CN115058237B

CN115058237B - Low-toxicity gel foam system, preparation method thereof and online monitoring method thereof

Info

Publication number: CN115058237B
Application number: CN202210836593.XA
Authority: CN
Inventors: 赖南君; 赵俊; 张啸晨; 何尧铃
Original assignee: Southwest Petroleum University
Current assignee: Southwest Petroleum University
Priority date: 2022-07-15
Filing date: 2022-07-15
Publication date: 2023-03-10
Anticipated expiration: 2042-07-15
Also published as: CN115058237A

Abstract

The invention relates to a low-toxicity gel foam system, a preparation method thereof and an online monitoring method thereof; the low-toxicity gel foam system is formed by introducing gas phase into low-toxicity gel foam base liquid, and is characterized in that: the low-toxicity gel foam base solution is prepared from the following components in parts by mass: 0.2 to 0.3 portion of polymer; 0.015-0.025 parts of a crosslinking agent; 0.2-0.3 part of foaming agent; 0.04-0.06 part of deoxidant; 0.015-0.025 parts of retarder; water; the total amount of the raw materials is 100 parts; the foaming agent is alkyl glycoside (APG-10) or betaine foaming agent; the cross-linking agent is an aluminum citrate cross-linking agent. The invention provides a low-toxicity gel foam profile control agent suitable for strong heterogeneous strata, a low-toxicity gel foam system, a preparation method and an online monitoring method thereof, which can reflect the real fluidity control capability and seepage process of the gel foam system.

Description

Low-toxicity gel foam system, preparation method thereof and online monitoring method thereof

Technical Field

The invention belongs to the technical field of profile control and water shutoff in oilfield development, and particularly relates to a low-toxicity gel foam system, a preparation method thereof and an online monitoring method thereof.

Background

In field tests of oil fields, severe oil reservoir conditions cause single foam instability, and large-scale field application of foam flooding is severely restricted. In recent years, in order to overcome the defects of weak profile control and plugging capability and short validity period of a common foam system, a new method for profile control and water plugging by adopting gel to keep foam stable is proposed by scholars. The gel foam is formed by dissolving a polymer in a surfactant solution and adding a cross-linking agent and then foaming under the action of gas, wherein the polymer in a foam wall and the cross-linking agent are subjected to a cross-linking reaction to form a three-dimensional space network structure to form a framework of the foam. The gel foam deep regulation and control technology integrates the dual advantages of gel and foam, can block fractured large pore canals, prevent water channeling and adjust water absorption profiles, and is a good selective profile control agent suitable for strong heterogeneous strata.

The crosslinking agent used for the gel foam can be classified into an inorganic metal crosslinking system and an organic phenol-formaldehyde crosslinking system. However, phenolic resins and chromium ions used in the past are extremely toxic and are extremely harmful to the environment and workers, and their use in large quantities has been prohibited from sustainable strategies. In order to reduce the toxicity of phenol and formaldehyde, some researchers have replaced resorcinol and hexamethylenetetramine, which are less toxic. However, the toxicity of the crosslinking agent is still large, and the formaldehyde substitute hexamethylenetetramine is prohibited by relevant regulations on oil exploitation. Therefore, there are few low toxicity gels to choose from the class of organic cross-linking agents. There are many more choices of metal crosslinking agents than those, such as boron-based crosslinking agents, titanium-based crosslinking agents, and aluminum ion crosslinking agents, which have been studied by many scholars. As the boron-based crosslinking agent after gel breaking can generate a large amount of residues, storage cakes are easily formed on the surface of rock, and huge damage is caused to the stratum. The titanium-based crosslinking agent has the defects of high cost, poor crosslinking effect and the like, so that the large-scale use of the titanium-based crosslinking agent is severely limited. However, the aluminum ion crosslinking agent has the advantages of low toxicity, low cost, high gelling strength, controllable gelling time and the like, and is widely used for indoor research and mine tests.

With the continuous and deep understanding of the importance of environmental protection, the development of low-toxicity and even non-toxic gel foam systems becomes a hot spot and frontier for research. Therefore, aiming at the problems, the invention adopts aluminum citrate as a crosslinking system, and introduces betaine surfactant or alkyl glycoside (APG-10) as a green foaming agent to prepare the low-toxicity gel foam profile control agent suitable for strong heterogeneous strata and the preparation method thereof, and the invention provides an online monitoring method of a gel foam system, which can really establish the fluidity control capability and the seepage process of the gel foam system.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a low-toxicity gel foam system, a preparation method thereof and an online monitoring method thereof; the gel foam profile control agent overcomes a plurality of defects in the prior art, and is suitable for strong heterogeneous strata, and the preparation method thereof, thereby being beneficial to protecting the environment and ensuring the body health of constructors; and provides an on-line monitoring method of the gel foam system, which can really establish the fluidity control capability and the seepage process of the gel foam system.

The purpose of the invention is realized by the following technical scheme:

in a first aspect of the present invention, a low toxicity gel foam system is provided, wherein the low toxicity gel foam system is formed by introducing a gas phase into a low toxicity gel foam base liquid;

the low-toxicity gel foam base solution is prepared from the following components in parts by mass: 0.2 to 0.3 portion of polymer; 0.015-0.025 parts of a crosslinking agent; 0.2-0.3 part of foaming agent; 0.04-0.06 part of deoxidant; 0.015-0.025 parts of retarder; water;

the total amount of the raw materials is 100 parts;

the foaming agent is alkyl glycoside (APG-10) or betaine foaming agent; the cross-linking agent is an aluminum citrate cross-linking agent.

Further, the gas phase is N ₂ And the low-toxicity gel foam system has the foam quality of 60 percent.

The foam quality, also called the foam characteristic value, is the percentage of the gas volume of the foam to the total foam volume.

Further, the polymer is selected from at least one of partially Hydrolyzed Polyacrylamide (HPAM), water-soluble hydrophobic associated polyacrylamide (APP-4) and temperature resistant anionic polyacrylamide (KYPAM-6S).

Further, the betaine foaming agent is selected from at least one of lauramidopropyl betaine (LAB-35) and dodecyl betaine (BS-12).

In one embodiment of the present invention, the oxygen scavenger is thiourea.

Further, the retarder is selected from at least one of sodium lignosulphonate, sodium citrate and sodium tartrate.

The invention also provides a preparation method of the low-toxicity gel foam system, which comprises the following steps:

(1) Respectively adding a polymer, a cross-linking agent, a foaming agent, a deoxidant, a retarder and water into a penicillin bottle in sequence according to the mass parts of the components, and uniformly stirring to obtain a uniformly mixed solution;

(2) Placing the uniformly mixed solution in a constant-temperature oven, and aging to form gel to obtain low-toxicity gel foam base liquid;

(3) Will N ₂ And (3) introducing the low-toxicity gel foam base solution into a foam evaluation device, pumping the low-toxicity gel foam base solution into the foam evaluation device, heating the foam evaluation device to 70-90 ℃, and stirring for a certain time by using a stirrer to obtain a low-toxicity gel foam system.

Further, the temperature of the constant-temperature oven is 70-90 ℃, and the aging and gelling time is 24-48 h.

The invention also provides an on-line monitoring method of the gel foam system, which can be used for monitoring the real fluidity control capability and the seepage process of the gel foam system, and comprises the following steps:

step a, establishing a rock core model: adopting a serial core, setting the temperature of a simulated oil reservoir, then injecting simulated formation water into the serial core at the flow rate of 1mL/min until the tail end of the serial core discharges liquid and the displacement pressure reaches stability, recording a stable pressure value delta P1, and calculating the permeability of the core;

b, injecting nitrogen gel foam: after the simulated formation water displacement serial core is stabilized, simultaneously starting a gel foam base liquid injection pump and a high-pressure nitrogen valve, injecting a gel foam system into the core at the injection flow rate of 0.5mL/min with the foam mass of 60%, and respectively recording the pressure changes at the inlet end, 1/4, 1/2 and 3/4 positions of the serial core;

step c, establishing dynamic pressure change curve graphs at different displacement stages: taking the number of injected PV as an abscissa and the injection pressure as an ordinate, and drawing pressure change curves at the inlet end, 1/4, 1/2 and 3/4 positions of the serial core;

step d, drawing a resistance coefficient comparison histogram: and calculating the resistance coefficient values of different displacement stage points under different injected PV numbers, and drawing a resistance coefficient comparison histogram by taking the displacement stage as a horizontal coordinate and the resistance coefficient as a vertical coordinate.

After the dynamic pressure change curve chart and the resistance coefficient comparison histogram are obtained through the steps c and d, the initial pressure mutation position on the pressure change curve can be found out from the dynamic pressure change curve chart, the injection amount at the moment is PVa, the mutation position is the position where the gel foam is firstly monitored to be gelatinized, and the mutation position is shown on the pressure curve at the position of 3/4. Similarly, the gelling and migration conditions at 1/2 can be monitored by observing the dynamic pressure change curve at 1/2.

According to the scheme, a resistance coefficient comparison histogram is drawn, in the graph, the gel foam at an inlet can establish a stronger resistance coefficient along with the increase of the injection amount, but the resistance coefficient at the moment does not belong to a gel foam system, but is the resistance coefficient of the ungelatinized polymer foam; when the gel foam is injected to the 3/4 position, the gel foam is gelatinized at the moment, the pressure is gradually increased, and the resistance coefficient at the 3/4 position is gradually increased, which shows that the gel foam can establish a stronger resistance coefficient belonging to a gel foam system at the 3/4 position. Therefore, the fluidity control capability and the seepage process of a gel foam system can be truly reflected by combining a dynamic pressure change curve chart and a resistance coefficient comparison histogram.

Further, step e and step f are included before step c;

step e: after the injection pressure at the inlet end, 1/4, 1/2 and 3/4 positions is stable, taking a small amount of gel foam samples at the 1/4, 1/2 and 3/4 positions and the tail end of the serial core respectively;

step f: and e, quickly injecting the gel foam sample collected in the step e into a visual observation device provided with a 70 ℃ heating sleeve, arranging S-EYE software equipped with a microscope, shooting the gel foam in the visual observation device, and recording a gel foam microscopic image.

Coefficient of Resistance (RF): indicating the ability to reduce the fluidity ratio, RF was calculated by the ratio of the fluidity of water to the fluidity of the gel foam.

The invention provides a low-toxicity gel foam system, which is formed by introducing gas phase into low-toxicity gel foam base liquid;

the low-toxicity gel foam base solution is prepared from the following components in parts by mass: 0.2 to 0.3 portion of polymer; 0.015-0.025 parts of a crosslinking agent; 0.2-0.3 part of foaming agent; 0.04-0.06 part of deoxidant; 0.015-0.025 parts of retarder; water; the total amount of the raw materials is 100 parts;

the foaming agent is at least one of alkyl glycoside (APG-10), lauramidopropyl betaine (LAB-35) and dodecyl betaine (BS-12);

the cross-linking agent is an aluminum citrate cross-linking agent;

the gas phase is N ₂ And the low-toxicity gel foam system has the foam mass of 60 percent;

the polymer is selected from at least one of partially Hydrolyzed Polyacrylamide (HPAM), water-soluble hydrophobic associated polyacrylamide (APP-4) and temperature-resistant anionic polyacrylamide (KYPAM-6S); the oxygen scavenger is thiourea; the retarder is selected from at least one of sodium lignosulphonate, sodium citrate and sodium tartrate.

The invention provides a preparation method of a low-toxicity gel foam system, which comprises the following steps:

(A) Respectively adding a polymer, a cross-linking agent, a foaming agent, a deoxidant, a retarder and water into a penicillin bottle in sequence according to the mass parts of the components, and uniformly stirring to obtain a uniformly mixed solution;

(B) Placing the uniformly mixed solution in a constant-temperature oven, and aging to form gel to obtain low-toxicity gel foam base liquid;

(C) And (2) adopting a foam evaluation device, pumping nitrogen into the foam evaluation device by a liquid discharge method, pumping the low-toxicity gel foam base liquid into the foam evaluation device by using a liquid inlet pump, heating the foam evaluation device at the same time, heating the solution in the foam evaluation device to 70-90 ℃, starting a stirrer in the foam evaluation device, adjusting the rotating speed to 6000rpm, and controlling the stirring time for 2min to obtain the low-toxicity gel foam system.

Nitrogen gas can be introduced into the foam evaluation device by a liquid introduction and discharge method, so that the device is filled with the nitrogen gas.

The foam evaluation device, also called foam generating device (foaming device), is a main instrument for evaluating performances such as foaming capacity of solution, stability and size distribution of foam, and is common equipment in laboratories in the technical field of oilfield development. Foam under the condition of a bulk phase state is evaluated according to simulated formation conditions, and evaluation indexes comprise foaming volume, half-life period (foam volume half-life period, liquid separation half-life period) and the like. The structure of the foam evaluation device mainly comprises a foam generator, a heating module and a visual observation window. Foam generators typically employ a stirring device to cause the injected gas phase to mix well with the liquid phase, thereby generating foam; the heating module can be used for simulating the formation temperature, and the heating module usually utilizes a heating sleeve or a heating pipe and other structures for heating; the visual observation window is used for observing the foam volume and the foam form in the foam generator.

The invention provides an on-line monitoring method of a gel foam system, which can be used for monitoring the real fluidity control capability and the seepage process of the gel foam system, and comprises the following steps:

s1, establishing a rock core model: adopting a serial core, setting the temperature of a simulated oil reservoir to be 70 ℃, then injecting simulated formation water into the serial core at the flow rate of 1mL/min until the tail end of the serial core discharges liquid and the displacement pressure reaches stability, stopping injection, recording the stable pressure value delta P1, and calculating the permeability of the core;

step S2, injecting nitrogen gel foam: after the simulated formation water displacement serial core is stabilized, simultaneously starting a gel foam base liquid injection pump and a high-pressure nitrogen valve, injecting a gel foam system into the core at the injection flow rate of 0.5mL/min with the foam mass of 60%, and respectively recording the pressure changes at the inlet end, 1/4, 1/2 and 3/4 positions of the serial core;

s4, establishing a dynamic pressure change curve chart at different displacement stages: drawing pressure change curves at the inlet end, 1/4, 1/2 and 3/4 positions of the serial core by taking the number of injected PV as an abscissa and the injection pressure as an ordinate;

s5, drawing a resistance coefficient comparison histogram: and calculating the resistance coefficient values of different displacement stage points under different injected PV numbers, and drawing a resistance coefficient comparison histogram by taking the displacement stage as a horizontal coordinate and the resistance coefficient as a vertical coordinate.

Further, step S6 and step S7 are also included before step S4;

step S6: after the injection pressure at the inlet end, 1/4, 1/2 and 3/4 positions is stable, taking a small amount of gel foam samples at the 1/4, 1/2, 3/4 and the tail end of the serial core respectively;

step S7: and (4) quickly injecting the gel foam sample collected in the step (S6) into a visual observation device provided with a 70 ℃ heating jacket, arranging S-EYE software equipped with a microscope, shooting the gel foam in the visual observation device, and recording a gel foam microscopic image. The heating jacket is utilized to keep the heat of the visual observation device, so that the heat loss in the observation process is reduced, and the temperature of the gel foam is close to the simulated oil reservoir temperature when the gel foam is shot.

The invention also provides a device for on-line monitoring of a gel foam system, which comprises the following components:

the on-line monitoring device comprises a serial core, wherein the serial core is arranged in a high-temperature oven, the inlet end of the serial core is connected with a six-way valve through a first three-way valve, a first pressure monitoring device is arranged at the six-way valve and used for monitoring the pressure value P1 at the inlet end of the serial core, and a second three-way valve, a third three-way valve and a fourth three-way valve are respectively and correspondingly arranged at 1/4, 1/2 and 3/4 parts of the serial core; and the second pressure monitoring device, the third pressure monitoring device and the fourth pressure monitoring device are respectively arranged on the second three-way valve, the third three-way valve and the fourth three-way valve, so that the corresponding pressure values P2, P3 and P4 at 1/4, 1/2 and 3/4 of the serial core can be monitored in real time.

Furthermore, the other interfaces of the first three-way valve, the second three-way valve, the third three-way valve and the fourth three-way valve are sampling ports and are provided with sampling valves, so that the gel foam can be conveniently sampled and observed.

Further, the right end of the series core is communicated with a back-pressure valve, and the output end of the back-pressure valve is connected to a tail liquid collecting measuring cylinder.

The invention has the beneficial effects that:

(1) The invention adopts aluminum citrate as a crosslinking system, and introduces betaine surfactant or alkyl glycoside (APG-10) as a green foaming agent; the aluminum citrate crosslinking system and the betaine surfactant or alkyl glycoside (APG-10) have the advantage of low toxicity, so that a low-toxicity gel foam profile control agent can be prepared; in addition, the foam wall of the gel foam is a foam framework with a three-dimensional network structure formed by the cross-linking reaction of a polymer and a cross-linking agent, so that the gel foam has higher strength and stability compared with the common foam; the low-toxicity gel foam deep regulation and control technology integrates the dual advantages of gel and foam, can block fractured large pore canals, prevent water channeling and adjust water absorption profiles, and is a good selective profile control agent suitable for strong heterogeneous strata;

(2) The invention provides an on-line monitoring method of a gel foam system, which comprises the steps of establishing a rock core model, arranging a plurality of pressure monitoring points at different displacement stage points on the rock core model, drawing a dynamic pressure change curve graph and a resistance coefficient comparison histogram at different displacement stage points according to the monitoring conditions of different monitoring points, analyzing the gel formation and migration conditions according to the curve change condition of the dynamic pressure change curve graph, the pressure mutation position on the curve and the comparison condition of the resistance coefficients among different displacement stage points in the resistance coefficient comparison histogram under the same injected PV number, and meanwhile, the pressure change curve presents a zigzag curve to highlight the foaming, breaking, re-foaming and re-breaking states of gel foam, so that the scheme can realize on-line monitoring of the four states of foaming, breaking, migration and gelling of the gel foam, thereby really establishing the real fluidity control capability and seepage process of the gel foam system; the method makes up the defect that the resistance coefficient of the gel foam system cannot be established in the prior art, and can truly reflect the fluidity control capability of the gel foam system; and the scheme also provides a safe, real and simple research means for the deep research of the gel foam system.

Drawings

FIG. 1 is a representation of the ESEM of the gel foam wall prepared in example 1 of the present invention;

FIG. 2 is a graph of the performance of gel foams at different temperatures;

FIG. 3 is a graph of the performance of gel foams at different degrees of mineralization;

FIG. 4 is a graph of the performance of gel foams at different levels of saturation;

FIG. 5 is a microscopic decay behavior of a low toxicity gel foam system;

FIG. 6 is an on-line monitoring of a gel foam displacement device;

FIG. 7 is a graph of dynamic pressure changes at different displacement stages;

FIG. 8 is a resistance coefficient versus histogram;

FIG. 9 is a microscopic view of gel foam at different sampling points during core displacement;

FIG. 10 is a graph of profile control performance of low toxicity gel foam systems at different permeability steps;

FIG. 11 is a plot of the pressure change of a pressure point gel foam (conventional method);

wherein, 1, a high-temperature oven; 2. a second pressure monitoring device; 3. a third pressure monitoring device; 4. a fourth pressure monitoring device; 5. a first pressure monitoring device; 6. a six-way valve; 7. a first three-way valve; 8. connecting rock cores in series; 9. collecting a measuring cylinder for tail liquid; 10. a back pressure valve; 12. a second three-way valve; 13. a third three-way valve; 14. and a three-way valve IV.

Detailed Description

Example 1

The embodiment provides a low-toxicity gel foam system, wherein the system comprises 0.2% of polymer solution, 0.02% of cross-linking agent, 0.3% of foaming agent, 0.03% of oxygen scavenger, 0.02% of retarder and the balance of water by mass fraction;

the foaming agent is lauramide propyl betaine (LAB-35), the oxygen scavenger is thiourea, the retarder is sodium lignosulphonate, and the crosslinking agent is an aluminum citrate crosslinking agent.

The low-toxicity gel foam system is prepared by the following preparation method, which comprises the following steps:

the method comprises the following steps: firstly, 50mL of polymer solution with the concentration of 4000mg/L, 10mL of aluminum citrate cross-linking agent solution with the concentration of 2000mg/L, 15mL of foaming agent solution with the concentration of 20000mg/L, 10mL of oxygen scavenger solution with the concentration of 3000mg/L, 10mL of retarder solution with the concentration of 2000mg/L and a proper amount of experimental water are measured, and the total amount of the above substances is 100g;

step two: then, sequentially adding the polymer, the cross-linking agent, the foaming agent, the oxygen scavenger, the retarder and water into a penicillin bottle, and stirring at room temperature for 20min to obtain a low-toxicity gel foam base solution with the total mass of 100g;

step three: placing the prepared low-toxicity gel foam base liquid in a constant-temperature oven at 70 ℃, and aging to form gel for 24 hours;

step four: introducing nitrogen into the foam evaluation device in a liquid discharge method, and pumping all the gel foam base liquid into the foam evaluation device by using a liquid inlet pump; simultaneously, starting a heating module, and heating the solution in the evaluation device to 70 ℃; and starting a speed regulating switch of the stirrer, regulating the rotating speed to 6000rpm, and stirring for 2min to obtain the gel foam system.

Further, in this example, the aluminum citrate crosslinker is prepared by the following preparation steps: weighing 7.16g of aluminum chloride hexahydrate, weighing 3.12g of citric acid monohydrate (citric acid: aluminum chloride = 0.5; citric acid was added dropwise to the aluminum chloride solution with stirring and additional experimental water was added to 100mL (effective amount of aluminum 0.8%); reacting for 3 hours at 70 ℃; stopping heating, cooling to 50 ℃, and adjusting the pH value to 5-7 by using ammonia water; aging at room temperature for 8h, and diluting to effective content of aluminum of 0.2%.

The microscopic ESEM image of the gel foam system prepared by the scheme is shown in figure 1.

Example 2

The embodiment provides a low-toxicity gel foam system, which comprises 0.25 mass percent of polymer solution, 0.02 mass percent of cross-linking agent, 0.3 mass percent of foaming agent, 0.03 mass percent of oxygen scavenger, 0.02 mass percent of retarder and the balance of water;

the polymer is partially Hydrolyzed Polyacrylamide (HPAM), the foaming agent is alkyl glycoside (APG-10), the deoxidant is thiourea, the retarder is sodium citrate, and the crosslinking agent is an aluminum citrate crosslinking agent.

The low toxicity gel foam system of this example is prepared by the following preparation method, which comprises:

the method comprises the following steps: firstly, 50mL of partially Hydrolyzed Polyacrylamide (HPAM) solution with the concentration of 5000mg/L, 10mL of aluminum citrate cross-linking agent with the concentration of 2000mg/L, 15mL of alkyl glycoside (APG-10) solution with the concentration of 20000mg/L, 10mL of thiourea solution with the concentration of 3000mg/L, 10mL of sodium citrate solution with the concentration of 2000mg/L and a proper amount of experimental water are measured, and the total amount of the above substances is 100g;

step two: then, sequentially adding the HPAM solution, the aluminum citrate cross-linking agent, the APG-10 solution, the thiourea solution, the sodium citrate solution and water into a penicillin bottle, and stirring at room temperature for 20min to obtain a low-toxicity gel foam base solution with the total mass of 100g;

step three: placing the prepared low-toxicity gel foam base liquid in a constant-temperature oven at 80 ℃, and aging to form gel for 36 hours;

step four: introducing nitrogen into the foam evaluation device in a liquid discharge method, and pumping all the gel foam base liquid into the foam evaluation device by using a liquid inlet pump; simultaneously, starting a heating module, and heating the solution in the foam evaluation device to 80 ℃; and starting a speed regulating switch of the stirrer, regulating the rotating speed to 6000rpm, and stirring for 2min to obtain the gel foam system.

Example 3

A method of preparing a low toxicity gel foam system comprising the steps of:

the method comprises the following steps: measuring 50mL of polymer solution (APP-4, the concentration of which is 6000 mg/L), 10mL of aluminum citrate cross-linking agent solution with the concentration of 2000mg/L, 15mL of foaming agent solution (BS-12, the concentration of which is 20000 mg/L), 10mL of deoxidant solution (thiourea, the concentration of which is 3000 mg/L), 10mL of retarder solution (sodium tartrate, the concentration of which is 2000 mg/L) and a proper amount of experimental water, and enabling the total amount of the above substances to be 100g;

step two: sequentially adding a polymer, a cross-linking agent, a foaming agent, a deoxidant, a retarder and water into a penicillin bottle, and stirring at room temperature for 20min to obtain a low-toxicity gel foam base solution with the total mass of 100g;

step three: placing the prepared low-toxicity gel foam base liquid in a constant-temperature oven at 90 ℃, and aging to form gel for 48 hours;

step four: introducing nitrogen into the foam evaluation device in a liquid discharge method, and pumping all the gel foam base liquid into the foam evaluation device by using a liquid inlet pump; simultaneously, starting a heating module, and heating the solution in the foam evaluation device to 90 ℃; and starting a speed regulating switch of the stirrer, regulating the rotating speed to 6000rpm, and stirring for 2min to obtain the gel foam system.

Example 4

Fluidity control capability represents the ability of the foam to establish a drag coefficient and a residual assist coefficient in the formation; for conventional foam systems, the initial injection can establish a certain resistivity in the formation; for the gel foam system, after the gel foam is injected into a stratum, a well needs to be closed, aging is carried out, and gelling is carried out, after gelling, only the residual resistance coefficient of the gel foam can be measured, but no resistance coefficient can be measured, and thus the fluidity control capability and the seepage process of the gel foam system cannot be truly reflected. However, when the gel foam is injected into the formation, foaming, fracturing, migration and gelling occur simultaneously; this example therefore presents a method for on-line monitoring of four states of foaming, breaking, migration and gelling of gel foam, i.e. a method for on-line monitoring of a low toxicity gel foam system, which can be used to on-line monitor the true fluidity control capability and the percolation process of a low toxicity gel foam system of example 1.

A method for on-line monitoring of a low toxicity gel foam system for on-line example 1 of preparing a low toxicity gel foam system, the method comprising the steps of:

step a, establishing a rock core model: adopting a serial core, setting the length of the serial core to be 60cm, setting the simulated reservoir temperature to be 70 ℃, then injecting simulated formation water into the serial core at the flow rate of 1mL/min until the tail end of the serial core discharges liquid and the displacement pressure reaches stability, recording the stable pressure value delta P1 to be 0.02MPa, and calculating the permeability K1 of the core to be 1000mD;

step b, injecting nitrogen gel foam: after the simulated formation water displaces the serial core and is stabilized, simultaneously opening a gel foam base liquid injection pump and a high-pressure nitrogen valve, injecting the low-toxicity gel foam system prepared in the example 1 into the core at the injection flow rate of 0.5mL/min with the foam mass of 60%, and respectively recording the pressure changes at the inlet end, 1/4, 1/2 and 3/4 positions of the serial core;

step c, establishing dynamic pressure change curve graphs at different displacement stages: the pressure change curves at the inlet ends, 1/4, 1/2 and 3/4 of the serial cores are drawn by taking the injected PV number as an abscissa and the injection pressure as an ordinate, and as shown in fig. 7, the pressure changes at the inlet ends, 1/4, 1/2 and 3/4 of the serial cores correspond to the pressure curve at the inlet, the pressure curve at the 1/4, the pressure curve at the 1/2 and the pressure curve at the 3/4 of the serial cores in fig. 7 respectively;

Further, in this embodiment, step e and step f are further included before step c;

step f: and e, quickly injecting the gel foam sample collected in the step e into a visual observation device with a heating sleeve (70 ℃), setting S-EYE software equipped with a microscope, shooting the gel foam in the visual observation device, and recording to obtain a gel foam microscopic image figure 9.

In the embodiment, serial cores are adopted, gel foam is injected in a small flow mode, different pressure test points are arranged on a core model, and pressure changes at inlet ends, 1/4, 1/2 and 3/4 of the serial cores are respectively measured. And simultaneously, correspondingly setting different sampling points for observing the stable state and the migration condition of the gel foam. The example inspects the seepage behavior of the gel foam in the injection process, and the online monitoring means can more truly reflect the fluidity control capability and the plugging capability of the gel foam in different displacement stages in the stratum.

The drag coefficient (RF) represents the ability to reduce the fluidity ratio, which is calculated by the ratio of the fluidity of water to the fluidity of gel foam;

the formula of the resistance coefficient (RF) is shown in formula 1, wherein Q _w Injecting flow rate (mL/min), Q for water drive _f Injecting the flow rate (mL/min) for the foam flooding; delta P _w Is the relative stable pressure (MPa) and delta P of water drive _f Is a relatively stable pressure (MPa) in the foam flooding stage;

plugging capability: the plugging rate (S) can directly reflect the plugging capability of a gel foam system, and is one of important indexes for evaluating the performance of the gel foam system; s formula 2, where K ₁ ,K ₂ Respectively the permeability of the porous medium before and after injecting the plugging agent, mD;

the pressure curve of each pressure measuring point of gel foam injected into the serial core is shown in figure 7; the resistance coefficients of the gel foam established at different displacement stages can be calculated according to formula 1, and then a histogram of the resistance coefficient comparison is plotted as shown in fig. 8.

In FIG. 7, the inlet pressure gradually increased and stabilized, and the gel foam did not reach gel formation time; as can be seen from FIGS. 7 and 8, when the injection volume is greater than 11PV, the pressure at 3/4 gradually rises and appears as a sudden accelerated rise, indicating that the gel foam initially injected into the core and moving to 3/4 has gelled, resulting in a stronger plugging capacity, labeled here as PV number PVa.

At 18PV, the pressure at 1/2 rises gradually and appears as a sudden accelerated rise, indicating that the gel foam at 1/2 has gelled, and the PV number is labeled PVb here. When the gel foam establishes a larger resistance coefficient at the tail end of the rock core, the gel foam is difficult to inject, the pressure at the injection end is gradually increased, and the injection is stopped.

It can also be seen from FIG. 8 that at the moment of injection number 15PV, the drag coefficient at 1/4 > 1/2 < 3/4; indicating that 3/4 gel is formed before the time, and at the time when the injection number is 10PV, indicating that 3/4 gel is not formed obviously at the time when the resistance coefficient at 1/4 is more than that at 1/2 and the resistance coefficient at 3/4; thus, it was shown that the gel foam injected at the early stage was gelled at 3/4 of the point during the continuous injection from 10PV to 15PV, and it was further confirmed that the gel foam began to gel when the injection number PVa was 11 PV.

Because 1/4 of the position in the injection process is close to the inlet end, the influence of the injection pressure is large, and because the subsequent injection is difficult, the glue may not be formed at the 1/4 position when the injection is stopped, and therefore, a pressure mutation position with the sudden acceleration and rise of the pressure cannot be observed on the pressure change curve at the 1/4 position.

As shown in fig. 8, the gel foam at the inlet was able to establish a stronger drag coefficient with increasing injection amount, but the drag coefficient at this time did not belong to the gel foam system, but was the drag coefficient of the ungelled polymer foam; it can be seen from fig. 7 and 8 that, only when the gel foam is injected to 3/4 of the injection site and the pressure suddenly increases, the gel foam is already gelled at this time, and the pressure gradually increases, that is, when the injected PV number is PVa, the 3/4 site is the first monitored gelling position, and the resistance coefficient of the gel foam system at the 3/4 site gradually increases.

In addition, when the gel foam establishes a larger resistance coefficient at the tail end of the rock core and stops injecting the gel foam, the plugging rate of the gel foam at different displacement stages of the homogeneous rock core can be calculated according to the formula 2; as a result, as shown in Table 1, the plugging rates at the inlet end, 1/4, 1/2 and 3/4 were 99.56%, 99.37%, 98.78% and 99.36%, respectively, indicating that the gel foam performed effective plugging at 1/2 and 3/4.

Due to the shear thinning of the formation pores, conventional foam systems typically only establish a strong drag coefficient at the inlet and 1/4, and not at 1/2 and 3/4. The gel foam system can establish a strong resistance coefficient in the whole displacement stage, which shows that the gel foam has strong plugging capability, and simultaneously plays a role in deep profile control, and can prevent local water channeling of strong heterogeneous strata.

The microcosmic gel foams at different sampling points during core displacement are shown in fig. 9, the gel foams generated in the core are similar to the gel foams sheared in the foam evaluation device, the foam form at the initial moment is fine and smooth, and the size of the bubbles is small. As the gel foam moves to the deep part of the porous medium, the number of the bubbles is reduced, and the size is gradually increased. The foam is a non-Newtonian fluid and has shear thinning property, and due to the fact that the shear stress of the porous medium is strong, the rupture of bubbles is easily caused, the number of bubbles subjected to the shear action is greatly reduced, the viscosity of the foam fluid is reduced, and therefore the shear action of the porous medium is one of the reasons for influencing the blocking rate of the gel foam, which is also the reason that the conventional foam cannot establish strong resistance coefficients at 1/2 and 3/4. The gel foam system is different, and although the shearing dilution of the formation pores reduces the number of the gel foam bubbles, the size of the gel foam bubbles gradually increases. The method can monitor four states of foaming, breaking, migration and gelling of gel foam on line and establish real fluidity control capability and seepage process of a gel foam system by drawing a dynamic pressure change curve graph and a resistance coefficient comparison histogram and microcosmic observation of a gel foam sampling sample, and overcomes the current situation that the real resistance coefficient and the reaction fluidity control capability of the gel foam system cannot be established in the prior art.

TABLE 1 blocking rate of gel foam at different displacement stages of homogeneous core

Example 5

This example provides a device that can be used for on-line monitoring of gel foam systems, which can be used to implement the monitoring method of example 4:

as shown in fig. 6, the on-line monitoring device includes a serial core 8, the serial core 8 is disposed in a high-temperature oven 1, an inlet end of the serial core 8 is connected to a six-way valve 6 through a first three-way valve 7, a first pressure monitoring device 5 is disposed at the six-way valve 6 for monitoring a pressure value P1 at the inlet end of the serial core 8, and a second three-way valve 12, a third three-way valve 13, and a fourth three-way valve 14 are respectively and correspondingly disposed at 1/4, 1/2, and 3/4 positions of the serial core 8; and the second three-way valve 12, the third three-way valve 13 and the fourth three-way valve 14 are respectively provided with a second pressure monitoring device 2, a third pressure monitoring device 3 and a fourth pressure monitoring device 4 on interfaces so as to monitor pressure values P2, P3 and P4 corresponding to 1/4, 1/2 and 3/4 positions of the serial core 8.

Furthermore, the other interfaces of the first three-way valve 7, the second three-way valve 12, the third three-way valve 13 and the fourth three-way valve 14 are sampling ports and are provided with sampling valves so as to be convenient for sampling and observing the gel foam.

Further, the right end of the serial core 8 is communicated with a back pressure valve 10, and the output end of the back pressure valve 10 is connected to a tail liquid collecting measuring cylinder 9;

the specific operation steps when carrying out the monitoring experiment include:

step a, establishing a rock core model: adopting a 60cm long serial core 8, setting the temperature of a high-temperature oven 1 to be 70 ℃ to simulate the oil reservoir temperature, then injecting simulated formation water into the serial core 8 at a flow rate of 1mL/min until the tail end of the serial core 8 collects the effluent at a measuring cylinder 11, recording a stable pressure value delta P1, and calculating the permeability of the core;

b, injecting nitrogen gel foam: after the simulated formation water displaces the serial core 8 and is stabilized, simultaneously starting a gel foam base liquid injection pump and a high-pressure nitrogen valve, injecting the low-toxicity gel foam system prepared in the embodiment 1 into the serial core 8 from the six-way valve 6 at an injection flow rate of 0.5mL/min according to the foam quality of 60%, and respectively recording pressure changes at the inlet end, 1/4, 1/2 and 3/4 positions of the serial core 8, namely pressure changes of a pressure monitoring device I5, a pressure monitoring device II 2, a pressure monitoring device III 3 and a pressure monitoring device IV 4;

step c, establishing a dynamic pressure change curve chart at different displacement stages: taking the number of injected PV as an abscissa and the injection pressure as an ordinate, drawing pressure change curves at inlet ends, 1/4, 1/2 and 3/4 of the serial cores 8, as shown in fig. 7, i.e. P1, P2, P3 and P4 respectively correspond to the pressure curve at the inlet, the pressure curve at 1/4, the pressure curve at 1/2 and the pressure curve at 3/4 in fig. 7;

step d, drawing a resistance coefficient comparison histogram: and calculating the resistance coefficient values of different displacement stage points under different injected PV numbers, and drawing a resistance coefficient comparison histogram 8 by taking the displacement stage as a horizontal coordinate and the resistance coefficient as a vertical coordinate.

step e: after the injection pressure at the inlet end, 1/4, 1/2 and 3/4 positions is stable, respectively taking a small amount of gel foam samples at the 1/4, 1/2, 3/4 and outlet ends, namely at sampling valves at the positions of the second three-way valve 12, the third three-way valve 13 and the fourth three-way valve 14 and at the output end of the back pressure valve 10;

step f: and e, quickly injecting the gel foam sample collected in the step e into a visual observation device with a heating sleeve (70 ℃), setting S-EYE software equipped with a microscope, shooting the gel foam in the visual observation device, and recording to obtain a gel foam microscopic image as shown in figure 9.

Experimental example 1: foam performance of low toxicity gel foam systems

A. Temperature resistance

The foam performance of the gel foam at different temperatures is researched, the gel foam base solution prepared in example 1 is placed in a foam evaluation device, a heating module of the foam evaluation device is started, and the solution in the evaluation device is heated to 60 ℃, 70 ℃, 80 ℃, 90 ℃ and 100 ℃ respectively. After stirring for 2min at 6000rpm, the foam volume V and the foam half-life T of the gel foam at different temperatures were recorded _1/2 And half life of eluent t _1/2 . Repeating the evaluation experiment for each group of foams for 3 times, and averaging when there is no abnormal value。

Performance of gel foams at various temperatures As shown in FIG. 2, as the temperature is increased from 60 ℃ to 100 ℃, the foaming volume increases with increasing temperature, the foam half-life (T) _1/2 ) And half life of eluent (t) _1/2 ) It decreases with increasing temperature. It can be seen that the foaming effect of the gel foam system exhibits some high temperature acceleration, but high temperatures destroy the stability of the gel foam.

B. Salt tolerance

Exploring the foam performance of gel foam under different mineralization degrees, and setting the mineralization degrees of the foam base fluid to be 0 and 5 multiplied by 10 respectively ⁴ mg/L、10×10 ⁴ mg/L、15×10 ⁴ mg/L、20×10 ⁴ mg/L. The simulated formation water with different degrees of mineralization is respectively composed of NaCl and CaCl ₂ 、MgCl ₂ ·6H ₂ O, and the ion composition is shown in a table 2. Placing the gel foam base liquid prepared in example 1 in a foam evaluation device, starting a heating module, stirring at 6000rpm for 2min, and recording the foaming volume V and the foam half-life T of the gel foam at different temperatures _1/2 And half life of eluent t _1/2 . Each group of foam performance evaluation experiments were repeated 3 times, and the average value was taken when there was no abnormal value.

The influence of the degree of mineralization on the foaming volume and half-life of the gel foam is shown in the graph of fig. 3. With increasing salt content, the foaming volume decreases gradually, T _1/2 And t _1/2 Both show a tendency to increase first and then decrease. The rule that the influence of the mineralization on the gel foam is low-concentration promotion and high-concentration inhibition is shown.

TABLE 2 ion composition of simulated formation water of different degrees of mineralization

Degree of mineralization (10) ⁴ mg/L)	NaCl(g/L)	CaCl ₂ (g/L)	MgCl ₂ ·6H ₂ O(g/L)
				1	8.131	0.277	0.835
5	40.655	1.385	4.175
				10	81.31	2.77	8.35
15	121.965	4.155	12.525
				20	162.62	5.54	16.7

C. Oil resistance

Exploring the foam properties of the gel foam at different oil contents, the base solutions of the gel foam prepared according to example 1 were added with crude oils having oil contents of 0, 5%, 10%, 15%, 20%, 30%, respectively. And placing the sample in a foam evaluation device, and starting a heating module. After stirring at 6000rpm for 2min, the foaming volume of the gel foam at different temperatures was recordedV, foam half-life period T _1/2 And half life of eluent t _1/2 . Each set of foam performance evaluation experiments were repeated 3 times, and the average was taken when there was no abnormal value.

The gel foam properties at different oil saturations are shown in figure 4. The experimental result shows that the foam foaming volume is increased and then reduced along with the increase of the oil saturation; in the range of crude oil content less than 10%, there is a small increase in the foaming volume of the gel foam and is comparable to that in the oil-free case. With the increase of the oil saturation, the stability of the gel foam shows a trend of increasing and then decreasing, and the gel foam shows higher foam stabilizing performance in the range of oil content less than 10%. It follows that, over a certain oil content range, gel foams are able to reverse the crude oil to foam-stabilizing behavior.

Experimental example 2: microscopic decay behavior of low toxicity gel foam systems

Based on the breaking behavior of the gel foam (mainly coarsening of the bubbles), a gel foam was prepared as in example 1. And (3) rapidly injecting the gel foam into a visual observation device with a heating sleeve, and observing the decay condition of the gel foam bubbles along with the change of time by using an industrial microscope. And shooting the gel foam inside the visual observation device every 1min, and recording a foam microscopic image. Meanwhile, the temperature of the visual observation device with the heating sleeve is kept at 70 ℃, so that the heat loss in the observation process is reduced. In this section, two-dimensional foam morphological changes (influence of gravity liquid separation can be partially eliminated) are recorded through a microscope, then, image analysis is carried out on a foam photo to quantitatively research the foam evolution law, and the experimental result is shown in fig. 5.

Experimental example 3: fluidity control capability of Low toxicity gel foam systems (conventional method)

The specific experimental steps are as follows:

1) Water flooding: injecting simulated formation water into the core model at the flow rate of 1mL/min until the injection pressure at the inlet of the model is stable, and stopping water drive;

2) Injecting nitrogen gel foam: and pressurizing by a back pressure valve at the outlet end to 1MPa, injecting 0.5PV nitrogen gel foam (the foam mass is 60%) into the rock core at the flow rate of 1mL/min, and recording the displacement pressure of the rock core and the outlet end effluent condition.

3) And (3) placing the core model in a 70 ℃ oven for 48h, performing subsequent water flooding at the injection flow rate of 1mL/min, recording the core displacement pressure and the outlet end liquid outflow condition, and calculating the plugging rate.

The prepared gel foam was used to perform plugging experiments on the core model, and the pressure difference change during the experiment is shown in fig. 11. As can be seen, the pressure gradually increased during the gel foam injection phase, indicating the formation of a gel foam system. And after 48h, the foam forms gel foam in the rock core, water flooding is carried out again, and the injection pressure of the secondary water flooding is greatly increased compared with that of the primary water flooding, so that the gel foam effectively blocks the rock core. Along with the increase of the injected water quantity, the gel foam continuously migrates to the deep part of the rock core, and the injection pressure shows the trend of step descending. The gel foam shows dynamic change of rupture and regeneration in the rock core, the pressure of the displacement body is gradually reduced, and the gel foam is maintained at a stable level after breakthrough. The calculated plugging rate of the gel foam is 99.14%, which shows that the stability of the gel foam system is good, the actual pressure acts on the whole gel foam barrier layer, the flow resistance is large, and the plugging effect is good.

TABLE 3 blocking Rate of Low toxicity gel foams

Serial number	K1/mD	Porosity/%)	Gas to liquid ratio	Injection pressure/MPa	K2/mD	Plugging Rate/%
							1	1000	37.3	2:1	1.451	8.6	99.14

The experimental example is a conventional way to evaluate the plugging effect of gel foam after aging to gel in the formation, however, when gel foam is injected into the formation, the gel foam bubbles, breaks, migrates and gels simultaneously. Therefore, the evaluation method cannot truly reflect the degree control capability and seepage condition of the gel foam in the stratum, and the evaluation means cannot reflect that the gel foam has the deep profile control effect.

Experimental example 4: profile control of low toxicity gel foam systems

The specific experimental process is as follows: a) Weighing the dry weight m of the core ₀ Loading the core into a core holder, and applying confining pressure to the core to 7MPa; b) Injecting formation water into the rock core at the flow rate of 1mL/min until the tail end of the rock core is discharged and the displacement pressure is stable, and recording the stable pressure value delta P ₂ And calculating the permeability of the rock core; taking out core and weighing wet weight m ₁ And calculating the pore volume of the core. Designing permeability grade difference conditions of 25, 50, 75 and 100, and selecting two rock cores meeting the conditions as one group, wherein the two rock cores are four groups; c) Replacing the rock core with simulated formation water, setting the injection flow rate to be 1mL/min, and recording the shunt flow change of the parallel rock core; d) After the simulated formation water displacement parallel core is stabilized, starting a high-pressure nitrogen valve, injecting a gel foam system into the core at the injection flow rate of 0.5mL/min with the foam mass of 60%, recording the shunt flow of the parallel core, stopping the pump when the injection volume reaches 0.5PV of the total pore volume of the parallel core, and aging the parallel core in an oven at 70 ℃ for 48 hours; e) Taking out the aged rock coreAnd (5) continuing water flooding, wherein the water flooding speed is 1mL/min, and recording the change condition of the core split flow.

The trend of the high and low permeability flow rate of the parallel core with different permeability grade differences along with the change of the injection volume is shown in figure 10. It can be seen that when the permeability level difference is 25-50, the low-toxicity gel foam system has strong capacity of improving heterogeneity, most gel foam enters the high-permeability core, and high seepage resistance is established for high permeability after gelling. The situation that the high-permeability core is blocked by gel foam at the moment, most of liquid flows pass through the low-permeability core, and the liquid flow is diverted is shown. When the permeability grade difference ranges from 75 to 100, the anisotropy improving capability of the low-toxicity gel foam system is reduced along with the increase of the grade difference, which indicates that the resistance built by the gel foam in the high-permeability core is not enough to fully start the fluid of the low-permeability core.

It should be noted that, in the online monitoring method of the present invention, more displacement stage points may also be set, for example, pressure monitoring points and sampling points are respectively set at the inlet end, 1/5, 2/5, 3/5, and 4/5; the gel foam system can realize on-line monitoring on the migration and gelling conditions of the gel foam at 2/5, 3/5 and 4/5 positions, and the more pressure monitoring points are arranged, the more beneficial the gelling and migration dynamic conditions of a plurality of monitoring points can be obtained, so as to reflect the real fluidity control capability and seepage condition of the gel foam system in more detail.

The on-line monitoring method can be used for on-line monitoring of other existing gel foam systems besides the low-toxicity gel foam system provided by the invention, and can be used for on-line monitoring of the real fluidity control capability and seepage condition of the gel foam system.

The foregoing is illustrative of the preferred embodiments of this invention, and it is to be understood that the invention is not limited to the precise form disclosed herein and that various other combinations, modifications, and environments may be resorted to, falling within the scope of the concept as disclosed herein, either as described above or as apparent to those skilled in the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. An on-line monitoring method of a gel foam system, which can be used for monitoring the real fluidity control capability and seepage process of the low-toxicity gel foam system, is characterized by comprising the following steps:

b, injecting nitrogen gel foam: after the simulated formation water displacement serial core is stabilized, simultaneously opening a gel foam base liquid injection pump and a high-pressure nitrogen valve, injecting a gel foam system into the core at the injection flow rate of 0.5mL/min with the foam mass of 60%, and respectively recording the pressure changes at the inlet end, 1/4, 1/2 and 3/4 positions of the serial core;

step d, drawing a resistance coefficient comparison histogram: calculating resistance coefficient values of different displacement stage points under different injected PV numbers, and drawing a resistance coefficient comparison histogram by taking the displacement stage as a horizontal coordinate and the resistance coefficient as a vertical coordinate;

wherein, the low-toxicity gel foam system is formed by introducing gas phase into low-toxicity gel foam base liquid;

the low-toxicity gel foam base solution is prepared from the following components in parts by mass:

0.2-0.3 part of a polymer;

0.015-0.025 parts of a crosslinking agent;

0.2-0.3 part of foaming agent;

0.04-0.06 part of deoxidant;

0.015-0.025 parts of retarder;

water;

the total amount of the raw materials is 100 parts;

the foaming agent is alkyl glycoside (APG-10) or betaine foaming agent;

the cross-linking agent is an aluminum citrate cross-linking agent.

2. The method for on-line monitoring of a gel foam system as claimed in claim 1, further comprising steps e, f;