Method for determining maximum productivity in initial production stage of unsaturated reservoir oil well

Abstract

The invention discloses a method for determining the maximum productivity at the initial stage of production of an unsaturated oil reservoir oil well. The method comprises the following steps: collecting a stratum crude oil sample and related data; obtaining saturation pressure; obtaining dissolved gas-oil ratio data under any pressure; obtaining dissolved gas volume coefficient data under any pressure; acquiring gas saturation data under any pressure; acquiring oil phase permeability ratio data under different gas saturation degrees; acquiring oil phase permeability ratio data under different pressures and saturation pressures; acquiring in-situ crude oil viscosity data under any pressure; acquiring crude oil viscosity ratio data under different pressures and saturation pressures; acquiring production pressure difference ratio data corresponding to different pressures serving as flow pressures and saturated pressures serving as the flow pressures; drawing a relation curve of the production pressure difference and the dimensionless capacity multiples; and obtaining the production pressure difference corresponding to the maximum productivity. The method provides a basis for increasing the oil extraction speed of an offshore oil field, shortening the development period and improving the economic benefit.

Description

Technical Field

[0001] The invention belongs to the field of oil well productivity determination methods, and in particular relates to a method for determining the maximum productivity of an oil well in an unsaturated oil reservoir at the initial stage of production. Background Art

[0002] Most of the Bohai oil reservoirs are unsaturated reservoirs. Considering the actual situation of the platform life limit, it is necessary to maximize the oil well productivity to increase the oil recovery rate and shorten the development cycle. Increasing the production pressure difference is the main way to increase the oil well productivity. In the early stage of unsaturated oil reservoir development, that is, before water is seen, the factors affecting the oil well productivity are mainly divided into two stages: ① When the production pressure difference is less than the ground saturation pressure difference, the reservoir is a single-phase flow of crude oil. In this stage, the permeability and viscosity of crude oil do not change much, and the oil well productivity is mainly affected by the single factor of production pressure difference; ② When the production pressure difference is greater than the ground saturation pressure difference, the crude oil in the unsaturated oil reservoir is degassed, the reservoir changes from single-phase flow of crude oil to two-phase flow of oil and gas, the permeability of crude oil decreases, and the viscosity of formation crude oil increases. The oil well productivity is affected by comprehensive factors such as production pressure difference, crude oil permeability, and crude oil viscosity. At present, the research on oil well productivity is mainly concentrated on the first stage, that is, when the production pressure difference is less than the ground-saturation pressure difference, the oil well productivity increases with the increase of the production pressure difference; in the second stage, that is, when the production pressure difference is greater than the ground-saturation pressure difference, there is little research on the law of change of oil well productivity with production pressure difference, and there is currently no solution. Summary of the invention

[0003] The present invention is proposed to solve the problem in the prior art that the working system for obtaining the maximum production capacity of an oil well in the early stage of production of an unsaturated oil reservoir is unclear, and its purpose is to provide a method for determining the maximum production capacity of an oil well in the early stage of production of an unsaturated oil reservoir.

[0004] The present invention is achieved through the following technical solutions:

[0005] A method for determining the maximum production capacity of an oil well in an unsaturated oil reservoir at the initial stage of production, characterized in that it comprises the following steps:

[0006] S1. Collect formation crude oil samples and related static data in the target area's production layer;

[0007] The relevant static data include the original oil saturation of the target area, formation pressure, pressure, production pressure difference and formation crude oil viscosity;

[0008] S2. Conduct a test experiment on the saturated pressure of crude oil in the target area, draw a curve of the relationship between pressure and cumulative pump reading difference, and obtain the saturated pressure of the target area;

[0009] The pressure corresponding to the inflection point of the curve of the relationship between the pressure and the cumulative pump reading difference is the saturation pressure of the target area;

[0010] According to the national standard GB / T26981-2020 "Analysis Method of Physical Properties of Oil and Gas Reservoir Fluids", the target area formation crude oil saturation pressure test experiment is carried out to obtain the cumulative pump reading difference under different pressures, and draw a pressure-cumulative pump reading difference relationship curve; the pressure-cumulative pump reading difference relationship curve takes the cumulative pump reading difference as the X-axis and the pressure as the Y-axis to establish a plane rectangular coordinate system, and the pressure corresponding to the inflection point of the curve is the saturation pressure;

[0011] S3. Conduct a degassing experiment on the formation crude oil in the target area, draw a curve of the relationship between the pressure and the dissolved gas-oil ratio in the target area, and obtain the dissolved gas-oil ratio data of the target area at any pressure by querying the curve of the relationship between the pressure and the dissolved gas-oil ratio; the formation crude oil degassing experiment is based on the national standard GB / T26981-2020 "Analysis Method of Physical Properties of Oil and Gas Reservoir Fluids";

[0012] The pressure and dissolved gas-oil ratio relationship curve uses pressure as the X-axis and the dissolved gas-oil ratio as the Y-axis to establish a plane rectangular coordinate system. The pressure and dissolved gas-oil ratio relationship curve is based on the national standard GB / T26981-2020 "Analysis Method for Physical Properties of Oil and Gas Reservoir Fluids". The crude oil in the target area is depressurized and degassed in stages to obtain the dissolved gas-oil ratio at each level of pressure, and then the pressure and dissolved gas-oil ratio relationship curve is drawn.

[0013] S4. Conduct a target area dissolved gas volume coefficient measurement experiment, draw a curve of the relationship between the target area pressure and the dissolved gas volume coefficient, and obtain the dissolved gas volume coefficient of the target area at any pressure by querying the curve of the relationship between the pressure and the dissolved gas volume coefficient;

[0014] The pressure-dissolved gas volume coefficient relationship curve establishes a plane rectangular coordinate system with pressure as the X-axis and the dissolved gas volume coefficient as the Y-axis; the pressure-dissolved gas volume coefficient relationship curve is based on the national standard GB / T26981-2020 "Analysis Method for Physical Properties of Oil and Gas Reservoir Fluids", and the crude oil in the target area is depressurized and degassed in stages to obtain the dissolved gas volume coefficient at each level of pressure, and then the pressure-dissolved gas volume coefficient relationship curve is drawn.

[0015] S5, drawing a curve of the relationship between the pressure and the gas saturation of the target area, and obtaining the gas saturation of the target area at any pressure by querying the curve of the relationship between the pressure and the gas saturation;

[0016] The specific method for drawing the relationship curve between pressure and gas saturation is:

[0017] S51, obtaining dissolved gas-oil ratio data at different pressures in the target area from the pressure-dissolved gas-oil ratio relationship curve drawn in step S3;

[0018] S52, obtaining dissolved gas volume coefficient data at different pressures in the target area from the pressure and dissolved gas volume coefficient relationship curve drawn in step S4;

[0019] S53, substituting the data obtained in steps S51 and S52 and the original oil saturation data of the target area in the relevant static data collected in step S1 into the gas saturation calculation formula to obtain the gas saturation data under different pressures, and then drawing a pressure-gas saturation relationship curve; the pressure-gas saturation relationship curve takes the gas saturation as the X-axis and the pressure as the Y-axis to establish a plane rectangular coordinate system;

[0020] The gas saturation calculation formula is:

[0021] S g(P) =(R si -R s(P) )×S o ×B g(P) ×100%(1)

[0022] Where: S g(P) is the gas saturation at P pressure, in %; R si is the dissolved gas-oil ratio at saturation pressure, in m 3 / m 3 ; R s(P) is the dissolved gas-oil ratio at pressure P, in m 3 / m 3 ; S o is the original oil saturation, in %; B g(P) is the volume coefficient of dissolved gas at pressure P, in m 3 / m 3 .

[0023] S6. Carry out oil-gas phase permeability experiment in the target area, draw the relationship curve between oil phase permeability ratio, gas phase permeability ratio and gas saturation in the target area, and obtain the oil phase permeability ratio data of the target area at any gas saturation by querying the relationship curve between oil phase permeability ratio, gas phase permeability ratio and gas saturation; the size of the oil phase permeability ratio is the impact of permeability change on oil well productivity;

[0024] According to the petroleum industry standard SYT5345-2007 "Method for Determining Relative Permeability of Two Phases in Rocks", oil and gas permeability experiments were carried out in the target area core, and experimental data of gas saturation, oil phase permeability ratio and gas phase permeability ratio were obtained. Relationship curves of oil phase permeability ratio, gas phase permeability ratio and gas saturation were plotted. The curves take gas saturation as the X-axis and the oil phase permeability ratio and gas phase permeability ratio as the Y-axis to establish a plane rectangular coordinate system.

[0025] S7, drawing a curve of relationship between pressure and oil phase permeability ratio, and obtaining the oil phase permeability ratio of the target area at any pressure by querying the curve of relationship between pressure and oil phase permeability ratio;

[0026] The variation law of the oil phase permeability ratio under different pressures and saturation pressure in the target area is consistent with the oil-gas permeability test results of step S6 (Formula 2); the oil phase permeability ratio under saturation pressure can also be obtained from the pressure and oil phase permeability ratio relationship curve;

[0027] The calculation formula of the oil phase permeability ratio is:

[0028]

[0029] J1 is the oil phase permeability ratio, that is, the impact of permeability changes under different pressures on oil well productivity, in mD / mD; is the oil phase permeability at saturation pressure, in mD; K (P) is the oil phase permeability at pressure P, in mD; It is the ratio of oil phase permeability at different gas saturations measured by phase permeability experiment, and the unit is mD / mD.

[0030] The specific method for drawing the relationship curve between pressure and oil phase permeability ratio is:

[0031] S71, obtaining the pressure of the target area at any gas saturation from the target area pressure and gas saturation relationship curve drawn in step S5;

[0032] S72, obtaining the oil phase permeability ratio data of the target area at any gas saturation from the relationship curves of the oil phase permeability ratio, gas phase permeability ratio and gas saturation of the target area drawn in step S6;

[0033] S73, using the data obtained in steps S71 and S72 to draw a curve showing the relationship between pressure and oil phase permeability ratio;

[0034] The pressure-oil phase permeability ratio relationship curve establishes a plane rectangular coordinate system with pressure as the X-axis and the oil phase permeability ratio as the Y-axis.

[0035] S8. Conduct an experiment to measure the viscosity of the formation crude oil at different pressures in the target area, draw a curve of the relationship between the pressure and the viscosity of the formation crude oil in the target area, and obtain the viscosity data of the formation crude oil at any pressure in the target area by querying the curve of the relationship between the pressure and the viscosity of the formation crude oil;

[0036] The pressure-to-formation crude oil viscosity relationship curve establishes a plane rectangular coordinate system with pressure as the X-axis and formation crude oil viscosity as the Y-axis; the pressure-to-formation crude oil viscosity relationship curve is based on the national standard GB / T26981-2020 "Analysis Method for Physical Properties of Oil and Gas Reservoir Fluids", tests the formation crude oil viscosity data under different pressures in the target area, and then draws the pressure-to-formation crude oil viscosity relationship curve.

[0037] S9, drawing a curve of the relationship between pressure and formation crude oil viscosity ratio, and obtaining the formation crude oil viscosity ratio under different pressures in the target area by querying the curve of the relationship between pressure and formation crude oil viscosity ratio;

[0038] The method for drawing the relationship curve between pressure and formation crude oil viscosity ratio is specifically as follows:

[0039] S91, obtaining the formation crude oil viscosity data under different pressures in the target area from the pressure and formation crude oil viscosity relationship curve drawn in step S8;

[0040] S92, substituting the data obtained in step S91 into the formation crude oil viscosity ratio calculation formula to calculate the formation crude oil viscosity ratio under different pressures;

[0041] The calculation formula of the formation crude oil viscosity ratio is:

[0042]

[0043] Where: J2 is the formation crude oil viscosity ratio, that is, the impact of formation crude oil viscosity changes under different pressures on oil well productivity, the unit is mPa·s / mPa·s; μ (P) is the viscosity of crude oil at pressure P, in mPa·s; is the viscosity of crude oil at saturation pressure, in mPa·s.

[0044] The magnitude of the formation crude oil viscosity ratio is the magnitude of the impact of the change in formation crude oil viscosity on the oil well productivity.

[0045] S93, according to the formation crude oil viscosity ratio under different pressures obtained in step S92, a relationship curve between different pressures and the formation crude oil viscosity ratio is plotted.

[0046] The relationship curve between pressure and formation crude oil viscosity ratio establishes a plane rectangular coordinate system with pressure as the X-axis and formation crude oil viscosity ratio as the Y-axis.

[0047] S10, drawing a pressure-to-production differential pressure ratio relationship curve, and obtaining production differential pressure ratio data corresponding to different pressures in the target area as flow pressures by querying the pressure-to-production differential pressure ratio relationship curve;

[0048] The method for drawing the relationship curve between the pressure and the production pressure difference ratio is specifically as follows:

[0049] S101, the target area formation pressure P collected in step S1 i , the target zone saturation pressure P obtained in step S2 b Substitute the pressure P into the production differential pressure ratio calculation formula to calculate the production differential pressure ratio under different pressures as the flow pressure; the size of the production differential pressure ratio is the impact of the change in production differential pressure on the oil well productivity;

[0050] The production pressure difference ratio calculation formula is:

[0051]

[0052] Where: J3 is the production pressure difference ratio, that is, the impact of production pressure difference changes on oil well productivity under different pressures as flow pressure, the unit is MPa / MPa; P i -P is the production pressure difference corresponding to the P pressure as the flow pressure, in MPa; P i -P b is the production pressure difference corresponding to the saturation pressure as the flow pressure, in MPa; P i is the formation pressure, in MPa; P is any pressure, in MPa; P b is the saturation pressure, in MPa;

[0053] S102, using the different pressures obtained in step S101 as the production pressure difference ratio under the flow pressure, and drawing a relationship curve between pressure and production pressure difference ratio.

[0054] The relationship curve between pressure and production pressure difference ratio is established by taking pressure as the X-axis and production pressure difference ratio as the Y-axis to establish a plane rectangular coordinate system.

[0055] S11. Draw a curve of the relationship between the production pressure difference and the dimensionless capacity multiple in the target area;

[0056] The method for drawing the relationship curve between the production pressure difference and the dimensionless capacity multiple is specifically as follows:

[0057] The oil phase permeability ratio data under different pressures obtained in step S7, the crude oil viscosity ratio data under different pressures obtained in step S9, and the different pressures obtained in step S10 are used as the production pressure difference ratio data corresponding to the flow pressure; they are substituted into the production pressure difference and dimensionless capacity multiple calculation formula to calculate the dimensionless capacity multiple, and then the production pressure difference and dimensionless capacity multiple relationship curve of the target area are plotted;

[0058] The production pressure difference and dimensionless capacity multiple calculation formula are:

[0059]

[0060] Where: J is the dimensionless capacity multiple, unit is m 3 / m 3 ;q (P) is the oil production capacity of the oil well with P pressure as the flowing pressure, in m 3 ; For oil wells, P b Saturation pressure is the oil production capacity as the flowing pressure, in m 3 ; is the oil phase permeability at saturation pressure, in mD; K (P) is the oil phase permeability under P pressure, in mD; μ (P) is the viscosity of crude oil at pressure P, in mPa·s; is the viscosity of crude oil at saturation pressure, in mPa·s; P i is the formation pressure, in MPa; P is any pressure, in MPa; P b is the saturation pressure, in MPa; J1 is the oil phase permeability ratio, i.e. the effect of permeability change on oil well productivity under different pressures, in mD / mD; J2 is the formation crude oil viscosity ratio, i.e. the effect of formation crude oil viscosity change on oil well productivity under different pressures, in mPa·s / mPa·s; J3 is the production pressure difference ratio, i.e. the effect of production pressure difference change on oil well productivity under different pressures as flow pressure, in MPa / MPa;

[0061] The production pressure difference and dimensionless capacity multiple relationship curve takes the production pressure difference as the X-axis and the dimensionless capacity multiple (the ratio of the capacity under any production pressure difference to the capacity under the saturated pressure production pressure difference) as the Y-axis to establish a plane rectangular coordinate system.

[0062] S12. According to the production pressure difference and dimensionless capacity multiple relationship curve drawn in step S11, query the production pressure difference and dimensionless capacity multiple relationship curve to determine the production pressure difference corresponding to the maximum capacity in the initial stage of production of the target area.

[0063] The beneficial effects of the present invention are:

[0064] The present invention provides a method for determining the maximum production capacity of an oil well in an unsaturated oil reservoir at the initial stage of production. The method can quickly obtain the variation law of the oil well production capacity with the production pressure difference when the production pressure difference is greater than the saturated pressure difference in the initial stage of development of the unsaturated oil reservoir. The method provides a basis for determining the production pressure difference (working system) required for the oil well to obtain the maximum production capacity, so as to maximize the reservoir capacity and improve the oil production rate in the initial stage of development of the unsaturated oil reservoir. The method is helpful for designing a plan to improve the oil production rate during the development of the oil field, which is scientific and reasonable and has ideal effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 is a flow chart of the method of the present invention;

[0066] Figure 2 is a schematic diagram of a curve showing the relationship between the target area pressure and the accumulated pump reading difference in Example 1 of the present invention;

[0067] Figure 3 is a schematic diagram of a curve showing the relationship between the target zone pressure and the dissolved gas-oil ratio in Example 1 of the present invention;

[0068] Figure 4is a schematic diagram of a curve showing the relationship between the target area pressure and the dissolved gas volume coefficient in Example 1 of the present invention;

[0069] Figure 5 is a schematic diagram of a curve showing the relationship between the target zone pressure and the gas saturation in Example 1 of the present invention;

[0070] Figure 6 Schematic diagram of the relationship curve between the oil phase permeability ratio, the gas phase permeability ratio and the gas saturation in the target area in Example 1 of the present invention;

[0071] Figure 7 is a schematic diagram of a curve showing a relationship between the target zone pressure and the oil phase permeability ratio in Example 1 of the present invention;

[0072] Figure 8 is a schematic diagram of a curve showing the relationship between the target zone pressure and the formation crude oil viscosity in Example 1 of the present invention;

[0073] Fig. 9 is a schematic diagram of a curve showing a relationship between the target zone pressure and the formation crude oil viscosity ratio in Example 1 of the present invention;

[0074] Fig.10 1 is a schematic diagram of a curve showing a relationship between the target zone pressure and the production pressure difference ratio in Example 1 of the present invention;

[0075] Fig.11 1 is a schematic diagram of a curve showing a relationship between a target area production pressure difference and a dimensionless production capacity multiple in Example 1 of the present invention;

[0076] Fig.12 1 is a schematic diagram of a curve showing the relationship between the JX1-1 oil field pressure and the accumulated pump reading difference in Example 2 of the present invention;

[0077] Fig.13 Schematic diagram of the relationship curve between the JX1-1 oil field pressure and the dissolved gas-oil ratio in Example 2 of the present invention;

[0078] Fig.14 1 is a schematic diagram of a curve showing the relationship between the JX1-1 oil field pressure and the dissolved gas volume coefficient in Example 2 of the present invention;

[0079] Fig.15 is a schematic diagram of a curve showing the relationship between pressure and gas saturation of the JX1-1 oil field in Example 2 of the present invention;

[0080] Fig.16 Schematic diagram of the relationship curve between the oil phase permeability ratio, gas phase permeability ratio and gas saturation of the JX1-1 oil field in Example 2 of the present invention;

[0081] Fig.17 1 is a schematic diagram of a curve showing a relationship between the pressure and the oil phase permeability ratio of the JX1-1 oil field in Example 2 of the present invention;

[0082] Fig.18 Schematic diagram of the relationship curve between the JX1-1 oil field pressure and the formation crude oil viscosity in Example 2 of the present invention;

[0083] Fig.19 It is a schematic diagram of the relationship curve between the JX1-1 oil field pressure and the formation crude oil viscosity ratio in Example 2 of the present invention;

[0084] Fig. 20 1 is a schematic diagram of a curve showing the relationship between the pressure and the production pressure difference ratio of the JX1-1 oil field in Example 2 of the present invention;

[0085] Fig.21 It is a schematic diagram of the relationship curve between the production pressure difference and the dimensionless production capacity multiple of the JX1-1 oil field in Example 2 of the present invention.

[0086] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0087] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0088] Example 1

[0089] like Figure 1 As shown, a method for determining the maximum production capacity of an oil well in an unsaturated oil reservoir at the initial stage of production comprises the following steps:

[0090] S1. Collect formation crude oil samples and formation pressure, oil saturation and other data in the target area; collect formation crude oil samples and formation pressure, oil saturation and other data in the production layer section of the target block (Table 1).

[0091] Table 1 Data collection table for determining dimensionless capacity multiples

[0092]

[0093] S2. Conduct a test experiment on the saturated pressure of crude oil in the target area to obtain the saturated pressure of the target area. According to the national standard GB / T26981-2020 "Analysis Method of Physical Properties of Oil and Gas Reservoir Fluids", conduct a test experiment on the saturated pressure of crude oil in the target area, obtain the cumulative pump reading difference under different pressures, and draw a curve of the relationship between pressure and cumulative pump reading difference. The characteristic of this curve is that in the rectangular coordinate system, the cumulative pump reading difference is used as the X-axis and the pressure is used as the Y-axis to establish a plane rectangular coordinate system. The pressure corresponding to the inflection point of the curve is the saturated pressure. The saturated pressure of crude oil in the target area is 10.5MPa ( Figure 2 , Table 1, column 4).

[0094] S3. Conduct degassing experiments on formation crude oil in the target area and draw curves of the relationship between pressure and dissolved gas-oil ratio. The characteristic of this curve is that in a rectangular coordinate system, a plane rectangular coordinate system is established with pressure as the X-axis and dissolved gas-oil ratio as the Y-axis. This curve is based on the national standard GB / T26981-2020 "Analysis Method of Physical Properties of Oil and Gas Reservoir Fluids". The formation crude oil in the target area is depressurized and degassed in stages to obtain the dissolved gas-oil ratio at each pressure level, and then the pressure and dissolved gas-oil ratio curve is drawn ( Figure 3 ). The dissolved gas-oil ratio data of the target area at any pressure can be obtained by querying the curve.

[0095] S4. Conduct a dissolved gas volume coefficient determination experiment in the target area and draw a curve of the relationship between pressure and dissolved gas volume coefficient. The characteristic of this curve is that in the rectangular coordinate system, a plane rectangular coordinate system is established with pressure as the X-axis and the dissolved gas volume coefficient as the Y-axis. This curve is based on the national standard GB / T26981-2020 "Analysis Method of Physical Properties of Oil and Gas Reservoir Fluids". The crude oil in the target area is depressurized and degassed in stages to obtain the dissolved gas volume coefficient at each pressure level, and then the pressure and dissolved gas volume coefficient relationship curve is drawn ( Figure 4 ). The dissolved gas volume coefficient data of the target area at any pressure can be obtained by querying the curve.

[0096] S5. Obtain the relationship curve between the pressure and gas saturation of the target area. The characteristic of this curve is that, in the rectangular coordinate system, the gas saturation is taken as the X-axis and the pressure is taken as the Y-axis to establish a plane rectangular coordinate system. According to S3 and S4, the dissolved gas-oil ratio data and dissolved gas volume coefficient data under different pressures of the target area are obtained. Examples are shown in columns 8 and 9 of Table 1, and examples of the original oil saturation data of the target area collected in step S1 are shown in column 2 of Table 1. Substitute them into formula (1) to calculate the gas saturation data under different pressures. Examples are shown in column 10 of Table 1, and then draw the relationship curve between pressure and gas saturation ( Figure 5 ). The gas saturation data of the target area at any pressure can be obtained by querying the curve.

[0097] S g(P) =(R si -R s(P) )×S o ×B g(P) ×100%(1)

[0098] S g(P) is the gas saturation at P pressure, %; R si is the dissolved gas-oil ratio at saturation pressure, m 3 / m 3 ; R s(P) is the dissolved gas-oil ratio m at pressure P 3 / m 3 ; S o is the original oil saturation, %; Bg(P) is the volume coefficient of dissolved gas at pressure P, in m 3 / m 3 .

[0099] S6. Carry out oil-gas phase permeability experiment in the target area to obtain oil phase permeability ratio data under different gas saturations. According to the petroleum industry standard SYT5345-2007 "Method for Determining Relative Permeability of Two Phases in Rocks", carry out core phase permeability experiment in the target area to obtain experimental data of gas saturation, oil phase permeability ratio, and gas phase permeability ratio, and draw the relationship curve between oil phase permeability ratio, gas phase permeability ratio and gas saturation. The characteristic of this curve is that in the rectangular coordinate system, the gas saturation is taken as the X-axis and the oil phase permeability ratio is taken as the X-axis. Gas permeability ratio As the Y axis, establish a plane rectangular coordinate system ( Figure 6 ). By querying the curve, the oil phase permeability ratio data and gas phase permeability ratio data of the target area at any gas saturation are obtained.

[0100] S7, obtain the oil phase permeability ratio data under different pressures and saturation pressures in the target area. The variation law of the oil phase permeability ratio under different pressures and saturation pressures in the target area conforms to the oil-gas permeability experimental results of step S6 (Formula 2). According to the pressure and oil phase permeability ratio data under different gas saturations queried in steps S5 and S6 (the size is the impact of the permeability change on the oil well production capacity), examples are shown in columns 10, 5, and 11 of Table 1, and a curve of the relationship between pressure and oil phase permeability ratio is drawn. The characteristic of this curve is that in a rectangular coordinate system, pressure is used as the X-axis and the oil phase permeability ratio is used as the Y-axis to establish a plane rectangular coordinate system ( Figure 7 ). The oil phase permeability ratio data of the target area at any pressure is obtained by querying the curve.

[0101]

[0102] J1 is the oil phase permeability ratio, that is, the impact of permeability changes under different pressures on oil well productivity, mD / mD; K (P) is the oil phase permeability at pressure P, mD; is the oil phase permeability at saturation pressure, mD; It is the ratio of oil phase permeability at different gas saturations measured by phase permeability experiment, mD / mD.

[0103] S8. Conduct experiments to measure the viscosity of formation crude oil at different pressures in the target area and draw a curve of the relationship between pressure and formation crude oil viscosity. The characteristic of this curve is that in a rectangular coordinate system, a plane rectangular coordinate system is established with pressure as the X-axis and formation crude oil viscosity as the Y-axis. This curve is based on the national standard GB / T26981-2020 "Analysis Method of Physical Properties of Oil and Gas Reservoir Fluids", and tests the formation crude oil viscosity data at different pressures in the target area, and then draws a curve of the relationship between pressure and formation crude oil viscosity ( Figure 8 ). The formation crude oil viscosity data of the target area at any pressure can be obtained by querying the curve.

[0104] S9, obtain the crude oil viscosity ratio data under different pressures and saturation pressure in the target area. According to step S8, query and obtain the formation crude oil viscosity data under different pressures in the target area. For example, see columns 5 and 7 of Table 1. Substitute it into formula (3) to calculate the formation crude oil viscosity ratio under different pressures and saturation pressure. The value is the influence of the change of formation crude oil viscosity on the oil well production capacity. For example, see column 12 of Table 1. Then draw the relationship curve between pressure and formation crude oil viscosity ratio ( Fig. 9 ). The characteristic of this curve is that in a rectangular coordinate system, a plane rectangular coordinate system is established with pressure as the X-axis and formation crude oil viscosity ratio as the Y-axis. By querying the curve, the formation crude oil viscosity ratio data of the target area under any pressure can be obtained.

[0105]

[0106] J2 is the formation crude oil viscosity ratio, that is, the impact of formation crude oil viscosity changes under different pressures on oil well productivity, mPa·s / mPa·s; μ (P) is the viscosity of crude oil at pressure P, mPa·s; is the viscosity of crude oil at saturation pressure in mPa·s.

[0107] S10, obtain the production pressure difference ratio data corresponding to different pressures in the target area as the flow pressure and the saturation pressure as the flow pressure. i , saturation pressure P b , pressure P, see examples in columns 3, 4, and 5 of Table 1, substitute into formula (4) to calculate the arbitrary pressure P as the flow pressure and saturation pressure P b As the ratio of the production pressure difference of the flow pressure, the size is the impact of the change of the production pressure difference on the oil well productivity. For example, see the 13th column of Table 1, and then draw the relationship curve between pressure and production pressure difference ratio ( Fig.10 ). The production pressure difference ratio data of the target area under different pressures and saturation pressures are obtained by querying the curve. The characteristic of this curve is that in a rectangular coordinate system, the pressure is taken as the X-axis and the production pressure difference ratio is taken as the Y-axis to establish a plane rectangular coordinate system.

[0108]

[0109] J3 is the production pressure difference ratio, that is, the effect of production pressure difference change on oil well productivity under different pressures as flow pressure, MPa / MPa; P i -P is the production pressure difference corresponding to the P pressure as the flow pressure, MPa; P i -P b is the production pressure difference corresponding to the saturation pressure as the flow pressure, MPa; P i is the formation pressure, MPa; P is any pressure, MPa; P b is the saturation pressure, MPa.

[0110] S11. Draw a curve of the relationship between the production pressure difference and the dimensionless capacity multiple in the target area. The characteristic of this curve is that in a rectangular coordinate system, the production pressure difference is taken as the X-axis, and the dimensionless capacity multiple (the ratio of the capacity under any production pressure difference to the capacity under the saturated pressure production pressure difference) is taken as the Y-axis, and a plane rectangular coordinate system is established ( Fig.11 ). According to the permeability ratio, formation crude oil viscosity ratio, and production pressure difference ratio obtained in step S7, step S9, and step S10, the production pressure difference and dimensionless capacity multiple data are calculated and obtained. Examples are shown in columns 6 and 14 of Table 1. Then, a curve of the relationship between the production pressure difference and the dimensionless capacity multiple of the target area is drawn.

[0111]

[0112] J is the dimensionless capacity multiple, m 3 / m 3 ;q (P) is the oil production capacity of the oil well with P pressure as the flowing pressure, m 3 ; For oil wells, P b Saturation pressure as oil production capacity of flowing pressure, m 3 .

[0113] S12. Query the chart to determine the production pressure difference corresponding to the maximum production capacity of the target area at the initial stage of production. Based on the plotted production pressure difference and dimensionless production capacity multiple relationship curve chart, query the production pressure difference (working system) corresponding to the maximum production capacity of the target area at the initial stage of production. The maximum production capacity can be obtained when the production pressure difference of the target area is 4.3MPa at the initial stage of production, which is 1.085 times the production capacity when the saturation pressure is used as the production pressure difference; the vertical lines in the figure are the production capacity increase multiples corresponding to different production pressure differences. The longer the vertical lines, the greater the production capacity ( Fig.11 ).

[0114] Example 2

[0115] Take the Bohai JX1-1 oilfield as an example. Figures 12 to 21 As shown, a method for determining the maximum production capacity of an unsaturated oil reservoir oil well at the initial stage of production mainly includes the following steps:

[0116] S1. Collect crude oil samples and formation pressure, oil saturation and other data in the target area.

[0117] Crude oil samples, formation pressure, oil saturation and other data were collected from the production layer of JX1-1 oilfield (Table 2).

[0118] Table 2: Data collection table for determining dimensionless production capacity multiples of JX1-1 oilfield

[0119]

[0120] S2. Conduct a target area formation crude oil saturation pressure test experiment to obtain the target area saturation pressure.

[0121] According to the national standard GB / T26981-2020 "Analysis Method of Physical Properties of Oil and Gas Reservoir Fluids", the JX1-1 oilfield formation crude oil saturation pressure test experiment was carried out to obtain the cumulative pump reading difference under different pressures, and draw a curve of the relationship between pressure and cumulative pump reading difference. The characteristic of this curve is that in the rectangular coordinate system, the cumulative pump reading difference is used as the X-axis and the pressure is used as the Y-axis to establish a plane rectangular coordinate system. The pressure corresponding to the inflection point of the curve is the saturation pressure. The saturation pressure of the crude oil in the JX1-1 oilfield formation is 13.2MPa ( Fig.12 , Table 2, column 4).

[0122] S3. Carry out degassing experiment on crude oil in the target area and draw the relationship curve between pressure and dissolved gas-oil ratio.

[0123] The characteristic of this curve is that in the rectangular coordinate system, the pressure is used as the X-axis and the dissolved gas-oil ratio is used as the Y-axis to establish a plane rectangular coordinate system. This curve is based on the national standard GB / T26981-2020 "Analysis Method of Physical Properties of Oil and Gas Reservoir Fluids". The JX1-1 oilfield formation crude oil is depressurized and degassed in stages to obtain the dissolved gas-oil ratio at each pressure level, and then the relationship curve between pressure and dissolved gas-oil ratio is drawn ( Fig.13 ). By querying the curve, the dissolved gas-oil ratio data of JX1-1 oil field at any pressure can be obtained.

[0124] S4. Carry out experiments to determine the dissolved gas volume coefficient in the target area and draw a curve showing the relationship between pressure and dissolved gas volume coefficient.

[0125] The characteristic of this curve is that in the rectangular coordinate system, the pressure is used as the X-axis and the dissolved gas volume coefficient is used as the Y-axis to establish a plane rectangular coordinate system. This curve is based on the national standard GB / T26981-2020 "Analysis Method of Physical Properties of Oil and Gas Reservoir Fluids". The JX1-1 oilfield formation crude oil is depressurized and degassed in stages to obtain the dissolved gas volume coefficient at each pressure level, and then the relationship curve between pressure and dissolved gas volume coefficient is drawn ( Fig.14). By querying the curve, the dissolved gas volume coefficient data of JX1-1 oil field at any pressure is obtained.

[0126] S5. Obtain the relationship curve between the pressure and gas saturation of the target area. The characteristic of this curve is that, in the rectangular coordinate system, the gas saturation is taken as the X-axis and the pressure is taken as the Y-axis to establish a plane rectangular coordinate system. According to step 3 and step 4, the dissolved gas-oil ratio data and dissolved gas volume coefficient data under different pressures of the JX1-1 oil field are obtained. Examples are shown in columns 8 and 9 of Table 2, and the original oil saturation data of the JX1-1 oil field collected in step 1 are shown in column 2 of Table 2. Substitute them into formula (1) to calculate the gas saturation data under different pressures. Examples are shown in column 10 of Table 2, and then draw the relationship curve between pressure and gas saturation ( Fig.15 ). By querying the curve, the gas saturation data of JX1-1 oil field at any pressure can be obtained.

[0127] S g(P) =(R si -R s(P) )×S o ×B g(P) ×100%(1)

[0128] S g(P) is the gas saturation at P pressure, %; R si is the dissolved gas-oil ratio at saturation pressure, m 3 / m 3 ; R s(P) is the dissolved gas-oil ratio m at pressure P 3 / m 3 ; S o is the original oil saturation, %; B g(P) is the volume coefficient of dissolved gas at pressure P, in m 3 / m 3 .

[0129] S6. Carry out oil-gas phase permeability experiment in the target area to obtain oil phase permeability ratio data under different gas saturations. According to the petroleum industry standard SYT5345-2007 "Method for Determining Relative Permeability of Two Phases in Rocks", carry out core phase permeability experiment of JX1-1 oil field, obtain experimental data of gas saturation, oil phase permeability ratio, and gas phase permeability ratio, and draw the relationship curve between oil phase permeability ratio, gas phase permeability ratio and gas saturation. The characteristic of this curve is that in the rectangular coordinate system, the gas saturation is taken as the X-axis and the oil phase permeability ratio is taken as the X-axis. Gas permeability ratio As the Y axis, establish a plane rectangular coordinate system ( Fig.16 ). By querying the curve, the oil phase permeability ratio data and gas phase permeability ratio data of JX1-1 oil field at any gas saturation are obtained.

[0130] S7, obtain the oil phase permeability ratio data under different pressures and saturation pressures in the target area. The variation law of the oil phase permeability ratio under different pressures and saturation pressures in the JX1-1 oil field is consistent with the oil-gas permeability experimental results (2) of step S6. According to the pressure and oil phase permeability ratio data under different gas saturations queried in steps S5 and S6 (the size is the impact of the permeability change on the oil well production capacity), the pressure and oil phase permeability ratio relationship curve is drawn as an example in the 10th, 5th and 11th columns of Table 2. The characteristic of this curve is that in the rectangular coordinate system, the pressure is taken as the X-axis and the oil phase permeability ratio is taken as the Y-axis to establish a plane rectangular coordinate system ( Fig.17 ). By querying the curve, the oil phase permeability ratio data of JX1-1 oil field at any pressure is obtained.

[0131]

[0132] J1 is the oil phase permeability ratio, that is, the impact of permeability changes under different pressures on oil well productivity, mD / mD; K (P) is the oil phase permeability at pressure P, mD; is the oil phase permeability at saturation pressure, mD; It is the ratio of oil phase permeability at different gas saturations measured by phase permeability experiment, mD / mD.

[0133] S8. Conduct experiments to measure the viscosity of formation crude oil at different pressures in the target area and draw a curve of the relationship between pressure and formation crude oil viscosity. The characteristic of this curve is that in a rectangular coordinate system, a plane rectangular coordinate system is established with pressure as the X-axis and formation crude oil viscosity as the Y-axis. This curve is based on the national standard GB / T26981-2020 "Analysis Method of Physical Properties of Oil and Gas Reservoir Fluids", and tests the formation crude oil viscosity data at different pressures in the JX1-1 oilfield, and then draws a curve of the relationship between pressure and formation crude oil viscosity ( Fig.18 ). By querying the curve, the formation crude oil viscosity data of JX1-1 oil field at any pressure is obtained.

[0134] S9, obtain the crude oil viscosity ratio data under different pressures and saturation pressures in the target area. According to step S8, the formation crude oil viscosity data under different pressures in the JX1-1 oil field are queried, and examples are shown in columns 5 and 7 of Table 2. Substitute it into formula (3) to calculate the formation crude oil viscosity ratio under different pressures and saturation pressure. The value is the influence of the change in formation crude oil viscosity on the oil well production capacity. An example is shown in column 12 of Table 2. Then, a relationship curve between pressure and formation crude oil viscosity ratio is drawn ( Fig.19 ). The characteristic of this curve is that in the rectangular coordinate system, the pressure is used as the X-axis and the formation crude oil viscosity ratio is used as the Y-axis to establish a plane rectangular coordinate system. By querying the curve, the formation crude oil viscosity ratio data of the JX1-1 oil field at any pressure can be obtained.

[0135]

[0136] J2 is the formation crude oil viscosity ratio, that is, the impact of formation crude oil viscosity changes under different pressures on oil well productivity, mPa·s / mPa·s; μ (P) is the viscosity of crude oil at pressure P, mPa·s; is the viscosity of crude oil at saturation pressure in mPa·s.

[0137] S10, obtain the production pressure difference ratio data corresponding to different pressures in the target area as the flow pressure and the saturation pressure as the flow pressure. i , saturation pressure P b , pressure P, see examples in columns 3, 4, and 5 of Table 2, substitute into formula (4) to calculate the arbitrary pressure P as the flow pressure and saturation pressure P b As the ratio of the production pressure difference of the flow pressure, the size is the impact of the change of the production pressure difference on the oil well productivity. For example, see the 13th column of Table 2, and then draw the relationship curve between the pressure and the production pressure difference ratio ( Fig. 20 ). By querying the curve, the production pressure difference ratio data of JX1-1 oil field at different pressures and saturation pressures are obtained. The characteristic of this curve is that in the rectangular coordinate system, the pressure is taken as the X-axis and the production pressure difference ratio is taken as the Y-axis to establish a plane rectangular coordinate system.

[0138]

[0139] J3 is the production pressure difference ratio, that is, the effect of production pressure difference change on oil well productivity under different pressures as flow pressure, MPa / MPa; P i -P is the production pressure difference corresponding to the P pressure as the flow pressure, MPa; P i -P b is the production pressure difference corresponding to the saturation pressure as the flow pressure, MPa; P i is the formation pressure, MPa; P is any pressure, MPa; P b is the saturation pressure, MPa.

[0140] S11. Draw a curve of the relationship between the production pressure difference and the dimensionless capacity multiple in the target area. The characteristic of this curve is that in a rectangular coordinate system, the production pressure difference is taken as the X-axis, and the dimensionless capacity multiple (the ratio of the capacity under any production pressure difference to the capacity under the saturated pressure production pressure difference) is taken as the Y-axis, and a plane rectangular coordinate system is established ( Fig.21 ). Based on the permeability ratio, formation crude oil viscosity ratio, and production pressure difference ratio obtained in steps S7, S9, and S10, the production pressure difference and dimensionless capacity multiple data are calculated and obtained. Examples are shown in columns 6 and 14 of Table 2. Then, a curve of the relationship between the production pressure difference and the dimensionless capacity multiple of the JX1-1 oil field is drawn.

[0141]

[0142] J is the dimensionless capacity multiple, m 3 / m 3 ;q (P) is the oil production capacity of the oil well with P pressure as the flowing pressure, m 3 ; For oil wells, P b Saturation pressure as oil production capacity of flowing pressure, m 3 .

[0143] S12. Check the chart to determine the production pressure difference corresponding to the maximum production capacity of the target area at the initial stage of production. Based on the plotted production pressure difference and dimensionless production capacity multiple relationship curve chart, check the production pressure difference (working system) corresponding to the maximum production capacity of the JX1-1 oil field at the initial stage of production. The maximum production capacity can be obtained with a production pressure difference of 6.5MPa at the initial stage of production of the JX1-1 oil field, which is 1.488 times the production capacity of the saturation pressure as the production pressure difference; the vertical lines in the figure are the production capacity increase multiples corresponding to different production pressure differences. The longer the vertical lines, the greater the production capacity ( Fig.21 ).

[0144] The present invention proposes that in a rectangular coordinate system, by establishing a dimensionless capacity multiple and a production pressure difference curve chart, the production pressure difference (working system) corresponding to the maximum capacity obtained in the early stage of unsaturated oil reservoir development can be quickly obtained, which provides a basis for increasing the oil production rate of offshore oil fields, shortening the development cycle, and improving economic benefits, and successfully solves the problem of unclear working system for obtaining the maximum capacity of oil wells in the early stage of unsaturated oil reservoir production.

[0145] The proposed method has been applied to multiple unsaturated oil reservoirs in Bohai Bay, and can provide guidance and reference for determining the maximum production capacity of unsaturated oil reservoirs in the early stage of development in Bohai Bay.

[0146] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for determining the maximum production capacity of an oil well in an unsaturated oil reservoir at the initial stage of production, characterized in that: The following steps are involved: S1. Collect formation crude oil samples and related static data in the target area's production layer; S2. Conduct a test experiment on the saturated pressure of crude oil in the target area, draw a curve of the relationship between pressure and cumulative pump reading difference, and obtain the saturated pressure of the target area; The pressure corresponding to the inflection point of the curve of the relationship between the pressure and the cumulative pump reading difference is the saturation pressure of the target area; S3. Conduct a degassing experiment on the formation crude oil in the target area, draw a curve of the relationship between the pressure and the dissolved gas-oil ratio in the target area, and obtain the dissolved gas-oil ratio data of the target area at any pressure by querying the curve of the relationship between the pressure and the dissolved gas-oil ratio; S4. Conduct a target area dissolved gas volume coefficient measurement experiment, draw a curve of the relationship between the target area pressure and the dissolved gas volume coefficient, and obtain the dissolved gas volume coefficient of the target area at any pressure by querying the curve of the relationship between the pressure and the dissolved gas volume coefficient; S5, drawing a curve of the relationship between the pressure and the gas saturation of the target area, and obtaining the gas saturation of the target area at any pressure by querying the curve of the relationship between the pressure and the gas saturation; S6. Carry out oil-gas phase permeability experiment in the target area, draw the relationship curve between oil phase permeability ratio, gas phase permeability ratio and gas saturation in the target area, and obtain the oil phase permeability ratio data of the target area at any gas saturation by querying the relationship curve between oil phase permeability ratio, gas phase permeability ratio and gas saturation; S7, drawing a curve of relationship between pressure and oil phase permeability ratio, and obtaining the oil phase permeability ratio of the target area at any pressure by querying the curve of relationship between pressure and oil phase permeability ratio; S8. Conduct an experiment to measure the viscosity of the formation crude oil at different pressures in the target area, draw a curve of the relationship between the pressure and the viscosity of the formation crude oil in the target area, and obtain the viscosity data of the formation crude oil at any pressure in the target area by querying the curve of the relationship between the pressure and the viscosity of the formation crude oil; S9, drawing a curve of the relationship between pressure and formation crude oil viscosity ratio, and obtaining the formation crude oil viscosity ratio under different pressures in the target area by querying the curve of the relationship between pressure and formation crude oil viscosity ratio; S10, drawing a pressure-to-production differential pressure ratio relationship curve, and obtaining production differential pressure ratio data corresponding to different pressures in the target area as flow pressures by querying the pressure-to-production differential pressure ratio relationship curve; S11. Draw a curve of the relationship between the production pressure difference and the dimensionless capacity multiple in the target area; S12. According to the production pressure difference and dimensionless capacity multiple relationship curve drawn in step S11, query the production pressure difference and dimensionless capacity multiple relationship curve to determine the production pressure difference corresponding to the maximum capacity in the initial stage of production of the target area.

2. The method for determining the maximum production capacity of an oil well in an unsaturated oil reservoir at the initial stage of production according to claim 1, characterized in that: The specific method for drawing the relationship curve between pressure and gas saturation is: S51, obtaining dissolved gas-oil ratio data at different pressures in the target area from the pressure-dissolved gas-oil ratio relationship curve drawn in step S3; S52, obtaining dissolved gas volume coefficient data at different pressures in the target area from the pressure and dissolved gas volume coefficient relationship curve drawn in step S4; S53, substituting the data obtained in steps S51 and S52 and the original oil saturation data of the target area in the relevant static data collected in step S1 into the gas saturation calculation formula to obtain gas saturation data under different pressures, and then drawing a pressure-gas saturation relationship curve; the gas saturation calculation formula is: S g(P) =(R si -R s(P) )×S o ×B g(P) ×100% (1) Where: S g(P) is the gas saturation at P pressure, in %; R si is the dissolved gas-oil ratio at saturation pressure, in m 3 / m 3 ; R s(P) is the dissolved gas-oil ratio at pressure P, in m 3 / m 3 ; S o is the original oil saturation, in %; B g(P) is the volume coefficient of dissolved gas at pressure P, in m 3 / m 3 .

3. The method for determining the maximum production capacity of an oil well in an unsaturated oil reservoir at the initial stage of production according to claim 1, characterized in that: The calculation formula of the oil phase permeability ratio is: J1 is the oil phase permeability ratio, that is, the impact of permeability changes under different pressures on oil well productivity, in mD / mD; is the oil phase permeability at saturation pressure, in mD; K (P) is the oil phase permeability at pressure P, in mD; It is the ratio of oil phase permeability at different gas saturations measured by phase permeability experiment, and the unit is mD / mD.

4. The method for determining the maximum production capacity of an oil well in an unsaturated oil reservoir at the initial stage of production according to claim 1, characterized in that: The specific method for drawing the relationship curve between pressure and oil phase permeability ratio is: S71, obtaining the pressure of the target area at any gas saturation from the target area pressure and gas saturation relationship curve drawn in step S5; S72, obtaining the oil phase permeability ratio data of the target area at any gas saturation from the relationship curves of the oil phase permeability ratio, gas phase permeability ratio and gas saturation of the target area drawn in step S6; S73. Using the data obtained in steps S71 and S72, a pressure-oil phase permeability ratio relationship curve is plotted.

5. The method for determining the maximum production capacity of an oil well in an unsaturated oil reservoir at the initial stage of production according to claim 1, characterized in that: The method for drawing the relationship curve between pressure and formation crude oil viscosity ratio is specifically as follows: S91, obtaining the formation crude oil viscosity data under different pressures in the target area from the pressure and formation crude oil viscosity relationship curve drawn in step S8; S92, substituting the data obtained in step S91 into the formation crude oil viscosity ratio calculation formula to calculate the formation crude oil viscosity ratio under different pressures; S93, according to the formation crude oil viscosity ratio under different pressures obtained in step S92, a relationship curve between different pressures and the formation crude oil viscosity ratio is plotted.

6. The method for determining the maximum production capacity of an oil well in an unsaturated oil reservoir at the initial stage of production according to claim 5, characterized in that: The calculation formula of the formation crude oil viscosity ratio is: Where: J2 is the formation crude oil viscosity ratio, that is, the impact of formation crude oil viscosity changes under different pressures on oil well productivity, the unit is mPa·s / mPa·s; μ (P) is the viscosity of crude oil at pressure P, in mPa·s; is the viscosity of crude oil at saturation pressure, in mPa·s.

7. The method for determining the maximum production capacity of an oil well in an unsaturated oil reservoir at the initial stage of production according to claim 1, characterized in that: The method for drawing the relationship curve between the pressure and the production pressure difference ratio is specifically as follows: S101, the target area formation pressure P collected in step S1 i , the target zone saturation pressure P obtained in step S2 b Substitute the pressure P into the production pressure difference ratio calculation formula to calculate the production pressure difference ratio under different pressures as the flow pressure; S102, using the different pressures obtained in step S101 as the production pressure difference ratio under the flow pressure, and drawing a relationship curve between pressure and production pressure difference ratio.

8. The method for determining the maximum production capacity of an oil well in an unsaturated oil reservoir at the initial stage of production according to claim 7, characterized in that: The production pressure difference ratio calculation formula is: Where: J3 is the production pressure difference ratio, that is, the impact of production pressure difference changes on oil well productivity under different pressures as flow pressure, the unit is MPa / MPa; P i -P is the production pressure difference corresponding to the P pressure as the flow pressure, in MPa; P i -P b is the production pressure difference corresponding to the saturation pressure as the flow pressure, in MPa; P i is the formation pressure, in MPa; P is any pressure, in MPa; P b is the saturation pressure, in MPa.

9. The method for determining the maximum production capacity of an oil well in an unsaturated oil reservoir at the initial stage of production according to claim 1, characterized in that: The method for drawing the relationship curve between the production pressure difference and the dimensionless capacity multiple is specifically as follows: using the oil phase permeability ratio data under different pressures obtained in step S7, the crude oil viscosity ratio data under different pressures obtained in step S9, and the different pressures obtained in step S10 as the production pressure difference ratio data corresponding to the flow pressure; substituting them into the production pressure difference and the dimensionless capacity multiple calculation formula, calculating the dimensionless capacity multiple, and then drawing the relationship curve between the production pressure difference and the dimensionless capacity multiple of the target area.

10. The method for determining the maximum production capacity of an oil well in an unsaturated oil reservoir at the initial stage of production according to claim 9, characterized in that: The production pressure difference and dimensionless capacity multiple calculation formula are: Where: J is the dimensionless capacity multiple, unit is m 3 / m 3 ;q (P) is the oil production capacity of the oil well with P pressure as the flowing pressure, in m 3 ; For oil wells, P b Saturation pressure is the oil production capacity as the flowing pressure, in m 3 ; is the oil phase permeability at saturation pressure, in mD; K (P) is the oil phase permeability under P pressure, in mD; μ (P) is the viscosity of crude oil at pressure P, in mPa·s; is the viscosity of crude oil at saturation pressure, in mPa·s; P i is the formation pressure, in MPa; P is any pressure, in MPa; P b is the saturation pressure, in MPa; J1 is the oil phase permeability ratio, in mD / mD; J2 is the formation crude oil viscosity ratio, in mPa·s / mPa·s; J3 is the production pressure difference ratio, in MPa / MPa.

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