Method for determining shale oil rock pore water

Abstract

The invention discloses a shale oil rock pore water determination method. The method comprises the following steps: cutting a frozen shale oil reservoir sample into a tested sample with the thickness of 10-20mm and the mass of 10-35g; the tested sample is placed in a vacuum container at the constant temperature of 60 DEG C for 8 h, the vacuum container is communicated with a liquid collector, and the liquid collector is connected with a freezing mechanism; liquid separated from the tested sample is frozen and recovered into the liquid collector, and the pore water volume in the collector is measured; the problems that the existing shale oil rock pore water determination needs a plurality of samples, the process is tedious, the working efficiency is low, errors are easily generated, and the accuracy of the determination result is influenced are effectively solved.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas exploration and development experimental testing, and in particular to an experimental method for rapidly removing pore water from shale rocks. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] At present, shale oil and gas exploration and development has become one of the hot spots in the international energy field and an important field of oil and gas exploration and development in China. Due to the particularity of shale, many current exploration and development technologies are difficult to adapt to the needs of mud shale. The same is true for petroleum geological experiments on shale oil samples. In the past, sandstone experimental technology was difficult to apply to shale oil samples. Shale has multiple water sources. Mud shale is mainly composed of clay minerals and has water-containing characteristics. Shale rocks contain pore water, clay-adsorbed water, structural water and other types of water. The main factors that affect the porosity and fluid content analysis of rocks are pore water and clay-adsorbed water. The release temperatures of the two are generally around 100°C. Shale has fine particles and a large specific surface area. Clay adsorbs a large amount of water, and its removal has a great influence on the analysis of rock porosity and fluid content. In the experiments on the porosity and oil content of shale oil reservoir rocks, experimental parameters under different conditions are required. It is necessary to carry out experimental analysis when clay-adsorbed water and pore water are removed at the same time, and to carry out experiments when clay-adsorbed water is retained in situ and only pore water is removed. The determination of pore water in shale oil rocks is of great significance to shale oil reservoir geological experiments.

[0004] At present, the main experimental method for determining pore water in shale oil rocks is parallel sample ethanol hot extraction method, that is, two parallel samples that can replace each other are used, one of which is a parallel sample (parallel sample 1) after removing pore water by vacuum at 60℃, and then the other parallel sample is extracted by ethanol hot extraction method under the same extraction time, extraction conditions and extraction method, and the water content of the sample is obtained. After obtaining the water volume of the two samples, the pore water content of the shale sample can be obtained after data processing. The pore water removal technology in this method is borrowed from the pore water removal technology of oil-free shale, that is, the sample is dehydrated to constant weight under vacuum at 60℃. The general practice is to dry the sample under vacuum at 60℃ for 4h, cool it to room temperature in a dryer, weigh it, and then use the same method to dry and weigh it until the sample weight is constant. For non-oil shale, it usually takes 3-4 times to dry a batch of samples to constant weight. As for shale oil reservoir samples, it is more difficult to keep constant weight under vacuum at 60°C because of the loss of different oil and gas in the samples. Even if the samples are dried under vacuum at 60°C for 6 hours, it takes at least 4 times to dry a batch of samples to constant weight (if 4 hours of drying is used, the number of experiments will be more). The experiment time is longer and the work efficiency is lower. Due to the outflow of clay water, the separation of pore water and clay adsorbed water will produce greater errors. Moreover, for shale samples with poor homogeneity, some parallel samples have certain differences. The use of two parallel samples to measure pore water will also affect the accuracy of pore water measurement. Therefore, there is currently a lack of an effective pore water measurement method suitable for single shale oil samples.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may contain information that does not constitute prior art. Summary of the invention

[0006] In view of this, the present disclosure provides a method for measuring pore water in shale oil rocks, which solves the problems that the existing pore water measurement of shale oil rocks requires multiple samples, the process is cumbersome, the work efficiency is low, and errors are easily generated, thus affecting the accuracy of the measurement results.

[0007] To achieve the above-mentioned purpose of the invention, the method for determining pore water in shale oil rock comprises:

[0008] Cut the frozen shale oil reservoir samples into test samples with a thickness of 10 to 20 mm and a mass of 10 to 35 g;

[0009] The sample to be tested is placed in a vacuum container at a constant temperature of 60° C. for 8 hours, wherein the vacuum container is connected to a liquid collector, and the liquid collector is connected to a freezing mechanism;

[0010] The liquid released from the sample to be tested is recovered into the liquid collector through freezing, and the amount of pore water in the collector is measured.

[0011] In the present disclosure and possible embodiments, the pore water amount is determined by an ethanol extraction method.

[0012] In the present disclosure and possible embodiments, the method for determining the amount of pore water includes:

[0013] Thawing the liquid in the liquid collector and adding a set amount of anhydrous ethanol as a sample to be tested;

[0014] Prepare several ethanol solutions with different water contents as standard samples, and use a chromatograph or a coulometer to measure the water content of the standard samples and the sample to be tested;

[0015] A linear equation is obtained by fitting the water content determination result of the standard sample, and the equation slope a and equation intercept b are obtained by using the linear equation;

[0016] Substituting the equation slope a and the equation intercept b into the following formula, the pore water volume is obtained:

[0017] V = aβ + b;

[0018] Where: V is the pore water volume, mL; β is the chromatographic water content of the sample to be tested, %.

[0019] In the present disclosure and possible embodiments, the thickness of the sample to be tested is 14-18 mm.

[0020] In the present disclosure and possible embodiments, the length of the sample to be tested is 20 to 25 mm.

[0021] In the present disclosure and possible embodiments, the width of the sample to be tested is 18 to 22 mm.

[0022] In the present disclosure and possible embodiments, the freezing mechanism is a Dewar flask filled with liquid nitrogen, and the Dewar flask is sleeved on the outside of the liquid collector.

[0023] In the present disclosure and possible embodiments, the liquid collector is a liquid collection tube. The present disclosure has the following beneficial effects:

[0024] The shale oil rock pore water determination method disclosed in the present invention can effectively remove and determine the shale oil rock sample pore water by only drying a single sample under vacuum at 60° C. for 8 hours, while the clay-adsorbed water will not be lost, thereby avoiding the disadvantages of using two parallel samples to determine pore water in the past, which leads to low accuracy of pore water determination due to poor sample homogeneity, and the disadvantages of too long drying time due to lack of oil-bearing shale pore water removal technology, which causes clay water to flow out, resulting in increased error or even distortion in pore water determination; the accuracy and reliability of pore water determination are improved; at the same time, the method provided by the patent greatly reduces the experimental work such as repeated vacuum heating and weighing, shortens the experimental cycle, reduces labor intensity, improves work efficiency, and complies with the HSE analysis and testing concept of health, safety and environmental protection; effectively solves the problems of multiple samples in the existing shale oil rock pore water determination, cumbersome process, low work efficiency and easy error, which affects the accuracy of the determination result. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0026] Figure 1 is the ethanol calibration fitting curve of the embodiment of the present disclosure. DETAILED DESCRIPTION

[0027] The present disclosure is described below based on embodiments, but it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, some specific details are described in detail. However, for the parts that are not described in detail, those skilled in the art can also fully understand the present disclosure.

[0028] At the same time, unless the context clearly requires otherwise, the words "include", "comprises" and similar words throughout the specification and claims should be interpreted as inclusive rather than exclusive or exhaustive; that is, the meaning is "including but not limited to".

[0029] The researchers of this application found that although both pore water and clay-adsorbed water can escape at about 100°C, the areas where pore water and clay-adsorbed water exist in the rock core are different. Among them, most of the clay-adsorbed water is adsorbed on the surface of clay particles, and pore water exists in the pores of rocks. The surface tension (that is, gravity) of the rock particle surface on water gradually increases from the center of the rock pore to the surface of the rock particle. Under the action of temperature and vacuum conditions, the pore water and clay-adsorbed water of the rock escape in a certain order, with pore water escaping first. To verify this discovery, this study conducted corresponding experiments. The specific experimental methods and results are as follows:

[0030] The experimental samples were selected from the shale oil layer samples of Well XX1. After the core was lifted from the wellbore to the ground, the required samples were obtained from the middle part of the core. The sample thickness was about 15 mm, the average length and width were 25 mm and 19 mm respectively, and the mass was 17.573 g. Due to conventional coring, the light components in the sample were lost during the process of lifting the core from the wellbore to the ground, but the pore water and clay adsorbed water in the core were basically distributed under the formation conditions.

[0031] To prevent water loss in the samples, they were frozen with liquid nitrogen and transported back to the laboratory. Nuclear magnetic resonance measurement was carried out immediately after thawing. The samples were then placed in a vacuum drying oven, evacuated, and heated to 60°C. The samples were kept in a vacuum state and dried at 60°C for 10 hours.

[0032] In order to understand the changes in clay-adsorbed water and pore water in the sample, two-dimensional nuclear magnetic resonance detection was performed every 2 hours to obtain nuclear magnetic distribution data at different times. Two-dimensional nuclear magnetic resonance analysis can separate pore water from structural water / crystallized water / clay-adsorbed water, oil from organic matter / asphalt, and oil from water, so 4 sets of data can be obtained, as shown in Table 1 below:

[0033] Table 1. 2D NMR analysis data of shale

[0034]

[0035] It can be seen from the experimental data in Table 1 that the data of structural water / crystallization water / clay adsorbed water and organic matter / asphalt remain basically unchanged, and the test data at different times are slightly different. The clay adsorbed water in the structural water / crystallization water / clay adsorbed water does not flow out. As the experimental time increases, the amount of water in the sample gradually decreases, and the reduction amplitude becomes smaller and smaller. When the drying time reaches 8h, the pore water content is less than 0.02mL, and when the same time is increased, the pore water of the tested sample changes very little. Therefore, after the tested shale oil sample is dried at 60℃ in vacuum for 8h, the pore water is basically removed, and the pore water content is less than 0.02mL, which can meet the accuracy requirements of geological experiments. However, the oil is in a decreasing trend with the increase of drying time. For oil-bearing shale samples, the mass constant method is used to determine the pore water. The oil removal will affect the degree of change in the sample mass. This shows that the oil-bearing shale samples are not suitable for the mass constant method to determine the pore water due to the loss of oil and gas during the heating and dehydration process.

[0036] Repeated experiments have shown that the optimal release time of pore water under vacuum and 60°C conditions is 8 hours.

[0037] Furthermore, the pore water of shale oil samples escapes from the sample in gaseous form under vacuum and 60°C conditions, and the gas will be dispersed in the container, so the pore water escaped from the core sample can be collected by low temperature. Moreover, when heating under vacuum conditions, the gas is extremely thin, and heat transfer is hindered. Only the heat removal device and the sample are at 60°C, and the temperature of the entire device is in a seriously unbalanced state. The very small amount of gas in the container flows faster (heat exchange) under thermal imbalance conditions, and the water vapor escaped from the sample will quickly flow through the liquid collection tube, and will be quickly frozen under liquid nitrogen freezing conditions. Therefore, the collection of the pore water lost from the sample is more thorough and accurate.

[0038] Example

[0039] A pressure-maintained core sample was selected from the shale oil reservoir in the exploration area, and the pore water content of the shale oil rock was measured using the method disclosed in the present invention. The specific process is as follows:

[0040] 1. Core freezing: To prevent shale oil from being lost along with the fluid in the rock sample, shale oil pressure cores are frozen with liquid nitrogen or dry ice, usually liquid nitrogen. The pressure-treated cores are stored in a freezer at -60°C.

[0041] 2. Preparation of flake samples: At the sampling depth, under liquid nitrogen cooling, use a core-specific chopper or core cutting tool to make full-diameter flake samples with a thickness of 12 to 18 mm along the core bedding plane.

[0042] 3. Preparation of block samples: Use a special core cutting tool to cut the frozen full-diameter flake samples into block samples in a direction perpendicular to the bedding and the bedding end faces. The sample geometric dimensions are: thickness 14-18 mm, length 20-25 mm, width 18-22 mm, and mass range 16 g-26 g.

[0043] 4. Confirmation of reliability and accuracy of vacuum drying and fluid collection devices

[0044] The specific confirmation is carried out through the water recovery rate experiment, and the confirmation method is:

[0045] Select 5 glass sample bottles, add different amounts of water, seal them and put them in the refrigerator for freezing. After the device is debugged, put them in the device respectively, evacuate them and heat them to 60℃, then put the Dewar flask on the liquid collection tube to enrich water by freezing. After 8h, stop heating, remove the liquid collection tube, and measure the water content after thawing according to the above method. The experimental results are shown in Table 2:

[0046] Table 2 Water recovery rate experimental data table

[0047]

[0048] As can be seen from Table 2, the difference between the added water and the collected water is less than ±0.02mL, the water recovery rate of less than 0.1mL can reach more than 90%, the absolute deviation of the collection is less than 0.02mL, and the sample recovery rate of water greater than 0.1mL is between 98% and 105, all less than 0.02mL, which can fully meet the accuracy requirements of geological experiments. Therefore, the device can accurately collect the pore water removed from the shale oil sample.

[0049] 5. Collect pore water:

[0050] Weigh the mass of all block samples (mass before measurement) and place them in a device with vacuum drying and fluid collection functions confirmed in step 4. Keep the device in vacuum and at 60°C, and put a Dewar flask filled with liquid nitrogen on the liquid collection tube under the device. After 8 hours, take out the samples and weigh their mass (mass after measurement). Remove the Dewar flask, take down the liquid collection tube, and seal them immediately. Record the number corresponding to the sample. The mass difference before and after the measurement and before and after the measurement of each sample is shown in Table 3.

[0051] In addition, before removing and collecting the pore water, sample No. 5 was selected for nuclear two-dimensional nuclear magnetic resonance measurement to obtain the pore water content, and then frozen and stored after the nuclear magnetic resonance measurement.

[0052] 6. Ethanol calibration: Inject 50 mL of anhydrous ethanol into 7 dried glass sample bottles respectively, and take 6 of them and add about 0.199g, 0.390g, 0.615g, 0.801g, 1.028g, and 1.294g of distilled water into the bottles respectively. The 7 glass bottle samples are the standard samples for chromatographic water content determination, and the glass bottle without water injection and filled with anhydrous ethanol is the 0 point standard sample for chromatographic ethanol water solution analysis.

[0053] Specifically, the percentage of anhydrous ethanol water in each standard sample was determined by a chromatograph according to the conventional technology in the art. According to the chromatographic results, the following was obtained by fitting: Figure 1 The linear relationship shown in FIG. 1 shows that a=0.3251 and b=0.0631 are obtained through the linear relationship. Moreover, the correlation coefficient reaches R=0.9999, which can ensure the accuracy of the shale oil sample being tested and fully meet the needs of water content determination.

[0054] 7. Pore water extraction: After the water in the liquid collection tube is thawed, inject 50 ml of anhydrous ethanol into the tube and seal it for testing.

[0055] 8. Determination of pore water content: The water content of the ethanol in each liquid collection tube in step 7 was determined using a chromatograph according to conventional techniques in the art (see Table 3).

[0056] Substitute the water content in the above ethanol into the formula: V = aβ + b; where a = 0.3251, b = 0.0631, and obtain the pore water content of each tested sample, see Table 3.

[0057] Table 3 Shale oil sample pore water content determination data

[0058]

[0059] From the experimental data in Table 3, it can be seen that the pore water amount of sample 5 measured by two-dimensional nuclear magnetic resonance is very close to that measured by the method of this patent, indicating that the pore water amount measured by the method of the present invention is accurate.

[0060] In addition, the mass difference before and after each tested sample is greater than the pore water volume, indicating that some oil and gas escaped from the sample during the pore water determination process. If the pore water is determined by the constant mass method, not only the pore water volume cannot be accurately determined, but the removed pore water cannot be collected. Therefore, the determination method provided by this patent can well meet the needs of pore water determination of shale oil rock samples because it does not require multiple mass measurements, and provides an effective experimental method for pore water determination of shale oil rock samples.

[0061] The above-described embodiments are only embodiments of the present disclosure, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the present disclosure. It should be noted that, for a person of ordinary skill in the art, without departing from the concept of the present disclosure, several variations, equivalent substitutions, improvements, etc. may be made, all of which fall within the scope of protection of the present disclosure. Therefore, the scope of protection of the present disclosure shall be subject to the attached claims.

Claims

1. A method for determining pore water in shale oil rock, characterized in that: include: Cut the frozen shale oil reservoir samples into test samples with a thickness of 10 to 20 mm and a mass of 10 to 35 g; The sample to be tested is placed in a vacuum container at a constant temperature of 60° C. for 8 hours, wherein the vacuum container is connected to a liquid collector, and the liquid collector is connected to a freezing mechanism; The liquid released from the sample to be tested is recovered into the liquid collector through freezing, and the amount of pore water in the collector is measured.

2. The method for determining pore water in shale oil rock according to claim 1, characterized in that: The pore water content was determined by ethanol extraction method.

3. The method for determining pore water in shale oil rock according to claim 2, characterized in that: The method for determining the amount of pore water comprises: Thawing the liquid in the liquid collector and adding a set amount of anhydrous ethanol as a sample to be tested; Prepare several ethanol solutions with different water contents as standard samples, and use a chromatograph or a coulometer to measure the water content of the standard samples and the sample to be tested; A linear equation is obtained by fitting the water content determination result of the standard sample, and the equation slope a and equation intercept b are obtained by using the linear equation; Substituting the equation slope a and the equation intercept b into the following formula, the pore water volume is obtained: V = aβ + b; Where: V is the pore water volume, mL; β is the chromatographic water content of the sample to be tested, %.

4. The method for determining pore water in shale oil rock according to any one of claims 1 to 3, characterized in that: The thickness of the tested sample is 14-18 mm.

5. The method for determining pore water in shale oil rock according to claim 4, characterized in that: The length of the tested sample is 20-25 mm.

6. The method for determining pore water in shale oil rock according to claim 5, characterized in that: The width of the tested sample is 18-22 mm.

7. The method for determining pore water in shale oil rock according to claim 5 or 6, characterized in that: The freezing mechanism is a Dewar flask filled with liquid nitrogen, and the Dewar flask is sleeved on the outside of the liquid collector.

8. The method for determining pore water in shale oil rock according to claim 7, characterized in that: The liquid collector is a liquid collecting tube.

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