An evaluation method for an oilfield produced water treatment system

Abstract

The present invention relates to an evaluation method for an oilfield produced water treatment system in the field of oilfield produced water treatment technology. By regularly extracting water samples from each unit of the produced water treatment system on-site and detecting the light transmittance and potential value, an evaluation model and an evaluation method are designed to realize the evaluation of the treatment efficiency and stability of each treatment unit and the overall treatment system of the produced water treatment system, and solve the problem that it is difficult to quickly quantify the on-site evaluation of chemical agents such as destabilization treatment during the produced water treatment process.

Description

Technical Field

[0001] The present invention relates to an evaluation method for an oilfield produced water treatment system suitable for quickly sampling, detecting and evaluating each treatment unit at the oilfield produced water treatment site during the oilfield produced water treatment process. Background Art

[0002] After the oilfield is put into development, as the production time increases, the energy of the oil reservoir itself will be continuously consumed, the reservoir pressure of the production will continue to decline, and the oil well output will drop significantly, resulting in the remaining oil being unable to be produced. In order to make up for the underground void caused by the production of crude oil, maintain or increase the reservoir pressure, and obtain a higher recovery rate, it is necessary to develop the underground reservoir by increasing the formation pressure. Oilfield water injection is still one of the most important means to supplement energy to the formation and improve the oil recovery rate during the oilfield development process. The object of water injection is an oil reservoir composed of tight rocks with different permeabilities. Therefore, it is required that the water injection quality meets certain index requirements. The quality of the injected water is an important factor determining the quality of the oilfield water injection development effect, and also determines the length of the overall development life of the oilfield.

[0003] The evaluation criteria for water quality are usually determined by the reservoir category and permeability physical properties of the corresponding development formation. In the industry, the test methods in the corresponding industry technical standards are often used for test analysis; the recommended indicators in the industry standards are used to evaluate the water quality. For example, the "Water Quality Index and Analysis Method for Water Injection in Clastic Rock Reservoirs" SY / T5329-2012 applicable to clastic rock reservoirs. The main control indicators of this standard water quality include 7 detection items such as suspended solids, median particle diameter, oil content, SRB, TGB, and IB, and the auxiliary control indicators include 5 detection items such as dissolved oxygen, hydrogen sulfide, corrosive carbon dioxide, iron, and pH value. The basic requirement for water injection quality is generally that the water quality is stable and does not produce obvious precipitation when mixed with the formation water phase. At the same time, the water should not carry a large amount of suspended solids to prevent blockage of the formation, resulting in the bad consequences of the water injection well not being able to inject water or the injection pressure of the water injection well continuing to rise. From the core requirements of oilfield produced water treatment, among the 12 water quality indicators, the most important and core indicator is the suspended solid content. Its change factors are highly correlated with the other 11 control indicators. At the same time, in the production management of upstream industry produced water treatment, the single indicator with the lowest compliance rate and the greatest control difficulty is also the suspended solid content. However, in actual production, there is still a lack of targeted evaluation devices corresponding to the suspended solid content suitable for on-site use and a quantitative evaluation analysis method with high repeatability.

[0004] In the prior art, the water quality evaluation and management in the oilfield produced water treatment process mainly rely on the following two tasks currently.

[0005] First, it is the water quality monitoring, analysis and management of the produced water treatment system. That is, through on-site detection of some data and laboratory detection of some on-site sampled data, water quality detection data of 12 items are obtained, and based on this, an objective assessment is made on the operation status of each unit of the surface produced water treatment system. Specifically, the method commonly adopted in the current oilfield industry is to rely on professional testing units within the oilfield to carry out water quality monitoring once every quarter to evaluate the operation status of each unit and the overall system of the produced water treatment. Generally, within 1-2 months after on-site sampling and testing, according to the detection data, the overall system operation status assessment and water quality compliance rate analysis of each site of the quarterly water quality monitoring are carried out, a water quality monitoring bulletin is compiled, and measure suggestions are put forward. After being reviewed by the superior department, the water quality monitoring bulletin is issued to the production management department and the technical management department of the oil production plant 1-2 months after the water quality monitoring. The latter makes production parameter adjustments or problem rectifications to the produced water treatment system according to the water quality situation and measure suggestions in the bulletin. There are the following three problems with this monitoring, assessment and management method: ① The testing cycle is too long, the test data is difficult to be quickly applied, on-site problems are difficult to be quickly feedback and rectified. The water quality monitoring includes 12 indicators. For each monitoring point of a site, it generally takes 7-15 days (the SRB culture cycle is generally 7-15 days) from the start of detection to obtaining the test results, and the next test at the same site is generally at an interval of 90 days; ② The testing cost is relatively high. Some testing items have a long cycle and high cost. For example, in the three bacteria monitoring, the secondary dilution method or the tertiary dilution method requires a large consumption of test bottles, and the cost increases year by year, and the testing cycle all requires 7 days; ③ During the sampling and testing process in accordance with SY / T5329, a large amount of oily hazardous waste and solid waste will be generated, which not only affects environmental safety but also increases the production cost of the enterprise.

[0006] Second, it is the dosing management of the produced water treatment chemicals in daily life. Due to the common problems such as corrosion and scaling in the process of oilfield produced water treatment and the purpose of reducing or effectively controlling 12 water quality indicators during the treatment process, different types of chemical agents need to be dosed and dynamically adjusted at different positions during the oilfield produced water treatment process. Therefore, the effective dosing of the produced water treatment chemicals in daily life to ensure quality and quantity is another important work content of the on-site produced water treatment work. Due to the current situation of the change of the produced water formation system or the mixing change of different produced waters during the oilfield production process, the chemical agents for oilfield produced water treatment need to be periodically evaluated, and the effect of the agents in treating the produced water needs to be monitored, which is highly related to the high or low water quality compliance rate of the produced water treatment. Currently, for the evaluation of the chemical agents used in the produced water treatment, we often use the method of collecting water samples on-site with a simulation device and carrying out indoor evaluation for periodic assessment.

[0007] Oilfield produced water treatment systems generally have the following characteristics. First, the treatment sites are numerous, wide-ranging, and relatively dispersed. The sites are often more than a hundred kilometers apart. The high transportation cost of produced water and the actual demand for water injection boosting have led the oilfield industry to generally adopt the process of treating produced fluid nearby and reinjecting it locally. Second, the treatment volume of produced water varies greatly, with the daily treatment volume of produced water ranging from dozens of cubic meters to tens of thousands of cubic meters (the fluctuation of the inlet water volume at the site exceeds 30%). Third, the quality of the inlet liquid water volume at the produced water treatment site changes significantly (the change in a single test parameter exceeds 50%). Generally speaking, for the operation status of oilfield produced water treatment systems, in the field of overall and unit dynamic evaluation, there is still a lack of simple, effective, and low-cost on-site rapid evaluation devices and methods.

[0008] Through literature retrieval and patent inquiries, for the problems encountered in the water quality evaluation and management during the treatment of oilfield produced water, such as the operation status of produced water treatment systems and units, and the lack of effective evaluation methods and means for the effectiveness of chemical agents used in the sedimentation unit of produced water treatment systems, the main solutions inside and outside the industry are mainly as follows:

[0009] In the field of on-site production management technology based on water quality evaluation, the operation modes of most stations for produced water in oilfields at home and abroad still mainly rely on periodic water quality detection and evaluation carried out in accordance with industry standards to achieve the production maintenance management of the produced water treatment system in oilfields. There are problems such as too long testing and feedback cycles, too high testing costs, and lagging on-site adjustment responses, lacking simple, fast, and low-cost evaluation methods. After querying relevant materials, in the field of wastewater treatment technology similar to oilfield produced water, including petrochemical, refining, chemical, etc., for the method of analyzing and evaluating the quality of produced water, there is a patented technology that uses on-line monitoring and evaluation alarms for produced water, especially the on-line turbidity testing method. For example, the sewage on-line turbidity detection system with the patent number ZL2018206300840 uses an optoelectronic system to establish an optoelectronic balance, which is installed at the inlet of the outlet of the pretreatment system and on the output pipeline at the outlet of the subsequent pipeline mixer to collect turbidity change data and achieve the effect of early warning and diversion for exceeding the standard. The sampling position of the detection system is at the rear end of the pretreatment, and it is impossible to realize the full process of the produced water treatment system, especially the water quality testing and evaluation analysis of the produced water at the inlet end of the front end of the produced water treatment. At the same time, due to the extremely unstable water volume and water quality of the inlet of the oilfield produced water treatment system, the sensors of the on-line testing system are easily contaminated, and the testing often cannot operate stably. The overall working procedure is complex and difficult to maintain. The patent with the patent number ZL2017800838595 discloses a turbidity meter device, a sludge thickening device, and a method for determining the turbidity of a liquid sample using the turbidity meter device. The turbidity meter test cavity container is filled with a vacuum pump while generating a low pressure to achieve degassing of the liquid sample. The patent realizes automatic liquid feeding, gas exhaust, and liquid discharge, but the device is complex and is mainly used for sludge turbidity testing in the activated sludge system. However, this system is only applicable to the activated sludge treatment process mode in the sewage treatment system. At present, most of the oilfield produced water treatment systems adopt the physical and chemical process modes of conventional flocculation, sedimentation, and filtration, and more than 90% of the remaining biological produced water treatment technologies adopt the contact oxidation method for treatment. This patent uses a vacuum pump to fill the turbidity meter test cavity container while forming a low pressure to achieve degassing of the liquid sample. However, the device is complex, mainly used for sludge turbidity testing in the activated sludge system, not suitable for use in the oilfield produced water system, with high costs and difficult maintenance. In the patent with the publication number CN114690700 A, a PLC-based intelligent sewage treatment decision optimization method and system: collect sewage quality evaluation index data, preprocess the evaluation index data, construct a hybrid sewage treatment decision optimization model, input the preprocessed sewage quality evaluation index data into the hybrid sewage treatment decision optimization model to obtain the PLC parameter configuration of the hybrid sewage treatment decision, and feedback the final PLC parameter configuration to the PLC console. The PLC console modifies the produced water treatment parameters according to the PLC parameter configuration, and finally realizes controlling the sewage treatment system to carry out optimized treatment of the produced water.A large number of sensors need to be installed at each node along the way. Through the decision-making and parameter configuration of the PLV system, the optimized treatment of sewage is realized. The anti-pollution, renewable properties of the water quality sensors related to this technology and their adaptability to oilfield wastewater are still technical problems that are difficult to overcome for such technologies. In the patent with the publication number CN109853704 A: A method for diagnosing problems in an urban sewage system uses sewage lift pump stations as nodes to diagnose data such as sewage treatment volume, water quality, and compliance rate, and combines the water treatment volume of produced water and the water quality data indicators of inlet and outlet water for diagnosis, providing an effective technical support and data support for the management of the municipal drainage system. The diagnosis and evaluation depend on the basic data of a large number of produced water treatment system water volume and water quality sensor test units on-site. The design parameters of this diagnosis method are all related indicators in the field of conventional external sewage treatment technology. The calculation method of the diagnosis is too cumbersome and is suitable for conventional municipal produced water. It is difficult to adapt to the characteristics of the oilfield produced water treatment system, such as numerous points and wide areas, and the simple and rapid solution technical route required. It also cannot solve the problems of abnormal sensor use and test errors caused by the pollution impact of oily sewage in oilfield produced water. Patent 5: A Chinese invention patent, a comprehensive water quality evaluation method (application publication number is CN108470234A), uses a method of integrating and calculating multiple pollution factors to evaluate water quality, and calculates its overall pollution degree by allocating weights according to the proportion of different pollution factors. Similar to many similar patents, the main focus of this application is on the comprehensive evaluation of the water quality of external sewage in a certain area, rather than targeting the oilfield produced water treatment system. The inspection objects and control standards are very different, and the proposed water quality evaluation method is suitable for overall evaluation. There is no intuitive data and no quantitative standard for the influencing factors of the operation status and treatment effect of the produced water treatment system unit, and it is impossible to achieve the direct production management and continuous improvement of water quality of the oilfield produced water treatment system.

[0010] In the technical field of evaluating the effect of chemical agents based on field applications, the evaluation method for the treatment effect of chemical agents at most stations of produced water in oilfields is still to evaluate in the laboratory by using relevant simulation devices, with only new innovations in the components and compositions inside the simulation devices. For example, in the patent with the patent number ZL202122957359: A dynamic evaluation simulation device for chemical agents in a produced water treatment system in offshore oilfields, a small-displacement indoor produced water treatment system test device including main components such as a chemical dosing system, a modulation tank, an oil skimmer, a flotation unit, an inclined plate oil separator, and a filtration device is constructed. By collecting field water in the form of indoor device simulation, the dynamic evaluation of chemical agents in the produced water treatment system in offshore oilfields is realized, and the simulation of field temperature and flow rate and the dynamic simulation of the treatment effect of chemical agents are achieved. However, it still adopts the method of collecting field produced water samples and using a small indoor simulation device composed of various treatment unit components in the laboratory to simulate and evaluate the treatment effect of field chemical agents. A large amount of field water samples need to be transported to the laboratory, resulting in a long test cycle and high test costs. At the same time, the actual effect evaluation under the field process conditions after the field chemical agent is added cannot be realized.

[0011] To sum up, there is a lack of rapid evaluation means on-site for the produced water treatment system in oilfields at present. In the actual production field, especially at the most important water inlet position of the produced water treatment system, there is no corresponding detection and evaluation technology continuously and stably applied at the on-site produced water treatment in oilfields. At the same time, due to the actual requirements of safety and explosion protection in the oilfield production system, the procurement and maintenance costs are too high, which objectively also limits the use of contact sensor-based produced water testing and decision-making systems in the produced water treatment system in oilfields; for the use of chemical agents for produced water treatment, there is still a lack of simple, efficient and convenient on-site evaluation technical methods. Summary of the Invention

[0012] Aiming at the problems in the prior art that there are many evaluation parameters for the produced water treatment system in oilfields and there is a lack of rapid, immediate and effective evaluation means in on-site evaluation, the present invention provides an evaluation method for the produced water treatment system in oilfields, which mainly solves the following technical problems: First, from the perspectives of controlling the main control indicators of the quality of produced water in oilfields, analyzing the correlation of multiple parameters, and the technical principles involved in the produced water treatment system in oilfields, an important parameter suitable for convenient detection and rapid evaluation of the on-site water quality of produced water treatment in oilfields is proposed; second, it is applicable to rapid detection of on-site samples and actual test data. Based on the classification and analysis of data under different treatment processes, an evaluation method is established to propose an operable evaluation method beneficial to guiding on-site production for the overall and unit operation conditions of the produced water treatment system in oilfields; third, by using the evaluation method, the problem that it is difficult to quickly quantify the on-site evaluation of chemical agents such as destabilization treatment often encountered in the process of produced water treatment is solved.

[0013] The object of the present invention is achieved as follows. An evaluation method for an oilfield produced water treatment system is characterized in that water samples are regularly extracted for detection and evaluation through the following steps:

[0014] Step 1: Regularly draw water samples for sampling from the water inlet of the oilfield produced water treatment system and the water outlets of each unit, encapsulate them in different glass sampling buckets, and mark the samples according to the units;

[0015] Step 2: Detect the initial light transmittance T 初1 、T 初2… T 初i of water, and the light transmittance T 末1 、T 末2… T 末i after standing for 30 - 60 minutes for each water sample, and detect the potential values E0, E 1… E2

[0016] Step 3: Calculate the treatment efficiency X i of each unit of the produced water treatment system and the overall treatment efficiency η

[0017] where the unit treatment efficiency is X i ,X i = unit purification rate D i + unit stability rate K i + unit auxiliary purification rate F i

[0018] D i =(T 初i - T 初i-1 )*100 / T 初i-1 Equation (1)

[0019] K i ==(T 末i - T 初i )*100 / T 初i Equation (2)

[0020] F i = (E i-1 - E i )*100 / E i-1 / 50 Equation (3)

[0021] Equation (4)

[0022] where 50 in Equation (3) is a normalization adjustment constant, and its data is based on the difference between the potential of the water sample with obvious flocculation effect after adding the destabilizing agent and the potential of the original water sample; Q iis the contribution weight of each unit to the overall system processing efficiency. For the current classification of the produced water treatment process in the oilfield, the values are 30%, 60%, and 10% respectively for the sedimentation unit, filtration unit, and water injection unit;

[0023] Step 4, calculate the treatment efficiency Y of the destabilizing agent in the existing sedimentation unit treatment system i ,

[0024] Y i =(E i-1 - E i )*100 / E i-1 Equation (5);

[0025] Step 5, according to the η value in Step 3, evaluate the overall operation effect of the oilfield produced water treatment system and formulate treatment measures;

[0026] Step 6, according to the Y i value of the sedimentation unit in Step 4, formulate the chemical addition measures.

[0027] The evaluation method of the oilfield produced water treatment system of the present invention introduces two detection items, light transmittance and potential, as key control evaluation indicators, forming an evaluation method for the operation status of each unit along the process of the oilfield produced water treatment system suitable for on-site rapid detection. It can realize the detection of key parameters such as light transmittance data highly correlated with the suspended solid content in the water sample and potential data related to sulfide, carbon dioxide content, destabilizing agent, etc. Through data processing, calculate the treatment efficiency of each unit and the effect of the overall system, and conduct a comprehensive and rapid evaluation of each functional unit and the overall system respectively, and make a rapid operation decision according to the evaluation results to ensure the stable operation of the treatment system and the continuous and stable improvement of water quality.

[0028] Furthermore, the oilfield produced water treatment system includes a produced water inlet, a sedimentation unit, a filtration unit, and a water injection unit connected in sequence, and sampling ports are respectively provided at the outlets of each unit.

[0029] Furthermore, in Step 1, the period of regular sampling is 48 hours.

[0030] Furthermore, when the same functional unit includes multiple stages of units connected in series, samples are respectively taken at the outlets of each stage of the unit.

[0031] Furthermore, in Step 4, the weight of each stage of the unit is the weight of this type of unit divided by the number of unit stages.

[0032] Furthermore, in Step 5, the evaluation standard for the overall operation effect of the produced water treatment system is: set the following intervention thresholds for the change of unit and system efficiency according to the empirical value. When the operation efficiency of the test unit or system is lower than the intervention threshold, intervention measures are adopted.

[0033] Further, in Step 5, the intervention measure is to shorten the period of regularly taking water samples for testing to half of the original period. When the following situations occur in two consecutive tests

[0034] η ≥ 5, indicating that the overall system is operating well and the unit is operating well;

[0035] X i ≥ 5, indicating that the unit system is operating well and normal regular sampling is carried out;

[0036] When -10 < X i <5, sampling is encrypted. If the X i results are continuously within this range, measures need to be taken for the unit where it is located;

[0037] When X i index < -10, directly take measures for the unit where it is located.

[0038] Further, in Step 6, the evaluation criteria for the current on-site chemical dosing effect of the sedimentation unit according to the Y i value are as follows: Y i ≤ 10, it is necessary to carry out chemical evaluation, screening and replacement, and judge again whether the existing chemicals match the water body; Y i ≥ 30, the chemicals match the on-site process conditions. When 10 < Y i <30, increase the dosage of sedimentation chemicals by 5% - 10%.

[0039] Further, in Step 2, before the test, each water sample is separately encapsulated in different glass test tubes, and nitrogen or inert gas is introduced into the water samples in the glass test tubes to remove the air in the tubes.

[0040] The above-mentioned evaluation method for the oilfield produced water treatment system of the present invention is based on the correlation analysis of the suspended solid content. When evaluating the oilfield produced water treatment efficiency, two parameters, light transmittance and potential value, are introduced, and converted into the calculation of the efficiency of each treatment unit and the overall system, realizing the on-site rapid evaluation of destabilizing and other related category chemicals for oilfield produced water treatment, realizing the quantitative evaluation of the operation status of the produced water treatment system unit and the overall system, and finding out the problem nodes and proposing targeted implementation plans according to the change of treatment efficiency. Specific embodiments

[0041] According to a large number of data comparison tests on the oilfield produced water treatment site, the correl function correlation between the suspended solid content and various parameters is analyzed, and it is concluded that there is a good correlation between the suspended solid content and the light transmittance as described in the chart.

[0042]

[0043] The main control index of suspended solids in produced water from oilfields mainly includes various particulate matters, etc. The evaluation of the operation status of the produced water treatment system and each unit system in the oilfield is based on the fact that such substances can cause the light incident on the produced water to scatter and transmit. The amount of particulate matter in the produced water is related to the size of the transmitted light; among the auxiliary control indexes, the content of sulfides, carbon dioxide and other auxiliary indexes are related to the electrical properties of the produced water body. Before the treatment of the produced water from the oilfield, the potential is generally between -100 and -200 mv. The addition of destabilizing flocculating sedimentation agents changes the electrical properties of the water body. By testing the change of the potential data of the unit, the effect of the added agent in the existing process can be judged, and thus its on-site applicability can be judged. Based on the significant correlation between the above-mentioned light transmittance and potential value, that is, the light transmittance is significantly positively correlated with the suspended solid content, and the potential value is significantly negatively correlated with the suspended solid content, the evaluation method of the produced water treatment system of the present invention is summarized. Example 1

[0044] In this example, the produced water treatment system of a certain oilfield includes in sequence along the way the produced water inlet (that is, the water produced from the formation), the flocculation sedimentation unit, the buffer tank, the first-stage filtration, the second-stage filtration, and the water sample at the outlet of the water injection tank. Glass sampling buckets are carried to sample and package at each outlet, and then the light transmittance and electrical value are detected separately by a light transmittance meter and a potentiometer at the treatment site. Before the detection, each water sample is respectively filled into a glass test tube and nitrogen is introduced above the liquid surface in the tube for at least five minutes to evacuate the space above the liquid surface to ensure the stability of the detection. The initial light transmittances of each water sample are 73.39, 74.97, 77.41, 92.71, 98.52, 97.35 in turn; after standing for 30 minutes, the light transmittances of each water sample are 75.67, 79.17, 92.75, 98.79, 98.19% in turn; the potential values of each water sample are -108, -50, -56, -48, -45, -51 mv in turn. According to these data, the purification rates D of the flocculation sedimentation unit, buffer tank, first-stage filtration, second-stage filtration, and water injection tank units along the way are calculated respectively according to formulas (1) to (5). i They are 2.15, 3.25, 19.76, 6.27, -1.19 respectively; the stability rates K of the units along the way i Are -1.53, -0.93, -2.27, -0.04, -0.27, -0.86 in turn; the auxiliary purification rates F of the units along the way i Are 1.07, -0.24, 0.29, 0.13, -0.27 in turn. From this, the treatment efficiency indexes of each unit along the way are calculated as 2.29, 0.74, 20.01, 6.12, -2.32; the treatment efficiency Y of the agents in the sedimentation unit (referring to the flocculation sedimentation unit and the buffer tank) i Is 53.7; the treatment efficiency η of the overall system is 8.06. It is evaluated that the operation status of the units and the system at this site is good. Example 2

[0045] In this example, sampling, testing, evaluation and analysis were carried out on-site in another oilfield produced water treatment system. The water treatment system used included produced water inflow, flocculation and sedimentation unit, buffer tank, primary filtration, secondary filtration, and injection water tank. Water samples were taken from their respective outlets through glass sampling buckets, and then each water sample was sealed in a glass test tube. Nitrogen was passed over the liquid surface of each test tube for 5 minutes for evacuation treatment, and then the transmittance T of each water sample was measured by a light transmittance meter. 初i They were 73.27, 74.74, 75.91, 85.83, 91.01, 78.32 in sequence; the transmittance T of each water sample after standing for 30 min 末i They were 75.89, 76.08, 85.98, 91.12, 92.17% in sequence; the potential values E of the water samples at the outlets of the inflow water, flocculation and sedimentation unit, buffer tank, primary filtration, secondary filtration, and injection water tank i They were -122, -126, -116, -105, -102, -184 mv in sequence. According to these data, the purification rates D of the flocculation and sedimentation unit, buffer tank, primary filtration, secondary filtration, and injection water tank units along the process were calculated respectively according to the above formulas (1) to (5). i They were 2.01, 1.57, 13.07, 6.04, -13.94 respectively; the stability rates K of the units along the process i They were -1.54, -0.22, -0.17, -0.12, -17.68 in sequence; the auxiliary purification rates F of the units along the process i They were -0.07, 0.16, 0.19, 0.06, -1.61 in sequence. Thus, the treatment efficiencies X of each unit along the process were calculated. i They were 0.40, 1.50, 13.08, 5.97, -33.24; the treatment efficiency Y of the chemical agent i was -3.28; the overall system treatment efficiency η was 2.68.

[0046] According to the evaluation criteria of each parameter preset by the method of the present invention, the operation status of the units and the system at this site was not good. After analysis, the main problems were low efficiency of the flocculation and sedimentation unit, secondary pollution in the injection water tank, and deterioration of the chemical agent effect.

[0047] After discovering this problem, conventional evaluation methods were used for evaluation. Tests on 12 indicators such as solid content were carried out, and the same conclusion was obtained after verification. At the same time, 1 month before the method of this example was used for evaluation at this site, no abnormalities were found in the conventional quarterly water quality monitoring; the on-site problems were not discovered in time.

[0048] According to the problems found in the on-site evaluation, the chemical agent screening and replacement were carried out within 1 week, making a quick response, and a new chemical agent system was replaced. After 4 days of application of the new chemical agent, the following follow-up evaluation was carried out. The produced water of the oilfield, the flocculation and sedimentation unit, the buffer tank, the first-stage filtration, the second-stage filtration, and the water samples at the outlet of the water injection tank were collected again. After being sealed in glass test tubes, nitrogen was purged, and then the initial transmittance T was measured respectively 初i were 73.83, 83.43, 82.48, 92.37, 98.59, 81.25 in sequence; after standing for 30 min, the transmittance T of each water sample 末 were 83.52, 84.67, 92.67, 98.73, 93.57% in sequence; the potential values E of each water sample i were -115, -65, -61, -63, -67, -68 mv in sequence. According to the above test data, the purification rates D of the flocculation and sedimentation unit, the buffer tank, the first-stage filtration, the second-stage filtration, and the water injection tank unit were calculated respectively according to the above formulas (1) to (5) i were 13.00, -1.14, 11.99, 6.73, -17.59 respectively; the stability rates K of the units along the way i were -0.11, -2.66, -0.32, -0.14, -17.68 in sequence; the auxiliary purification rates F of the units along the way i were 0.87, 0.12, -0.07, -0.13, -0.03 in sequence. The treatment efficiencies X of each unit along the way i were 13.76, -3.67, 11.60, 6.46, -35.30 respectively; the chemical agent action efficiency index Y i was 43.48; the overall system treatment efficiency η was 3.40. From this evaluation result, it can be judged that the chemical agent efficiency has been significantly improved, but the overall system still needs to be improved, and the key is to improve the efficiency of the water injection unit.

[0049] Therefore, the second-step measure adjustment was carried out. Two water injection tanks used in parallel were adopted, and the silt cleaning and washing work was carried out in sequence within two weeks. After 4 days, the following follow-up evaluation was carried out. The water samples at the outlet of each unit system were collected again and the initial transmittance T was measured respectively 初i were 68.95, 82.69, 82.57, 93.56, 98.19, 98.51 in sequence; after standing for 30 min, the transmittance T of each water sample 末i were 83.76, 85.12, 93.69, 98.35, 98.39% in sequence; the potential values of each water sample were -105, -58, -61, -59, -65, -62 mv in sequence. Therefore, according to the above formulas, the purification rates D of each unit were further calculated i were 19.93, -0.15, 13.31, 4.95, 0.33 respectively; the stability rates K of each unit along the way iThey are 1.29, 3.09, 0.14, 0.16, -0.12 in sequence; the auxiliary purification rate F of each unit along the way i They are 0.90, -0.10, 0.07, -0.20, 0.09 in sequence. From this, the treatment efficiency X of each unit along the way is calculated i They are 22.12, 2.84, 13.51, 4.91, 0.3; the treatment efficiency Y of the sedimentation unit treatment system i It is 44.76; the overall system treatment efficiency η is 9.30. Based on this, it is evaluated that the agent efficiency is significantly improved, the overall system efficiency index is significantly improved, and the on-site evaluation is rapid and corresponding

[0050] In this embodiment, through the above on-site sampling, detection, evaluation, analysis and gradually taking corresponding targeted improvement measures for the unit systems with low efficiency, after on-site sampling, rapid detection, evaluation, rapid response and improvement are realized to ensure the stable operation of the oilfield produced water treatment system

Claims

1. An evaluation method for an oilfield produced water treatment system, characterized in that, Regularly extract water samples for testing and evaluation through the following steps: Step 1: Regularly draw water samples for sampling from the water inlet of the oilfield produced water treatment system and the water outlet of each unit, encapsulate them in different glass sampling buckets, and mark the samples according to the units; Step 2: Detect the initial light transmittance T of each water sample 初1 and T 初2… T 初i , the light transmittance T of each water sample after standing for 30 - 60 minutes 末1 and T 末2… T 末i , and detect the potential values E0 and E of each water sample 1… E2 Step 3: Calculate the treatment efficiency X of each unit of the produced water treatment system based on the measured light transmittance and potential value in Step 2 i and the overall treatment efficiency η Among them, the unit processing efficiency is X i , X i = unit purification rate D i + unit stability rate K i + unit auxiliary purification rate F i D i = (T 初i - T 初i-1 ) * 100 / T 初i-1 Equation (1) K i == (T 末i - T 初i ) * 100 / T 初i Equation (2) F i = (E i-1 - E i )*100 / E i-1 / 50 Equation (3) Formula (4) Among them, 50 in formula (3) is a normalization adjustment constant, and its data is based on the difference between the water sample potential of the water sample with obvious flocculation effect after adding the deflocculation agent and the original water sample potential; Q i is the contribution weight of each unit to the overall system treatment efficiency. For the current classification of the produced water treatment process in the oilfield, the values are 30%, 60%, and 10% respectively for the sedimentation unit, the filtration unit, and the water injection unit; Step 4, calculate the treatment efficiency Y of the destabilizing agent in the existing sedimentation unit treatment system i , Y i =(E i-1 - E i )*100 / E i-1 Equation (5); Step 5: Evaluate the overall operation effect of the oilfield produced water treatment system according to the η value in Step 3 and formulate treatment measures; Step 6. Based on the Y value of the sedimentation unit in Step 4, formulate a chemical dosing measure. i ​ 2. The evaluation method of the oilfield produced water treatment system according to claim 1, wherein The produced water treatment system includes a produced water inlet, a settling unit, a filtration unit, and a water injection unit connected in sequence, and a sampling port is provided at the outlet of each unit.

3. The evaluation method of the oilfield produced water treatment system according to claim 1, characterized in that In Step 1, the period of regular sampling is 48 hours.

4. The evaluation method of the oilfield produced water treatment system according to claim 2, wherein When the same functional unit includes multiple levels of units connected in series in sequence, samples are taken separately from the water outlets of each level of the unit.

5. The evaluation method of the oilfield produced water treatment system according to claim 4, characterized in that In Step 4, the weight of each level of the unit is the weight of this type of unit divided by the number of levels of the unit.

6. The evaluation method of the oilfield produced water treatment system according to claim 1, wherein In Step 5, the evaluation criteria for the overall operation effect of the produced water treatment system are as follows: Set the following intervention thresholds for the changes in the unit and system efficiency according to the empirical values. When the operating efficiency of the test unit or system is lower than the intervention threshold, intervention measures are taken.

7. The evaluation method of the oilfield produced water treatment system according to claim 6, characterized in that In Step 5, the intervention measure is to shorten the period of regularly taking water samples for testing to half of the original period. When the following situation occurs in two consecutive tests η≥5 indicates that the overall system operates well and the unit operates well; X i ≥5 indicates that the unit system is operating well and regular sampling is carried out normally; When -10 < X i < 5, encrypted sampling, X i If the results continuously fall within this range, measures need to be taken for the corresponding unit; When X i The exponent < -10, directly take measures for the unit where it is located.

8. The evaluation method of the oilfield produced water treatment system according to claim 2, wherein In step 6, according to Y i The evaluation criteria for the current on-site chemical dosing effect of the sedimentation unit based on the value of Y are as follows: Y i ≤ 10, it is necessary to carry out evaluation, screening and replacement of chemicals, and judge again whether the existing chemicals match the water body; Y i ≥ 30, the chemicals match the on-site process conditions. When 10 < Y i < 30, increase the dosage of sedimentation chemicals by 5% - 10%.

9. The evaluation method of the oilfield produced water treatment system according to claim 2, characterized in that, In Step 2, before the test, each water sample is encapsulated in a different glass test tube, and nitrogen or inert gas is introduced into the water samples in the glass test tubes to remove the air in the tubes.

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