A method and device for high pressure oil reservoir miscible flooding

Abstract

The present invention relates to a high-pressure oil reservoir miscible drive method and device, wherein lean gas and liquefied petroleum gas are mixed to obtain a required mixed gas, during which the pressure and phase state of the lean gas and the liquefied petroleum gas in the pipeline will not cause damage to the equipment, and the mixed gas can be used as rich gas for oil reservoir miscible drive after being output. Correspondingly, in practical applications, the mixed gas directly enters the formation through the pipeline and the wellbore for miscible drive, which can not only realize effective oil reservoir development, but also solve the problem that directly pressurizing the rich gas is likely to damage the valve parts of the pressurizing equipment.

Description

Technical Field

[0001] The invention relates to the field of petroleum development, and in particular to a high-pressure oil reservoir miscible phase drive method and device. Background Art

[0002] It is difficult to increase the recovery rate of oil fields in the later stage of water flooding. The gas injection miscible phase flooding process can improve the crude oil recovery rate. There are two gas injection miscible phase flooding methods in the existing technology, namely, lean gas injection miscible phase flooding and rich gas injection miscible phase flooding. Natural gas with less than 100ml of hydrocarbons above propane (C3) per cubic meter in liquid state is lean gas; natural gas with more than 100ml of hydrocarbons above propane (C3) per cubic meter in liquid state is rich gas.

[0003] When lean gas miscible drive is used, Wang Jinan et al. stated in "Indoor Experimental Study on Hydrocarbon Gas Drive in Low Permeability Volatile Reservoirs" in 2002 that the miscible pressure of crude oil and injected lean gas is as high as 47MPa, and the injection pressure needs to be increased, which will increase the investment and operating costs of ground injection equipment. If the injection pressure is not increased, the lean gas and crude oil cannot reach the miscible conditions and miscible drive cannot be achieved, and the gas drive recovery factor is not high.

[0004] Considering that rich gas miscible drive does not require a high injection pressure, the reservoir can adopt rich gas miscible drive. When rich gas is used as the injection medium, although it does not require too high an injection pressure, the rich gas is prone to phase change during the pressurization stage, that is, liquefaction. The resulting liquid will cause a surge in pressure during the pressurization process, thereby damaging the valve components of the pressurization equipment. Summary of the invention

[0005] The purpose of the present invention is to provide a high-pressure oil reservoir miscible drive method, which is used to solve the problem that the use of rich gas miscible drive in the prior art is prone to damage the valve components of the boosting equipment; the present invention also provides a high-pressure oil reservoir miscible drive device, which is used to solve the problem that the use of rich gas miscible drive in the prior art is prone to damage the valve components of the boosting equipment.

[0006] To achieve the above object, the present invention provides a high-pressure reservoir miscible flooding method, comprising the following steps: respectively pressurizing lean gas and liquefied petroleum gas; mixing the pressurized lean gas and the pressurized liquefied petroleum gas to obtain a mixed gas, and using the mixed gas to perform reservoir miscible flooding.

[0007] The beneficial effects of the present invention are as follows: the required mixed gas is obtained by mixing the lean gas with the liquefied petroleum gas. During this process, the pressure and phase state of the lean gas and the liquefied petroleum gas in the pipeline will not cause damage to the equipment, and the mixed gas can be used as rich gas for miscible drive of the oil reservoir after being output. Correspondingly, in actual applications, the mixed gas directly enters the wellbore for miscible drive, which can not only realize effective oil reservoir development, but also solve the problem that directly pressurizing the rich gas is likely to damage the valve parts of the pressurizing equipment.

[0008] Further, when the formation pressure is 29.6 MPa, the lean gas and liquefied petroleum gas are pressurized to 29.6 MPa.

[0009] Furthermore, the pressurized lean gas and the pressurized liquefied petroleum gas are mixed according to a set ratio to obtain a mixed gas, and the ratio of the lean gas to the liquefied petroleum gas ranges from 27:73 to 100:0.

[0010] In the present invention, lean gas and liquefied petroleum gas are mixed in a set ratio so that the liquefied petroleum gas, which is originally in liquid form, can be converted into gas under pressure after being mixed with the lean gas, so that the mixed gas is discharged in gas form to achieve subsequent gas injection mixed phase drive.

[0011] The present invention also provides a high-pressure oil reservoir miscible drive device, comprising a first booster pump and a second booster pump, wherein the first booster pump is connected to a first piston cylinder for storing lean gas, and the second booster pump is connected to a second piston cylinder for storing liquefied petroleum gas; the first piston cylinder is connected to a first input end of an oil-gas mixing container; the second piston cylinder is connected to a second input end of the oil-gas mixing container; and the oil-gas mixing container is provided with an output end.

[0012] The present invention injects lean gas and liquefied petroleum gas into an oil-gas mixing container through two booster pumps for sufficient mixing, and then uses the mixed gas as rich gas for miscible drive, thereby realizing gas injection miscible drive development of the oil reservoir. In this process, the rich gas is not directly pressurized, which solves the problem that the rich gas is easily liquefied during pressurization, thereby damaging the valve parts of the boosting equipment.

[0013] Furthermore, the output end and the second input end are arranged at the upper end of the oil-gas mixing container, and the first input end is arranged at the lower end.

[0014] The present invention arranges an output end and a second input end at the upper end of the oil-gas mixing container, and arranges a first input end at the lower end, so as to inject liquid liquefied petroleum gas into the oil-gas mixing container from the second input end, and inject gaseous lean gas into the oil-gas mixing container from the first input end, so that the lean gas and the liquefied petroleum gas can be fully mixed.

[0015] Furthermore, the oil-gas mixing container is a tank or a pipeline. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a flow chart of the high pressure reservoir miscible flooding method of the present invention;

[0017] Figure 2 This is a schematic diagram of the structure of a high-pressure oil reservoir miscible flooding device according to the present invention;

[0018] Figure 3Schematic diagram of minimum miscible pressure under different dry gas contents of the present invention;

[0019] In the attached drawings: 1 is a booster pump; 2 is a booster pump; 3 is a piston container; 4 is a piston container; 5 is an oil-gas mixing container; 6 is an annular pressure pump; 7 is a core holder; and 8 is a data collector. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below with reference to the accompanying drawings and examples.

[0021] like Figure 1 As shown, the present invention mixes lean gas (lean gas composition see Table 1) and liquefied petroleum gas (composition see Table 2) to obtain rich gas. The lean gas and liquefied petroleum gas are pressurized separately, the pressurized lean gas and liquefied petroleum gas are mixed according to a set ratio, and the mixed gas obtained after mixing is injected into the oil reservoir as rich gas for miscible flooding.

[0022] Table 1

[0023] Components <![CDATA[C1]]> <![CDATA[C2]]> <![CDATA[C3]]> <![CDATA[C4]]> <![CDATA[C5]]> <![CDATA[C6]]> <![CDATA[C7]]> <![CDATA[C8]]> <![CDATA[CO2]]> <![CDATA[N2]]> content(%) 92.582 3.94 0.794 0.313 0.123 0.069 0.074 0.046 1.4 0.659

[0024] Table 2

[0025] Components C1 C2 C3 iC4 nC4 iC5 nC5 content(%) 0.43 19.11 22.21 45.20 6.36 4.95 1.74

[0026] Method Example:

[0027] In this embodiment, the lean gas and the liquefied petroleum gas are first pressurized at a certain pressure, respectively, and then the flow rate of the injection pump is controlled to mix the pressurized lean gas and the liquefied petroleum gas according to a set ratio. Before mixing, the lean gas exists in a gaseous form, and the liquefied petroleum gas exists in a liquid form. After mixing according to the set ratio, the mixture has the property of rich gas, that is, the liquid will become a gas after the pressure is greater than the critical value. Therefore, the pressurized lean gas and the liquefied petroleum gas are mixed to form rich gas (the rich gas composition and the mixed phase pressure under different lean gas and liquefied petroleum gas mixing ratios are shown in Table 3) and discharged. When the formation pressure is 29.6 MPa, the lean gas and the liquefied petroleum gas can be pressurized to 29.6 MPa, which is 17.4 MPa lower than the mixed phase pressure of 47 MPa when the lean gas is injected, and the reduction rate is 37%.

[0028] Therefore, the obtained rich gas is injected into the formation for miscible drive. The process of miscible drive belongs to the prior art and will not be described here.

[0029] Table 3

[0030]

[0031] In the above-mentioned boosting process, the phase state of the lean gas and the liquefied petroleum gas will not change with the pressure change, so the valve components of the boosting equipment will not be damaged. The components of the mixed gas obtained after mixing meet the component requirements of the rich gas. At the same time, the pressure of the mixed gas also meets the mixed phase pressure when the rich gas is used. Therefore, the obtained mixed gas can be directly injected into the well as a rich gas for mixed drive. In this way, it can be avoided that when the rich gas is directly pressurized, the rich gas will produce phase changes and pressure fluctuations to cause damage to the valve components of the boosting equipment.

[0032] Specifically, different booster pumps are required for lean gas and liquefied petroleum gas in the above-mentioned boosting process. For example, a booster pump suitable for liquid boosting is used for liquefied petroleum gas, so there will be no problem of damaging valve components due to liquid boosting; and a booster pump suitable for gas is used for lean gas. Pressurizing the lean gas will not cause liquefaction of the lean gas, nor will it cause damage to valve components, thereby solving the problem of excessively high requirements for mine equipment hardware in rich gas mixed phase drive.

[0033] In this embodiment, the key lies in the ratio of lean gas to LPG. If the ratio is not appropriate, two problems will occur: if the ratio of LPG is small, the required mixed phase pressure will increase, resulting in an increase in the operating cost of the injection pump; if the ratio of LPG is too large, the cost of using LPG will increase significantly. Figure 3 The results shown show that the ratio of lean gas to liquefied petroleum gas can reach a range of 27:73 to 100:0, but considering the formation pressure, the ratio of lean gas to liquefied petroleum gas in this example ranges from 75.6:24.4 to 100:0.

[0034] Device Example:

[0035] The device in this embodiment is as follows Figure 2 As shown, it includes a booster pump 1 and a booster pump 2, the booster pump 1 is connected to a piston container 4, the booster pump 2 is connected to a piston container 3, and the piston container 3 and the piston container 4 are preferably piston cylinders. Lean gas is stored in the piston container 3, and liquefied petroleum gas is stored in the piston container 4. A movable piston is provided in each of the piston containers 3 and 4. The two booster pumps inject water (or gas) into the space below the movable piston in the corresponding piston container, and push the movable piston to move upward, so that the lean gas and liquefied petroleum gas are injected into the oil-gas mixing container 5, and the required rich gas is formed after mixing. The composition and pressure of the rich gas can be adjusted as needed. Among them, the liquefied petroleum gas is injected from the top of the oil-gas mixing container 5, and the lean gas is injected from the bottom of the oil-gas mixing container 5, so that the lean gas and the liquefied petroleum gas can be fully mixed; the oil-gas mixing container 5 is provided with a contact net for increasing the contact area between the lean gas and the liquefied petroleum gas, and the type of the oil-gas mixing container 5 can be a tank or a pipeline, and its main function is to simulate the process of lean gas and liquefied petroleum gas being fully mixed in the wellbore.

[0036] Under experimental conditions, the mixed gas is injected into the experimental physical model as rich gas. The experimental physical model includes a core holder 7. The core holder 7 can be a rubber sleeve. The rubber sleeve completely wraps the experimental core. The ring pressure pump 6 is used to simulate the confining pressure of the core in the formation. For example, the rubber sleeve is placed in a cavity filled with water, and the pressure of water on the rubber sleeve is adjusted by the ring pressure pump 6. A heater for simulating the formation temperature of the core can also be provided. The heater can be provided separately, or a core holder 7 with a self-heating function can be selected. Of course, as other embodiments, other forms of core holders, ring pressure pumps and other equipment in the prior art can also be used.

[0037] The rich gas is injected into the core in the experimental physical model, and then the data acquisition device 8 is used to collect the oil production data of the core, including the gas volume, the oil volume, etc., so as to judge whether the mixed rich gas meets the requirements of miscible drive. The core holder, the ring pressure pump and the data acquisition device involved in this embodiment are all prior art, and are often used in laboratories for those skilled in the art, so they are not described in detail here.

[0038] At the same time, the application places of the above-mentioned device embodiments are not limited. It can be used not only in laboratories but also in oil reservoir development sites. When used in different places, each device can be specifically selected according to needs. For example, in the laboratory, the oil and gas mixing container 5 uses a tank body, and in the actual oil reservoir development site, the oil and gas mixing container 5 uses a pipeline and a wellbore.

[0039] The specific implementation methods of the present invention are given above, but the present invention is not limited to the described implementation methods. Under the idea given by the present invention, the technical means in the above-mentioned embodiments are transformed, replaced, and modified in a way that is easy for a person skilled in the art to think of, and the effect is basically the same as the corresponding technical means in the present invention, and the purpose of the invention is basically the same. The technical solution formed in this way is formed by fine-tuning the above-mentioned embodiments, and this technical solution still falls within the protection scope of the present invention.

Claims

1. A high pressure reservoir miscible flooding method, characterized in that: The following steps are involved: Lean gas and liquefied petroleum gas are pressurized separately; the pressurized lean gas and the pressurized liquefied petroleum gas are mixed according to a set ratio to obtain a mixed gas, and the mixed gas is used for miscible flooding of the oil reservoir; before mixing, the lean gas exists in the form of gas, and the liquefied petroleum gas exists in the form of liquid. After mixing according to the set ratio, the mixture has the property of rich gas and can be changed into gas under the action of pressure, so that the mixed gas is discharged in the form of gas, realizing the subsequent gas injection miscible flooding; When the formation pressure is 29.6 MPa, the lean gas and liquefied petroleum gas are pressurized to 29.6 MPa; the setting ratio ranges from 27:73 to 100:

0.

2. A high-pressure reservoir miscible flooding device, characterized in that: It comprises a first booster pump and a second booster pump, wherein the first booster pump is connected to a first piston cylinder for storing lean gas, and the second booster pump is connected to a second piston cylinder for storing liquefied petroleum gas; the first piston cylinder is connected to a first input end of an oil-gas mixing container; the second piston cylinder is connected to a second input end of the oil-gas mixing container; the oil-gas mixing container is provided with an output end; the high-pressure reservoir miscible drive device is used to implement the high-pressure reservoir miscible drive method according to claim 1.

3. The high pressure reservoir miscible flooding device according to claim 2, characterized in that: The output end and the second input end are arranged at the upper end of the oil-gas mixing container, and the first input end is arranged at the lower end.

4. The high pressure reservoir miscible flooding device according to claim 2 or 3, characterized in that: The oil-gas mixing container is a tank or a pipeline.

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