A method for measuring pore water in shale oil reservoir rocks

Abstract

The present invention discloses a method for measuring pore water in shale oil reservoir rocks, including: preparing a first sample and a second sample of the rock to be measured in parallel; removing the pore water in the first sample; extracting the water in the first sample and the second sample under the same conditions and measuring the water content of the first sample and the second sample respectively; the difference between the water content of the second sample and the water content of the first sample is the pore water content of the rock to be measured; solving the problems that various existing methods for measuring pore water in shale oil reservoir rocks are not ideal due to inaccurate measurement results caused by the inability to accurately separate pore water from clay-adsorbed water or high measurement costs and other factors.

Description

Technical Field

[0001] The present invention relates to the field of experimental testing for oil and gas exploration and development, and in particular to a method for determining pore water in shale oil reservoir 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] In recent years, shale oil and gas exploration and development has become a new highlight in the international energy field and one of the hot spots of oil and gas exploration in China. Due to the particularity of mud shale, many exploration and development technologies need to be improved or re-established. Mud shale is composed of clay minerals, which are rich in water, including not only pore water, but also clay adsorbed water and structural water. Structural water exists in the lattice of clay minerals, and the release temperature is generally above 500°C, which will not affect conventional analysis. Porous water exists in the pores of rocks and can be released at around 100°C. Adsorbed water exists in the interlayer domain of clay adsorption. Clay adsorbed water is divided into free water between clay layers and bound water between clay layers. The release temperature of bound water between clay layers is generally between 120°C and 500°C, and free water between clay layers will be released at around 100°C. In petroleum geological experiments for some analytical items (such as oil-water saturation), it is necessary to accurately measure the pore water content. However, due to the presence of a large amount of clay-adsorbed water in shale and the presence of oil-water two-phase media in shale oil reservoir rocks, it is difficult to accurately measure the pore water in shale oil reservoir rocks.

[0004] The national standard GB / T 29172 "Core Analysis Method" (equivalent to the American standard API RP 40) stipulates that shale or other high-clay rock should be dried to constant weight in a conventional vacuum oven at 60°C or in a controlled humidity oven at 60°C and 40% relative humidity to remove pore water, but the amount of pore water removed cannot be measured. High-frequency nuclear magnetic resonance core analysis can determine the pore water content, but it cannot remove pore water from the core. In addition, the cost of high-frequency nuclear magnetic resonance analysis equipment and analysis costs are very high. High-frequency nuclear magnetic resonance analysis has not yet been popularized and is not a routine analysis project. Therefore, there is still a lack of an effective and accurate method for determining pore water in shale oil reservoir rocks.

[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 determining pore water in shale oil reservoir rocks, which solves the problems of inaccurate measurement results due to the inability to accurately separate pore water from clay adsorbed water in various existing methods for determining pore water in shale oil reservoir rocks, or the unsatisfactory performance of various measurement methods due to high measurement costs and other factors.

[0007] To achieve the above-mentioned invention object, the method for determining pore water in shale oil reservoir rocks includes:

[0008] Preparing a first sample and a second sample of the rock to be measured into parallel samples;

[0009] Removing the pore water in the first sample;

[0010] Extracting the water in the first sample and the second sample under the same conditions, and respectively measuring the water content of the first sample and the second sample;

[0011] Calculating the pore water content of the rock to be measured through the water content of the second sample and the water content of the first sample.

[0012] In some embodiments of the present disclosure, the method for removing the pore water in the first sample includes:

[0013] Vacuum drying the first sample at 60 °C until it reaches a constant weight.

[0014] In some embodiments of the present disclosure, the rock to be measured is prepared into the first sample and the second sample under freezing conditions.

[0015] In some embodiments of the present disclosure, the extraction method includes:

[0016] Using ethanol to extract the first sample and the second sample.

[0017] In some embodiments of the present disclosure, the ethanol extraction method is:

[0018] The first sample and the second sample are respectively soaked in anhydrous ethanol for at least 72 h, and then dried at 115 °C for 16 h simultaneously.

[0019] In some embodiments of the present disclosure, a chromatograph or a coulometer is used to measure the water content of the first sample and the second sample.

[0020] In some embodiments of the present disclosure, the total volume of the first sample and the second sample is measured respectively;

[0021] The overall volume measurement method is as follows: Place the first sample and the second sample in kerosene to be self-absorbed and saturated, then measure their masses in kerosene and their masses after being saturated with kerosene respectively, and calculate the overall volumes of the first sample and the second sample by using the density of kerosene.

[0022] In some embodiments of the present disclosure, the formula for calculating the pore water content of the rock to be measured is:

[0023]

[0024]

[0025]

[0026]

[0027] In the formula:

[0028] V 1t —The overall volume of the first sample, in cubic centimeters (cm 3 );

[0029] M 1k —The mass of the first sample after being saturated with kerosene, in grams (g);

[0030] M 1c —The mass of the first sample weighed in kerosene, in grams (g);

[0031] ρ k —The density of kerosene, in grams per milliliter (g / ml);

[0032] V 2t —The overall volume of the second sample, in cubic centimeters (cm 3 );

[0033] M 2k —The mass of the second sample after being saturated with kerosene, in grams (g);

[0034] M 2c —The mass of the second sample weighed in kerosene, in grams (g);

[0035] V 2w —The ethanol extraction water volume of the second sample, in milliliters (ml);

[0036] V 1w —The ethanol extraction water volume of the first sample, which is also the clay adsorption water volume of the first sample, in milliliters (ml);

[0037] v 1pw —The pore water content of the first sample, in milliliters (ml)

[0038] v 2pw — The pore water content of the second sample, in milliliters (ml).

[0039] The present disclosure has the following beneficial effects:

[0040] In the measurement method of the present disclosure, before measuring the water content of the rock to be measured, the pore water in the first sample is removed in advance, and then the first sample and the second sample are subjected to water extraction under the same conditions. At this time, the water extracted from the first sample is the clay adsorbed water, and the water extracted from the second sample is the pore water and the clay adsorbed water. Therefore, the measured water content of the first sample represents the clay adsorbed water amount, the water content of the second sample represents the sum of the pore water and the clay adsorbed water, and the difference between the water contents of the two must represent the pore water content of the rock to be measured, solving the problems of various existing methods for measuring the pore water of shale oil reservoir rocks, such as inaccurate measurement results due to the inability to accurately separate the pore water from the clay adsorbed water, or the unsatisfactory measurement methods due to high measurement costs and other factors. Description of the Drawings

[0041] Through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, the above and other objects, features, and advantages of the present disclosure will become clearer. In the drawings:

[0042] Figure 1-1 is the nuclear magnetic measurement spectrum of the first sample in the first group of the parallel sample consistency experiment of the embodiment of the present disclosure;

[0043] Figure 1-2 is the nuclear magnetic measurement spectrum of the second sample in the first group of the parallel sample consistency experiment of the embodiment of the present disclosure;

[0044] Figure 2-1 is the nuclear magnetic measurement spectrum of the first sample in the second group of the parallel sample consistency experiment of the embodiment of the present disclosure;

[0045] Figure 2-2 is the nuclear magnetic measurement spectrum of the second sample in the second group of the parallel sample consistency experiment of the embodiment of the present disclosure. Detailed Embodiments

[0046] The following is a description of the present disclosure based on embodiments. However, it should be noted that the present disclosure is not limited to these embodiments. In the following detailed description of the present disclosure, 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.

[0047] At the same time, unless the context clearly requires, the words such as "including" and "comprising" in the whole specification and claims should be interpreted as having the meaning of including rather than exclusive or exhaustive; that is, the meaning of "including but not limited to".

[0048] Example

[0049] The method for measuring the pore water of the shale oil reservoir rock in the embodiments of the present disclosure is as follows:

[0050] 1) Sample preparation: Prepare the rock to be measured into parallel first and second samples. The specific preparation process is as follows:

[0051] Under the protection of liquid nitrogen cooling, cut a sheet sample with a thickness of about 15 mm from a frozen full-diameter shale sample at a specified depth (the shale sample is stored in a freezer (freezer temperature is lower than -40 °C) after being quickly frozen with liquid nitrogen at the well site and transported back to the laboratory); cut a long strip sample with a length of about 50 mm and a width of about 20 mm in the middle of the sheet sample with a sample cutting device; continue to cut in the middle of the sample to become 2 parallel samples (the first sample and the second sample), weigh the mass, and record the sample number, as well as information such as the sample horizon, depth, and lithology at the same time. Sample cutting method: The layered cross-section of the measured shale sample is always perpendicular to the cutting saw blade, and the saw blade and the cut shale rock sample are always cooled with liquid nitrogen.

[0052] Measurement of the total volume of the sample: Place the 2 parallel samples of the frozen shale to be measured prepared above in kerosene for slow thawing and self-absorption saturation. Use a buoyancy measurement device to measure the mass of the two in kerosene and the mass after they are saturated with kerosene respectively, and then use a densitometer to measure the density of the kerosene used, and calculate the total volume of the first sample and the second sample respectively.

[0053] 2) Remove the pore water in the first sample. The specific removal method is:

[0054] Place the first sample in a vacuum drying oven, dry it to a constant weight at a vacuum of 60 °C, take it out, place it in a desiccator, and weigh the mass of the first sample after cooling to room temperature.

[0055] Of course, it is also possible to choose to remove the pore water in the second sample, and the specific removal method is the same.

[0056] In the method of removing pore water in this step, since the water cannot be collected, the water content of the pore water in the shale cannot be measured in this step.

[0057] 3) Extract the water in the first sample and the second sample under the same conditions. The specific extraction method is:

[0058] Put the first sample from which pore water has been removed and the second sample stored in a freezer into dry sample bags with known masses and corresponding numbers for the samples. At the same time, put them separately into heat extraction bottles with heat resistance and pressure resistance corresponding to the samples and filled with 50 ml of anhydrous ethanol. After soaking for 72 h, place them in an electrothermal blast drying oven and keep them at a constant temperature of 115 °C for 16 h. Then take out the first sample and the second sample from the heat extraction bottles and cool them to room temperature under natural conditions.

[0059] 4) Measure the water content of the first sample and the second sample respectively.

[0060] Use a chromatograph or other equipment, such as a coulometer, to measure the water content in the ethanol in the heat extraction bottles corresponding to the first sample and the second sample according to relevant standards.

[0061] 5) Calculation of pore water content: Obtain the pore water content of the shale to be measured through the water content of the second sample, the water content of the first sample and the pore water calculation mathematical model. Specifically, the following formula can be used. The pore water calculation mathematical model for the water content in the embodiments of the present disclosure is:

[0062]

[0063]

[0064]

[0065]

[0066] In the formula:

[0067] V 1t —— The total volume of the first sample, in cubic centimeters (cm 3 );

[0068] M 1k —— The mass of the first sample saturated with kerosene, in grams (g);

[0069] M 1c —— The mass of the first sample weighed in kerosene, in grams (g);

[0070] ρ k —— Kerosene density, in grams per milliliter (g / ml);

[0071] V 2t —— The total volume of the second sample, in cubic centimeters (cm 3 );

[0072] M 2k —— The mass of the second sample saturated with kerosene, in grams (g);

[0073] M 2c —— Mass of the second sample weighed in kerosene, unit: gram (g);

[0074] V 2w —— Water extraction amount of ethanol from the second sample, unit: milliliter (ml);

[0075] V 1w —— Water extraction amount of ethanol from the first sample, which is also the water adsorbed by clay in the first sample, unit: milliliter (ml);

[0076] v 1pw —— Pore water content of the first sample, unit: milliliter (ml)

[0077] v 2pw —— Pore water content of the second sample, unit: milliliter (ml)

[0078] Experimental Example

[0079] 1. Parallel sample consistency experiment:

[0080] Prepare 2 groups of parallel samples, and use high-frequency two-dimensional nuclear magnetic resonance scanning to measure the clay-adsorbed water and pore water of two groups of shales, as well as the distribution of the nuclear magnetic resonance T2 spectrum of the samples. High-frequency two-dimensional nuclear magnetic resonance can distinguish and measure pore water and clay-adsorbed water (but it is impossible to remove pore water or clay-adsorbed water from the core). Use this feature to verify the water content consistency between parallel samples. The nuclear magnetic resonance experimental results are as Figure 1-1 , Figure 1-2 , Figure 2-1 , Figure 2-2 and Table 1.

[0081]

[0082] Judging from the nuclear magnetic resonance measurement spectrum, the map of two samples in each group shows high consistency. The clay-adsorbed water, solid organic matter, pore water, and oil in the sample are distributed in different regions of the map, and the size, shape, and distribution position of their energy groups are also the same, indicating that the clay-adsorbed water, solid organic matter, pore water, and oil content of each group of parallel samples are similar or the same. Judging from the T2 spectrum, the T2 spectrum distributions of the two groups of samples are the same, and the pore structures of each group of samples are also similar or the same. There are slight differences in the amplitudes of different relaxation times of the T2 spectrum, and the reasons are that the quality of each group of samples is different, the fluid content in the shale is different, and there are interferences during the sample measurement.

[0083] Table 1 shows that the oil and water content per unit mass and the organic matter content per unit mass of several fluids are very similar, and the difference in the content of pore water and clay-adsorbed water is even smaller. When analyzing the saturation with a 30 g mass sample, the maximum difference in the content of pore water and clay-adsorbed water is less than 0.02 ml, and the sample consistency can fully meet the requirements of saturation analysis.

[0084] 2. Experiment on Measuring the Water Content of Samples

[0085] Prepare 9 groups of shale parallel samples according to the parallel sample preparation method provided by the present invention. Among them, after measuring the pore water content by two-dimensional nuclear magnetic resonance analysis on one sample in each group, the parallel sample A for nuclear magnetic resonance analysis is degreased at low temperature, that is, degreased with chloroform reagent, then dehumidified under vacuum at 60 °C until constant weight, and then the parallel sample B corresponding to the parallel sample A and the parallel sample A are simultaneously placed in a special steel heat extraction bottle containing a certain amount of anhydrous ethanol and soaked for 72 h, and then placed in a forced-air drying oven at 115 °C for 16 h. Then, the water content of the ethanol solution is measured by chromatography, and the measurement results are shown in Table 2.

[0086] Table 2 Measurement Results of the Water Content of Samples

[0087]

[0088]

[0089] From the sample measurement data in Table 2, it can be seen that the difference in the pore water content of the parallel samples and the pore water content measured by nuclear magnetic resonance is very small, with a maximum difference of 0.022 mL, a minimum of 0.12 mL, and an average of 0.015 mL, which can meet the requirements of shale saturation testing.

[0090] The above embodiments are only for expressing the implementation modes of the present disclosure. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present disclosure. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present disclosure, several deformations, equivalent replacements, improvements, etc. can be made, and these all belong to the protection scope of the present disclosure. Therefore, the protection scope of the patent of the present disclosure should be subject to the appended claims.

Claims

1. A method for determining pore water in shale oil reservoir rocks, characterized in that, Including: Preparing the rock to be measured into a parallel first sample and a second sample; Removing the pore water in the first sample; Extracting the moisture in the first sample and the second sample under the same conditions, and respectively measuring the moisture contents of the first sample and the second sample; Calculating the pore water content of the rock to be measured through the moisture content of the second sample and the moisture content of the first sample; The formula for calculating the pore water content of the rock to be measured is: In the formula: V 1t — Total volume of the first sample, in cm 3 ; M 1k — Mass of the first sample after being saturated with kerosene, unit: g; M 1c — Mass of the first sample weighed in kerosene, unit: g; ρ k — Density of kerosene, unit: g / ml; V 2t — Total volume of the second sample, unit: cm 3 ; M 2k — Mass of the second sample after being saturated with kerosene, unit: g; M 2c — Mass of the second sample weighed in kerosene, unit: g; V 2w — Water extraction amount of the second sample, unit: ml; V 1w — Water content extracted by ethanol from the first sample, which is also the water content adsorbed by clay in the first sample, unit: ml; v 1pw — The water content of the first sample pore, unit: ml; v 2pw — The water content of the second sample in pore, unit: ml.

2. The method for determining the pore water of shale oil reservoir rocks according to claim 1, characterized in that: The method for removing the pore water in the first sample includes: Vacuum drying the first sample at 60 °C until constant weight.

3. The method for measuring the pore water of the shale oil reservoir rock according to claim 1 or 2, wherein: Preparing the rock to be measured into the first sample and the second sample under freezing conditions.

4. The method for determining pore water in shale oil reservoir rocks according to claim 3, characterized in that, The extraction method includes: Using ethanol to extract the first sample and the second sample.

5. The method for determining pore water in shale oil reservoir rocks according to claim 4, characterized in that, The method of ethanol extraction is: After the first sample and the second sample are respectively soaked in anhydrous ethanol for at least 72 h, they are simultaneously dried at 115 °C for 16 h.

6. The method for measuring the pore water of the shale oil reservoir rock according to claim 1, wherein: Using a chromatograph or a coulometer to measure the moisture contents of the first sample and the second sample.

7. The method for measuring the pore water of the shale oil reservoir rock according to claim 5, wherein: Respectively measuring the total volumes of the first sample and the second sample; The method for measuring the total volume is: placing the first sample and the second sample in kerosene to be self-saturated by absorption, respectively measuring their masses in kerosene and the masses after being saturated with kerosene, and using the density of kerosene to calculate the total volumes of the first sample and the second sample respectively.

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