Detection method of oil displacement rate
The oil-containing sand is prepared by formation sand and oil-cleaning treatment and heat weight loss analysis is carried out, which solves the error problem in oil-cleaning rate detection and achieves a more accurate and environmentally friendly oil-cleaning rate calculation.
Patent Information
- Application Number
- CN202510049894.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-13
- Publication Date
- 2025-08-12
Smart Images
Figure BDA0005239666360000021 
Figure BDA0005239666360000041 
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Abstract
Description
Technical Field
[0001] The invention relates to a method for detecting an oil washing rate, and belongs to the technical field of oilfield exploitation. Background Art
[0002] Surfactants are oilfield chemicals that can significantly increase oil recovery. Whether used as a primary or auxiliary flooding agent, surfactants play an invaluable role in significantly improving oil recovery. Currently, chemical flooding technologies such as binary composite flooding, ternary composite flooding, and heterogeneous composite flooding, which have been industrialized both domestically and internationally, all use surfactants as a key component of the flooding system.
[0003] The oil removal efficiency (OER) is the percentage of immobilized oil removed from a formation by a detergent. It is a key indicator for evaluating the performance of detergents (surfactants and their flooding systems). With the continued expansion of applications and in-depth theoretical research on surfactants and their flooding systems, the OER has become a key indicator for evaluating and screening surfactants and their combined flooding systems, and is attracting increasing attention.
[0004] The oil recovery rate of surfactants and their composite systems is typically determined by soaking oil sands with a fixed oil content using a surfactant solution or composite system. The recovery rate is calculated by measuring the difference in oil content before and after the wash. The main technical difficulty of this method lies in accurately measuring the oil content of oil sands before and after the wash.
[0005] The industry currently primarily determines the oil content of oil sands before washing by mixing crude oil and formation sand in a specific mass ratio, then aging the mixture in a constant temperature oven. Current methods for determining oil washing efficiency involve mixing simulated formation sand and crude oil in a specific ratio, aging the mixture in an oven at reservoir temperature for seven days, and obtaining oil sands with a fixed oil content. This process cannot guarantee that all the crude oil is adsorbed onto the surface of the simulated formation sand; a small amount of crude oil may remain free, leading to inaccurate initial oil content in the oil sands and, in turn, significant errors in the calculated oil washing efficiency of surfactants or their composite systems.
[0006] As for the mass fraction of residual crude oil on oil sands after oil washing, the industry currently generally uses organic reagents such as petroleum ether to completely elute the residual oil on the oil sands after oil washing into an organic solvent, and then uses analytical techniques such as colorimetry to detect and calculate the content of residual oil on the oil sands after oil washing. For specific test methods, please refer to Section 6.9 of the China Petroleum and Chemical Corporation Enterprise Standard Q / SH CG0079-2021 "Technical Requirements for Surfactants for Oil Displacement". The large amount of organic reagents used in the implementation of this method poses an environmental pollution risk and will cause harm to the health of the inspectors, posing an occupational hazard risk. Moreover, during the implementation of this method, it is difficult to ensure that the residual oil on the oil sands is completely eluted, and the organic reagents evaporate during use, resulting in inaccurate measurement, which leads to large errors in the calculation results of the oil washing rate of the surfactant or its composite system. Summary of the Invention
[0007] The object of the present invention is to provide a method for detecting oil washing rate, which can solve the problem of large error in the results when determining the oil washing rate of oil washing agents such as surfactants on crude oil in oil sands.
[0008] In order to achieve the above objectives, the technical solution adopted by the oil washing rate detection method of the present invention is:
[0009] A method for detecting an oil washing rate comprises the following steps: preparing oil-bearing sand from formation sand, then washing the oil-bearing sand with an oil washing agent to obtain washed oil sand, then performing thermogravimetric analysis on the formation sand, the oil-bearing sand, and the washed oil sand, and finally calculating the oil washing rate using the thermogravimetric rates of the formation sand, the oil-bearing sand, and the washed oil sand.
[0010] The present invention's oil washing rate detection method calculates the oil washing rate using the thermal weight loss of formation sand, oil-bearing sand, and washed oil sand. This objectively reflects the ability of the oil washing agent to remove the oil film from the formation and reduce the amount of unavailable crude oil. This method eliminates the influence of free crude oil that is not fully adsorbed on the rock surface on the test results, making the test results more objective and more consistent with actual conditions. Furthermore, this method consumes a small amount of sample during the detection process and does not use any organic reagents other than crude oil, making it more environmentally friendly.
[0011] Preferably, the temperature range of thermal weight loss rate is 120°C to 600°C.
[0012] Preferably, the temperature range during thermogravimetric analysis is from room temperature to 700° C., the heating rate is 5 to 15° C. / min, and the atmosphere is oxygen or air.
[0013] Preferably, the calculation formula of the oil washing rate is as follows:
[0014]
[0015] Where η is the oil washing rate, w0 is the thermal weight loss rate of formation sand, w1 is the thermal weight loss rate of oil-bearing sand, and w2 is the thermal weight loss rate of oil sand after oil washing.
[0016] Preferably, the method for preparing oil-bearing sand from formation sand is as follows: the formation sand is immersed in dehydrated crude oil from the target block until adsorption equilibrium is reached, followed by solid-liquid separation. The resulting solid is then washed with hot water, and the washed solid is then dried to obtain the oil-bearing sand. Dehydration of the crude oil removes moisture, dissolved gas, and unstable light components, resulting in stable physical and chemical properties of the dehydrated crude oil, which improves the stability and reliability of analytical results.
[0017] Preferably, the temperature of the dehydrated crude oil is the same as the temperature of the target block oil reservoir, and the temperature of the hot water is higher than the freezing point of the crude oil.
[0018] Preferably, the oil washing treatment method includes the following steps: mixing the oil washing agent and oil-containing sands and then aging them, then separating the solid and the liquid, then washing the solid obtained by the solid-liquid separation with water, and then drying the washed solid to obtain oil sands after oil washing.
[0019] Preferably, the aging temperature is the same as the target block reservoir temperature.
[0020] Preferably, the oil cleaning agent is a surfactant solution or a composite system containing a surfactant.
[0021] In the present invention, the formation sand is simulated formation sand, or natural formation sand that has been subjected to oil washing treatment, and the oil content in the formation sand is zero. DETAILED DESCRIPTION
[0022] The present invention's method for detecting oil washing rate is a groundbreaking invention. It involves soaking formation sand in dehydrated crude oil, then washing it with hot water to remove free crude oil that is not fully adsorbed on the rock surface, thereby improving the accuracy of the test results. The oil washing process is then followed by thermogravimetric analysis of the formation sand, oil-bearing sand, and washed oil sand to fully volatilize and precipitate the crude oil in the rock, thereby improving the accuracy of the test results. Finally, the oil washing rate is calculated using the thermogravimetric rates of the formation sand, oil-bearing sand, and washed oil sand.
[0023] In some preferred embodiments, the method for preparing oil-bearing sand using formation sand is as follows: the formation sand is soaked in dehydrated crude oil from the target block until adsorption equilibrium is reached, followed by solid-liquid separation, and the solid obtained from the solid-liquid separation is washed with hot water, and the washed solid is then dried to obtain the oil-bearing sand; the temperature of the dehydrated crude oil is the same as the temperature of the target block's oil reservoir, and the temperature of the hot water is higher than the freezing point of the crude oil. The formation sand is soaked in the dehydrated crude oil from the target block for aging for a period of generally no less than 7 days. To accelerate adsorption equilibrium, the sand is stirred multiple times during this period to ensure that the crude oil is fully adsorbed on the surface of the simulated formation sand or natural formation sand; after the soaking and aging process is completed, the sand is rinsed with hot water at a temperature no lower than the freezing point of the crude oil to simulate a water flooding and oil washing process to elute the free crude oil not adsorbed on the simulated formation sand or natural formation sand.
[0024] In some preferred embodiments, the oil washing method includes the following steps: mixing the oil washing agent and the oil-containing sand and then aging them, then performing solid-liquid separation, then washing the solid obtained by the solid-liquid separation with water, and then drying the washed solid to obtain the washed oil sand. During the oil washing process, the ratio of the oil washing agent to the oil-containing sand can be determined according to the specific situation or needs; the oil washing process can adopt a static oil washing mode or an oscillating dynamic oil washing mode; in order to ensure that the detection process is more in line with the actual situation, the oil washing setting temperature should be the reservoir formation temperature; after the oil washing is completed, the oil-containing sand should be flushed to wash off the oil washing agent adhering to the oil sand surface to prevent the oil washing agent adhering to the oil sand surface from affecting the detection results.
[0025] In some preferred embodiments, the aging temperature is the same as the target block reservoir temperature, and the aging time is no less than 24 hours.
[0026] In some preferred embodiments, the temperature range of the thermal weight loss rate is 120°C to 600°C. During thermal weight loss analysis, the thermal weight loss curve is first detected using a thermal weight loss analyzer, and then the thermal weight loss rate corresponding to the temperature range of 120°C to 600°C is obtained from the thermal weight loss curve. The weight loss before 120°C is mainly caused by water evaporation and is not considered within the scope of the oil washing rate detection method; the weight loss between 120°C and 600°C is caused by the oxidation and degradation of crude oil, which is the key data to be recorded by this method. After the temperature reaches 600°C, the oxidation and degradation of crude oil is complete, thus completing the purpose of recording key data in this method.
[0027] In some preferred embodiments, the temperature range during thermogravimetric analysis is from room temperature to 700° C., the heating rate is 5-15° C. / min, and the atmosphere is oxygen or air.
[0028] In some preferred embodiments, the calculation formula for the oil washing rate is as follows:
[0029]
[0030] Where η is the oil washing rate, w0 is the thermal weight loss rate of formation sand, w1 is the thermal weight loss rate of oil-bearing sand, and w2 is the thermal weight loss rate of oil sand after oil washing.
[0031] The deduction process of the thermal weight loss rate calculation formula is as follows:
[0032] During the thermal gravimetric analysis of oil sand, the weight loss includes the crude oil adsorbed on the sand surface and the weight loss of the natural formation sand or simulated formation sand used in the experiment during the thermal analysis process.
[0033] So: Thermal weight loss rate of oil sands
[0034] During the thermal gravimetric analysis of oil-bearing sand after oil washing, the weight loss includes the crude oil remaining adsorbed on the sand surface after oil washing and the weight loss of the natural formation sand or simulated formation sand used in the experiment during the thermal analysis process.
[0035] So: The thermal weight loss rate of oil sand after oil washing
[0036] From formula (1), we can get:
[0037] From formula (2), we can get:
[0038] Throughout the experimental process, the quality of the natural formation sand or simulated formation sand used is certain.
[0039] so:
[0040] From formula (5), we can get:
[0041] The oil washing rate η represents the ratio of oil film stripping from the formation to reduce the proportion of immobile crude oil.
[0042] so:
[0043] Substituting formula (6) into formula (7), we get:
[0044]
[0045] The symbols in the formula have the following meanings:
[0046] η: oil washing rate;
[0047] w0: thermal weight loss rate of formation sand;
[0048] w1: thermal weight loss rate of oil sand;
[0049] w2: thermal weight loss rate of oil sand after oil washing;
[0050] m砂 : The quality of natural formation sand or simulated formation sand used in the experimental process;
[0051] m 油1 : The mass of crude oil adsorbed by natural formation sand or simulated formation sand, that is, the mass of crude oil adsorbed by oil-bearing sand;
[0052] m 油2 : The mass of crude oil remaining adsorbed in oil sands after oil sands are washed.
[0053] The technical solution of the present invention will be further described below with reference to specific embodiments.
[0054] Example 1
[0055] The oil washing rate detection method of this embodiment specifically includes the following steps:
[0056] (1) Take natural core sand (formation sand) of 50-80 mesh that has been treated with oil washing, wash, dry, group, weigh, and then soak it in dehydrated crude oil from an oil field. Constant temperature aging is performed at reservoir temperature for 7 days, during which the sand is stirred several times to ensure that the crude oil is fully adsorbed on the surface of the formation sand. After the constant temperature aging is completed, the excess crude oil is poured out and filtered out. The oil sand is fully washed with hot water and dried at reservoir temperature for 24 hours to obtain oil-containing sand for use.
[0057] (2) The oil sand was immersed in a 3% by mass A3-2 surfactant solution (the mass ratio of the oil sand to the surfactant solution was 1:10), and the oil was washed by keeping it in a closed state at the reservoir temperature for 24 h. The crude oil adhering to the liquid surface and the bottle wall was wiped off with absorbent cotton and the surfactant solution was poured off. The surfactant adhering to the surface of the oil sand was washed with distilled water, and the washed oil sand was obtained after drying.
[0058] (3) The formation sand and oil-bearing sand in step (1) and the oil-washed oil sand in step (2) were subjected to thermogravimetric analysis using a TGA thermogravimetric analyzer from METTLERTOLEDO, with a temperature range of room temperature to 700°C, a heating rate of 10°C / min, and a high-purity oxygen atmosphere. Based on the thermogravimetric curves, the thermogravimetric rates in the temperature range of 120°C to 600°C were obtained, and the thermogravimetric rate w0 of the formation sand, the thermogravimetric rate w1 of the oil-bearing sand, and the thermogravimetric rate w2 of the oil-washed oil sand were obtained to be 11.43%, 26.55%, and 21.54%, respectively. The oil washing rate was then calculated.
[0059] Example 2
[0060] The oil washing rate detection method of this embodiment specifically includes the following steps:
[0061] (1) Take natural core sand (formation sand) of 50-80 mesh that has been treated with oil washing, wash, dry, group, weigh, and then soak it in dehydrated crude oil from an oil field. Constant temperature aging is performed at reservoir temperature for 7 days, during which the sand is stirred several times to ensure that the crude oil is fully adsorbed on the surface of the formation sand. After the constant temperature aging is completed, the excess crude oil is poured out and filtered out. The oil sand is fully washed with hot water and dried at reservoir temperature for 24 hours to obtain oil-containing sand for use.
[0062] (2) The oil sand was immersed in a B-1 surfactant solution with a mass fraction of 3% (the mass ratio of oil sand to surfactant solution was 1:10), and the oil was washed by keeping it in a closed state at a constant temperature for 24 hours at the reservoir temperature. The crude oil adhering to the liquid surface and the bottle wall was wiped off with absorbent cotton and the surfactant solution was poured off. The surfactant adhering to the surface of the oil sand was washed with distilled water, and the washed oil sand was obtained after drying.
[0063] (3) The formation sand and oil-bearing sand in step (1) and the oil-washed oil sand in step (2) were subjected to thermogravimetric analysis using a TGA thermogravimetric analyzer from METTLERTOLEDO, with a temperature range of room temperature to 700°C, a heating rate of 5°C / min, and a high-purity oxygen atmosphere. Based on the thermogravimetric curves, the thermogravimetric rates in the temperature range of 120°C to 600°C were obtained, and the thermogravimetric rate w0 of the formation sand, the thermogravimetric rate w1 of the oil-bearing sand, and the thermogravimetric rate w2 of the oil-washed oil sand were obtained to be 11.43%, 28.33%, and 23.33%, respectively. The oil washing rate was then calculated.
[0064] Example 3
[0065] The oil washing rate detection method of this embodiment specifically includes the following steps:
[0066] (1) Take natural core sand (formation sand) of 50-80 mesh that has been treated with oil washing, wash, dry, group, weigh, and then soak it in dehydrated crude oil from an oil field. Constant temperature aging is performed at reservoir temperature for 7 days, during which the sand is stirred several times to ensure that the crude oil is fully adsorbed on the surface of the formation sand. After the constant temperature aging is completed, the excess crude oil is poured out and filtered out. The oil sand is fully washed with hot water and dried at reservoir temperature for 24 hours to obtain oil-containing sand for use.
[0067] (2) The oil-bearing sand is immersed in an oil displacement system (3% A3-2 + 1% NaCl) prepared by A3-2 type surfactant, sodium chloride and water (the mass ratio of oil-bearing sand to oil displacement system is 1:10), and the oil is kept in a closed state at a constant temperature for 24 hours at the reservoir temperature for oil washing. The crude oil adhering to the liquid surface and the bottle wall is wiped off with absorbent cotton and the oil displacement system is poured out. The oil displacement system adhering to the surface of the oil sand is washed with distilled water, and the oil sand after oil washing is obtained after drying.
[0068] (3) The formation sand and oil-bearing sand in step (1) and the oil-washed oil sand in step (2) were subjected to thermogravimetric analysis using a TGA thermogravimetric analyzer from METTLERTOLEDO, with a temperature range of room temperature to 700°C, a heating rate of 15°C / min, and a high-purity oxygen atmosphere. Based on the thermogravimetric curves, the thermogravimetric rates in the temperature range of 120°C to 600°C were obtained, and the thermogravimetric rate w0 of the formation sand, the thermogravimetric rate w1 of the oil-bearing sand, and the thermogravimetric rate w2 of the oil-washed oil sand were obtained to be 11.43%, 27.15%, and 23.51%, respectively. The oil washing rate was then calculated.
[0069] Example 4
[0070] The oil washing rate detection method of this embodiment specifically includes the following steps:
[0071] (1) Take natural core sand (formation sand) of 50-80 mesh that has been treated with oil washing, wash, dry, group, weigh, and then soak it in dehydrated crude oil from an oil field. Constant temperature aging is performed at reservoir temperature for 7 days, during which the sand is stirred several times to ensure that the crude oil is fully adsorbed on the surface of the formation sand. After the constant temperature aging is completed, the excess crude oil is poured out and filtered out. The oil sand is fully washed with hot water and dried at reservoir temperature for 24 hours to obtain oil-containing sand for use.
[0072] (2) The oil-bearing sand is immersed in an oil displacement system (3% B-1 + 1% NaCl) prepared by B-1 type surfactant, sodium chloride and water (the mass ratio of oil-bearing sand to oil displacement system is 1:10), and is kept in a closed and constant temperature environment for 24 hours at the reservoir temperature for oil washing. The crude oil adhering to the liquid surface and the bottle wall is wiped off with absorbent cotton and the oil displacement system is poured out. The oil displacement system adhering to the surface of the oil sand is washed with distilled water, and the washed oil sand is obtained after drying.
[0073] (3) The formation sand and oil-bearing sand in step (1) and the oil-washed oil sand in step (2) were subjected to thermogravimetric analysis using a TGA thermogravimetric analyzer from METTLERTOLEDO, with a temperature range of room temperature to 700°C, a heating rate of 10°C / min, and a high-purity oxygen atmosphere. Based on the thermogravimetric curves, the thermogravimetric rates in the temperature range of 120°C to 600°C were obtained, and the thermogravimetric rate w0 of the formation sand, the thermogravimetric rate w1 of the oil-bearing sand, and the thermogravimetric rate w2 of the oil-washed oil sand were obtained to be 11.43%, 29.17%, and 23.69%, respectively. The oil washing rate was then calculated.
[0074] Example 5
[0075] The oil washing rate detection method of this embodiment specifically includes the following steps:
[0076] (1) Take natural core sand (formation sand) of 50-80 mesh that has been treated with oil washing, wash, dry, group, weigh, and then soak it in dehydrated crude oil from an oil field. Constant temperature aging is performed at reservoir temperature for 7 days, during which the sand is stirred several times to ensure that the crude oil is fully adsorbed on the surface of the formation sand. After the constant temperature aging is completed, the excess crude oil is poured out and filtered out. The oil sand is fully washed with hot water and dried at reservoir temperature for 24 hours to obtain oil-containing sand for use.
[0077] (2) The oil-bearing sand is immersed in an oil displacement system (0.1% 1630S + 0.5% B-1 + 1% NaCl) prepared by B-1 type surfactant, sodium chloride, 1630S polymer and water (the mass ratio of oil-bearing sand to oil displacement system is 1:10), and the oil is kept in a closed state at a constant temperature for 24 hours at the reservoir temperature for oil washing. The crude oil adhering to the liquid surface and the bottle wall is wiped off with absorbent cotton and the oil displacement system is poured out. The oil displacement system adhering to the surface of the oil sand is washed with distilled water, and the oil sand after oil washing is obtained after drying.
[0078] (3) The formation sand and oil-bearing sand in step (1) and the oil-washed oil sand in step (2) were subjected to thermogravimetric analysis using a TGA thermogravimetric analyzer from METTLERTOLEDO, with a temperature range of room temperature to 700°C, a heating rate of 10°C / min, and a high-purity oxygen atmosphere. Based on the thermogravimetric curves, the thermogravimetric rates in the temperature range of 120°C to 600°C were obtained, and the thermogravimetric rate w0 of the formation sand, the thermogravimetric rate w1 of the oil-bearing sand, and the thermogravimetric rate w2 of the oil-washed oil sand were obtained to be 11.43%, 28.49%, and 24.73%, respectively. The oil washing rate was then calculated.
[0079] Example 6
[0080] The oil washing rate detection method of this embodiment specifically includes the following steps:
[0081] (1) Take natural core sand (formation sand) of 50-80 mesh that has been treated with oil washing, wash, dry, group, weigh, and then soak it in dehydrated crude oil from an oil field. Constant temperature aging is performed at reservoir temperature for 7 days, during which the sand is stirred several times to ensure that the crude oil is fully adsorbed on the surface of the formation sand. After the constant temperature aging is completed, the excess crude oil is poured out and filtered out. The oil sand is fully washed with hot water and dried at reservoir temperature for 24 hours to obtain oil-containing sand for use.
[0082] (2) The oil-bearing sand is immersed in an oil displacement system (0.1% 1630S + 0.5% B-1 + 1% Na2CO3) prepared by B-1 type surfactant, sodium carbonate, 1630S polymer and water (the mass ratio of oil-bearing sand to oil displacement system is 1:10), and the oil is kept in a closed state at a constant temperature for 24 hours at the reservoir temperature for oil washing. The crude oil adhering to the liquid surface and the bottle wall is wiped off with absorbent cotton and the oil displacement system is poured out. The oil displacement system adhering to the surface of the oil sand is washed with distilled water, and the oil sand after oil washing is obtained after drying.
[0083] (3) The formation sand and oil-bearing sand in step (1) and the oil-washed oil sand in step (2) were subjected to thermogravimetric analysis using a TGA thermogravimetric analyzer from METTLERTOLEDO, with a temperature range of room temperature to 700°C, a heating rate of 10°C / min, and a high-purity oxygen atmosphere. Based on the thermogravimetric curves, the thermogravimetric rates in the temperature range of 120°C to 600°C were obtained, and the thermogravimetric rate w0 of the formation sand, the thermogravimetric rate w1 of the oil-bearing sand, and the thermogravimetric rate w2 of the oil-washed oil sand were obtained to be 11.43%, 28.04%, and 24.99%, respectively. The oil washing rate was then calculated.
[0084] Example 7
[0085] The oil washing rate detection method of this embodiment specifically includes the following steps:
[0086] (1) Take natural core sand (formation sand) of 50-80 mesh that has been treated with oil washing, wash, dry, group, weigh, and then soak it in dehydrated crude oil from an oil field. Constant temperature aging is performed at reservoir temperature for 7 days, during which the sand is stirred several times to ensure that the crude oil is fully adsorbed on the surface of the formation sand. After the constant temperature aging is completed, the excess crude oil is poured out and filtered out. The oil sand is fully washed with hot water and dried at reservoir temperature for 24 hours to obtain oil-containing sand for use.
[0087] (2) The oil sand was immersed in a 0.1% by mass 1630S polymer solution (the mass ratio of the oil sand to the polymer solution was 1:10), and the oil sand was kept in a closed and constant temperature environment for 24 h at the reservoir temperature for oil washing. The crude oil adhering to the liquid surface and the bottle wall was wiped off with absorbent cotton and the polymer solution was poured off. The polymer solution adhering to the surface of the oil sand was washed with distilled water, and the washed oil sand was obtained after drying.
[0088] (3) The formation sand and oil-bearing sand in step (1) and the oil-washed oil sand in step (2) were subjected to thermogravimetric analysis using a TGA thermogravimetric analyzer from METTLERTOLEDO, with a temperature range of room temperature to 700°C, a heating rate of 10°C / min, and a high-purity oxygen atmosphere. Based on the thermogravimetric curves, the thermogravimetric rates in the temperature range of 120°C to 600°C were obtained, and the thermogravimetric rate w0 of the formation sand, the thermogravimetric rate w1 of the oil-bearing sand, and the thermogravimetric rate w2 of the oil-washed oil sand were obtained to be 11.43%, 29.20%, and 28.29%, respectively. The oil washing rate was then calculated.
[0089] Example 8
[0090] The oil washing rate detection method of this embodiment specifically includes the following steps:
[0091] (1) Take natural core sand (formation sand) of 50-80 mesh that has been treated with oil washing, wash, dry, group, weigh, and then soak it in dehydrated crude oil from a certain oil field block. Constant temperature aging is performed at reservoir temperature for 7 days. During the period, it is stirred several times to ensure that the crude oil is fully adsorbed on the surface of the formation sand. After the constant temperature aging is completed, the excess crude oil is poured out and filtered out. The oil sand is fully washed with hot water and dried at reservoir temperature for 24 hours to obtain oil-containing sand for use.
[0092] (2) The oil sand was immersed in a 0.5% by mass SH-VI-7 surfactant solution (the mass ratio of the oil sand to the surfactant solution was 1:10), and after being fully mixed, the oil sand was kept in a closed state at the reservoir temperature for 24 h for oil washing. The crude oil adhering to the liquid surface and the bottle wall was wiped off with absorbent cotton and the surfactant solution was poured off. The oil sand was rinsed with distilled water to elute the surfactant solution adhering to the surface of the oil sand. The oil sand was obtained after drying.
[0093] (3) The formation sand and oil-bearing sand in step (1) and the oil-washed oil sand in step (2) were subjected to thermogravimetric analysis using a TGA thermogravimetric analyzer from METTLERTOLEDO, with a temperature range of room temperature to 650°C, a heating rate of 10°C / min, and a high-purity oxygen atmosphere. Based on the thermogravimetric curves, the thermogravimetric rates in the temperature range of 120°C to 600°C were obtained, and the thermogravimetric rate w0 of the formation sand, the thermogravimetric rate w1 of the oil-bearing sand, and the thermogravimetric rate w2 of the oil-washed oil sand were obtained to be 10.44%, 28.87%, and 22.11%, respectively. The oil washing rate was then calculated.
[0094] Example 9
[0095] This example repeats the experiment according to the experimental steps of Example 8.
[0096] After the experiment, the thermal weight loss rate in the temperature range of 120℃ to 600℃ was extracted according to the thermal weight loss curve. The thermal weight loss rate w0 of the formation sand was 10.44%, the thermal weight loss rate w1 of the oil sand was 29.01%, and the thermal weight loss rate w2 of the oil sand after oil washing was 22.28%. Then the oil washing rate was calculated.
[0097] Example 10
[0098] This example repeats the experiment according to the experimental steps of Example 8.
[0099] After the experiment, the thermal weight loss rate in the temperature range of 120℃ to 600℃ was extracted according to the thermal weight loss curve. The thermal weight loss rate w0 of the formation sand was 10.44%, the thermal weight loss rate w1 of the oil sand was 28.76%, and the thermal weight loss rate w2 of the oil sand after oil washing was 22.01%. Then the oil washing rate was calculated.
[0100] Comparative Example 1
[0101] (1) The simulated formation sand was mixed with dehydrated crude oil from a certain block in a mass ratio of 4:1, placed in an oven and aged at reservoir temperature for 7 days with stirring to obtain oil-bearing sand with an oil content of 20%.
[0102] (2) Immerse the oil sand in a 0.5% (mass fraction) X-1 surfactant solution (mass ratio of oil sand to surfactant solution is 1:10). After thorough mixing, allow to age at reservoir temperature for 24 hours. Use absorbent cotton to remove the crude oil adhering to the liquid surface and the bottle wall, and then pour off the surfactant solution. After drying, the oil sand is obtained.
[0103] (3) Rinse the dried oil sands with a small amount of petroleum ether several times and collect the rinsed petroleum ether in a volumetric flask. Rinse several times until the color of the rinsed petroleum ether does not change, then dilute to volume with petroleum ether.
[0104] (4) Use the dehydrated crude oil from this block and petroleum ether to accurately prepare crude oil petroleum ether solutions with concentrations of 0.05 g / L, 0.1 g / L, 0.2 g / L, 0.3 g / L, 0.4 g / L, and 0.5 g / L. Use a spectrophotometer to measure the absorbance at a wavelength of 220 nm, and draw a standard curve based on the measured absorbance values and the corresponding oil content.
[0105] (5) The absorbance of the crude oil petroleum ether solution in step (3) was measured using a spectrophotometer, and the residual oil content in the volumetric flask was calculated by substituting the absorbance into the standard curve. The residual oil content in the oily sand after washing was calculated to be 10.38% based on the mass of the oily sand used in step (2).
[0106] (6) Using the oil mass fractions of 20% and 10.38% before and after oil sand washing, the oil washing efficiency of the surfactant was calculated to be 48.12%.
[0107] Comparative Example 2
[0108] This comparative example repeated the experiment according to the experimental steps of comparative example 1.
[0109] In this comparative example, the oil content of the oil sand before and after oil washing is 20% and 11.73%, respectively. The calculated oil washing efficiency of the surfactant is 41.33%.
[0110] According to the experimental results of Examples 1-10, the oil washing rate was calculated. The calculation formula of the oil washing rate of Examples 1-10 is as follows:
[0111]
[0112] Where η is the oil washing rate, w0 is the thermal weight loss rate of formation sand, w1 is the thermal weight loss rate of oil-bearing sand, and w2 is the thermal weight loss rate of oil sand after oil washing.
[0113] The oil washing rates calculated based on the experimental results of Examples 1-10 and the oil washing rates of Comparative Examples 1-2 are shown in Table 1.
[0114] Table 1 Oil washing rates calculated based on the experimental results of Examples 1-10 and the oil washing rates of Comparative Examples 1-2
[0115]
[0116]
[0117] As shown in Table 1, in Examples 1-7, after soaking and aging the natural core sands with crude oil, they were thoroughly rinsed with hot water, and the free crude oil on the surface was eluted. The resulting oil-bearing sands were composed of a film of immobile crude oil. This simulated scenario involved high-magnitude water flooding of underground crude oil, leaving the remaining oil largely bound and immobile.
[0118] In Example 1, a 3% concentration of A3-2 surfactant solution was used as the oil washing agent. Under static conditions, the self-emulsifying and solubilizing ability of the surfactant was relied upon to strip the oil film from the core surface and reduce the immobilized crude oil. The oil washing rate was 37.38%.
[0119] In Example 2, a 3% concentration of B-1 surfactant solution was used as the oil washing agent. Under static conditions, the self-emulsifying and solubilizing ability of the surfactant was relied upon to strip the oil film from the core surface and reduce the immobilized crude oil. The oil washing rate was 34.18%.
[0120] In Example 3, a displacement system consisting of a 3% A3-2 surfactant solution and a 1% NaCl solution was used as the oil-washing agent. Under static conditions, the oil-washing efficiency was 26.85%, a decrease compared to Example 1. This indicates that the high concentration of NaCl inhibits the activity of the A3-2 surfactant, resulting in a decrease in its oil-washing performance and a lower oil-washing rate.
[0121] In Example 4, a displacement system consisting of a 3% B-1 surfactant solution and a 1% NaCl solution was used as the oil-washing agent. Under static conditions, the oil-washing efficiency was 35.86%, an improvement over Example 2. This indicates that the high concentration of NaCl enhances the activity of the B-1 surfactant, improving its oil-washing performance and increasing the oil-washing rate.
[0122] In Example 5, a ternary composite flooding system consisting of 0.5% B-1 surfactant, 0.1% 1630S polymer, and 1% NaCl was used as an oil washing agent, and the oil washing rate was 25.94%.
[0123] In Example 6, a ternary composite flooding system consisting of 0.5% B-1 surfactant, 0.1% 1630S polymer, and 1% NaCO was used as the oil wash agent, achieving an oil wash efficiency of 21.65%. Comparison of Examples 5 and 6 shows that NaCl significantly enhances the oil wash performance of the B-1 surfactant, and the NaCl-containing ternary composite flooding system achieves a higher oil wash efficiency.
[0124] Example 7 uses a 0.1% 1630S polymer solution as an oil washing agent. Since the polymer itself has no interfacial activity, it cannot achieve emulsification and solubilization under static conditions, so its oil washing rate is low, only 6.37%.
[0125] The experimental test results of Examples 1 to 7 demonstrate that this method can detect the oil removal rate of an oil-displacement surfactant or its composite system, objectively reflecting the ability of the surfactant or its composite system to remove the oil film from the formation and reduce the amount of unavailable crude oil. This method eliminates the influence of free crude oil that is not fully adsorbed on the rock surface on the test results, making the test results more objective and more consistent with actual conditions. Furthermore, this method consumes a small amount of sample during the test process and does not use any organic reagents other than crude oil, making it more environmentally friendly.
[0126] Examples 8, 9, and 10 are parallel experiments using this method to detect the oil washing rate of surfactant solutions. It can be seen that the test results of the three examples are similar, indicating that the detection error of this method is small.
[0127] Comparative Examples 1 and 2 are parallel experiments using an organic solvent elution method to test the oil removal efficiency of surfactants. The significant discrepancies in the results of these parallel experiments indicate significant experimental error. This method does not involve washing during the oil sand preparation process, which results in some free oil remaining unadsorbed on the core sand surface. While this method yields a high oil removal efficiency, it does not accurately reflect the surfactant's ability to remove immobilized crude oil. Furthermore, this method requires the use of large amounts of petroleum ether or other organic solvents, making it less environmentally friendly.
Claims
1. A method for detecting oil washing rate, characterized in that: The following steps are involved: Oil-bearing sand is prepared using formation sand, and then the oil-bearing sand is washed with an oil washing agent to obtain washed oil sand. The formation sand, oil-bearing sand and washed oil sand are then subjected to thermogravimetric analysis. Finally, the oil washing rate is calculated using the thermogravimetric rates of the formation sand, oil-bearing sand and washed oil sand.
2. The method for detecting oil washing rate as claimed in claim 1, wherein The temperature range of thermal weight loss rate is 120℃~600℃.
3. The detection method for oil washing rate as claimed in claim 1, wherein The temperature range during the thermogravimetric analysis is from room temperature to 700°C, the heating rate is 5-15°C / min, and the atmosphere is oxygen or air.
4. The detection method for oil washing rate as claimed in claim 1, wherein The calculation formula of oil washing rate is as follows: Where η is the oil washing rate, w0 is the thermal weight loss rate of formation sand, w1 is the thermal weight loss rate of oil-bearing sand, and w2 is the thermal weight loss rate of oil sand after oil washing.
5. The method for detecting the oil washing rate according to any one of claims 1 to 4, wherein The method for preparing oil-bearing sand using formation sand is as follows: the formation sand is soaked in dehydrated crude oil from the target block until adsorption equilibrium is reached, followed by solid-liquid separation, and the solid obtained by the solid-liquid separation is washed with hot water, and the washed solid is then dried to obtain oil-bearing sand.
6. The method for detecting the oil washing rate as claimed in claim 5, wherein: The temperature of the dehydrated crude oil is the same as the target block reservoir temperature, and the temperature of the hot water is higher than the freezing point of the crude oil.
7. The method for detecting the oil washing rate according to any one of claims 1 to 4, wherein: The oil washing treatment method includes the following steps: mixing the oil washing agent and oil-containing sand and then aging, then solid-liquid separation, then washing the solid obtained by solid-liquid separation with water, and then drying the washed solid to obtain oil sand after oil washing.
8. The method for detecting the oil washing rate as claimed in claim 7, wherein: The aging temperature is the same as the reservoir temperature in the target block.
9. The method for detecting the oil washing rate according to any one of claims 1 to 4, wherein: The oil cleaning agent is a surfactant solution or a composite system containing a surfactant.