Shale oil sample oil-water saturation determination method based on dry distillation technology

Abstract

The invention discloses a shale oil sample oil-water saturation determination method based on a dry distillation technology. The problem that the oil-water saturation of the shale oil reservoir rock sample is difficult to accurately measure by using a single sample is solved. Comprising the following steps: S1, preparing a full-diameter flaky shale sample to be detected; s2, performing a sample pore water removal experiment on the tested shale sample; s3, carrying out a low-temperature dry distillation water recovery rate measurement experiment; s4, carrying out low-temperature dry distillation, and measuring the mass of the moisture trap and the shale sample; s5, measuring the total volume of the shale sample; s6, removing oil from the shale sample; s7, dehumidifying the shale sample subjected to oil removal; s8, measuring the volume of the skeleton; s9, correcting and measuring the total volume of the fracture sample; and S10, calculating the oil-water saturation of the shale sample. According to the method, on the basis of a low-temperature dry distillation technology, the pore water of the shale sample and the oil-water saturation of the shale oil sample with the effective porosity can be determined on the same sample, and the determination and analysis method is convenient, rapid and accurate.

Description

Technical Field

[0001] This invention relates to the field of experimental testing technology in oil and gas exploration and development, and in particular to a method for determining the oil-water saturation of shale oil samples based on dry distillation technology. Background Technology

[0002] In recent years, shale oil and gas exploration and development has become a hot topic in China's oil and gas exploration. However, due to the late start of shale and mudstone exploration, many exploration and development technologies need to be improved or re-established to adapt to the lithological requirements of shale and mudstone. Oil-water saturation analysis technology is one of the key technologies in the field of experimental geological testing for shale and mudstone oil and gas exploration and development. Its analytical methods are also constrained by lithology, and conventional methods are no longer suitable for shale and mudstone samples. Shale and mudstone are dense, with low porosity and low permeability, making it difficult to accurately measure oil and water content within the pores. Moreover, shale and mudstone have well-developed bedding fractures and are brittle, easily generating fractures upon contact with water or dehydration, making them prone to fracture and breakage during experiments. Another characteristic of shale and mudstone is its complex water-bearing structure, containing not only pore water but also clay-adsorbed water and structural water. Structural water exists within the mineral lattice and has a high extraction temperature, thus not affecting saturation analysis of shale and mudstone. Clay-adsorbed water, however, exists in the interlayer of clay adsorption layers, adsorbed onto the surface of clay particles. Shale and mudstone particles are fine with a large specific surface area, resulting in a significant amount of clay-adsorbed water. Its extraction, or partial extraction, greatly impacts water content determination. Similar to pore water, it can generally be extracted at around 100℃, increasing the difficulty of pore water separation and determination. Conventional oil-water saturation analysis methods cannot separate and determine clay water and pore water, making it even more difficult to accurately determine the oil-water saturation of shale oil samples. The experimental results directly affect the level of shale oil reservoir research and the accuracy of reserve evaluation. To determine pore water in situ while retaining clay-adsorbed water, previous methods used two parallel samples. One sample was dewatered, and then both were heated and extracted under identical extraction times, conditions, and methods. The pore water content was calculated by difference, thus obtaining the effective pore space oil-water saturation of the shale oil rock sample. This method uses two samples, both requiring thermal extraction analysis. The sample analysis process is lengthy and labor-intensive. Furthermore, shale oil exhibits significant heterogeneity, with substantial differences between some parallel samples, which can affect the accuracy of saturation determination. Therefore, a convenient, rapid, and effective analytical method for fluid saturation in shale oil samples under pore water conditions is currently lacking.

[0003] High-frequency nuclear magnetic resonance (NMR) can measure pore water and crystallized / adsorbed water through T1-T2 simultaneous measurements, but it cannot remove pore water or crystallized / adsorbed water from the core. Moreover, the NMR method for determining the oil-water saturation of shale is still in the experimental stage, and the testing equipment and technology are not yet widely available. The measurement cost is high, and it is a high-end, unconventional measurement technology that cannot yet replace conventional shale oil-water saturation analysis technology. Summary of the Invention

[0004] This invention addresses the problem in the prior art that it is difficult to conveniently, quickly, and accurately analyze and determine the oil-water saturation of shale oil reservoir samples using a single sample. Instead, it provides a method for determining the oil-water saturation of shale oil samples based on dry distillation technology. This method achieves the in-situ retention of clay-adsorbed water in a single sample while simultaneously removing and measuring the pore oil-water content and effective porosity of the shale oil sample. The analytical method is convenient, fast, and accurate.

[0005] The present invention solves its problem through the following technical solution: A method for determining the oil-water saturation of shale oil samples based on dry distillation technology includes the following steps:

[0006] S1. Prepare full-diameter sheet-like shale samples for testing;

[0007] S2. Conduct a pore water removal experiment on the shale sample being tested;

[0008] S3. Low-temperature dry distillation experiment to determine water recovery rate of the shale sample under test;

[0009] S4. After low-temperature dry distillation of the shale sample, the mass of the moisture trap and the shale sample are measured.

[0010] S5. Determine the total volume of the shale sample;

[0011] S6. Remove oil from shale samples;

[0012] S7. Dehumidify the degreased shale sample;

[0013] S8. Determine the volume of the shale sample skeleton;

[0014] S9. Correction and determination of the total volume of the fractured sample;

[0015] S10. Calculate the oil-water saturation of the shale sample using the measured data.

[0016] Furthermore, the method for preparing full-diameter flaky shale samples in step S1 is as follows: under liquid nitrogen cooling protection, for shale obtained at a specified depth, prepare full-diameter flaky shale samples with the required thickness (10mm to 20mm); cut the prepared full-diameter flaky shale samples into shale samples with a mass of 10g to 35g along the direction perpendicular to the bedding and the bedding end face, which are the samples to be tested; store the prepared shale oil samples in liquid nitrogen or a freezer for later use, and record the sample number at the same time.

[0017] Furthermore, the specific method for the sample pore water removal experiment in step S2 of the tested shale sample is as follows: after the sample is subjected to two-dimensional nuclear magnetic resonance analysis, the sample is placed on the heating plate in the low-temperature dry distillation device, first evacuated, and then heated to 60°C. The sample is taken out every 2 hours for two-dimensional nuclear magnetic resonance analysis until the amount of pore water remaining after removal on the two-dimensional nuclear magnetic resonance spectrum is less than 0.02 mL, at which point the experiment is stopped.

[0018] Furthermore, the experimental method for determining the water recovery rate in step S3, low-temperature dry distillation, is as follows: After sealing a glass sample bottle containing a measured amount of water and freezing it in a freezer, the low-temperature dry distillation apparatus is adjusted. A water trap of known mass and a sample bottle containing a measured amount of water (with the cap removed) are placed on the water trap holder and the sample heating plate in the dry distillation apparatus, respectively. A vacuum is first drawn, and then the temperature is heated to 60°C and maintained for the experimental time specified in step S2. Heating is then stopped, the water trap and sample bottle are removed, and the mass of the water trap is weighed.

[0019] The collected water is determined by the mass difference before and after the water trap. On a Cartesian coordinate system, the water collected by the water trap is plotted on the x-axis, and the measured amount of water added to the glass bottle is plotted on the y-axis. A functional relationship between the two is established, and the regression equation y = k is obtained. w x, determine the correction factor k for collecting pore water. w .

[0020] Furthermore, the method for measuring the mass of the moisture trap and the shale sample in step S4, low-temperature dry distillation, is as follows: the known mass of the shale sample to be tested and the moisture trap are respectively placed on the sample heating plate and the moisture trap holder in the dry distillation device. After evacuation, the sample is heated to 60°C and kept for 8 hours. Then, the heating system is turned off, the moisture trap and the sample are taken out, and their masses are weighed separately.

[0021] Furthermore, the method for determining the total volume of the sample in step S5 is as follows: the samples after low-temperature dry distillation are immersed in kerosene according to their numbers until they are saturated by self-absorption. According to Archimedes' principle, the total volume of the sample can be determined by the incomplete inclusion method, and the density of the saturated kerosene can also be determined.

[0022] Furthermore, in step S6, the method for removing oil from the shale sample is as follows: the sample is placed in a dry cloth bag of known mass and numbered one-to-one with the sample, and chloroform is used as the oil removal reagent. The oil is removed using a Soxhlet extractor and in accordance with the operating methods specified in the relevant standards.

[0023] Furthermore, step S7 involves dehumidifying the shale sample after oil removal: after the sample has been naturally volatilized for 4-8 hours, it is then dehumidified in a drying oven at 60°C for 8 hours to remove the reagents from the sample pores, and the sample mass is weighed.

[0024] Furthermore, the method for determining the skeleton volume in step S8 involves using a gas injection method to determine the sample skeleton volume, and simultaneously determining the mass of the sample participating in the skeleton volume determination and the mass of particles and dust remaining in the sample bag that cannot participate in the skeleton volume determination. During the oil removal process, some samples have particles and dust falling off. Therefore, by using different sample masses and the measured skeleton volume, a method for calculating the skeleton volume of particles and dust can be established, thereby obtaining the skeleton volume of the shale sample to be tested.

[0025] Furthermore, the method for correcting and determining the total volume of the fractured sample in step S9 is as follows: Select a sample with visible fractures, separate it along the fractures, take a larger piece without fractures, measure its mass, perform self-absorption saturation, and measure the total volume of the sample after separation along the fractures according to the method in step S5.

[0026] Furthermore, the method for calculating the oil-water saturation of the shale sample in step S10 is as follows: and the oil-water saturation calculation method provided in this patent is established using the measured parameters:

[0027] Based on the acquired measurement data, the water saturation of shale oil is calculated using the shale oil-water saturation expression.

[0028] The expressions for water saturation of shale oil are as follows:

[0029]

[0030]

[0031] in:

[0032]

[0033] Compared with the above-mentioned background technology, the present invention has the following beneficial effects:

[0034] This invention provides a method for determining the oil-water saturation of shale oil samples based on dry distillation technology. It employs a vacuum drying device capable of collecting water, using low-temperature vacuum dehydration technology to limit or control the retention of clay-adsorbed water in situ while releasing pore water only in gaseous form. The highly uneven temperature within the experimental apparatus accelerates the movement of gas molecules, allowing the released pore water to be completely captured by a water trap inside the container, accurately obtaining the pore water content of the sample. Further employing low-temperature oil and moisture removal technology, as well as porosity correction technology to address inaccuracies in porosity measurement due to dust particles and visible cracks, the oil content and porosity of the sample are obtained without destroying the clay-adsorbed water, thus accurately determining the oil-water saturation of the shale oil sample.

[0035] This technology, based on low-temperature dry distillation, is a shale oil sample oil-water saturation analysis technique that can simultaneously retain clay-adsorbed water in situ on the same sample while removing and measuring the pore oil-water content of shale samples. It overcomes the drawbacks of previous methods that required two samples and heated extraction, resulting in a long process, numerous steps, and significant time and labor costs. It also avoids the significant errors in oil-water saturation caused by using two samples with poor homogeneity. Furthermore, it employs low-temperature oil and moisture removal technology and porosity correction techniques to address inaccurate porosity measurements due to dust particles and visible fractures. This improves the accuracy of shale sample oil-water saturation test data, shortens the testing cycle, reduces labor intensity, and increases production efficiency. Moreover, it is non-toxic and harmless, complying with HSE (Health, Safety, and Environmental) principles. Attached Figure Description

[0036] Figure 1 This is a flowchart of the oil-water saturation determination method of the present invention;

[0037] Figure 2 The figure shows the experimental results of water recovery rate of the experimental device in an embodiment of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0039] like Figure 1 As shown, a method for determining the oil-water saturation of shale oil samples based on dry distillation technology includes the following steps:

[0040] S1. Prepare full-diameter sheet-like shale samples for testing;

[0041] Under liquid nitrogen cooling protection, for shale obtained at a specified depth, a full-diameter flaky shale sample of the required thickness (generally 10mm to 20mm) is prepared. This full-diameter flaky shale sample is then cut along a direction perpendicular to the bedding planes and bedding end faces into shale samples with a mass generally between 10g and 35g, which are then used as the test samples. The prepared shale oil samples are stored in liquid nitrogen or a freezer for later use, and the sample numbers are recorded. The sample mass is generally between 10g and 35g. This mass range is sufficient for saturation analysis, and combined with the sample thickness of 10mm to 20mm, it limits the sample dimensions, preventing them from being too large or too small, thus facilitating analysis.

[0042] S2. Conduct a pore water removal experiment on the shale sample being tested;

[0043] After performing two-dimensional nuclear magnetic resonance (NMR) analysis on the shale sample, the sample was placed on a heating plate in a low-temperature dry distillation apparatus. A vacuum was first applied, followed by heating to 60°C. The sample was removed every 2 hours for further NMR analysis until the amount of pore water remaining on the NMR spectrum was less than 0.02 mL, at which point the experiment was stopped. The shale contains various types of water, and saturation analysis requires the removal of pore water while retaining clay-adsorbed water. This experiment aimed to determine the optimal conditions for pore water removal. Since chloroform was used for oil removal (its boiling point is 61.5°C), the experiment was conducted under vacuum at 60°C, which is more conducive to subsequent dehumidification of the sample. Therefore, this experiment primarily determined the pore water removal time under these conditions.

[0044] S3. Low-temperature dry distillation experiment to determine water recovery rate;

[0045] After sealing the glass sample bottle containing a measured amount of water and freezing it in a freezer, adjust the low-temperature dry distillation apparatus. Place the known mass of the water trap and the sample bottle (with cap removed and containing a measured amount of water) onto the water trap holder and sample heating plate of the dry distillation apparatus, respectively. First, evacuate the vacuum, then heat to 60°C and maintain the temperature for the experimental time specified in step S2. Then stop heating, remove the water trap and sample bottle, weigh the water trap, and determine the water recovery rate of the experimental apparatus.

[0046] The collected water is determined by the mass difference before and after the water trap. On a Cartesian coordinate system, the water collected by the water trap is plotted on the x-axis, and the measured amount of water added to the glass bottle is plotted on the y-axis. A functional relationship between the two is established, and the regression equation y = k is obtained. w x, determine the correction factor k for collecting pore water. w .

[0047] S4. Low-temperature dry distillation was performed to determine the mass of the moisture trap and the shale sample.

[0048] The shale sample to be tested, with a known mass, and the moisture trap were placed on the sample heating plate and the moisture trap holder in the dry distillation apparatus, respectively. After evacuation, the sample was heated to 60°C and held for 8 hours. Then, the heating system was turned off, the moisture trap and the sample were removed, and their masses were weighed separately.

[0049] A vacuum distillation apparatus is used to conduct low-temperature dry distillation experiments on samples to obtain pore water. The principle or process involves the pore water extracted through low-temperature vacuum distillation being captured by a water trap within the apparatus. The water trap can contain water adsorbents such as silica gel, molecular sieves, or calcium chloride. The experimental temperature is typically 60℃-65℃, determined experimentally. Specific experimental conditions are sufficient to allow the pore water in the shale oil sample to be extracted while retaining clay-adsorbed water in situ, and to collect the extracted pore water. The apparatus is designed with the water trap separated from the sample. The sample, placed on a heating plate, is below the water trap, with a spatial distance between them. Under vacuum and heating, the pore water escapes from the sample as a gaseous stream. Due to the vacuum heat source, the temperature inside the container is extremely uneven, causing rapid convection of the gaseous water, which is then completely captured by the water trap. The test sample is separated from the hygroscopic agent in the moisture trap, and the moisture trap does not affect the removal of pore water from the test sample (if the two come into contact, the hygroscopic agent will plunder the water in the test sample). This design helps to improve the accuracy of pore water collection.

[0050] S5. Determine the total volume of the shale sample;

[0051] After low-temperature dry distillation, the samples are immersed in kerosene according to their numbers until they are saturated by self-absorption. According to Archimedes' principle, the total volume of the samples can be determined by the incomplete inclusion method, and the density of the saturated kerosene can also be determined.

[0052] S6. Remove oil from shale samples;

[0053] The sample was placed in a dry cloth bag of known mass and numbered accordingly. Chloroform was used as the oil removal reagent, and the oil was removed using a Soxhlet extractor and in accordance with the operating procedures specified in the relevant standards.

[0054] The deoiling process for the shale samples utilizes chloroform, which is insoluble in water and has a low boiling point (61.2℃), as the deoiling agent. This method does not disrupt the clay water within the sample, and its low boiling point facilitates removal. It also facilitates the removal of reagents from the sample. Vacuum treatment at 60℃ for 8 hours effectively removes water and residual reagents from the sample pores.

[0055] S7. Dehumidify the degreased shale sample;

[0056] After the oil is removed, the sample is allowed to evaporate naturally for 4-8 hours, then dehumidified in a drying oven at 60°C for 8 hours to remove the reagent from the pores of the sample, and the sample mass is weighed.

[0057] Sample dehumidification involves removing pore water from the sample through low-temperature dry distillation. Dehumidification essentially removes the reagent, chloroform, from the pores. Chloroform is a volatile reagent, so a temperature slightly above its boiling point is sufficient.

[0058] S8. Skeleton volume measurement:

[0059] The sample skeleton volume was determined by gas injection method, and the mass of the sample used in the skeleton volume determination and the mass of particles and dust remaining in the sample bag that could not be used in the skeleton volume determination were also determined simultaneously.

[0060] When determining the sample skeleton volume, it is necessary to measure the sample mass to calculate the volume of dust and particles that detached from the sample but were not included in the skeleton volume measurement.

[0061] During the oil removal process, some samples shed particles and dust. Therefore, by using different sample masses and the measured skeleton volume, a method for calculating the skeleton volume of particles and dust can be established, thereby obtaining the skeleton volume of the shale sample to be tested.

[0062] S9. Correction and determination of the total volume of the fractured sample:

[0063] Select samples with visible cracks, separate them along the cracks, and take the larger, crack-free section (all separated samples can be measured; the total volume of each sample after separation along the cracks is V). t ), perform self-absorption saturation, and determine the total volume of the sample after it is separated along the crack according to step S5.

[0064] The total volume of the tested shale sample, excluding fractures, is determined. For shale samples with good homogeneity, the total volume can be obtained by measuring the density of a portion of the sample, thus eliminating the influence of fractures. (For samples with poor homogeneity, the total volume of each separated sample can be measured; the sum of the total volumes of all samples separated along the fracture is V.) t， The total volume of the original shale sample before it was separated along the fractures is inaccurate due to the poor fluid release caused by the fractures. This method is suitable for samples with visible fractures, but it is difficult to calibrate the total volume for samples with smaller or invisible fractures. This calibration method cannot replace the incomplete saturation method. The incomplete saturation method avoids the fractures caused by the complete saturation of the sample and avoids the generation of both visible and invisible fractures. This method calibrates the fractures generated in the sample due to the small pore size and poor connectivity of the sample during the release of fluid containing high pressure. It can only calibrate larger fractures.

[0065] S10. Calculate the oil-water saturation of the shale sample using the measured data.

[0066] Based on the acquired measurement data, an expression for the water saturation of shale oil by low-temperature dry distillation was established, and the water saturation of shale oil was calculated.

[0067] The expressions for water saturation of shale oil are as follows:

[0068]

[0069] in:

[0070]

[0071] In the formula:

[0072] V – Total volume of the rock sample being tested, in cubic centimeters (cm³) 3 );

[0073] M2—The mass of the tested shale sample in the saturated liquid (anhydrous ethanol or kerosene), in grams (g); M1—The mass of the tested shale sample in the saturated liquid, in grams (g).

[0074] ρ1—Saturated liquid density, in grams per milliliter (g / ml);

[0075] V m1 —The skeletal volume of the sample is determined, and the unit is cubic centimeters (cm). 3 );

[0076] m2 — the dehumidified mass of particles and / or dust that fell out of the sample bag, expressed in grams (g);

[0077] m1 — The mass of the skeleton sample after dehumidification, measured in grams (g);

[0078] m3—The mass of the portion of the sample separated along the crack after being saturated with the saturated liquid, in grams (g); m4—The mass of the portion of the sample separated along the crack after being saturated with the saturated liquid, in grams (g).

[0079] m5 — The mass of the dry sample of the portion of the tested sample separated along the crack, in grams (g);

[0080] V t —The total volume of the sample after separation along the crack (V for samples without crack porosity correction) is measured. t =V), the unit is cubic centimeters (cm) 3 );

[0081] ρ w — The density of water at room temperature, expressed in grams per milliliter (g / ml);

[0082] ρ o — Crude oil density of shale oil storage samples, in grams per milliliter (g / ml);

[0083] M t —The mass of the prepared sample, in grams (g);

[0084] G1 — Mass of the moisture trap after low-temperature dry distillation of the sample, in grams (g);

[0085] G2 — Mass of the moisture trap before low-temperature dry distillation of the sample, in grams (g);

[0086] k w —Collected pore water correction factor, in percentage (%);

[0087] S w —Water saturation of the sample being tested, expressed as a percentage (%);

[0088] S o —Oil and gas saturation of the tested sample, in percentage (%);

[0089] To make the objectives, technical solutions, and advantages of this invention clearer, the following description, using a shale oil reservoir pressure-maintaining core sample from a certain exploration area as an example, will be further detailed in conjunction with the accompanying drawings.

[0090] Example 1: Sample pore water removal experiment

[0091] The saturation test method provided by this invention requires determining the experimental conditions for pore water removal. The experimental samples were selected from the shale oil layer of well XX1. After the core was retrieved from the wellbore to the surface, samples were selected, transported back to the laboratory using liquid nitrogen freezing, and two samples were prepared under liquid nitrogen cooling conditions. The sample thickness was approximately 15 mm, and the average length of each sample was approximately 25 mm and 28 mm; the width was approximately 19 mm, and the sample masses were 18.564 g and 20.149 g, respectively. Due to conventional core sampling, some light hydrocarbons were lost from the samples during the process of retrieving the core from the wellbore to the surface, but the pore water and clay-adsorbed water in the core were basically distributed under formation conditions.

[0092] Experimental method: After the sample was thawed and slowly melted, NMR was performed immediately. Then the sample was placed on the heating plate in the experimental device, evacuated into a vacuum, and then heated to 60°C. The sample was kept in a vacuum state and at a temperature of 60°C for 10 hours.

[0093] To understand the changes in clay-adsorbed water and pore water within the samples, two-dimensional nuclear magnetic resonance (NMR) analysis was performed every 2 hours to obtain NMR data at different time points. Two-dimensional NMR analysis was able to separate pore water from structural water / crystallization water / clay-adsorbed water, and the data are shown in Table 1 below.

[0094] As can be seen from the experimental data in Table 1, the data for structural water / crystallization water / clay-adsorbed water remained basically constant, with slight differences at different times. No clay-adsorbed water flowed out of the crystallization water / clay-adsorbed water. The pore water content in the sample gradually decreased with increasing experimental time, and the rate of decrease became smaller and smaller. When the drying time reached 8 hours, the pore water content was less than 0.02 mL. Moreover, with the same increase in drying time, the change in pore water content in the tested sample was very small. Therefore, after drying the tested shale oil sample at 60℃ under vacuum for 8 hours, the pore water was basically removed, and the pore water content was less than 0.02 mL, which meets the accuracy requirements of geological experiments. For oil-bearing shale samples, the constant mass method for determining pore water affects the degree of sample mass change due to oil loss. This indicates that the constant mass method is not suitable for determining pore water in oil-bearing shale samples due to the loss of oil and gas during the heating and dehydration process.

[0095] Table 1

[0096]

[0097]

[0098] This experiment shows that drying shale oil samples at 60℃ in a vacuum for 8 hours can effectively remove pore water while retaining clay-adsorbed water.

[0099] Example 2: Sample Saturation Analysis Experiment

[0100] To overcome the shortcomings in the background, this patent provides an effective and rapid experimental method for determining pore water in shale rocks. Following this method, shale oil reservoir samples are selected for sample analysis. 1. Sample freezing: Pressure-preserving core samples from the shale oil reservoir in the exploration area are selected. After the pressure-preserving cores are brought to the surface, they are frozen using liquid nitrogen. Under freezing conditions, the pressure-preserving cores are obtained and stored in liquid nitrogen or a 60°C freezer for later use.

[0101] 2. Preparation of sheet-like samples: At the sampling depth of the frozen shale oil reservoir full-diameter sample, under liquid nitrogen cooling, use a core-specific cutter (along the core bedding plane) or core cutting tool to prepare a full-diameter sheet-like sample of the required thickness (generally 10mm to 20mm).

[0102] 3. Sample preparation: The frozen sheet-like full-diameter sample is cut into shale samples with a mass of 10g to 35g using a special core cutting tool along the direction perpendicular to the bedding and the end face of the bedding. These are the test samples, which include 3 pairs of parallel samples with the 3 shale samples to be tested using the oil-water saturation analysis provided by this patent. These are used for the oil-water saturation experiment of the dual-sample thermal extraction method.

[0103] 4. Low-temperature dry distillation water recovery rate experiment: Seven glass bottles were filled with unequal amounts of water, sealed, and frozen in a freezer. A specially designed low-temperature dry distillation apparatus was set up. A water trap containing a known mass and dry water-trapping medium and a sample bottle containing a measured amount of water (with the cap removed) were placed on the water trap holder and the sample heating plate in the dry distillation apparatus, respectively. The apparatus was sealed, a vacuum was first drawn, and then the temperature was raised to 60°C and maintained for 8 hours. Heating was then stopped, the water trap was removed, and its mass was measured. The amount of water collected by the water trap before and after water collection was obtained.

[0104] On a Cartesian coordinate system, the water collected by the moisture trap is plotted on the x-axis, and the measured amount of water added to the glass bottle is plotted on the y-axis. A functional relationship between the two is established, and the regression equation is obtained: y = k w x determines the correction factor k for collecting pore water. w The experimental results are shown in Figure 2 As can be seen from the experimental results graph, the difference between the added quantitative water and the collected water is very small, and the two are distributed along the 45° angle bisector. The correlation coefficient of their regression equation reaches 0.9997. This experimental result can be used for correction of collected pore water.

[0105] When 1 mL of water is added, 1.0008 mL of water can be collected, a difference of only 0.0008 mL, which is much smaller than the standard deviation of 0.02 mL. This equation is used to calculate the experimentally collected water and the pore water in the sample.

[0106] 5. Comparative Experiment: To verify the accuracy of pore water extraction using this method, two samples were randomly selected for high-frequency two-dimensional nuclear magnetic resonance (NMR) analysis to determine the pore water content (NMR analysis is a non-destructive assay that does not damage the sample and does not affect the pore water determination); the results are shown in Table 1. For parallel samples, the oil-water saturation was determined using a dual-sample thermal extraction method. The method was as follows: after removing the pore water from one sample, it was heated to 115℃ and held for 15 hours with another parallel sample under identical extraction time, conditions, and methods to extract the water. The pore water content of the shale sample was calculated by subtracting the two samples, and then the oil-water saturation of the shale oil rock sample was obtained through porosity analysis, as shown in Table 2.

[0107] 6. Low-temperature dry distillation: After weighing the shale sample to be tested, place it on the sample heating plate in a specially designed dry distillation apparatus. Then, weigh the water trap containing the dry water-collecting medium and place it on the water trap holder. After sealing the device, first evacuate the vacuum, then heat to 60°C and maintain for 8 hours. Then, turn off the heating system, take out the water trap and the shale sample, and weigh them separately. Measure the amount of water collected based on the weight of the water trap, and use step 4 to calibrate the collected water.

[0108] 7. Total volume determination: The samples after low-temperature dry distillation are immersed in kerosene according to their numbers until they are saturated by self-absorption. After 15 minutes, the total volume of the samples can be determined by the incomplete inclusion method according to Archimedes' principle, and the density of the saturated kerosene is also determined.

[0109] 8. Oil removal from samples: The samples are placed in dry cloth bags of known mass and numbered one-to-one with the samples. Low-boiling-point and water-insoluble chloroform is used as the oil removal reagent. The oil and gas in the samples are removed by Soxhlet extraction for 72 hours.

[0110] 9. After dehumidifying and removing oil from the sample, the sample is placed in a fume hood and allowed to evaporate naturally for 4-8 hours. Then, it is dehumidified in a drying oven at 60°C for 8 hours to remove the reagents from the pores. The sample mass is then measured to obtain a dry sample with the pore water and oil and gas removed from the pores, along with its mass.

[0111] 10. Skeleton Volume Determination: The sample skeleton volume is determined by gas injection method. At the same time, the mass of the sample participating in the skeleton volume determination and the mass of particles and dust remaining in the sample bag that cannot participate in the skeleton volume determination are also determined. During the oil removal process, some particles and dust fall off the sample. Therefore, by using different sample masses and the measured skeleton volume, a method for calculating the skeleton volume of particles and dust can be established, thereby obtaining the skeleton volume of the shale sample to be tested.

[0112] 11. Correction and determination of total volume of cracked sample: Select a sample with visible cracks, separate it along the cracks, take the larger piece without cracks, measure its dry sample mass, and then use self-absorbed saturated anhydrous ethanol (or saturated kerosene, but the sample has already been de-oiled, and for the convenience of other experiments, saturated ethanol does not need to be de-oiled again) to determine the total volume of the sample after it has been separated along the cracks, according to the method in step 7.

[0113] 12. Calculation: A suitable method for calculating oil-water saturation in this low-temperature dry distillation method was established using the measured parameters. The results of the oil-water saturation analysis of the samples are shown in Table 2.

[0114]

[0115]

[0116] Table 2

[0117]

[0118] As shown in Table 2 of the experimental data, the maximum difference between the water volume measured by NMR and the water volume collected by dry distillation for the two samples was 0.012 mL, which is not significantly different from the oil-water saturation measured by the dual-sample method. Both are within the allowable error range, indicating that the data obtained by the oil-water saturation analysis method for shale samples provided by this patent is accurate and the method is reliable and feasible. In actual use in shale oil reservoir oil content experiments, the results obtained truly reflect the oil and gas distribution of shale oil reservoirs, providing more valuable data for reserve evaluation and reservoir research.

[0119] The above description is only a preferred embodiment of the present invention and is not intended to limit the patent scope of the present invention. Other equivalent variations that utilize the patent spirit of the present invention should all fall within the patent scope of the present invention.

Claims

1. A method for determining the oil-water saturation of shale oil samples based on dry distillation technology, characterized in that: Includes the following steps: S1. Prepare full-diameter sheet-like shale samples for testing; S2. Conduct a pore water removal experiment on the shale sample being tested; S3. Low-temperature dry distillation experiment to determine water recovery rate of the shale sample under test; S4. After low-temperature dry distillation of the shale sample, the mass of the moisture trap and the shale sample are measured. S5. Determine the total volume of the shale sample; S6. Remove oil from shale samples; S7. Dehumidify the degreased shale sample; S8. Determine the volume of the shale sample skeleton; S9. Correction and determination of the total volume of the fractured sample; S10. Calculate the oil-water saturation of the shale sample using the measured data.

2. The method for determining the oil-water saturation of shale oil samples based on dry distillation technology according to claim 1, characterized in that: The method for preparing full-diameter flaky shale samples in step S1 is as follows: Under liquid nitrogen cooling protection, for shale obtained at a specified depth, prepare full-diameter flaky shale samples of the required thickness; cut the prepared full-diameter flaky shale samples into shale samples with a mass of 10g to 35g along the direction perpendicular to the bedding and the end face of the bedding, which are the samples to be tested; store the prepared shale oil samples in liquid nitrogen or a freezer for later use, and record the sample number at the same time.

3. The method for determining the oil-water saturation of shale oil samples based on dry distillation technology according to claim 1, characterized in that: The specific method for the sample pore water removal experiment in step S2 of the tested shale sample is as follows: After the sample is subjected to two-dimensional nuclear magnetic resonance analysis, the sample is placed on the heating plate in the low-temperature dry distillation device. After evacuation, it is heated to 60°C. The sample is taken out every 2 hours for two-dimensional nuclear magnetic resonance analysis until the amount of pore water remaining after removal on the two-dimensional nuclear magnetic resonance spectrum is less than 0.02 mL, at which point the experiment is stopped.

4. The method for determining the oil-water saturation of shale oil samples based on dry distillation technology according to claim 1, characterized in that: The experimental method for determining the water recovery rate in step S3, low-temperature dry distillation, is as follows: After sealing a glass sample bottle containing a fixed amount of water and freezing it in a freezer, adjust the low-temperature dry distillation apparatus. Place a water trap of known mass and a sample bottle containing a fixed amount of water (with the cap removed) onto the water trap holder and the sample heating plate in the dry distillation apparatus, respectively. First, evacuate the vacuum, then heat to 60°C and maintain the experimental time specified in step S2. Then, stop heating, remove the water trap and the sample bottle, and weigh the water trap. The collected water is determined by the mass difference before and after the water trap. On a Cartesian coordinate system, the water collected by the water trap is plotted on the x-axis, and the measured amount of water added to the glass bottle is plotted on the y-axis. A functional relationship between the two is established, and the regression equation y = k is obtained. w x, determine the correction factor k for collecting pore water. w .

5. The method for determining the oil-water saturation of shale oil samples based on dry distillation technology according to claim 1, characterized in that: The method for measuring the mass of the moisture trap and shale sample in step S4, low-temperature dry distillation, is as follows: The known mass of the shale sample to be tested and the moisture trap are respectively placed on the sample heating plate and the moisture trap holder in the dry distillation device. After evacuation, the sample is heated to 60°C and kept for 8 hours. Then, the heating system is turned off, the moisture trap and the sample are taken out, and their masses are weighed separately.

6. The method for determining the oil-water saturation of shale oil samples based on dry distillation technology according to claim 1, characterized in that: The method for determining the total volume of the sample in step S5 is as follows: the samples after low-temperature dry distillation are immersed in kerosene according to their numbers until they are saturated by self-absorption. According to Archimedes' principle, the total volume of the sample can be determined by the incomplete inclusion method, and the density of the saturated kerosene can also be determined.

7. The method for determining the oil-water saturation of shale oil samples based on dry distillation technology according to claim 1, characterized in that: Step S6, the method for removing oil from shale samples: The samples are placed in dry cloth bags of known mass and numbered one-to-one with the samples, and chloroform is used as the oil removal reagent. The oil is removed using a Soxhlet extractor and in accordance with the operating methods specified in relevant standards.

8. The method for determining the oil-water saturation of shale oil samples based on dry distillation technology according to claim 1, characterized in that: The method for dehumidifying the shale sample after oil removal in step S7 is as follows: after the sample is naturally volatilized for 4-8 hours after oil removal, it is dehumidified for 8 hours at 60°C in a drying oven to remove the reagent in the sample pores, and the sample mass is weighed.

9. The method for determining the oil-water saturation of shale oil samples based on dry distillation technology according to claim 1, characterized in that: The method for determining the skeleton volume in step S8 is as follows: The sample skeleton volume is determined by gas injection, and the mass of the sample participating in the skeleton volume determination and the mass of particles and dust remaining in the sample bag that cannot participate in the skeleton volume determination are determined simultaneously. During the oil removal process, some particles and dust fall off the sample. Therefore, by using different sample masses and the measured skeleton volume, a method for calculating the skeleton volume of particles and dust can be established, thereby obtaining the skeleton volume of the shale sample to be tested.

10. A method for determining the oil-water saturation of shale oil samples based on dry distillation technology according to claim 1 or 6, characterized in that: The method for correcting and determining the total volume of the fractured sample in step S9 is as follows: Select a sample with visible fractures, separate it along the fracture, take a larger piece without fractures, measure its mass, perform self-absorption saturation, and measure the total volume of the sample after separation along the fracture according to the method in step S5.

11. The method for determining the oil-water saturation of shale oil samples based on dry distillation technology according to claim 1, characterized in that: The method for calculating the oil-water saturation of the shale sample in step S10 is as follows: and the oil-water saturation calculation method provided in this patent is established using the measured parameters: Based on the acquired measurement data, the water saturation of shale oil is calculated using the shale oil-water saturation expression. The expressions for water saturation of shale oil are as follows: in: In the formula: V – Total volume of the rock sample being tested, in cubic centimeters (cm³) 3 ); M2—The mass of the tested shale sample in the saturated liquid (anhydrous ethanol or kerosene), in grams (g); M1—The mass of the tested shale sample in the saturated liquid, in grams (g). ρ1—Saturated liquid density, in grams per milliliter (g / ml); V m1 —The skeletal volume of the sample is determined, and the unit is cubic centimeters (cm). 3 ); m2 — the dehumidified mass of particles and / or dust that fell out of the sample bag, expressed in grams (g); m1 — The mass of the skeleton sample after dehumidification, measured in grams (g); m3—The mass of the portion of the sample separated along the crack after being saturated with the saturated liquid, in grams (g); m4—The mass of the portion of the sample separated along the crack after being saturated with the saturated liquid, in grams (g). m5 — The mass of the dry sample of the portion of the tested sample separated along the crack, in grams (g); V t —The total volume of the sample after separation along the crack (V for samples without crack porosity correction) is measured. t =V), the unit is cubic centimeters (cm) 3 ); ρ w — The density of water at room temperature, expressed in grams per milliliter (g / ml); ρ o — Crude oil density of shale oil storage samples, in grams per milliliter (g / ml); M t —The mass of the prepared sample, in grams (g); G1 — Mass of the moisture trap after low-temperature dry distillation of the sample, in grams (g); G2 — Mass of the moisture trap before low-temperature dry distillation of the sample, in grams (g); k w —Collected pore water correction factor, in percentage (%); S w —Water saturation of the sample being tested, expressed as a percentage (%); S o —Oil and gas saturation of the tested sample, expressed as a percentage (%).

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