Shale expansion rate calculation method

Abstract

The invention relates to a shale expansion rate calculation method, and belongs to the technical field of shale oil and gas development. The method comprises the following specific steps: carrying out shale linear expansion rate determination experiments at different soaking times, and calculating the expansion rate value of a shale sample; obtaining the TOC content, the quartz and clay mineral content, the porosity value and the particle density value of the shale sample; establishing a shale expansion rate calculation model by taking the linear expansion rate as a dependent variable, taking the TOC content, the quartz content, the clay mineral content, the porosity and the particle density as independent variables and adopting a multiple linear regression method; and establishing a shale expansion rate calculation model based on different soaking times. According to the method, a shale expansion rate calculation model is established through multiple shale expansion rate sensitive parameters by adopting a multiple linear regression method, and the method has the effects of being simple, economical, practical, scientific and effective.

Description

Technical Field

[0001] The present invention relates to a method for calculating the shale expansion rate, belonging to the technical field of shale oil and gas development. Background Art

[0002] Hydraulic fracturing technology is an important engineering technical means to ensure the efficient development of unconventional oil and gas resources. Shale reservoirs usually contain a large amount of clay minerals, such as illite, chlorite, montmorillonite, and kaolinite, etc. When these clay minerals come into contact with water molecules in the fracturing fluid, due to the weak intermolecular force between the clay mineral layers, water molecules can easily enter the crystal layers of the clay minerals, resulting in the dissociation and diffusion of cations on the crystal layer surface in water, generating the clay mineral water absorption and swelling effect, blocking pores and throats, greatly reducing the permeability of the shale reservoir, and affecting the development effect of shale oil and gas. Therefore, reducing the damage of the shale oil and gas reservoir caused by the clay water absorption and swelling effect is a necessary measure to increase production, and the use of clay anti-swelling agents is the main means to prevent clay swelling. To evaluate the effect of clay anti-swelling agents, it is necessary to carry out shale expansion rate experiments and calculate the shale expansion rate.

[0003] In the prior art, the invention patent with the patent publication number CN 114839101 A provides a method for evaluating the inhibition effect of anti-swelling agents on the hydration swelling of shale reservoirs. This method determines the effect of anti-swelling agents by carrying out displacement experiments on shale samples with different clay mineral contents and measuring the changes in parameters such as porosity and permeability before and after the displacement of the shale samples, so as to determine the optimal dosage of organic anti-swelling agents for reservoirs with different clay contents. Although this method gives a calculation method for the optimal dosage of organic anti-swelling agents, it does not give a quantitative calculation method for the shale expansion rate under different soaking times.

[0004] The traditional method uses the linear expansion rate to measure the shale expansion rate, and evaluates the hydration swelling characteristics of rock samples or the anti-swelling performance of inhibitors, fracturing fluids, and drilling fluids by calculating the amount of hydration swelling that occurs after the interaction between the rock sample and the test solution. The problems of the traditional method are: the experimental process of the linear expansion rate is complex, and it takes a lot of time to obtain the calculation results of the shale expansion rate under different soaking times. The experimental period is usually more than 10 days, which is difficult to meet the requirements of rapid fracturing transformation and rapid production of shale reservoirs. Therefore, it is necessary to carry out research to find an alternative method that can provide the calculation results of the shale expansion rate in a short time and guide the evaluation of the fracturing transformation effect of on-site shale oil and gas reservoirs. Summary of the Invention

[0005] The present invention discloses a method for calculating the shale expansion rate to guide the evaluation of the fracturing effect of on-site shale oil and gas reservoirs.

[0006] The technical solution adopted by the present invention is: a method for calculating the shale expansion rate, and the specific steps are as follows:

[0007] Step 1: Conduct experiments on the linear expansion rate of shale with different soaking times, and calculate the linear expansion rate values of shale samples;

[0008] Step 2: Conduct experiments on the total organic carbon of shale samples to obtain the TOC content of shale samples;

[0009] Step 3: Conduct mineral analysis experiments on shale samples to obtain the contents of quartz and clay minerals in the samples;

[0010] Step 4: Conduct experiments on the porosity of shale samples to obtain the porosity values of shale samples;

[0011] Step 5: Conduct experiments on the particle density of shale samples to obtain the particle density values of shale samples;

[0012] Step 6: Using the linear expansion rate as the dependent variable and the TOC content, quartz content, clay mineral content, porosity, and particle density as independent variables, adopt the multiple linear regression method to establish a calculation model for the shale expansion rate;

[0013] Step 7: Establish a calculation model for the shale expansion rate based on different soaking times.

[0014] Furthermore, in the above-mentioned Step 1, the experiment on the linear expansion rate of shale includes core preparation, expansion experiment, and calculation of the expansion rate.

[0015] Furthermore, in the above-mentioned Step 1, the different soaking times are 2h, 4h, 8h, 24h, 48h, and 72h respectively.

[0016] Furthermore, in the above-mentioned Step 1, the calculation of the linear expansion rate of shale is carried out through Formula 1:

[0017]

[0018] V H : Linear expansion rate of shale at soaking time t, unit: %;

[0019] R t : Linear expansion amount at soaking time t, unit: mm;

[0020] H 1 : Height of the measuring cylinder before loading the shale sample powder, unit: mm;

[0021] H 2 : Height of the part of the measuring cylinder without the shale sample powder after loading the shale sample powder, unit: mm.

[0022] Furthermore, in the above-mentioned Step 2, specifically, the shale samples need to be pretreated before the total organic carbon content determination experiment, and the specific process is as follows:

[0023] (1) Grind the shale sample into 100-mesh powder using an agate mortar;

[0024] (2) Add the shale powder to dilute hydrochloric acid and react for 2 hours to completely remove inorganic minerals;

[0025] (3) Rinse the shale sample treated with dilute hydrochloric acid with distilled water for 10 minutes until neutral;

[0026] (4) Place the powdered shale sample in a constant-temperature drying oven and dry it at 60 °C for 24 hours.

[0027] Further, in step 3, the sample needs to be pretreated before the mineral content determination experiment. The specific process is as follows:

[0028] (1) Wash the shale sample with oil. The organic solvent used for washing is chloroform, and the treatment is carried out until the fluorescence is below grade four;

[0029] (2) Dry the shale sample after washing with oil using a constant-temperature drying oven at a temperature of 50 °C for 24 hours;

[0030] (3) Grind the shale sample after washing and drying with oil into 100-mesh powder using an agate mortar.

[0031] Further, in step 4, the gas method is used for the porosity determination experiment. The measuring medium is helium, the measuring pressure is 0.7 MPa, and the confining pressure is 1.2 MPa.

[0032] Further, in step 5, when conducting the particle density determination experiment on the shale sample, the shale particle density is calculated according to the density formula by measuring the shale volume and weight.

[0033] Further, the shale linear expansion rate calculation model in step 6 can be expressed by formula two:

[0034] Linear expansion rate = a × TOC + b × Q ua + c × C la + d × D en + e × P oro + f(2)

[0035] Where: TOC is the total organic carbon content, %; Q ua is the quartz mineral content, %; C la is the clay mineral content, %; D en is the shale particle density value, cm 3 / g; P oro is the shale porosity value, %; a, b, c, d, e are formula fitting coefficients, and f is a constant, dimensionless.

[0036] The present invention discloses a method for calculating the shale expansion rate. The beneficial effect is that the method provided by the present invention uses multiple shale expansion rate sensitive parameters and adopts the multiple linear regression method to establish a shale expansion rate calculation model, which has the effects of simple method, economic practicality, scientific validity. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0038] Figure 1 The figure shows the relationship diagram between the shale expansion rate calculated by the model and the shale expansion rate calculated by the experiment under different soaking time conditions;

[0039] Figure 2 The figure shows the curve of the shale expansion rate calculated by the model of shale sample 1 changing with the soaking time.

[0040] SPECIFIC IMPLEMENTATION METHODS

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments.

[0042] The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. Embodiment 1

[0043] In this embodiment, the shale sample is taken from the Zigong area in the southern part of the Sichuan Basin; a method for calculating the shale expansion rate is provided, and the specific steps are as follows:

[0044] Step 1: Conduct experiments on the linear expansion rate of shale with different soaking times, and calculate the expansion rate values of the shale samples;

[0045] Specifically: The experimental process for measuring the linear expansion rate of shale is carried out with reference to the petroleum and natural gas industry standard SY / T 5613-2016 "Drilling Fluid Testing - Test Methods for Physical and Chemical Properties of Shale and Mudstone";

[0046] The experimental instrument is produced by Jiangsu Tuochuang Petroleum Instrument Co., Ltd., and the model is NP-03 high-temperature and high-pressure shale dilatometer;

[0047] The linear expansion rate measurement experiment includes three steps: core preparation, expansion experiment, and expansion rate calculation;

[0048] Perform the linear expansion rate measurement experiment on shale samples with different soaking times, and the different soaking times are 2h, 4h, 8h, 24h, 48h, and 72h respectively;

[0049] Calculate the linear expansion rate of shale through Formula 1:

[0050]

[0051] V H : The linear expansion rate of shale at soaking time t, %;

[0052] R t : The linear expansion amount at soaking time t, mm;

[0053] H 1 : The height of the measuring cylinder before loading the shale sample powder, mm;

[0054] H 2 : The height of the part of the measuring cylinder without the shale sample powder after loading the shale sample powder, mm.

[0055] Step 2: Conduct a total organic carbon measurement experiment on the shale sample to obtain the TOC content of the shale sample;

[0056] Specifically, a CS744 carbon-sulfur analyzer is used for the total organic carbon measurement experiment, and the experiment is carried out in accordance with the national standard GB / T 19145-2003 "Determination of Total Organic Carbon in Sedimentary Rocks";

[0057] Before the total organic carbon content measurement experiment, the shale sample needs to be pretreated, and the specific process is as follows:

[0058] (1) Grind the shale sample into 100-mesh powder using an agate mortar;

[0059] (2) Add the shale powder to dilute hydrochloric acid and react for 2 hours to completely remove inorganic minerals;

[0060] (3) Rinse the shale sample treated with dilute hydrochloric acid with distilled water for 10 minutes until it is neutral;

[0061] (4) Place the powdered shale sample in a constant temperature drying oven and dry it at 60°C for 24 hours.

[0062] Step 3: Conduct a mineral analysis experiment on the shale sample to obtain the quartz and clay mineral contents of the sample;

[0063] The instrument for the mineral analysis experiment is a D8 DISCOVER type X-ray diffractometer;

[0064] The mineral analysis experiment is carried out in accordance with the industry standard SY / T 5163-2010 "X-ray Diffraction Analysis Method for Clay Minerals and Common Non-Clay Minerals in Sedimentary Rocks" of the oil and gas industry;

[0065] Before the mineral content determination experiment, the sample needs to be pretreated. The specific process is as follows:

[0066] (1) Wash the shale sample with oil. The organic solvent used for washing oil is chloroform, and it is processed until the fluorescence is below grade four;

[0067] (2) Use a constant temperature drying oven to dry the washed shale sample. The temperature is 50°C and the time is 24 hours;

[0068] (3) Use an agate mortar to grind the washed and dried shale sample into a powder with a mesh size of 100.

[0069] Step 4: Carry out a porosity determination experiment on the shale sample to obtain the porosity value of the shale sample;

[0070] Specifically, the gas method is used to measure the porosity of the shale sample, and the measuring medium is helium;

[0071] The experimental instrument is the HKXD-C type helium porosity automatic measuring instrument;

[0072] The experimental temperature is 25°C, the measuring pressure is 0.7 MPa, and the confining pressure is 1.2 MPa.

[0073] Step 5: Carry out a particle density determination experiment on the shale sample to obtain the particle density value of the shale sample;

[0074] Specifically, the shale particle density determination experiment includes the following steps:

[0075] (1) Measure the rock volume. The instrument model is the HKXD-C type helium porosity automatic measuring instrument;

[0076] (2) Measure the weight of the shale. The instrument model is the DX-100E type high-precision balance, and the measuring accuracy is 0.0001 g;

[0077] (3) Calculate the shale particle density according to the density formula.

[0078] Step 6: Take the linear expansion rate as the dependent variable, and the TOC content, quartz content, clay mineral content, particle density and porosity as the independent variables, and use the multiple linear regression method to establish a shale expansion rate calculation model.

[0079] As shown in Table 1: The shale linear expansion rate and the corresponding calculation results of TOC content, quartz content, clay mineral content, particle density and porosity under different soaking time conditions:

[0080] Table 1

[0081]

[0082]

[0083] The calculation model of the linear expansion rate of shale can be expressed by Formula 2:

[0084] Linear expansion rate = a × TOC + b × Q ua + c × C la + d × D en + e × P oro + f (2)

[0085] In the formula: TOC is the total organic carbon content, %; Q ua is the quartz mineral content, %; C la is the clay mineral content, %; D en is the shale particle density value, cm 3 / g; P oro is the shale porosity value, %; a, b, c, d, e are the formula fitting coefficients, and f is a constant, dimensionless.

[0086] As shown in Table 2, they are the fitting coefficients and the constant f value in Formula 2 under different soaking time conditions;

[0087] Table 2

[0088]

[0089] According to Formula 2, the linear expansion rates of 10 shale samples under different soaking times were calculated, and the calculation results are shown in Table 3:

[0090] Table 3

[0091]

[0092] The relationship between the experimentally calculated shale expansion rate and the model-calculated shale expansion rate is as Figure 1 shown. There is a good linear relationship between the two, and all data points are located near Y = X. In addition, the error analysis results show (Table 4) that the average value of the relative error calculated by the model is only 4.2%, indicating that the calculation model provided by the examples of the present invention has high accuracy.

[0093] Table 4

[0094]

[0095] Step 7: Establish a calculation model of shale expansion rate based on different soaking times

[0096] Taking the shale sample 1 as an example, the swelling rate of the sample under different soaking time conditions can be calculated by Formula 2, as shown in Table 5:

[0097] Table 5

[0098]

[0099]

[0100] Taking the soaking time as the abscissa and the swelling rate of the shale calculated by the model as the ordinate, the relationship curve between the two is plotted; as Figure 2 shown, there is a very strong power function relationship between the two, and the correlation coefficient R2 is as high as 0.9909, which can be expressed by Formula 3:

[0101] y = 10.556x 0.0314 (3)

[0102] According to Formula 3, the swelling rate of the shale sample under any soaking time condition can be calculated;

[0103] Taking the soaking time equal to 30 hours as an example, the swelling rate of the shale is calculated to be 10.556×30 0.0314 = 11.75%.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating the shale expansion rate, characterized in that, it includes the following steps: Step 1: Conduct experiments on measuring the linear expansion rate of shale at different soaking times, and calculate the linear expansion rate value of the shale sample; Step 2: Conduct experiments on measuring the total organic carbon of the shale sample to obtain the TOC content of the shale sample; Step 3: Conduct mineral analysis experiments on the shale sample to obtain the quartz and clay mineral contents of the sample; Step 4: Conduct experiments on measuring the porosity of the shale sample to obtain the porosity value of the shale sample; Step 5: Conduct experiments on measuring the particle density of the shale sample to obtain the particle density value of the shale sample; Step 6: Taking the linear expansion rate as the dependent variable, and taking the TOC content, quartz content, clay mineral content, porosity and particle density as independent variables, use the multiple linear regression method to establish a calculation model for the shale expansion rate; Step 7: Establish a calculation model for the shale expansion rate based on different soaking times.

2. A method for calculating the shale expansion rate according to claim 1, characterized in that, in Step 1, the experiment on measuring the linear expansion rate of shale includes core preparation, expansion experiment and expansion rate calculation.

3. A method for calculating the shale expansion rate according to claim 1, characterized in that, in Step 1, the different soaking times are 2h, 4h, 8h, 24h, 48h and 72h respectively.

4. A method for calculating the shale expansion rate according to claim 1, characterized in that, in Step 1, the calculation of the shale linear expansion rate is carried out through Formula 1: V H : Linear expansion rate of shale at soaking time t; R t : Linear expansion amount at soaking time t; H 1 : Height of the measuring cylinder before loading the shale sample powder; H 2 : The height of the measuring cylinder in the part where no shale sample powder is loaded after loading the shale sample powder.

5. A method for calculating the shale expansion rate according to claim 1, characterized in that, in Step 2, specifically, the shale sample needs to be pretreated before the total organic carbon content measurement experiment, and the specific process is as follows: Step 2.1: Use an agate mortar to grind the shale sample into a powder of 100 mesh; Step 2.2: Add the shale powder into dilute hydrochloric acid, and the reaction time is 2 hours to completely remove inorganic minerals; Step 2.3: Rinse the shale sample treated with dilute hydrochloric acid with distilled water for 10 minutes until it is neutral; Step 2.4: Place the powdered shale sample in a constant temperature drying oven and dry it at 60°C for 24 hours.

6. A method for calculating the shale expansion rate according to claim 1, characterized in that, in Step 3, the sample needs to be pretreated before the mineral content measurement experiment, and the specific process is as follows: Step 3.1: Wash the shale sample with an organic solvent of chloroform until the fluorescence is below grade four; Step 3.2: Use a constant temperature drying oven to dry the shale sample after washing with oil, the temperature is 50°C, and the time is 24 hours; Step 3.3: Use an agate mortar to grind the shale sample after washing and drying with oil into a powder of 100 mesh.

7. A method for calculating the shale expansion rate according to claim 1, characterized in that, in Step 4, the porosity measurement experiment uses the gas method, the measurement medium is helium, the measurement pressure is 0.7MPa, and the confining pressure is 1.2MPa.

8. A method for calculating the shale expansion rate according to claim 1, characterized in that, In Step 5, when conducting the particle density measurement experiment on the shale sample, the shale particle density is calculated according to the density formula by measuring the shale volume and weight.

9. A method for calculating the shale expansion rate according to any one of claims 1-8, characterized in that in Step 6, the shale linear expansion rate calculation model can be expressed by Formula 2: Coefficient of linear expansion = a × TOC + b × Q ua + c × C la + d × D en + e × P oro + f(2) where: TOC is the total organic carbon content, %; Q ua is the quartz mineral content, %; C la is the clay mineral content, %; D en is the shale particle density value, cm 3 / g; P oro is the shale porosity value, %; a, b, c, d, e are formula fitting coefficients, and f is a constant, dimensionless.

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