CN113533128B - Shale adsorption gas and free gas content testing method based on pressure maintaining coring - Google Patents
Shale adsorption gas and free gas content testing method based on pressure maintaining coring Download PDFInfo
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- 238000001179 sorption measurement Methods 0.000 title claims abstract description 40
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- 238000004458 analytical method Methods 0.000 claims abstract description 31
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Abstract
The invention discloses a shale adsorption gas and free gas content testing method based on pressure maintaining coring. The method comprises the following steps: s10, reducing the pressure of a pressure-maintaining coring barrel for obtaining the core, and measuring the amount of gas released in the coring barrel by a drainage gas production method, namely, the free gas amount; s20, opening a pressure-maintaining coring barrel, taking a short core with the full diameter of 20-25cm, putting the short core into an analysis tank, and testing the total amount of analysis gas to obtain the adsorption gas amount; s30, calculating the free gas content, the adsorbed gas content and the total gas content of the shale core by combining the weights of the obtained core and the short core. The method can simultaneously measure the content of the adsorbed gas and the free gas, simplifies the testing steps and saves the testing time; the method widens the application range of the pressure maintaining and coring technology, and can rapidly acquire the important evaluation parameter of the gas content on site.
Description
Technical Field
The invention relates to the technical field of geological exploration, in particular to a shale adsorption gas and free gas content testing method based on pressure maintaining and coring.
Background
Shale gas is a typical unconventional natural gas resource, and industrial development of shale gas is realized in China, so that the yield in 2018 breaks through 100 hundred million. The shale gas resources in China are quite rich, the geological reserves exceeding 17000 hundred million are detected in the accumulation in 2019, and the method has good prospect of exploration and development. Shale gas is an important field of natural gas yield increase in China, and is developed greatly, so that the shale gas has important significance in meeting the continuously and rapidly increasing energy demand and clean and efficient utilization of energy in China.
The determination of shale gas content is of great significance to shale gas reservoir evaluation and reserve calculation. Because shale gas is mainly in two states of adsorption state and free state and is stored in pores and cracks, when the shale gas content is calculated, the adsorption gas content and the free gas content are generally tested respectively, and then the adsorption gas content and the free gas content are added to obtain the total shale gas content. Thus, determining the adsorbed and free gas content of shale is the basis for calculating the total gas content and the geological reserves. At present, isothermal adsorption experiments are mainly adopted to determine the content of shale adsorption gas, and the free gas quantity is determined through the porosities, the gas saturation and the like. There are some problems: (1) Isothermal adsorption experiments can only simulate shale adsorption capacity under certain temperature and pressure conditions, and the actual adsorption capacity of the shale under stratum conditions cannot be accurately determined; (2) The pore space occupied by the adsorption gas is subtracted in the calculation process of the shale free gas quantity, and the space occupied by the adsorption gas cannot be accurately and quantitatively determined, so that the determination of the free gas quantity is also inaccurate. Therefore, determining shale adsorption gas and free gas content through new methods such as numerical simulation and nuclear magnetic resonance is a research hot spot and difficulty in the industry.
For shale gas wells, a conventional coring technology is adopted, and a sample is taken to the ground for on-site gas content test, so that the method and the device are an important evaluation method and means in the current shale gas geological exploration. However, with conventional coring techniques, the gas (methane) is inevitably lost in large amounts during the coring process, and the amount of this portion of the gas (the lost gas amount) cannot be tested, resulting in that it can ultimately only be recovered and calculated mathematically. The determination of the total air content must be error-prone due to differences in the calculation methods. In order to reduce the loss of gas during drilling, engineering operators have developed pressure maintaining and coring techniques. The technology has the greatest advantages that gas cannot be lost in the process of taking the core to the ground, and the technology has important significance for directly and accurately determining the shale gas content.
Therefore, an experimental test method for the contents of shale adsorption gas and free gas matched with pressure maintaining and coring is needed to be established.
Disclosure of Invention
The invention aims to establish an experimental test method for the contents of shale adsorption gas and free gas matched with pressure-maintaining coring, and provides a test method for the contents of shale adsorption gas and free gas based on pressure-maintaining coring so as to accurately determine the total gas content of shale.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
the invention provides a shale adsorption gas and free gas content testing method based on pressure maintaining coring, which comprises the following steps:
s10, reducing the pressure of a pressure-maintaining coring barrel for obtaining the core, and measuring the amount of gas released in the coring barrel by a drainage gas production method, namely, the free gas amount;
s20, opening a pressure-maintaining coring barrel, taking a short core with the full diameter of 20-25cm, putting the short core into an analysis tank, and testing the total amount of analysis gas to obtain the adsorption gas amount;
s30, calculating the free gas content, the adsorbed gas content and the total gas content of the shale core by combining the weights of the obtained core and the short core.
The following is a detailed description for each step:
step S10: and (3) depressurizing the pressure-maintaining coring barrel for obtaining the core, and measuring the amount of gas released in the coring barrel by a drainage gas production method, namely, the free gas amount.
In a preferred scheme of the invention, in S10, the pressure-maintaining coring barrel is connected with the water drainage and gas collection device through a pipeline, then the pressure-maintaining coring barrel is depressurized, and the amount of gas released in the coring barrel is measured through a water drainage and gas collection method.
In a preferred embodiment of the present invention, the pressure-maintaining coring barrel for obtaining the core is depressurized, and the amount V of the gas released from the coring barrel is measured by a drainage gas production method f The process of (1) comprises:
s11, taking out a pressure-maintaining coring barrel (about 1m in length) for obtaining a core from a coring drill rod, and horizontally placing the coring barrel on the ground of a well site; the determination of the free gas quantity of the invention must be completed at the well site to reduce the influence; if the gradient is too large during placement, slurry in the cylinder can flow, gas analysis can be affected, and horizontal placement is needed;
s12, connecting the pressure-maintaining coring barrel with a water and gas drainage and collection device through a pipeline, and filling water in a metering barrel in the water and gas drainage and collection device and stably placing the metering barrel;
s13, slowly opening a pressure-maintaining coring barrel valve, enabling the gas to flow into a measuring barrel along a pipeline, and enabling the water surface in the measuring barrel to descend; when the water surface falls to 1/2-4/5 (2/3 in general) of the measuring cylinder range, the pressure-maintaining coring cylinder valve is closed, the scale of the water surface in the measuring cylinder is read, and the scale value V is recorded f1 ；
This step requires attention to: observing the water surface descending speed at any time, and adjusting the opening and closing degree of the valve of the pressure-maintaining coring barrel to enable the water surface in the metering barrel to stably and slowly descend; in general, the measurement process needs to be repeated for many times to completely release the pressure in the pressure maintaining coring barrel, and the total gas amount measured by multiple times of drainage is calculated to be the shale free gas amount, i.e. the process generally further comprises the following step S14.
S14, continuously filling the metering cylinder with water, opening a pressure-maintaining coring cylinder valve, repeating the step S13, and recording the scale value V of the water surface in the metering cylinder f2 The method comprises the steps of carrying out a first treatment on the surface of the Repeating for a plurality of times until the pressure in the pressure maintaining coring barrel is completely released, and closing the pressure maintaining coring barrel valve; free air volume V f Namely, the sum of the gas amounts measured for a plurality of times is shown as the formula (1):
V f ＝V f1 +V f2 +···+V fn (1)
where n is the number of measurements.
In S14, before the metering cylinder is filled with water, the gas collected in the metering cylinder can be directly discharged, the gas quantity is not very large, the speed is very low, and no influence is caused to the air; of course, it can be transferred to other containers for subsequent disposal.
Step S20: and opening the pressure-maintaining coring barrel, taking a short core with the full diameter of 20-25cm for analysis, and testing the total amount of analysis gas to obtain the adsorption gas amount.
In a preferred embodiment of the present invention, the length of the short core in S20 is 25cm.
In a preferred embodiment of the present invention, a natural analysis method is used in S20.
In a preferred scheme of the invention, the process of opening the pressure-maintaining coring barrel, taking a 20-25cm full-diameter rock core for analysis, and testing the total amount of analysis gas to be the adsorption gas amount comprises the following steps:
s21, taking out the core after the pressure in the pressure maintaining coring barrel is completely released, wherein the length of the core is about 1 m;
s22, selecting a core with the length of 20-25cm from the core, cleaning, drying, and then placing the core into an analysis tank;
s23, sealing the analysis tank and connecting the analysis tank with analysis metering equipment; the gas analyzed by the core enters a flow meter arranged in analysis and metering equipment to measure the flow;
s24, continuously and naturally resolving until the resolving power is not more than 5cm every day for three continuous days 3 Ending the analysis and measurement;
s25, the total gas quantity measured by the flowmeter is the adsorption gas quantity.
Step S30: and calculating the free gas content, the adsorbed gas content and the total gas content of the shale core by combining the weights of the obtained core and the short core.
In a preferred embodiment of the present invention, the free gas content is calculated by formula (4), the adsorbed gas content is calculated by formula (5), and the total gas content is calculated by formula (6):
G f ＝V f /m 1 (4)
G a ＝V a /m 2 (5)
G t ＝G f +G a (6)
in the above, m 1 The core weight g is actually obtained for the core barrel; m is m 2 G, the weight of the selected short core; v (V) f For the measured free air quantity cm 3 ；V a Cm for the measured adsorption gas amount 3 ；G f Is the free gas content, cm 3 /g；G a To adsorb gas content, cm 3 /g；G t The total air content is cm 3 /g。
Because the actual core is too long, it is inconvenient to weigh it directly. Thus, in a preferred embodiment of the present invention, the core density is obtained from the selected short core, and then the weight of the actual obtained core is calculated from the core density and the size of the actual obtained core. In a preferred embodiment of the invention, the method comprises the following steps:
s31, measuring the length and the diameter of the actually obtained rock core;
s32, weighing the selected short rock core, and measuring the length and the diameter of the selected short rock core; calculating according to the formula (2) to obtain the core density;
s33, calculating the weight of the actually obtained rock core according to the formula (3);
in the above, ρ s Core density, g/cm 3 ；m 1 G, for actually obtaining the weight of the core; l (L) 1 The length of the core is cm for actual acquisition; d, d 1 The diameter of the core is cm for actual acquisition; m is m 2 G, the weight of the selected short core; l (L) 2 The length of the selected short core is cm; d, d 2 The diameter of the short core is selected to be cm.
In a preferred scheme of the invention, the shale adsorption gas and free gas content testing method based on pressure maintaining coring comprises the following steps of:
s101, taking out a pressure-maintaining coring barrel for obtaining a core from a coring drill rod, and horizontally placing the pressure-maintaining coring barrel on the ground of a well site;
s102, connecting a pressure maintaining coring barrel with a water and gas collecting device through a pipeline, and filling water in a metering barrel in the water and gas collecting device and placing the metering barrel stably;
s103, slowly opening a pressure-maintaining coring barrel valve, enabling a gas delay pipeline to flow into a metering barrel, and enabling the water surface in the metering barrel to descend; when the water surface descends to the measuring range of the measuring cylinder by about 2/3, the pressure-maintaining coring cylinder valve is closed, the scale of the water surface in the measuring cylinder is read, and the scale value V is recorded f1 ；
S104, continuously filling the metering cylinder with water, opening a pressure-maintaining coring cylinder valve, repeating the step S13, and recording the scale value V of the water surface in the metering cylinder f2 The method comprises the steps of carrying out a first treatment on the surface of the Repeating for a plurality of times until the pressure in the pressure maintaining coring barrel is completely released, and closing the pressure maintaining coring barrel valve; free air volume V f Namely, the sum of the gas amounts measured for a plurality of times is shown as the formula (1):
V f ＝V f1 +V f2 +···+V fn (1)
wherein n is the number of measurements;
s201, taking out the core after the pressure in the pressure-maintaining coring barrel is completely released, and measuring the length and the diameter of the actually obtained core;
s202, selecting a long and short rock core from the above, cleaning, drying, weighing the rock core, measuring the length and the diameter, and placing the rock core into an analysis tank; calculating according to the formula (2) to obtain the core density;
s203, sealing the analysis tank and connecting the analysis tank with analysis metering equipment; the gas analyzed by the core enters a flow meter arranged in analysis and metering equipment to measure the flow;
s204, continuously and naturally resolving until the resolving power is not more than 5cm every day for three continuous days 3 Ending the analysis and measurement;
s205, the total gas quantity measured by the flowmeter is the adsorption gas quantity;
s300, calculating through a formula (4) to obtain free gas content, calculating through a formula (5) to obtain adsorption gas content, and calculating through a formula (6) to obtain total gas content:
G f ＝V f /m 1 (4)
G a ＝V a /m 2 (5)
G t ＝G f +G a (6)
in the above, ρ s Core density, g/cm 3 ；m 1 G, for actually obtaining the weight of the core; l (L) 1 The length of the core is cm for actual acquisition; d, d 1 The diameter of the core is cm for actual acquisition; m is m 2 G, the weight of the selected short core; l (L) 2 The length of the selected short core is cm; d, d 2 The diameter of the selected short rock core is cm; v (V) f For the measured free air quantity cm 3 ；V a Cm for the measured adsorption gas amount 3 ；G f Is the free gas content, cm 3 /g；G a To adsorb gas content, cm 3 /g；G t The total air content is cm 3 /g。
The invention has the following beneficial effects:
1) The invention establishes a new shale adsorption gas and free gas content testing method;
2) The method can simultaneously measure the content of the adsorbed gas and the free gas, simplifies the testing steps and saves the testing time;
3) The method widens the application range of the pressure maintaining and coring technology, and can rapidly acquire the important evaluation parameter of the gas content on site.
Drawings
FIG. 1 is a schematic diagram of a test flow in an embodiment of the invention;
FIG. 2 is a graph showing the amount of analysis gas over time in an embodiment of the present invention;
Detailed Description
In order to more clearly illustrate the present invention, the present invention will be further described with reference to preferred embodiments. It is to be understood by persons skilled in the art that the following detailed description is illustrative and not restrictive, and that this invention is not limited to the details given herein.
The embodiment of the invention provides a shale gas adsorption gas and free gas content testing method based on pressure maintaining coring, which comprises the following steps of:
(1) And depressurizing the pressure-maintaining coring barrel, and collecting and measuring the amount of gas released in the coring barrel by a drainage gas production method.
(1) The pressure maintaining coring barrel 1 (about 1m long) is taken out of the coring drilling rod and horizontally placed on the surface of a well site.
(2) The pressure-maintaining coring barrel 1 is connected with a water and gas collecting device 2 through a hose 3, and a metering barrel 4 is filled with water and is stably placed.
(3) Slowly opening the pressure-maintaining coring barrel valve, enabling the gas to flow into the measuring barrel 4 along the pipeline, and lowering the water surface in the measuring barrel 4. In the process, the water surface descending speed is observed, and the degree of the switching valve is adjusted until the water surface steadily and slowly descends.
(2) Repeating the collection for a plurality of times until the pressure in the pressure maintaining and coring cylinder is completely released, and calculating the total gas quantity measured by a plurality of times of drainage, namely the shale free gas quantity.
(1) When the gas enters the metering cylinder 4 and the water surface descends to about 2/3 of the measuring cylinder measuring range, the valve of the coring cylinder is closed, the scale of the water surface in the metering cylinder 4 is read, and the scale value V is recorded f1 。
(2) Continuously filling the metering cylinder 4 with water, opening a pressure-maintaining coring cylinder valve, repeating the steps, and recording the scale value V of the water surface in the metering cylinder 4 f2 。
(3) Repeating the steps for a plurality of times until the pressure in the pressure maintaining coring barrel 1 is completely released, and closing the pressure maintaining coring barrel valve.
(4) Free air volume V f I.e., the sum of the measured amounts of gas, as shown in the following formula.
V f ＝V f1 +V f2 +···+V fn
(3) And opening the pressure-maintaining coring barrel, taking a full-diameter core with the diameter of about 25cm, putting the core into the analysis tank 5, and testing the total amount of analysis gas to obtain the adsorption gas amount.
(1) After the pressure in the pressure maintaining coring barrel 1 is released, taking out the core, and the length of the core is about 1 m.
(2) Short cores with a length of about 25cm are selected from the above, cleaned and wiped dry, and then placed in a desorption tank 5.
(3) The analytical tank 5 is sealed and connected to analytical metering equipment. The gas analyzed by the core enters a flowmeter 6 arranged in the equipment, and the flow rate of the gas can be measured.
(4) Continuously and naturally resolving until resolving power is not more than 5cm every day for three continuous days 3 The analytical measurement is ended. The analytical curve of one of the samples is shown in FIG. 2.
(5) The total gas quantity measured by the flowmeter 6 is the adsorption gas quantity and is recorded as V a 。
(4) And calculating the free gas content, the adsorbed gas content and the total gas content of the shale core by combining the weight of the obtained core.
(1) After the pressure maintaining coring barrel 1 is opened, the length l of the actually obtained core is measured 1 And diameter d 1 . Since the core is too long, it cannot be weighed directly.
(2) Weigh the weight m of the selected short core 2 Measuring the length l of the selected short core 2 And diameter d 2 。
(3) Calculating the density ρ of the shale core s Calculating the weight m of the core actually obtained by the core barrel 1 。
(4) According to the mass of the rock core, calculating the free gas content G f Adsorbed gas content G a Total air content G t . The calculation results are shown in the accompanying table 1.
The calculation formula in the step (4) is as follows:
G f ＝V f /m 1 (4)
G a ＝V a /m 2 (5)
G t ＝G f +Ga (6)
in the above, ρ s Core density, g/cm 3 ；m 1 G, for actually obtaining the weight of the core; l (L) 1 The length of the core is cm for actual acquisition;d 1 the diameter of the core is cm for actual acquisition; m is m 2 G, the weight of the selected short core; l (L) 2 The length of the selected short core is cm; d, d 2 The diameter of the selected short rock core is cm; v (V) f For the measured free air quantity cm 3 ；V a Cm for the measured adsorption gas amount 3 ；G f Is the free gas content, cm 3 /g；G a To adsorb gas content, cm 3 /g；G t The total air content is cm 3 /g。
The method can be used for directly and simultaneously testing the content of the adsorbed gas and the free gas in the shale, and is only suitable for testing the drilling site by adopting the pressure maintaining coring technology.
Table 1 below exemplifies the test results of another sample conducted using the above method.
TABLE 1 calculation results of adsorbed gas amount and free gas amount
There are no other methods available to directly measure the adsorbed and free gas amounts and total gas content. However, for shale gas development, the adsorption gas is generally 30-40% in proportion, and the total gas content is generally 3-5cm 3 /g; the adsorption gas ratio in this test example was 39.8%, and the total gas content was 4.45cm 3 The test method according to the invention is empirically possible.
It should be understood that the foregoing examples of the present invention are provided merely for clearly illustrating the present invention and are not intended to limit the embodiments of the present invention, and that various other changes and modifications may be made therein by one skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.
Claims (1)
1. The shale adsorption gas and free gas content testing method based on pressure maintaining coring is characterized by comprising the following steps of:
s101, taking out a pressure-maintaining coring barrel for obtaining a core from a coring drill rod, and horizontally placing the pressure-maintaining coring barrel on the ground of a well site;
s102, connecting a pressure maintaining coring barrel with a water and gas collecting device through a pipeline, and filling water in a metering barrel in the water and gas collecting device and placing the metering barrel stably;
s103, slowly opening a pressure-maintaining coring barrel valve, enabling a gas delay pipeline to flow into a metering barrel, and enabling the water surface in the metering barrel to descend; when the water surface descends to 2/3 of the measuring range of the measuring cylinder, the pressure-maintaining coring cylinder valve is closed, the scale of the water surface in the measuring cylinder is read, and the scale value V is recorded f1 ；
S104, continuously filling the metering cylinder with water, opening a pressure-maintaining coring cylinder valve, repeating the step S13, and recording the scale value V of the water surface in the metering cylinder f2 The method comprises the steps of carrying out a first treatment on the surface of the Repeating for a plurality of times until the pressure in the pressure maintaining coring barrel is completely released, and closing the pressure maintaining coring barrel valve; free air volume V f Namely, the sum of the gas amounts measured for a plurality of times is shown as the formula (1):
V f ＝V f1 +V f2 +···+V fn (1)
wherein n is the number of measurements;
s201, taking out the core after the pressure in the pressure-maintaining coring barrel is completely released, and measuring the length and the diameter of the actually obtained core;
s202, selecting a core with the length of 20-25cm from the core, cleaning, drying, weighing the core, measuring the length and the diameter, and placing the core into an analysis tank; calculating according to the formula (2) to obtain the core density;
s203, sealing the analysis tank and connecting the analysis tank with analysis metering equipment; the gas analyzed by the core enters a flow meter arranged in analysis and metering equipment to measure the flow;
s204, continuously and naturally resolving until the resolving power is not more than 5cm every day for three continuous days 3 Ending the analysis and measurement;
s205, the total gas quantity measured by the flowmeter is the adsorption gas quantity;
s300, calculating through a formula (4) to obtain free gas content, calculating through a formula (5) to obtain adsorption gas content, and calculating through a formula (6) to obtain total gas content:
G f ＝V f /m 1 (4)
G a ＝V a /m 2 (5)
G t ＝G f +G a (6)
in the above, ρ s Core density, g/cm 3 ；m 1 G, for actually obtaining the weight of the core; l (L) 1 The length of the core is cm for actual acquisition; d, d 1 The diameter of the core is cm for actual acquisition; m is m 2 G, the weight of the selected short core; l (L) 2 The length of the selected short core is cm; d, d 2 The diameter of the selected short rock core is cm; v (V) f For the measured free air quantity cm 3 ；V a Cm for the measured adsorption gas amount 3 ；G f Is the free gas content, cm 3 /g；G a To adsorb gas content, cm 3 /g；G t The total air content is cm 3 /g。
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|---|---|---|---|---|
| CN102707333A (en) * | 2012-06-06 | 2012-10-03 | 陕西延长石油(集团)有限责任公司研究院 | Shale gas resource/reserve measurement method |
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| CN108761024A (en) * | 2018-05-24 | 2018-11-06 | 大连理工大学 | A kind of boat-carrying detection method of gas hydrates core fidelity sample |
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| CN102707333A (en) * | 2012-06-06 | 2012-10-03 | 陕西延长石油(集团)有限责任公司研究院 | Shale gas resource/reserve measurement method |
| CN108761024A (en) * | 2018-05-24 | 2018-11-06 | 大连理工大学 | A kind of boat-carrying detection method of gas hydrates core fidelity sample |
| CN108547614A (en) * | 2018-06-20 | 2018-09-18 | 河南理工大学 | A kind of closed coal sample collection device of pressurize and acquisition method |
| CN109540735A (en) * | 2019-01-15 | 2019-03-29 | 国家地质实验测试中心 | A kind of shale gas-bearing property comprehensive analysis device and its method |
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