Salt lake leakage monitoring method based on boron isotope tracer

Abstract

The invention relates to the technical field of salt lake leakage, in particular to a salt lake leakage monitoring method based on a boron isotope tracer. The monitoring method specifically comprises the following steps: screening a tracer agent; selecting a detection instrument; forming an injection well in the salt lake detection area and forming a plurality of monitoring wells along the periphery of the injection well; a tracer agent is put into the injection well, sampling detection and data analysis are conducted on the monitoring well, and the position of a leakage point is determined. The monitoring method provided by the invention is beneficial to mastering the leakage flowing direction of the salt lake and identifying the specific position of the leakage point.

Description

Technical Field

[0001] The present application relates to the technical field of salt lake leakage, and in particular to a salt lake leakage monitoring method based on a boron isotope tracer. Background Art

[0002] China's salt lakes are famous for their large number, large area, rich resources, complete types, and rich in rare elements. The best way to exploit salt lake resources is to combine well mining, where the brine from the wells is introduced into the salt pans through channels, and the salt mines are obtained by natural evaporation and then further processed to obtain products. During the channel transportation and salt pan evaporation process, the brine inevitably leaks into the groundwater, causing part of the brine in the salt pans to flow underground before being evaporated and converted into solid ore.

[0003] The identification of salt pan leakage areas and flow fields is a common difficulty encountered in brine mining in various regions across the country today.

[0004] First, there is no effective technical method to accurately identify salt pan water leakage areas. Common methods for groundwater leakage monitoring include groundwater monitoring method, diffusion tube method, capacitance sensor method, electrochemical induction cable method, resistivity method, geological instrument detection method, elastic wave method, etc. However, these monitoring methods are not accurate or difficult to implement, so they have not been adopted.

[0005] Second, the salt pan area is large, and the leakage performance of the anti-seepage clay layer in the salt pan area is uneven. In particular, the sodium salt pool, which is the primary evaporation stage of brine, is mainly a natural impermeable clay layer. Without engineering anti-seepage treatment, some brine leakage is inevitable. In addition, due to the influence of large-scale brine extraction in production, the hydrogeological conditions and physical and chemical properties of brine in the salt lake mining area will continue to change, making the water-richness and permeability of the ore deposit develop in a variable direction, making it difficult to comprehensively characterize the regional salt pan water leakage points.

[0006] Therefore, it is urgent to find new methods to realize salt field leakage monitoring. Summary of the invention

[0007] The present application provides a salt lake leakage monitoring method based on boron isotope tracers. The method uses boron isotope tracers to conduct all-round monitoring of salt lake parameters and wells, thereby helping to solve the salt lake leakage problem.

[0008] The present application provides a salt lake leakage monitoring method based on boron isotope tracer, which adopts the following technical scheme:

[0009] A salt lake leakage monitoring method based on boron isotope tracers, the monitoring method specifically comprises the following steps: screening of tracers; selection of detection instruments; opening an injection well in a salt lake detection area and opening a plurality of monitoring wells along the periphery thereof; injecting tracers into the injection wells, sampling and detecting the monitoring wells, and analyzing data to determine the location of the leakage point.

[0010] Isotope tracer technology is widely used in various fields, including biology, physics and environmental science. Its advantages include strong specificity, high sensitivity and real-time tracking. Boron isotope tracers can specifically track specific elements or molecules. Even at very low concentrations, tracers can be detected. They can also track processes in real time to provide dynamic information. The first geochemical study of stable isotopes was conducted in 1947. In the following decades, researchers have successively analyzed and tested traditional stable isotopes of smaller elements such as carbon (C), hydrogen (H), oxygen (O), and nitrogen (N). At the end of the 20th century, with the emergence of inductively coupled multi-collector plasma mass spectrometry, research on non-traditional stable isotopes entered a new stage. This technology provides an important means for people to accurately understand and recognize the environment and chemical behavior of these elements.

[0011] Optionally, sampling is performed in the area to be detected to obtain time series data of the boron isotope tracer concentration produced in each monitoring well. Specifically, it includes:

[0012] (1) Before collecting samples from the detection wells in the salt lake monitoring area, the residual liquid in the monitoring wells must be extracted for 1-2 minutes to ensure that the collected samples are not disturbed by the residual liquid; then, the samples are extracted through the sampling port of the detection wells, the collection depth is 1.2m, and the amount collected each time is fixed at 50g; the collected samples should be filtered and divided into special sampling containers marked with the corresponding date and well number;

[0013] (2) The samples collected daily must be stored in a dry environment away from direct sunlight to maintain the stability of the samples;

[0014] (3) Strict handover management is required for samples collected daily, and detailed records of the specific conditions of each test well are required to ensure the accuracy and completeness of the information;

[0015] (4) Perform preliminary separation and filtration operations on each collected sample, then reseal the filtered sample into a new container and attach the corresponding date and hashtag for subsequent identification and processing.

[0016] The optional sample collection schedule is as follows: starting from the day after the tracer injection is completed, sample collection is performed twice a day for the next 180 days, with an interval of 12 hours between each collection. All collected samples must be analyzed in the laboratory within one week to ensure the timeliness and accuracy of the data.

[0017] Optionally, the tracer production curve takes time as the horizontal axis and the tracer isotope ratio as the vertical axis. The time series data is a set of discrete points including several peaks, and the production curve is generated by fitting the discrete points.

[0018] Optionally, dynamic parameters such as breakthrough time, peak time, peak ratio and continuous production duration of the corresponding boron isotope tracer of each corresponding detection well are determined according to the production curve of each boron isotope tracer; the direction of water flow is determined according to the breakthrough time of the boron isotope tracer and the corresponding injection well and detection well positions.

[0019] Optionally, the connectivity between each detection well and the injection well is obtained based on the variation of the production curve of each boron isotope tracer.

[0020] Optionally, the following steps are also included: numerical analysis of boron isotope tracer extraction curve fitting, and finding the position distribution of primary flow points, secondary flow points and leakage points based on corresponding time and corresponding position.

[0021] In summary, the present application includes at least one of the following beneficial technical effects:

[0022] The monitoring method provided in this application helps to grasp the flow direction of the water injected into the salt lake in all directions on the plane. The permeability of the salt lake layer in all directions on the plane is different. After injecting the preferred tracer into the injection well, sampling is then carried out in the relevant benefit wells. By analyzing the arrival time of these tracers, the flow direction of the water in the injection well can be determined.

[0023] The monitoring method provided in this application also helps to identify the distribution and specific location of leakage points. By using the curve produced by the boron isotope tracer, combined with the breakthrough time and specific location analysis, the leakage point and the time to reach the leakage point can be accurately found. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flow chart of the steps of the salt lake leakage monitoring method based on boron isotope tracers.

[0025] Figure 2 This is an example map of the location of the salt lake detection area, including the locations of injection wells and monitoring wells.

[0026] Figure 3 This is a diagram of the salt lake brine tracer flow platform.

[0027] Figure 4 This is an example of a linear graph of boron element ratio.

[0028] Figure 5 This is an example of data from monitoring well No. 1.

[0029] Figure 6 This is an example of data from monitoring well No. 4.

[0030] Figure 7 This is an example of data from monitoring well No. 6. DETAILED DESCRIPTION

[0031] Before describing the embodiments of the present application in detail, it should be understood that the terms used herein are only used for the purpose of describing specific embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by ordinary technicians in the field to which the terms belong.

[0032] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. Further, in the description of this application, unless otherwise specified, the meaning of "plurality" is two or more.

[0033] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0034] In the present application, the terms "comprise" or "include" are open expressions, that is, including the contents specified in the present application but not excluding other contents.

[0035] The present application provides a salt lake leakage monitoring method based on a boron isotope tracer.

[0036] like Figure 1 As shown, the monitoring method specifically includes the following steps: screening of tracers; selection of detection instruments; opening an injection well in the salt lake detection area and opening a number of monitoring wells along its periphery; injecting tracers into the injection wells, sampling and testing the monitoring wells, and analyzing the data to determine the location of the leakage point.

[0037] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application. The embodiments described below are exemplary and are only used to explain the present application, and cannot be interpreted as limiting the present application.

[0038] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0039] The present application is further described in detail below in conjunction with the embodiments and test results.

[0040] Example

[0041] This embodiment provides a salt lake leakage monitoring method based on boron isotope tracer.

[0042] The specific steps include:

[0043] (I) Tracer screening

[0044] According to the requirements for water flooding tracer properties in SY / T 5925-2012 "Selection Method of Chemical Tracers for Oilfield Water Injection" and Q / SY 127-2005 "Technical Specifications for Interwell Tracers in Water-flooded Oilfields", the tracer screening principles are as follows:

[0045] (1) The effective tracer substance has no background in the injected fluid and salt lake fluid, or the background is very low and stable.

[0046] (2) The analysis method of effective tracer substances is simple and reliable, with high detection sensitivity and analysis error <5%.

[0047] (3) The effective tracer substance should have good solubility with the tracking fluid, and the flow characteristics of its aqueous solution should be similar to those of the tracking fluid.

[0048] (4) Effective tracer substances must have good biological stability, thermal stability, and chemical stability.

[0049] (5) There is no chemical reaction or isotope exchange between the effective tracer substance and the reservoir fluid or reservoir material that may cause the loss of the effective tracer substance.

[0050] (6) The effective tracer substance is not absorbed or is poorly adsorbed by reservoir mud or salt substances.

[0051] (7) The tracer is non-toxic, non-radioactive or has low toxicity and low radioactivity levels within the permitted public limits.

[0052] (8) The price is low, the supply is wide, and the liquid preparation and injection process are simple.

[0053] This application uses isotope interwell tracer monitoring, and the selected tracer is 10B tracer, the selected boron isotope tracer is safe and environmentally friendly, non-toxic, non-radioactive, with high detection accuracy, small adsorption amount in the formation, good stability, strong applicability, and can fully meet the requirements of water flooding tracers.

[0054] (II) Selection of testing instruments

[0055] The selection of detection instruments and experimental steps are as follows:

[0056] Determination of background concentration: Before injecting the tracer, the injection medium and the fluid produced by the adjacent wells must be sampled to determine the original concentration of the tracer. This data will be used as a key comparative indicator for subsequent evaluation of whether the injected tracer has successfully migrated to the surrounding test wells.

[0057] Selection of detection instrument: Inductively coupled plasma mass spectrometry can analyze boron isotopes at the ug / L level, and has the advantages of low detection limit, high sensitivity, high selectivity, wide linear region, short analysis time, and small injection volume. Inductively coupled ion mass spectrometer was selected as the detection instrument.

[0058] The inductively coupled ion mass spectrometer detects the element cps value (counts per second, also known as element response value), the formula is: N CPS =K*C. Where: N CPS - counts per second, dimensionless; K-count coefficient, ug -1 L; C-element concentration, ug / L.

[0059] Isotope fractionation correction model: In order to improve the accuracy of instrument detection, the correction model uses the standard sample-sample crossover method, which can produce accurate isotope ratios. The premise of this method is that the isotope composition of the same element is known. When testing together, two standard samples are inserted before and after the sample to be tested. The calculation formula of the standard sample-sample crossover method is:

[0060]

[0061] Where: R std --The true isotope ratio of the standard sample, dimensionless; r std --The test isotope ratio of the standard sample, dimensionless; The average value of the standard fractionation factor k, dimensionless; r sample --Test value of the sample, dimensionless; R sample --The true value of the sample, dimensionless.

[0062] In order to avoid the influence of ultrapure water background sample on the analysis results, the element signal response value of ultrapure water background sample needs to be deducted when calculating the ratio between the two. The isotope ratio calculation formula is:

[0063]

[0064] Where: N A测量 —The element signal response value at the Nth measurement, dimensionless; N A背景 —Ultrapure water signal response value at the Nth measurement, dimensionless.

[0065] Quantitative detection: Under the same conditions, a certain volume of brine solution was measured 11 times continuously, and the standard deviation was calculated. Three times the standard deviation was used as the detection limit of boron, and 10 times the standard deviation was used as the quantitative limit of boron.

[0066] If the brine solution 10 B and 11 The detection limit of the ratio of B is A. After adding Bug / L tracer to the brine solution, the standard sample-sample crossover method was used to correct the measured 10 B and 11 The difference between the average value of the ratio of B and the average value of brine is C. If C>3A, then Bug / L is reasonable. The closer C is to 3A, the more accurate this value is. 10 Solution B, 10 B and 11 The ratio of B changes significantly and linearly, so this B value can be determined as the minimum delivery amount.

[0067] Compatibility test: Under normal temperature and pressure, 10 The salt lake solution of tracer B was left to stand for 72 hours without precipitation, and the change rates of solution concentration and tracer ratio were both less than 5%. The transmittance was greater than 90%. Different gradients of bug / L tracer solutions were added to the brine solution and measured multiple times. If the recovery rate was between 90 and 110%, the compatibility was good.

[0068] Adsorption experiment: NaCl salt pond surface crystals in salt lakes, abandoned NaCl salt pond surface crystals and calcium-containing Glauber's salt gypsum clay used for salt pan waterproofing are added to a mixture of tracer and brine, and referred to as fine salt, coarse salt and silt. After standing for 72 hours, if the adsorption rate of the tracer is less than 10%, the adsorption test is good.

[0069] Liquidity test: Figure 3 As shown in the figure, a salt lake brine tracer flow platform was built. The device consists of a high-pressure pump, a pressure sensor, an intermediate container, and a sand-filled pipe. The sand-filled pipe is filled with coarse salt, fine salt, and silt to simulate a silt layer or raw salt. A certain volume of tracer solution is injected into the intermediate container, and then displaced with brine. At the same time, the output fluid is collected during the entire test process, and the concentration of the boron isotope tracer in the output fluid is measured. The flow loss rate is less than 10%, and the fluidity is good.

[0070] The power can be adjusted by using a high-pressure pump to fix the pressure at 0.1MPa, the capacity of the intermediate container is about 1-3L, and the pore volume of the sand filling tube is 150-300cm 3 Coarse salt, fine salt and silt are ground to between 20-40 mesh.

[0071] (III) Precautions for opening injection wells and testing wells in the salt lake testing area

[0072] Wellsite survey: Survey the wellsite at least 2 days before construction to identify the geographical location of the injection wells, ensure smooth road traffic to the wellsite, and ensure that the wellsite is ready for injection construction.

[0073] Clarify the structure of the downhole tubing: Make sure that the cementing quality of the water injection well is good and the downhole tubing is not damaged.

[0074] like Figure 2 Shown is an example map of the location of the salt lake detection area, including the locations of injection wells and monitoring wells.

[0075] (IV) Process parameter requirements and precautions during tracer injection construction

[0076] (1) Inject the tracer solution in accordance with the total water injection volume of the well. The injection time should be no less than 2 hours and should be as close to the instantaneous flow rate of the well as possible.

[0077] (2) Clean water should be used to prepare the tracer solution. Hot water should be used whenever possible.

[0078] (3) During the preparation process, the tracer must be completely dissolved before it can be injected into the well.

[0079] Note:

[0080] (1) Liquid preparation. Prepare the tracer solution according to the liquid preparation parameters. During the liquid preparation process, the tracer loss should be minimized and the material packaging bags should be properly handled and not thrown away or discarded.

[0081] (2) Injection. Prepare the tracer solution strictly according to the liquid volume and concentration designed in the construction plan. In actual use, the tracer solution is injected into the water at about 300m 3 Inject 10g of boron isotope tracer solution into the salt lake detection area. The injection pressure shall not exceed the oil layer fracture pressure and the rated pressure of the pipe string. Always pay attention to the changes in the injection pressure at the wellhead and adjust the pump displacement in time to prevent the injection pressure from exceeding the formation fracture pressure or the rated pressure of the wellhead and pipe string.

[0082] It is strictly forbidden to perform well flushing operations after the tracer is injected into the well.

[0083] (V) When sampling in the area to be monitored, obtain the time series data of the concentration of each boron isotope tracer produced in each detection well, including:

[0084] (1) Before collecting samples from the detection wells in the salt lake detection area, the residual liquid in the monitoring wells must be extracted for 1-2 minutes to ensure that the collected samples are not disturbed by the residual liquid. Subsequently, the samples are extracted through the sampling port of the detection wells, with a collection depth of 1.2m and a fixed amount of 50g each time. The collected samples should be filtered and divided into special sampling containers marked with the corresponding date and well number.

[0085] (2) The samples collected daily must be stored in a dry environment away from direct sunlight to maintain the stability of the samples.

[0086] (3) Strict handover management is required for samples collected daily, and detailed records of the specific conditions of each test well are required to ensure the accuracy and completeness of the information.

[0087] (4) Perform preliminary separation and filtration operations on each collected sample, then reseal the filtered sample into a new container and attach the corresponding date and hashtag for subsequent identification and processing.

[0088] The sample collection schedule is as follows: starting from the day after the tracer injection is completed, sample collection will be carried out twice a day for the following 20 days, with an interval of 12 hours between each collection. All collected oil samples must be analyzed in the laboratory within one week to ensure the timeliness and accuracy of the data.

[0089] The tracer production curve takes time as the horizontal axis and the tracer isotope ratio as the vertical axis. The time series data is a set of discrete points including several peaks. The production curve is generated by fitting the discrete points.

[0090] According to the production curve of each boron isotope tracer, the dynamic parameters such as the breakthrough time, peak time, peak ratio and continuous production time of each corresponding detection well are determined; the direction of water flow is determined according to the breakthrough time of the boron isotope tracer and the corresponding injection well and detection well positions.

[0091] The connectivity between each detection well and the injection well is obtained based on the variation of the production curve of each boron isotope tracer.

[0092] The numerical analysis of tracer output curve fitting is as follows: Figure 4 As shown, the direction of water flow can be determined based on the change in the boron ratio and its corresponding time. The difference in the change of water flow through the monitoring well may be that it rises first on AB day and decreases on BC day, and the change amplitude is the largest. 10 B and 11 The B ratio is much greater than the background value, indicating that this monitoring well is a primary flow point. If the monitoring well AB days remain unchanged, BC days increase, CD days decrease and 10 B and11 If the B ratio is greater than the background value, it means that this monitoring well is a secondary flow point. 10 B and 11 The B ratio is greater than the background value, indicating that this monitoring well is a leakage point.

[0093] like Figure 5 , Figure 6 , Figure 7 According to the boron isotope ratio change data, the boron isotope ratio of Well No. 1 increased sharply from 1 to 3 days, gradually decreased from 3 to 7 days, and tended to be stable from 7 to 20 days. The ratio of Well No. 1 changed the most compared with other wells, indicating that Well No. 1 is a first-level circulation well. The ratio of Well No. 4 tended to be stable from 1 to 4 days, increased sharply from 4 to 8 days, gradually decreased from 8 to 12 days, and tended to be stable from 12 to 20 days. The change range was small, indicating that Well No. 4 is a second-level circulation well. Well No. 6 tended to be stable from 1 to 5 days, gradually increased from 5 to 15 days, and tended to be stable from 15 to 20 days, indicating that the water flow direction flows through Well No. 6 but does not flow out, so Well No. 6 is a leakage point.

[0094] Based on a comprehensive analysis of the injection wells and observation well locations, Well No. 6 in this salt lake area is a leakage point, and the flow direction is also known, which is from northeast to southwest. If leakage materials or other anti-seepage measures are added to Well No. 6, the leakage problem can be solved.

[0095] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A salt lake leakage monitoring method based on boron isotope tracer, characterized in that: The monitoring method specifically comprises the following steps: Screening of tracers; selection of detection instruments; opening of injection wells in the salt lake detection area and several monitoring wells along its periphery; injecting tracers into the injection wells, sampling and testing in the monitoring wells, and data analysis to determine the location of the leakage point.

2. The monitoring method according to claim 1, characterized in that: Sampling is carried out in the area to be tested to obtain time series data of the boron isotope tracer concentration produced in each monitoring well.

3. The monitoring method according to claim 1, characterized in that: The sample collection schedule is as follows: starting from the day after the tracer injection is completed, samples will be collected twice a day for the next 180 days, with an interval of 8-12 hours between each collection. All collected samples must be analyzed in the laboratory within 3 weeks.

4. The monitoring method according to claim 1, characterized in that: The tracer production curve takes time as the horizontal axis and the tracer isotope ratio as the vertical axis. The time series data is a set of discrete points including several peaks. The production curve is generated by fitting the discrete points.

5. The monitoring method according to claim 4, characterized in that: According to the production curve of each boron isotope tracer, the dynamic parameters such as the breakthrough time, peak time, peak ratio and continuous production time of each corresponding detection well are determined; the direction of water flow is determined according to the breakthrough time of the boron isotope tracer and the corresponding injection well and detection well positions.

6. The monitoring method according to claim 5, characterized in that: The connectivity between each detection well and the injection well is obtained based on the variation of the production curve of each boron isotope tracer.

7. The monitoring method according to claim 6, characterized in that: The following steps are also included: The boron isotope tracer extraction curve is fitted with numerical analysis, and the location distribution of the primary flow point, secondary flow point and leakage point is found according to the corresponding time and corresponding position.

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