Method for preparing high-molecular polymer oil-displacing agent by efficiently recycling heavy water

Abstract

The invention provides a method for preparing a high-molecular polymer oil-displacing agent by efficiently recycling heavy water, and belongs to the technical field of oilfield development. Comprising the following steps: firstly, preparing a high-molecular polymer oil-displacing agent from heavy water, then carrying out rock core saturation and online nuclear magnetic resonance displacement experiments, dynamically monitoring oil-water distribution and collecting produced liquid; and freezing the produced liquid to separate crude oil, and recovering 70-75% by volume of heavy water from the separated oil-displacing agent under the conditions of negative pressure vacuum and 65-75 DEG C by adopting a rotary distillation technology. And adding an ethanol solution into the residual liquid to precipitate the polymer, and carrying out vacuum filtration and separation. And finally, heating the filtrate in a water bath, evaporating ethanol, and monitoring the refractive index through an Abbe refractometer until the refractive index is the same as that of pure heavy water to complete heavy water recovery. According to the invention, high-efficiency cyclic utilization of heavy water is realized, and the preparation cost of the oil-displacing agent is obviously reduced.

Description

Technical Field

[0001] This invention relates to the field of oilfield development technology, specifically including a method for efficiently recycling heavy water to prepare a polymer flooding agent. Background Technology

[0002] In recent years, nuclear magnetic resonance (NMR) technology has been increasingly widely used in oilfield development. Many scholars have combined online NMR technology with core displacement experiments, utilizing the correspondence between T2 relaxation time spectra and rock pore structure to establish a quantitative characterization method for the remaining oil occurrence state. By dynamically monitoring the mobilization of remaining oil in rock pores, key indicators such as oil displacement efficiency and sweep efficiency are obtained, thereby evaluating the displacement effect of oil displacement agents. Since NMR detects the signal of hydrogen nuclei (¹H), and the hydrogen nuclei (¹H) in ordinary water (H2O) and crude oil produce superimposed signals in the T2 relaxation time spectrum, it is impossible to accurately distinguish the distribution of remaining oil, severely restricting the accuracy and reliability of oil displacement agent performance evaluation. Therefore, heavy water (D2O) was used instead of ordinary water in the experiment. The deuterium nuclei (²H) in heavy water do not produce significant signals in conventional ¹H NMR detection, and its physicochemical properties (such as density, viscosity, and wettability) are similar to those of ordinary water, thus effectively eliminating the interference of ordinary water (¹H) signals. This improvement enables researchers to accurately analyze key displacement characteristics such as oil-water distribution and crude oil mobilization in pore throats during oil displacement processes.

[0003] However, heavy water is an expensive experimental material, and its large-scale use increases the experimental cost of online nuclear magnetic resonance (NMR) displacement experiments. Particularly noteworthy is that the produced fluid still contains a significant amount of heavy water after the experiment, resulting in wasted consumables. Currently, the common practice in the industry is to directly discard this produced fluid without effectively recycling and reusing the heavy water. This not only wastes heavy water but also leads to increased costs for online NMR displacement experiments, significantly hindering the large-scale application of online NMR technology in oilfield development. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a novel method for efficiently recycling heavy water to prepare polymer flooding agents. This method effectively improves the heavy water recovery rate, reduces experimental costs, and helps promote the large-scale application of online nuclear magnetic resonance technology in oilfield development.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for efficiently recycling heavy water to prepare a polymer-based oil displacement agent, comprising:

[0006] Heavy water was used to formulate the polymer-based oil displacement agent;

[0007] Conduct core-based experiments simulating mineralized water in target saturated reservoirs and simulating oil in target saturated reservoirs.

[0008] Online nuclear magnetic resonance displacement experiments were conducted using polymer flooding agents. During the experiments, the fluid changes in the core were dynamically monitored using online nuclear magnetic resonance technology, and the produced fluid was collected simultaneously.

[0009] The produced fluid is frozen to solidify the crude oil and separate it from the polymer flooding agent. The solidified crude oil is then discarded.

[0010] The separated polymer oil displacement agent was treated by rotary distillation under negative pressure vacuum and 65℃~75℃ conditions to obtain heavy water with an initial volume of 70%~75% of the polymer oil displacement agent.

[0011] Add 0.1 to 0.3 times the volume of ethanol solution to the remaining polymer displacement agent after rotary distillation, stir thoroughly and let stand to allow the polymer to precipitate.

[0012] Vacuum filtration technology is used to separate polymer precipitates in polymer-based oil displacement agents;

[0013] The polymer oil displacement agent was mixed with ethanol and heated in a water bath to evaporate the ethanol. During this process, the refractive index of the mixed solution was measured periodically using an Abbe refractometer until the refractive index was the same as that of pure heavy water. Then the water bath heating was stopped, and the heavy water recovery was completed.

[0014] Furthermore, the online nuclear magnetic resonance displacement experiment includes: loading a core treated with saturated oil into an online nuclear magnetic resonance holder, then placing the holder into a nuclear magnetic resonance imaging instrument; after applying the set confining pressure conditions and reaching a stable state, acquiring initial nuclear magnetic resonance data (including T2 spectra and nuclear magnetic resonance imaging). Then, the experiment is carried out using a displacement agent prepared with heavy water, and nuclear magnetic resonance scanning is continuously performed during the displacement process to monitor the dynamic changes in fluid saturation and T2 spectra within the core in real time.

[0015] Furthermore, the rotary distillation technique includes: placing the separated polymer oil displacement agent into a dome flask and fixing it on a rotary evaporator; connecting a condenser, a vacuum pump, and a collection bottle to form a closed system; maintaining a negative pressure of 0.08 MPa to 0.1 MPa with the vacuum pump; adjusting the water bath temperature to 50°C to 60°C; preheating the solution in the dome flask for 10 to 20 minutes; turning on the rotary evaporator; adjusting the rotation speed to 20 rpm to 40 rpm; and performing distillation.

[0016] Further, the method for preparing the polymer flooding agent using heavy water includes: adding heavy water to the corresponding target reservoir mineralization material, stirring with a stirrer at a speed of 300 r / min to 500 r / min for 0.5 h to 1.5 h until the mineralization material is completely dissolved to obtain mineralized water, adding polymer dry powder to the mineralized water, stirring with a stirrer at a speed of 300 r / min to 500 r / min for 1 h to 3 h until the polymer dry powder is completely dissolved to obtain a polymer solution mother liquor, adding mineralized water to the polymer mother liquor to dilute to the target concentration, stirring with a stirrer at a speed of 200 r / min to 300 r / min for 0.5 h to 1 h, and mixing thoroughly to obtain the polymer flooding agent.

[0017] Furthermore, the vacuum filtration technology includes: installing a Buchner funnel on a filtration flask and connecting it to a vacuum pump to form a closed system; maintaining a negative pressure of 0.08 MPa to 0.1 MPa with the vacuum pump; pouring a polymer displacement agent with polymer precipitate into the Buchner funnel; turning on the vacuum pump to perform filtration and remove the polymer precipitate remaining on the filter paper.

[0018] Furthermore, the polymer oil displacement agent and ethanol mixture solution are heated in a water bath to evaporate the ethanol. During this process, the refractive index of the solution is measured every 30 minutes using an Abbe refractometer and compared with the standard refractive index of heavy water (1.3280) to ensure the purity of the recovered heavy water.

[0019] Furthermore, the freezing method includes: pouring the extracted liquid into a beaker and placing it in a refrigerator, setting the temperature to 0℃~5℃, and freezing for 2h~4h.

[0020] Furthermore, the core flooding experimental device includes a nuclear magnetic resonance core holder, an intermediate container, and an injection pump, with the injection rate set to 0.5 mL / min to 1 mL / min.

[0021] Furthermore, the heavy water recovery method can achieve a heavy water recovery rate of 75% to 85%, and the purity of the finally recovered heavy water is greater than 99%.

[0022] According to one or more technical solutions of the present invention, the present invention has the following beneficial effects:

[0023] 1. Significantly improves heavy water recovery rate

[0024] By combining rotary distillation technology with ethanol precipitation and vacuum filtration, the efficient separation and recovery of heavy water in polymer flooding agents has been achieved. The final heavy water recovery rate can reach 75%~85%, and the purity of the recovered heavy water reaches 99%, which greatly reduces the waste of heavy water resources and improves resource utilization.

[0025] 2. Low energy consumption

[0026] Rotary distillation is carried out under negative pressure (0.08MPa~0.1MPa) and temperature conditions (65℃~75℃), which significantly reduces energy consumption compared to traditional atmospheric distillation (usually >100℃).

[0027] 3. Easy to operate

[0028] It employs modular technology (such as rotary distillation and vacuum filtration) and standardized equipment (rotary evaporators, Buchner funnels, etc.), with closely linked steps that eliminate the need for complex operations.

[0029] 4. Safe and environmentally friendly

[0030] The entire process adopts relatively low temperature and low pressure operation, avoiding the risks of traditional high temperature and high pressure processes; polymer precipitation is centrally treated through vacuum filtration, with no harmful substances emitted; the purity of the recovered heavy water reaches the standard refractive index (1.3280), with no secondary pollution, meeting the requirements of green chemistry. Attached Figure Description

[0031] Figure 1 This is a flowchart of the heavy water recycling process provided by the present invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] This embodiment provides a method for efficient recovery of heavy water using polymer-based oil displacement agents, comprising at least the following:

[0034] Heavy water was used to prepare a polymer-based oil displacement agent; core experiments simulating mineralized water and oil in saturated target reservoirs were conducted; online nuclear magnetic resonance (NMR) displacement experiments were performed using the polymer-based oil displacement agent, with produced fluid dynamically monitored and collected during the experiments; the produced fluid was then subjected to freezing treatment until the crude oil solidified and separated from the polymer-based oil displacement agent, and the solidified crude oil was discarded; the separated polymer-based oil displacement agent was treated using rotary distillation under negative pressure vacuum and 65℃~75℃ conditions to obtain the initially prepared high-molecular-weight polymer-based oil displacement agent. The polymer displacement agent is mixed with 70% to 75% heavy water by volume. An ethanol solution of 0.1 to 0.3 times its volume is added to the remaining polymer displacement agent after rotary distillation. The mixture is stirred thoroughly and allowed to stand to allow the polymer to precipitate. The polymer precipitate is separated from the polymer displacement agent using vacuum filtration. The mixture of polymer displacement agent and ethanol is heated in a water bath to evaporate the ethanol. During this process, the refractive index of the heated mixture is measured periodically using an Abbe refractometer until the refractive index is the same as that of pure heavy water. The water bath heating is then stopped, completing the heavy water recovery process.

[0035] The aforementioned method solves the core problems of serious heavy water waste, high experimental costs, and limited technology promotion in traditional online nuclear magnetic resonance displacement experiments. It achieves a triple breakthrough in resource conservation, cost reduction, and technology popularization, laying a key foundation for the large-scale application and promotion of online nuclear magnetic resonance technology in oilfield development.

[0036] Example 1

[0037] Preparation of polymer-based oil displacement agent using heavy water: Weigh an appropriate amount of heavy water and, based on the field conditions of a certain oilfield, add an appropriate amount of mineralizing material to prepare simulated mineralized water for that oilfield. Then, add an appropriate amount of polymer dry powder and stir with a stirrer for 1 hour at a speed of 250 r / min to ensure uniform mixing, finally obtaining 200 mL of the target polymer-based oil displacement agent.

[0038] Online nuclear magnetic resonance (NMR) core displacement experiment: First, the core was saturated with simulated mineralized water to calculate the pore volume. Then, the core was saturated with oil to calculate the oil saturation. An online NMR core displacement experiment was conducted using a polymer flooding agent prepared with heavy water. The core displacement experimental apparatus included an NMR core holder, an NMR imaging analyzer, an intermediate container, and an injection pump. The injection rate was set to 0.5 mL / min. During the experiment, NMR imaging technology was simultaneously activated to scan the core in real time, dynamically monitoring the evolution of fluid saturation and T2 spectrum within the core, while simultaneously collecting produced fluid.

[0039] It should be noted that the core saturated mineral water test, core saturated oil test, and core displacement test are all conventional techniques in this field and will not be further explained here.

[0040] Cryogenic treatment to separate produced fluid: The produced fluid was placed in a beaker and placed in a refrigerator at 2°C. After freezing for 3 hours, the crude oil solidified, resulting in oil-water separation. The solidified crude oil in the beaker was removed, and approximately 130 mL of polymeric displacement agent was collected.

[0041] Rotary distillation extraction of pure heavy water: The remaining 60 mL of polymeric displacing agent in the intermediate container and the collected 500 mL of polymeric displacing agent were placed into a dome-shaped flask and fixed on a rotary evaporator. A condenser, vacuum pump, and collection flask were connected to form a closed system. A vacuum pump was used to maintain a negative pressure of 0.1 MPa to promote solution distillation. The water bath temperature was adjusted to 55°C, and the solution in the dome-shaped flask was preheated for 15 min. The vacuum pump was started until the system reached a negative pressure of 0.1 MPa, and then the rotary evaporator was turned on, adjusting the rotation speed to 35 rpm. The heavy water evaporated to form vapor, which was condensed through the condenser and collected in the collection flask. After distillation, the mixture was allowed to stand for 1 h until all the liquid in the condenser dripped into the collection flask. Finally, approximately 130 mL of pure heavy water was collected in the collection flask, and approximately 50 mL of polymeric displacing agent (heavy water and polymer) remained in the dome-shaped flask.

[0042] To precipitate the polymer, add ethanol: Pour the remaining 50 mL of the polymer displacement agent from the rotary distillation in the dome flask into a beaker, and add 10 mL of ethanol. After adding, stir with a stirrer at 250 rpm for 3 min. Let stand for 1 h to allow the polymer to precipitate completely.

[0043] Filtration of polymer precipitate: Attach the Buchner funnel to the filtration flask, connect the vacuum pump, and place filter paper on the flask to form a closed system. Maintain a negative pressure of 0.1 MPa using the vacuum pump to accelerate solution filtration. Pour the polymer displacement agent containing polymer precipitate into the Buchner funnel, turn on the vacuum pump to reduce the system pressure to a negative pressure of 0.1 MPa, and perform suction filtration. Collect approximately 50 mL of a mixed solution of polymer displacement agent and ethanol in the filtration flask, and remove any remaining polymer precipitate from the filter paper.

[0044] Ethanol evaporation by water bath heating: A mixture of 50 mL of polymer oil displacement agent and ethanol was heated in a water bath at 65 °C to accelerate ethanol evaporation. The refractive index of the initial mixture was measured simultaneously. During heating, the refractive index of the heated mixture was measured every 30 minutes using an Abbe refractometer and compared with the refractive index of pure heavy water (standard refractive index 1.3280). Heating was continued until the refractive index of the mixture approached the standard value of pure heavy water, at which point heating was stopped, completing the heavy water recovery. After evaporation, 30 mL of heavy water remained in the beaker. A total of 160 mL of pure heavy water was recovered, representing a recovery rate of 80%, equivalent to a cost saving of approximately 80%.

[0045] Example 2

[0046] Preparation of polymer flooding agent using heavy water: Weigh an appropriate amount of heavy water and, based on the field conditions of a certain oilfield, add an appropriate amount of mineralizing material to prepare simulated mineralized water for that oilfield. Then, add an appropriate amount of polymer dry powder to it and stir with a stirrer for 1 hour at a speed of 250 r / min to ensure uniform mixing, finally obtaining 300 mL of the target polymer flooding agent.

[0047] Online nuclear magnetic resonance (NMR) displacement core experiment: A core saturation water experiment was conducted to calculate the pore volume, followed by a core saturation oil experiment to calculate the oil saturation, and then a core-driven oil displacement experiment. The core-driven oil displacement experimental apparatus included a NMR core holder, a NMR analyzer, an intermediate container, and an injection pump, with the injection rate set at 0.3 mL / min. During the experiment, NMR imaging technology was simultaneously activated to scan the core in real time, dynamically monitoring the evolution of fluid saturation and T2 spectrum within the core, while simultaneously collecting the produced fluid.

[0048] It should be noted that the core saturated mineral water test, core saturated oil test, and core displacement test are all conventional techniques in this field and will not be further explained here.

[0049] Cryogenic treatment to separate produced fluid: Pour the produced fluid into a beaker and place it in a refrigerator at 3°C. After freezing for 4 hours, the crude oil solidifies, resulting in oil-water separation. Remove the solidified crude oil from the beaker and collect approximately 240 mL of polymeric displacement agent.

[0050] Rotary distillation for extraction of pure heavy water: The remaining 50 mL of polymeric displacing agent in the intermediate container and the collected 400 mL of polymeric displacing agent were poured into a dome-shaped flask and fixed on a rotary evaporator. A condenser, vacuum pump, and collection flask were connected to form a closed system. A vacuum pump was used to maintain a negative pressure of 0.1 MPa to promote solution distillation. The water bath temperature was adjusted to 50 °C, and the solution in the dome-shaped flask was preheated for 15 min. The vacuum pump was started until the system reached a negative pressure of 0.1 MPa, and then the rotary evaporator was turned on, with the rotation speed adjusted to 30 rpm. The heavy water evaporated to form vapor, which was condensed through the condenser and collected in the collection flask. After distillation, the mixture was allowed to stand for 1 h until all the liquid in the condenser dripped into the collection flask. Finally, approximately 200 mL of pure heavy water was collected in the collection flask, and approximately 40 mL of polymeric displacing agent remained in the dome-shaped flask.

[0051] To precipitate the polymer, add ethanol: Pour the remaining 40 mL of the polymer oil displacement agent from the rotary distillation in the dome flask into a beaker, and add 15 mL of ethanol. After adding, stir with a stirrer at 200 rpm for 3 min. Let stand for 1 h to allow the resulting polymer hydrolyzed polyacrylamide to fully precipitate.

[0052] Filtration of polymer precipitate: Attach the Buchner funnel to the filtration flask, connect the vacuum pump, and place filter paper on the flask to form a closed system. Maintain a negative pressure of 0.1 MPa using the vacuum pump to accelerate solution filtration. Pour the polymer displacement agent containing polymer precipitate into the Buchner funnel, turn on the vacuum pump to reduce the system pressure to a negative pressure of 0.1 MPa, and perform suction filtration. Collect approximately 50 mL of a mixed solution of polymer displacement agent and ethanol in the filtration flask, and remove any remaining polymer precipitate from the filter paper.

[0053] Ethanol evaporation by water bath heating: A mixture of 50 mL of polymer oil displacement agent and ethanol was heated in a water bath at 60 °C to accelerate ethanol evaporation. The refractive index of the initial mixture was measured simultaneously. During heating, the refractive index of the heated mixture was measured every 30 minutes using an Abbe refractometer and compared with the refractive index of pure heavy water (standard refractive index 1.3280). Heating was continued until the refractive index of the mixture approached the standard value of pure heavy water, at which point heating was stopped, completing the heavy water recovery. After evaporation, 30 mL of heavy water remained in the beaker. A total of 260 mL of pure heavy water was recovered, representing a recovery rate of 77%, equivalent to a cost saving of approximately 77%.

Claims

1. A method for efficiently recycling heavy water to prepare a polymer-based oil displacement agent, characterized in that, include: Heavy water was used to formulate the polymer-based oil displacement agent; Conduct core-based experiments simulating mineralized water in target saturated reservoirs and simulating oil in target saturated reservoirs. Online nuclear magnetic resonance displacement experiments were conducted using polymer flooding agents. During the experiments, the oil and water distribution changes in the core were dynamically monitored using online nuclear magnetic resonance technology, and the produced fluid was collected simultaneously. The produced fluid is frozen until the crude oil solidifies and separates from the polymer flooding agent, and the solidified crude oil is discarded. The separated polymer oil displacement agent was treated by rotary distillation under negative pressure vacuum and 65℃~75℃ conditions to obtain heavy water with an initial volume of 70%~75% of the polymer oil displacement agent. Add 0.1 to 0.3 times the volume of ethanol solution to the remaining polymer displacement agent after rotary distillation, stir thoroughly and let stand to allow the polymer to precipitate. Vacuum filtration technology is used to separate polymer precipitates in polymer-based oil displacement agents; The polymer oil displacement agent was mixed with ethanol and heated in a water bath to evaporate the ethanol. During this process, the refractive index of the mixed solution was measured periodically using an Abbe refractometer until the refractive index was the same as that of pure heavy water. Then the water bath heating was stopped, and the heavy water recovery was completed.

2. The method according to claim 1, characterized in that, The online nuclear magnetic resonance displacement experiment includes: loading the oil-saturated core into an online nuclear magnetic resonance holder, then placing it into a nuclear magnetic resonance imager, applying confining pressure, acquiring initial nuclear magnetic data, starting the oil displacement experiment and simultaneously performing nuclear magnetic scanning, and dynamically monitoring changes in fluid saturation and T2 spectrum.

3. The method according to claim 1, characterized in that, The rotary distillation technique includes: placing the separated polymer oil displacement agent into a dome flask and fixing it on a rotary evaporator; connecting a condenser, a vacuum pump, and a collection bottle to form a closed system; maintaining a negative pressure of 0.08 MPa to 0.1 MPa with the vacuum pump; adjusting the water bath temperature to 50°C to 60°C; preheating the solution in the dome flask for 10 to 20 minutes; turning on the rotary evaporator; adjusting the rotation speed to 20 rpm to 40 rpm; and performing distillation.

4. The method according to claim 1, characterized in that, The method for preparing a polymer flooding agent from heavy water includes: adding the corresponding target reservoir mineralization material to heavy water, stirring with a stirrer at a speed of 300 r / min to 500 r / min for 1 h to 2 h until the mineralization material is completely dissolved to obtain simulated mineralized water; adding polymer dry powder to the simulated mineralized water, stirring with a stirrer at a speed of 300 r / min to 500 r / min for 3 h to 4 h until the polymer dry powder is completely dissolved to obtain a polymer solution mother liquor; adding simulated mineralized water to the polymer mother liquor and diluting it to the target concentration; stirring with a stirrer at a speed of 200 r / min to 300 r / min for 0.5 h to 1 h; and mixing thoroughly to obtain the polymer flooding agent.

5. The method according to claim 1, characterized in that, The vacuum filtration technology includes: installing a Buchner funnel on a filtration flask and connecting it to a vacuum pump to form a closed system. The vacuum pump maintains a negative pressure of 0.08 MPa to 0.1 MPa. A polymer displacement agent with polymer precipitate is placed into the Buchner funnel, and the vacuum pump is turned on to perform filtration to remove the polymer precipitate remaining on the filter paper.

6. The method according to claim 1, characterized in that, The polymer oil displacement agent is mixed with ethanol and heated in a water bath to evaporate the ethanol. During this process, the refractive index of the mixed solution is measured every 30 minutes using an Abbe refractometer and compared with the standard refractive index of pure heavy water to ensure the purity of the recovered heavy water.

7. The method according to claim 1, characterized in that, The freezing process includes: placing the extracted fluid into a beaker and placing it in a refrigerator, setting the temperature to 0℃~5℃, and freezing for 2h~4h.

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