Viscosity reduction and production method for deep ultra-heavy oil reservoirs

Abstract

The present application relates to a kind of for deep layer super heavy oil reservoir's viscosity reduction mining method, comprising: obtaining the reservoir evaluation of target well;According to reservoir evaluation, the first theoretical injection amount of carbon dioxide in target well is calculated;According to reservoir evaluation, the second theoretical injection amount of viscosity reducer is calculated;According to the first theoretical injection amount of carbon dioxide, carbon dioxide is injected into target well;According to the second theoretical injection amount of viscosity reducer, viscosity reducer is injected into target well;Fracturing treatment is carried out to the formation of target well using combustion fracturing process;And, mining is carried out using the target well after processing.The present application exerts the synergistic effect of CO2 dissolving light component and viscosity reducer viscosity reduction, realizes physical and chemical double viscosity reduction;Again, by combustion fracturing process, main channel of percolation is obtained, so that oil production rate is significantly improved, and effective use of deep layer super heavy oil reservoir is realized;Solve the core problem of deep layer super heavy oil poor flowability, large percolation resistance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oilfield development, and particularly relates to a viscosity reduction and exploitation method for deep super-heavy oil reservoirs. BACKGROUND

[0002] Global heavy oil resources are abundant. In addition to conventional heavy oil, deep heavy oil reservoirs have a burial depth of more than 2000 m, high formation pressure, and strong heterogeneity, which leads to great development difficulty. Deep heavy oil resources in China are mainly concentrated in Lukuqin Oilfield of Tuha Oilfield, Wangzhuang Oilfield of Shengli Oilfield and other oilfields. These areas have abundant heavy oil resources, and the well depth is generally more than 2000 meters, which is an important area for heavy oil development. Overseas, countries such as Kuwait and Venezuela are representative.

[0003] The development of deep heavy oil has broad prospects, but it also faces a series of technical and economic challenges. According to the viscosity, domestic and foreign methods such as mixing light oil, injecting nitrogen, injecting carbon dioxide, injecting natural gas, injecting oxygen-reduced air, and chemical viscosity reduction and cold production are mainly used. Different regions adopt appropriate exploitation measures according to the differences in oil viscosity, well depth, and reservoirs of different oilfields. The key is to solve the problem of wellbore flowability. The main problems of using conventional steam injection for development are deep burial, high crude oil viscosity, high steam injection pressure, low heat utilization rate, and large heat loss. Taking a deep super-heavy oil reservoir as an example, the well depth can reach 3000 meters, the underground viscosity at 88℃ is 18000 MPa.s, and the formation pressure reaches 30 MPa. If conventional steam stimulation is used, combined with the conditions of surface steam injection, the surface injection is at 280-300℃, the wellhead injection rate is 6-8t / h, the wellhead injection pressure does not exceed the fracture pressure, the bottom hole injection temperature is 200-210℃, and the specific enthalpy is 908.867 KJ / Kg calculated by the international water and steam property equation (IAPWS-IF97). The heat carried is low, and the injected steam in the reservoir is difficult to effectively convert into oil production. Therefore, there are problems such as poor viscosity reduction effect and low single well production.

[0004] The biggest challenge for super-heavy oil is high viscosity and poor flowability. In addition to thermal recovery, physical and chemical methods can be used to reduce viscosity, and the reservoir can be modified to increase permeability and improve recovery.

[0005] Studies have shown that carbon dioxide has a high solubility in heavy oil, such as 105 kg of carbon dioxide can be dissolved in one cubic meter of oil sample under the pressure of 12.49 MPa. Such a large amount of carbon dioxide is completely miscible with heavy oil, which has a great dilution effect, which is one of the main reasons for the great decrease in viscosity of heavy oil and the increase in recovery efficiency. Carbon dioxide viscosity reduction technology has been applied in some oilfields. On the basis of carbon dioxide viscosity reduction technology, carbon dioxide, nitrogen and flue gas huff and puff oil recovery technology is used, and good recovery effect is obtained.

[0006] Oil-soluble viscosity reducer is a widely used viscosity-reducing chemical product. In deep heavy oil reservoirs, it can effectively reduce the viscosity of heavy oil, improve its flowability and increase the recovery efficiency. For example, in Tahe oilfield, AOSV viscosity reducer is used to treat heavy oil with a viscosity of 3892 MPa.s, and the viscosity reduction rate reaches 66.3%.

[0007] For reservoir reconstruction, detonation fracturing technology is a technology that uses explosion energy to produce cracks in the formation to improve the productivity of oil and gas wells; it is mainly used for deblocking fracturing and yield improvement of low-permeability, ultra-low-permeability carbonate rock and sandstone oil and gas layers. If detonation fracturing is used to reconstruct the reservoir in combination with supercritical carbon dioxide and oil-soluble viscosity reducer, the physical and chemical viscosity reduction can be fully utilized, and the permeability of the near-wellbore zone can be increased, so as to realize the exploitation of deep super-heavy oil. However, this technology has not been reported, and there is no relevant experience. How to implement this process in combination with the characteristics of deep super-heavy oil reservoirs, the sequence of implementation, parameter optimization and process design need to be studied and optimized.

[0008] Therefore, there is a need for a viscosity reduction and recovery method for deep super-heavy oil reservoirs. SUMMARY

[0009] To solve all or part of the above problems, the purpose of the present application is to provide a viscosity reduction and recovery method for deep super-heavy oil reservoirs, which effectively solves the core problems of poor flowability and large seepage resistance of deep super-heavy oil.

[0010] According to one aspect of the present application, a viscosity reduction and recovery method for deep super-heavy oil reservoirs is provided, comprising:

[0011] obtaining a reservoir evaluation of a target well;

[0012] According to the reservoir evaluation, a first theoretical injection amount of carbon dioxide in the target well is calculated;

[0013] According to the reservoir evaluation, a second theoretical injection amount of viscosity reducer is calculated;

[0014] According to the first theoretical injection amount of carbon dioxide, carbon dioxide is injected into the target well;

[0015] injecting the viscosity reducer into the target well according to a second theoretical injection amount of the viscosity reducer;

[0016] fracturing the formation of the target well by using the combustion fracturing process; and

[0017] exploiting the target well after the treatment.

[0018] Further, the obtaining the reservoir evaluation of the target well specifically comprises: obtaining the oil saturation, the reservoir thickness and the reservoir porosity of the target well.

[0019] Further, the calculating the first theoretical injection amount of the carbon dioxide in the target well according to the reservoir evaluation further comprises:

[0020] determining the solubility of the carbon dioxide in the crude oil under the temperature and pressure of the oil well;

[0021] obtaining the first action radius of the carbon dioxide in the crude oil;

[0022] calculating the first theoretical injection amount of the carbon dioxide in the target well according to the solubility, the first action radius and the reservoir evaluation.

[0023] Further, the calculating the first theoretical injection amount of the carbon dioxide in the target well according to the solubility, the first action radius and the reservoir evaluation specifically comprises: the first theoretical injection amount of the carbon dioxide in the target well is equal to the product of the circular constant, the square of the first action radius, the reservoir thickness, the reservoir porosity, the oil saturation, the solubility and the density of the carbon dioxide under the temperature and pressure of the oil well.

[0024] Further, the calculating the second theoretical injection amount of the viscosity reducer according to the reservoir evaluation further comprises:

[0025] obtaining the second action radius of the viscosity reducer in the crude oil;

[0026] calculating the second theoretical injection amount of the viscosity reducer according to the second action radius and the reservoir evaluation.

[0027] Further, the calculating the second theoretical injection amount of the viscosity reducer according to the second action radius and the reservoir evaluation specifically comprises: the second theoretical injection amount of the viscosity reducer is equal to the product of the circular constant, the square of the second action radius, the reservoir thickness, the oil saturation, the density of the viscosity reducer under the temperature and pressure of the oil well and the reservoir porosity.

[0028] Further, the injecting the carbon dioxide into the target well according to the first theoretical injection amount of the carbon dioxide further comprises:

[0029] calculating a first theoretical injection intensity of the carbon dioxide according to the first theoretical injection amount of the carbon dioxide and a set range of the first injection intensity;

[0030] calculating a first actual injection intensity of the carbon dioxide according to the first theoretical injection intensity and the set range of the first injection intensity;

[0031] injecting the carbon dioxide of the first theoretical injection amount into the target well according to the first actual injection intensity.

[0032] Further, the injecting the viscosity reducer according to the second theoretical injection amount of the viscosity reducer into the target well further comprises:

[0033] calculating a second theoretical injection intensity of the viscosity reducer according to the second theoretical injection amount of the viscosity reducer;

[0034] calculating a second actual injection intensity of the viscosity reducer according to the second theoretical injection intensity and a set range of the second injection intensity;

[0035] injecting the viscosity reducer of the second theoretical injection amount into the target well according to the second actual injection intensity.

[0036] Further, the fracturing treatment of the formation of the target well by using the fuel explosion fracturing process further comprises:

[0037] calculating a charge amount of the solid propellant grain in the fracturing treatment process;

[0038] fracturing the formation of the target well by using the solid propellant grain of the charge amount.

[0039] Further, the charge amount is equal to a quotient of a first term divided by a second term, the first term is equal to a product of the peak pressure and the wellbore volume, and the second term is equal to a product of the gas constant and the oil well temperature.

[0040] According to the technical solution, the viscosity reduction and mining method for deep super heavy oil reservoirs has the following beneficial effects:

[0041] The comprehensive action benefits maximize the flowability of heavy oil, combines the physicochemical coupling viscosity reduction system and the stereoscopic displacement-percolation coupling mechanism, plays the synergistic effect of the CO2 dissolved light components and the viscosity reduction of the viscosity reducer, realizes the physical and chemical double viscosity reduction, and further obtains the percolation main channel by the fuel explosion fracturing process, and the CO2 and the viscosity reducer form the composite low-viscosity zone percolation front, so that the oil production rate is significantly improved, and the deep super heavy oil reservoir is effectively utilized under the condition of no thermal recovery.

[0042] The present application does not need to consume fresh water resources, and is especially suitable for water-deficient areas; the process measure of the present application is simple, and effectively solves the core problems of poor flowability and large seepage resistance of deep super heavy oil; the present application has the advantages of efficient development, low carbon environmental protection and economy. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 A flow chart of a viscosity reduction and mining method for deep super heavy oil reservoirs according to an embodiment of the present application;

[0044] Figure 2 A process design flow chart of a viscosity reduction and mining method for deep super heavy oil reservoirs according to an embodiment of the present application;

[0045] Figure 3 is a viscosity change chart of the heavy oil of the oil well before and after CO2 and viscosity reducer are added;

[0046] Figure 4 is a production change chart of the oil well before and after CO2 and viscosity reducer are added;

[0047] Figure 5 is a viscosity field partition change chart during viscosity reduction and efficiency improvement mining of deep super heavy oil reservoirs;

[0048] Figure 6 is Figure 5 is a top view corresponding to the viscosity field partition change chart during viscosity reduction and efficiency improvement mining of deep super heavy oil reservoirs. DETAILED DESCRIPTION

[0049] In order to better understand the purpose, structure and function of the present application, a viscosity reduction and mining method for deep super heavy oil reservoirs will be further described in detail below in combination with the drawings.

[0050] The viscosity reduction and mining method for deep super heavy oil reservoirs according to the embodiment of the present application first relies on the characteristics of supercritical carbon dioxide, such as gas diffusion, liquid solubility and solubility of light components of crude oil, to reduce the injection pressure of the oil reservoir and improve the seepage conditions of the near wellbore zone; secondly, the oil-soluble viscosity reducer is injected into the formation after being pressurized, which reduces the viscosity of the heavy oil, increases the flowability of the heavy oil, and further expands the action radius and the range of low-viscosity heavy oil; finally, the deflagration fracturing technology is adopted, the number of deflagration fracturing and the action radius are designed according to the characteristics of different oil reservoirs, a plurality of cracks are formed, the permeability of the reservoir is improved, the low-viscosity heavy oil after the action of supercritical carbon dioxide and oil-soluble viscosity reducer is easily mined, a pressure drop funnel is formed, and stable production is continued.

[0051] Among them, the deep super heavy oil reservoir according to the embodiment of the present application generally refers to an oil reservoir with a ground crude oil viscosity greater than 150000 MPa.s and a well depth exceeding 2000 meters, and the deep super heavy oil reservoir according to the embodiment of the present application includes offshore heavy oil reservoirs and onshore heavy oil reservoirs.

[0052] Specifically, as shown in FIG. 1, a method for viscosity reduction and exploitation of deep super heavy oil reservoirs according to an embodiment of the present application comprises the following steps: Figure 1

[0053] Step S001: obtaining reservoir evaluation of a target well;

[0054] Step S002: calculating a first theoretical injection amount of carbon dioxide in the target well according to the reservoir evaluation;

[0055] Step S003: calculating a second theoretical injection amount of viscosity reducer according to the reservoir evaluation;

[0056] Step S004: injecting carbon dioxide into the target well according to the first theoretical injection amount of carbon dioxide;

[0057] Step S005: injecting viscosity reducer into the target well according to the second theoretical injection amount of viscosity reducer;

[0058] Step S006: performing fracturing treatment on the formation of the target well by using combustion fracturing process; and

[0059] Step S007: exploiting the target well after the treatment.

[0060] For deep super heavy oil reservoirs (formation pressure reaches 30 MPa, formation breakdown pressure is 51 MPa), the crude oil viscosity is high (underground crude oil viscosity is more than 10,000 MPa.s), and the starting pressure gradient is large (usually reaches 10 MPa / m). When not injecting gas for dissolution viscosity reduction and directly injecting viscosity reducer in the conventional way, the viscosity reducer can play a viscosity reduction effect only when it reaches a fully mixed state with the crude oil. Reaching the fully mixed state requires a certain amount of time on the one hand, and on the other hand, since the viscosity reducer is a liquid, it has the characteristics of poor compressibility and fast pressure transmission speed. Therefore, in order to avoid exceeding the formation breakdown pressure and causing process failure, the injection speed and injection amount of the viscosity reducer need to be controlled. According to the calculation of the starting pressure gradient, the effective swept range of the viscosity reducer for viscosity reduction is at most 2 m away from the wellbore center.

[0061] ​When CO2 is injected first and then the viscosity reducer is injected according to the present process, because CO2 has reached a supercritical state under the condition of 30 MPa, the dissolving viscosity-reducing effect of CO2 will be quickly exerted, and the injection pressure of this process can be ignored. After the viscosity reducer is injected, in addition to the CO2 dissolved in the near-well crude oil, the CO2 free in the formation fluid and the CO2 in the wellbore will be migrated to the far-well area 5-15 m away from the wellbore center under the driving action of the viscosity reducer (similar to the piston effect). In this process, the crude oil dissolved with CO2 has a lower viscosity and a smaller migration resistance of the viscosity reducer, and the free CO2 reaches a supercritical state and does not have a Jamin effect, but adds a part of migration resistance. The change of the two resistances is superimposed, which will affect the injection pressure of the viscosity reducer. This effect will be different according to the different dissolving viscosity-reducing effects of CO2 on the crude oil, and should be determined according to the situation. According to experimental experience, in a deep heavy oil reservoir (formation pressure reaches 30 MPa), the viscosity reduction rate of the crude oil saturated with CO2 can usually reach more than 75%. At this time, the injection pressure of the viscosity reducer can be slightly increased, but will not exceed the formation fracture pressure (51 MPa) and the pumping pressure range.

[0062] Therefore, in the embodiment of the present application, CO2 can realize viscosity reduction in the far-well area 5-15 m away from the wellbore center under the driving action of the viscosity reducer, and the main action range of the viscosity reducer is the near-well area 2-5 m away from the wellbore center. Therefore, compared with the prior art, the present application realizes viscosity reduction in the far-well area 5-15 m away from the wellbore.

[0063] In the step S001, the oil reservoir evaluation of the target well is obtained, which specifically includes obtaining the crude oil saturation, the oil well reservoir thickness and the oil reservoir porosity of the target well.

[0064] For the step S001 of obtaining the oil reservoir evaluation of the target well, the purpose is to make a detailed oil reservoir description of the target well, so as to evaluate the exploitation potential of the oil well by using indoor experiments combined with numerical simulation methods. The oil reservoir evaluation includes parameters such as the depth of the oil well, the oil well reservoir thickness, the lithology of the reservoir, the porosity, the permeability, the crude oil viscosity, the crude oil saturation and the like.

[0065] After obtaining the oil reservoir evaluation of the target well, it further includes obtaining basic experimental data such as oil and water analysis, sampling and analyzing the oil and water samples of the target well, and obtaining basic data such as the composition of the crude oil, the carbon number distribution, the thermal physical properties, the mineral composition of water, the salinity and the like.

[0066] In the step S002, the first theoretical injection amount of carbon dioxide in the target well is calculated according to the oil reservoir evaluation, which further includes:

[0067] The solubility of carbon dioxide in the crude oil under the temperature and pressure of the oil well is determined;

[0068] The first action radius of carbon dioxide in the crude oil is obtained;

[0069] According to the solubility, the first action radius and the oil reservoir evaluation, the first theoretical injection amount of carbon dioxide in the target well is calculated.

[0070] Specifically, by carrying out high-temperature and high-pressure physical property experiments of the target crude oil under the conditions of formation temperature and pressure, the changes of the viscosity, volume coefficient and other properties of the crude oil before and after dissolving CO2 are obtained, so as to obtain the solubility of carbon dioxide in the crude oil. The CO2 in the embodiment of the present application refers to supercritical carbon dioxide, that is, carbon dioxide exceeding the critical condition, that is, CO2 under the condition of temperature greater than 31.04℃ and pressure greater than 7.377 MPa.

[0071] For supercritical carbon dioxide: for example, the carbon dioxide gas is compressed to supercritical pressure (combined with the reservoir pressure, generally compressed to more than 25 MPa) by using a compressor, and then the compressed carbon dioxide is heated to supercritical temperature (generally heated to more than 31.1℃) by using a heat exchanger. The compressor for compressing carbon dioxide can be commonly used in the art, and the heating method can be commonly used in the art.

[0072] The supercritical carbon dioxide is injected into the oil well by the high-pressure pump and the injection pipeline. During the injection process, the parameters such as the pressure, temperature and flow rate of carbon dioxide should be monitored in real time, so as to adjust the first theoretical injection amount of carbon dioxide according to the monitoring results, so as to ensure the stability and effectiveness of the injection process.

[0073] In specific implementation, the first theoretical injection amount of injected carbon dioxide is determined in combination with the different needs of different reservoirs, in combination with the porosity, thickness, oil saturation, crude oil viscosity, carbon dioxide solubility and other parameters of the oil well.

[0074] Finally, the first theoretical injection amount of carbon dioxide is obtained by indoor experiment, and the indoor experiment refers to the PVT analysis experiment of heavy oil.

[0075] Specifically, according to the solubility, the first action radius and the oil reservoir evaluation, the first theoretical injection amount of carbon dioxide in the target well is calculated. Specifically, the first theoretical injection amount of carbon dioxide in the target well is equal to the product of the circular constant, the square of the first action radius, the reservoir thickness of the oil well, the porosity of the reservoir, the saturation of the crude oil, the solubility and the density of carbon dioxide under the temperature and pressure of the oil well. That is, the first theoretical injection amount of carbon dioxide can be calculated by the following formula one:

[0076]

[0077] In formula one, represents the first theoretical injection amount of carbon dioxide in the target well, and the unit is ton (t); represents a first action radius of carbon dioxide in crude oil, and a unit is meter (m) ; h represents a reservoir thickness of an oil well, and a unit is meter (m) ; and φ represents a reservoir porosity; represents a crude oil saturation; represents a solubility of carbon dioxide in crude oil, and a unit is cubic meter per cubic meter (m 3 / m 3 ) ; represents a density of carbon dioxide under a temperature and pressure of an oil well, and a unit is ton per cubic meter (t / m 3 ) ; wherein, the first action radius of carbon dioxide in crude oil is generally considered as 5-15 meters; and the solubility of carbon dioxide in crude oil is obtained by an experimental method.

[0078] The purpose of injecting carbon dioxide into the target well is to reduce reservoir pressure and improve percolation conditions of heavy oil in the reservoir by using low viscosity and high diffusion of carbon dioxide.

[0079] In the step S003, before the second theoretical injection amount of the viscosity reducer is calculated according to the reservoir evaluation, the adaptability and viscosity reduction effect of the viscosity reducer under the temperature and pressure of the formation are evaluated.

[0080] In the step S003, the second theoretical injection amount of the viscosity reducer is calculated according to the reservoir evaluation, and the step further includes:

[0081] a second action radius of the viscosity reducer in crude oil is obtained;

[0082] the second theoretical injection amount of the viscosity reducer is calculated according to the second action radius and the reservoir evaluation.

[0083] The viscosity reducer in the embodiment of the present application refers to an oil-soluble viscosity reducer, that is, a chemical additive capable of reducing the viscosity of crude oil. The effective component of the viscosity reducer can interact with components such as resin and asphaltene in crude oil, thereby destroying or weakening the aggregate association between these components, and further reducing the viscosity of crude oil and improving the flowability of crude oil.

[0084] In the embodiment of the present application, the oil-soluble viscosity reducer is injected through an oil well by a high-pressure pump and an injection pipeline. During the injection process, parameters such as the pressure, temperature and flow of carbon dioxide are monitored in real time, so as to adjust the second theoretical injection amount of the viscosity reducer according to the monitoring results, so as to ensure the stability and effectiveness of the injection process.

[0085] In specific implementation, the second theoretical injection amount of the viscosity reducer is determined in combination with different needs of different reservoirs, in combination with parameters such as the porosity, thickness, oil saturation, viscosity of crude oil, viscosity reduction rate after the viscosity reducer is mixed with crude oil, and the like.

[0086] Finally, the second theoretical injection amount of the viscosity reducer is obtained according to numerical simulation and experimental analysis, and the second theoretical injection amount of the viscosity reducer is equal to the product of the circular constant, the square of the second action radius, the oil well reservoir thickness, the crude oil saturation, the density of the viscosity reducer under the oil well temperature and pressure and the reservoir porosity; that is, the second theoretical injection amount of the viscosity reducer can be calculated by formula two:

[0087]

[0088] In formula two, the second theoretical injection amount of the viscosity reducer is represented, and the unit is ton (t); the second action radius of the viscosity reducer in the crude oil is represented, and the unit is meter (m); the physical meaning of φ is the same as that in formula one, the reservoir porosity is represented, h represents the oil well reservoir thickness, and the unit is meter (m), the density of the viscosity reducer under the oil well temperature and pressure is represented, and the unit is ton per cubic meter (t / m 3 ), and is usually 1; the crude oil saturation is represented; for the viscosity reducer, the second action radius thereof in the crude oil is generally 2-5 meters; and for the viscosity reduction rate of the mixture of the viscosity reducer and the crude oil, the viscosity reduction rate is obtained by experimental method.

[0089] The numerical simulation needs to be combined with experimental data or calculated data of heavy oil PVT analysis, the experimental analysis refers to the viscosity reduction experiment of the oil-soluble viscosity reducer under the formation condition, the viscosity reduction rate of the mixture of the viscosity reducer and the crude oil and other parameters can be obtained through the experimental analysis, and the feasibility of using the viscosity reducer to reduce viscosity is also explained.

[0090] The purpose of injecting the viscosity reducer into the target well in the embodiment of the application is to reduce the viscosity of the heavy oil and improve the flowability of the heavy oil.

[0091] The step S004 of injecting the carbon dioxide into the target well according to the first theoretical injection amount of the carbon dioxide further includes:

[0092] The first theoretical injection intensity of the carbon dioxide is calculated according to the first theoretical injection amount of the carbon dioxide;

[0093] The first actual injection intensity of the carbon dioxide is calculated according to the first theoretical injection intensity and the set range of the first injection intensity;

[0094] The first theoretical injection amount of the carbon dioxide is injected into the target well according to the first actual injection intensity.

[0095] Specifically, the injection intensity refers to the injection amount per unit thickness of the oil well reservoir. After the first theoretical injection amount of carbon dioxide is calculated, the first theoretical injection intensity of carbon dioxide can be calculated according to the first theoretical injection amount of carbon dioxide and the thickness of the oil well reservoir, that is, the first theoretical injection intensity of carbon dioxide can be calculated by the following formula three:

[0096]

[0097] In formula three, represents the first theoretical injection intensity of carbon dioxide, and the unit is ton / meter (t / m).

[0098] In specific implementation, the range of the set first injection intensity is 5.6 t / m-30.9 t / m; according to the first theoretical injection intensity and the range of the set first injection intensity, the first actual injection intensity of carbon dioxide is calculated as follows: it is determined whether the calculated first theoretical injection intensity of carbon dioxide is within the range of the set first injection intensity, if yes, the first theoretical injection intensity of carbon dioxide is equal to the first actual injection intensity of carbon dioxide; if no, the boundary value close to the first theoretical injection intensity in the aforementioned range is selected as the first actual injection intensity of carbon dioxide.

[0099] After the first actual injection intensity of carbon dioxide is calculated, the first theoretical injection amount of carbon dioxide is injected into the target well according to the first actual injection intensity.

[0100] The step S005 of injecting the viscosity reducer into the target well according to the second theoretical injection amount of the viscosity reducer further includes:

[0101] The second theoretical injection intensity of the viscosity reducer is calculated according to the second theoretical injection amount of the viscosity reducer;

[0102] The second actual injection intensity of the viscosity reducer is calculated according to the second theoretical injection intensity and the range of the set second injection intensity;

[0103] The second theoretical injection amount of the viscosity reducer is injected into the target well according to the second actual injection intensity.

[0104] Specifically, after the second theoretical injection amount of the viscosity reducer is calculated, the second theoretical injection intensity of the viscosity reducer can be calculated according to the second theoretical injection amount of the viscosity reducer and the thickness of the oil well reservoir, that is, the second theoretical injection intensity of the viscosity reducer can be calculated by the following formula four:

[0105]

[0106] In formula four, represents the second theoretical injection intensity of the viscosity reducer, and the unit is ton / meter (t / m).

[0107] In the implementation, the range of the set second injection intensity is 2.4 t / m-10.2 t / m; according to the second theoretical injection intensity and the range of the set second injection intensity, the second actual injection intensity of the viscosity reducer is calculated as follows: it is determined whether the calculated second theoretical injection intensity of the viscosity reducer is within the range of the set second injection intensity, if yes, the second theoretical injection intensity of the viscosity reducer is equal to the second actual injection intensity of the viscosity reducer; if no, the boundary value of the range close to the second theoretical injection intensity is selected as the second actual injection intensity of the viscosity reducer.

[0108] After the second actual injection intensity of the viscosity reducer is calculated, the second theoretical injection amount of the viscosity reducer is injected into the target well according to the second actual injection intensity.

[0109] The step S006 of fracturing the formation of the target well by using the combustion fracturing process further includes:

[0110] The charge amount of the solid propellant charge column in the combustion fracturing process is calculated.

[0111] The formation of the target well is fractured by using the solid propellant charge column with the charge amount.

[0112] The combustion fracturing process of the embodiment refers to a process of using explosion energy to generate cracks in the formation, thereby improving the permeability of the reservoir and improving the productivity of the oil and gas well. In the implementation, the number of combustion fracturing in the same well section can be optimized according to the characteristics of different reservoirs, so as to further expand and optimize the crack network.

[0113] For the step S006, the charge amount of the solid propellant charge column is equal to the quotient of the first term divided by the second term, the first term is equal to the product of the peak pressure and the wellbore volume, and the second term is equal to the product of the gas constant and the oil well temperature, that is, the charge amount of the solid propellant charge column can be calculated by the following formula five:

[0114]

[0115] In formula five, represents the charge amount of the solid propellant charge column, and the unit is kilogram (Kg); represents the peak pressure in the combustion fracturing process, and the unit is pascal (Pa); V represents the wellbore volume, and the unit is cubic meter (m 3 ); R represents the gas constant, and the unit is J / (Kg·K); and T represents the oil well temperature, and the unit is Kelvin (K).

[0116] In the embodiment, the solid propellant charge is loaded into the perforating gun with an opening, and then the high-pressure gas generated by combustion is used to fracture the stratum to form multiple cracks and improve the permeability of the stratum.

[0117] Through multiple experiments, it is determined that the radius of action of the deflagration fracturing process is 5-25 meters.

[0118] For different types of heavy oil reservoirs, the arrangement combination and parameter optimization of the supercritical carbon dioxide, oil-soluble viscosity reducer and deflagration fracturing process are used in the embodiment to ensure the production effect of the production step.

[0119] The production effect of the embodiment is mainly affected by the viscosity of heavy oil, drainage radius and the like.

[0120] Specifically, the viscosity reduction production method for deep heavy oil reservoirs in the embodiment is used to obtain the production capacity formula as follows.

[0121]

[0122] In formula six, represents the oil production of the target well per day, and the unit is cubic meters per day (m3 / d); A is a time conversion coefficient, and the unit is 10 9 s / d, and the value is 11600; represents the formation pressure difference, and the unit is megapascal (MPa); K represents the original permeability of the formation, and the unit is 10 -3 μm 2 ; represents the relative permeability of the oil phase; H represents the length of the vertical well section, and the unit is meters (m); represents the viscosity of the heavy oil after CO2 injection and viscosity reducer, and the unit is megapascal second (MPa.s); represents the viscosity of the heavy oil in the cold zone, and the unit is megapascal second (MPa.s); S represents the skin factor; represents the maximum value of the action radius in the CO2 injection viscosity reduction, viscosity reducer viscosity reduction and deflagration fracturing process, and the unit is meters (m); R e represents the drainage radius, and the unit is meters (m); represents the minimum value of the action radius in the CO2 injection viscosity reduction, viscosity reducer viscosity reduction and deflagration fracturing process, and the unit is meters (m).

[0123] In formula six, for , the viscosity of the heavy oil after adding a certain amount of carbon dioxide and viscosity reducer under the formation pressure is measured through the PVT experiment, and the viscosity corresponding to the combined effect of the two is obtained; for It is obtained according to the measure demand of the oil well, and generally ranges from 12m to 45m; and for the skin factor S, it is obtained through indoor experiment and / or numerical simulation method.

[0124] For the drainage radius R e , under the synergistic effect of fluid viscosity reduction, fracture propagation, phase change and other multi-physical fields, the formula thereof under the steady state condition in the embodiment of the application is as follows:

[0125]

[0126] In formula seven, K B represents the equivalent permeability of the near wellbore zone, and the unit is 10 -3 μm 2 ; ω is a coefficient related to viscosity, and the unit is (10 -9 MPa·s) -1 , and generally takes a value of 0.0036; t represents the production time, and the unit is second (s); and φ is the same as above, and represents the porosity of the reservoir; represents the comprehensive compressibility, and the unit is 1 / MPa.

[0127] The purpose of calculating the oil production in the application is to facilitate the control of the production system and avoid the sand production caused by production stimulation. That is, in the specific implementation, for the exploitation of step S007, the oil production is first calculated, and then the target well is exploited according to the oil production.

[0128] The viscosity reduction exploitation method for deep super heavy oil reservoirs in the embodiment of the application has the following beneficial effects:

[0129] The comprehensive action benefit realizes the maximization of the flowability of heavy oil, combines the physicochemical coupling viscosity reduction system and the stereoscopic displacement-percolation coupling mechanism, plays the synergistic effect of CO2 dissolution light component and viscosity reducer viscosity reduction, realizes physical and chemical double viscosity reduction, and then obtains the percolation main channel through the combustion and explosion fracturing process, and the CO2 and viscosity reducer form a composite low viscosity zone percolation front, so that the oil production rate is significantly improved.

[0130] The embodiment of the application realizes the effective utilization of deep super heavy oil reservoirs under the condition of no thermal recovery, and in the specific implementation, the process combination can be selected and optimized according to the reservoir characteristics, the advantages of multiple processes are integrated, and the use amount of chemical agents and carbon dioxide is reduced, for example, the recommended injection intensity of carbon dioxide for the medium-high permeability reservoir is 25-55t / m, and the injection intensity of carbon dioxide in the embodiment of the application is 5.6-30.9t / m, that is, the range of the injection intensity of carbon dioxide is reduced, and the economic benefit is optimized; at the same time, after the process is implemented, due to the formation of the pressure funnel, the natural energy (formation pressure, gravity) drives the low viscosity crude oil to the wellbore, which is beneficial to prolong the stable production period.

[0131] Zero water consumption and ecological friendliness: the embodiment of the present application avoids the high temperature (>300℃) and high pressure risk of steam heat extraction, reduces the damage to the wellbore and casing; the embodiment of the present application does not consume fresh water resources, and is especially suitable for water-deficient areas; the process measures of the embodiment of the present application are simple, and effectively solve the core problems of poor fluidity and large seepage resistance of deep super heavy oil; the embodiment of the present application has the advantages of efficient development, low carbon environmental protection and economy.

[0132] The following takes a deep super heavy oil well in a land oilfield as an example to illustrate the viscosity reduction and mining method of the embodiment of the present application.

[0133] The 50℃ ground degassed crude oil viscosity of the heavy oil reservoir is 280000MPa.s, the well depth of the oil well is 2743m, and it belongs to a deep super heavy oil reservoir. The permeability of the oil well is 1600mD, the oil layer thickness is 23m, and the formation pressure is 31.3MPa.

[0134] Before specific mining, the supercritical carbon dioxide, oil-soluble viscosity reducer and detonation fracturing combined process are used.

[0135] Reference Figure 2 , first, the reservoir evaluation of the target well is obtained, the target well is described in detail according to the obtained reservoir evaluation of the target well, the depth, thickness, lithology, porosity, permeability, crude oil viscosity and other parameters of the oil well are determined, and the mining potential of the oil well is evaluated; through indoor experimental research, the solubility of carbon dioxide in crude oil under the temperature and pressure of the oil well is determined by experimental method, and under the formation pressure and formation temperature, the solubility of CO2 in heavy oil is 0.8 m 3 / m 3 When calculating, the viscosity of the heavy oil is 915.6 MPa.s, which can be further reduced after adding the oil-soluble viscosity reducer, and the viscosity can be reduced to 360~550 MPa.s under different amounts, and after adding CO2 and the viscosity reducer, the production capacity of the target well is obviously improved, specifically, the heavy oil viscosity change of the oil well before and after adding CO2 and the viscosity reducer is as shown in Figure 3 , as shown in Figure 3 , it can be known that the addition of supercritical CO2 and the viscosity reducer can significantly reduce the viscosity of the heavy oil, and the production change of the oil well before and after adding CO2 and the viscosity reducer is as shown in Figure 4 , as shown in Figure 4 , it can be known that the production of the same oil well is obviously improved after adding CO2 and the viscosity reducer.

[0136] Secondly, reference is made to Figure 5 and Figure 6: For the c area far from the wellbore, the main viscosity reduction effect is CO2, and the effect of the viscosity reducer is small; for the a area close to the wellbore, the viscosity reduction effect is CO2 and the viscosity reducer; for the b area between the c area and the a area, the viscosity reduction effect is mainly the viscosity reduction effect of the viscosity reducer, and the viscosity reduction effect of CO2 is auxiliary. Therefore, the viscosity reduction of the chemical viscosity reducer and the viscosity reduction of CO2 in the embodiment of the application realize the viscosity reduction of each area from near to far.

[0137] To realize the viscosity reduction and mining of deep super heavy oil, the influence of different processes needs to be fully considered, and the overall mining effect is combined. First, the amount of carbon dioxide injection is calculated. The well depth of the well is 2743m, the oil well reservoir thickness is 23m, the oil reservoir porosity is 17.8%, the 50℃ ground degassed crude oil viscosity is 280000MPa.s, the oil saturation is 70%, the formation pressure is 31.3MPa, the CO2 solubility in heavy oil is 0.8m 3 / m 3 , the first action radius is 8m, the CO2 density is 0.72t / m 3 under the conditions of 30MPa and 60℃, the first theoretical injection amount of carbon dioxide is 332t, the first theoretical injection intensity corresponding to the oil well reservoir thickness of the oil well is 14.4t / m, and the first injection intensity is within the set range.

[0138] Then the calculation of the injection of the viscosity reducer is performed. The oil well reservoir thickness is 23m, the oil reservoir porosity is 17.8%, the oil saturation is 70%, the second action radius of the viscosity reducer in the crude oil is 3m, the second theoretical injection amount of the viscosity reducer is 81t, the second theoretical injection intensity corresponding to the oil well reservoir thickness of the oil well is 3.52t / m, and the second injection intensity is within the set range.

[0139] Finally, the design of the deflagration fracturing process is performed. The peak pressure, that is, the formation breakdown pressure, needs to be determined through rock mechanics experiments or empirical formulas. The sandstone breakdown pressure is generally about 80-120MPa. The molar mass of the propellant can be calculated using the general gas constant. In the charge amount design of the deflagration fracturing, according to the outer diameter of the 5in oil pipe being 127mm, the oil well reservoir thickness being 23m, the wellbore volume being about 0.112 cubic meters, the peak pressure being 100MPa, and the oil well temperature being 60℃, the calculated charge amount is 168kg-1121kg. In specific implementation, the amount can be adjusted according to the length of the well section to be modified. In operation, the solid propellant charge is loaded into the perforating gun with openings, and after being lowered to the modified well section position, high-pressure gas generated by combustion is used to fracture the formation to form multiple cracks to improve the permeability of the reservoir.

[0140] Taking the implementation case as an example, the mining effect of the process is simulated and predicted through indoor experiments and theoretical calculations. FromFigure 4 The simulation prediction result in the table can show that for the deep super heavy oil well, the cold production mode has almost no production, which shows that the oil well cannot obtain the production capacity without the efficiency increasing measures; when the process method is adopted, the production is greatly increased, and through analogy and numerical simulation calculation, it is shown that the daily production is increased from 0.8 cubic meters to 17 cubic meters. Therefore, the physical and chemical dual viscosity reduction of the embodiment can effectively solve the poor flowability problem of the super heavy oil formation, and the burst fracture provides a main seepage channel for the subsequent continuous and stable production.

[0141] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in the present application should be understood as the general meanings understood by the skilled person in the field to which the present application belongs.

[0142] In addition, the terms "one", "two" and the like are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implying the number of the indicated technical features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly specified and limited.

[0143] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection", "fixing" and the like should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integrated; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0144] Finally, it should be pointed out that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the description of the present application. Especially, as long as there is no structural conflict, each technical feature mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. A viscosity-reducing extraction method for deep extra-heavy oil reservoirs, wherein the deep extra-heavy oil reservoir refers to a reservoir with a surface crude oil viscosity greater than 150,000 MPa.s and a well depth exceeding 2,000 meters, characterized in that, include: Obtain reservoir evaluation for the target well; Based on the reservoir evaluation, the first theoretical injection rate of carbon dioxide in the target well was calculated. Based on the reservoir evaluation, the second theoretical injection volume of the viscosity reducer was calculated; Carbon dioxide is injected into the target well according to the first theoretical injection volume of carbon dioxide; The viscosity reducer is injected into the target well according to the second theoretical injection volume of the viscosity reducer; The formation of the target well was fracturing using a combustion-explosive fracturing process; as well as, The treated target well will be used for extraction. The specific steps for obtaining reservoir evaluation of the target well are: obtaining the crude oil saturation, reservoir thickness, and reservoir porosity of the target well; Based on the reservoir evaluation, the first theoretical injection rate of carbon dioxide in the target well is further calculated, including: The solubility of carbon dioxide in crude oil was determined under the temperature and pressure conditions of an oil well. To determine the first radius of action of carbon dioxide in crude oil; Based on the solubility, the first radius of action, and the reservoir evaluation, the first theoretical injection amount of carbon dioxide in the target well is calculated. The first theoretical injection amount of carbon dioxide in the target well is equal to the product of pi, the square of the first radius of action, the reservoir thickness, the reservoir porosity, the crude oil saturation, the solubility, and the density of carbon dioxide at the temperature and pressure of the well. The step of injecting carbon dioxide into the target well according to the first theoretical injection amount of carbon dioxide further includes: The first theoretical injection intensity of carbon dioxide is calculated based on the first theoretical injection amount of carbon dioxide, wherein the first theoretical injection intensity of carbon dioxide is equal to the first theoretical injection amount of carbon dioxide divided by the thickness of the oil well reservoir. Based on the first theoretical injection intensity and the set range of the first injection intensity, the first actual injection intensity of carbon dioxide is calculated; the set range of the first injection intensity is 5.6 tons / meter to 30.9 tons / meter. Inject a first theoretical amount of carbon dioxide into the target well according to the first actual injection intensity; Specifically, the calculation of the first actual injection intensity of carbon dioxide based on the first theoretical injection intensity and the set range of the first injection intensity is as follows: it is determined whether the calculated first theoretical injection intensity of carbon dioxide is within the set range of the first injection intensity. If it is, the first theoretical injection intensity of carbon dioxide is equal to the first actual injection intensity of carbon dioxide; if not, the boundary value of the aforementioned range close to the first theoretical injection intensity is selected as the first actual injection intensity of carbon dioxide.

2. The method according to claim 1, characterized in that, The calculation of the second theoretical injection volume of the viscosity reducer based on the reservoir evaluation further includes: The second radius of action of the viscosity reducer in crude oil was obtained; Based on the second radius of action and the reservoir evaluation, the second theoretical injection amount of the viscosity reducer is calculated.

3. The method according to claim 2, characterized in that, The second theoretical injection amount of the viscosity reducer, calculated based on the second radius of action and the reservoir evaluation, is specifically: the second theoretical injection amount of the viscosity reducer is equal to the product of pi, the square of the second radius of action, the reservoir thickness, the crude oil saturation, the density of the viscosity reducer under the oil well temperature and pressure, and the reservoir porosity.

4. The method according to claim 1, characterized in that, The step of injecting the viscosity reducer into the target well according to the second theoretical injection volume of the viscosity reducer further includes: The second theoretical injection intensity of the viscosity reducer is calculated based on the second theoretical injection amount of the viscosity reducer, wherein the second theoretical injection intensity of the viscosity reducer is equal to the second theoretical injection amount of the viscosity reducer divided by the thickness of the oil well reservoir. Based on the second theoretical injection intensity and the set range of the second injection intensity, the second actual injection intensity of the viscosity reducer is calculated. The set range of the second injection intensity is 2.4 tons / meter to 10.2 tons / meter. Inject the second theoretical amount of viscosity reducer into the target well according to the second actual injection intensity; The second actual injection intensity of the viscosity reducer is calculated based on the second theoretical injection intensity and the set range of the second injection intensity. Specifically, it is determined whether the calculated second theoretical injection intensity of the viscosity reducer is within the set range of the second injection intensity. If it is, the second theoretical injection intensity of the viscosity reducer is equal to the second actual injection intensity of the viscosity reducer. If not, the boundary value of the aforementioned range close to the second theoretical injection intensity is selected as the second actual injection intensity of the viscosity reducer.

5. The method according to claim 1, characterized in that, The fracturing treatment of the formation in the target well using the combustion and explosion fracturing process further includes: The amount of solid propellant in the combustion-explosion fracturing process was calculated. The formation of the target well is fracturing using a solid propellant charge of the specified amount.

6. The method according to claim 5, characterized in that, The charge amount is equal to the quotient of the first term divided by the second term, where the first term is equal to the product of the peak pressure and the wellbore volume, and the second term is equal to the product of the gas constant and the well temperature.

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