Method for quantitatively estimating gas content based on full-diameter core of shale gas well
Through the method of recovering the original state and desorption method of pressure-down mining experiments on shale samples, the problem of large error in determining the gas content in the existing technology is solved, and more accurate gas content detection is achieved.
Patent Information
- Application Number
- CN202311633528.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-01
- Publication Date
- 2025-06-03
AI Technical Summary
There are large errors in determining the gas content of shale in the existing desorption method, which is mainly due to the rapid decay of the gas concentration at the core boundary, resulting in the total length of gas loss.
The quantitative gas content estimation method based on the full diameter core of the shale gas well was used, including the original state recovery experiment of the shale sample and the desorption method of the pressure-down mining experiment. In the recovery experiment, the shale sample was placed in a constant temperature chamber to simulate the original formation temperature conditions and pressurized to 15 MPa to achieve gas saturation. Then, a desorption method of pressure-down mining experiment was carried out to simulate the centering process of lifting shale cores in the wellbore.
By first restoring the shale sample to saturation state, and then performing desorption and pressure reduction mining experiments, the gas content detection error is reduced and the rigor of detection is improved.
Smart Images
Figure CN120083494A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of shale gas content estimation, and specifically to a method for quantitatively estimating the gas content based on the full-diameter core of a shale gas well. Background Art
[0002] Shale gas refers to the natural gas with commercial value that is stored and preserved in rich organic matter, mature dark shale or high-carbon shale due to the adsorption of organic matter or the existence of fractures and matrix pores in the rock. Its main component is methane. For the detection of shale gas, the commonly used method is carbon isotope detection, which is a method of determining the age or original source of substances by using the proportional difference of different isotopes of carbon elements. For the determination method of gas content, there are desorption method, isothermal adsorption method, logging interpretation method, etc. Among them, the desorption method is the most direct method for measuring the shale gas content, which can simulate the actual formation environment conditions to measure the shale gas content, so it is used as the basic method for measuring the shale gas content.
[0003] However, in the prior art, the research on the desorption method for determining the shale gas content focuses on numerical simulation methods, and there are errors to varying degrees. When the core is taken out, the gas concentration at the core boundary is higher, and the diffusion rate is faster. Therefore, the gas concentration at the boundary decays faster, and the total time for gas loss in the core is shorter. Therefore, there are large errors in the detection of shale gas content. Summary of the Invention
[0004] The purpose of the present invention is to provide a method for quantitatively estimating the gas content based on the full-diameter core of a shale gas well, so as to solve the problem that the prior desorption method for determining the shale gas content focuses on numerical simulation and has large errors.
[0005] To achieve the above purpose, the present invention adopts the following technical solutions: The present invention provides a method for quantitatively estimating the gas content based on the full-diameter core of a shale gas well, including: Conducting an original state restoration experiment on the extracted shale sample of the full-diameter core of the shale gas well; Measuring the shale gas content of the restored shale sample by the desorption method.
[0006] Further, the conducting of the original state restoration experiment on the extracted shale sample of the full-diameter core of the shale gas well includes: Placing the shale sample in an incubator to simulate the original formation temperature conditions, and pressurizing the shale sample.
[0007] Further, the temperature of the incubator is set at 60°C.
[0008] Further, the pressurizing of the shale sample means: Pressurize the shale sample to 15 MPa.
[0009] Furthermore, the pressurization process of the shale sample includes: Place the shale sample in a full-diameter core holder, inject methane gas into the intermediate container, connect the intermediate container and the standard chamber, and use a piston pump to pressurize the methane gas until it reaches 15 MPa; Connect the standard chamber and the full-diameter core holder, saturate the shale sample with gas, and end the saturation when the pressures at both ends of the standard chamber and the full-diameter core holder are stable. Then close the valve between the standard chamber and the full-diameter core holder.
[0010] Furthermore, the desorption method is used to measure the gas content of the restored shale sample, including: Set up a desorption method pressure reduction production experiment system and evacuate and inject water; Place the shale sample in a full-diameter core holder and saturate it with gas; Reduce the pressure of the full-diameter core holder. When the pressure drops to 0.1 MPa, conduct a lost gas volume measurement experiment; when the gas production rate is lower than 0.6 cm 3 / min, conduct a desorbed gas volume measurement experiment, and record the time, pressure, and gas production data during the pressure reduction process; Record the sum of the lost gas volume under standard conditions, the desorbed gas volume under standard conditions, and the residual gas volume under standard conditions, which is the estimated gas content.
[0011] Furthermore, use Origin numerical simulation software to fit the residual gas volume under standard conditions.
[0012] Furthermore, during the pressure reduction process, the pressure drop rates are set to: 1.25 MPa / min, 1 MPa / min, 0.75 MPa / min, 0.5 MPa / min, 0.25 MPa / min, and 0.125 MPa / min.
[0013] Compared with the prior art, the beneficial effects of the present invention are: In the present invention, first, a shale original state restoration experiment is carried out to saturate the gas content of the sample, that is, restore it to the state before collection. Then, a desorption method pressure reduction production experiment is carried out. The above two groups of experiments are used to simulate the pressure reduction production of shale, that is, simulate the coring process of the shale core being lifted in the wellbore, ensuring the rigor of the shale gas content detection and reducing the gas content detection error. Description of the Drawings
[0014] Figure 1 It is a flow chart of a method for quantitatively estimating the gas content of a full-diameter core of a shale gas well provided by the present invention; Figure 2The flow chart of the experiment for measuring the permeability of the shale sample, which is a method for quantitatively estimating the gas content based on the full-diameter core of a shale gas well provided by the present invention; Figure 3 The flow chart of the experiment for restoring the original state of shale and the experiment for pressure reduction production by desorption method, which is a method for quantitatively estimating the gas content based on the full-diameter core of a shale gas well provided by the present invention. Specific implementation manners
[0015] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.
[0016] This embodiment provides a method for quantitatively estimating the gas content based on the full-diameter core of a shale gas well. Refer to Figure 1 , including the following steps: Step 1: Conduct an experiment to restore the original state of the shale sample of the full-diameter core of the shale gas well, and calculate the porosity and permeability of the shale sample. Specifically, it includes the following steps: (1) Dry the shale sample for at least 12 hours or more until the mass no longer changes, and measure the length, diameter, and weight of the shale sample; (2) Take out the shale sample and put it into the full-diameter core holder, and measure the porosity; Measuring the porosity specifically includes the following steps: 21) Before the experiment starts, evacuate the experimental shale sample for 24 hours; 22) Check the airtightness of the vacuum device; 23) Use a vernier caliper to measure and record the shale sample and the standard calibration steel disc; 24) Put the shale sample into the sample chamber for sealing, open the sample valve and the vent valve, and make the initial pressures of the standard chamber and the sample chamber stable at atmospheric pressure; 25) After the pressure is stable, close the sample valve and the vent valve, open the gas source valve and the gas supply valve, and adjust the pressure reducing valve to make the pressure in the standard chamber stable at the standard atmospheric pressure P; 26) After the pressure in the standard chamber is stable, record the pressure data, open the sample valve for balancing, and record the balanced pressure after the pressure is stable; 27) Open the vent valve, open the sample chamber, and put the No. 1, 2, 3, and 4 standard calibration steel discs into the sample chamber respectively, and then repeat steps 22)-25), and record the obtained pressure balance data; 28) Calculate the porosity of the shale sample according to the recorded data. The calculation is as follows: Total porosity (%) = [(W3 - W1) - (W2 - W1)] / V × 100%; Weigh a container with a known volume (V) and record its weight (W1). Then fill the container with the matrix to be measured and weigh it again (W2). Next, immerse the container with the matrix in water for a whole day and night, and then weigh it again (W3).
[0017] (3) Measure the permeability of the shale sample. For the experimental device, please refer to Figure 2 It should be noted that the experimental device for measuring the shale permeability is well-known and commonly used in this technical field, so its specific structure will not be described in detail here.
[0018] The measurement process specifically includes the following steps: 31) Calibrate the pressure sensor and check the airtightness of the vacuum device; 32) Place the experimental shale sample in a full-diameter core holder and seal it. Close valve 12, open the remaining valves, and evacuate for 24 hours; 33) After the evacuation is completed, close valve 13, apply a confining pressure of 10 MPa to the shale sample; open valve 12, and introduce helium gas into the experimental device until the pressure reaches about 7 MPa; close valve 12 and let it stand for 24 hours until the pressure is completely stable; 34) After the pressure is stable, close valves 9 and 11, open valve 12, introduce a small amount of additional helium gas into the upstream initial container and then close it, so that the pressure increase in the upstream gas storage container is about 0.2 MPa; 35) After the pressure in the upstream gas storage container is stable, open valve 9 and conduct a gas permeability measurement experiment until the pressures in the upstream and downstream containers reach equilibrium; 36) Calculate the permeability of the shale sample based on the recorded data.
[0019] (4) Place the shale sample in an incubator to simulate the original formation temperature condition. Set the temperature of the incubator to 60 °C and apply a pressure of 15 MPa to the shale sample; (5) Use the Figure 3 experimental system. Place the shale sample in a full-diameter core holder, inject a certain amount of methane gas into the intermediate container, connect the intermediate container and the standard chamber, and use a piston pump to pressurize the methane gas until it reaches 15 MPa; (6) Connect the standard chamber and the full-diameter core holder, and saturate the shale sample with gas. When the pressure gauge readings at both ends of the standard chamber and the full-diameter core holder are stable, the saturation ends, and close the valve between the standard chamber and the full-diameter core holder.
[0020] Step 2: Conduct a desorption method pressure reduction production experiment, which specifically includes the following steps: (1) Evacuate and inject water: Use a vacuum pump for Figure 3The entire experimental system is evacuated. When the reading of the vacuum pump pressure gauge reaches -0.09 MPa and stabilizes, this process stops. When water is pumped into the vacuum pump, the water injection is completed. It should be noted that this experimental system is a commonly known and general experimental system for technicians in the field to conduct desorption method pressure reduction mining experiments, so its specific structure will not be described in detail here. (2)Gas injection and pressurization: First, inject gas into the standard chamber through a methane gas cylinder. Use an intermediate container and a piston pump to make its pressure reach the required value, then stop gas injection. Then connect the standard chamber and the full-diameter core holder to saturate the shale sample with gas, let it stand to balance. When the reading of the pressure gauge stabilizes, close the connection valve between the standard chamber and the full-diameter core holder. (3)Pressure reduction mining: First, set the back pressure valve pressure to be the same as the system pressure. Then open the outlet valve, control the hand pump, and adjust the back pressure valve to start pressure reduction, so that the pressure of the full-diameter core holder slowly decreases to atmospheric pressure. In this embodiment, six groups of pressure drop rates are set for comparison, specifically 1.25 MPa / min, 1 MPa / min, 0.75 MPa / min, 0.5 MPa / min, 0.25 MPa / min, 0.125 MPa / min. When the pressure drops to 0.1 MPa, the lost gas volume measurement experiment is completed; when the gas production rate is lower than 0.6 cm 3 / min, the desorbed gas volume measurement experiment is completed, and data such as time, pressure, and gas production volume during the pressure reduction process are recorded.
[0021] Taking the pressure drop rate of 1.25 MPa / min as an example, the initial pressure is 15 MPa. Starting from the time when the pressure drop begins, at 12 minutes, the pressure drops to 0.1 MPa. Then the cumulative gas production volume within 0 - 12 minutes is the lost gas volume under standard conditions. After that, the pressure no longer drops, but the gas production rate will gradually decrease. When the gas production rate is first lower than 0.6 cm 3 / min at 175 minutes, the cumulative gas production volume within 12 - 175 minutes is the desorbed gas volume under standard conditions; when the gas production rate is 0, the cumulative gas production volume in this stage is the residual gas volume under standard conditions. Since the experimental time is too long and the gas production volume cannot be accurately counted when the gas production rate is too low, which affects the experimental accuracy, the residual gas volume is calculated by fitting using Origin numerical simulation software.
[0022] The sum of the lost gas under standard conditions, the desorbed gas under standard conditions, and the residual gas under standard conditions is the estimated gas content.
[0023] The present invention first conducts an experiment on the restoration of the original state of shale to saturate the gas content of the sample, that is, to restore it to the state before collection, and then conducts a desorption method pressure reduction exploitation experiment. The above two groups of experiments are used to simulate the pressure reduction exploitation of shale, that is, to simulate the coring process of the shale core being lifted in the wellbore. Three shale samples are selected in the experiment, and six groups of pressure drop rates of 1.25 MPa / min, 1 MPa / min, 0.75 MPa / min, 0.5 MPa / min, 0.25 MPa / min, and 0.125 MPa / min are set for the shale restoration and desorption method pressure reduction exploitation experiments; the desorption method pressure reduction exploitation of shale can be divided into three stages: the lost gas recovery stage, the rapid desorption stage, and the slow desorption stage. The lost gas recovery stage simulates the coring process of the shale core from being taken out of the formation to being loaded into the desorption tank. There is a negative correlation between the desorption rate and the pressure. The desorbed gas volume in this stage is the lost gas volume; in the rapid desorption stage, the gas production rate rises rapidly and the gas production rate is basically unchanged, showing a linear growth; in the slow desorption stage, the gas production rate is still rising continuously, but the gas production rate gradually decreases; the sum of the gas production volumes in the latter two stages is the desorbed gas volume. The method of the present invention ensures the rigor of the shale gas content detection and reduces the gas content detection error.
[0024] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.
Claims
1. A method for quantitatively estimating gas content based on the full-diameter core of a shale gas well, characterized in that, it includes: Conducting an original state restoration experiment on the extracted shale samples from the full-diameter core of the shale gas well; Measuring the gas content of the shale by the desorption method for the restored shale samples.
2. The method for quantitatively estimating gas content based on the full-diameter core of a shale gas well according to claim 1, characterized in that, the conducting of the original state restoration experiment on the extracted shale samples from the full-diameter core of the shale gas well includes: Placing the shale samples in an incubator to simulate the original formation temperature conditions and subjecting the shale samples to pressure treatment.
3. The method for quantitatively estimating gas content based on the full-diameter core of a shale gas well according to claim 2, characterized in that, the temperature of the incubator is set at 60 °C.
4. The method for quantitatively estimating gas content based on the full-diameter core of a shale gas well according to claim 3, characterized in that, the subjecting of the shale samples to pressure treatment means: Pressurizing the shale samples to 15 MPa.
5. The method for quantitatively estimating gas content based on the full-diameter core of a shale gas well according to claim 4, characterized in that, the subjecting of the shale samples to pressure treatment includes: Placing the shale samples in a full-diameter core holder, injecting methane gas into the intermediate container, connecting the intermediate container and the standard chamber, and using a peristaltic pump to pressurize the methane gas until 15 MPa; Connecting the standard chamber and the full-diameter core holder, saturating the shale samples with gas, and ending the saturation when the pressures at both ends of the standard chamber and the full-diameter core holder are stable, and closing the valve between the connected standard chamber and the full-diameter core holder.
6. The method for quantitatively estimating gas content based on the full-diameter core of a shale gas well according to claim 1, characterized in that, the measuring of the gas content of the shale by the desorption method for the restored shale samples includes: Building a desorption method pressure reduction production experiment system and evacuating and injecting water; Placing the shale samples in a full-diameter core holder and saturating them with gas; Reduce the pressure of the full-diameter core holder. When the pressure drops to 0.1 MPa, conduct an experiment to measure the gas loss volume; when the gas production rate is lower than 0.6 cm 3 / min, conduct an experiment to measure the desorbed gas volume, and record the time, pressure, and gas production volume data during the pressure reduction process; Recording the sum of the volume of lost gas under standard conditions, the volume of desorbed gas under standard conditions, and the volume of residual gas under standard conditions as the estimated gas content.
7. The method for quantitatively estimating gas content based on the full-diameter core of a shale gas well according to claim 6, characterized in that, Using Origin numerical simulation software to fit the volume of residual gas under standard conditions.
8. The method for quantitatively estimating gas content based on the full-diameter core of a shale gas well according to claim 6, characterized in that, during the pressure reduction process, the pressure drop rate is set to: 1.25 MPa / min, 1 MPa / min, 0.75 MPa / min, 0.5 MPa / min, 0.25 MPa / min, and 0.125 MPa / min.