A method for determining the maximum production capacity of an oil well in an unsaturated reservoir during the initial production period

Abstract

The present invention discloses a method for determining the maximum production capacity of an oil well in an unsaturated oil reservoir at the initial stage of production, comprising the following steps: collecting formation crude oil samples and related data; obtaining saturation pressure; obtaining dissolved gas-to-oil ratio data at any pressure; obtaining dissolved gas volume coefficient data at any pressure; obtaining gas saturation data at any pressure; obtaining oil phase permeability ratio data at different gas saturations; obtaining oil phase permeability ratio data at different pressures and saturation pressure; obtaining formation crude oil viscosity data at any pressure; obtaining crude oil viscosity ratio data at different pressures and saturation pressure; obtaining production pressure differential ratio data corresponding to different pressures as flowing pressure and saturation pressure as flowing pressure; plotting a curve showing the relationship between production pressure differential and dimensionless production capacity multiples; obtaining the production pressure differential corresponding to the maximum production capacity, etc. The present invention provides a basis for increasing oil reservoir oil production rate, shortening development cycle, and improving economic benefits in offshore oil fields.

Description

Technical Field

[0001] The present 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 Bohai oil reservoirs are unsaturated. Considering the limited platform lifespan, it is crucial to maximize well productivity to increase reservoir recovery and shorten development cycles. Increasing the production differential pressure is the primary method for improving well productivity. In the early stages of unsaturated reservoir development, before water breakthrough, factors influencing well productivity are primarily divided into two phases: 1. When the production differential pressure is less than the in-situ saturation pressure, the reservoir flows in a single phase. During this phase, crude oil permeability and viscosity change little, and well productivity is primarily influenced by the production differential pressure alone. 2. When the production differential pressure exceeds the in-situ saturation pressure, crude oil in the unsaturated reservoir degasses, shifting from single-phase flow to two-phase flow, resulting in a decrease in crude oil permeability and an increase in formation crude viscosity. Well productivity is influenced by a combination of factors, including the production differential pressure, crude oil permeability, and crude oil viscosity. At present, research on oil well productivity mainly focuses 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 the 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 by comprising the following steps:

[0006] S1. Collect crude oil samples and related static data from the production layer of the target area;

[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 crude oil saturation pressure test experiment in the target area, draw a curve showing the relationship between pressure and the difference between cumulative pump readings, and obtain the saturation 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", a crude oil saturation pressure test experiment was carried out in the target area. The cumulative pump reading difference under different pressures was obtained, and a pressure-cumulative pump reading difference relationship curve was plotted. The pressure-cumulative pump reading difference relationship curve was established with the cumulative pump reading difference as the X-axis and the pressure as the Y-axis to establish a plane rectangular coordinate system. The pressure corresponding to the inflection point of the curve was the saturation pressure.

[0011] S3. Conduct a degassing experiment on the target area's formation crude oil, plot a curve showing the relationship between pressure and dissolved gas-oil ratio in the target area, and obtain dissolved gas-oil ratio data for the target area at any pressure by querying the curve. The degassing experiment is conducted in accordance with the national standard GB / T26981-2020, "Analysis Methods for Physical Properties of Oil and Gas Reservoir Fluids."

[0012] The pressure-dissolved gas-oil ratio relationship curve establishes a plane rectangular coordinate system with pressure as the X-axis and the dissolved gas-oil ratio as the Y-axis. The pressure-dissolved gas-oil ratio relationship 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 formation is depressurized and degassed in stages to obtain the dissolved gas-oil ratio at each pressure level, and then the pressure-dissolved gas-oil ratio relationship curve is drawn.

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

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

[0015] S5. Draw a curve showing the relationship between pressure and gas saturation of the target area, and obtain the gas saturation of the target area at any pressure by querying the curve showing the relationship between pressure and 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-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 gas saturation data under different pressures, and then plotting a pressure-gas saturation relationship curve; the pressure-gas saturation relationship curve is established with 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. Conduct an oil-gas permeability test in the target area, draw a relationship curve between the 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 the oil-phase permeability ratio, gas-phase permeability ratio, and gas saturation; the magnitude of the oil-phase permeability ratio is the magnitude of the impact of the permeability change on the oil well productivity;

[0024] According to the petroleum industry standard SYT5345-2007 "Method for Determination of Relative Permeability of Two Phases in Rocks", oil and gas permeability experiments were carried out in the target area cores to obtain experimental data of gas saturation, oil phase permeability ratio and gas phase permeability ratio. Relationship curves between the oil phase permeability ratio, gas phase permeability ratio and gas saturation were plotted. The curves have 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 relationship curve between pressure and oil phase permeability ratio, and obtaining the oil phase permeability ratio of the target area at any pressure by querying the relationship curve between pressure and oil phase permeability ratio;

[0026] The variation pattern of the oil phase permeability ratio at 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 at saturation pressure can also be obtained from the pressure-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, the unit is 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 experiments, 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 curve of the relationship between pressure and oil phase permeability ratio 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 showing 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 showing 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 of Physical Properties of Oil and Gas Reservoir Fluids", and the formation crude oil viscosity data under different pressures in the target area are tested to obtain the pressure-to-formation crude oil viscosity relationship curve.

[0037] S9, drawing a relationship curve between pressure and formation crude oil viscosity ratio, and obtaining formation crude oil viscosity ratios at different pressures in the target area by querying the relationship curve 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 formation crude oil viscosity data at different pressures in the target area from the pressure-to-formation crude oil viscosity relationship curve drawn in step S8;

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

[0041] The calculation formula for 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 ratios at different pressures obtained in step S92, relationship curves between different pressures and formation crude oil viscosity ratios are 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, plotting a relationship curve between pressure and production differential pressure ratio, and obtaining production differential pressure ratio data corresponding to different pressures in the target area as flow pressures by querying the relationship curve between pressure and production differential pressure ratio;

[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 obtain the production differential pressure ratio under different pressures as the flow pressure; the size of this production differential pressure ratio is the impact of the production differential pressure change 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 when different pressures are used as flow pressures, 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 X-axis and production pressure difference ratio as Y-axis to establish a plane rectangular coordinate system.

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

[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 at different pressures obtained in step S7, the crude oil viscosity ratio data at 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; these are substituted into the production pressure difference and dimensionless production capacity multiple calculation formula to calculate the dimensionless production capacity multiple, and then a relationship curve between the production pressure difference and the dimensionless production capacity multiple of the target area is plotted;

[0058] The calculation formula for the production pressure difference and the dimensionless capacity multiple is:

[0059]

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

[0061] The relationship curve between the production pressure difference and the dimensionless capacity multiple is established with 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. Based on 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 in the initial stage of production. The method can quickly obtain the variation pattern of the oil well production capacity with the production pressure difference when the production pressure difference is greater than the ground-saturated pressure difference in the initial stage of development of the unsaturated oil reservoir. This method provides a basis for determining the production pressure difference (working system) required for the oil well to obtain the maximum production capacity, thereby maximizing the reservoir capacity and improving the oil production rate in the initial stage of development of the unsaturated oil reservoir. This method is helpful for designing a plan to increase the oil production rate during oil field development, and is scientific, reasonable and effective. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0067] Figure 3 1 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 41 is 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 1 is a schematic diagram of a curve showing the relationship between target zone pressure and 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 1 is a schematic diagram of a curve showing the relationship between the target zone pressure and the oil phase permeability ratio in Example 1 of the present invention;

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

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

[0074] Figure 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] Figure 11 1 is a schematic diagram of a curve showing the relationship between the target area production pressure difference and the dimensionless production capacity multiple in Example 1 of the present invention;

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

[0077] Figure 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] Figure 14 Schematic diagram of the relationship curve between the pressure and the dissolved gas volume coefficient of the JX1-1 oil field in Example 2 of the present invention;

[0079] Figure 15 Schematic diagram of the relationship curve between pressure and gas saturation of the JX1-1 oil field in Example 2 of the present invention;

[0080] Figure 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] Figure 17 2 is a schematic diagram of a curve showing the relationship between the pressure and the oil phase permeability ratio of the JX1-1 oil field in Example 2 of the present invention;

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

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

[0084] Figure 20 Schematic diagram of the relationship curve between the pressure and the production pressure difference ratio of the JX1-1 oil field in Example 2 of the present invention;

[0085] Figure 21 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 will be 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 crude oil samples and formation pressure, oil saturation and other data in the target area; collect 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 saturated pressure test experiment on 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 saturated pressure test experiment on the target area 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 saturated pressure. The saturated pressure of the target area is 10.5MPa ( Figure 2 , column 4 of Table 1).

[0094] S3. Conduct degassing experiments on 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 crude oil in the target area is degassed by graded pressure reduction 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 ( Figure 3 ). By querying the curve, the dissolved gas-oil ratio data of the target area at any pressure is obtained.

[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 a rectangular coordinate system, a plane rectangular coordinate system is established with pressure as the X-axis and 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 is 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 at 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 at 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 test in target area to obtain oil phase permeability ratio data under different gas saturation. According to the petroleum industry standard SYT5345-2007 "Method for determination of two-phase relative permeability in rock", carry out core phase permeability test in 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 is consistent with 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 productivity), 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, with pressure as the X-axis and oil phase permeability ratio as the Y-axis, a plane rectangular coordinate system is established ( 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; is the oil phase permeability ratio at different gas saturations measured by phase permeability experiments, 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 showing 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 showing the relationship between pressure and formation crude oil viscosity ( Figure 8 ). The viscosity data of the formation crude oil in the target area at any pressure can be obtained by querying the curve.

[0104] S9. Obtain the crude oil viscosity ratio data at different pressures and saturation pressures in the target area. According to step S8, query and obtain the formation crude oil viscosity data at different pressures in the target area. Examples are shown in columns 5 and 7 of Table 1. Substitute the data into formula (3) to calculate the formation crude oil viscosity ratio at different pressures and saturation pressure. The value is the impact of the change in formation crude oil viscosity on the oil well productivity. Examples are shown in column 12 of Table 1. Then, a relationship curve between pressure and formation crude oil viscosity ratio is drawn ( Figure 9 The characteristic of this curve is that it establishes a rectangular coordinate system with pressure as the X-axis and the formation crude oil viscosity ratio as the Y-axis. By querying the curve, the formation crude oil viscosity ratio data for the target area at 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 saturation pressure as the flow pressure. i , saturation pressure P b , pressure P, see examples in columns 3, 4, and 5 of Table 1, and substitute into formula (4) to calculate the arbitrary pressure P as the flow pressure and saturation pressure P b As the production pressure differential ratio of the flow pressure, the magnitude is the impact of the production pressure differential change on the oil well productivity. For example, see column 13 of Table 1, and then draw the relationship curve between pressure and production pressure differential ratio ( Figure 10 By querying the curve, we can obtain the production pressure differential ratio data of the target area at different pressures and saturation pressures. The characteristic of this curve is that in a rectangular coordinate system, the pressure is used as the X-axis and the production pressure differential ratio is used 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 changes 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 the arbitrary pressure, MPa; P b is the saturation pressure, MPa.

[0110] S11. Draw the relationship curve between the production pressure difference of the target area and the dimensionless capacity multiple. The characteristic of this curve is that in the rectangular coordinate system, the production pressure difference is the X-axis and the dimensionless capacity multiple (the ratio of the capacity under any production pressure difference to the capacity under the saturation pressure production pressure difference) is the Y-axis, and a plane rectangular coordinate system is established ( Figure 11 ). Based on the permeability ratio, formation crude oil viscosity ratio, and production pressure differential ratio obtained in steps S7, S9, and S10, they are substituted into formula (5) to calculate the production pressure differential and dimensionless production capacity multiple data. Examples are shown in columns 6 and 14 of Table 1. A curve is then drawn showing the relationship between the production pressure differential and the dimensionless production capacity multiple in the target area.

[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 the oil production capacity of the flow 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, 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 ( Figure 11 ).

[0114] Example 2

[0115] Take the Bohai JX1-1 oilfield as an example. Figures 12-21 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 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, the cumulative pump reading difference under different pressures was obtained, and a curve of the relationship between pressure and cumulative pump reading difference was drawn. 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 ( Figure 12 , Table 2, column 4).

[0122] S3. Conduct degassing experiments on crude oil in the target area and draw curves showing the relationship between pressure and dissolved gas-oil ratio.

[0123] 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 crude oil in the JX1-1 oilfield formation is degassed by graded pressure reduction 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 ( Figure 13 By querying the curve, the solution gas-oil ratio data of the JX1-1 oil field at any pressure can be obtained.

[0124] S4. Conduct a dissolved gas volume coefficient measurement experiment 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 a 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 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 ( Figure 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 of the JX1-1 oil field under different pressures are obtained. Examples are shown in columns 8 and 9 of Table 2. As well as the original oil saturation data of the JX1-1 oil field collected in step 1, examples 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. Then, the relationship curve between pressure and gas saturation is drawn ( Figure 15 ). By querying the curve, the gas saturation data of the JX1-1 oil field at any pressure is 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 test in target area to obtain oil phase permeability ratio data under different gas saturation. According to the petroleum industry standard SYT5345-2007 "Method for determination of two-phase relative permeability in rock", carry out core phase permeability test in JX1-1 oil field, obtain experimental data of gas saturation, oil phase permeability ratio, 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 16 By querying the curve, the oil phase permeability ratio data and gas phase permeability ratio data of the JX1-1 oil field at any gas saturation are obtained.

[0130] S7. Obtain the oil permeability ratio data under different pressures and saturation pressures in the target area. The variation pattern of the oil permeability ratio under different pressures and saturation pressures in the JX1-1 oil field is consistent with the oil-gas permeability test results (2) in step S6. According to the pressure and oil 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 productivity), an example is shown in columns 10, 5, and 11 of Table 2. A curve of the relationship between pressure and oil 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 permeability ratio is used as the Y-axis to establish a plane rectangular coordinate system ( Figure 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; is the oil phase permeability ratio at different gas saturations measured by phase permeability experiments, 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 showing 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 showing the relationship between pressure and formation crude oil viscosity ( Figure 18 By querying the curve, the viscosity data of the formation crude oil at any pressure in the JX1-1 oil field can be obtained.

[0134] S9. Obtain the crude oil viscosity ratio data at different pressures and saturation pressures in the target area. According to step S8, query the JX1-1 oilfield formation crude oil viscosity data at different pressures. Examples are shown in columns 5 and 7 of Table 2. Substitute the data into formula (3) to calculate the formation crude oil viscosity ratio at different pressures and saturation pressure. The value is the impact of the change in formation crude oil viscosity on the oil well productivity. Examples are shown in column 12 of Table 2. Then, a relationship curve between pressure and formation crude oil viscosity ratio is drawn ( Figure 19 The characteristic of this curve is that it establishes a rectangular coordinate system with pressure as the X-axis and the formation crude oil viscosity ratio as the Y-axis. By querying the curve, the formation crude oil viscosity ratio data at any pressure in the JX1-1 oilfield 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 saturation pressure as the flow pressure. i , saturation pressure P b , pressure P, see examples in columns 3, 4, and 5 of Table 2, and 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 pressure and production pressure difference ratio ( Figure 20 By querying the curve, we obtain the production pressure differential ratio data for the JX1-1 oilfield at different pressures and saturation pressures. This curve is characterized by establishing a rectangular coordinate system with pressure as the X-axis and the production pressure differential ratio as the Y-axis.

[0138]

[0139] J3 is the production pressure difference ratio, that is, the effect of production pressure difference changes 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 the arbitrary pressure, MPa; P b is the saturation pressure, MPa.

[0140] S11. Draw the relationship curve between the production pressure difference of the target area and the dimensionless capacity multiple. The characteristic of this curve is that in the rectangular coordinate system, the production pressure difference is the X-axis and the dimensionless capacity multiple (the ratio of the capacity under any production pressure difference to the capacity under the saturation pressure production pressure difference) is the Y-axis, and a plane rectangular coordinate system is established ( Figure 21 ). Based on the permeability ratio, formation crude oil viscosity ratio, and production pressure differential ratio obtained in steps S7, S9, and S10, they are substituted into formula (5) to calculate the production pressure differential and dimensionless production capacity multiple data. Examples are shown in columns 6 and 14 of Table 2. A curve is then drawn showing the relationship between the production pressure differential and dimensionless production capacity multiple for the JX1-1 oilfield.

[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 the oil production capacity of the flow 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, 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 when the production pressure difference of the JX1-1 oil field is 6.5MPa, 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 ( Figure 21 ).

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

[0146] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection 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 fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for determining the maximum production capacity of an oil well in an unsaturated oil reservoir during the initial production period, characterized by: The following steps are involved: S1. Collect crude oil samples and related static data from the production layer of the target area; S2. Conduct a crude oil saturation pressure test experiment in the target area, draw a curve showing the relationship between pressure and the difference between cumulative pump readings, and obtain the saturation 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 crude oil degassing experiment in the target area, draw a curve showing the relationship between pressure and dissolved gas-oil ratio in the target area, and obtain dissolved gas-oil ratio data of the target area at any pressure by querying the curve. S4. Conduct a dissolved gas volume coefficient measurement experiment in the target area, draw a curve showing the relationship between the pressure and the dissolved gas volume coefficient in the target area, and obtain the dissolved gas volume coefficient of the target area at any pressure by querying the curve showing the relationship between the pressure and the dissolved gas volume coefficient; S5. Draw a curve showing the relationship between pressure and gas saturation of the target area, and obtain the gas saturation of the target area at any pressure by querying the curve showing the relationship between pressure and gas saturation; S6. Conduct oil-gas permeability experiments in the target area, draw relationship curves between the oil-phase permeability ratio, gas-phase permeability ratio, and gas saturation in the target area, and obtain oil-phase permeability ratio data at any gas saturation in the target area by querying the relationship curves between the oil-phase permeability ratio, gas-phase permeability ratio, and gas saturation; S7, drawing a relationship curve between pressure and oil phase permeability ratio, and obtaining the oil phase permeability ratio of the target area at any pressure by querying the relationship curve 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 showing 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 showing the relationship between the pressure and the viscosity of the formation crude oil; S9, drawing a relationship curve between pressure and formation crude oil viscosity ratio, and obtaining formation crude oil viscosity ratios at different pressures in the target area by querying the relationship curve between pressure and formation crude oil viscosity ratio; S10, plotting a relationship curve between pressure and production differential pressure ratio, and obtaining production differential pressure ratio data corresponding to different pressures in the target area as flow pressures by querying the relationship curve between pressure and production differential pressure ratio; S11. Draw a curve showing the relationship between the target area's production pressure difference and the dimensionless capacity multiple; S12. Based on 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-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 plotting 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, the unit is 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 experiments, 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 permeability ratio 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 formation crude oil viscosity data at different pressures in the target area from the pressure-to-formation crude oil viscosity relationship curve drawn in step S8; S92, substituting the data obtained in step S91 into the formula for calculating the viscosity ratio of the formation crude oil to calculate the viscosity ratio of the formation crude oil under different pressures; S93. According to the formation crude oil viscosity ratios at different pressures obtained in step S92, relationship curves between different pressures and formation crude oil viscosity ratios are 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 for 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 obtain 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 when different pressures are used as flow pressures, 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 dimensionless capacity multiple calculation formula to calculate 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 calculation formula for the production pressure difference and the dimensionless capacity multiple is: Where: J is the dimensionless capacity multiple, unit is m 3 / m 3 ;q (P) The oil production capacity of the oil well with P pressure as the flowing pressure, unit is m 3 ; For oil wells, P b Saturation pressure is the oil production capacity as the flow pressure, the unit is m 3 ; is the oil phase permeability at saturation pressure, in mD; K (P) is the oil phase permeability at pressure P, 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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