A method and experimental device for quickly evaluating the cleaning efficiency of oil displacement agents for heavy oil

Abstract

The present invention belongs to the technical field of petroleum development, and specifically relates to a method and experimental device for quickly evaluating the cleaning efficiency of oil displacement agents on heavy oil. This rapid evaluation method first weighs the mass of a special measuring device with a groove; then fills the groove on the special measuring device with heavy oil to form a heavy oil ring, and after aging for 48 hours under reservoir temperature conditions, weighs the total mass of the special measuring device containing the heavy oil ring; places the aged special measuring device containing the heavy oil ring in a conical flask for an oil washing experiment; after the oil washing experiment is completed, take out the special measuring device, wipe the entire surface of the special measuring device clean, and weigh the total mass again; finally, calculate the oil washing efficiency based on the mass difference. The method can quickly and accurately test and evaluate the ability of a chemical agent for displacing heavy oil to clean heavy oil, thereby overcoming the shortcomings of existing evaluation methods that are time-consuming and have large errors when used for heavy oil with high viscosity and strong adhesion.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum development, and particularly relates to a method and an experimental device for rapidly evaluating the cleaning efficiency of an oil displacement agent on heavy oil. Background Art

[0002] my country's heavy oil resources are widely distributed and have vast reserves. Heavy oil accounts for over 20% of total oil resources, making it a crucial component of oil development. High viscosity and poor fluidity are the primary characteristics of heavy oil, leading to poor water flooding effectiveness and low recovery rates in heavy oil reservoirs. Increasing the ability to clean heavy oil from formations by injecting chemical flooding agents (such as surfactants, viscosity reducers, and composite flooding agents) to improve recovery rates has become a research hotspot in heavy oil chemical flooding. Therefore, the efficiency of heavy oil cleaning is a crucial criterion for evaluating and optimizing chemical flooding agents.

[0003] At present, the evaluation method of oil washing efficiency is mainly based on the technical requirements of "Q / SLCG 0257-2018". The specific experimental method is as follows: 1) the simulated formation sand and the target block crude oil are mixed in a ratio of 4:1 (mass ratio), placed in a constant temperature drying oven, aged at reservoir temperature for 7 days, and stirred once a day to ensure uniform mixing of the oil sand; 2) a 0.3% oil displacement agent solution is prepared with water injected from the target block; 3) approximately 5 g of the aged oil sand is accurately weighed into a 100 mL conical flask, and the mass is measured as m1, accurate to 0.001 g; 4) 50 g of the prepared oil displacement agent solution is added to the sample in step 3), mixed thoroughly, and allowed to stand at reservoir temperature for 48 h; 5) the floating crude oil and the crude oil on the wall of the oil displacement agent solution after standing in step 4) are wiped out with clean cotton yarn, and the oil displacement agent solution is poured out. The conical flask is placed in a 105°C oven and dried to constant weight to obtain m2; 6) the oil sand in step 5) is eluted with petroleum ether until the petroleum ether is colorless. Place the conical flask containing the formation sand after washing out the crude oil in a 120℃ oven and dry it to constant weight, and weigh it to obtain m3.

[0004] Finally, the oil washing efficiency is calculated according to the formula:

[0005]

[0006] Where:

[0007] σ——oil washing rate;

[0008] m1——total mass of oil sand and conical flask before oil washing, g;

[0009] m2——total mass of oil sand and conical flask after oil washing, g;

[0010] m3——Total mass of formation sand and conical flask after elution, g.

[0011] The static oil washing method used in accordance with the technical requirements of "Q / SLCG 0257-2018" to evaluate the cleaning efficiency of oil displacement agents is suitable for light crude oil with low viscosity and density. However, it has the following obvious drawbacks when used to evaluate the cleaning efficiency of oil displacement agents for heavy oil: First, due to the high viscosity and poor fluidity of heavy oil, the heavy oil washed away by the oil displacement agent is difficult to separate from the oil sands and, therefore, difficult to float to the surface of the solution; second, the heavy oil adheres to the inner wall of the conical flask and is difficult to wipe clean with cotton yarn. Both of these factors lead to a serious deviation between the measured oil washing efficiency and the actual value.

[0012] Another study designed an oil-washing efficiency test device consisting of an oil-washing bottle, a heat preservation unit, a magnetic stirring unit, and an observation window. The oil-washing bottle includes a graduated cylinder, a ground-mouth conical flask, a sealed connector, and a top cover; the heat preservation unit consists of an insulated box, a hot plate, a fan, a temperature sensor, and a temperature-controllable chip; and the magnetic stirring unit comprises a magnetic stirring table, an electromagnetic converter, and a magnetic stirring bar. The procedure involves first saturating the oil sands, pouring them into a conical flask, and inserting a magnetic stirring bar. After heating the flask, the magnetic stirring bar is activated to stir and mix the oil sands and chemicals, simulating the oil-washing process. The volume of oil removed from the oil sands is measured using a graduated cylinder in the upper portion of the conical flask, and the oil-washing efficiency is then calculated.

[0013] This method is essentially the same as the static oil washing method, except that it incorporates magnetic stirring, making it a dynamic oil washing process. The weighing process is replaced by a volumetric measurement process. However, heavy oil has high viscosity and strong adhesion, so washed crude oil tends to adhere to the container walls, resulting in measurement errors and affecting the accuracy of oil washing efficiency assessment. Summary of the Invention

[0014] The present invention aims to provide a method and experimental device for rapidly evaluating the cleaning efficiency of oil-displacing agents on heavy oil. The method is used to quickly and accurately test and evaluate the cleaning capacity of chemical agents used to displace heavy oil, thereby overcoming the shortcomings of existing evaluation methods, such as long time consumption and large errors, when applied to heavy oil with high viscosity and strong adhesion.

[0015] The technical solution of the present invention is: a method for quickly evaluating the cleaning efficiency of an oil displacement agent on heavy oil, comprising the following steps:

[0016] (1) Accurately weigh the mass of a special measuring device with a groove, recorded as m1; the groove is used to form a heavy oil ring with a ring height of 2-5 mm and a ring width of 2-5 mm.

[0017] When the viscosity of the cleaned heavy oil is less than 5000 mPa·s, the size of the groove on the dedicated measuring device can be designed and adjusted so that the ring height of the heavy oil ring formed is 2 to 3 mm; when the viscosity of the cleaned heavy oil is greater than 5000 mPa·s, the size of the groove on the dedicated measuring device can be designed and adjusted so that the ring height of the heavy oil ring formed is 2 to 5 mm.

[0018] (2) Fill the groove of the special measuring device with heavy oil to form a heavy oil ring. After aging for 48 hours under reservoir temperature conditions, weigh the total mass of the special measuring device containing the heavy oil ring and record it as m2;

[0019] (3) Place the aged special measuring device containing the heavy oil ring in a conical flask, and then pour the oil displacement agent solution to be evaluated into the conical flask so that the oil displacement agent solution completely immerses the groove on the special measuring device;

[0020] (4) placing the conical flask containing the oil displacement agent solution and the special measuring device in step (3) into a constant temperature shaking table, setting the reservoir temperature and shaking speed, and conducting an oil washing experiment;

[0021] (5) After the oil washing experiment is completed, take out the special measuring device, wipe the entire surface of the special measuring device clean, and weigh the total mass again, which is recorded as m3;

[0022] (6) Calculate the oil washing efficiency by the following formula:

[0023] Where, m1 is the mass of the dedicated measuring device;

[0024] m2 - the total mass of heavy oil and special measuring devices before washing;

[0025] m3 - the total mass of heavy oil and special measuring devices after oil washing;

[0026] η - oil washing efficiency.

[0027] Furthermore, in the method for rapidly evaluating the cleaning efficiency of an oil-displacing agent for heavy oil, the dedicated measuring device comprises two detachable parts, namely, device I and device II; wherein device I and device II are fixedly connected to form the groove. The detachable design facilitates thorough cleaning of the dedicated measuring device, preventing residue from affecting the next evaluation result.

[0028] Furthermore, in the method for rapidly evaluating the cleaning efficiency of an oil-displacing agent for heavy oil, the device I and the device II are fixedly connected to form an annular groove.

[0029] Furthermore, the device I and the device II described in the method for rapidly evaluating the cleaning efficiency of an oil-displacing agent on heavy oil are fixedly connected by threads.

[0030] Furthermore, the device I described in the method for rapidly evaluating the cleaning efficiency of the oil-displacing agent for heavy oil consists of a cylindrical rod I and a screw fixed to one end of the cylindrical rod I, wherein the difference between the outer diameter of the cylindrical rod I and the outer diameter of the screw is 2-5 mm; the device II consists of a cylindrical rod II and a screw hole provided at the center of one end of the cylindrical rod II, the screw hole cooperates with the screw of the cylindrical rod I, wherein the difference between the outer diameter of the cylindrical rod II and the diameter of the screw hole is 2-5 mm; the outer diameter of the cylindrical rod I is the same as the outer diameter of the cylindrical rod II; and the difference between the length of the screw and the depth of the screw hole is 2-5 mm.

[0031] A special measuring device for the above method of quickly evaluating the cleaning efficiency of oil displacement agent on heavy oil is provided on the special measuring device, which is used to form a groove for forming a heavy oil ring with a ring height of 2-5mm and a ring width of 2-5mm.

[0032] The beneficial effect of the present invention is that the interconnected pores in actual reservoir rocks can be regarded as capillaries of extremely low diameter. Due to the different wettability of the porous surface to the two phases (water and oil), different forces are distributed on the contact surface. When the contact surface is small enough, it will cause bending inside one of the phases. This means that the pressures of the two phases on the contact surface are not equal. In this case, the lower pressure is related to the phase with the inward curvature of its surface. This difference is called capillary pressure. Capillary pressure is related to different factors such as the properties of the rock and fluid and the structure of the porous medium. The heavy oil located in the pores of the reservoir rock will be affected by the capillary force and is not easy to clean.

[0033] In addition to capillary forces, heavy oil in actual reservoirs is also subject to the Jamin effect. This is a drag effect whereby bubbles in oil or oil droplets in water try to maintain a spherical shape due to interfacial tension. When these bubbles or oil droplets pass through small pore throats, the difference in radius between the pore and throat causes the capillary forces at the ends of the bubbles or oil droplets to manifest as resistance. To pass through the smaller throat, the bubbles or oil droplets must stretch and change shape. This deformation consumes some energy, slowing their movement and adding additional resistance. This phenomenon is known as the Jamin effect. This effect constrains the heavy oil, making it less easily displaced by oil displacement agents.

[0034] To address these two influencing factors and make the evaluation method more practical, the present inventors first innovatively designed a dedicated measuring device with a groove designed to form a heavy oil ring with a ring height of 2-5 mm and a ring width of 2-5 mm. This heavy oil ring simulates the actual state of heavy oil in formation pores, making it more scientific, realistic, and objective to evaluate the cleaning efficiency of oil displacement agents.

[0035] In addition, the present invention abandons the traditional evaluation method of first cleaning the crude oil washed with the oil displacement agent and then obtaining a poor quality test idea. Instead, it innovatively provides a method based on a designed special measuring device to obtain the poor quality by directly processing the special measuring device itself. This completely avoids the phenomenon of weighing errors caused by incomplete treatment of problems such as crude oil adhesion. The operation is fast, simple and has low error. More importantly, it is suitable for heavy oil with high viscosity and poor fluidity. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the structure of the dedicated measuring device in a specific embodiment of the present invention.

[0037] Figure 2 This is a state diagram of the dedicated measurement device used in the specific embodiment of the present invention.

[0038] Figure 3 This is a schematic diagram of a device for using an oil displacement agent to clean heavy oil in an evaluation method according to a specific embodiment of the present invention.

[0039] Among them, 1 is cylindrical rod I, 2 is screw, 3 is cylindrical rod II, 4 is screw hole, 5 is special measuring device, 6 is conical flask, 7 is oil displacement agent solution, 8 is heavy oil ring, and 9 is groove. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is described in detail below with reference to the accompanying drawings. The above description is only a specific embodiment and steps of the method of the present invention and is not intended to limit the scope of the present invention. Any equivalent changes and modifications made by any person skilled in the art without departing from the concept and principle of the present invention should fall within the scope of protection of the present invention.

[0041] The method for rapidly evaluating the cleaning efficiency of an oil-displacing agent on heavy oil comprises the following steps:

[0042] (1) Accurately weigh the mass of the special measuring device 5 provided with the groove 9, recorded as m1, with an accuracy of 0.001 g.

[0043] The dedicated measuring device 5 is composed of two detachable parts, namely device I and device II.

[0044] The device I consists of a cylindrical rod I1 and a screw 2 fixed to one end of the cylindrical rod I1, wherein the difference between the outer diameter R of the cylindrical rod I1 and the outer diameter r of the screw 2 (ie, the ring width) Rr=2-5mm.

[0045] Device II consists of a cylindrical rod II3 and a screw hole 4 located at the center of one end of the cylindrical rod II3. The screw hole 4 cooperates with the screw rod 2 of the cylindrical rod I1, and the difference between the outer diameter of the cylindrical rod II3 and the diameter of the screw hole 4 (i.e., the ring width) is 2-5mm.

[0046] The outer diameter of the cylindrical rod body I1 is the same as the outer diameter of the cylindrical rod body II3.

[0047] The difference between the length l1 of the screw rod 2 and the depth l2 of the screw hole 4 (ie the ring height) l1-l2=2-5 mm.

[0048] When the viscosity of the cleaned heavy oil is less than 5000 mPa·s, the length l1 of the screw 2 and the depth l2 of the screw hole 4 can be adjusted to make l1-l2=2-3 mm, so that the height of the heavy oil ring formed by the groove is 2-3 mm.

[0049] When the viscosity of the cleaned heavy oil is greater than 5000 mPa·s, the length l1 of the screw 2 and the depth l2 of the screw hole 4 can be adjusted to make l1-l2=2-5 mm, so that the height of the heavy oil ring formed by the groove is 2-5 mm.

[0050] The screw rod 2 of the device I is inserted into the screw hole 4 of the device II and screwed together to form an annular groove.

[0051] (2) drip or fill the heavy oil into the annular groove formed by the screw 2 and the screw hole 4, ensuring that the groove is completely filled with heavy oil; after tightening, carefully and quickly wipe off the excess heavy oil with a wipe paper to form a regular and flat heavy oil ring 8 in the annular groove, and then weigh the total mass of the device containing the heavy oil ring after aging for 48 hours under reservoir temperature conditions, recorded as m2;

[0052] (3) Place the aged special measuring device containing the heavy oil ring in a conical flask 6, and then pour the oil-displacing agent solution 7 to be evaluated into the conical flask 6 so that the oil-displacing agent solution 7 completely submerges the groove 9 on the special measuring device 5;

[0053] (4) placing the conical flask 6 containing the oil-displacing agent solution 7 and the special measuring device 5 in step (3) into a constant temperature shaking table, setting the reservoir temperature and shaking speed, and conducting an oil washing experiment;

[0054] (5) After the oil washing experiment is completed, carefully remove the special measuring device 5 with tweezers, carefully wipe off the oil displacement solution on the surface of the heavy oil ring with a wipe, wipe the rest of the device dry, and weigh the total mass again, recorded as m3;

[0055] (6) Calculate the oil washing efficiency by the following formula:

[0056] Where, m1 is the mass of the dedicated measuring device;

[0057] m2 - the total mass of heavy oil and special measuring devices before washing;

[0058] m3 - the total mass of heavy oil and special measuring devices after oil washing;

[0059] η - oil washing efficiency.

[0060] Application Example 1

[0061] The evaluation method is used to evaluate the effect of the oscillation speed on the oil washing efficiency during the oil displacement process of the oil displacement agent.

[0062] 1. Experimental Method: During the experiment, the constant temperature shaker temperature was set at 50°C, the viscosity of the heavy oil was 3510.8 mPa·s, and the oil-water interfacial tension of the oil displacement agent was 0.009 mN / m. The constant temperature shaker was set at different oscillation speeds and the experiment was carried out according to the above method. Each experiment was repeated three times. The oil washing efficiency was calculated using the above formula (1) and the average value was taken.

[0063] 2. Experimental results: See Table 1 for specific results.

[0064] Table 1 Oil washing efficiency at different oscillation speeds

[0065]

[0066]

[0067] 3. Data Analysis

[0068] 1. As can be seen from Table 1, the faster the vibration speed, the higher the oil washing efficiency.

[0069] 2. It can be seen from the average deviation value that the evaluation method of the present invention has good stability and accuracy.

[0070] Application Example 2

[0071] The evaluation method is used to evaluate the effect of interfacial tension of oil displacement agents on oil washing efficiency.

[0072] 1. Experimental Method: Set the shaker's shaking speed to 150 r / min and the temperature to 50°C. Select oil-displacing agents with different interfacial tensions for oil washing, and measure the oil-washing efficiency of different systems. Each experiment is repeated three times, and the oil-washing efficiency is calculated using formula (1) and the average value is taken.

[0073] 2. Experimental results: See Table 2 for specific results.

[0074] Table 2 Oil washing efficiency of oil displacement agents with different interfacial tensions

[0075]

[0076] 3. Data Analysis

[0077] 1. As can be seen from Table 2, the lower the interfacial tension between the oil displacement agent and the heavy oil, the higher the oil washing efficiency.

[0078] 2. It can be seen from the average deviation value that this evaluation method has high stability and accuracy.

[0079] Application Example 3

[0080] The evaluation method is used to evaluate the effect of oil displacement agent viscosity on oil washing efficiency.

[0081] 1. Experimental Method: The shaking speed of the thermostatic shaker was set at 150 r / min, the temperature was set at 50°C, and the oil-water interfacial tension was maintained at 0.861 mN / m. Oil displacement agents of different viscosities were prepared and the oil washing efficiency of different systems was measured. Each experiment was repeated three times, and the oil washing efficiency was calculated using formula (1) and the average value was taken.

[0082] 2. Experimental results: See Table 3 for specific results.

[0083] Table 3 Oil washing efficiency of oil displacement agents with different viscosities

[0084]

[0085] 3. Data Analysis

[0086] 1. As shown in Table 3, the viscosity of the oil displacement agent has a certain influence on the oil washing efficiency. Under the condition of the same oil-water interfacial tension, the higher the viscosity, the higher the oil washing efficiency.

[0087] 2. The stability and accuracy of the evaluation method can be seen from the average deviation value.

[0088] Comparative Example 1

[0089] The oil washing efficiency of the oil displacing agent was evaluated using the existing evaluation method of the following steps.

[0090] 1. Experimental methods:

[0091] 1) Mix the simulated formation sand and the target block crude oil in a 4:1 ratio (mass ratio), place it in a constant temperature drying oven, and age it at reservoir temperature for 7 days, stirring it once a day to ensure uniform mixing of the oil sand;

[0092] 2) Prepare a 0.3% oil displacement agent solution using injection water from the target area;

[0093] 3) Accurately weigh approximately 5 g of aged oil sand into a 100 mL conical flask and determine its mass as m1 to the nearest 0.001 g.

[0094] 4) Add 50 g of the prepared oil displacement agent solution with a viscosity of 26.3 mPa·s to the sample in step 3), and measure the oil-water interfacial tension to be 0.861 mN / m. After thorough mixing, let it stand at a reservoir temperature of 50°C for 48 h;

[0095] 5) After step 4), the floating crude oil in the oil-displacing agent solution and the crude oil on the bottle wall are wiped out with clean cotton yarn, and the oil-displacing agent solution is poured out. The conical flask is placed in a 105° C. oven and dried to a constant weight to obtain m2;

[0096] 6) Elute the oil sands from step 5) with petroleum ether until the petroleum ether is colorless. Place the conical flask containing the formation sand after the crude oil is completely eluted in a 120°C oven and dry it to a constant weight, and weigh it to obtain m3.

[0097] Each experiment was repeated three times, and the oil washing efficiency was calculated using formula (2) and the average value was taken.

[0098] Finally, the oil washing efficiency is calculated according to the formula:

[0099]

[0100] Where: σ——oil washing rate;

[0101] m1——total mass of oil sand and conical flask before oil washing, g;

[0102] m2——total mass of oil sand and conical flask after oil washing, g;

[0103] m3——Total mass of formation sand and conical flask after elution, g.

[0104] 2. Experimental Data

[0105] Table 4 Evaluation of oil washing efficiency of oil displacement agent by oil sand washing method

[0106]

[0107] 3. Experimental data analysis:

[0108] 1. As shown in Table 4, the oil sand washing method is highly unstable when evaluating the oil displacement agent's efficiency for heavy oil with a viscosity of 26.3 mPa·s. Furthermore, significant test errors are present during the experiment due to factors such as heavy oil adhesion. The higher the viscosity of the heavy oil, the greater the measurement error due to factors such as adhesion, resulting in more unstable results.

[0109] 2. The average deviation value of the comparison ratio shows that the stability of the existing evaluation method is poor, the average deviation of the experiment is large, and the accuracy is also low.

Claims

1. A method for rapidly evaluating the cleaning efficiency of an oil displacement agent for heavy oil, characterized in that: The following steps are involved: (1) Accurately weigh the mass of a special measuring device with a groove, recorded as m1; the groove is used to form a heavy oil ring with a ring height of 2-5 mm and a ring width of 2-5 mm; When the viscosity of the cleaned heavy oil is less than 5000 mPa·s, the height of the heavy oil ring formed by the groove on the dedicated measuring device is 2-3 mm; The special measuring device is composed of two detachable parts, namely device I and device II; wherein device I and device II are fixedly connected by threads to form the annular groove; The device I is composed of a cylindrical rod I and a screw fixed to one end of the cylindrical rod I, wherein the difference between the outer diameter of the cylindrical rod I and the outer diameter of the screw is 2-5 mm; the device II is composed of a cylindrical rod II and a screw hole provided at the center of one end of the cylindrical rod II, the screw hole being matched with the screw of the cylindrical rod I, wherein the difference between the outer diameter of the cylindrical rod II and the diameter of the screw hole is 2-5 mm; the outer diameter of the cylindrical rod I is the same as the outer diameter of the cylindrical rod II; the difference between the length of the screw and the depth of the screw hole is 2-5 mm; (2) Fill the groove of the special measuring device with heavy oil to form a heavy oil ring. After aging for 48 hours under reservoir temperature conditions, weigh the total mass of the special measuring device containing the heavy oil ring and record it as m 2; (3) Place the aged special measuring device containing the heavy oil ring in a conical flask, and then pour the oil displacement agent solution to be evaluated into the conical flask so that the oil displacement agent solution completely immerses the groove on the special measuring device; (4) Place the conical flask containing the oil displacement agent solution and the special measuring device in step (3) into a constant temperature shaker, set the reservoir temperature and shaking speed, and conduct the oil washing experiment; (5) After the oil washing experiment is completed, take out the special measuring device, wipe the entire surface of the special measuring device clean, and weigh the total mass again, which is recorded as m3; (6) Calculate the oil washing efficiency using the following formula: ; Where, m1 is the mass of the dedicated measuring device; m 2-Total mass of heavy oil and special measuring devices before oil washing; m3 - the total mass of heavy oil and special measuring devices after oil washing; η - oil washing efficiency.

2. A special measuring device for the method for rapidly evaluating the cleaning efficiency of an oil displacement agent on heavy oil according to claim 1, characterized in that: The special measuring device is provided with a groove for forming a heavy oil ring with a ring height of 2-5 mm and a ring width of 2-5 mm.

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