A method for preparing a hydrate reservoir with controllable hydrate saturation

Abstract

The present invention discloses a method for preparing a hydrate-containing reservoir with controllable hydrate saturation, so as to realize the indoor precise preparation of hydrate-containing reservoirs with different contents. First, the sediment density and porosity are tested, and the specific density value and the corresponding porosity of the sediment are quantified through multiple water injection-stationary processes of the sediment samples; and on this basis, the sediment samples used are filled in a reactor of known volume, and the mass used when the sediment samples are filled is recorded, and then the gas pressure required to be injected to form the hydrate saturation is calculated and inferred, and after the gas injection volume reaches the calculated pressure, water injection and cooling operations are performed to finally form a system with a specific hydrate saturation. This scheme prepares hydrates under specific hydrate saturation conditions by controlling the injected gas target pressure and the water injection volume, and can produce hydrate-containing reservoirs with any hydrate saturation, providing technical support for the analysis of differential decomposition processes of different reservoirs.

Description

Technical Field

[0001] The invention belongs to the field of indoor experimental simulation serving the development of natural gas hydrate resources, and specifically relates to a method for preparing a hydrate-containing reservoir with controllable hydrate saturation. Background Art

[0002] The results of global hydrate drilling and coring voyages show that in different storage areas, the production form, saturation, thermal stability conditions and other characteristics of hydrates are not the same. For pore-filling hydrate types, hydrates can exist in three forms: suspended in the pores, in contact with the sediment skeleton, or as a component of the sediment skeleton. Regardless of the form, hydrates can be part of the pore space. The ratio of hydrate content to the total pore space is defined as hydrate saturation, which is a key parameter affecting the amount of hydrate storage resources and the flow capacity and effective permeability of pore channels during the development of hydrate reservoirs.

[0003] In order to explore the influence of hydrate content on gas and water production during decomposition and provide support for target site selection and production increase design during hydrate development, it is necessary to prepare hydrate reservoirs with precise hydrate saturation in the laboratory to simulate the actual hydrate decomposition. In particular, the preparation of different hydrate saturations under different sediment types, different burial depths, different temperatures and pressures, but there is no relevant preparation scheme for hydrate reservoirs with different hydrate saturations in the prior art. Based on this background, a fully controllable solution is urgently needed. Summary of the invention

[0004] In order to solve the defects in the prior art, the present invention proposes a method for preparing a hydrate reservoir with controllable hydrate saturation, so as to effectively prepare a hydrate reservoir with any hydrate saturation, and provide effective support for analyzing the dynamic sensible heat changes during the decomposition process of the hydrate system.

[0005] The present invention is implemented by adopting the following technical scheme: a method for preparing a hydrate reservoir with controllable hydrate saturation, comprising the following steps:

[0006] Step A: Test the sediment density ρ of a sediment sample A. s and porosity

[0007] (1) In the range V L Gradually add sediment sample A to the measuring barrel / cup until the volume of sediment sample A reaches the volume of the measuring cylinder V. L0 Scale, V L0 >1 / 2V L , the mass of the sediment sample A added is m A0 ;

[0008] (2) Use a high-precision pipette to inject deionized water in small amounts and multiple times, and let it stand for several hours after each injection. Repeat the operation multiple times until the liquid level of the injected deionized water just reaches the level of the measuring cylinder V. L0 Scale, record the cumulative deionized water injection volume m w0 ; then:

[0009] Density of sediment sample A

[0010] Porosity of sediment sample A

[0011] Step B: Based on sediment sample A, at temperature T 3 Under the conditions, the hydrate saturation is S h0 Hydrate reservoirs, specifically including:

[0012] Step B1: When the volume is V r0 The reactor is filled with sediment sample A in batches and the amount of sediment used after filling is recorded. A1 ; and calculate the pore volume V after the reactor is filled with sediment sample A P0 ;

[0013] Step B2: stabilize the temperature of the reactor after filling the sediment sample A in step B1 at any constant temperature T 1 Under the conditions, methane gas is continuously and stably injected into the reactor to a specified pressure P 1 After the temperature and pressure of the system are further stabilized, record the system temperature T 2 , so that T 2 =T 1 ;P 1 The following conditions are met:

[0014]

[0015] Among them, S h0 is the saturation of the hydrate to be prepared; ρ h is the hydrate density, M h is the molar volume of the hydrate, Z m1 The gas compression coefficient of methane at this time is T 2 With P 1 Function of

[0016] Step B3: Inject V into the stable system of step B2 w1 Deionized water / or saline, V w1 The following two conditions are met:

[0017] Article 1, Where R is the gas constant; Z m1 is the gas compressibility factor of methane, M H2O is the molar mass of water;

[0018] Second, cool the system after water injection to 1°C. When the entire mixed system is stable again, record the pressure in the reactor as P. 2 At this time, the temperature is increased at a certain rate until the required temperature T is reached. 3 At this time, the system reaches stability again, and the temperature T is recorded. 4 and pressure P 3 , and P 3 =P 2 , T 4 =T 3 , P 3 The following conditions are met:

[0019]

[0020] If the above equation is not satisfied when the system stabilizes again in step B3, then by continuing to increase the V w1 By repeating step B3 multiple times, any temperature T 3 Under the condition of hydrate saturation S h0 Preparation of hydrate-containing reservoirs.

[0021] Furthermore, in step B1, the pore volume V after the reactor is filled with sediment sample A is P0 for:

[0022]

[0023] Among them, V r0 is the volume of the reactor, ρ s is the density of sediment sample A.

[0024] Compared with the prior art, the advantages and positive effects of the present invention are:

[0025] The scheme of the present invention is aimed at a certain sediment sample. The sediment sample used is filled in a reactor of known volume, and the mass used when the sediment sample is filled is recorded. Then, the gas pressure required to form the hydrate saturation is calculated and inversely inferred. After the gas injection volume reaches the calculated pressure, water is injected and the temperature is lowered to finally form a system with a specific hydrate saturation. The hydrate-containing reservoir with a specific hydrate saturation is achieved by controlling the target pressure of the injected gas and the amount of water injected, providing technical support for the analysis of the differential decomposition process of different reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is the specific hydrate saturation Sh0 Schematic diagram of the synthesis experiment process;

[0027] Among them, 1. Unknown sediment sample; 2. Cylinder / measuring cup with scale; 3. Add sediment sample exceeding 1 / 2 range to V L0 ; 4. Inject deionized water - after standing for several times, the water level just reaches V L0 ; 5. Methane gas injected into the synthesis reactor after the sediment sample is filled; 6. Synthesized natural gas hydrate. DETAILED DESCRIPTION

[0028] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and therefore, the present invention is not limited to the specific embodiments disclosed below.

[0029] This embodiment provides a method for preparing a hydrate-containing reservoir with controllable hydrate saturation, such as Figure 1 As shown, the following steps are included:

[0030] Step A, testing sediment density and porosity;

[0031] (1) In the range V L mL measuring barrel / cup, gradually add sediment sample A several times until the sample volume reaches the volume of the measuring cylinder V L0 Scale(V L0 >1 / 2V L ), the mass of the sediment sample added m A0 , unit: g.

[0032] (2) Use a high-precision pipette to inject deionized water in small amounts and multiple times, and let it stand for 8 hours after each injection. Repeat the operation multiple times until the liquid level of the injected deionized water just reaches the V of the measuring cylinder. L0 Scale, record the cumulative deionized water injection volume m w0 , unit: g;

[0033] The density of sediment sample A can be measured as:

[0034] Unit: g / mL

[0035] Because the mass of deionized water is equal to the volume, only numbers are substituted into the parameters in this formula;

[0036] Porosity of sediment sample A It can be measured as:

[0037] Unit 100%.

[0038] Step B: Based on step A, the preparation of a hydrate-containing reservoir with a specific hydrate saturation is achieved by injecting gas and liquid phases and controlling the temperature, which specifically includes the following steps:

[0039] (1) Sand filling: When the volume V is known r0 The reactor is filled with sediment sample A in batches and the amount of sediment used after filling is recorded. A1 ;

[0040] According to the above-mentioned sediment density and porosity determination method, the pore volume V after the reactor is filled with sediment can be obtained. P0 for:

[0041]

[0042] (2) Gas injection: The temperature of the reactor filled with sediment in the first step is stabilized at an arbitrary constant temperature T 1 (Unit: K) and continuously and stably inject methane gas into the reactor to a specified pressure P 1 (Unit: MPa), after the system is further stabilized, record the system temperature as T 2 , and make T 2 =T 1 , and P 1 The following conditions are met:

[0043]

[0044] After the system stabilizes according to the steps, T2 and T1 should be equal. If T2 is not equal to T1, the temperature of the reactor has not yet stabilized. Further accurately adjust the temperature of the reactor's cold water bath and appropriately lower the room temperature to make T2 and T1 equal.

[0045] In the above formula, S h0 is the hydrate saturation of the specified synthesis; ρ h is the hydrate density, 0.92 g / mL; R is the gas constant, 8.314 J / mol.K; M h is the molar volume of the hydrate, 124 g / mol, and usually T 1 The set value is higher, 20-25℃. m1 The gas compression coefficient of methane at this time is T 2 With P 1 The function is a mature technology, which is determined according to the invention patent "A method for calculating and analyzing hydrate saturation in experimental and numerical simulation processes" (patent number ZL201910327973.9).

[0046] (3) Water injection: Inject V into the second step stabilization system w1 Deionized water / or saline, V w1 The following two conditions must be met:

[0047] Article 1, Among them, M H2O is the molar mass of water, which is 18 g / mol.

[0048] Second, after the water injection, the system is cooled to 1°C and the pressure is recorded as P when the entire mixed system is stable again. 2 At this time, the temperature is increased at a rate of 1°C / h until the specific required temperature T is reached. 3 After that, the system reaches a stable state again. The temperature and pressure conditions at this time are T 4 and P 3 , requiring P 3 =P 2 , T 4 =T 3 , and P 3 To meet:

[0049]

[0050] If the above equation is not satisfied when the system stabilizes again, then by continuing to increase the V w1 , increase to (V w1 +100) mL, by repeating step (3) multiple times, the 3 Under the condition of hydrate saturation S h0 Preparation of hydrate-containing reservoirs.

[0051] So far, through P 1 and V w1 The present invention can accurately prepare any hydrate saturation S h0 The hydrate-containing sediment system is provided for subsequent research.

[0052] Example description:

[0053] Case 1:

[0054] A hydrate reservoir with a hydrate saturation of 10% at 3°C ​​was prepared in a field sediment sample I with a median particle size of about 100 μm for further experiments. The specific operation is as follows:

[0055] (1) Take sediment sample I and fill it into a 50 mL measuring cylinder until the sediment sample is filled to the 40 mL mark. Record the difference in sample volume before and after filling, m. A0 =m A20 -m A10 ;

[0056] (2) Using a high-precision pipette, add the liquid sample to the sediment sample I in the first step in batches, 1 mL at a time, and let the sediment sample stand for more than 8 hours after each addition;

[0057] (3) Repeat step (2) and gradually reduce the amount of liquid added in the later stage of injection until the liquid level in the sediment just reaches the 40 mL mark. Record the cumulative amount of liquid injected at this time m w0 .

[0058] (4) When the volume is V r0 Fill the high-pressure reactor layer by layer until it is full of sediment sample I, and record the amount of sediment used after filling m A1 ;

[0059] (5) placing the reactor filled with sediment in step (4) in a cold water bath, and setting the temperature of the cold water bath so that the temperature in the reactor can be stabilized at a constant 25° C.;

[0060] (6) Continuously inject methane gas into the reactor until the pressure of the reactor reaches 2.3 MPa. h =10%,ρ h =0.92g / mL,Z m1 Determined to be 0.9619, T 2 =25℃, R is 8.314J / mol.K, M h is 124 g / mol).

[0061] (7) Continue to inject 100 mL (greater than 83.93 mL) of water into the reactor after gas injection;

[0062] (8) Cooling the reactor temperature to 1°C;

[0063] (9) After the system is stable, the temperature is raised at a rate of 1°C / h until the system temperature is stabilized at 3°C ​​and the pressure remains stable before and after the temperature is raised. At the same time, the stable pressure condition satisfies the requirement of being greater than 3.53 MPa (f(T 4 =3°C),

[0064] At this time, the hydrate saturation of the prepared hydrate-containing system is exactly 10%.

[0065] Case 2:

[0066] To prepare a hydrate reservoir with a hydrate saturation of 64.8% at 12°C in a field sediment sample II with a median particle size of about 250 μm, the specific operation is as follows:

[0067] (1) Take sediment sample II and fill it into a 20 mL measuring cylinder until the sediment sample is filled to the 15 mL mark. Record the difference in sample volume before and after filling (m). B0 =m B20 -m B10 ;

[0068] (2) Using a high-precision pipette, add the liquid sample to the sediment sample II in step (1) in batches of 0.5 mL each time, and let the sediment sample stand for more than 8 hours after each addition;

[0069] (3) Repeat step (2) and gradually reduce the amount of liquid added in the later stage of injection until the liquid level in the sediment just reaches the 15 mL mark. Record the cumulative amount of liquid injected at this time m w0 .

[0070] (4) When the volume is V r02 Fill the high-pressure reactor layer by layer, fill it with sediment sample II, and record the amount of sediment used after filling m B1 ;

[0071] (5) placing the reactor filled with sediment in step (4) in a cold water bath, and setting the temperature of the cold water bath so that the temperature in the reactor can be stabilized at a constant 20° C.;

[0072] (6) Continuously inject methane gas into the reactor until the pressure of the reactor reaches 10.0 MPa. h =64.8%,ρ h =0.92g / mL,Z m1 Determined to be 0.8395, T 2 =20℃, R is 8.314J / mol.K,M h is 124 g / mol).

[0073] (7) Continue to inject 420 mL (greater than 418.0 mL) of water into the reactor after gas injection;

[0074] (8) Cooling the reactor temperature to 1°C;

[0075] (9) When the reactor is stable again, the system temperature is raised at a rate of 1°C / h until the system temperature is finally stabilized at 12°C, and the pressure remains stable before and after the temperature rise, and the stable pressure meets the condition of being greater than 8.98 MPa (f(T 4 =12°C),

[0076] (10) If in the previous step, when the system temperature is stable at 12°C, the stable pressure condition is less than or equal to 8.98 MPa, 100 mL of liquid is injected into the reactor again, and the temperature is lowered to 1°C. After the system is stabilized again, the temperature is raised to 12°C. Repeat the above operation until the system temperature is finally stable at 12°C and the stable pressure condition is greater than 8.98. At this time, the hydrate reservoir prepared in the reactor is a hydrate reservoir with a saturation of 64.8%.

[0077] The invention is suitable for the operation of synthesizing a specific hydrate concentration in an unknown sediment sample, and is particularly useful for guiding the operation of synthesizing hydrates in sediments with unknown density and porosity obtained from the field.

[0078] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a hydrate reservoir with controllable hydrate saturation, characterized in that: The following steps are involved: Step A: Test the sediment density ρ of a sediment sample A. s and porosity Step B: Based on sediment sample A, at temperature T3, prepare a hydrate saturation S h0 Hydrate reservoirs, specifically including: Step B1: When the volume is V r0 The reactor is filled with sediment sample A in batches and the amount of sediment used after filling is recorded. A1 ; and calculate the pore volume V after the reactor is filled with sediment sample A P0 ; Step B2, stabilize the temperature of the reactor filled with sediment sample A in step B1 at any constant temperature T1, and continuously and stably inject methane gas into the reactor to a specified pressure P1. After the temperature and pressure of the system are further stabilized, record the system temperature T2 so that T2=T1; P1 meets the following conditions: Among them, S h0 is the saturation of the hydrate to be prepared; ρ h is the hydrate density, M h is the molar volume of the hydrate, Z m1 The gas compressibility coefficient of methane at this time is a function of T2 and P1; Step B3: Inject V into the stable system of step B2 w1 Deionized water / or saline, V w1 The following two conditions are met: Article 1, Where R is the gas constant; Z m1 is the gas compressibility factor of methane, M H2O is the molar mass of water; The second method is to cool the system after water injection to 1°C. When the whole mixed system is stable again, the pressure in the reactor is recorded as P2. At this time, the temperature is increased at a certain heating rate until the required temperature T3 is reached. At this time, the system is stable again. The temperature T4 and pressure P3 are recorded, and P3 = P2, T4 = T3. Under the condition of temperature T3, the hydrate saturation is S h0 Preparation of hydrate-containing reservoirs.

2. The method for preparing a hydrate reservoir with controllable hydrate saturation according to claim 1, characterized in that: In step B3, P3 satisfies the following conditions: If the above equation is not satisfied when the system stabilizes again in step B3, then by continuing to increase the V w1 By repeating step B3 multiple times, the hydrate saturation S is achieved at any temperature T3. h0 Preparation of hydrate-containing reservoirs.

3. The method for preparing a hydrate reservoir with controllable hydrate saturation according to claim 1, characterized in that: In step A, when testing the sediment density and porosity, the following method is used: (1) In the range V L Gradually add sediment sample A to the measuring barrel / cup until the volume of sediment sample A reaches the volume of the measuring cylinder V. L0 Scale, V L0 >1 / 2V L , the mass of the sediment sample A added is m A0 ; (2) Use a high-precision pipette to inject deionized water in small amounts and multiple times, and let it stand for several hours after each injection. Repeat the operation multiple times until the liquid level of the injected deionized water just reaches the level of the measuring cylinder V. L0 Scale, record the cumulative deionized water injection volume m w0 ; then: Density of sediment sample A Porosity of sediment sample A 4. The method for preparing a hydrate reservoir with controllable hydrate saturation according to claim 3, characterized in that: In step B1, the pore volume V after the reactor is filled with sediment sample A P0 for: Among them, V r0 is the volume of the reactor, ρ s is the density of sediment sample A.

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