Method for calculating reasonable gas recovery speed of shale gas

Abstract

The invention belongs to the technical field of shale gas development and research, and discloses a reasonable shale gas recovery speed calculation method which comprises the following steps: sampling shale; carrying out a flow velocity sensitivity experiment on the shale sample, drawing a change curve of the permeability loss rate along with the injection velocity, and determining a critical flow velocity according to a curve inflection point; and the reasonable gas production speed is determined. A traditional method depends on a numerical simulation technology and calculation of a theoretical model when the reasonable gas production speed is calculated, and a true value under the stratum condition is difficult to obtain. According to the method provided by the invention, the flow velocity sensitive rock physical simulation experiment is carried out on the natural rock core of the reservoir, the reasonable gas production speed under the stratum condition can be obtained, and the calculation precision is effectively improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of shale gas development research, and relates to a shale gas reasonable production rate calculation method. BACKGROUND

[0002] The shale gas development process will produce a velocity sensitivity effect, which refers to the phenomenon that particles in the reservoir pore migrate and block the throat due to gas flow during the exploitation of shale gas, which will cause the permeability of the reservoir to decrease and affect the development effect of shale gas. Shale gas is usually developed in a depletion mode, that is, relying on the energy of the formation itself as the driving force for shale gas production. If the production rate is too high, the velocity sensitivity effect will cause the permeability of the reservoir to decrease, and if the production rate is too low, it will affect the development effect of the gas field, increase the investment recovery period and affect the economic benefit. Therefore, it is crucial to determine a reasonable production rate.

[0003] Geologists have conducted a lot of research on the calculation of reasonable production rate. The invention patent with the application publication number CN115705507A provides a method for evaluating the reasonable production rate of an abnormal high-pressure gas reservoir, which uses numerical simulation technology to obtain sensitive parameters affecting the reasonable production rate interval and establishes a production rate calculation model. The invention patent with the application publication number CN115600520A provides a method for calculating the reasonable production rate of a gas storage, which can calculate the reasonable production rate under different wellhead pressures and formation pressures by taking the critical sand production flow as a constraint condition. The invention patent with the authorization announcement number CN110984974B provides a method for determining the reasonable production rate of a water-bearing gas reservoir based on water invasion speed, which combines water invasion speed, water invasion index, number of production wells and gas well productivity to finally determine the reasonable production rate of a water-bearing gas reservoir.

[0004] The above methods for calculating the reasonable production rate rely on numerical simulation technology and theoretical model calculation, lack rock physics simulation experiments based on natural cores of reservoirs, and errors cannot be avoided. Moreover, the research on the reasonable production rate of different types of reservoirs is not considered, which leads to limitations in application effect. SUMMARY

[0005] The purpose of the present application is to provide a shale gas reasonable production rate calculation method to solve the problem of insufficient calculation precision of traditional methods, provide a shale reasonable production rate calculation model based on sample permeability, and scientifically guide the compilation of shale gas development schemes.

[0006] To achieve the above purpose, the technical solution adopted by the present application is as follows:

[0007] A shale gas reasonable production rate calculation method, comprising the following steps:

[0008] (1) sampling shale;

[0009] (2) Conducting flow rate sensitivity experiment on shale samples, drawing the curve of permeability loss rate changing with injection rate, and determining the critical flow rate according to the inflection point of the curve;

[0010] (3) Determining the reasonable gas production rate.

[0011] In step (1), the shale gas reservoir is divided into gas layer and poor gas layer according to the single well comprehensive interpretation results;

[0012] In step (1), the number of samples taken from the two types of shale reservoirs is not less than 3 pieces;

[0013] In step (2), the flow rate sensitivity experiment sample is a columnar slug with a diameter of 2.5 cm and a length of 5 cm;

[0014] In step (2), the flow rate sensitivity experiment is carried out in accordance with the provisions of the People's Republic of China Petroleum and Natural Gas Industry Standard SY / T5358-2010 "Reservoir Sensitivity Flow Experiment Evaluation Method".

[0015] In step (2), the permeability loss rate can be represented by formula (1):

[0016]

[0017] In the formula: F KL is the permeability loss rate, %; K D is the permeability of the shale sample flow rate sensitivity experiment, mD; K Y is the original permeability of the shale sample, mD.

[0018] In step (2), the specific operation method for determining the critical flow rate is: draw the binary first-order equation of the permeability loss rate changing with the injection rate, which is represented by formula (2):

[0019] F KL = AV Flu 2 +B V Flu +C (2)

[0020] In formula (2), K LR is the permeability loss rate, %; V Flu is the injection rate, mL / min; A and B are binary quadratic equation coefficients, dimensionless; C is a constant.

[0021] Differentiate formula (2), and the point where the derivative is equal to zero is the critical flow rate, denoted as V Flu-C .

[0022] In step (2), a flow rate sensitivity experiment was conducted on the shale sample at different injection rates, with the injection rates being 0.25 mL / min, 0.5 mL / min, 0.75 mL / min, 1 mL / min, 2 mL / min, 3 mL / min, etc., and then increasing by 1 mL / min until the end of the experiment.

[0023] In step (2), when the permeability loss rate F KL When the value is greater than 70%, the flow rate sensitivity experiment ends.

[0024] In step (3), the reasonable gas collection rate is the average value of the critical flow rates of multiple samples.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] Traditional methods for calculating reasonable gas production rates rely on numerical simulation techniques and theoretical models, making it difficult to obtain realistic values ​​under formation conditions. The method provided by this invention uses petrophysical simulation experiments on flow rate sensitivity in natural reservoir cores to determine reasonable gas production rates under formation conditions, effectively improving calculation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the comprehensive histogram of Well Z301;

[0028] Figure 2 This is the intersection diagram of injection velocity and permeability loss rate of sample No. 6. DETAILED DESCRIPTION

[0029] In order to make the technical means adopted by the present invention and the objectives achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0030] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0031] Example 1

[0032] This specific embodiment adopts the following technical solution: a method for calculating the reasonable gas production rate of shale gas, comprising the following steps:

[0033] (1) Sampling shale

[0034] The shale samples of the present invention were taken from the Z303 well in the Zigong area of ​​the Sichuan Basin, with a total of 12 samples;

[0035] like Figure 1 The figure shows the comprehensive histogram of Well Z303. According to the comprehensive interpretation results of a single well, shale gas reservoirs can be divided into two types: gas layers and poor gas layers.

[0036] 8 samples were drilled in gas reservoirs, and 4 samples were drilled in poor gas reservoirs;

[0037] The shale samples were processed into core columns with a diameter of 2.5 cm and a length of 5 cm by using a DK7716 wire cutting machine.

[0038] (2) The flow rate sensitivity experiment was carried out on the shale sample, and the permeability loss rate curve was drawn with the change of flow rate,

[0039] The critical flow rate was determined according to the inflection point of the curve.

[0040] The flow rate sensitivity experiment was carried out according to the provisions of the People's Republic of China Petroleum and Natural Gas Industry Standard SY / T 5358-2010 "Reservoir Sensitivity Flow Experiment Evaluation Method".

[0041] The injection rate was 0.25 mL / min, 0.50 mL / min, 0.75 mL / min, 1 mL / min, 2 mL / min, 3 mL / min, etc., and the subsequent increase was 1 mL / min until the end of the experiment;

[0042] When the permeability loss rate F KL > 70%, the flow rate sensitivity experiment was ended;

[0043] The permeability loss rate can be expressed by formula (1):

[0044]

[0045] In the formula: F KL is the permeability loss rate, %; K D is the permeability of shale sample flow rate sensitivity experiment, mD; K Y is the original permeability of shale sample, mD.

[0046] Taking sample No. 6 as an example, the injection rate and permeability loss rate intersection diagram is shown in Figure 1 , and the related data is shown in Table 1;

[0047] Table 1

[0048]

[0049] When the injection rate was 4 mL / min, the permeability loss rate F KL = 70.5%, the experiment was ended;

[0050] The permeability loss rate gradually increased with the increase of injection rate, and the two had a multiple linear relationship, the correlation coefficient R 2 = 0.9806, which can be expressed by formula (2):

[0051] y = -5.7667x2 +41.331x-5.0585 (2)

[0052] The critical flow rate corresponding to y'=0 is 3.58 mL / min when the formula (2) is differentiated.

[0053] (3) Determining reasonable gas production rate

[0054] The critical flow rates of the 12 samples are shown in Table 2:

[0055] Table 2

[0056]

[0057] The reasonable gas production rate is the average value of the critical flow rates of multiple samples of the same type.

[0058] The calculation result shows that the reasonable gas production rate of the gas layer is 5.57 mL / min, and the reasonable gas production rate of the poor gas layer is 2.80 mL / min, and the reasonable gas production rate of the gas layer is about twice that of the poor gas layer.

[0059] Although some embodiments of the present application have been described herein, those skilled in the art will understand that changes can be made to the embodiments herein without departing from the spirit of the present application. The above embodiments are only exemplary and should not be taken as limiting the scope of the present application.

Claims

1. A method for calculating a reasonable gas production rate of shale gas, characterized in that, The method comprises the following steps: (1) sampling shale; (2) conducting a flow rate sensitivity experiment on the shale sample, drawing a curve of permeability loss rate changing with injection rate, and determining a critical flow rate according to an inflection point of the curve; (3) determining a reasonable gas production rate.

2. The method of claim 1, wherein, In step (1), the shale gas reservoir is divided into two types of gas layers and poor gas layers according to single-well comprehensive interpretation results.

3. The method of claim 1, wherein, In step (1), the number of samples of the two types of shale reservoirs is not less than 3.

4. The method of claim 1, wherein, In step (2), the flow rate sensitivity experiment sample is a columnar slug with a diameter of 2.5 cm and a length of 5 cm.

5. The method of claim 1, wherein, In step (2), the flow rate sensitivity experiment is performed according to the provisions of the People's Republic of China Petroleum and Natural Gas Industry Standard SY / T5358-2010 "Reservoir Sensitivity Flow Experiment Evaluation Method".

6. The method of claim 1, wherein, In step (2), the permeability loss rate can be represented by formula (1): where: F KL is the permeability loss rate, %; K D is the permeability of the shale sample flow rate sensitivity experiment, mD; K Y is the original permeability of the shale sample, mD.

7. The method of calculating a reasonable gas production rate for shale gas according to claim 1, wherein, In step (2), the specific operation method for determining the critical flow rate is as follows: a binary first-order equation of the permeability loss rate changing with the injection rate is drawn, which is represented by formula (2): F KL = AV Flu 2 + B V Flu + C (2) In formula (2), K LR is the permeability loss rate, %; V Flu is the injection rate, mL / min; A, B are the coefficients of the first degree equation, dimensionless; C is the constant; Taking the derivative of equation (2), the point where the derivative equals zero is the critical flow velocity, denoted as V Flu-C .

8. The method of calculating a reasonable gas production rate for shale gas according to claim 1, wherein, In step (2), the flow rate sensitivity experiment of the shale sample is conducted at different injection rates, and the injection rates are 0.25 mL / min, 0.5 mL / min, 0.75 mL / min, 1 mL / min, 2 mL / min, 3 mL / min, and so on, and the subsequent injection rates are increased by 1 mL / min until the experiment is completed.

9. The method of claim 1, wherein, In step (2), when the permeability loss rate F KL > 70%, the flow rate sensitivity experiment is ended.

10. The method of claim 1, wherein, In step (3), the reasonable gas production rate is an average value of the critical flow rates of the multiple samples.

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