Chemical flooding ground injection method and device

Abstract

The invention relates to a chemical flooding ground injection method and device, and belongs to the technical field of oil exploitation. According to the chemical flooding ground injection method, the formation water in the water layer of the waste oil well near the oil well to be exploited is adopted as a water source, the water cost for liquid preparation is reduced, sulfide and ferrous ions in the formation water are removed through oxygen exposure treatment and solid-liquid separation, and the viscosity loss rate of a subsequently prepared polymer flooding agent can be reduced. According to the chemical flooding ground injection method, throttling metering is carried out at the low-pressure end in front of the injection pump, polymer viscosity loss caused by high-pressure throttling can be reduced (the viscosity loss rate is reduced by about 10%), and the dosage of a chemical flooding agent is saved. According to the chemical flooding ground injection method, the water cost for liquid preparation can be reduced, the dosage of a chemical flooding agent is saved, and the operation cost is low.

Description

Technical Field

[0001] The invention relates to a chemical flooding surface injection method and device, belonging to the technical field of petroleum extraction. Background Art

[0002] At present, chemical flooding plays an important role in increasing and stabilizing the production of old oil fields. However, due to the lack of surface supporting injection systems for small-scale blocks in remote areas, the traditional surface supporting injection technology of chemical flooding adopts the station construction or skid-mounted liquid preparation mode (such as Figure 1 As shown in Figure 2, long construction cycles, large investments in surface construction, and high costs hinder the efficient implementation of chemical flooding, making it more difficult to profitably develop low-efficiency water-flooded reservoirs in small, remote areas. Therefore, reducing surface construction costs, shortening the construction cycle, and conserving investment in supporting processes to promote efficient and cost-effective chemical flooding in small, remote areas has become a pressing issue.

[0003] Chinese patent document CN109113696B discloses a surface injection method for chemical flooding. The method involves assembling a tank, pipelines, a feed pump, a discharge pump, and other devices on-site. The tank is used to prepare the chemical flooding solution. Liquid raw materials enter the tank through a feed pump connected to the tank, and the feed rate is controlled by adjusting the feed pump's pump speed. Solid raw materials are weighed and added directly to the tank. The prepared chemical flooding solution is then injected into the well via the discharge pump, with the injection rate controlled by the pump speed. However, the source of the water used for preparation is not specified in the surface injection method. In some remote, water-scarce areas or where there is no surface water pipeline network, the conventional method is to transport the water by tank truck, which is expensive.

[0004] Chinese patent document CN111662701A discloses a method for oil production using produced water. The method disclosed in the patent document specifically includes the following steps: first, adding an ecological viscosity stabilizer to a dosing tank, then adding oilfield produced water to the dosing tank, stirring and dissolving, preparing an ecological viscosity stabilizer mother liquor, and storing it in the dosing tank; then, pumping the ecological viscosity stabilizer mother liquor into the oilfield produced water via a dosing pump to obtain ready-to-use oilfield produced water; finally, using the ready-to-use oilfield produced water as a solvent to prepare a polymer mother liquor, then diluting the polymer mother liquor with the ready-to-use oilfield produced water, and then using it for oil production. Although the method disclosed in the patent document can reduce the cost of transporting the prepared water by tank truck to a certain extent, the use of ecological viscosity stabilizers to treat oilfield produced water still has problems such as high treatment cost, instability, and poor compatibility with polymers.

[0005] Therefore, there is an urgent need to develop a low-cost chemical flooding surface injection method and its supporting equipment. Summary of the Invention

[0006] The purpose of the present invention is to provide a chemical flooding surface injection method, which can solve the problem of high operating cost of the current chemical flooding surface injection method.

[0007] Another object of the present invention is to provide a chemical flooding surface injection device that can solve the problem of high operating costs of the devices used in the current chemical flooding surface injection method.

[0008] In order to achieve the above objectives, the technical solution adopted by the chemical flooding ground injection method of the present invention is:

[0009] A chemical flooding surface injection method comprises the following steps: perforating the upper water layer of an abandoned oil well located near an oil well to be mined to obtain formation water, then subjecting the formation water to oxygenation treatment and solid-liquid separation in sequence to remove sulfide and ferrous ions in the formation water to obtain preparation water, then using the preparation water to prepare a chemical flooding system, and pumping the chemical flooding system to the well to be injected after throttling and metering; the total iron content of the preparation water is ≤0.2 mg / L, the sulfur content is ≤0.1 mg / L, and the concentration of sulfate-reducing bacteria is <2.5 cells / mL.

[0010] The chemical flooding surface injection method of the present invention uses formation water from the upper water layer of an abandoned oil well located near the oil well to be mined as a water source, reducing the cost of water for liquid preparation. It utilizes oxygenation treatment and solid-liquid separation to remove sulfides and ferrous ions from the formation water, thereby reducing the viscosity loss rate of the subsequent polymer flooding agent preparation. In the chemical flooding surface injection method of the present invention, throttling and metering are performed at the low-pressure end before the injection pump, which can reduce the polymer viscosity loss caused by high-pressure throttling (reducing the viscosity loss rate by approximately 10%) and save the amount of chemical flooding agent used. The chemical flooding surface injection method of the present invention can reduce the cost of water for liquid preparation, save the amount of chemical flooding agent used, and has low operating costs.

[0011] The upper water layer is generally 100 to 200 meters deep. The total mineralization of the upper water layer is lower than that of the lower formation water and is close to the mineralization of surface water (total mineralization ≤ 2000 mg / L). The viscosity of the polymer prepared with the prepared water is higher.

[0012] It is understandable that the sulfides in formation water are mainly divalent sulfide ions.

[0013] Preferably, the aeration treatment and solid-liquid separation method is as follows: the formation water is subjected to two or more sedimentation cycles under aeration conditions, and the sedimentation system is then filtered. The aeration time during each of the two or more sedimentation cycles is adjusted based on the treatment effect of the formation water.

[0014] Preferably, the mesh diameter of the filter used for filtration is not greater than 0.8 mm.

[0015] Preferably, the formation water is subjected to two sedimentation steps under oxygen exposure conditions, the temperature of the first sedimentation step is 30-80°C, and the temperature of the second sedimentation step is 40-80°C.

[0016] Preferably, the method for preparing chemical flooding using liquid preparation water is as follows: the liquid preparation water, polymer and surfactant are mixed, matured and filtered to obtain a chemical flooding system.

[0017] Preferably, the polymer is type II or type III polyacrylamide, and the surfactant is an anionic water-soluble surfactant; when the chemical flooding system is prepared using liquid preparation water, the temperature of the liquid preparation water is 38-80°C.

[0018] Preferably, the mixing time is not less than 2 hours, and the aging time is not less than 1 hour.

[0019] Preferably, during the maturation process, the concentration of sulfate-reducing bacteria in the system is controlled to be less than 25 cells / mL; and the mesh diameter of the filter used for filtration when using liquid water to prepare chemical flooding is not greater than 3 mm.

[0020] Preferably, the viscosity of the prepared chemical flooding is 60 to 90 mPa·s, and the pump efficiency of the pump used for pumping the chemical flooding is 50% to 70%.

[0021] The technical solution adopted by the chemical flooding ground injection device of the present invention is:

[0022] A chemical flooding surface injection device for implementing the chemical flooding surface injection method described above comprises a settling device, a water storage device, a liquid distribution water filtration device, a liquid distribution device, a maturation device, a chemical flooding filtration device, and an injection pump, which are connected in sequence; the inlet of the settling device is connected to the water layer of an abandoned oil well near the oil well to be recovered, and the outlet of the injection pump is connected to the wellhead of the oil well to be recovered; the settling device and the water storage device are respectively connected to an aeration device; and a throttling metering device is provided on the connecting pipeline between the chemical flooding filtration device and the injection pump.

[0023] The chemical flooding ground injection device of the present invention has a simple structure, is easy to operate, and has low cost. When using the chemical flooding ground injection device of the present invention for chemical flooding ground injection, the cost of water preparation can be reduced, the amount of chemical flooding agent used can be saved, and the operating cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the conventional surface injection process of chemical flooding in the present invention;

[0025] Figure 2 A schematic diagram of a device used in a surface injection method for chemical flooding according to an embodiment of the present invention;

[0026] Figure 3 Schematic diagram of the whole process of viscosity loss analysis and treatment in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present invention's surface injection method for chemical flooding is a groundbreaking invention. It includes the following steps: perforating the upper water layer of an abandoned oil well located near an oil well to be recovered to obtain formation water; then subjecting the formation water to aeration and solid-liquid separation to remove sulfides and ferrous ions from the formation water to obtain a preparation water solution; then, using the preparation water solution to prepare a chemical flooding solution, the chemical flooding solution is throttled and metered before being pumped to the oil well to be recovered; the preparation water solution has a total iron content of ≤0.2 mg / L, a sulfur content of ≤0.1 mg / L, and a sulfate-reducing bacteria concentration of <2.5 cells / mL.

[0028] The chemical flooding surface injection method of the present invention uses formation water from the water layer of an abandoned oil well located near the oil well to be mined as a water source, reducing the cost of water for liquid preparation. It utilizes oxygenation treatment and solid-liquid separation to remove sulfides and ferrous ions from the formation water, thereby reducing the viscosity loss rate of the subsequent polymer flooding agent preparation. In the chemical flooding surface injection method of the present invention, throttling metering is performed at the low-pressure end before the injection pump, which can reduce the polymer viscosity loss caused by high-pressure throttling (reducing the viscosity loss rate by approximately 10%) and save the amount of chemical flooding agent used. The chemical flooding surface injection method of the present invention can reduce the cost of water for liquid preparation, save the amount of chemical flooding agent used, and has lower operating costs.

[0029] In some preferred embodiments, the method of aeration treatment and solid-liquid separation is as follows: the formation water is settled under aeration conditions, the settled formation water is aerated again, and finally the aerated formation water is filtered.

[0030] In some preferred embodiments, the mesh diameter of the filter used for filtration is no greater than 0.8 mm.

[0031] In some preferred embodiments, the temperature of the formation water during sedimentation under oxygenation conditions is 30-80°C, and the temperature of the sedimented formation water during re-oxygenation conditions is 40-80°C.

[0032] In some preferred embodiments, the method for preparing a chemical flooding system using the dosing water is as follows: the dosing water, a polymer and a surfactant are mixed, matured and filtered to obtain the chemical flooding system.

[0033] In some preferred embodiments, the polymer is type II or type III polyacrylamide, and the surfactant is an anionic water-soluble surfactant.

[0034] In some preferred embodiments, when using dosing water for chemical flooding, the dosing water temperature is 38-80°C. Controlling the dosing water temperature to 38-80°C ensures that the polymer and surfactant are fully dissolved and mixed, improves the uniformity of the system, reduces polymer viscosity loss, and prevents the prepared polymer aqueous solution from rapidly thickening or increasing in viscosity, which could cause high operating power or blockage of surface pumping equipment, leading to construction difficulties. Since the anionic water-soluble surfactant used in the present invention (in a white, paste-like, semi-fluid state) has a dissolution temperature above 40°C and is difficult to dissolve when the water temperature is below 35°C, heating of the anionic water-soluble surfactant can be avoided by controlling the dosing water temperature to 38-80°C.

[0035] In some preferred embodiments, the mixing time is not less than 2 hours, and the aging time is not less than 1 hour.

[0036] In some preferred embodiments, the concentration of sulfate-reducing bacteria in the system is controlled to be less than 25 cells / mL during the aging process.

[0037] In some preferred embodiments, the filter used for filtration of chemical flooding using the dosing water has a mesh diameter of no greater than 3 mm. Filtration can remove fish eyes and lumps in the chemical flooding and reduce polymer viscosity loss.

[0038] In some preferred embodiments, the viscosity of the prepared chemical flooding is 60-90 mPa·s.

[0039] In some preferred embodiments, the pump efficiency of the pump used for chemical flooding is 50% to 70%. Experimental results show that when the pump efficiency of the injection pump is 50% to 70%, the viscosity loss of polymer can be effectively reduced, and the material and operating costs can be reduced.

[0040] In some preferred embodiments, the viscosity of the chemical flooding when pumped to the wellhead of the oil well to be produced is ≥40 mPa·s.

[0041] The low-cost and simplified surface injection process for chemical flooding of small blocks without a surface injection system of the present invention comprises four parts: 1. water supply process flow; 2. liquid preparation process flow; 3. injection process flow; and 4. monitoring process flow.

[0042] The incoming water process primarily utilizes the following devices: a water source well, two elevated water tanks, and a backup and a standby liquid preparation water filtration device. First, utilizing an abandoned oil well closest to the injection well or located in the same well field, the water layer is perforated and the formation water is pumped to the first surface sedimentation tank A using a pumping unit for natural sedimentation and precipitation of coarse impurities. The formation water then enters the second water storage tank B, utilizing the height difference between the inlet and outlet liquid columns of the two water tanks. Aeration, sulfur removal, and iron removal are performed using an aeration device. The electric heating device within tank B heats the formation water to the optimal temperature required for liquid preparation. Finally, the formation water from tank B is filtered through a parallel water quality filtration device. Only when the water quality meets the standards can it enter the next liquid preparation stage.

[0043] The sedimentation water tank A and the water storage tank B are both subjected to internal rust removal and anti-corrosion paint application operations before commissioning in accordance with the "Technical Standards for Internal Anti-corrosion Layers of Liquid Coatings for Steel Storage Tanks" to avoid water source pollution. At the same time, both tanks are equipped with temperature-adjustable electric heaters to heat the liquid water, and liquid level gauges are installed on the outside of the tanks for easy measurement.

[0044] The aeration device connects the settling water tank A and the water storage tank B via a three-way interface to effectively remove sulfur and iron from the water inside the water tanks. The rear end of the outlet of the water storage tank B is connected to a corrosion-resistant and heat-insulated (Φ73mm×3.51mm) oil pipe to the liquid distribution tank. Two liquid distribution water filtration devices, one for backup and one for use, are connected between the water storage tank B and the liquid distribution tank. Its process features a "secondary natural sedimentation + aeration for iron and sulfur removal + primary filtration + full-process corrosion and heat preservation" treatment process, enabling "on-site water extraction, on-site sedimentation, and on-site aeration" operations for liquid distribution water. By pumping formation water locally from abandoned wells, the cost of conventional chemical flooding liquid distribution water is saved, solving the problem of difficult and expensive water supply for surface injection systems. First, it saves the cost of water for liquid preparation and laying surface pipelines, and reduces the viscosity loss rate of polymers along the process caused by long surface pipelines. For small-scale chemical flooding construction without a surface injection system, water for liquid preparation must be transported by tank trucks or laid through surface pipelines, resulting in high investment costs. By perforating the abandoned oil wells or inefficient oil wells closest to the injection well to open the water layer above or below, the water for liquid preparation can be obtained locally using pumping units. Compared with conventional chemical flooding, there is no need to lay surface pipelines for water from water source wells, saving the cost of conventional chemical flooding water preparation and surface pipeline laying, and solving the problem of large viscosity loss of polymers along the process caused by long conventional surface pipelines. Secondly, the cost is reduced by eliminating the transfer process between the two water tanks. The water source well uses a pump to draw formation water and pump it directly into two elevated water tanks on the ground (one water tank is mainly used for sedimentation, and the other water tank is mainly used for water storage, and sedimentation occurs in both water tanks). By utilizing the liquid column pressure difference generated by the difference in liquid level height between the inlet and outlet of the two elevated water tanks, there is no need for a matching transfer pump for transportation between the two water tanks (the water source well is pumped into the first sedimentation tank A by the pump, with low inlet and high outlet; the first sedimentation tank A and the second water storage tank B use the liquid column pressure difference generated by the high inlet and low outlet liquid level to transport the distribution water). Compared with the conventional chemical flooding surface water system, the transfer process of the transfer pump is reduced, and power consumption and costs are saved. Third, simplified aeration equipment and filtration devices reduce costs compared to conventional chemical flooding. Both water tanks are connected to the aerator, enabling flexible, uninterrupted aeration of either settling tank A or storage tank B via a tee. The aeration time schedule is tailored to chemical flooding water quality requirements for iron, sulfur, and oxygen (the oxygen content in the water must be no more than 1 mg / L). Two filters with an internal diameter of 0.8 mm are installed in parallel between the outlet of storage tank B and the flooding tank, providing a backup and uninterrupted supply of filtered water during filter replacement or equipment maintenance. After settling, aeration, and filtration, the water from storage tank B meets the required flooding quality. This reduces costs compared to conventional chemical flooding systems using desulfurization towers, aeration devices, and filtration equipment. Fourth, chemical flooding meets the requirements for chemical preparation, ensuring the smooth progress of chemical flooding operations in extremely cold weather.The two water tanks are equipped with electric heating devices with adjustable temperature within the range of 30 to 80°C. The temperature of the heated water can be adjusted to the optimal dissolution temperature required for surfactant preparation, which can accelerate the dissolution rate of surfactants and polymers, meet the requirements of chemical agent preparation, and improve the preparation efficiency and quality. At the same time, it can solve the problems of conventional chemical flooding ground processes such as surfactant solidification due to low temperature and difficulty in preparation due to severe winter climate (minus 20 to 30°C), freezing or temperature drop, and the viscosity of the prepared polymer aqueous solution increases as the temperature drops, which makes the ground pumping equipment operate at high power, making chemical flooding construction difficult and posing safety hazards.

[0045] The liquid preparation process primarily utilizes the following equipment: a liquid preparation unit capable of dispersing and dissolving the polymer while simultaneously mixing it with a surfactant, and a maturation unit. The process is characterized by the ability to utilize a single unit to meet the requirements of both chemical flooding and profile control liquid preparation, saving investment in injection equipment for the supporting processes. The liquid preparation unit consists of a dedicated jet pump, a liquid preparation tank, two agitators, two motors, and pipelines. Water from the incoming water process flows through the negative pressure generated by the dedicated jet pump, along with the required chemicals, into the liquid preparation unit for agitation and preparation. The water then enters the maturation unit for maturation for at least one hour.

[0046] The chemical agent can be directly put into the liquid preparation tank by manual loading to stir and mix surfactants, polymers and different types of profile control agents (granular profile control agents, gel profile control agents, etc.) in any combination. Conventional chemical ground liquid preparation equipment can only prepare surfactants or polymers, and cannot be prepared together with profile control agents.

[0047] The liquid preparation device in the present invention can realize the preparation of any combination of profile control agents, chemical flooding agents, and profile control + chemical flooding agents, without the need to replace equipment or carry out ground modifications to increase ground investment costs. First, it can realize on-site liquid preparation and on-site injection. During the chemical flooding process, the profile control process measures can be implemented at any time, and the connection time of different process measures can be shortened, which greatly saves the equipment investment cost and improves the operation efficiency of the measures. Second, it simplifies the mixing process flow of polymers and surfactants, saves costs and improves the mixing quality. When conventional chemical flooding polymers are mixed with surfactants, a static mixer needs to be used to dissolve the two. The liquid preparation device of the present invention directly drives two stirring blades with two motors in the liquid preparation tank to fully mix and dissolve the polymer and surfactant at an adjustable speed, thereby saving costs and improving the mixing quality. Third, the liquid preparation quality is improved by improving the inlet and outlet pipelines of the liquid preparation device and optimizing the liquid preparation method. The liquid dispensing device of the present invention has made additional modifications to the inlet and outlet pipelines of the liquid dispensing tank on the basis of the conventional dispersing and dissolving device, that is, between the water storage tank B and the liquid dispensing tank, an inlet pipeline is transformed into two parallel injection pipelines, one pipeline directly enters the liquid dispensing device through a surface pump, and the delivered liquid dispensing water is used to prepare polymers, surfactants, etc., and the other pipeline enters the liquid dispensing tank as a reflux pipeline, and the system just prepared in the liquid dispensing tank is circulated and refluxed as needed by the surface pump according to the actual liquid dispensing quality. The purpose is to solve the problem of insufficient dissolution caused by the inability of the stirring blades to fully reach the edges and bottoms of the liquid dispensing device, improve the liquid dispensing uniformity of chemical flooding, and reduce system waste. In addition, during conventional operation, the matured high-concentration polymer mother liquor and injection water are mixed in the pipeline to form a low-concentration polymer solution and then injected into each oil well. In actual operation, the polymer mother liquor and injection water are often mixed unevenly, and a local high-concentration polymer solution (similar to a colloid) will be generated in the pipeline and directly injected into the formation, causing stagnation and blockage in the blasthole and near-well area. The injection process of the present invention is to prepare the liquid directly according to the required concentration requirements, realizing immediate injection after preparation. There is no step of mixing the polymer mother liquid with water, which reduces the unevenness of the liquid mixing and further improves the liquid quality of the chemical flooding agent.

[0048] The injection process primarily utilizes the following equipment: a chemical filtration device connected after the maturation tank, a remote flow meter, an injection pump, and ground-based corrosion-resistant and insulated pipelines. This injection process offers the following advantages: First, it reduces equipment failure rates, enables continuous and uninterrupted injection, and ensures efficient injection. The composite system in the maturation tank passes through a backup filtration device, which then filters through two parallel 3mm internal filter screens. (Unlike water filtration devices, the filter screens have a precision difference. For polymer solutions with viscosities of 50-100 mPa·s, screens with diameters below 3mm are prone to low polymer throughput and localized blockage, resulting in high pressure and pipeline perforation. Screens with diameters above 3mm have poor filtration of impurities and polymer colloids, leading to clumps entering the formation and causing blockage.) This backup and backup feature ensures impurity-free injection of the composite system and prevents pipeline blockage caused by clumps resulting from incomplete polymer dissolution. This reduces equipment failure rates and enables continuous and uninterrupted chemical flooding injection. Secondly, a pre-placed flowmeter is used to reduce polymer viscosity loss, and the use of old oil pipes saves on the investment cost of chemical flooding surface pipelines. The composite system after the filter is connected to the injection pump through a surface anti-corrosion and insulation pipeline. Conventional chemical flooding processes install the flowmeter after the injection pump, while the present invention installs the flowmeter before the injection pump. The pre-placed flowmeter reduces the polymer viscosity loss caused by high pressure. Whenever a polymer system passes through a flowmeter, it will inevitably cause system viscosity loss due to the reduction in the flowmeter's cross-sectional area. Compared with low pressure, the viscosity loss rate is greater at high pressure. Therefore, the remote flowmeter in the present invention is installed at the low-pressure end after the filter and before the injection pump. Compared with the high-pressure end after the conventional chemical flooding flowmeter is installed, this can reduce the polymer viscosity loss caused by high-pressure throttling (reducing the viscosity loss rate by 12-15%), improving the quality of the liquid preparation while saving the amount of chemical flooding agent.

[0049] Furthermore, all the ground injection pipelines (ground anti-corrosion and insulation pipelines) used in the present invention are lined anti-corrosion oil pipes that have been replaced after being discarded in old oil fields. The anti-corrosion pipelines can avoid the viscosity loss of polymers caused by factors such as rust and bacteria inside the pipelines. Reusing old oil pipes saves the investment cost of chemical drive ground pipelines.

[0050] The monitoring process mainly includes four aspects: dosing water quality monitoring, dosing quality monitoring, dosing operation standard monitoring, and output fluid monitoring. First, the dosing water quality and dosing quality of the injection end are monitored. If significant viscosity loss is found, it is necessary to conduct a viscosity loss investigation and cause analysis at each node. Second, the dosing process is monitored to standardize the dosing requirements and standards for construction personnel. Finally, based on the principle of "improving dosing quality, facilitating management, and achieving efficient and high-quality injection," comprehensive management is achieved through full-process monitoring, including system and water quality indicator monitoring, construction personnel operating standards, process calibration, and cleaning of surface dosing equipment. By investigating viscosity loss at each node of the dosing system, analyzing its causes, and comprehensively managing the entire process, a monitoring system for operational specifications for each link in the mine application of composite flooding technology has been developed, and a viscosity loss analysis and management process for the entire mine application process has been established, effectively reducing viscosity loss and improving dosing quality.

[0051] In summary, the entire surface supporting injection equipment is based on the principles of simplicity, low cost, and efficient implementation, realizing the surface injection process flow of "on-site water extraction, on-site sedimentation, on-site liquid preparation, and on-site injection" for chemical flooding surface well sites. To address the problem of large investment in surface gathering and transportation for small-scale units, the present invention can significantly shorten the surface construction period and thus reduce investment costs by utilizing reused equipment, simplifying processes, and sharing a set of equipment and monitoring processes with profile adjustment and composite flooding. This solves the problem of large polymer viscosity loss along the way caused by long surface pipelines. Compared with conventional chemical flooding surface processes, the chemical flooding surface injection process of the present invention can achieve low-cost and efficient implementation for chemical flooding of small blocks without a surface injection system, significantly reducing costs and achieving beneficial development.

[0052] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0053] Example

[0054] In this embodiment, the chemical flooding surface injection method is used to take Block A as an example. Block A has a small area and a small reserve scale (geological reserves are only 670,000 tons and the oil-bearing area is 0.63 km). 2), for the development of strong edge water of natural energy, high water content production in the later stage of development, the unit enters the high water content stage at low recovery rate (recovery rate of 14.1%, water content of 96%), in order to further increase production capacity, the development mode is converted to chemical drive, but the current status of surface gathering and transportation in Block A is that there is no supporting surface injection system, and the water for liquid preparation must be transported by tank trucks. Because the block is located in a remote area and the transportation cost is high, the investment cost of surface gathering and transportation for chemical drive is high. For blocks with small reserves and small room for oil production, if conventional ground station-based supporting equipment with high investment cost is adopted, the input-output ratio is low, which increases the difficulty of efficient development. In order to carry out low-cost chemical drive and realize increased production and efficiency in Block A, a low-cost and simplified ground injection process was studied. By reusing old products and optimizing process flow, the ground investment cost of chemical drive was greatly reduced, the ground construction period was shortened, and the efficient development of Block A was achieved. The main process (the corresponding device schematic diagram is as follows) Figure 2 As shown) are as follows:

[0055] ① Water process flow

[0056] First, the abandoned oil well C2-01, which is closest to the injection well C2-04 (80m from the wellhead) and in the same well field, is used as the water source well. The water layer above the oil layer of well C2-01 at a depth of 250m is opened by perforation, and the formation water is extracted by a pumping unit (the formation water needs to meet the following conditions: the total mineralization is not higher than 20,000mg / L, that is, the total amount of calcium and magnesium ions is ≤2000mg / L, and the chloride ion is ≤18,000mg / L). The C2-04 injection well is used for liquid water supply. The formation water supply capacity reaches 100 cubic meters per day. The injection displacement of the injection well C2-04 is 30 to 60 cubic meters per day. The water supply capacity can meet the needs of the on-site injection well. Secondly, the wellhead of the water source well C2-01 is connected to the oil field abandoned anti-corrosion lined oil pipe with a size of Φ73mm×3.51mm to the two reused oil pulling elevated tanks, one as sedimentation tank A and the other as water storage tank B, with a capacity of 40m 3 Before commissioning, both water tanks underwent internal rust removal and anti-corrosion painting in accordance with the "Technical Standard for Internal Anti-Corrosion Coatings of Liquid Coatings for Steel Storage Tanks" to prevent water contamination. Both tanks were equipped with electric heaters with adjustable temperatures between 30 and 80°C to heat the water used for liquid distribution. Liquid level gauges were installed on the outside of the tanks for convenient metering. The outlet of Tank B was connected to the distribution tank via a corrosion-resistant and insulated Φ73mm x 3.51mm oil pipe. A backup and backup distribution water filtration device, equipped with a 0.8mm filter screen, was installed between Tank B and the distribution tank. An aeration system was connected to Tank A and Tank B via a three-way connection to effectively remove sulfur and iron from the water inside the tanks.

[0057] When removing sulfur and iron, the process parameters of aeration are as follows: if the suspended solid content in the sedimentation tank A is ≤30 mg / L and the dissolved oxygen content is ≤1 mg / L, the process parameters of aeration are continuous aeration for 2 hours / day, and the frequency of impurity cleaning in the sedimentation tank A is 1 time / month; if the suspended solid content in the water storage tank B is ≤30 mg / L, the dissolved oxygen content is ≤1 mg / L, the total iron content is ≤0.2 mg / L, the sulfur content is ≤0.1 mg / L, and the concentration of sulfate-reducing bacteria is <2.5 cells / mL, the process parameters of aeration are once in the morning and once in the evening, each time for continuous aeration for 2 hours, and the frequency of impurity cleaning in the water storage tank B is 1 time / month. If the aeration process parameters of water tank B cannot meet the water quality requirements: adjust the aeration process parameters of sedimentation tank A to: once in the morning and once in the evening, each time for 2 hours of continuous aeration / day, and the frequency of impurity cleaning in sedimentation tank A is 2 times / month; adjust the aeration process parameters of water tank B to: aeration process parameters are 1 time / 4 hours, each time for 2 hours of continuous aeration, and the frequency of impurity cleaning in water tank B is 1 time / month, and add fungicide at the same time. You can also adjust the corresponding process parameters as needed until the water quality and sulfate-reducing bacteria parameters of water tank B meet the standards.

[0058] Sedimentation tank A is used to remove large particles in formation water. The suspended solids concentration of formation water flowing out of sedimentation tank A is ≤30mg / L. The purpose of removing large particles by sedimentation tank A is as follows: Suspended solids may contain colloids, which often contain Fe 2+ , S 2- Therefore, in order to avoid the influence of these ions on the viscosity of the polymer solution, the suspended solid content in the water should be controlled. The liquid water filtration device between the water storage tank B and the liquid distribution tank is used to remove solid particles in the liquid distribution water. The solid suspended matter concentration of the formation water flowing out of the liquid distribution water filtration device is ≤30mg / L. The purpose of removing solid particles in the liquid distribution water by the liquid distribution water filtration device is to remove mechanical impurities, FeS, Fe2O3 and other Fe2O3 that may exist at the bottom of the water storage tank B after exposure to oxygen. 2+ , S 2- Precipitation produced by oxidation reactions, etc.

[0059] In this embodiment, the treated water obtained after the formation water passes through the settling tank A, the water storage tank B, and the filtration device must meet the following conditions: total iron content ≤ 0.2 mg / L, sulfur content ≤ 0.1 mg / L, and sulfate-reducing bacteria concentration < 2.5 cells / mL (when the sulfate-reducing bacteria concentration in the water is too high, 80-100 ppm of cationic fungicide is added to the water storage tank B to ensure that the sulfate-reducing bacteria concentration meets the standard). The total iron content and sulfur content are tested according to the provisions of the standard Q / SH3135 "Test Method for Suspended Solids in Oilfield Wastewater", and the sulfate-reducing bacteria concentration is tested according to the provisions of the standard SY / T 5329-2012 "Water Quality Indicators and Analysis Methods for Injection Water in Clastic Reservoirs".

[0060] Furthermore, the water in Tank B needs to be heated to above 40°C to fully dissolve the surfactant in Block A (the temperature must be above 38°C; surfactants are difficult to dissolve below 35°C). Block A is located in a remote area with cold winters, so maintaining the water temperature above 40°C ensures that the prepared polymer solution will not thicken or increase in viscosity when temperatures reach -20 to 30°C, which could cause high power consumption or blockage of surface pumping equipment, leading to construction difficulties.

[0061] ②Liquid preparation process

[0062] The treated water (liquid preparation water) provided by the water process in step ① enters the liquid preparation device (20m 3 ), two spiral stirring blades (speed 50-60 rpm) driven by two 15kW motors on the liquid dispensing device are used to stir the surfactant required for block A added to the liquid dispensing tank by manual feeding together with the liquid dispensing water in the liquid dispensing tank to prepare a surfactant aqueous solution; then the liquid dispensing water is passed through a ground pump (jet pump) to generate a negative pressure of 1-2MPa and enter the jet tube. The solid polymer powder on the jet pump is sucked into the jet tube and quickly mixed with the liquid dispensing water in the jet tube to form a dispersion that enters the liquid dispensing tank and is stirred and mixed with the prepared surfactant aqueous solution to form a composite system. Finally, the configured composite system enters the aging device (40m 3 ) and mature for more than 1 hour.

[0063] In this embodiment, the inlet and outlet pipelines of the liquid preparation tank are additionally modified. That is, between the water storage tank B and the liquid preparation tank, the inlet pipeline is modified into two parallel injection pipelines. One pipeline directly enters the liquid preparation device through a surface pump, and the delivered liquid preparation water is used to dissolve polymers, surfactants, etc. The other pipeline is connected to the liquid preparation tank as a return pipeline ( Figure 2The system just prepared in the liquid preparation tank is circulated and refluxed as needed using a surface pump according to the actual liquid preparation quality. The purpose is to solve the problem of insufficient dissolution caused by the inability of the stirring blades to fully reach the sides and bottom of the liquid preparation device, improve the liquid preparation uniformity of chemical flooding, and reduce system waste. The reflux line is only used in special circumstances. That is, if the quality of the liquid preparation meets the standards, there is no need to open the ground pump for reflux. Only when the viscosity of the polymer inside the liquid preparation tank is uneven, the ground pump connected between the filter device and the liquid preparation tank is opened. This ground pump and the liquid preparation tank are connected to two pipelines at the same time, one is the liquid preparation pipeline, and the other is the reflux line (the reflux line is a surrounding reflux line system formed inside the liquid preparation tank, close to the edge of the tank). When the polymer is uneven, the liquid preparation pipeline gate is closed, the reflux pipeline gate is opened, and the ground pump is turned on. At this time, the liquid preparation sent by the ground pump enters the liquid preparation tank through the reflux pipeline and circulates in a wireless closed loop in the circulation pipeline inside the liquid preparation tank. The purpose is to fully stir the polymer that is unevenly stirred at the edge again. In specific implementation, samples are taken from the liquid preparation tank body, and samples are taken from the upper, middle, lower and edge of the tank body respectively to test the viscosity. If there is a viscosity difference of ≥12%, the circulation reflux needs to be turned on.

[0064] In this embodiment, in order to prevent the polymer from being degraded and causing the viscosity of the polymer to decrease, according to the test results, when the concentration of sulfate-reducing bacteria in the water is too high, 80-100 ppm of cationic bactericide is added to the water storage tank B to ensure that the aging device (40m 3 The concentration of sulfate-reducing bacteria in the composite system met the standard (<25 cells / mL). The composite system is a polymer solution with a certain viscosity. Directly adding the fungicide cannot fully dissolve it, resulting in a high concentration of the fungicide locally, which cannot evenly spread to the sulfate-reducing bacteria in other parts.

[0065] ③Injection process

[0066] In step ②, the material in the maturation tank is filtered by a filter device (two sets of 3mm filter screens are installed in parallel inside) to obtain a material without fish eyes and lumps. The filtered material is then accurately measured by a remote flow meter and then injected into the tank using a high-pressure pump (0-5m 3 / h adjustable, pressure-resistant 20MPa) is injected into the C2-04 wellhead.

[0067] In this embodiment, the flow meter is installed at the low-pressure end after the filter device and before the injection pump. Compared with the conventional chemical flooding flow meter installed at the high-pressure end after the pump, it can reduce the polymer viscosity loss caused by high-pressure throttling (the viscosity loss rate is reduced by 12% to 15%).

[0068] During the implementation of this embodiment, the entire process is monitored, including four aspects: liquid preparation water quality monitoring, liquid preparation quality monitoring, process parameter monitoring, and output liquid monitoring. Based on the principle of "improving liquid preparation quality, facilitating management, and efficient and high-quality injection", through the investigation of sticky damage at each node of the injection system, analysis of the causes, and comprehensive management of the entire process, the injection end liquid preparation process operation standards and the production end output liquid monitoring system were formulated, and a full-process sticky damage analysis and management process for mine application was established (see Figure 3 ), the quality of the prepared liquid has been effectively improved, and the viscosity loss has been effectively reduced. A monitoring system for the operation specifications of each link in the field application of the composite flooding technology has been established (see Table 1). The preparation temperature in Table 1 refers to the material temperature inside the preparation tank; the sampling temperature refers to the temperature at which the prepared sample is taken out and placed in a water bath to be heated to the end point, that is, 42°C (because the formation temperature of the reservoir is 42°C). The purpose is to monitor the viscosity value of the system at the formation temperature (polymer viscosity varies at different temperatures). Therefore, the sampling temperature is higher than the preparation temperature. The preparation viscosity and wellhead viscosity in Table 1 are both viscosities at simulated formation temperature (viscosity when placed in a water bath and heated to 42°C at the formation temperature). During specific implementation, the surface pipeline is insulated and anti-corrosion. At the same time, to avoid mechanical shear, plunger pumps are used, and pipe right-angle bends are reduced (the more right-angle bends, the greater the shear on the polymer). Measures such as reducing mechanical shear on polymer molecules are used to reduce mechanical shear. At the same time, a polymer viscosity sampler is installed at the wellhead to sample and monitor the viscosity of the polymer entering the well at any time. The viscosity reduction rate of the liquid system in Table 1 represents a ratio of the viscosity of the heavy oil after reduction to the viscosity before reduction of less than 10%, which is a quantitative indicator of the surfactant's ability to reduce the viscosity of the heavy oil. In Table 1, the polymer mixing time is between 120 and 150 minutes. Too long or too short a time will result in a decrease in polymer viscosity. A time of less than 120 minutes will result in uneven polymer mixing and the formation of lumps. A time of more than 150 minutes will cause excessive shearing time due to mechanical stirring, leading to the breakage of some polymer chains and a decrease in polymer viscosity.

[0069] In addition, comprehensive measures to control viscosity loss in the entire process were implemented, and the viscosity of the well fluid used in the actual field was ≥50mPa.s

[0070] Table 1A Oilfield Composite Flooding Field Application Operation Specification Monitoring System for Each Link

[0071]

[0072]

[0073] like Figure 3As shown, by controlling the ferrous ion content and sulfate-reducing bacteria concentration in the mixing water, reducing the sulfate-reducing bacteria concentration in the material in the maturation tank by adding a bactericide, detecting the material in the mixing tank for fisheyes and lumps and removing them using a filter, reducing the number of elbows between the high-pressure injection pump and the C2-04 wellhead, and adjusting the high-pressure injection pump efficiency to 50% to 70%, viscosity loss can be effectively reduced, achieving the goal of controlling viscosity loss. Experimental results show that when other conditions are the same, when the injection pump efficiency is 40%, the polymer viscosity loss is 11.5%; when the injection pump efficiency is 50%, the polymer viscosity loss is 8%; when the injection pump efficiency is 60%, the polymer viscosity loss is 6.5%; when the injection pump efficiency is 70%, the polymer viscosity loss is 5%; when the injection pump efficiency is 80%, the polymer viscosity loss is 3.2%.

[0074] In addition, after analysis, it was found that the foam generated during the surfactant mixing process, the uniformity of the polymer liquid preparation and the continuity of the stirring time will affect the liquid preparation quality. In order to improve the liquid preparation quality, the foam generated during the surfactant mixing process is controlled by the following methods: First, the stirring time of the surfactant and water is controlled to 20 to 30 minutes, and it should not exceed 30 minutes to avoid too long time and increased foam; second, when a large amount of foam is generated during the stirring process, the speed is reduced from 50 to 60 rpm to 40 to 50 rpm to slow down the generation of a large amount of foam during the stirring process. After the foam is reduced, the speed is adjusted to 50 to 60 rpm; third, after the surfactant aqueous solution is prepared, it is allowed to stand for at least 1 hour to fully defoam or a small amount of defoaming agent is added for defoaming. After defoaming, it is mixed with the polymer aqueous dispersion flowing out of the jet tube. The following methods are used to improve the uniformity of polymer preparation: First, ensure that the surfactant aqueous solution does not have too much foam, otherwise the polymer will remain on the foam surface, causing polymer powder to clump together and affect the polymer viscosity; second, ensure the continuity of the stirring time. Stirring cannot be stopped during the stirring process to ensure the continuity of stirring. At the same time, stirring time that is too long or too short will affect the uniformity of the preparation. The stirring time is controlled at 120 to 150 minutes.

[0075] After the implementation of composite flooding in the C2-04 well group in Block A, the causes of surface viscosity loss were investigated, analyzed and comprehensively managed, and the surface viscosity loss rate was controlled from about 30% to within 5%, saving 80,000 yuan in chemical agent costs.

[0076] The chemical flooding surface injection method of the present invention significantly shortens the surface construction period (7-10 days, investment of approximately 1 million yuan) by reusing old equipment, streamlining the process, and sharing the same equipment with the combined flooding process. This method saves 2.48 million yuan in pipeline and pipeline costs, and reduces losses and investment costs by 6 million yuan, for a total savings of 8.56 million yuan. Compared with conventional chemical flooding surface processes (200-300 days, investment of approximately 8 million yuan), the simplified surface injection process achieved superior results and benefits in the combined flooding test well C2-04 in Block A, increasing oil production by 2,600 tons and achieving an output-to-input ratio of 3.1, achieving profitable development (see Table 2). The simplified surface injection process of the present invention can be implemented cost-effectively for small-scale pilot test wells.

[0077] Table 2 Statistics of the application effect and benefits of composite flooding in C2-04 well group of A oilfield

[0078] Phased oil increase (tons) 2600 Oil production plant crude oil sales price (yuan / ton) 3142 Crude oil sales revenue (10,000 yuan) 817 Output-input ratio 3.1 Tons of oil-enhancing agent 59 Investment per ton of oil (yuan) 1020 Stage benefit (10,000 yuan) 552

[0079] The chemical flooding surface injection device of this embodiment is as follows Figure 2 As shown, it includes a sedimentation water tank A, a water storage tank B, an aerator, a liquid water filtration device, a surface pump, a jet pump, a liquid distribution tank, a maturation tank, a chemical flooding filtration device, a flow meter and an injection pump, wherein the outlet of the sedimentation water tank A is connected to the inlet of the water storage tank B, the height of the sedimentation water tank A is greater than the height of the water storage tank B to ensure that the water in the sedimentation water tank A can flow into the water storage tank B by gravity, the sedimentation water tank A and the water storage tank B are respectively connected to the aerator, the outlet of the water storage tank B is connected to the inlet of the liquid water filtration device, and the liquid water filtration device is connected to the inlet of the liquid water filtration device. The outlet of the device is connected to the inlet of the surface pump and the inlet of the jet pump through the liquid delivery pipeline respectively. The outlet of the surface pump and the outlet of the jet pump are connected to the inlet of the liquid distribution tank through the delivery pipeline respectively. The outlet of the liquid distribution tank is connected to the inlet of the maturation tank. The outlet of the maturation tank is connected to the inlet of the chemical drive filtration device. The outlet of the chemical drive filtration device is connected to the inlet of the injection pump. A flow meter is installed on the connecting pipeline between the chemical drive filtration device and the injection pump. The outlet of the injection pump is connected to the wellhead of the injection well C2-04 through the chemical drive delivery pipeline.

Claims

1. A chemical flooding surface injection method, characterized in that: The following steps are involved: The upper water layer of an abandoned oil well located near the oil well to be produced is perforated to obtain formation water. The formation water is then subjected to aeration treatment and solid-liquid separation in sequence to remove sulfide and ferrous ions in the formation water to obtain preparation water. The preparation water is then used to prepare a chemical flooding system, which is pumped to the well to be injected after throttling and metering. The total iron content of the preparation water is ≤0.2 mg / L, the sulfur content is ≤0.1 mg / L, and the concentration of sulfate-reducing bacteria is <2.5 cells / mL.

2. The chemical flooding surface injection method according to claim 1, characterized in that: The method of aeration treatment and solid-liquid separation is as follows: the formation water is settled twice or more under aeration conditions, and then the settled system is filtered.

3. The chemical flooding surface injection method according to claim 2, characterized in that: The mesh diameter of the filter used for filtration shall not exceed 0.8mm.

4. The chemical flooding surface injection method according to claim 2, characterized in that: The formation water is settled twice under oxygen exposure conditions, with the temperature of the first settling being 30-80°C and the temperature of the second settling being 40-80°C.

5. The chemical flooding surface injection method according to any one of claims 1 to 4, characterized in that: The method for preparing chemical flooding using liquid preparation water is as follows: the liquid preparation water, polymer and surfactant are mixed, matured and filtered to obtain a chemical flooding system.

6. The chemical flooding surface injection method according to claim 5, characterized in that: The polymer is type II or type III polyacrylamide, and the surfactant is an anionic water-soluble surfactant. When the chemical flooding system is prepared using the mixing water, the temperature of the mixing water is 38-80°C.

7. The chemical flooding surface injection method according to claim 5, characterized in that: The mixing time should be no less than 2 hours and the aging time should be no less than 1 hour.

8. The chemical flooding surface injection method according to claim 5, characterized in that: During the maturation process, the concentration of sulfate-reducing bacteria in the system is controlled to be less than 25 cells / mL; the mesh diameter of the filter used for filtration when using liquid water to prepare chemical flooding is not greater than 3mm.

9. The chemical flooding surface injection method according to any one of claims 1 to 4, characterized in that: The viscosity of the prepared chemical flooding is 60-90 mPa·s, and the pump efficiency of the pump used for pumping the chemical flooding is 50%-70%.

10. A chemical flooding surface injection device for implementing the chemical flooding surface injection method according to any one of claims 1 to 9, characterized in that: It includes a sedimentation device, a water storage device, a liquid water filtration device, a liquid distribution device, a maturation device, a chemical flooding filtration device and an injection pump connected in sequence; the inlet of the sedimentation device is connected to the water layer of an abandoned oil well near the oil well to be mined, and the outlet of the injection pump is connected to the wellhead of the oil well to be mined; the sedimentation device and the water storage device are respectively connected to an aeration device; a throttling metering device is provided on the connecting pipeline between the chemical flooding filtration device and the injection pump.

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