring well, and draw a tracer concentration curve graph of the monitoring wells.

[0053] The tracer concentrations of each monitoring well are recorded in detail, and the corresponding tracer concentration curves of the monitoring wells are plotted based on the recorded data. The detailed tracer concentration situations of monitoring wells KeS241 and KeS241-2 under different types of tracers are shown in Table 2 and Table 3 respectively. Refer to Figure 2 , Figure 3 , which are the tracer concentration curves of monitoring wells KeS241 and KeS241-2 respectively. The higher the peak value of the tracer concentration curve, the more tracer dose is detected in the monitoring well during this time period, indicating that there are multiple main channels and multiple fracture channels between the monitoring well and the tracer injection well. For example Figure 2 in the tracer concentration curve of well KeS241, only the tracer of model JWST-1 is detected and the peak value of the concentration curve is relatively high within a certain time period, indicating that there is a main channel fracture between well KeS241 and well KeS241-J1, and there is no main channel fracture or a relatively small fracture between well KeS241 and well KeS241-4.

[0054] Table 2 Water sample test results of well KeS241

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

[0061] Table 3 Water sample test results of well KeS241-2

[0062]

[0063]

[0064]

[0065]

[0066]

[0067] Step 5. Calculate the water invasion rate

[0068] The water invasion rates of monitoring wells KeS241 and KeS241-2 are obtained by using the well spacing data between the tracer injection well and the monitoring wells and the time interval data obtained in Step 3.

[0069] For the tracer well KeS241-J1, the water invasion rates of its monitoring wells KeS241 and KeS241-2 were measured to be 45 m / d and 32 m / d respectively; for the tracer well KeS241-4, the water invasion rate of its monitoring well KeS241-2 was measured to be 20 m / d.

[0070] The above detailed results are shown in Table 1.

[0071] Step 6: Analyze the connectivity and fracture development between the monitoring wells and the tracer wells

[0072] First, analyze the connectivity between the wells. There is connectivity between well KeS241-J1 and both wells KeS241 and KeS241-2. By analyzing the water invasion rate, it can be seen that the connectivity between well KeS241-J1 and well KeS241 is stronger than that between well KeS241-J1 and well KeS241-2.

[0073] Secondly, analyze the fracture development. The level of tracer concentration and the time interval between the first detection of the tracer and the injected tracer can clearly reflect the fracture development between the wells. The higher the tracer concentration and the shorter the time interval between the injection of the tracer and the first detection of the tracer, the more fractures are developed. Combining this experiment, compared with well KeS241-4 and KeS241-2, the tracer concentration between well KeS241-J1 and well KeS241-2 is higher, and the time interval between the two is approximately the same, indicating that more fractures are developed between well KeS241-J1 and well KeS241-2.

[0074] Finally, based on the overall analysis of the connectivity and fracture development of the wells, it is obtained that: the more fractures are developed between the wells, the stronger the connectivity, the easier it is for water invasion to occur and the water invasion path is more complex.

[0075] Reference for tracer test results Figure 4 .

[0076] (1) The tracer test results of well KeS241-J1 show that the edge water advances from west to east. And since the tracer injected into well KeS241-J1 was not detected in well KeS241-4, it indicates that well KeS241-2 and well KeS241-4 are not on the same main channel, or there is an obstruction between the two wells.

[0077] (2) The detection of the tracer of well KeS241-4 in well KeS241-2 indicates that: after increasing the drainage of well KeS241-2, the water distributed around well KeS241-4 can be pumped back to the main channel along the medium and small scale fractures.

[0078] (3) The tracer in Well KeS24-5 was not detected in Well KeS241-4, indicating poor connectivity in the saddle area of this block.

[0079] Therefore, it can be seen that the method for identifying water invasion paths based on tracers in the present invention is feasible and has the advantages of simple operation steps and relatively accurate results.

[0080] A method for identifying water invasion paths based on tracers in the present invention monitors and analyzes the concentration, rate, and propagation path of tracers to infer the water invasion path, rate, and source. It combines theoretical knowledge in fields such as hydrogeology, hydraulics, and tracer technology, and has high accuracy and reliability. The present invention plays a supporting role in the development of oilfield operations, especially the main business, and also promotes the relevant professional technology: (1) It improves the efficiency of oilfield exploration and development. It can accurately track and identify the path and source of water invasion, providing important information support. (2) It reduces the operating costs of the oilfield. By only analyzing the concentration distribution of tracers in groundwater, accurate results can be obtained in a short time, which can reduce the cost and time consumption in the water invasion assessment process, improve the operating efficiency of the oilfield, and reduce production risks and losses. (3) It provides early warning and prediction capabilities. Water invasion has an adverse impact on oilfield production and exploitation, and is more likely to cause problems such as a decrease in oil and gas production, wellbore blockage, and equipment damage. The method for identifying water invasion paths based on tracers can timely identify the path and source of water invasion, which helps to take corresponding prevention and control measures in a timely manner, reduce production risks and losses, and ensure the stable operation of the main business of the oilfield.

[0081] It should be noted that the above embodiments do not limit the present invention in any form. Any technical solutions obtained by means of equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A tracer-based method for identifying water invasion paths, characterized in that, It includes the following steps: S1 Select a tracer well, inject a tracer into the tracer well, and obtain the tracer injection time; S2 Select multiple wells around the tracer well as monitoring wells, and monitor the concentration and time of the first appearance of the tracer in the multiple monitoring wells; S3 Respectively draw tracer concentration curves of the multiple monitoring wells according to the concentration and time of the first appearance of the tracer in the monitoring wells, and identify the water invasion path between the monitoring wells and the tracer well according to the tracer concentration curves.

2. The method for identifying water invasion path based on tracer according to claim 1, wherein In S3, determine the water invasion direction according to whether the tracer appears in the monitoring well.

3. The method for identifying water invasion path based on tracer according to claim 1, wherein In S3, confirm whether each monitoring well is on the same main channel or whether there is an obstruction according to whether the tracer appears in the monitoring well.

4. The method for identifying water invasion path based on tracer according to claim 1, wherein In S3, in the tracer concentration curve, use the curve peak value of the tracer concentration to represent the number of main channels and fracture channels between the monitoring well and the tracer well.

5. The method for identifying water invasion path based on tracer according to claim 4, wherein, In S3, the higher the curve peak value of the tracer concentration, the more fracture channels there are between the monitoring well and the tracer well.

6. The method for identifying water invasion path based on tracer according to claim 1, wherein, In S3, respectively obtain the distances between the multiple monitoring wells and the tracer well, and the time intervals between the tracer injection time and the appearance time of the tracer in each monitoring well, and obtain the water invasion speed.

7. The method for identifying water invasion path based on tracer according to claim 6, characterized in that, Judge the connectivity between the monitoring well and the tracer well according to the water invasion speed.

8. A tracer-based water invasion path identification method according to claim 7, characterized in that The greater the water invasion speed, the stronger the connectivity.

9. A tracer-based water invasion path identification method according to claim 1, characterized in that, The tracer is a fluorescent dye, water-soluble sodium iodide, non-ionic polymer or water-soluble salt.

10. A tracer-based water invasion path identification method according to claim 1, characterized in that, The injection depth of the tracer in the tracer well matches the depth of the monitoring well.

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