Experimental device and method for determining the solubility of methane in oil-based drilling fluid

Abstract

The invention discloses an experimental device and a method for determining the solubility of methane in oil-based drilling fluid, comprising a pressure-resistant gas chamber and a balance kettle, both of which are arranged in a constant-temperature oil bath heating box and are interconnected; further comprising a gas booster pump, both of which are connected to the pressure-resistant gas chamber; the gas booster pump is connected to a driving gas source inlet; a gas one-way valve is arranged on a pipeline between the pressure-resistant gas chamber and the gas booster pump; the gas booster pump is also connected to a high-pressure gas cylinder; the cavity in the balance kettle is divided into an upper dissolution balance chamber and a lower hydraulic oil chamber through a high-pressure dynamic sealing structure; the dissolution balance chamber is connected to a liquid inlet funnel through a fourth stop valve; the hydraulic oil chamber is connected to a high-pressure metering pump for replenishing hydraulic oil therein; further comprising a vacuum system for evacuating the pressure-resistant gas chamber and the balance kettle and a data acquisition device for acquiring temperature and pressure signals; the invention can determine the solubility of methane under high temperature and high pressure, and the operation is simpler; and the data obtained are more accurate.

Description

Technical Field

[0001] The invention relates to the field of ultra-deep oil and gas layer drilling engineering in oil and natural gas exploration and development engineering, and in particular to an experimental device and a method for determining the solubility of methane in oil-based drilling fluid. Background Art

[0002] my country has stepped up efforts to promote the drilling and development of ultra-deep oil and gas formations to achieve increased production, stable production and increased reserves of oil and gas. However, deep formation drilling is in a high temperature and high pressure environment, which is more conducive to the dissolution of methane in oil-based drilling fluids. When dealing with overflow problems, on-site well control personnel ignore the impact of dissolved gas. Under high temperature and high pressure conditions, the increased solubility of methane in drilling fluids will significantly change the rheology and stability of drilling fluids, causing the risk of gas channeling or overflow accidents on the ground or in the drilling fluid column. At 30°C and 40MPa, 1 cubic meter of oil-based drilling fluid dissolves about 3 cubic meters of methane, and the amount of methane dissolved in oil-based drilling fluids is 100 times that in water-based drilling fluids. Therefore, predicting the amount of methane dissolved in oil-based drilling fluids under high temperature and high pressure conditions helps to explain the law of methane-drilling fluid mixing migration and the reasons for the change of overflow wellbore pressure, which has positive significance for the design of drilling engineering for ultra-deep oil and gas formations and improving on-site well control treatment decision-making measures. At present, domestic researchers are limited by the temperature and pressure range of the solubility test system, which cannot simulate the high temperature and high pressure environment of actual ultra-deep oil and gas formations, and know very little about the solubility of methane in oil-based drilling fluids.

[0003] At present, the equilibrium liquid sampling method is widely used to determine the solubility of gas in liquid under high temperature and high pressure. Figure 3 and Figure 4The figure shows the structure of the test equipment and the experimental flow diagram of the publicly disclosed test method for measuring the solubility of methane in drilling fluid by using the balanced liquid sampling method, which covers a high-temperature and high-pressure dissolution experimental system and a normal-pressure metering experimental system. The high-temperature and high-pressure dissolution experimental system includes a gas cylinder 1, a valve I (2), a booster (3), an intermediate container (4), a valve II (5), a coil tube (6), a high-temperature and high-pressure sample dispenser 7, a valve III (8) and a constant-pressure pump (9); the normal-pressure metering experimental system includes a constant-pressure pump (9) and a high-temperature and high-pressure sample dispenser (7) shared with the high-temperature and high-pressure dissolution experimental system, as well as a valve IV (10), a separation bottle (11), a dryer (12) and a gas meter (13) unique to the normal-pressure metering experimental system. The first step of the method is sample transfer, where the drilling fluid with measured density is loaded into the sample dispenser, and then the gas in the gas cylinder is pressurized and injected into the sample dispenser. After reaching the specified pressure, the high-temperature and high-pressure sample dispenser is closed; the second step is dissolution equilibrium, where the temperature in the sample dispenser is controlled by a heating resistor to reach the set temperature, and a constant pressure pump is used to pressurize to the specified pressure to keep the pressure stable during the dissolution process, and the sample dispenser is rotated to accelerate the dissolution reaction, and generally the dissolution equilibrium is reached in about 3 hours; the third step is separation and metering, where the valve at the lower end of the sample dispenser is opened, and a small amount (3 to 10 ml) of dissolved saturated liquid is released into a separation bottle filled with coolant that has been measured in advance, and the gas separated by flash evaporation in the separation bottle enters the gas meter to measure the gas volume. Finally, the released drilling fluid volume is calculated by the drilling fluid density and the mass difference before and after flash evaporation in the separation bottle, and the ratio of the precipitated gas volume to the degassed liquid volume is the solubility at this temperature and pressure.

[0004] The existing methods have the following shortcomings: 1) After sampling, the original temperature and pressure conditions are changed, the original equilibrium state is destroyed, the solubility results obtained are less consistent, and the sampling process may cause leakage and damage the sample; 2) Due to the limitations of the measurement experimental system, it takes a long time to reach gas-liquid equilibrium, and it may even take a day to measure one data, and data under high pressure are often not available; 3) Different measuring instruments are used for high-temperature and high-pressure gas-liquid dissolution equilibrium and normal pressure separation analysis, resulting in more measuring equipment, complex equipment composition, complicated connections between equipment, difficult manufacturing technology, and high cost; 4) The dead volume such as the space above the liquid solvent and the pipeline is ignored, and the high-temperature and high-pressure sampled liquid is not converted into the standard condition (room temperature) state when processing the experimental data, and the gas-liquid volume is directly recorded; 5) It is considered that the liquid is incompressible during the pressure increase process, and the volume of the liquid that decreases with the increase of pressure is ignored. Especially for liquids under high-pressure stirring, the measurement results have large errors. Summary of the invention

[0005] Aiming at the problems existing in the prior art, the invention provides an experimental device and a method for determining the solubility of methane in oil-based drilling fluid.

[0006] The technical solution adopted by the present invention is:

[0007] A methane solubility determination experimental device in oil-based drilling fluid comprises a pressure-resistant gas chamber and a balance kettle, both of which are arranged in a constant temperature oil bath heating box and are interconnected; a gas booster pump connected to the pressure-resistant gas chamber; the gas booster pump is connected to a driving gas source inlet; a gas check valve is arranged on the pipeline between the pressure-resistant gas chamber and the gas booster pump; the gas booster pump is also connected to a high-pressure gas cylinder; the balance kettle is divided into an upper dissolution balance chamber and a lower hydraulic oil chamber by a high-pressure dynamic sealing structure; the dissolution balance chamber is connected to a liquid inlet funnel through a fourth stop valve; the hydraulic oil chamber is connected to a high-pressure metering pump for replenishing hydraulic oil therein; and a vacuum system for evacuating the pressure-resistant gas chamber and the balance kettle is also included;

[0008] A first temperature sensor and a first pressure sensor for collecting temperature and pressure signals are arranged in the pressure-resistant gas chamber; a second temperature sensor and a second pressure sensor for collecting temperature and pressure signals are arranged in the dissolution equilibrium chamber; the first temperature sensor, the first pressure sensor, the second temperature sensor, and the second pressure sensor are connected to a data acquisition device.

[0009] Furthermore, a gas filter, a first pressure reducing valve, a second pressure gauge and an electric valve are arranged on the pipeline between the gas source inlet and the gas booster pump.

[0010] Furthermore, it also includes a first pressure gauge for measuring the pressure of the high-pressure gas cylinder and a first stop valve for controlling the switch thereof.

[0011] Furthermore, a second pressure reducing valve and a second stop valve are provided on the pipeline between the pressure-resistant gas chamber and the gas booster pump.

[0012] Furthermore, a stirring blade for stirring is arranged in the dissolution equilibrium chamber, and the stirring blade is connected to a stirring motor.

[0013] Furthermore, the vacuum system comprises a vacuum pump, a fifth stop valve is arranged between the vacuum pump and the equilibrium kettle, and a third stop valve is arranged between the pressure-resistant gas chamber and the equilibrium kettle.

[0014] Furthermore, the data acquisition device is connected to a control device.

[0015] A method for determining the solubility of methane in oil-based drilling fluid comprises the following steps:

[0016] Step 1: Calibrate and verify the experimental device and pipeline;

[0017] Step 2: Clean the equilibrium kettle, start the vacuum system to evacuate the air, and check the air tightness of the experimental device;

[0018] Step 3: Heat the pressure-resistant gas chamber and the balance kettle to the target temperature, start the vacuum system to evacuate the air; inject the required drilling fluid into the dissolving balance chamber in the balance kettle through the feed funnel;

[0019] Step 4: Fill a certain amount of methane into the pressure-resistant gas chamber, heat the pressure-resistant gas chamber to a target temperature, and obtain the temperature T1 and pressure P1 of the methane in the pressure-resistant gas chamber after the pressure is stabilized;

[0020] Step 5: inject methane from the pressure-resistant gas chamber into the dissolving equilibrium chamber in the equilibrium kettle until it reaches the set pressure; after the pressure stabilizes, obtain T2 and pressure P2 after the pressure-resistant gas chamber releases gas;

[0021] Step 6: Adjust the constant temperature oil bath heating box to make the temperature reach the required temperature, and observe the pressure change in the dissolution equilibrium chamber in real time. If the pressure drops, inject hydraulic oil into the hydraulic oil chamber through the high-pressure metering pump until the set pressure is reached; record T3 and pressure P3 in the equilibrium kettle after the pressure stabilizes;

[0022] Step 7: Calculate the solubility of methane in the oil-based drilling fluid based on the measured parameters.

[0023] Furthermore, the solubility of methane in oil-based drilling fluid is R S The calculation process is as follows:

[0024] n=Δn g -n g3 =(n g1 -n g2 )-n g3

[0025] Where: n is the number of moles of methane dissolved in the oil-based drilling fluid, n g3 The number of moles of methane in the equilibrium reactor 25 after reaching dissolution equilibrium, △n g is the number of moles of methane released from the pressure-resistant gas chamber 15 into the equilibrium reactor 25, n g1 is the number of moles of methane in the pressure-resistant gas chamber 15 before the methane is released into the equilibrium reactor 25, n g2 is the number of moles of methane in the pressure-resistant gas chamber 15 after the methane is released into the equilibrium reactor 25;

[0026] Solubility Rs is:

[0027] R S =(n×22.4×10 3 ) / V L

[0028] Where: V L is the volume of oil-based drilling fluid at room temperature and atmospheric pressure.

[0029] Furthermore, it also includes correcting the molar number n of methane dissolved in the oil-based drilling fluid, and the correction process is as follows:

[0030] S1: The number of moles of methane dissolved in the oil-based drilling fluid, n, is converted into the following formula:

[0031]

[0032] Where: V GC is the volume of the pressure-resistant gas chamber (15), V EC is the volume of the equilibrium kettle (25), V L is the volume of oil-based drilling fluid added to the balance kettle (25), ρ i is the density of methane in the pressure-resistant gas chamber (15) before releasing methane into the equilibrium reactor (25), ρ f is the density of methane in the pressure-resistant gas chamber (15) after methane is released into the equilibrium reactor (25), ρ g To achieve the molar density of methane in the equilibrium kettle after dissolution equilibrium, M g is the molar mass of methane;

[0033] S2: Correction for the effects of temperature and pressure on drilling fluid density;

[0034] ρ2=ρ1 / (1+C T ΔT+C P ΔP) (2)

[0035] Where: ρ1 is the density of drilling fluid at room temperature and atmospheric pressure, C T is the coefficient of thermal expansion, C p is the elastic compression coefficient, ΔT is the temperature difference between the measured target temperature and room temperature, and ΔP is the pressure difference between the measured target pressure and atmospheric pressure;

[0036] S3: Correction of the effect of temperature and pressure on the volume change of drilling fluid;

[0037]

[0038] Where: ρ2 is the drilling fluid density at the target temperature and pressure, ρ1 is the drilling fluid density at room temperature and atmospheric pressure, V L is the volume of oil-based drilling fluid at room temperature and atmospheric pressure, △V is the volume change of drilling fluid caused by temperature and pressure changes;

[0039] S4: Corrected molar number n of methane dissolved in oil-based drilling fluid under high temperature and high pressure conditions:

[0040]

[0041] Where: V pumpV is the volume change caused by the high pressure metering pump (23) being filled with hydraulic oil, pipe The volume occupied by the valve.

[0042] The beneficial effects of the present invention are:

[0043] (1) The pressure-resistant gas chamber 15 and the balance kettle 25 used in the present invention measure the solubility of methane in the oil-based drilling fluid under high temperature and high pressure conditions, and can simulate the high temperature and high pressure environment of the overflow gas and the drilling fluid in the ultra-deep oil and gas layer. It is relatively simple, technologically advanced, and has a reasonable structural design. It has the characteristics of high temperature resistance, high pressure resistance, good sealing effect, small size, light weight, and beautiful appearance;

[0044] (2) All pressure-bearing parts of the gas booster system used in the present invention are standard parts specified in the specification, which are easy to disassemble, have a high safety factor, and a long service life. They are easy to maintain;

[0045] (3) The present invention adopts the equal volume saturation method, which does not require dynamic sampling to destroy the saturated liquid composition of the equilibrium system, thereby improving the experimental efficiency;

[0046] (4) The present invention provides a highly reliable measurement process and data processing method, which calculates the solubility of methane in oil-based drilling fluid based on the corrected pressure and volume data to improve the reliability of the solubility measurement data. The obtained solubility results are closer to actual engineering applications, thereby providing scientific data support for ultra-deep oil and gas exploration and development work. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the structure of the experimental device of the present invention.

[0048] Figure 2 Schematic diagram of the assay method of the present invention.

[0049] Figure 3 This is a diagram of the existing high temperature and high pressure dissolution experimental device.

[0050] Figure 4 This is a diagram of the existing normal pressure measurement experimental device.

[0051] In the figure: 1-high pressure gas cylinder, 2-first pressure gauge, 3-first stop valve, 4-boosting pump, 5-driving gas source inlet, 6-gas filter, 7-first pressure reducing valve, 8-second pressure gauge, 9-electric valve, 10-gas one-way valve, 11-second pressure reducing valve, 12-second stop valve, 13-first temperature sensor, 14-first pressure sensor, 15-pressure gas chamber, 16-third stop valve, 17-second temperature sensor, 18-stirring motor, 19-stirring blade, 20-high pressure dynamic sealing structure, 21-liquid inlet funnel, 22-fourth stop valve, 23-high pressure metering pump, 24-second pressure sensor, 25-balance kettle, 26-constant temperature oil bath heating box, 27-hydraulic oil chamber, 28-fifth stop valve, 29-vacuum pump, 30-vacuum system, 31-data acquisition device, 32-control device;

[0052] 33-gas cylinder, 34-valve I, 35-booster, 36-intermediate container, 37-valve II. 38-coil tube, 39-high temperature and high pressure sample dispenser, 40-valve III, 41-constant pressure pump, 42-valve IV, 43-separation bottle, 44-dryer, 45-gas meter. DETAILED DESCRIPTION

[0053] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0054] like Figure 1 As shown, an experimental device for determining the solubility of methane in oil-based drilling fluid includes a pressure-resistant gas chamber 15 and a balance kettle 25, which are both arranged in a constant temperature oil bath heating box 26 and are interconnected; it also includes a gas booster pump 4 connected to the pressure-resistant gas chamber 15; the gas booster pump 4 is connected to a driving gas source inlet 5; a gas one-way valve 10 is arranged on the pipeline between the pressure-resistant gas chamber 15 and the gas booster pump 4; the gas booster pump 4 is also connected to a high-pressure gas cylinder 1; the balance kettle 25 is divided into an upper dissolution balance chamber and a lower hydraulic oil chamber 27 by a high-pressure dynamic sealing structure 20; the dissolution balance chamber is connected to a liquid inlet funnel 21 through a fourth stop valve 22; the hydraulic oil chamber 27 is connected to a high-pressure metering pump 23 for replenishing hydraulic oil therein; it also includes a vacuum system 30 for evacuating the pressure-resistant gas chamber 15 and the balance kettle 25; the high-pressure metering pump 23 adopts a hand-cranked high-pressure metering pump.

[0055] The constant temperature oil bath heating box 26 adopts intelligent control to automatically adjust its temperature. A gas filter 6, a first pressure reducing valve 7, a second pressure gauge 8 and an electric valve 9 are arranged on the pipeline between the gas source inlet 5 and the gas booster pump 4. When the electric valve 9 is opened, the air passes through the gas filter 6 and the first pressure reducing valve 7 as the driving gas source of the booster pump 4, and the high-pressure piston in the pump controlled by the gas check valve 10 continuously discharges the gas. The methane in the high-pressure gas cylinder 1 is pressurized to the target experimental pressure and injected into the pressure-resistant gas chamber 15.

[0056] It also includes a first pressure gauge 2 for measuring the pressure of the high-pressure gas cylinder 1 and a first stop valve 3 for controlling its switch. A second pressure reducing valve 11 and a second stop valve 12 are also provided on the pipeline between the pressure-resistant gas chamber 15 and the gas booster pump 4. A stirring blade 19 for stirring is provided in the dissolution balance chamber, and the stirring blade 19 is connected to the stirring motor 18, which can accelerate the dissolution of methane in the oil-based drilling fluid. The vacuum system 30 includes a vacuum pump 29, a fifth stop valve 28 is provided between the vacuum pump 29 and the balance kettle 25, and a third stop valve 16 is provided between the pressure-resistant gas chamber 15 and the balance kettle 25. By opening the third stop valve 16, the methane in the pressure-resistant gas chamber 15 can be released into the balance kettle 25, so as to accurately obtain the injection amount of methane in the pressure-resistant gas chamber 15.

[0057] A first temperature sensor 13 and a first pressure sensor 14 for collecting temperature and pressure signals are arranged in the pressure-resistant gas chamber 15; a second temperature sensor 17 and a second pressure sensor 24 for collecting temperature and pressure signals are arranged in the dissolution equilibrium chamber; the first temperature sensor 13, the first pressure sensor 14, the second temperature sensor 17, and the second pressure sensor 24 are connected to the data acquisition device 31.

[0058] The data acquisition device 31 is connected to a control device 32 , which can be a computer. The signals output by the temperature sensor and the pressure sensor are processed by the data acquisition device 31 and converted into digital signals, which are displayed on the computer.

[0059] like Figure 2 As shown, a method for determining the solubility of methane in oil-based drilling fluid by an experimental device comprises the following steps:

[0060] Before the experiment, the samples should be checked first. When the samples are received, check whether the quantity and label information of the samples are consistent with the sample delivery form, and whether there are any leaks on the appearance of the sample container.

[0061] Step 1: Calibrate and verify the experimental device and pipeline;

[0062] Volume calibration: Before the methane solubility determination, the volume of the pressure-resistant gas chamber 15 and the balance kettle 25 is calibrated by filling them with liquid water at room temperature and atmospheric pressure. The specific calibration steps are: first, the mass of the filled water is weighed with an electronic analytical balance, and after measuring the atmospheric pressure at room temperature, the density of water at the atmospheric pressure at room temperature is obtained using the software REFPROP. After calibration, the volumes of the pressure-resistant gas chamber 15 and the balance kettle 25 are consistent with the factory parameters, which are 500ml and 400ml respectively.

[0063] Calibration of pipeline valve volume: open the first stop valve 3 and the second stop valve 12, and inject a certain pressure of gas into the pressure-resistant gas chamber 15; close the first stop valve 3 and the second stop valve 12, and record the pressure and temperature of the pressure-resistant gas chamber 15 after stabilization for a period of time. Open the third stop valve 16, release the gas in the pressure-resistant gas chamber 15 to the balance kettle 25, close the third stop valve 16, and record the temperature and pressure in the balance kettle 25 after stabilization for 30 minutes. After measurement, the volume of the pipeline and valve is 28.61cm 3 .

[0064] Step 2: Clean the equilibrium kettle 25, start the vacuum system 30 to evacuate the air, and check the air tightness of the experimental device;

[0065] Connect the test device in advance, first add petroleum ether into the equilibrium kettle 25, and then introduce air into the equilibrium kettle 25 to blow out the petroleum ether and other impurities after stirring for 1 hour, and repeat the cleaning 2 to 3 times to ensure that the kettle is clean.

[0066] In order to ensure the accuracy of pressure measurement, the device is first evacuated to the ultimate vacuum pressure using the vacuum system 30, and then methane is introduced into the device, and the device is evacuated again for ventilation. This is repeated 2 to 3 times to allow the device to reach the ultimate vacuum degree.

[0067] After the whole device is evacuated, close the stop valve 5 28 and check whether the device can maintain the vacuum degree to determine whether the test device is leaking. If there is no leakage, open the high-pressure gas cylinder 1 and use the gas booster pump 4 to pump methane into the pressure-resistant gas chamber 15 and the balance kettle 25 to make the pressure reach about 30MPa. After 1 hour, observe the pressure changes in the gas chamber 15 and the balance kettle 25. If the pressure change of the device is higher than 0.02MPa, it means that the experimental device is not sealed. Use a leak test liquid to check each joint until there is no leakage.

[0068] Step 3: Heat the pressure-resistant gas chamber 15 and the balance kettle 25 to the target temperature, start the vacuum system 30 to evacuate the gas; inject the required drilling fluid into the dissolving balance chamber in the balance kettle 25 through the liquid inlet funnel 21;

[0069] The specific process is as follows:

[0070] The liquid sample transfer process is as follows: evacuate the balance kettle 25 and the external pipeline to 133 Pa and continue evacuating for 30 minutes; evacuate the entire device to vacuum. Transfer a certain mass of drilling fluid weighed by the electronic analytical balance to the liquid inlet funnel 21, and suck it into the balance kettle 25 through the fourth stop valve 22.

[0071] Step 4: Fill a certain amount of methane into the pressure-resistant gas chamber 15, heat the pressure-resistant gas chamber 15 to a target temperature, and obtain the temperature T1 and pressure P1 of the methane in the pressure-resistant gas chamber 15 after the pressure is stabilized;

[0072] The process of transferring the gas sample is as follows: open the first stop valve 3 and the second stop valve 12, close the third stop valve 16, fill a certain amount of methane into the pressure-resistant gas chamber 15, and adjust the constant temperature oil bath heating box 26 to reach the experimental target temperature, wait for the pressure to stabilize, and record the temperature T1 and pressure P1 of the methane in the pressure-resistant gas chamber 15. The maximum working pressure of the high-pressure gas cylinder 1 is 13.5MPa. If the pressure of the high-pressure gas cylinder 1 is lower than the pressure to be measured, the gas booster pump 4 needs to be used to increase the pressure of the gas.

[0073] Step 5: injecting methane from the pressure-resistant gas chamber 15 into the dissolving equilibrium chamber in the equilibrium kettle 25 until it reaches the set pressure; after the pressure stabilizes, obtaining T2 and pressure P2 after the pressure-resistant gas chamber 15 releases gas;

[0074] At room temperature and normal pressure, move the hand-cranked high-pressure metering pump 23 to the starting position at 0 scale, and rotate the scale of the hand-cranked metering pump forward by 1ml, that is, the volume of the equilibrium kettle 25 decreases by 1ml. Open the third stop valve 16, close the second stop valve 12, and slowly inject a certain amount of methane from the pressure-resistant gas chamber 15 into the equilibrium kettle 25, so that the equilibrium kettle 25 reaches the set pressure, close the third stop valve 16, and after the pressure stabilizes, record the temperature T2 and pressure P2 after the pressure-resistant gas chamber 15 releases the gas.

[0075] Step 6: Adjust the constant temperature oil bath heating box 26 to make the temperature reach the required temperature, and observe the pressure change in the dissolution equilibrium chamber in real time. If the pressure drops, inject hydraulic oil into the hydraulic oil chamber 27 through the high-pressure metering pump 23 until the set pressure is reached; record T3 and pressure P3 in the equilibrium kettle 25 after the pressure stabilizes;

[0076] Adjust the constant temperature oil bath heating box 26 so that the temperature reaches the experimental setting temperature and the temperature is kept stable. At the same time, turn on the stirring motor 18 to drive the stirring blade 19 to stir the oil-based drilling fluid in the balance kettle 25, accelerate the dissolution rate of the measured methane in the oil-based drilling fluid, and shorten the time to reach the dissolution equilibrium. As methane dissolves into the oil-based drilling fluid, the pressure in the balance kettle 25 decreases at the fixed temperature. At this time, use the high-pressure metering pump 23 to slowly push the hydraulic oil into the hydraulic oil chamber 27 in the balance kettle 25, replenish the pressure to reach the experimental setting pressure, and record the scale of the high-pressure metering pump 23. Usually, the oil-based drilling fluid in the balance kettle 25 is stirred for about 1 hour. During the stirring period, the pressure of the balance kettle 25 is observed. If it drops, the metering pump 23 needs to be used to replenish the pressure and re-record the pump scale. When the system pressure in the balance kettle 25 is stable and unchanged and reaches equilibrium, turn off the stirring motor 18, and record the temperature T3 and pressure P3 in the balance kettle when the methane dissolution equilibrium occurs.

[0077] Step 7: Calculate the solubility of methane in the oil-based drilling fluid based on the measured parameters.

[0078] Solubility of methane in oil-based drilling fluid R S The calculation process is as follows:

[0079] n=Δn g -n g3 =(n g1 -n g2 )-n g3

[0080] Where: n is the molar fraction of methane dissolved in the oil-based drilling fluid, n g3 The number of moles of methane in the equilibrium reactor 25 after reaching the dissolution equilibrium, mol, △n g is the number of moles of methane released from the pressure-resistant gas chamber 15 into the equilibrium reactor 25, mol, n g1 is the number of moles of methane in the pressure-resistant gas chamber 15 before releasing methane into the equilibrium reactor 25, mol, n g2 It is the number of moles of methane in the pressure-resistant gas chamber 15 after the methane is released into the equilibrium reactor 25, mol.

[0081] Since the volume of the pressure-resistant gas chamber 15, the temperature T1 and the pressure P1 of the methane are all known, the number of moles of methane in the pressure-resistant gas chamber 15 before the methane is released to the equilibrium reactor 25 can be calculated. g1 The temperature T2 and pressure P2 of methane in the pressure-resistant gas chamber 15 after the methane is released into the equilibrium kettle 25 are recorded. Since the PVT data of methane are known, the number of moles of methane remaining in the pressure-resistant gas chamber 15 after the methane is released can be determined. g2 Considering the volume change caused by the rotation of the high-pressure metering pump 23 and the volume occupied by the pipeline and valve, the volume V of the oil-based drilling fluid can be easily obtained by combining the mass and density of the added oil-based drilling fluid. L , in order to correct the volume of the equilibrium kettle 25 occupied by methane when it reaches dissolution equilibrium in the oil-based drilling fluid; Moreover, the temperature T3 and pressure P3 in the equilibrium kettle 25 at the time of dissolution equilibrium are known, so the number of moles of gas in the equilibrium kettle after dissolution equilibrium is reached n can be determined g3 .

[0082] Solubility Rs is:

[0083] R S =(n×22.4×10 3 ) / V L

[0084] Where: V L is the volume of oil-based drilling fluid at room temperature and atmospheric pressure.

[0085] The mole fraction n of methane dissolved in the oil-based drilling fluid is corrected as follows:

[0086] S1: The molar fraction n of methane dissolved in the oil-based drilling fluid is converted into the following formula:

[0087]

[0088] Where: V GC is the volume of the pressure-resistant gas chamber 15, ml, V EC is the volume of the equilibrium kettle 25, ml, V L is the volume of oil-based drilling fluid added to the balance kettle 25, ml, ρ i The density of methane in the pressure-resistant gas chamber 15 before releasing methane into the equilibrium reactor 25, g / cm 3 , ρ f The density of methane in the pressure-resistant gas chamber 15 after the methane is released into the equilibrium reactor 25, g / cm 3 , ρ g The molar density of methane in the equilibrium kettle after reaching dissolution equilibrium, g / cm 3 , M g is the molar mass of methane, 16 g / mol. i , f and ρ g Obtained from the software REFPROP 9.1 database.

[0089] S2: Correction for the effects of temperature and pressure on drilling fluid density;

[0090] ρ2=ρ1 / (1+C T ΔT+C P ΔP) (2)

[0091] Where: ρ1 is the density of drilling fluid at room temperature and atmospheric pressure, g / cm 3 , C T is the thermal expansion coefficient, MPa, C p is the elastic compression coefficient, MPa, ΔT is the temperature difference between the measured target temperature and room temperature, °C, ΔP is the pressure difference between the measured target pressure and atmospheric pressure, MPa;

[0092] C T =bρ1 / (1+aΔP), C p =kρ1ΔP n , ΔT=TT o , ΔP=PP o

[0093] Where: T o is room temperature, °C, p o is atmospheric pressure, MPa, T is target temperature, ℃, P is target pressure, MPa; a, b, k, n are calculated empirical values.

[0094] S3: Correct the effect of temperature and pressure on the volume change of drilling fluid; the volume or density of drilling fluid will change with the pressure it is subjected to, that is, when the pressure increases by one unit value, the volume of drilling fluid will decrease by one value. As the pressure increases, the volume of the liquid decreases, but the mass does not change, that is, dm = 0, so the density increases. The relationship between their relative increments can be known from dm = d(ρV) = ρdV + Vdρ = 0:

[0095]

[0096] Where: ρ2 is the drilling fluid density at the target temperature and pressure, g / cm 3 , ρ1 is the density of drilling fluid at room temperature and atmospheric pressure, g / cm 3 , V L is the volume of oil-based drilling fluid at room temperature and atmospheric pressure, cm 3 , △V is the volume change of drilling fluid caused by temperature and pressure changes, cm 3 ;

[0097] S4: Correction of the number of moles of methane dissolved in oil-based drilling fluid under high temperature and high pressure conditions n: Considering the volume of oil-based drilling fluid that decreases with increasing pressure △V, and the volume change V caused by the rotation of the high-pressure metering pump pump And the volume V occupied by pipelines and valves pipe These three influencing factors; combined with equations (1) to (3), we get:

[0098]

[0099] Where: V pump V is the volume change caused by the hydraulic oil being charged into the high pressure metering pump 23. pipe The volume occupied by the valve.

[0100] The present invention adopts the high temperature and high pressure balance kettle 25 made of 316L stainless steel, which is a container for accommodating a mixture of gas solutes and drilling fluids. The high pressure flange bolts are opened and closed, and the sealing structure is a combination of a metal O-ring and a metal corrugated gasket. Overpressure automatic pressure relief, maximum working temperature of 200°C, maximum working pressure of 75MPa, and volume of 400ml. It has the characteristics of corrosion resistance, high temperature resistance, and high pressure resistance, and can simulate the high temperature and high pressure conditions existing in the actual ultra-deep oil and gas layer drilling process, which is closer to engineering production, and obtains accurate experimental data while avoiding leakage problems caused by long-term use, high temperature and high pressure, etc., which greatly improves the safety and stability of experimental operation. The pressure-resistant gas chamber 15 made of 316L stainless steel is a container for accommodating gas solutes, with a maximum working temperature of 200°C, a maximum pressure bearing capacity of 150MPa, and a volume of 500ml. The pressure-resistant gas chamber 15 can strictly control the amount of methane released into the balance kettle 25, so as to accurately obtain the injection amount of methane in the balance kettle 25.

[0101] The stirring motor 18 is an adjustable speed automatic stirring motor 18 integrally formed with the top cover of the balancing kettle 25, the motor explosion-proof grade is BT4, and drives the stirring blade 19 built into the kettle body, with low noise and stable speed regulation, which accelerates the dissolution rate of the measured methane in the oil-based drilling fluid, shortens the measurement time to reach the dissolution equilibrium, and greatly improves the experimental efficiency.

[0102] A high-precision dynamic seal structure 20 is added to the balance kettle 25. The high-precision dynamic seal structure 20 divides the balance kettle 25 into a dissolution balance chamber located above the high-precision dynamic seal structure 20 and a hydraulic oil chamber 27 located below the high-precision dynamic seal structure. The hydraulic oil chamber 27 is connected to the high-pressure metering pump 23 through a pipeline output from the bottom cover of the balance kettle 25. The high-pressure metering pump 23 has a working range of 310ml, a minimum scale resolution of 0.01ml, and a rated maximum working pressure of 75MPa. As time goes by, when the dissolution equilibrium is reached, the pressure in the high-temperature and high-pressure reactor (balance kettle) 25 will decrease. The function of the pump is to maintain the pressure in the balance kettle 25 constant at the predetermined target experimental pressure. The hydraulic oil at the bottom of the pressurized balance kettle 25 is pushed forward by the hand-cranked rotating rod of the high-pressure metering pump 23 to supplement the pressure reduced by the dissolution of methane in the oil-based drilling fluid, thereby realizing the determination of the solubility of methane in the oil-based drilling fluid at a specified pressure. Compared with the liquid balance sampling method, the dissolution equilibrium offset caused by sampling is avoided.

[0103] The constant temperature oil bath heating box 26 uses an electric heater to heat the high temperature heat transfer oil in the box, with a heating power of 4000W, a maximum heating rate of 15℃ / min, a temperature control range from room temperature to 150℃, and a temperature control accuracy of ±0.5℃. Through the intelligent high-precision temperature control of the oil bath box program, a constant temperature environment of the experimental target temperature is provided for the pressure-resistant gas chamber 15 and the balance kettle 25 immersed in the oil bath, with a fast heating rate, high temperature control and insulation accuracy, ensuring the safety and environmental protection of the entire measurement process and improving the measurement efficiency.

[0104] The gas booster pump 4 is a device for boosting the pressure of the pressure-resistant gas chamber 15. Compressed air can be used as the driving air source of the pump. The driving air pressure range is 0.1-0.8 MPa and the driving flow range is 0.3-1 m 3 / min, the inlet pressure is 5-25MPa, and the outlet pressure can reach up to 160MPa. The present invention uses a gas booster pump 4 to pressurize the methane in the high-pressure gas cylinder 1 to the target experimental pressure and inject it into the pressure-resistant gas chamber 15, which can easily achieve adjustable and controllable output pressure. The precision insertion type K-type thermocouple first temperature sensor 13, the second temperature sensor 17 and the first pressure sensor 14 and the second pressure sensor 24 with high temperature compensation function assembled in the pressure-resistant gas chamber 15 and the balance kettle 25 have a temperature measurement accuracy of ±0.05°C and a pressure measurement accuracy of 0.5% FS. They monitor the temperature and pressure in the pressure-resistant gas chamber 15 and the balance kettle 25, and automatically collect and process the pressure and temperature measurement signals through the data acquisition system 31 and display them on the computer 32 panel, so as to achieve accurate measurement of the temperature and pressure of the materials in the balance kettle 25 and the pressure-resistant gas chamber 15. Taking into account the three influencing factors, namely, the volume of oil-based drilling fluid that decreases with the increase of pressure, the volume change caused by the rotation of the hand-cranked high-pressure metering pump 23, and the volume occupied by pipelines and valves, a method for correcting the volume of the equilibrium kettle 25 occupied by methane when it reaches dissolution equilibrium in the oil-based drilling fluid is proposed, which avoids the influence of these three influencing factors on the experimental results and improves the reliability of the measurement data.

[0105] The present invention provides a device and method for measuring the solubility of methane in oil-based drilling fluid under high temperature and high pressure conditions based on the equal volume saturation method; the solubility of methane in oil-based drilling fluid under the conditions of temperature of 30°C to 150°C and pressure of 0 to 70MPa can be measured without sampling and analyzing the saturated drilling fluid under pressurized state, and the operation is simpler; the technical means of high-pressure dynamic sealing structure and high-pressure metering pump displacement of hydraulic oil solve the problem that the traditional equal volume saturation method is difficult to measure the gas solubility under a specified pressure; considering the volume compression of the drilling fluid under high pressure, the volume change caused by the rotation of the high-pressure metering pump, and the volume occupied by the pipeline and the valve, the volume V of the oil-based drilling fluid can be easily obtained in combination with the known mass and density of the added oil-based drilling fluid. L , in order to correct the volume of the equilibrium kettle occupied by methane when it reaches solubility equilibrium in the oil-based drilling fluid, so as to obtain more reliable solubility measurement data.

Claims

1. An experimental device for determining the solubility of methane in oil-based drilling fluid, characterized in that: The invention comprises a pressure-resistant gas chamber (15) and a balance kettle (25) both of which are arranged in a constant temperature oil bath heating box (26) and are interconnected; a gas booster pump (4) connected to the pressure-resistant gas chamber (15); the gas booster pump (4) is connected to a driving gas source inlet (5); a gas check valve (10) is arranged on the pipeline between the pressure-resistant gas chamber (15) and the gas booster pump (4); the gas booster pump (4) is also connected to a high-pressure gas cylinder (1); the cavity of the balance kettle (25) is divided into an upper dissolving balance chamber and a lower hydraulic oil chamber (27) by a high-pressure dynamic sealing structure (20); the dissolving balance chamber is connected to a liquid inlet funnel (21) via a fourth stop valve (22); the hydraulic oil chamber (27) is connected to a high-pressure metering pump (23) for replenishing hydraulic oil therein; and a vacuum system (30) for evacuating the pressure-resistant gas chamber (15) and the balance kettle (25); A first temperature sensor (13) and a first pressure sensor (14) for collecting temperature and pressure signals are arranged in the pressure-resistant gas chamber (15); a second temperature sensor (17) and a second pressure sensor (24) for collecting temperature and pressure signals are arranged in the dissolution equilibrium chamber; the first temperature sensor (13), the first pressure sensor (14), the second temperature sensor (17), and the second pressure sensor (24) are connected to a data acquisition device (31).

2. The experimental device for determining the solubility of methane in oil-based drilling fluid according to claim 1, characterized in that: A gas filter (6), a first pressure reducing valve (7), a second pressure gauge (8) and an electric valve (9) are arranged on the pipeline between the gas source inlet (5) and the gas booster pump (4).

3. The experimental device for determining the solubility of methane in oil-based drilling fluid according to claim 1, characterized in that: It also includes a first pressure gauge (2) for measuring the pressure of the high-pressure gas cylinder (1) and a first stop valve (3) for controlling the switch thereof.

4. The experimental device for determining the solubility of methane in oil-based drilling fluid according to claim 1, characterized in that: A second pressure reducing valve (11) and a second stop valve (12) are also provided on the pipeline between the pressure-resistant gas chamber (15) and the gas booster pump (4).

5. The experimental device for determining the solubility of methane in oil-based drilling fluid according to claim 1, characterized in that: A stirring blade (19) for stirring is arranged in the dissolution equilibrium chamber, and the stirring blade (19) is connected to a stirring motor (18).

6. The experimental device for determining the solubility of methane in oil-based drilling fluid according to claim 1, characterized in that: The vacuum system (30) comprises a vacuum pump (29), a fifth stop valve (28) is arranged between the vacuum pump (29) and the equilibrium kettle (25), and a third stop valve (16) is arranged between the pressure-resistant gas chamber (15) and the equilibrium kettle (25).

7. The experimental device for determining the solubility of methane in oil-based drilling fluid according to claim 1, characterized in that: The data acquisition device (31) is connected to a control device (32).

8. A method for measuring the solubility of methane in oil-based drilling fluid using any one of the experimental devices for measuring the solubility of methane in oil-based drilling fluids as claimed in claims 1 to 7, characterized in that: The following steps are involved: Step 1: Calibrate and verify the experimental device and pipeline; Step 2: Clean the equilibrium kettle (25), start the vacuum system (30) to evacuate the air, and check the air tightness of the experimental device; Step 3: Heat the pressure-resistant gas chamber (15) and the equilibrium kettle (25) to the target temperature, start the vacuum system (30) to evacuate the air; inject the required drilling fluid into the dissolving equilibrium chamber in the equilibrium kettle (25) through the liquid inlet funnel (21); Step 4: a certain amount of methane is charged into the pressure-resistant gas chamber (15), and the pressure-resistant gas chamber (15) is heated to a target temperature. After the pressure is stabilized, the temperature T1 and the pressure P1 of the methane in the pressure-resistant gas chamber (15) are obtained; Step 5: injecting methane from the pressure-resistant gas chamber (15) into the dissolving equilibrium chamber in the equilibrium kettle (25) until the pressure reaches a set pressure; after the pressure stabilizes, obtaining T2 and pressure P2 after the gas is released from the pressure-resistant gas chamber (15); Step 6: Adjust the constant temperature oil bath heating box (26) so that the temperature reaches the required temperature, and observe the pressure change in the dissolution equilibrium chamber in real time. If the pressure drops, inject hydraulic oil into the hydraulic oil chamber (27) through the high-pressure metering pump (23) until the set pressure is reached; record T3 and pressure P3 in the equilibrium kettle (25) after the pressure stabilizes; Step 7: Calculate the solubility of methane in the oil-based drilling fluid based on the measured parameters.

9. The method for determining the solubility of methane in oil-based drilling fluid according to claim 8, characterized in that: The solubility of methane in oil-based drilling fluid is R S The calculation process is as follows: n=Δn g -n g3 =(n g1 -n g2 )-n g3 Where: n is the number of moles of methane dissolved in the oil-based drilling fluid, n g3 The number of moles of methane in the equilibrium reactor 25 after reaching the dissolution equilibrium, △n g is the number of moles of methane released from the pressure-resistant gas chamber 15 into the equilibrium reactor 25, n g1 is the number of moles of methane in the pressure-resistant gas chamber 15 before the methane is released into the equilibrium reactor 25, n g2 is the number of moles of methane in the pressure-resistant gas chamber 15 after the methane is released into the equilibrium reactor 25; Solubility Rs is: R S =(n×22.4×10 3 ) / V L Where: V L is the volume of oil-based drilling fluid at room temperature and atmospheric pressure.

10. The method for determining the solubility of methane in oil-based drilling fluid according to claim 9, characterized in that: It also includes a correction for the number of moles of methane dissolved in the oil-based drilling fluid, n, and the correction process is as follows: S1: The number of moles of methane dissolved in the oil-based drilling fluid, n, is converted into the following formula: Where: V GC is the volume of the pressure-resistant gas chamber (15), V EC is the volume of the equilibrium kettle (25), V L is the volume of oil-based drilling fluid added to the balance kettle (25), ρ i is the density of methane in the pressure-resistant gas chamber (15) before releasing methane into the equilibrium reactor (25), ρ f is the density of methane in the pressure-resistant gas chamber (15) after methane is released into the equilibrium reactor (25), ρ g To achieve the molar density of methane in the equilibrium kettle after dissolution equilibrium, M g is the molar mass of methane; S2: Correction for the effects of temperature and pressure on drilling fluid density; p2=p1 / (1+C T ΔT+C P ΔP) (2) Where: ρ1 is the density of drilling fluid at room temperature and atmospheric pressure, C T is the coefficient of thermal expansion, C p is the elastic compression coefficient, ΔT is the temperature difference between the measured target temperature and room temperature, and ΔP is the pressure difference between the measured target pressure and atmospheric pressure; S3: Correction of the effect of temperature and pressure on the volume change of drilling fluid; Where: ρ2 is the drilling fluid density at the target temperature and pressure, ρ1 is the drilling fluid density at room temperature and atmospheric pressure, V L is the volume of oil-based drilling fluid at room temperature and atmospheric pressure, △V is the volume change of drilling fluid caused by temperature and pressure changes; S4: Corrected molar number n of methane dissolved in oil-based drilling fluid under high temperature and high pressure conditions: Where: V pump V is the volume change caused by the high pressure metering pump (23) being filled with hydraulic oil, pipe The volume occupied by the valve.

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