Method for exploiting common heavy oil reservoir in shallow and ultra-thin layers of vertical well

Abstract

The invention relates to the technical field of heavy oil recovery, in particular to a vertical well shallow layer and ultra-thin layer common heavy oil reservoir recovery method which comprises the steps that elastic recovery is conducted on a target vertical well in a work area to obtain the actual daily oil production; if it is judged that the actual daily oil production is lower than the economic limit daily oil production, steam huff-puff exploitation is conducted on the target vertical well, and when the designed steam injection rate is reached, steam huff-puff exploitation is stopped; determining parameters related to the steam injection intensity during steam huff and puff exploitation, and determining the steam injection intensity according to the related parameters; determining the designed steam injection amount according to the steam injection intensity; and performing blowout operation and oil pumping unit production on the target vertical well, and re-performing steam huff and puff oil displacement on the target vertical well if the daily oil production is judged to be lower than the economic limit daily oil production. The problems that when an existing steam huff and puff and steam drive thermal recovery technology is used for conducting steam injection development on stratums which are deep in oil reservoir burying depth, insufficient in stratum natural energy and thin in oil layer thickness, heat loss is large, the steam heat utilization rate is low, and economic benefits of steam injection development are low are solved.

Description

Technical Field

[0001] This invention relates to the field of heavy oil extraction technology, and in particular to a method for extracting shallow, ultrathin ordinary heavy oil reservoirs. Background Technology

[0002] Heavy oil generally refers to crude oil with high viscosity. my country's petroleum and natural gas industry standards stipulate that degassed crude oil with a viscosity of 100-10000 mPa·s at its original reservoir temperature, or a density of 934-1000 kg / m³ at 15.6℃ and atmospheric pressure, is considered heavy oil. 3 Crude oil includes heavy oil, high-viscosity oil, oil sands, natural bitumen, and oil shale. As conventional crude oil development is limited by reserve growth, heavy oil development plays an increasingly important role in compensating for insufficient conventional crude oil production.

[0003] Steam injection is a common method for developing heavy oil reservoirs. Steam injection involves periodically injecting a certain amount of steam into an oil well, simmering the well, and then opening it to produce oil. Steam injection is generally used in the initial stages of heavy oil reservoir development.

[0004] Currently, existing steam injection parameter design for steam huff and puff involves setting a chart of effective thickness, crude oil viscosity, and steam injection intensity at a given pressure level. The optimal steam injection intensity is determined based on the reservoir pressure, effective thickness, and crude oil viscosity of the production well, combined with the chart. However, actual development results show that this method yields relatively low output and is not economically viable. Furthermore, for shallow, ultra-thin layers of ordinary heavy oil, there are issues such as shallow reservoir depth and insufficient natural formation energy. The thin oil layer thickness leads to significant heat loss during steam injection, resulting in low steam heat utilization and poor economic efficiency. Currently, there are no domestic or international examples of this type of shallow, thin-layer heavy oil extraction. Summary of the Invention

[0005] This invention proposes a method for developing shallow, ultra-thin ordinary heavy oil reservoirs to solve the problems of high heat loss, low steam heat utilization rate, and low economic benefits of existing steam injection and steam-driven thermal recovery technologies when developing reservoirs with shallow burial depth, insufficient natural energy in the formation, and thin oil layer.

[0006] According to one aspect of the present invention, a method for developing shallow, ultra-thin layers of conventional heavy oil reservoirs in vertical wells is provided, comprising:

[0007] Flexible extraction was carried out on the target vertical well in the work area to obtain the actual daily oil production;

[0008] Determine whether the actual daily oil production is lower than the economic limit daily oil production. If so, steam injection is carried out on the target vertical well until the designed steam injection volume is reached.

[0009] The method for determining the designed steam injection volume includes: determining parameters related to the steam injection intensity during steam huff and puff mining; determining the steam injection intensity based on the parameters; and determining the designed steam injection volume based on the steam injection intensity.

[0010] A blowout operation is performed on the target vertical well. After the blowout is completed, the pumping unit is used for production. It is determined whether the daily oil production is lower than the economic limit daily oil production. If so, the target vertical well is subjected to steam injection and discharge again.

[0011] Preferably, before determining whether the actual daily oil production is lower than the economic limit daily oil production, the method for determining the economic limit daily oil production includes:

[0012] Obtain the daily operating cost of a single well in the work area, the crude oil commodity rate, the crude oil price, and the comprehensive tax rate;

[0013] Based on the single-well daily operating cost, crude oil commodity rate, crude oil price and comprehensive tax rate, the economic limit daily oil production is determined using formula (1).

[0014]

[0015] In the formula: Q o The economically limited daily oil production, in yuan; C e The daily operating cost per well is expressed in yuan; α represents the crude oil commodity rate; P o R represents the price of crude oil, in yuan / ton; R represents the comprehensive tax rate, in percent.

[0016] Preferably, the method for steam injection extraction of the target vertical well includes:

[0017] The injected water is circulated within the water treatment system.

[0018] The steam generated by heating the circulated injection water in a high-temperature and high-pressure water boiler is then injected into the wellhead through the steam injection pipeline.

[0019] During the injection process, the steam injection rate is increased to the maximum while ensuring that the injection pressure does not exceed 1.2 times the formation fracturing pressure.

[0020] Preferably, during the injection process, the boiler outlet steam dryness is ≥75% and the vertical well steam injection rate is ≥100t / d.

[0021] Preferably, prior to the injection, the formation fracturing pressure is determined, the method comprising:

[0022] Obtain the formation fracture constant and formation pressure in the work area;

[0023] Based on the formation fracturing constant and formation pressure, the formation fracturing pressure is determined using formula (2);

[0024] P f =0.0223α×H+(1.03-α)×P R (2);

[0025] In the formula: P f α is the formation fracture pressure, MPa; α is the formation fracture constant; H is the depth in the middle of the reservoir, m; P R ρ represents the formation pressure, in MPa.

[0026] Preferably, before obtaining the formation fracture constant, the formation fracture constant is determined, and the method includes:

[0027] Obtain the rock pressure gradient, reservoir pressure in the middle, and reservoir depth in the work area;

[0028] Based on the rock pressure gradient, the pressure in the middle of the reservoir, and the depth in the middle of the reservoir, the formation fracture constant is determined using formula (3);

[0029] α=0.2307×{0.1×β+4.335×(4.335×C-β)×P / H} (3);

[0030] In the formula: β is the rock fracture constant; C is the rock pressure gradient, MPa / m; P is the pressure in the middle of the reservoir, MPa; H is the depth in the middle of the reservoir, m.

[0031] Preferably, the method for determining the design steam injection volume based on the steam injection intensity includes:

[0032] Obtain the effective thickness of the oil layer in the work area;

[0033] Based on the steam injection intensity and the effective thickness of the oil layer, the design steam injection amount is determined using formula (4);

[0034] Q j =y×h (4)

[0035] In the formula: y is the steam injection intensity; h is the effective thickness of the oil layer, in meters.

[0036] Preferably, the method for determining parameters related to steam injection intensity during steam huff and puff extraction includes:

[0037] Obtain basic parameters of the work area;

[0038] A geological model is established based on the aforementioned basic parameters, and the steam injection intensity corresponding to each basic parameter under different parameter values ​​is determined through numerical simulation.

[0039] The grey relational analysis method is used to determine the correlation between each basic parameter and the steam injection intensity. The predetermined number of basic parameters with the highest correlation are the parameters related to the steam injection intensity.

[0040] Preferably, the parameters related to steam injection intensity include: cycle number, effective oil layer thickness, fluid production during the elastic extraction stage, and initial oil saturation.

[0041] Preferably, the method for determining the steam injection intensity based on the relevant parameters includes:

[0042] A three-dimensional geological model of the work area was established, and each relevant parameter was determined through numerical simulation. The corresponding steam injection intensity under different parameter values ​​was determined, and the relationship between each relevant parameter and the steam injection intensity was established.

[0043] Based on the relationship between each relevant parameter and the steam injection intensity, determine the relationship between the steam injection intensity and all relevant parameters;

[0044] The steam injection intensity is determined based on the relationship between the steam injection intensity and all relevant parameters.

[0045] Preferably, the relationship between the steam injection intensity and all relevant parameters is as follows:

[0046] y=a×Ln(x1)+b×Ln(x2)+c×power(x3,2)+d×x3+e×power(x4,2)

[0047] +f×x4+g(5);

[0048] In the formula: a, b, c, d, e, f, g are coefficients; x1 is the cycle number; x2 is the effective thickness of the oil layer, m; x3 is the fluid production during the elastic extraction stage, t; x4 is the original oil saturation, f.

[0049] Preferably, in formula (5), the method for determining the coefficient includes:

[0050] Based on the different parameter values ​​and their corresponding steam injection intensities, the coefficients are determined using the quasi-Newton method and / or the general global optimization method.

[0051] Preferably, the relationship between each relevant parameter and the steam injection intensity includes:

[0052] y = a × Ln(x1) + g1;

[0053] y = b × Ln(x²) + g²;

[0054] y=c×power(x3,2)+d×x3+g3;

[0055] y=e×power(x4,2)+f×x4+g4;

[0056] In the formula: a, b, c, d, e, f, g1, g2, g3, g4 are coefficients; x1 is the cycle number; x2 is the effective thickness of the oil layer, m; x3 is the fluid production during the elastic extraction stage, t; x4 is the original oil saturation, f.

[0057] Preferably, during the blowout operation, the wellhead production is controlled, wherein the daily fluid production of the vertical well is less than or equal to 20 tons.

[0058] Preferably, during the production of the pumping unit, the pumping efficiency is adjusted so that the daily fluid production of the vertical well is less than or equal to 10 tons.

[0059] Preferably, before performing the blowout operation on the target vertical well, the wellhead oil pressure and casing pressure are monitored. When the oil pressure and casing pressure drop below a predetermined value or remain stable for a predetermined time, the wellhead is opened to perform the blowout operation.

[0060] The present invention has at least the following beneficial effects:

[0061] This invention proposes a method for developing shallow, ultra-thin ordinary heavy oil reservoirs. By combining elastic development with steam injection, and determining the steam injection intensity by determining relevant parameters during steam injection, the accurate design steam injection volume can be determined. This achieves the goals of reducing development costs, improving steam heat utilization, reducing heat loss, and improving economic benefits. Attached Figure Description

[0062] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present invention and, together with the specification, serve to explain the technical solutions of the present invention.

[0063] Figure 1 A flowchart illustrating a method for developing shallow, ultra-thin conventional heavy oil reservoirs in vertical wells according to an embodiment of the present invention is shown.

[0064] Figure 2 This diagram illustrates the relationship between crude oil viscosity and temperature according to an embodiment of the present invention.

[0065] Figure 3 This diagram illustrates the relationship between the number of cycles and the optimal steam injection intensity according to an embodiment of the present invention.

[0066] Figure 4 This diagram illustrates the relationship between the effective and optimal steam injection intensity of the oil reservoir according to an embodiment of the present invention.

[0067] Figure 5 This diagram illustrates the relationship between the initial oil saturation and the optimal steam injection intensity according to an embodiment of the present invention.

[0068] Figure 6 A graph showing the relationship between the fluid production rate and the optimal steam injection intensity during the elastic mining stage according to an embodiment of the present invention is provided. Detailed Implementation

[0069] Various exemplary embodiments, features, and aspects of the present invention will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0070] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0071] In this document, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Furthermore, the term "at least one" in this document means any combination of at least two of any one or more elements. For example, including at least one of A, B, and C can mean including any one or more elements selected from the set consisting of A, B, and C.

[0072] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art will understand that the present invention can be practiced without certain specific details. In some instances, methods, means, elements, and circuits well known to those skilled in the art have not been described in detail in order to highlight the spirit of the invention.

[0073] Figure 1 A flowchart illustrating a method for developing shallow, ultra-thin conventional heavy oil reservoirs in vertical wells according to an embodiment of the present invention is shown. Figure 2 This diagram illustrates the relationship between crude oil viscosity and temperature according to an embodiment of the present invention. Figure 3 This diagram illustrates the relationship between the number of cycles and the optimal steam injection intensity according to an embodiment of the present invention. Figure 4 This diagram illustrates the relationship between the effective and optimal steam injection intensity of the oil reservoir according to an embodiment of the present invention. Figure 5 This diagram illustrates the relationship between the initial oil saturation and the optimal steam injection intensity according to an embodiment of the present invention. Figure 6 A graph showing the relationship between fluid production and optimal steam injection intensity during the elastic extraction stage according to an embodiment of the present invention is provided. Figure 1-6As shown, a method for developing shallow, ultra-thin, conventional heavy oil reservoirs in vertical wells includes: Step S01: performing elastic production on the target vertical well in the work area to obtain the actual daily oil production; Step S02: determining whether the actual daily oil production is lower than the economic limit daily oil production; if so, performing steam injection on the target vertical well until the designed steam injection volume is reached; wherein, the method for determining the designed steam injection volume includes: determining parameters related to the steam injection intensity during steam injection, determining the steam injection intensity based on the parameters, and determining the designed steam injection volume based on the steam injection intensity; Step S03: performing a blowout operation on the target vertical well, and after the blowout is completed, pumping unit production is carried out, determining whether the daily oil production is lower than the economic limit daily oil production; if so, re-performing steam injection on the target vertical well.

[0074] The method for developing shallow, ultra-thin layers of ordinary heavy oil reservoirs in vertical wells provided in this embodiment of the invention specifically includes the following steps:

[0075] Step S01: Perform flexible extraction on the target vertical well in the work area to obtain the actual daily oil production.

[0076] In this embodiment of the invention, a shallow ultrathin layer ordinary heavy oil reservoir refers to a heavy oil reservoir with a reservoir depth of less than or equal to 800m, an average effective thickness of 1.5-4m, and a crude oil viscosity of less than or equal to 2000cp.

[0077] After drilling is completed and production is put into operation in the target work area, the energy of the natural formation is used to carry out elastic mining of the vertical well, that is, self-flowing mining, and the bottom hole flowing pressure is controlled to be ≤1MPa during the mining process.

[0078] Step S02: Determine whether the actual daily oil production is lower than the economic limit daily oil production. If so, steam injection is carried out on the target vertical well until the designed steam injection volume is reached. The method for determining the designed steam injection volume includes: determining parameters related to the steam injection intensity during steam injection, determining the steam injection intensity based on the parameters, and determining the designed steam injection volume based on the steam injection intensity.

[0079] In this invention, before determining whether the actual daily oil production is lower than the economic limit daily oil production, the method for determining the economic limit daily oil production includes: obtaining the daily operating cost of a single well in the work area, the crude oil commodity rate, the crude oil price, and the comprehensive tax rate; and determining the economic limit daily oil production using formula (1) based on the daily operating cost of a single well, the crude oil commodity rate, the crude oil price, and the comprehensive tax rate.

[0080]

[0081] In the formula: Q o The economically limited daily oil production, in yuan; C eThe daily operating cost per well is expressed in yuan; α represents the crude oil commodity rate; P o R represents the price of crude oil, in yuan / ton; R represents the comprehensive tax rate, in percent.

[0082] In this embodiment of the invention, when the economic benefits brought by the actual daily oil production after flexible extraction are insufficient to cover the daily oil extraction costs, flexible extraction needs to be stopped. The daily operating cost of the target vertical well during flexible extraction, along with the current crude oil commodity rate, crude oil price, and comprehensive tax rate, are substituted into the above formula (1) to calculate the corresponding economic limit daily oil production. This economic mechanical daily oil production is the minimum daily oil production required during the flexible extraction period. If the actual oil production of the target vertical well is lower than the economic limit daily oil production, flexible extraction is stopped, and steam injection extraction begins.

[0083] In this invention, the method for steam injection and extraction of the target vertical well includes: circulating the injected water through a water treatment system; heating the circulated injected water with steam generated by a high-temperature and high-pressure water boiler, and injecting the steam into the wellhead through a steam injection pipeline; during the injection process, increasing the steam injection rate to the maximum while ensuring that the injection pressure does not exceed 1.2 times the formation fracturing pressure.

[0084] In this invention, during the injection process, the boiler outlet steam dryness is ≥75% and the vertical well steam injection rate is ≥100t / d.

[0085] In this embodiment of the invention, when the actual daily oil production is lower than the economic limit daily oil production, water is injected for circulation in the water treatment system to remove impurities and reduce the hardness of the water.

[0086] Using natural gas, fuel oil, or coal as fuel, the circulated water is heated by a high-temperature and high-pressure water boiler, and the generated steam is injected into the wellhead through a steam injection pipeline, and then reaches the target layer in the well.

[0087] Among them, the dryness of the steam at the boiler outlet is ≥75%, and the steam injection rate of the vertical well is ≥100t / d.

[0088] While ensuring the injection pressure does not exceed 1.2 times the formation fracturing pressure, the steam injection rate should be increased as much as possible. Increased injection pressure acts as a fracturing agent in shallow, ultra-thin formations, creating fractures that allow steam to be injected into the formation to the maximum extent possible, while simultaneously displacing as much formation crude oil as possible. If the injection pressure exceeds 1.2 times the formation fracturing pressure, it may lead to formation collapse; therefore, the injection pressure should be controlled within 1.2 times the formation fracturing pressure.

[0089] In this invention, before the injection, the formation fracturing pressure is determined by means of: obtaining the formation fracturing constant and formation pressure of the work area; and determining the formation fracturing pressure using formula (2) based on the formation fracturing constant and formation pressure.

[0090] P f =0.0223α×H+(1.03-α)×P R (2);

[0091] In the formula: P f α is the formation fracture pressure, MPa; α is the formation fracture constant; H is the depth in the middle of the reservoir, m; P R ρ represents the formation pressure, in MPa.

[0092] In this embodiment of the invention, the value of the formation fracturing constant α (the fracturing constant of the target layer rock in the reservoir) in equation (2) is usually between 0.02307 and 0.01529, and the specific value depends on different oilfields and formation conditions. In practical applications, the fracturing pressure constant needs to be determined by empirical formulas.

[0093] In this invention, before obtaining the formation fracture constant, the formation fracture constant is determined by means of: obtaining the rock pressure gradient of the work area, the pressure in the middle of the reservoir and the depth in the middle of the reservoir; and determining the formation fracture constant using formula (3) based on the rock pressure gradient, the pressure in the middle of the reservoir and the depth in the middle of the reservoir.

[0094] α=0.2307×{0.1×β+4.335×(4.335×C-β)×P / H} (3);

[0095] In the formula: β is the rock fracture constant; C is the rock pressure gradient, MPa / m; P is the pressure in the middle of the reservoir, MPa; H is the depth in the middle of the reservoir, m.

[0096] In this embodiment of the invention, the formation fracturing constant determined by formula (3) should be within the above-mentioned range. Substituting the obtained formation fracturing constant and formation pressure into formula (2), the corresponding formation fracturing pressure is calculated.

[0097] In this invention, the method for determining the design steam injection amount based on the steam injection intensity includes: obtaining the effective thickness of the oil layer in the work area; and determining the design steam injection amount using formula (4) based on the steam injection intensity and the effective thickness of the oil layer.

[0098] Q j =y×h (4)

[0099] In the formula: y is the steam injection intensity; h is the effective thickness of the oil layer, in meters.

[0100] In this embodiment of the invention, when determining the design steam injection volume, the steam injection intensity is often calculated based on personal experience or a single parameter. This can lead to a discrepancy between the resulting design steam injection volume and the optimal steam injection volume required during actual formation mining, resulting in difficulties in steam injection and low utilization rates. Therefore, it is necessary to identify multiple (several) relevant parameters that are strongly correlated with the steam injection intensity to participate in the calculation, thereby obtaining a more accurate mining and construction plan.

[0101] In this invention, the method for determining parameters related to steam injection intensity during steam huff and puff mining includes: obtaining basic parameters of the work area; establishing a geological model based on the basic parameters; determining the steam injection intensity corresponding to each basic parameter under different parameter value conditions through numerical simulation; and determining the correlation degree between each basic parameter and the steam injection intensity using grey relational analysis, wherein a predetermined number of basic parameters with the highest correlation degree are the parameters related to steam injection intensity.

[0102] In this embodiment of the invention, the basic parameters of the work area include at least: original oil saturation, effective thickness, number of cycles, net-total ratio, porosity, permeability, and production volume during the elastic mining stage.

[0103] A three-dimensional geological model is established based on the basic parameters. The specific value of one of the basic parameters is changed while the other parameters remain unchanged. Numerical simulations are performed sequentially to calculate the optimal steam injection intensity corresponding to the change of a specific value of a certain basic parameter.

[0104] Based on the optimal steam injection intensity corresponding to different values ​​of each basic parameter, the grey relational analysis method is used to determine the grey relational degree between the original oil saturation, effective thickness, cycle number, net-total ratio, porosity, permeability, and production volume in the elastic mining stage and the steam injection intensity. The four basic parameters with the highest correlation are selected as parameters related to the steam injection intensity.

[0105] In this invention, the parameters related to steam injection intensity include: cycle number, effective oil layer thickness, fluid production during the elastic extraction stage, and initial oil saturation.

[0106] In this embodiment of the invention, through the numerical simulation and correlation analysis of the basic parameters, it was finally determined that the four parameters of original oil saturation, effective thickness, cycle number and production volume in the elastic mining stage have the highest gray correlation with steam injection intensity, and are therefore related parameters of steam injection intensity.

[0107] In this invention, the method for determining the steam injection intensity based on the relevant parameters includes: establishing a three-dimensional geological model of the work area; determining the steam injection intensity corresponding to each of the relevant parameters under different parameter values ​​through numerical simulation; and establishing a relationship between each relevant parameter and the steam injection intensity; determining a relationship between the steam injection intensity and all relevant parameters based on the relationship between each relevant parameter and the steam injection intensity; and determining the steam injection intensity based on the relationship between the steam injection intensity and all relevant parameters.

[0108] In this embodiment of the invention, a three-dimensional geological model of the target area is first established based on the relevant parameters of steam injection intensity. The three-dimensional geological model is then numerically simulated to calculate the optimal steam injection intensity when one of the four parameters—cycle number, effective oil layer thickness, fluid production during the elastic mining stage, and original oil saturation—is changed while the other three parameters remain unchanged.

[0109] After sequential calculations, the optimal steam injection intensity data corresponding to the changes in the four relevant parameters are obtained. The parameter value of each relevant parameter change, the corresponding value of the other three constant parameters, and the steam injection intensity obtained from the simulation are combined into a set of data, resulting in four sets of data.

[0110] In this invention, the relationship between each relevant parameter and the steam injection intensity includes:

[0111] y = a × Ln(x1) + g1 (5-1);

[0112] y = b × Ln(x²) + g² (5-2);

[0113] y=c×power(x3,2)+d×x3+g3 (5-3);

[0114] y=e×power(x4,2)+f×x4+g4(5-4);

[0115] In the formula: a, b, c, d, e, f, g 1. g2, g3, and g4 are coefficients; x1 is the cycle number; x2 is the effective thickness of the oil layer (m); x3 is the production volume during the elastic extraction stage (t); and x4 is the initial oil saturation (f). In this embodiment of the invention, based on the change values ​​of each relevant parameter and the corresponding optimal steam injection intensity, a relationship curve between each relevant parameter value and the corresponding optimal steam injection intensity is plotted. After fitting, the relationship between each relevant parameter and the optimal steam injection intensity can be obtained. For example... Figure 3-6 As shown, Figure 3 The curve shows the relationship between the number of cycles and the optimal steam injection intensity. Figure 4 This is the curve showing the relationship between the effective thickness of the oil layer and the optimal steam injection intensity. Figure 5 This is the curve showing the relationship between the original oil saturation and the optimal steam injection intensity. Figure 6 This is the curve showing the production rate of liquid and the optimal steam injection intensity during the elastic mining stage.

[0116] The relationships between the four sets of relevant parameter values ​​and the corresponding steam injection intensity are shown in equations (5-1) to (5-4). Among them, (5-1) is the relationship between the cycle number and the steam injection intensity, (5-2) is the relationship between the effective thickness of the oil layer and the steam injection intensity, (5-3) is the relationship between the production volume of the elastic mining stage and the steam injection intensity, and (5-4) is the relationship between the original oil saturation and the steam injection intensity.

[0117] The method for determining the relationship between steam injection intensity and all relevant parameters based on the relationship between each relevant parameter and steam injection intensity includes: adding the relationship between each relevant parameter and steam injection intensity to obtain the relationship between steam injection intensity and all relevant parameters, i.e.:

[0118] In this invention, the relationship between the steam injection intensity and all relevant parameters is as follows:

[0119] y=a×Ln(x1)+b×Ln(x2)+c×power(x3,2)+d×x3+e×power(x4,2)

[0120] +f×x4+g(5);

[0121] In the formula: a, b, c, d, e, f, g are coefficients; x1 is the cycle number; x2 is the effective thickness of the oil layer, m; x3 is the fluid production during the elastic extraction stage, t; x4 is the original oil saturation, f.

[0122] In this invention, the method for determining the coefficient in formula (4) includes:

[0123] Based on the different parameter values ​​and their corresponding steam injection intensities, the coefficients are determined using the quasi-Newton method and / or the general global optimization method.

[0124] In this embodiment of the invention, in equation (4), the effective thickness of the oil layer = the thickness of the oil layer sandstone × the net-total ratio. Furthermore, to determine the steam injection intensity y based on the obtained equation (4), it is necessary to determine the values ​​of each coefficient a to g in the equation.

[0125] The method for determining each coefficient value specifically includes: substituting the different parameter values ​​of each relevant parameter set during the above numerical simulation, the other unchanging relevant parameter values ​​in addition to the changing relevant parameters during the simulation, and the corresponding steam injection intensity value obtained, i.e., the four sets of data, into equation (4) to obtain the coefficient value corresponding to the different parameter values ​​of each relevant parameter.

[0126] If each relevant parameter has 5 different parameter values, then the four relevant parameters will have a total of 20 substitution calculations. For example, if there are 5 different parameter values ​​set for each cycle, and the other three relevant parameters are the initial set values ​​during simulation, then the value of each cycle and the corresponding three initial set values ​​of the relevant parameters are substituted into the model for numerical simulation to obtain 5 corresponding steam injection intensities, which is a set of data. Substituting this set of data, i.e., the data from the 5 simulations, into equation (4) will yield 5 corresponding coefficient values. The other four relevant parameters are calculated in the same way.

[0127] After substituting the different parameter values ​​corresponding to all relevant parameters and their corresponding steam injection intensity into equation (4) to obtain the corresponding coefficient values, statistical optimization software is used to calculate the four sets of data and their corresponding coefficient values ​​using Newton's method and general optimization global statistical method to obtain the final coefficient values ​​of a, b, c, d, e, f, and g.

[0128] Substitute the final coefficient value into formula (4), and then substitute the actual relevant parameter values ​​of the target vertical well, namely the cycle number, effective oil layer thickness, fluid production during the elastic mining stage, and the original oil saturation value, into formula (4) to calculate the corresponding steam injection intensity. Multiply the steam injection intensity by the effective oil layer thickness to obtain the accurate design steam injection volume. The target vertical well is then exploited based on the design steam injection volume.

[0129] Step S03: Perform blowout operation on the target vertical well. After the blowout is completed, pumping unit production is carried out to determine whether the daily oil production is lower than the economic limit daily oil production. If so, steam injection is performed on the target vertical well again.

[0130] In this invention, during the blowout operation, the wellhead production is controlled, wherein the daily fluid production of the vertical well is less than or equal to 20 tons.

[0131] In this invention, during the production of the oil pumping unit, the pump efficiency of the oil pumping unit is adjusted so that the daily fluid production of the vertical well is less than or equal to 10 tons.

[0132] In this invention, before the blowout operation is carried out on the target vertical well, the wellhead oil pressure and casing pressure are monitored. When the oil pressure and casing pressure drop below a predetermined value or remain stable for a predetermined time, the wellhead is opened to carry out the blowout operation.

[0133] In this embodiment of the invention, when the amount of steam injected during steam huff and puff mining reaches the designed steam injection amount, steam injection is stopped and the wellhead is closed.

[0134] Monitor the wellhead oil pressure and casing pressure values. When the pressure difference between the oil pressure and casing pressure drops below the predetermined value (3MPa), or remains basically unchanged for a predetermined time (24h) after dropping to a certain value, reopen the wellhead and carry out the blowout operation.

[0135] Using matching nozzles, wellhead production is controlled, with a daily fluid production of ≤20t for vertical wells. Production is then switched to the pumping unit; adjusting the pumping unit efficiency, the daily fluid production for vertical wells is ≤10t.

[0136] When the daily oil production is lower than the economic limit, return to step S02 and restart the steam injection process until the periodic oil production of the target vertical well reaches below the economic limit.

[0137] In this embodiment of the invention, taking a certain work area in an oil field as an example, the implementation process of the invention is described in detail:

[0138] Acquire basic static data and economic evaluation data for the target area. This includes: effective reservoir thickness, crude oil viscosity, formation pressure, rock fracture constant of the target reservoir layer, rock pressure gradient, pressure in the middle of the reservoir, depth in the middle of the reservoir, daily operating cost per well, crude oil commercialization rate, crude oil price, and comprehensive tax rate.

[0139] After drilling and commissioning of the target block, the target vertical well was exploited using the energy of the natural formation for elastic extraction, with the bottom hole flowing pressure controlled to ≤1MPa during the extraction process. The cumulative oil production was 808 tons.

[0140] The method for determining the economic limit daily oil production includes: calculating it using formula (1) based on the daily operating cost of a single well, the oil commodity rate, the crude oil price, and the comprehensive tax rate. When the calculated oil price is US$50 / barrel, the economic limit daily oil production is 1.12 tons;

[0141] When it is determined that the daily oil production is lower than the economic limit, the injected water will be circulated through a water treatment system to remove impurities and reduce the water hardness. Natural gas, fuel oil, or coal will be used as fuel, and the water will be heated by a high-temperature and high-pressure water boiler to generate steam, which will then be injected into the wellhead through a steam injection pipeline.

[0142] The formation fracture pressure was determined by the following method: It was calculated using equation (2) based on the formation fracture constant and the formation pressure, wherein the formation fracture constant was calculated using formula (3) based on the rock pressure gradient, the pressure in the middle of the reservoir, and the depth in the middle of the reservoir. The final formation fracture pressure was determined to be 15.4296 MPa.

[0143] During the steam injection process, the dryness of the steam at the boiler outlet is ≥75%, and the steam injection rate is 140t / d; at the same time, the injection pressure is guaranteed not to exceed 1.2 times the formation fracturing pressure; the injection pressure is 18.5-155MPa.

[0144] A three-dimensional geological model of the work area was established, and numerical simulations were performed on the obtained basic parameters. The steam injection intensity corresponding to each basic parameter was obtained, and the correlation between each basic parameter and the steam injection intensity was analyzed using grey relational analysis. Among them, four parameters were selected as parameters related to the steam injection intensity: cycle number, effective oil layer thickness, fluid production in the elastic mining stage, and original oil saturation.

[0145] Based on the three-dimensional geological model of the work area, the optimal steam injection intensity was calculated through numerical simulation when one of the four parameters (cycle number, effective oil layer thickness, fluid production during elastic mining stage, and original oil saturation) was changed (to set different parameter values) while the other three parameters remained unchanged (to set the initial parameter values).

[0146] The calculations yielded four sets of data, including the optimal steam injection intensity when one parameter changed while the other four remained constant. The relationship between each relevant parameter and the steam injection intensity is as follows:

[0147] y = 16.318 × ln(x1) + 129.85;

[0148] y = 48.137 × ln(x²) + 72.536;

[0149] y = 3E -5 ×x3 2 -0.0005×x3+121.8;

[0150] y = -1374.5 × x4 2 +1847.7×x4-498.75;

[0151] Therefore, the optimal steam injection intensity y is related to the four relevant parameters as follows:

[0152] y=a×Ln(x1)+b×Ln(x2)+c×power(x3,2)+d×x3+e×power(x4,2)+f×x4+g;

[0153] Using statistical optimization software, the four sets of data were combined and subjected to Newton's and optimized global statistical methods to calculate the coefficient values ​​of a, b, c, d, e, f, and g. The four sets of data are shown in Table 1 below. The initial parameter values ​​corresponding to the cycle number, effective oil layer thickness, fluid production during the elastic production stage, and original oil saturation are 1, 2.7, 0, and 0.64, respectively.

[0154] Table 1: Numerical Simulation Data Table of Relevant Parameters

[0155]

[0156]

[0157]

[0158] The model parameters during the numerical simulation were as follows: iteration number 26; computation time (hours:minutes:seconds:microseconds): 00:00:03:533; optimization algorithm: quasi-Newton method (BFGS) + general global optimization method; reason for termination: convergence criterion met; root mean square error (RMSE): 0.809877135721904; sum of squared residuals (SSE): 31.4832467983255; correlation coefficient. (R): 0.999365464518336; Correlation coefficient squared (R^2): 0.998731331671949; Coefficient of determination (DC): 0.998731331671949; Chi-square coefficient: 0.122168467641128; F-statistic: 36212.4916663563.

[0159] The final formula for calculating the steam injection intensity y is as follows:

[0160] y=16.1651765708831×Ln(x1)+47.4956443097375×

[0161] Ln(x2)+0.0000322053424730756×power(x3,2)+0.00264705414735965×

[0162] x3-1391.96977195182×power(x4,2)+1865.70682796744×

[0163] x4-550.528384273617.

[0164] Substitute the four relevant parameter values ​​corresponding to the target well into the above formula to calculate the corresponding steam injection intensity.

[0165] Multiply the obtained steam injection intensity by the effective thickness of the oil layer to obtain the designed steam injection volume.

[0166] When the amount of steam injected into the target well reaches the designed steam injection amount, stop injecting steam and close the wellhead.

[0167] The wellhead was reopened on the 5th day after steam injection was completed for venting operations; the wellhead production was controlled using a matching nozzle, with a daily fluid production of ≤20t.

[0168] Switch to oil pumping unit production, adjust the pumping unit efficiency, and the daily liquid production is ≤10t.

[0169] When the daily oil production falls below the economic limit, steam injection will resume.

[0170] The final target well produced a cumulative oil yield of 1224 tons. The calculated input-output ratio is 1:1.91.

[0171] It is understood that the various method embodiments mentioned above in this invention can be combined with each other to form combined embodiments without violating the principle and logic. Due to space limitations, this invention will not elaborate further.

[0172] Those skilled in the art will understand that, in the above-described method of the specific implementation, the order in which each step is written does not imply a strict execution order and does not constitute any limitation on the implementation process. The specific execution order of each step should be determined by its function and possible internal logic.

[0173] In this embodiment of the invention, based on my country's current heavy oil classification standard (see Table 1 below), heavy oil is divided into four categories using viscosity as the primary indicator and density as the secondary indicator. Category II of ordinary heavy oil, as well as extra-heavy oil and super-heavy oil, are used for thermal recovery development. Thermal recovery technologies include steam injection and steam drive technologies.

[0174] Table 1: Classification Standards for Heavy Crude Oil in China

[0175]

[0176] Steam injection is a method of oil extraction that involves periodically injecting a certain amount of steam into an oil well, simmering the well, and then opening it to produce oil. Steam injection technology is suitable for reservoirs with poor inter-well connectivity, excessively high crude oil viscosity, asphaltene content, and those unsuitable for steam drive. Because steam injection is a single-well operation relying on natural energy, it can only extract crude oil from the reservoirs near each well, leaving large dead oil zones between wells, with a typical recovery rate of only 10%–20%. With the development of steam injection technology, steam injection is no longer considered a crucial stage, but rather an important auxiliary measure in the steam drive process. The selection criteria for heavy oil reservoirs suitable for steam injection include reservoir depth, crude oil viscosity, total effective layer thickness, net-total layer thickness ratio, and reserve coefficient. Table 2 below shows the basic principles for selecting heavy oil reservoirs for steam injection in China. Note: Crude oil viscosity refers to the viscosity of devaporized crude oil at the reservoir temperature.

[0177] Table 2 Screening Criteria for Heavy Oil Steam Huff and Puff Extraction in China

[0178]

[0179]

[0180] Steam drive is a production method in which high-temperature wet steam is continuously injected into the reservoir through an injection well to heat and displace the crude oil, which is then extracted from the production well. Steam drive technology is suitable for shallow reservoirs with high viscosity and low relative density, where the crude oil viscosity is less than 50,000 mPa·s, the depth is less than 1600 m, the reservoir has high residual oil saturation, and the geological structure is simple. The distance between the injection well and the production well is 100–150 m smaller than the typical well distance. Since the 1970s, the global production from steam injection development has been continuously increasing, accounting for more than 60% of the total EOR (Excess Oil Retention) production. The suitability of heavy oil reservoirs for steam drive is constrained by reservoir depth, sandstone thickness, net-total oil layer ratio, porosity, permeability, oil saturation, and planar connectivity. Table 3 below shows the principles for selecting heavy oil reservoirs for steam drive both domestically and internationally.

[0181] Table 3: Principles for Steam Drive Screening of Heavy Oil Reservoirs at Home and Abroad

[0182] Reservoir geological parameters domestic foreign Oil layer burial depth, m ＜1500 ＜1500 Effective thickness, m ＞8 ＞6 <![CDATA[φ.S o ]]> ＞0.1 ＞0.1 Porosity φ, decimal ＞0.2 - <![CDATA[Oil saturation S o , decimal]]> ＞0.45 ＞0.4 Net total ratio, decimal ＞0.4 - Permeability coefficient of variation, decimal ＜0.7 - <![CDATA[Kh / μ o ,10 -3 μm 2 .m / (mpa.s)]]> - ＞30

[0183] According to China's heavy oil classification standards, the target area's heavy oil reservoir belongs to Class II of ordinary heavy oil, but the average oil layer thickness of 3m is at the lower limit of the technical and economic conditions for steam injection and steam drive development.

[0184] In 2007, steam injection and steam drive field tests were conducted in the target area's heavy oil reservoir, mainly going through two stages: steam injection and steam drive. The reservoir is shallow, with insufficient natural formation energy; the oil layer is thin, resulting in large heat losses during steam injection development, low steam heat utilization rate, a recovery rate of 19.34%, and an overall water cut of 86.1%. Based on the benefit calculation, under the condition of an oil price of $50 / barrel, the input-output ratio is calculated to be 1:0.38, which is not economically satisfactory and cannot be developed economically effectively. The specific input-output situation is shown in Table 4 below.

[0185] Table 4: Input-Output Ratio Table

[0186]

[0187] In summary, the problems in the development of this type of reservoir are as follows: shallow reservoir depth and insufficient natural energy in the formation; thin oil layer thickness, large heat loss in steam injection development, low steam heat utilization rate, and unsatisfactory economic benefits of steam injection development.

[0188] This invention determines an accurate steam injection intensity by identifying multiple parameters related to the injection intensity. This allows for the calculation of the designed steam injection rate suitable for steam huff and puff production of the target well. Combined with a determined economic limit for daily oil production, the method controls the production of the target well, thereby reducing the production cost of ultra-thin ordinary heavy oil reservoirs and achieving the goal of generating economic benefits from the development of shallow ultra-thin ordinary heavy oil reservoirs. Simultaneously, accurate steam injection intensity solves the problems of difficult steam injection and low steam heat utilization in shallow ultra-thin ordinary heavy oil reservoirs. It prevents the steam from failing to enter the oil layer due to insufficient injection intensity, or the formation from collapsing due to excessive injection intensity, thus failing to achieve the economic development objective.

[0189] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for developing shallow, ultra-thin layers of ordinary heavy oil reservoirs in vertical wells, characterized in that, include: Flexible extraction was carried out on the target vertical well in the work area to obtain the actual daily oil production; Determine whether the actual daily oil production is lower than the economic limit daily oil production. If so, steam injection is carried out on the target vertical well until the designed steam injection volume is reached. The method for determining the designed steam injection volume includes: determining parameters related to the steam injection intensity during steam huff and puff mining; determining the steam injection intensity based on the parameters; and determining the designed steam injection volume based on the steam injection intensity. A blowout operation is performed on the target vertical well. After the blowout is completed, the pumping unit is used for production. It is determined whether the daily oil production is lower than the economic limit daily oil production. If so, the target vertical well is subjected to steam injection and discharge again.

2. The method for developing shallow, ultra-thin layers of ordinary heavy oil reservoirs in vertical wells according to claim 1, characterized in that, Before determining whether the actual daily oil production is lower than the economic limit daily oil production, the method for determining the economic limit daily oil production includes: Obtain the daily operating cost of a single well in the work area, the crude oil commodity rate, the crude oil price, and the comprehensive tax rate; Based on the single-well daily operating cost, crude oil commodity rate, crude oil price and comprehensive tax rate, the economic limit daily oil production is determined using formula (1). In the formula: Q o The economically limited daily oil production, in yuan; C e The daily operating cost per well is expressed in yuan; α represents the crude oil commodity rate; P o R represents the price of crude oil, in yuan / ton; R represents the comprehensive tax rate, in percent.

3. The method for developing shallow, ultra-thin layers of ordinary heavy oil reservoirs in vertical wells according to claim 1, characterized in that, The method for steam injection and extraction of the target vertical well includes: The injected water is circulated within the water treatment system. The steam generated by heating the circulated injection water in a high-temperature and high-pressure water boiler is then injected into the wellhead through the steam injection pipeline. During the injection process, the steam injection rate is increased to the maximum while ensuring that the injection pressure does not exceed 1.2 times the formation fracturing pressure.

4. The method for developing shallow, ultra-thin layers of ordinary heavy oil reservoirs in vertical wells according to claim 3, characterized in that: During the injection process, the dryness of the steam at the boiler outlet is ≥75%, and the steam injection rate at the vertical well is ≥100t / d.

5. The method for developing shallow, ultra-thin layers of ordinary heavy oil reservoirs in vertical wells according to claim 3, characterized in that, Prior to the injection, the formation fracturing pressure is determined, the method comprising: Obtain the formation fracture constant and formation pressure in the work area; Based on the formation fracturing constant and formation pressure, the formation fracturing pressure is determined using formula (2); P f =0.0223α×H+(1.03-α)×P R (2); In the formula: P f α is the formation fracture pressure, MPa; α is the formation fracture constant; H is the depth in the middle of the reservoir, m; P R ρ represents the formation pressure, in MPa.

6. The method for developing shallow, ultra-thin layers of ordinary heavy oil reservoirs in vertical wells according to claim 5, characterized in that, Determining the formation fracture constant before obtaining it includes the following methods: Obtain the rock pressure gradient, reservoir pressure in the middle, and reservoir depth in the work area; Based on the rock pressure gradient, the pressure in the middle of the reservoir, and the depth in the middle of the reservoir, the formation fracture constant is determined using formula (3); α=0.2307×{0.1×β+4.335×(4.335×C-β)×P / H} (3); In the formula: β is the rock fracture constant; C is the rock pressure gradient, MPa / m; P is the pressure in the middle of the reservoir, MPa; H is the depth in the middle of the reservoir, m.

7. The method for developing shallow, ultra-thin layers of ordinary heavy oil reservoirs in vertical wells according to claim 1, characterized in that, The method for determining the design steam injection volume based on the steam injection intensity includes: Obtain the effective thickness of the oil layer in the work area; Based on the steam injection intensity and the effective thickness of the oil layer, the design steam injection amount is determined using formula (4); Q j =y×h (4) In the formula: y is the steam injection intensity; h is the effective thickness of the oil layer, in meters.

8. The method for developing shallow, ultra-thin layers of ordinary heavy oil reservoirs in vertical wells according to claim 1, characterized in that, The method for determining parameters related to steam injection intensity during steam huff and puff mining includes: Obtain basic parameters of the work area; A geological model is established based on the aforementioned basic parameters, and the steam injection intensity corresponding to each basic parameter under different parameter values ​​is determined through numerical simulation. The grey relational analysis method is used to determine the correlation between each basic parameter and the steam injection intensity. The predetermined number of basic parameters with the highest correlation are the parameters related to the steam injection intensity.

9. The method for developing shallow, ultra-thin layers of ordinary heavy oil reservoirs in vertical wells according to claim 8, characterized in that: The parameters related to steam injection intensity include: cycle number, effective oil layer thickness, fluid production during the elastic extraction stage, and initial oil saturation.

10. The method for developing shallow, ultra-thin layers of ordinary heavy oil reservoirs in vertical wells according to claim 9, characterized in that, The method for determining the steam injection intensity based on the relevant parameters includes: A three-dimensional geological model of the work area was established, and each relevant parameter was determined through numerical simulation. The corresponding steam injection intensity under different parameter values ​​was determined, and the relationship between each relevant parameter and the steam injection intensity was established. Based on the relationship between each relevant parameter and the steam injection intensity, determine the relationship between the steam injection intensity and all relevant parameters; The steam injection intensity is determined based on the relationship between the steam injection intensity and all relevant parameters.

11. The method for developing shallow, ultra-thin layers of ordinary heavy oil reservoirs in vertical wells according to claim 10, characterized in that, The relationship between the steam injection intensity and all relevant parameters is as follows: In the formula: a, b, c, d, e, f, g are coefficients; x1 is the cycle number; x2 is the effective thickness of the oil layer, m; x3 is the fluid production during the elastic extraction stage, t; x4 is the original oil saturation, f.

12. The method for developing shallow, ultra-thin layers of ordinary heavy oil reservoirs in vertical wells according to claim 11, characterized in that: In formula (5), the method for determining the coefficients includes: Based on the different parameter values ​​and their corresponding steam injection intensities, the coefficients are determined using the quasi-Newton method and / or the general global optimization method.

13. The method for developing shallow, ultra-thin layers of ordinary heavy oil reservoirs in vertical wells according to claim 12, characterized in that, The relationship between each relevant parameter and the steam injection intensity includes: y = a × Ln(x1) + g1; y = b × Ln(x²) + g²; y=c×power(x3,2)+d×x3+g3; y=e×power(x4,2)+f×x4+g4; In the formula: a, b, c, d, e, f, g1, g2, g3, g4 are coefficients; x1 is the cycle number; x2 is the effective thickness of the oil layer, m; x3 is the fluid production during the elastic extraction stage, t; x4 is the original oil saturation, f.

14. The method for developing shallow, ultra-thin layers of ordinary heavy oil reservoirs in vertical wells according to claim 1, characterized in that: During the blowout operation, the wellhead production is controlled, wherein the daily fluid production of vertical wells is less than or equal to 20 tons.

15. The method for developing shallow, ultra-thin layers of ordinary heavy oil reservoirs in vertical wells according to claim 1, characterized in that: During the production of the oil pumping unit, the pump efficiency of the oil pumping unit is adjusted so that the daily fluid production of the vertical well is less than or equal to 10 tons.

16. The method for developing shallow, ultra-thin layers of ordinary heavy oil reservoirs in vertical wells according to any one of claims 1-15, characterized in that: Before performing blowout operation on the target vertical well, monitor the wellhead oil pressure and casing pressure. When the oil pressure and casing pressure drop below the predetermined value or remain stable for a predetermined time, open the wellhead to perform blowout operation.

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