Production cycle calculation method for in-situ conversion of oil shale by using high-salinity brine composite electric heating

Abstract

The invention belongs to the technical field of oil shale recovery efficiency improvement, and discloses a production cycle calculation method for in-situ conversion of oil shale through composite electric heating of high-salinity brine, and the method comprises the following steps: selecting two horizontal wells which are opposite up and down as an electric heating positive electrode and an electric heating negative electrode respectively; fracturing is conducted on the two horizontal wells, and fracturing fluid is retained in a fracturing crack net; the two horizontal wells are powered on, and the shale reservoir is heated; in the heating process, the time of the temperature rising stage of the electric heating stratum, the time # imgabs 0 # of the upward migration stage of oil gas generated by thermal cracking conversion of organic matter in the oil shale reservoir under the action of buoyancy and # imgabs 1 # of the upper horizontal well opening production time are calculated; and calculating the production cycle of the high-salinity brine composite electric heating in-situ conversion oil shale according to the results. According to the method, the time required by each stage is calculated respectively, and the total time of in-situ conversion production of the oil shale for one period when the oil shale uses the electric heating method is finally obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of oil shale enhanced recovery, and in particular relates to a production cycle calculation method for in-situ conversion of oil shale using high-mineralization brine composite electric heating. Background Art

[0002] In-situ conversion technology is the trend of oil shale resource development. The underground in-situ conversion of oil shale is a physical and chemical process that uses electric heating light-weighting technology to convert heavy oil, asphalt and various organic matter in shale with a burial depth of 300~3000 m into light oil and natural gas on a large scale. It has obvious advantages in clean mining, total scale and output quality. Based on the mechanism of hydrocarbon generation and expulsion of organic matter, the study believes that in the low-maturity (Ro value less than 1.0%) organic-rich shales in continental facies, the retained liquid hydrocarbons account for about 25% of the total oil generation, and the unconverted organic matter accounts for 40%~100%. Organic-rich shales suitable for underground in-situ conversion must meet the following conditions: the TOC value of the concentrated section of the shale is greater than 6%, and the higher the better; the Ro value is 0.5%~1.0%; the thickness is greater than 15m; the burial depth is less than 3000 m and the area is greater than 50 km 2 ; The top and bottom plates of the shale section have good sealing properties; the formation water content is less than 5%.

[0003] In traditional oil shale heating conversion experiments or simulations, there have been a large number of research cases on the hydrocarbon generation conversion time of oil shale under high temperature conditions, but calculations for the entire production cycle from oil shale heating to oil and gas generation and production are still lacking. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the main purpose of the present invention is to provide a method for calculating the production cycle of in-situ conversion of oil shale using high-mineralization brine composite electric heating, so as to calculate the time of electric heating and the production cycle during the in-situ mining of oil shale.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A production cycle calculation method for in-situ conversion of oil shale using high-mineralization brine composite electric heating includes the following process: Two horizontal wells facing each other are selected as positive and negative electrodes for electric heating respectively; the upper horizontal well is used as an oil and gas production well, and both horizontal wells are subjected to fracturing operations, and the fracturing fluid is selected as high-mineralized salt water. After the fracturing operation is completed, the fracturing fluid is retained in the fracturing network; An oil and gas production wellhead device is installed on the wellhead of the upper horizontal well, and a wellhead device is installed on the lower horizontal well; The two horizontal wells are electrified, and the fracturing fluid retained in the formation generates heat as a conductive medium, heating the shale reservoir, and the formation temperature rises; During the heating process, calculate the time of the electric heating formation temperature rise stage , where the formation temperature rise stage is the stage where the organic matter in the oil shale reservoir has not yet been thermally cracked; the time of the thermal cracking and conversion stage of the organic matter in the oil shale reservoir is calculated ; Calculate the time of the upward migration stage of oil and gas generated by thermal cracking of organic matter under the action of buoyancy ; Calculate the production time of the upper horizontal well ; Calculation of the production cycle of in-situ conversion of oil shale by composite electric heating of high-salinity brine .

[0006] Preferably, the temperature dividing point between the formation temperature rising stage and the thermal cracking conversion stage of organic matter in the oil shale reservoir is 350°C.

[0007] Preferably, the time of the temperature rise phase of the electrically heated formation is calculated according to the range of the formation temperature rise and the electrical energy injected into the formation. .

[0008] Preferred: Formation temperature rise range ΔT The calculation formula is as follows:

[0009] The electrical energy injected into the formation E j The calculation formula is as follows:

[0010] The time of the electric heating formation temperature rising stage T The calculation formula of 1 is as follows:

[0011] In the formula, T 1 is the time of electric heating of the formation, in minutes; ΔT is the amount of formation temperature rise, in °C; E j is the electrical energy injected into the formation, in kJ; r is the diameter of the horizontal well, in m; d is the distance between two horizontal wells, in m; U is the voltage between two horizontal wells, in V; L is the horizontal section length of the horizontal well, in meters; I It is the current after the formation is electrified, the unit is A; K is the mineralization degree, in g / L; K is the mineralization of the brine; a, b, α and β are constants measured experimentally.

[0012] Preferably, the time of the thermal cracking conversion stage of organic matter in the oil shale reservoir is Calculated by the following formula:

[0013] Where A is the frequency factor, which is the number of molecular collisions per unit time and unit volume; E is the activation energy; R is the gas constant; T is the absolute temperature; c ０ and c represent the original concentration of organic matter and the reaction time, respectively. t The concentration of reactants at Reaction time t Satisfies the following relationship:

[0014] Where d is a constant and is calculated as follows: .

[0016] Preferably, the time for the upward migration of oil and gas generated by thermal cracking of organic matter under the action of buoyancy is The calculation formula is as follows:

[0017] In the formula, d is the distance between two horizontal wells, in m; is the viscosity of the converted oil and gas, in mPa·s; is the porosity of the formation, as a decimal; is the permeability of the formation, in μm 2 ; is the pressure gradient drop of the formation, in MP / m; The density of converted oil and gas, in kg / m 3 ; is the acceleration due to gravity, in m / s².

[0018] Preferably, the upper horizontal well production time The calculation formula is as follows:

[0019] In the formula, is the amount of oil and gas converted in the formation, is the horizontal well production index, P is the reservoir pressure; is the bottom hole flowing pressure of the horizontal well.

[0020] Preferably, the hydraulic fractures of the two horizontal wells are distributed in a staggered manner, and the fracture length is greater than 1 / 2 of the well spacing.

[0021] Preferably, the high-mineralization brine has a mineralization degree of 3000-10000 mg / L.

[0022] Preferably, when the two horizontal wells are powered on, the voltage is controlled at 300-900V.

[0023] The present invention has the following beneficial effects: The present invention aims at the problem of slow heat transfer and long heating cycle of existing ICP electric heating. After the fracturing operation is carried out in the oil shale formation, the fracturing fluid is not returned after the fracturing is completed. This part of the salt water generates heat under the thermal effect of the electric current to directly heat the formation, and the heating range is larger and the heating cycle is shorter. At the same time, the present invention divides the cycle of in-situ conversion of oil shale into four stages, which are: the stage of rising temperature of the formation by electric heating, in which the organic matter in the oil shale reservoir has not yet been cracked; the stage of thermal cracking and conversion of organic matter in the oil shale reservoir under high temperature conditions (i.e. the stage of thermal cracking and conversion of organic matter in the oil shale reservoir); the stage of upward migration of the converted oil and gas under the action of buoyancy and the stage of oil and gas generated by high-temperature thermal cracking and conversion in the upper horizontal well. The present invention calculates the time required for each stage respectively, and finally obtains the total time of one cycle of in-situ conversion of oil shale when using this heating electric heating method. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of a hydraulic fracturing network in an embodiment of the present invention; Figure 2 Schematic diagram of oil and gas migration during electric heating in an embodiment of the present invention; Figure 3 Schematic diagram of electrode arrangement in an embodiment of the present invention.

[0025] In the figure, 1-production well, 2-perforation position, 3-electric heating cathode, 4-electric heating anode, 5-fracture network. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0027] The present invention proposes a production cycle calculation method for in-situ conversion of oil shale using high-mineralization brine composite electric heating. At the same time, in order to solve the problems of slow heat transfer and long heating cycle of the existing ICP heating method for in-situ conversion of oil shale, the present invention proposes a new electric heating method based on traditional electric heating, and shortens the heating cycle in conjunction with the fracturing process. This heating method mainly uses high-mineralization brine compatible with the formation as fracturing fluid during the fracturing process, and uses the non-flowback brine fracturing fluid as a heating method for the conductive medium for subsequent heating; heat energy enters the oil shale reservoir, and the solid kerogen of the oil shale or medium-low maturity shale oil reservoir begins to crack and convert into light oil and natural gas under the action of high temperature; the oil and gas generated by the conversion enter the upper production well under the action of buoyancy; the upper production well is opened to mine the converted light oil and natural gas. In order to calculate the time required for a production cycle of in-situ electric heating conversion, the calculation formula for the time required for the four stages of in-situ conversion is derived.

[0028] For details, see Figure 1-Figure 3 The present invention provides a method for calculating the production cycle of in-situ conversion of oil shale using high-mineralization brine composite electric heating, comprising the following steps: Step S1: Select two dual horizontal wells, the two horizontal wells are respectively the positive and negative electrodes of the electric heating. Specifically, the upper horizontal well can be used as the negative electrode 3 of the electric heating, and the lower horizontal well can be used as the positive electrode 4 of the electric heating. At the same time, the upper horizontal well is also used as an oil and gas production well (i.e., a production well). Both horizontal wells are subjected to fracturing operations to form a fracture network. The fracturing fluid is selected as high-mineralized brine. After the fracturing operation is completed, the fracturing fluid is not returned. The brine (i.e., high-mineralized brine) retained in the fracture network and the formation minerals together form an electric heater; Step S2: installing an oil and gas production wellhead device on the wellhead of the upper oil and gas production well (i.e., the upper horizontal well), and installing a wellhead device on the lower horizontal well; Step S3: The upper and lower heating horizontal wells are powered on, and the salt water retained in the formation generates heat as a conductive medium, directly heating the shale reservoir. The formation temperature begins to gradually rise, and the organic matter in the shale is converted into oil and gas, which is produced in the upper horizontal well; Calculate the time T1 of the formation heating stage, and fit the power-on time of the formation and the formation temperature change curve, and the following approximate relationship is obtained:

[0029] In the formula, a and b can be measured by experiment; According to the range of formation temperature increase ΔT and the electrical energy injected into the formation E j Finally, the corresponding formation heating time is calculated by the following formula: T 1:

[0030]

[0031] In the formula, T 1 is the time of electric heating of the formation, in minutes; ΔT The amount of formation temperature rise, in °C; E j is the electrical energy injected into the formation, in kJ; r is the diameter of the horizontal well, in m; d is the distance between two horizontal wells, in m; U is the voltage between two horizontal wells, in V; L is the horizontal section length of the horizontal well, in meters; I It is the current after the formation is electrified, the unit is A; K is the mineralization degree, in g / L; K is the mineralization degree of brine; α and β can be measured experimentally.

[0032] Step S4: When the formation temperature rises to above 350°C, the organic matter between the two horizontal wells begins to be converted and cracked to generate oil and gas under the action of heat; it is found through experiments that when the formation temperature is above 350°C, the hydrocarbon generation rate in the formation is faster; the time T2 required for the organic matter in the formation to be converted to generate a large amount of oil and gas is calculated (if the organic matter conversion rate reaches above 60%, the conversion and cracking time of the organic matter in the formation can be calculated based on the relationship between the temperature during the conversion and the time required for the conversion). In the formation, when organic matter such as kerogen is cracked under high temperature conditions, for a certain fixed reaction degree, or for different reactions with the same reaction degree, the relationship between the conversion time and the formation temperature is as follows:

[0033] in, d is a constant and is calculated as follows:

[0034] In the formula, t is the reaction time; A is the frequency factor, i.e. the number of molecular collisions per unit time and unit volume; E is the activation energy; R is the gas constant, 8.3144 J / (mol·K); T is the absolute temperature; c ０ and c represent the original concentration of reactants and t The concentration of reactants at time.

[0035] According to the temperature of the stratum, the required conversion time T2 can be calculated when the organic matter conversion rate in the stratum reaches a certain level. The calculation method is as follows:

[0036] Step S5: The oil and gas generated by the conversion and cracking migrate to the upper oil and gas production well through the fracture network under the action of buoyancy; the time required for the oil and gas generated in the formation to migrate to the upper horizontal well is calculated. , calculate the time required for oil and gas seepage considering gravity:

[0037] In the formula, d is the distance between two horizontal wells, in m; is the viscosity of the converted oil and gas, in mPa·s; is the porosity of the formation, as a decimal; is the permeability of the formation, in μm 2 ; is the pressure gradient drop of the formation, in MP / m; The density of converted oil and gas, in kg / m 3 ; is the acceleration due to gravity, in m / s²; Step S6: The production method of the upper horizontal well is to open the upper production well, and the oil and gas generated by the heating and conversion of the oil shale, under the action of buoyancy, reach the upper horizontal well through the fracture network generated by fracturing, and then be mined. The details are as follows: open the oil and gas wellhead device of the upper horizontal well, perform heat recovery treatment, purification and dust removal treatment, and desulfurization treatment on the mixed fluid discharged from the oil wellhead device in turn, and store the separated oil and gas; calculate the opening and production time of the well According to the horizontal well production formula and the amount of oil and gas converted in the formation, G can be calculated. , The calculation formula is as follows:

[0038] In the formula, J h is the horizontal well production index, P is the reservoir pressure; P wf is the bottom hole flowing pressure of the horizontal well; Step S7: Calculate the total time T of one cycle of oil shale in-situ conversion production, that is, the sum of the time of the above four stages:

[0039] Further, in step S1: at least two horizontal wells are involved, the upper horizontal well is selected as the production well and the negative electrode of the electric heating, the lower well is the positive electrode of the electric heating, and the two horizontal wells are connected by fracturing technology; further, when performing the fracturing operation, the fracturing fluid selects high-mineralized brine with a mineralization between 3000mg / L and 10000mg / L. After the fracturing operation is completed, the fracturing fluid does not perform a backflow operation. The conductive ions contained in the high-mineralized brine used in the fracturing operation should also be compatible with the original formation water, so as not to scale and block the formation, and not hinder the subsequent development work. The electric heating wells are two upper and lower horizontal wells, and the two horizontal wells are fracturing at the same time, and the fracturing fractures are staggered, and the fracture length is greater than 1 / 2 of the well spacing. Compared with the traditional heating method, the formation is heated by the electric current in the brine, and the heating range is also larger due to the larger distribution range of the fracturing network.

[0040] Furthermore, in step S4, alternating current is passed through the upper and lower horizontal wells, and the voltage should be set to 300~900V according to the heating speed requirements. The voltage can be adjusted according to the heating speed required for the oil shale, and the current passes through a heater composed of external brine in the formation to generate heat; wherein, the higher the power-on voltage, the faster the reservoir temperature rises, and the reservoir temperature can reach the target heating temperature faster. Accordingly, the temperature of the heated shale reservoir can be controlled by controlling the power-on voltage.

[0041] Furthermore, in step S6, when measuring the components of the mixed gas at the gas wellhead, it is necessary to measure the components of the mixed gas a preset number of times at preset time intervals, record the measurement results within the preset number of times through the control device, and analyze the measurement results. When the output begins to decrease, the power-on voltage can be increased to increase the conversion efficiency to increase the output.

[0042] By applying the technical solution of the present invention, the production cycle of the oil shale in-situ conversion process can be calculated. Specifically, the present invention can calculate the time required for the four stages in the oil shale in-situ conversion process to calculate the entire production cycle of the oil shale in-situ conversion.

[0043] Since horizontal wells extend vertically and horizontally, the underground conversion method requires the creation of longitudinal connecting channels so that the oil and gas can rise to the upper horizontal wells under the action of buoyancy.

[0044] Example The production cycle calculation method of this embodiment using high-mineralization brine composite electric heating in-situ conversion of oil shale includes the following steps: Step S1: See Figure 1-Figure 3, select two double horizontal wells, the two horizontal wells are respectively the positive and negative electrodes of the electric heating, specifically, the upper horizontal well can be used as the negative electrode 3 of the electric heating, and the lower horizontal well can be used as the positive electrode 4 of the electric heating, and the upper horizontal well can be used as the oil and gas production well, and the two horizontal wells are both subjected to fracturing operations, and the fracturing fluid is selected as high-mineralized brine. After the fracturing operation is completed, the fracturing fluid is not returned, and the brine (i.e., high-mineralized brine) retained in the fracturing network and the formation minerals together form an electric heater; Step S2: installing an oil and gas production wellhead device on the wellhead of the upper oil and gas production well (i.e., the upper horizontal well), and installing a wellhead device on the lower horizontal well; Step S3: The upper and lower horizontal wells are powered on, and the salt water retained in the formation generates heat as a conductive medium, directly heating the shale reservoir, and the formation temperature begins to gradually rise; the time T1 of the formation heating stage is calculated based on the relationship between the input of electrical energy and the change in temperature; Step S4: When the formation temperature rises to above 350°C, the organic matter between the two horizontal wells begins to be converted and cracked to generate oil and gas under the action of heat, and the time T2 required for the conversion rate of organic matter in the formation to reach 60% is calculated; Step S5: The oil and gas generated by the conversion and cracking migrate to the upper oil and gas production well through the fracture network under the action of buoyancy; the time T3 required for the oil and gas generated in the formation to migrate to the upper horizontal well is calculated according to the Darcy formula considering the influence of gravity and the true seepage velocity calculation formula; Step S6: Open the oil and gas production wellhead device of the upper horizontal well, perform heat recovery treatment, purification and dust removal treatment, and desulfurization treatment on the mixed fluid discharged from the oil production wellhead device in sequence, and store the separated oil and gas; and calculate T4 according to the production capacity formula of the horizontal well and the amount of oil and gas converted and generated in the formation G; Step S7: Calculate the total time T of one cycle of oil shale in-situ conversion production, that is, the sum of the time of the above four stages.

[0045]

[0046] By applying the technical solution of this embodiment, the production cycle of the in-situ conversion process of oil shale can be calculated. Specifically, this embodiment uses an electric heating method to convert and crack oil shale. This embodiment selects two horizontal wells as the positive and negative electrodes of electric heating, and uses fracturing to form a seam network to connect the two horizontal wells to form a passage for oil and gas flow. Among them, wellhead devices are installed at the wellheads of the two horizontal wells, and the sealing effect of the continuous channel and the oil and gas wells is achieved through the above-mentioned device.

[0047] It should be noted that during the fracturing operation, the fracturing fluid is selected from high-mineralized salt water, which can be sourced from non-drinking water extracted from other layers. After the fracturing operation is completed, the two horizontal wells must be cemented and the wellhead device must be installed. The cementing operation includes installing production casing in the two horizontal wells, installing a casing head at the upper end of the production casing, and the casing head is used to fix it with the gas production wellhead device. In actual production, if the production casing has been installed in the selected horizontal well, it does not need to be installed again.

[0048] Specifically, in step S3: during the process of energizing the two wells, it is necessary to control the voltage between the two wells so that the underground has a reasonable heating rate, wherein the current after energization is calculated by the following formula:

[0049] Where: r is the diameter of the horizontal well, in m; d is the distance between two horizontal wells, in m; U is the voltage between two horizontal wells, in V; L is the horizontal section length of the horizontal well, in meters; I It is the current after the formation is electrified, the unit is A; K is the mineralization degree, the unit is g / L.

[0050] Mineralization can directly affect the conductivity of the solution σ , and the conductivity σ and mineralization K There is a linear relationship between them, where α is 1659.5 and β is 2339.3

[0051] Where: σ is the conductivity of the solution, in µS / cm; K is the mineralization degree, the unit is g / L.

[0052] In this embodiment, when r is 0.089m, d The cable is 10m and the voltage is 300V. L When the depth is 50m and the salinity of the salt water is 10000mg / L, the conductivity σ is 14255.7µS / cm. The current at this time I is 1A.

[0053] In this embodiment, when the formation is heated to 350°C, for the calculation formula of T1, a=0.33242, b=0.78916, based on the heating cracking model ratio of 1:200, it is calculated that the energy required to heat the actual formation is 1254640.988 kJ, and the time required is 69703 minutes, or 49 days.

[0054] In this embodiment, the organic matter conversion time required when the formation temperature reaches 350°C and the organic matter conversion rate reaches 60% is calculated: At this time, the activation energy E of the reaction is 264 kJ / mol, and the frequency factor A is 2.282565×10 15 mol / (L·s), the formula can be written as:

[0055] The corresponding conversion time T2 is as follows:

[0056] In this embodiment, when the formation temperature reaches 350° C. and the organic matter conversion rate reaches 60%, it is calculated that the time for high-temperature cracking and conversion of organic matter in the formation is 60.95 days.

[0057] In this embodiment, when the viscosity of the converted oil and gas is is 10 mPa·s, and the porosity of the formation is 0.1, the permeability of the formation fracture 272×10 -3 μm 2 , the pressure gradient of the formation drops is 10×10 -3 MP / m, density of converted oil and gas 0.9×10 3 kg / m 3 , the acceleration due to gravity When it is 9.8 m / s²;

[0058] The corresponding migration time is 22.6 days.

[0059] In this embodiment, when the horizontal well production index J h The production pressure difference is 50 t / d·MPa. When the amount of oil and gas converted is 300 t,

[0060] Calculate the production time of horizontal wells T4 for 6 days.

[0061] In this embodiment, in summary, the production cycle as follows: (Unit: d) In this example, the time for one production cycle of in-situ conversion of oil shale using this technology is 135.55 days.

[0062] In this embodiment, in step S1: the horizontal well includes an upper well and a lower well, the upper well is selected as an oil and gas production well, and the two wells are connected by a fracture network.

[0063] In this embodiment, step S3 includes: step S31: in the early stage of electric heating, in order to have a higher heating rate and quickly increase the temperature of the underground oil shale, the power-on voltage can be appropriately increased; step S32: after the formation temperature rises to the critical temperature of conversion, the voltage is reduced to save electric energy while maintaining the formation temperature; step S33: In actual production, the power supply voltage can be adjusted according to the output of the oil and gas wells to keep the formation temperature within a reasonable range.

[0064] In this embodiment, in step S5, the oil and gas formed by the conversion will gradually seep into the fracture network around the upper oil and gas production well due to the buoyancy effect. These oil and gas enter the wellbore of the oil and gas production well through the fracture network and are produced using appropriate lifting methods.

[0065] In this embodiment, in step S6, when measuring the mixed gas components at the gas wellhead, it is necessary to measure the components of the produced oil and gas a preset number of times at preset time intervals, and the measurement results within the preset number of times are recorded by the control device, and the measurement results are analyzed. When the output begins to decrease, the power-on voltage can be increased to increase the conversion efficiency to increase the output.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for calculating the production cycle of in-situ conversion of oil shale using high-mineralization brine composite electric heating, characterized in that: The process includes the following: Two horizontal wells facing each other are selected as positive and negative electrodes for electric heating respectively; the upper horizontal well is used as an oil and gas production well, and both horizontal wells are subjected to fracturing operations, and the fracturing fluid is selected as high-mineralized salt water. After the fracturing operation is completed, the fracturing fluid is retained in the fracturing network; An oil and gas production wellhead device is installed on the wellhead of the upper horizontal well, and a wellhead device is installed on the lower horizontal well; The two horizontal wells are electrified, and the fracturing fluid retained in the formation generates heat as a conductive medium, heating the shale reservoir, and the formation temperature rises; During the heating process, calculate the time of the electric heating formation temperature rise stage , where the formation temperature rise stage is the stage where the organic matter in the oil shale reservoir has not yet been thermally cracked; the time of the thermal cracking and conversion stage of the organic matter in the oil shale reservoir is calculated ; Calculate the time of the upward migration stage of oil and gas generated by thermal cracking of organic matter under the action of buoyancy ; Calculate the production time of the upper horizontal well ; Calculation of the production cycle of in-situ conversion of oil shale by composite electric heating of high-salinity brine .

2. The method for calculating the production cycle of in-situ conversion of oil shale using high-mineralization brine composite electric heating according to claim 1 is characterized in that: The temperature dividing point between the formation temperature rising stage and the organic matter thermal cracking conversion stage in the oil shale reservoir is 350°C.

3. The method for calculating the production cycle of in-situ conversion of oil shale using high-mineralization brine composite electric heating according to claim 1 is characterized in that: According to the range of formation temperature rise and the electrical energy injected into the formation, calculate the time of the electric heating formation temperature rise stage .

4. The method for calculating the production cycle of in-situ conversion of oil shale using high-mineralization brine composite electric heating according to claim 3, characterized in that: Formation temperature rise range ΔT The calculation formula is as follows: The electrical energy injected into the formation E j The calculation formula is as follows: The time of the electric heating formation temperature rising stage T The calculation formula of 1 is as follows: In the formula, T 1 is the time of electric heating of the formation, in minutes; ΔT is the amount of formation temperature rise, in °C; E j is the electrical energy injected into the formation, in kJ; r is the diameter of the horizontal well, in m; d is the distance between two horizontal wells, in m; U is the voltage between two horizontal wells, in V; L is the horizontal section length of the horizontal well, in meters; I It is the current after the formation is electrified, the unit is A; K is the mineralization degree, in g / L; K is the mineralization of the brine; a, b, α and β are constants measured experimentally.

5. The method for calculating the production cycle of in-situ conversion of oil shale using high-mineralization brine composite electric heating according to claim 1 is characterized in that: Time of thermal cracking and conversion stage of organic matter in oil shale reservoirs Calculated by the following formula: Where A is the frequency factor, which is the number of molecular collisions per unit time and unit volume; E is the activation energy; R is the gas constant; T is the absolute temperature; c ０ and c represent the original concentration of organic matter and the reaction time, respectively. t The concentration of reactants at Reaction time t Satisfies the following relationship: Where d is a constant and is calculated as follows: 。 6. The method for calculating the production cycle of in-situ conversion of oil shale using high-mineralization brine composite electric heating according to claim 1, characterized in that: The time of the upward migration stage of oil and gas generated by thermal cracking of organic matter under the action of buoyancy The calculation formula is as follows: In the formula, d is the distance between two horizontal wells, in m; is the viscosity of the converted oil and gas, in mPa·s; is the porosity of the formation, as a decimal; is the permeability of the formation, in μm 2 ; is the pressure gradient drop of the formation, in MP / m; The density of converted oil and gas, in kg / m 3 ; is the acceleration due to gravity, in m / s².

7. The method for calculating the production cycle of in-situ conversion of oil shale using high-mineralization brine composite electric heating according to claim 1, characterized in that: The time for the upper horizontal well to start production The calculation formula is as follows: In the formula, is the amount of oil and gas converted in the formation, is the horizontal well production index, P is the reservoir pressure; is the bottom hole flowing pressure of the horizontal well.

8. The method for calculating the production cycle of in-situ conversion of oil shale using high-mineralization brine composite electric heating according to claim 1 is characterized in that: The hydraulic fractures of the two horizontal wells are distributed in a staggered manner, and the fracture length is greater than 1 / 2 of the well spacing.

9. The method for calculating the production cycle of in-situ conversion of oil shale using high-mineralization brine composite electric heating according to claim 1, characterized in that: The high-mineralization brine has a mineralization degree of 3000-10000 mg / L.

10. The method for calculating the production cycle of in-situ conversion of oil shale using high-mineralization brine composite electric heating according to claim 1, characterized in that: When the two horizontal wells are powered on, the voltage is controlled at 300-900V.

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