A carbon dioxide / crude oil promoting agent of a polysaccharide esterification type, and a preparation method and application thereof

Abstract

This invention discloses a polysaccharide esterified carbon dioxide / crude oil blending agent, its preparation method, and its application, relating to the technical field of carbon dioxide enhanced oil recovery (CEAR). The blending agent is an oligopolysaccharide esterified derivative or a mixture containing oligopolysaccharide esterified derivatives. The oligopolysaccharide molecule has one C12-18 long-chain ester group at one site and C2-C4 short-chain ester groups at the remaining sites. The blending agent is used to reduce the minimum miscibility pressure between crude oil and carbon dioxide. The preparation method involves using long-chain alkyl oligopolysaccharide esters and short-chain anhydrides as raw materials. Chain oligopolysaccharides are added to the reactor at a feed ratio of 1:3a+1, and cyclic oligopolysaccharides are added at a feed ratio of 1:3a-1. Copper perchlorate is used as a catalyst, and the reaction is carried out at 90-140℃ for 12-36 hours. After the reaction, the resulting product does not require purification to obtain the blending agent. The raw materials of this invention are readily available, the synthetic route is short, and the product can be used directly after the reaction without purification.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide flooding and enhanced oil recovery technology, and in particular to a polysaccharide esterified carbon dioxide / crude oil blending agent, its preparation method, and its application. Background Technology

[0002] Carbon dioxide flooding is a crucial technology for enhancing oil recovery. Carbon dioxide reaches a supercritical state at temperatures above 31.1℃ and pressures above 7.38 MPa. Under most reservoir conditions, carbon dioxide is in a supercritical state, exhibiting characteristics such as high density, low viscosity, large diffusion coefficient, and easy penetration into low-permeability reservoirs. It can extract, swell, reduce viscosity, and carry light components to crude oil. Compared to nitrogen and dry gas, it is more likely to achieve a miscible or near-miscible state with crude oil. Therefore, carbon dioxide flooding technology plays an increasingly important role in tertiary oil recovery. In recent years, with the continuous rise in demand for greenhouse gas emission reduction, carbon dioxide flooding technology also possesses the dual value of geological utilization and storage of carbon dioxide, offering the advantage of synergistic promotion of economic development and environmental protection.

[0003] In practical applications, the effectiveness of carbon dioxide flooding is largely limited by the minimum miscibility pressure (MPP) between carbon dioxide and crude oil. Higher MPPs require greater injection pressures to achieve miscible flooding, necessitate higher requirements for surface equipment and wellbore integrity, and increase injection costs and operational risks. For low-pressure, low-permeability, thin-layer, or highly heterogeneous reservoirs, if the formation pressure cannot reach the MPP, carbon dioxide and crude oil can only contact in an immiscible or weakly miscible manner, thus limiting sweep efficiency, displacement efficiency, and ultimate recovery. Therefore, developing miscible enhancers that promote carbon dioxide / crude oil miscibility at lower pressures is crucial for broadening the reservoir range suitable for carbon dioxide flooding.

[0004] Existing methods for reducing the minimum miscibility pressure of carbon dioxide / crude oil mainly include adjusting the composition of the injection medium, adding light hydrocarbons or alcohol co-solvents, and using conventional surfactants or polymer additives. However, these methods may still have some shortcomings. For example, some small-molecule additives are highly volatile and have poor formation adaptability; some conventional surfactants have limited solubility in supercritical carbon dioxide; and some polymer systems have problems such as cumbersome preparation steps, high dosage, or inconvenience in field use. Especially for supercritical carbon dioxide systems, the mixing agent molecule needs to have both carbon dioxide affinity and lipophilic ability, so that it can be dispersed or dissolved in supercritical carbon dioxide and can effectively regulate the carbon dioxide / crude oil interface and phase behavior. Traditional surfactant molecular structures designed based on oil-water two-phase systems often cannot simultaneously meet the above requirements. Summary of the Invention

[0005] In order to overcome the above-mentioned problems in the prior art, the present invention proposes a polysaccharide esterified carbon dioxide / crude oil blending agent, its preparation method and application.

[0006] The technical solution adopted by this invention to solve its technical problem is: a polysaccharide esterified carbon dioxide / crude oil blending agent, wherein the blending agent is an oligopolysaccharide esterified derivative or a mixed product containing oligopolysaccharide esterified derivatives, wherein the oligopolysaccharide molecule has one C12~18 long-chain ester group at one site and C2~C4 short-chain ester groups at the remaining sites, and the structural formula is shown in Formula I and Formula II: ; Where a = 2~8, b = 11~18, c = 1~3.

[0007] In the aforementioned polysaccharide esterification type carbon dioxide / crude oil blending agent, the C12-18 long-chain ester groups are derived from long-chain alkyl oligopolysaccharide esters, and the C2-C4 short-chain ester groups are derived from the esterification reaction of the corresponding acid anhydride on the remaining hydroxyl sites.

[0008] A method for preparing a polysaccharide esterified carbon dioxide / crude oil blending agent, specifically comprising: using long-chain alkyl oligopolysaccharide esters and short-chain anhydrides as raw materials, adding the chain oligopolysaccharide to the reactor at a feed ratio of 1:(3a+1), and adding the cyclic oligopolysaccharide to the reactor at a feed ratio of 1:(3a-1), using copper perchlorate as a catalyst, and reacting at 90-140℃ for 12-36 hours. The product obtained after the reaction does not require purification and is the carbon dioxide / crude oil blending agent. The amount of copper perchlorate is 0.01wt%~1.0wt% of the total mass of the reaction system, preferably 1wt%~5wt%, and more preferably 3wt%.

[0009] Application of a polysaccharide esterified carbon dioxide / crude oil blending agent, wherein the blending agent is the blending agent described above or a blending agent prepared based on the above preparation method, for reducing the minimum miscibility pressure between crude oil and supercritical carbon dioxide.

[0010] The above-mentioned polysaccharide esterified carbon dioxide / crude oil blending agent is applicable to carbon dioxide flooding processes at temperatures of 40°C to 100°C, preferably at 50°C to 80°C, and more preferably at 58°C.

[0011] The beneficial effects of this invention are: (1) the raw materials are readily available, the synthesis route is short, and it can be used directly without purification after the reaction; (2) the molecular structure is clear, which makes it easy to carry out further optimization around the relationship between the substituent structure and the anti-miscibility performance; (3) it can meet the 3wt% usage concentration requirement under a certain pressure range at 58℃; (4) it takes into account both the two application goals of reducing minimum miscibility pressure and improving displacement recovery rate, and is suitable for supercritical carbon dioxide flooding scenarios. Attached Figure Description

[0012] Figure 1 This is a graph showing the dissolution mass ratio of the mixing agent of the present invention under different pressures versus pressure. Figure 2 The mixture-pressure curves of the system without mixing accelerator under different pressures; Figure 3 The mixture-pressure curves of the system with added blending accelerator under different pressures; Figure 4 This is a comparison chart of the recovery rates of the system without and with the mixing agent under different displacement pressures according to the present invention. Detailed Implementation

[0013] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0014] This invention discloses a polysaccharide esterified carbon dioxide / crude oil blending agent. The blending agent is an oligopolysaccharide esterified derivative or a mixture containing oligopolysaccharide esterified derivatives. The oligopolysaccharide molecule has one C12-18 long-chain ester group at one site and C2-C4 short-chain ester groups at the remaining sites. The structural formula is shown in Formula I and Formula II. ; Where a = 2~8, b = 11~18, c = 1~3.

[0015] The C12-18 long-chain ester groups are derived from long-chain alkyl oligopolysaccharide esters, and the C2-C4 short-chain ester groups are derived from the esterification reaction of the corresponding acid anhydride on the remaining hydroxyl sites.

[0016] This invention also discloses a method for preparing a polysaccharide esterified carbon dioxide / crude oil blending agent as described above. Specifically, long-chain alkyl oligopolysaccharide esters and short-chain anhydrides are used as raw materials. The chain oligopolysaccharide is added to the reactor at a feed ratio of 1:(3a+1), and the cyclic oligopolysaccharide is added to the reactor at a feed ratio of 1:(3a-1). Copper perchlorate is used as a catalyst, and the reaction is carried out at 90-140℃ for 12-36 hours. After the reaction, the product obtained does not require purification and is the carbon dioxide / crude oil blending agent. In this embodiment, the preferred reaction temperature is 110℃~130℃, more preferably 120℃; the preferred reaction time is 12-36 hours, more preferably 18-30 hours, and more preferably 24 hours.

[0017] The amount of copper perchlorate used is 0.01wt%~1.0wt% of the total mass of the reaction system, preferably 0.05wt%~0.2wt%, and more preferably 0.1wt%. The specific synthesis route is shown below:

[0018]

[0019] The aforementioned mixing aid, or the mixing aid prepared by the aforementioned method, is used to reduce the minimum miscibility pressure between crude oil and carbon dioxide. The mixing aid is suitable for carbon dioxide flooding processes at temperatures ranging from 40°C to 100°C.

[0020] Example 1 In this embodiment, "mixing accelerator" refers to a compound or composition that can reduce the minimum miscibility pressure between crude oil and carbon dioxide; "supercritical carbon dioxide" refers to a carbon dioxide fluid with a temperature and pressure higher than the critical point of carbon dioxide. The minimum miscibility pressure in this invention is determined using the height rise method; the solubility of the mixing accelerator in supercritical carbon dioxide is characterized by gradually increasing the system pressure at 58°C and measuring the dissolution mass ratio; the core displacement effect is evaluated through a long core displacement physical simulation experiment.

[0021] In this embodiment, the mixing agent has a structure in which one site on the oligopolysaccharide molecule has a C16 long-chain ester group and the remaining seven sites have short-chain acyl groups.

[0022] The preparation method of the blending accelerator is as follows: long-chain alkyl oligopolysaccharide ester and short-chain acid anhydride are added to a reactor, with a feed ratio of long-chain alkyl oligopolysaccharide ester to short-chain acid anhydride of 1:3.5; then, copper perchlorate (0.1 wt% of the total mass of the reaction system) is added as a catalyst. The reaction is carried out at 120℃ for 24 h, and after the reaction is completed, it is cooled to room temperature to obtain the target blending accelerator product.

[0023] The resulting product is an esterified derivative of an oligopolysaccharide molecule with a C16 long-chain ester group at one site and short-chain acyl groups at the remaining seven sites. This product can be used directly in subsequent supercritical carbon dioxide experiments without purification.

[0024] The prepared mixing accelerator was added to the sample cell, and the test temperature was fixed at 58℃. Supercritical carbon dioxide was injected into the sample cell, and the pressure of the sample cell was gradually increased. Simultaneously, the pressure value and the percentage of sample dissolution were monitored. The dissolution-mass ratio was used to characterize the solubility of the mixing accelerator in supercritical carbon dioxide, and a dissolution-mass ratio-pressure curve was plotted. Figure 1 As shown. The concentration of the mixing accelerator was set at 3 wt%.

[0025] The dissolution was characterized by the dissolution mass ratio, and the results are shown in Table 1. As the pressure increased, the dissolution mass ratio of the mixing accelerator in supercritical carbon dioxide gradually increased; when the pressure reached 15.58 MPa and above, the dissolution mass ratios reached 3.23% and 3.56%, respectively, both exceeding the set concentration of 3 wt%, indicating that the mixing accelerator of the present invention can meet the requirement of complete dissolution at a concentration of 3 wt% within this pressure range under the condition of 58℃.

[0026] Table 1

[0027] The minimum miscibility pressure was determined using the height rise method. In a constant-volume autoclave with a transparent window and liquid level markings, at a constant temperature of 58°C, an equal volume of oil sample, mixing agent, and magnetic stir bar were added, and the initial liquid level height H0 was recorded. Then, supercritical carbon dioxide was injected, and the pressure p was adjusted. As the pressure increased, the supercritical carbon dioxide gradually dissolved in the oil phase, and the oil phase liquid level height H gradually increased. After each pressure adjustment, the system was stabilized for several minutes, and a set of Hp data was recorded. This process continued until the container was completely filled with the oil phase; at this point, the liquid level height was Hm. This state was defined as perfectly miscible, and the corresponding pressure pm was the minimum miscibility pressure of the system.

[0028] The control group consisted of a carbon dioxide / crude oil system without a mixing accelerator; the experimental group consisted of a system containing the mixing accelerator prepared in Example 1 at a concentration of 3 wt% in supercritical carbon dioxide. The miscibility ratio was calculated based on changes in liquid level, and the pressure corresponding to a miscibility ratio of 100.0% was taken as the minimum miscibility pressure. The miscibility ratio-pressure curves of the system without the mixing accelerator at different pressures are shown below. Figure 2 As shown, the mixture-pressure curves of the system with added mixing accelerator under different pressures are as follows: Figure 3 As shown.

[0029] Test results show that, compared with the control group without the mixing agent, the minimum miscibility pressure between crude oil and supercritical carbon dioxide decreased from 24.48 MPa to 18.31 MPa after adding the mixing agent of the present invention, a decrease of approximately 25.2%, indicating that the mixing agent of the present invention can significantly improve the miscibility of the carbon dioxide / crude oil system.

[0030] Based on core displacement physical simulation gas drive tests and actual field data of the Daqing Aonan Oilfield, the oilfield has an oil-bearing area of ​​131.2 km². 2 The geological reserves are 2105×10 4 The reservoir primarily consists of grape-blossom oil layers, with an average sandstone thickness of 6.0 m encountered during drilling, an effective thickness of 2.5 m, an average reservoir porosity of 17.5%, and an average permeability of 13.3 × 10⁻⁶. -3 μm 2 It is a medium-porosity, low-permeability oil reservoir with an average formation crude oil viscosity of 5.54 mPa·s and a surface crude oil density of 0.8539 g / cm³. 3 The original formation pressure was 18.43 MPa, the original saturation pressure was 6.69 MPa, and the average formation temperature was 58.8℃.

[0031] The experimental temperature was 58℃, and the experimental gas was carbon dioxide, specifically supercritical carbon dioxide under the experimental conditions. The experimental oil was a simulated live oil prepared by mixing degassed crude oil and n-decane. The simulated live oil was mixed with crude oil to achieve a viscosity of approximately 6 mPa·s, the same as live oil, with a final ratio of V(crude oil):V(n-decane) = 3:7. The core used in the experiment was an artificial core, 2.5 cm in diameter and 110 cm in length, with a porosity of 17.5% ± 2.5% and a permeability of 13 × 10⁻⁶. -3 μm 2 ±2×10 -3 μm 2 .

[0032] A long core displacement device was used to conduct physical simulation gas drive tests on core displacement. The device mainly consists of a displacement system, a temperature control device, a long core holder system, a back pressure controller, and an oil gauging device. The specific steps are as follows: ① Select and dry the core, measure the core size, and apply epoxy resin to the core surface for corrosion protection; ② Place the core in the core holder, apply an annular pressure of 5-6 MPa, and evacuate for 8-12 hours; ③ Saturate the formation with water, measure the pore volume from the saturated water volume, and calculate the porosity; ④ Place the core holder in a temperature control chamber and heat it to 58°C, maintain the temperature, and measure the permeability; ⑤ Gradually increase the annular pressure to saturate the simulated live oil, record the saturated oil volume, and calculate the original oil saturation; ⑥ Set the back pressure through the back pressure valve, inject supercritical carbon dioxide at a constant rate, record the injection pressure, the volume of injected supercritical carbon dioxide, and the production volume at the outlet, and calculate the recovery rate; ⑦ Replace the core, gradually increase the outlet pressure, and repeat the above steps to obtain the recovery rate under different displacement pressure conditions.

[0033] The test results at displacement pressures of 15 MPa, 18 MPa, 21 MPa, 24 MPa, and 27 MPa are shown in Table 2 and... Figure 2 Test results show that when the displacement pressures are 15 MPa, 18 MPa, 21 MPa, 24 MPa, and 27 MPa, the recovery rates of the systems with added blending agents are 30.27%, 48.14%, 63.56%, 70.09%, and 75.23%, respectively, all higher than the 27.62%, 30.45%, 42.41%, 47.66%, and 51.53% of the systems without blending agents. The corresponding recovery rate increases are 2.65, 17.69, 21.15, 22.43, and 23.70 percentage points, respectively. When the displacement pressure exceeds the miscibility pressure of 18.31 MPa, under the action of the blending agent, supercritical carbon dioxide and crude oil more easily reach a miscible or near-miscible state, thus achieving a significant increase in recovery rate.

[0034] Table 2 Results of Physical Simulation of Core Displacement and Gas Drive Tests

[0035] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its scope and spirit, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of the present invention.

Claims

1. A polysaccharide esterified carbon dioxide / crude oil blending agent, characterized in that, The blending accelerator is an oligopolysaccharide esterification derivative or a mixture containing oligopolysaccharide esterification derivatives. The oligopolysaccharide molecule has one C12-18 long-chain ester group at one site and C2-C4 short-chain ester groups at the other sites, with the structural formulas shown in Formula I and Formula II. ; Where a = 2~8, b = 11~18, c = 1~3.

2. The polysaccharide esterification type carbon dioxide / crude oil blending agent according to claim 1, characterized in that, The C12-18 long-chain ester groups are derived from long-chain alkyl oligopolysaccharide esters, and the C2-C4 short-chain ester groups are derived from the esterification reaction of the corresponding acid anhydride on the remaining hydroxyl sites.

3. A method for preparing a polysaccharide esterified carbon dioxide / crude oil blending agent, characterized in that, The preparation of a polysaccharide esterified carbon dioxide / crude oil blending agent as described in any one of claims 1-2 is specifically as follows: using long-chain alkyl oligopolysaccharide esters and short-chain anhydrides as raw materials, the chain oligopolysaccharides are added to the reactor at a feed ratio of 1:(3a+1), and the cyclic oligopolysaccharides are added to the reactor at a feed ratio of 1:(3a-1). Copper perchlorate is used as a catalyst, and the reaction is carried out at 90-140℃ for 12h-36h. After the reaction is completed, the product obtained does not need to be purified and is the carbon dioxide / crude oil blending agent.

4. The preparation method of a polysaccharide esterified carbon dioxide / crude oil blending agent according to claim 3, characterized in that, The amount of copper perchlorate used is 0.01wt% to 1.0wt% of the total mass of the reaction system.

5. The application of a polysaccharide esterified carbon dioxide / crude oil blending agent, characterized in that, The blending agent is the blending agent according to claim 1 or 2 or the blending agent prepared based on the preparation method according to any one of claims 3-4, and is used to reduce the minimum miscibility pressure between crude oil and carbon dioxide.

6. The application of the polysaccharide esterified carbon dioxide / crude oil blending agent according to claim 5, characterized in that, The mixing agent is suitable for carbon dioxide flooding processes under conditions of 40℃~100℃.

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