A method for determining a paraffin removal and viscosity reduction scheme for an oil well

Abstract

The present application relates to a kind of methods for determining oil well wax removal viscosity reduction scheme, comprising the following steps: continuous 7 days sampling test is carried out to oil reservoir well, the water content of sample is obtained by test, and the oil well with water content greater than 30% is screened out;The screened oil well is continuously sampled for 3 days, and the oil well with clear water or without clear water is obtained respectively;Chemical wax removal viscosity reducer is added to the oil well with water content greater than 30% screened out, and from the first day of adding chemical wax removal viscosity reducer, the situation after adding chemical wax removal viscosity reducer is observed and recorded, and the pumping unit motor current and pumping unit maximum load of the oil well after adding chemical wax removal viscosity reducer are obtained, to determine the corresponding oil well wax removal viscosity reduction scheme;The present application can not only improve the cleaning effect, but also reduce the cleaning cost and save the cleaning cost by formulating different wax removal viscosity reduction schemes for different oil wells.

Description

Technical Field

[0001] This invention belongs to the field of oil production engineering technology, and in particular relates to a method for determining a wax removal and viscosity reduction scheme for oil wells. Background Technology

[0002] The close-packing theory of solid geometry posits that crude oil with a water content <25.98% should form a stable W / O type emulsion, while a water content >74.2% should form a stable O / W type emulsion. The water content range of 25.98%-74.02% is considered unstable, and either W / O or O / W type emulsions can form. However, due to the presence of natural surfactants such as paraffin and asphaltenes in crude oil, the crude oil flowing in the wellbore often forms complex, multi-layered mixed-phase emulsions with complex structures such as (O / W) / O and (W / O) / W. In some wells with a water content >30%, standing water can be observed in wellhead samples.

[0003] Oil well dewaxing and viscosity reduction is a crucial issue that must be addressed during oilfield development. The effectiveness of dewaxing and viscosity reduction significantly impacts the extension of pump inspection cycles and is also a key indicator for evaluating oilfield management. Common methods for oil well dewaxing and viscosity reduction include hot washing and chemical washing. For some oil wells, these two methods are often used in combination and alternately; that is, after 5-6 cycles of chemical washing and viscosity reduction, a hot washing and viscosity reduction cycle is required. Other oil wells can only undergo hot washing and viscosity reduction.

[0004] The article "Comparative Study on the Application of Wax Removal Technology in Jiudong Oilfield," published by Zhang Pengju et al. in the journal *Drilling and Production Technology*, Volume 43, Issue 2, 2020, describes the testing of crude oil composition and chemical components in Jiudong Oilfield, analysis of the relationship between crude oil temperature and viscosity, and determination of wax precipitation temperature and wax sample composition. This led to a summary of the characteristics of wax deposition in mechanically produced wells in Jiudong Oilfield. Based on this, and according to production conditions, a comparative study was conducted on the oil casing backwashing wax removal process, the solid sucker rod pump-driven forward washing process, and the hollow sucker rod hot medium circulation well washing wax removal process. Finally, it was concluded that the hot washing wax removal process using hollow sucker rods as the channel can effectively solve the wax removal problem in this oilfield, and it is recommended that this process be used in similar wells in Jiudong Oilfield for wax removal and prevention operations to ensure normal oil well production.

[0005] In his article "Application of Pumping Unit Suspension Point Load Testing in Hot Washing Management," published in *Petroleum & Petrochemical Energy Conservation*, Vol. 10, No. 8, 2020, Meng Zetian describes how wax buildup inside the tubing of pumping unit wells increases frictional load, resulting in increased suspension point load during the upstroke and decreased load during the downstroke. Therefore, tracking and analyzing the alternating suspension point load of pumping unit wells can effectively assess the hot washing and wax removal status of plants, mines, and teams. By analyzing the variation law of alternating suspension point load in single wells, the hot washing cycle can be optimized, and hot washing and wax removal can be performed on wells with significant variations in suspension point load. Managing hot washing using pumping unit load changes allows for better control of the hot washing effect and reduction of suspension point load. Field tests showed an average decrease of 9.73 kN in suspension point load of pumping unit wells, a reduction of 2.68 kW in active power, and annual electricity savings of 5,574 yuan.

[0006] In their article "Experimental Study on the Wax Removal Effect of a Recyclable and Reusable Wax Removal Agent," published in *Qingxi Petrochemicals*, Vol. 38, No. 3, 2021, Ma Lei et al. described a recyclable and reusable chemical wax remover that addresses the problems of existing oil-soluble chemical wax removers, which are mostly benzene-based, have high costs, and are toxic. Based on the mature "flash evaporation" separation and recovery technology in oilfields, they reverse-engineered reagents with low vapor pressure at room temperature and tested their wax-dissolving and recovery performance. Using a device for measuring the wax dissolving rate and recovery ratio of wax removers under pressure, experiments were conducted on 10 widely available reagents. The results showed that dimethyl ether (DME) had good wax dissolving and recovery performance. At 45℃, the wax dissolving rate was 0.086 g / min, significantly higher than that of toluene, xylene, and other wax removers. At 60℃, the volume recovery rate reached 95%, and after four repeated recovery cycles, its wax dissolving rate still reached 0.060 g / min.

[0007] The article "Research Progress on Paraffin Crystallization and Removal in Crude Oil" published by Dong Ke et al. in Chemical Technology and Development, Vol. 48, No. 10, 2019, reviews the mechanism of paraffin crystallization in waxy crude oil, introduces several paraffin removal technologies at home and abroad, discusses the advantages and disadvantages of various paraffin removal technologies, analyzes in detail the influencing factors of paraffin removal effect, and proposes that environmentally friendly, low-cost, high-efficiency and highly adaptable new paraffin removal agents will be the research direction of future paraffin removal agents.

[0008] Chinese Patent CN 113372892A discloses an oil well chemical dewaxing agent, its preparation method, its application, and an oil well dewaxing method. The oil well chemical dewaxing agent, based on 100% of its total mass, comprises the following components: 1-10% C10-C18 hydrocarbon carboxylates, 8-30% C4-C17 mixed hydrocarbons, 5-25% alcohol-ether miscible solvents, and 35-84% water. This invention provides an oil well chemical dewaxing agent, its preparation method, and its application. The dewaxing agent of this invention is an emulsion-type dewaxing agent, safe to operate, and exhibits good solubility and dispersibility with oil well wax, resulting in excellent dewaxing and anti-wax effects.

[0009] Chinese Patent CN 104962267 A discloses a wax remover comprising the following components and parts by weight: 5-20 parts of a special surfactant, 80-200 parts of an anti-icing agent, 100-600 parts of a wax crystal modifier, 2-20 parts of an emulsifier, and 200-400 parts of water. This invention also discloses a method for preparing a low-temperature oil well chemical wax remover. This invention enables the use of a safe, non-flammable, and relatively dense emulsion wax remover for wax removal and prevention operations in low-temperature oil wells.

[0010] Chinese patent CN112812759A discloses a cleaning agent for hot washing of oil wells and its preparation method. The cleaning agent comprises the following components by weight percentage: 10-30% dispersant, 0.1%-5% wax remover, 1%-5% pour point depressant, 3-5% co-solvent, and the balance being water. This invention utilizes a combination of wax remover, dispersant, and pour point depressant to ensure the system's stable performance in high-temperature hot water, promoting wax removal during hot washing and dispersing wax lumps, thus meeting the technical requirements for hot washing and wax removal in oil wells. This cleaning agent has a high flash point, is safe and efficient, and is odorless and pollution-free. The raw materials used are readily available, the preparation process is simple, and it is highly operable, effectively solving the problem of poor cleaning effect of commonly used hot water for oil rods and tubing.

[0011] Chinese Patent CN 112796704 A discloses a method including: Step 1, determining the structural parameters of the hot washing well and calculating the total heat transfer coefficient; Step 2, studying the temperature field distribution law of hot washing based on the total heat transfer coefficient and establishing a mathematical model of temperature distribution; Step 3, analyzing the characteristics of water-bearing wax precipitation in different regions of the oil well through experimental testing, and calculating the wax precipitation model of the oil well based on the oil layer temperature distribution and oil sample physical properties; Step 4, inputting the wax deposition parameters into the heat transfer model to calculate the heat required for hot washing; Step 5, selecting the optimal hot washing scheme based on different hot washing structures and by calculating the conditions of the required hot washing fluid. This method of optimizing the hot washing wax removal method and parameters effectively integrates the degree of wax deposition, wax removal technology, and operation management, improving the treatment effect of wax-deposited wells, effectively increasing the operating rate of wax-deposited wells, predicting the cleaning cycle, and is convenient, simple, and easy to promote.

[0012] Currently, the commonly used hot washing and chemical dewaxing methods in oilfields have achieved good results. The dewaxing and viscosity reduction plan is determined based on the maximum suspension point load of the oil well pumping unit and the change in pumping unit motor current. In reality, some oil wells experience very little change in the maximum suspension point load and pumping unit motor current during production. However, to prevent pump inspection operations from being necessary due to untimely dewaxing and viscosity reduction, this approach has at least the following drawbacks:

[0013] ① Hot washing of oil wells removes wax and reduces viscosity. After hot washing, the oil well has a drainage period of 2-3 days, which affects the oil production of the oil well. The hot washing medium enters the oil layer, causing oil layer pollution and reducing oil production. At the same time, hot washing also requires certain production costs.

[0014] ② Chemical wax removal and viscosity reduction in oil wells requires the addition of chemical wax removal and viscosity reduction agents to the oil wells at regular intervals and in specific quantities. Chemical wax removal and viscosity reduction agents are relatively expensive.

[0015] Therefore, determining the appropriate chemical viscosity reduction scheme for oil wells to ensure normal production has become a pressing technical problem for engineers. Summary of the Invention

[0016] The technical problem solved by this invention is achieved through the following technical solution:

[0017] A method for determining a wax removal and viscosity reduction scheme for oil wells includes the following steps:

[0018] The oil reservoir wells were sampled and tested for 7 consecutive days to obtain the water cut of the samples, and wells with a water cut greater than 30% were screened.

[0019] For oil wells with a water cut greater than 30% selected, samples were taken continuously for 3 days, and oil wells with or without visible water were obtained during sampling.

[0020] Chemical wax remover and viscosity reducer were added to the selected oil wells with a water content greater than 30%. Starting from the first day of adding the chemical wax remover and viscosity reducer, the condition of the oil well after adding the chemical wax remover and viscosity reducer was observed and recorded. The current of the oil well pumping unit motor and the maximum load of the oil well pumping unit suspension point were obtained after adding the chemical wax remover and viscosity reducer.

[0021] Based on the observation and recording of the well conditions after the chemical dewaxing and viscosity reducing agent was added, as well as the obtained oil well pumping unit motor current and the maximum load at the oil well pumping unit suspension point after the chemical dewaxing and viscosity reducing agent was added, the corresponding oil well dewaxing and viscosity reducing scheme was determined.

[0022] Furthermore, the process involves adding a chemical dewaxing and viscosity-reducing agent to oil wells with a selected water cut greater than 30%, and observing and recording the condition of the oil wells after the addition of the chemical dewaxing and viscosity-reducing agent from the first day of application. Specifically, this includes the following three scenarios:

[0023] a) After adding chemical dewaxing and viscosity reducing agents to oil wells where visible water is visible, observe and record the number of days A during which the color of the visible water changes from its original color to the point where the visible water is no longer visible, and then changes back to the point where the visible water is visible. Obtain the corresponding well number.

[0024] b) After adding chemical dewaxing and viscosity reducing agents to oil wells where visible water is visible, observe and record the number of days (B) during which the color of the visible water remains the same as the original color of the produced water, and obtain the corresponding well number.

[0025] c) After adding chemical dewaxing and viscosity reducing agents to oil wells where no open water can be observed, observe and record the number of days (C) during sampling where no open water can be observed, and obtain the corresponding well number.

[0026] Furthermore, the method for obtaining the motor current of the oil well pumping unit and the maximum load at the suspension point of the oil well pumping unit after the addition of the chemical dewaxing and viscosity reducing agent is as follows:

[0027] Obtain the motor current of the oil well pumping unit after the addition of chemical dewaxing and viscosity reducing agent, and record the number of days E that reached the maximum value limited by the engineering design.

[0028] Obtain the maximum load at the suspension point of the oil well pumping unit after the addition of chemical dewaxing and viscosity reducing agent, and record the number of days F that reached the maximum value limited by the engineering design.

[0029] Furthermore, the method for determining the corresponding oil well dewaxing and viscosity reduction scheme based on the observed and recorded conditions after the well was injected with the chemical dewaxing and viscosity reducing agent, and the obtained oil well pumping unit motor current and maximum load at the oil well pumping unit suspension point after the injection of the chemical dewaxing and viscosity reducing agent, is as follows:

[0030] For oil wells in condition a), a combination of chemical dewaxing and hot washing dewaxing and viscosity reduction is used for oil well dewaxing and viscosity reduction.

[0031] For oil wells in case b), hot washing is used to remove wax and reduce viscosity.

[0032] For oil wells in case c), when the oil well pumping unit motor current or the maximum load at the pumping unit suspension point reaches the maximum value specified in the engineering design first, chemical dewaxing and viscosity reduction or hot washing dewaxing and viscosity reduction shall be performed.

[0033] Furthermore, for oil wells in case a), when using a combination of chemical dewaxing and hot washing for dewaxing and viscosity reduction, the time interval for chemical dewaxing and viscosity reduction should be the minimum value among A, E, and F. After 5-6 cycles of chemical dewaxing and viscosity reduction, a hot washing dewaxing and viscosity reduction should be performed once.

[0034] Furthermore, for oil wells in case b), when hot washing is used to remove wax and reduce viscosity, the time interval for hot washing and removing wax is the minimum value among B, E, and F.

[0035] The advantages and positive effects of this invention are:

[0036] 1) The method of the present invention can not only improve the cleaning effect by formulating different wax removal and viscosity reduction schemes for different oil wells, but also reduce the cleaning cost and save cleaning expenses.

[0037] 2) The method of this invention has been applied to more than 574 oil wells in 27 oil reservoirs with a success rate of 100%. Among them, 106 oil wells did not require chemical dewaxing or hot washing for dewaxing and viscosity reduction. 412 oil wells that combined chemical dewaxing and viscosity reduction with hot washing extended the time for adding chemical dewaxing and viscosity reduction agents, saving an average of 0.56 tons of chemical dewaxing and viscosity reduction agents per well per year, with a unit price of 6,800 yuan / ton. The average number of hot washings per well per year was saved by 0.72 wells, with a hot washing cost of 9,800 yuan / well. 56 oil wells that underwent hot washing for dewaxing and viscosity reduction extended the time for hot washing, saving an average of 3.25 hot washings per well per year, with a hot washing cost of 9,800 yuan / well. Detailed Implementation

[0038] First, it should be noted that the specific structure, features, and advantages of the present invention will be illustrated by way of examples below. However, all descriptions are for illustrative purposes only and should not be construed as limiting the present invention in any way. Furthermore, any single technical feature described or implied in the embodiments mentioned herein can still be arbitrarily combined or deleted among these technical features (or their equivalents) to obtain more other embodiments of the present invention that may not be directly mentioned herein.

[0039] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0040] Example 1

[0041] This embodiment provides a method for determining an oil well dewaxing and viscosity reduction scheme, comprising the following steps:

[0042] The oil reservoir wells were sampled and tested for 7 consecutive days to obtain the water cut of the samples, and wells with a water cut greater than 30% were screened.

[0043] For oil wells with a water cut greater than 30% selected, samples were taken continuously for 3 days, and oil wells with or without visible water were obtained during sampling.

[0044] Chemical wax remover and viscosity reducer were added to the selected oil wells with a water content greater than 30%. Starting from the first day of adding the chemical wax remover and viscosity reducer, the condition of the oil well after adding the chemical wax remover and viscosity reducer was observed and recorded. The current of the oil well pumping unit motor and the maximum load of the oil well pumping unit suspension point were obtained after adding the chemical wax remover and viscosity reducer.

[0045] Based on the observation and recording of the well conditions after the chemical dewaxing and viscosity reducing agent was added, as well as the obtained oil well pumping unit motor current and the maximum load at the oil well pumping unit suspension point after the chemical dewaxing and viscosity reducing agent was added, the corresponding oil well dewaxing and viscosity reducing scheme was determined.

[0046] Specifically, the process involves adding a chemical dewaxing and viscosity-reducing agent to oil wells with a water cut greater than 30%, and observing and recording the condition of the wells after the addition of the chemical dewaxing and viscosity-reducing agent, starting from the first day of application. This includes the following three scenarios:

[0047] a) After adding chemical dewaxing and viscosity reducing agents to oil wells where visible water is visible, observe and record the number of days A during which the color of the visible water changes from its original color to the point where the visible water is no longer visible, and then changes back to the point where the visible water is visible. Obtain the corresponding well number.

[0048] b) After adding chemical dewaxing and viscosity reducing agents to oil wells where visible water is visible, observe and record the number of days (B) during which the color of the visible water remains the same as the original color of the produced water, and obtain the corresponding well number.

[0049] c) After adding chemical dewaxing and viscosity reducing agents to oil wells where no open water can be observed, observe and record the number of days (C) during sampling where no open water can be observed, and obtain the corresponding well number.

[0050] The method for obtaining the motor current of the oil well pumping unit and the maximum load at the suspension point of the oil well pumping unit after the addition of chemical dewaxing and viscosity reducing agents is as follows:

[0051] Obtain the motor current of the oil well pumping unit after the addition of chemical dewaxing and viscosity reducing agent, and record the number of days E that reached the maximum value limited by the engineering design.

[0052] Obtain the maximum load at the suspension point of the oil well pumping unit after the addition of chemical dewaxing and viscosity reducing agent, and record the number of days F that reached the maximum value limited by the engineering design.

[0053] Furthermore, the method for determining the corresponding oil well dewaxing and viscosity reduction scheme based on the observed and recorded conditions after the well was injected with the chemical dewaxing and viscosity reducing agent, and the obtained oil well pumping unit motor current and maximum load at the oil well pumping unit suspension point after the injection of the chemical dewaxing and viscosity reducing agent, is as follows:

[0054] For oil wells in case a), a combination of chemical dewaxing and hot washing dewaxing is used to dewax and reduce viscosity. The time interval for chemical dewaxing is the minimum value among A, E, and F. After 5-6 cycles of chemical dewaxing and viscosity reduction, a hot washing dewaxing and viscosity reduction is required.

[0055] For oil wells in case b), hot washing is used to remove wax and reduce viscosity. The time interval for hot washing and wax removal is the minimum value among B, E, and F.

[0056] For oil wells in case c), when the oil well pumping unit motor current or the maximum load at the pumping unit suspension point reaches the maximum value specified in the engineering design first, chemical dewaxing and viscosity reduction or hot washing dewaxing and viscosity reduction shall be performed.

[0057] As an example, in this embodiment, the above method was applied to 51 oil wells in the XX oil reservoir, and the results show:

[0058] ① There are 13 oil wells that do not require chemical or hot washing for wax removal and viscosity reduction.

[0059] ② In 35 oil wells where chemical dewaxing and viscosity reduction were combined with hot washing dewaxing and viscosity reduction, the time for adding chemical dewaxing and viscosity reduction and hot washing dewaxing and viscosity reduction was extended. On average, each well saved 0.61 tons of chemical dewaxing and viscosity reduction per year, with a unit price of 6,800 yuan / ton for chemical dewaxing and viscosity reduction agents; on average, each well saved 0.88 hot washings per year, with a hot washing cost of 9,800 yuan / well.

[0060] ③ The three oil wells that underwent hot washing to remove wax and reduce viscosity extended the time for hot washing to remove wax and reduce viscosity. On average, each well saved 4.16 hot washing sessions per year, with a hot washing cost of 9,800 yuan per well.

[0061] The above embodiments have provided a detailed description of the present invention, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent variations and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for determining a wax removal and viscosity reduction scheme for oil wells, characterized in that, Includes the following steps: The oil reservoir wells were sampled and tested for 7 consecutive days to obtain the water cut of the samples, and wells with a water cut greater than 30% were selected. For oil wells with a water cut greater than 30% selected, samples were taken continuously for 3 days, and oil wells with or without visible water were obtained during sampling. Chemical wax remover and viscosity reducer were added to the selected oil wells with a water content greater than 30%. Starting from the first day of adding the chemical wax remover and viscosity reducer, the condition of the oil wells after adding the chemical wax remover and viscosity reducer was observed and recorded. The current of the oil well pumping unit motor and the maximum load of the oil well pumping unit suspension point were obtained after adding the chemical wax remover and viscosity reducer. Based on the observation and recording of the well after the chemical dewaxing and viscosity reducing agent was added, and the obtained oil well pumping unit motor current and oil well pumping unit suspension point maximum load after the chemical dewaxing and viscosity reducing agent was added, the corresponding oil well dewaxing and viscosity reducing scheme was determined. The process involves adding a chemical dewaxing and viscosity-reducing agent to oil wells with a water cut greater than 30%, and observing and recording the condition of the oil wells after the addition of the chemical dewaxing and viscosity-reducing agent, starting from the first day of the addition. Specifically, this includes the following three scenarios: a) After adding chemical dewaxing and viscosity reducing agents to oil wells where visible water is visible, observe and record the number of days A during which the color of the visible water changes from its original color to the point where the visible water is no longer visible, and then changes back to the point where the visible water is visible. Obtain the corresponding well number. b) After adding chemical dewaxing and viscosity reducing agents to oil wells where visible water is visible, observe and record the number of days (B) during which the color of the visible water remains the same as the original color of the produced water, and obtain the corresponding well number. c) After adding chemical dewaxing and viscosity reducing agents to oil wells where no visible water can be observed, observe and record the number of days (C) during sampling where no visible water can be observed, and obtain the corresponding well number. The method for obtaining the motor current of the oil well pumping unit and the maximum load at the suspension point of the oil well pumping unit after the addition of chemical dewaxing and viscosity reducing agents is as follows: Obtain the motor current of the oil well pumping unit after the addition of chemical dewaxing and viscosity reducing agent, and record the number of days E that reached the maximum value limited by the engineering design. Obtain the maximum load at the suspension point of the oil well pumping unit after the addition of chemical dewaxing and viscosity reducing agent, and record the number of days F that reached the maximum value limited by the engineering design. The method for determining the appropriate oil well dewaxing and viscosity reduction scheme based on the observed and recorded conditions after the well is injected with chemical dewaxing and viscosity reducing agent, and the obtained oil well pumping unit motor current and maximum load at the oil well pumping unit suspension point after the injection of chemical dewaxing and viscosity reducing agent, is as follows: For oil wells in condition a), a combination of chemical dewaxing and hot washing dewaxing and viscosity reduction is used for oil well dewaxing and viscosity reduction. For oil wells in case b), hot washing is used to remove wax and reduce viscosity. For oil wells in case c), when the oil well pumping unit motor current or the maximum load at the pumping unit suspension point reaches the maximum value specified in the engineering design first, chemical dewaxing and viscosity reduction or hot washing dewaxing and viscosity reduction shall be performed.

2. The method for determining an oil well dewaxing and viscosity reduction scheme according to claim 1, characterized in that: For oil wells in case a), when using a combination of chemical dewaxing and hot washing for dewaxing and viscosity reduction, the time interval for chemical dewaxing and viscosity reduction should be the minimum of A, E, and F. After 5-6 cycles of chemical dewaxing and viscosity reduction, a hot washing dewaxing and viscosity reduction should be performed.

3. The method for determining an oil well dewaxing and viscosity reduction scheme according to claim 1, characterized in that: For oil wells in case b), when hot washing is used to remove wax and reduce viscosity, the time interval for hot washing and reducing viscosity is the minimum value among B, E, and F.