A characterization method for imbibition displacement of surfactant with ultra-low interfacial tension

Abstract

The present invention discloses a characterization method for imbibition displacement of surfactants with ultra-low interfacial tension, including fabricating a planar imbibition model or a cylindrical imbibition model and obtaining the basic parameters of the planar imbibition model or the cylindrical imbibition model; conducting an imbibition experiment through the planar imbibition model or the cylindrical imbibition model and acquiring the relevant parameters during the imbibition process; respectively calculating the surfactant solubilization parameter, the surfactant solubilized emulsified oil amount, the imbibition efficiency of the surfactant, the imbibition distance, the displacement degree parameter, the lower limit of the oil saturation, and the upper limit of the oil saturation. The present invention can, during the imbibition process, measure data such as formation water, the injection amount of the surfactant with ultra-low interfacial tension, and the oil recovery amount through experiments, and can calculate parameters such as the oil saturation of the formation oil, the displacement degree, the absorption efficiency, and the imbibition distance during the imbibition process, and can fully describe the process of surfactant displacement with ultra-low interfacial tension during the imbibition process. The calculation method is simple and the result is accurate.

Description

Technical Field

[0001] The present invention relates to a characterization method for imbibition displacement of surfactants with ultra-low interfacial tension, belonging to the technical field of petrochemical industry. Background Art

[0002] Due to the continuous large-scale exploration and production globally, traditional oil and gas reserves have decreased sharply, leading to an imbalance between energy supply and demand. Ultra-low permeability reservoirs have gradually become a research hotspot, with poor pore and permeability conditions, strong reservoir heterogeneity, and poor water absorption capacity. Imbibition is a method that can improve oil recovery under the conditions of ultra-low permeability reservoirs. Its mechanism is that under the action of capillary force, the wetting-phase fluid spontaneously enters the porous medium and displaces the non-wetting-phase fluid originally present in the porous medium. Surfactants with ultra-low interfacial tension can improve the imbibition effect and enhance oil recovery by solubilizing and emulsifying, increasing the imbibition distance, etc.

[0003] In summary, imbibition with surfactants having ultra-low interfacial tension can effectively improve crude oil recovery. However, current domestic and international research is limited to studying the imbibition effect, and no reasonable quantitative evaluation has been carried out on parameters such as imbibition distance, formation oil saturation, and solubilized and emulsified oil volume. Summary of the Invention

[0004] In order to overcome the defects existing in the prior art, the present invention aims to provide a characterization method for imbibition displacement of surfactants with ultra-low interfacial tension. Through this method, parameters such as oil saturation, imbibition distance, and solubilized and emulsified crude oil volume in matrix-fracture ultra-low permeability reservoirs can be measured after surfactant imbibition, which has practical significance for evaluating the imbibition displacement process of surfactants with ultra-low interfacial tension.

[0005] The technical solution provided by the present invention to solve the above technical problems is: a characterization method for imbibition displacement of surfactants with ultra-low interfacial tension, comprising the following steps:

[0006] Step S10: fabricate a planar imbibition model or a cylindrical imbibition model, and obtain the basic parameters of the planar imbibition model or the cylindrical imbibition model;

[0007] Step S20: conduct an imbibition experiment through the planar imbibition model or the cylindrical imbibition model, and obtain relevant parameters during the imbibition process;

[0008] Step S30: calculate the solubilization parameter of the surfactant with ultra-low interfacial tension, the solubilized and emulsified oil volume of the surfactant with ultra-low interfacial tension, the imbibition efficiency of the surfactant with ultra-low interfacial tension, the imbibition distance, the displacement degree parameter, the lower limit of oil saturation, and the upper limit of oil saturation respectively according to the basic parameters and the relevant parameters during the imbibition process.

[0009] A further technical solution is that the basic parameters of the planar imbibition model include planar area, pore volume, initial oil saturation, porosity, and initial oil volume.

[0010] A further technical solution is that the basic parameters of the cylindrical imbibition model include cylinder height, cylinder radius, pore volume, initial oil saturation, porosity, and initial oil volume.

[0011] A further technical solution is that the relevant parameters during the imbibition process include formation water injection volume, ultra-low interfacial tension surfactant injection volume, interfacial tension, formation water content in the produced fluid, and crude oil content in the produced fluid.

[0012] A further technical solution is that the calculation formula for the planar imbibition model in step S30 is:

[0013]

[0014]

[0015]

[0016]

[0017]

[0018] In the formula: is the absorption efficiency of the surfactant; is the displacement degree parameter; are respectively the lower limit and upper limit of the oil saturation; is the initial oil volume in the matrix, mL; is the pore volume, cm 3 ; is the produced oil volume, mL; is the imbibition distance, cm; is the produced formation water volume, mL; is the formation water injection volume, mL; is the surfactant injection volume, mL; is the interfacial tension, mN / m; is the volume of crude oil transferred from the matrix to the fracture, mL; is the volume of surfactant transferred from the matrix to the fracture, mL; is the volume of the i-th component transferred from the matrix to the fracture, mL; is the displacement degree parameter of component i for crude oil; is the imbibition area, i.e., the planar area, cm 2 ; is the initial oil saturation.

[0019] A further technical solution is that the calculation formula of the cylindrical imbibition model in step S30 is as follows:

[0020]

[0021]

[0022]

[0023]

[0024]

[0025] In the formula: is the absorption efficiency of the surfactant; is the displacement degree parameter; are respectively the lower limit and the upper limit of the oil saturation; is the initial oil volume in the matrix, mL; is the pore volume, cm 3 ; is the produced oil volume, mL; is the imbibition distance, cm; is the produced formation water volume, mL; is the formation water injection volume, mL; is the surfactant injection volume, mL; is the interfacial tension, mN / m; is the volume of crude oil transferred from the matrix to the fracture, mL; is the volume of surfactant transferred from the matrix to the fracture, mL; is the volume of the i-th component transferred from the matrix to the fracture, mL; is the displacement degree parameter of component i for crude oil; is the cylinder radius, cm; is the cylinder height, cm; is the initial oil saturation.

[0026] The present invention has the following beneficial effects: During the imbibition process, the present invention can measure data such as formation water, injection volume of ultra-low interfacial tension surfactant, and oil recovery through experiments, and can calculate parameters such as oil saturation, displacement degree, absorption efficiency, and imbibition distance of formation oil during the imbibition process. It can fully describe the process of ultra-low interfacial tension surfactant displacement during the imbibition process. The calculation method is simple and the result is accurate. It has practical significance for the evaluation of ultra-low interfacial tension surfactant in the imbibition displacement process. Description of the Drawings

[0027] Figure 1 is a schematic diagram of the planar imbibition model;

[0028] Figure 2 is a plan view of planar imbibition;

[0029] Figure 3 is a schematic diagram of the planar imbibition area;

[0030] Figure 4 is a schematic diagram of a cylindrical imbibition model;

[0031] Figure 5 is a side view of cylindrical imbibition;

[0032] Figure 6 is a schematic diagram of the cylindrical imbibition area. Embodiment

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0034] A method for characterizing surfactant imbibition displacement with ultra-low interfacial tension of the present invention includes the following steps:

[0035] Step S10: Fabricate a planar imbibition model or a cylindrical imbibition model, and obtain the basic parameters of the planar imbibition model or the cylindrical imbibition model. The basic parameters of the planar imbibition model include planar area, pore volume, initial oil saturation, porosity, and initial oil volume; the basic parameters of the cylindrical imbibition model include cylinder height, cylinder radius, pore volume, initial oil saturation, porosity, and initial oil volume.

[0036] The model assumptions are as follows:

[0037] 1) The whole system is divided into two regions: the matrix region and the fracture region;

[0038] 2) The whole system only has component exchange with the injection port and the output port;

[0039] 3) Any chemical reactions during the dynamic imbibition process are not considered;

[0040] 4) The volume change caused by component mixing is not considered;

[0041] 5) The imbibition effect at each point on the imbibition contact surface is the same, and all the oil at the imbibition action site is displaced;

[0042] Fabricate a planar imbibition model as shown in Figure 1 The plan view of this model for planar imbibition is as shown in Figure 2 shown,

[0043] At time there is volume exchange between the fracture and the matrix, as Figure 1 , Figure 2 shown below:

[0044] For the volume changes of the matrix and fracture at this time, they can be expressed by Equation (1):

[0045]

[0046] In the formula: are the volume change amounts of the fracture and the matrix respectively within time, mL; is the volume transferred from the matrix to the fracture by the i-th component within time, mL; , are the volumes injected from the injection port and output from the output port by the i-th component within time, mL respectively.

[0047] The relationship between the value of i and the components is as follows in the table;

[0048] Table 1 Relationship between the value of i and the components

[0049]

[0050] When the system reaches a stable imbibition state, at this time, injection from the injection port, volume exchange between the fracture and the matrix, and output from the output port form a dynamic balance among the three. The volume of each component in the fracture does not change, that is:

[0051]

[0052] At the same time, for the matrix, its total volume change amount is also 0, that is:

[0053]

[0054] At the same time, because the injected liquid does not contain crude oil components, that is:

[0055]

[0056] From Equations (2), (3), and (4), Equation (5) can be derived by simultaneous deduction:

[0057]

[0058] The absorption efficiency of the surfactant can then be expressed by Equation (6):

[0059]

[0060] In the formula The corresponding data can be obtained from the experiment, so the absorption of surfactant by the matrix during the infiltration process can be easily calculated.

[0061] Considering that ultra-low interfacial tension surfactants have the effect of solubilizing and emulsifying, It consists of two parts, one part will be directly measured by the produced fluid, recorded as , and part of the oil will be solubilized and emulsified by the surfactant and cannot be read directly, recorded as , then:

[0062]

[0063] Thus the present invention introduces the solubilization parameter The concept refers to the volume of oil phase that can be solubilized by unit volume of surfactant. The calculation formula is as follows:

[0064]

[0065] Where: is the interfacial tension, mN / m.

[0066] The amount of oil to be solubilized and emulsified can be calculated using the following formula:

[0067]

[0068] By combining equations (5), (7), (8), and (9), the amount of oil to be solubilized and emulsified can be obtained as follows:

[0069]

[0070] By combining equations (3) and (5), the volume of crude oil produced can be expressed by equation (11):

[0071]

[0072] At the same time, the displacement degree parameter of component i on crude oil is defined as , the definition is shown in formula (12):

[0073]

[0074] The displacement degree parameter can be used to indicate the imbibition effect of water and surfactant components on crude oil in the matrix.

[0075] The oil saturation can be calculated by formula (13):

[0076]

[0077] Where: , are the lower and upper limits of oil saturation, respectively; is the initial matrix oil volume, mL; is the pore volume, cm 3 .

[0078] During the imbibition process, the influence of residual oil is not considered. As shown in the imbibition distance It can be calculated by Equation (14):

[0079]

[0080] In the formula: is the imbibition area, that is, the planar area, cm 2 ; is the imbibition distance, cm, is the initial oil saturation.

[0081] Fabricate a cylindrical imbibition model as Figure 4 shown. The side view of the imbibition of this cylindrical imbibition model is as Figure 5 shown,

[0082] The imbibition process of the cylinder is as Figure 6 shown. During this imbibition process, it is considered that the side, top, and bottom surfaces of the cylinder all undergo imbibition. At time within, there is a volume exchange between the fracture and the matrix. Its equilibrium steady-state process is similar to planar imbibition, and the absorption efficiency, displacement degree, and oil saturation of the surfactant can still be calculated using Equations (6), (12), and (13)

[0083]

[0084] In the formula: is the absorption efficiency of the surfactant; is the displacement degree parameter; are the lower and upper limits of the oil saturation, respectively; are the volume change amounts of the fracture and the matrix within time, mL; is the volume transferred from the matrix to the fracture by the i-th component within time, mL; 、 are the volumes injected from the injection port and output from the output port by the i-th component within time, mL; is the initial matrix oil volume, mL; is the pore volume, cm 3 .

[0085] However, since the imbibition contact surface is different from planar imbibition, the imbibition distance needs to be calculated using a new formula. The imbibition area is shown as follows.

[0086] From the figure, the imbibition distance can be obtained and the produced oil volume have the following relationship:

[0087]

[0088] In the formula: is the matrix porosity; is the initial oil saturation; is the produced oil volume, mL; is the imbibition distance, cm; is the cylinder radius, cm; is the cylinder height, cm.

[0089] After arrangement, it can be obtained:

[0090]

[0091] Step S20: Conduct an imbibition experiment through a planar imbibition model or a cylindrical imbibition model, and obtain relevant parameters during the imbibition process (formation water injection volume, ultra-low interfacial tension surfactant injection volume, interfacial tension, formation water content in the produced fluid, crude oil content in the produced fluid);

[0092] Step S30: Calculate the solubilization parameter of the ultra-low interfacial tension surfactant, the solubilized and emulsified oil volume of the ultra-low interfacial tension surfactant, the imbibition efficiency of the ultra-low interfacial tension surfactant, the imbibition distance, the displacement degree parameter, the lower limit of the oil saturation, and the upper limit of the oil saturation respectively according to the basic parameters and the relevant parameters during the imbibition process.

[0093] Example 1

[0094] During the imbibition process of the planar imbibition model, a total of 10 mL of formation water and 0.01 mL of ultra-low interfacial tension surfactant were injected. The interfacial tension was 0.001 mN / m. 8.9 mL of formation water and 1 mL of crude oil were produced from the produced fluid. The planar area was 50 cm 2 , the porosity was 5.5%, the initial oil saturation was 100%, the pore volume was 3.15 cm 3 , and the initial crude oil volume was 3.15 cm 3 .

[0095] The solubilization parameter of the ultra-low interfacial tension surfactant calculated from Equation (8) was 17.32;

[0096] The solubilized and emulsified oil volume of the ultra-low interfacial tension surfactant calculated from Equation (10) was 0.106 mL;

[0097] The imbibition efficiency of the ultra-low interfacial tension surfactant calculated from Equation (6) was 61.27%;

[0098] Calculated from Equation (12) = 99.45%, = 0.55%;

[0099] Calculated from Equation (13) = 0.6488, 0.6507; imbibition distance = 0.40 cm 3 .

[0100] Example 2

[0101] During the imbibition process of the cylindrical imbibition model, a total of 10 mL of formation water and 0.01 mL of ultra-low interfacial tension surfactant were injected. The interfacial tension was 0.001 mN / m. 8.9 mL of formation water and 1 mL of crude oil were produced from the produced fluid. The height of the cylinder was 5 cm, the radius was 1.9 cm, the porosity was 5.5%, the initial oil saturation was 100%, and the pore volume was 3.15 cm 3 , and the initial oil volume was 3.15 cm 3 .

[0102] The solubilization parameter of the ultra-low interfacial tension surfactant was also calculated to be 17.32, the solubilized and emulsified oil volume was 0.106 mL, and the imbibition efficiency was 61.27% by Equations (6), (8), (10), (12), and (13). = 99.45%, , = 0.6488, 0.6507;

[0103] And the imbibition distance was calculated by Equation (17) = 0.28 cm.

[0104] As mentioned above, it is not a restriction on the present invention in any form. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the disclosed technical content within the scope of the technical solution of the present invention to obtain equivalent embodiments with equivalent changes. However, as long as it does not depart from the technical solution of the present invention, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A characterization method for imbibition displacement of surfactant with ultra-low interfacial tension, characterized in that, it includes the following steps: Step S10: Fabricate a planar imbibition model or a cylindrical imbibition model, and obtain the basic parameters of the planar imbibition model or the cylindrical imbibition model; Step S20: Conduct an imbibition experiment through the planar imbibition model or the cylindrical imbibition model, and acquire the relevant parameters during the imbibition process; Step S30: Calculate the solubilization parameter of the surfactant with ultra-low interfacial tension, the solubilized emulsified oil volume of the surfactant with ultra-low interfacial tension, the imbibition efficiency of the surfactant with ultra-low interfacial tension, the imbibition distance, the displacement degree parameter, the lower limit of oil saturation, and the upper limit of oil saturation respectively according to the basic parameters and the relevant parameters during the imbibition process; The calculation formula for the planar imbibition model is: In the formula: is the absorption efficiency of the surfactant; is the displacement degree parameter; are respectively the lower limit and the upper limit of the oil saturation; is the initial oil volume in the matrix, mL; is the pore volume, cm 3 ; is the produced oil volume, mL; is the imbibition distance, cm; is the produced formation water volume, mL; is the formation water injection volume, mL; is the surfactant injection volume, mL; is the interfacial tension, mN / m; is the volume of the crude oil transferred from the matrix to the fracture, mL; is the volume of the surfactant transferred from the matrix to the fracture, mL; is the volume of the i-th component transferred from the matrix to the fracture, mL; is the displacement degree parameter of the component i to the crude oil; is the imbibition area, i.e., the planar area, cm 2 ; is the initial oil saturation; The calculation formula for the cylindrical imbibition model is: Wherein: is the absorption efficiency of the surfactant; is the displacement degree parameter; are respectively the lower limit and the upper limit of the oil saturation; is the initial oil volume in the matrix, mL; is the pore volume, cm 3 ; is the produced oil volume, mL; is the imbibition distance, cm; is the produced formation water volume, mL; is the formation water injection volume, mL; is the surfactant injection volume, mL; is the interfacial tension, mN / m; is the volume of crude oil transferred from the matrix to the fracture, mL; is the volume of surfactant transferred from the matrix to the fracture, mL; is the volume of the i-th component transferred from the matrix to the fracture, mL; is the displacement degree parameter of component i for crude oil; is the cylinder radius, cm; is the cylinder height, cm; is the initial oil saturation.

2. The characterization method for imbibition displacement of surfactant with ultra-low interfacial tension according to claim 1, characterized in that, the basic parameters of the planar imbibition model include planar area, pore volume, initial crude oil saturation, porosity, and initial crude oil volume.

3. The characterization method for imbibition displacement of surfactant with ultra-low interfacial tension according to claim 1, characterized in that, the basic parameters of the cylindrical imbibition model include cylinder height, cylinder radius, pore volume, initial crude oil saturation, porosity, and initial crude oil volume.

4. The characterization method for imbibition displacement of surfactant with ultra-low interfacial tension according to claim 1, characterized in that, the relevant parameters during the imbibition process include formation water injection volume, surfactant injection volume with ultra-low interfacial tension, interfacial tension, formation water content in the produced fluid, and crude oil content in the produced fluid.

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