A method for determining temperature and pressure parameters for efficient oil extraction from underground in-situ pyrolysis of organic-rich rocks

Abstract

The present invention provides a method for determining temperature and pressure parameters for efficient oil extraction by underground in-situ pyrolysis of organic-rich rocks. The method uses indoor simulation experiments to establish a P-T phase diagram and a viscosity change model for the pyrolysis product fluid, and then obtains the saturation pressure of the downhole fluid under different temperature conditions, thereby inversely calculating the efficient extraction temperature and pressure parameters of the pyrolysis products at different pyrolysis stages. Based on this, combined with underground in-situ pyrolysis reaction process monitoring, the optimal oil and gas extraction temperature and pressure conditions are determined to avoid wellbore blockage, and the efficient extraction temperature and pressure parameters of underground in-situ pyrolysis oil and gas resources are regulated in real time. Combined with the adjustment of the flow rate and pressure of the injected heat-carrying fluid, the efficient extraction of oil and gas fluid produced by underground in-situ pyrolysis of organic-rich rocks can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of underground in-situ development of energy resources, and specifically relates to a method for determining temperature and pressure parameters for efficient oil extraction by underground in-situ pyrolysis of organic-rich rocks. Background Art

[0002] In recent years, underground in-situ pyrolysis technology of oil shale and coal has attracted more and more attention. This method uses existing drilling technology and fracturing methods to create an artificial fracture network in the rock formation, and then injects high-temperature heat carriers such as superheated steam or superheated hydrocarbon gas or other inert gases into it, so that the underground rock formation is heated and the organic matter is pyrolyzed to form oil and gas, and finally the formed oil and gas resources are pumped to the ground and utilized.

[0003] According to the source rock evaluation theory, the organic-rich rock layers that can be used for underground pyrolysis conversion are all low-maturity source rocks. Therefore, the pyrolysis products contain a large number of high-density and high-viscosity components, which often have relatively high condensation temperatures. Therefore, it is necessary to foresee the condensation of underground tar, and even the possibility of wellbore blockage, which will eventually make it difficult to extract the product. At present, no dedicated solution to this problem has been proposed in the existing technical methods. Summary of the invention

[0004] The purpose of the present invention is to provide a method for determining temperature and pressure parameters for efficient oil extraction by underground in-situ pyrolysis of organic-rich rocks, which can prevent wellbore blockage and facilitate the extraction of pyrolysis products.

[0005] To achieve the above-mentioned object, the present invention provides a method for determining temperature and pressure parameters for efficient oil extraction by underground in-situ pyrolysis of organic-rich rocks, comprising the following steps:

[0006] Step 1: Sampling the organic-rich rock layer in the in-situ pyrolysis area to obtain representative pyrolysis samples; conducting a simulation experiment with the same underground pyrolysis conditions through an indoor experimental device, and accurately obtaining the pyrolysis products of each reaction stage during the experiment;

[0007] Step 2: According to the pyrolysis products of each reaction stage, a PT phase diagram of the fluid at each reaction stage is established, and the phase characteristics of the fluid under different temperature and pressure conditions are determined by the PT phase diagram, and the fluid phase is identified in combination with the downhole temperature and pressure conditions;

[0008] Step 3: Determine the saturation pressure at different reaction stages through the PT phase diagram, and calculate the viscosity of the fluid in the well using the viscosity calculation model combined with the downhole temperature and pressure;

[0009] Step 4: Establish a model for the change trend of the phase state, saturation pressure, and viscosity of the fluid in the extraction well as the pyrolysis process, establish a model for the change of the pyrolysis conversion rate as the pyrolysis process, and determine the wellhead temperature and pressure of efficient extraction at the corresponding stage based on the fluid saturation pressure;

[0010] Step 5: Determine the pyrolysis conversion rate according to the characteristic parameters of the wellhead products, and determine the corresponding temperature and pressure parameters of the wellhead based on the pyrolysis conversion rate through the model established in step 4.

[0011] Furthermore, the fluid PT phase diagram is established through the PR state equation.

[0012] Furthermore, in step 3, the viscosity of the fluid in the well is calculated by the CS viscosity model, and the calculation formula is:

[0013]

[0014] In the above formula, μ mix and μ o are the viscosities of the mixture and the reference substance, Pa·s; p, T are the pressure Pa and temperature K of the mixture, respectively; T cmix and T o are the critical temperatures of the mixture and the reference substance, K; p cmix and p o are the critical pressures of the mixture and the reference, Pa; MW mix and MW o are the molecular weights of the mixture and the reference substance, g / mol; a mix and a o are the coupling coefficients of the mixture and the reference substance; T o is the temperature of the reference substance, K; p o is the pressure of the reference substance, Pa.

[0015] The advantages of the present invention are as follows: the present invention provides a method for determining temperature and pressure parameters for efficient oil extraction by underground in-situ pyrolysis of organic-rich rocks. The method utilizes indoor simulation experiments to establish a PT phase diagram of the pyrolysis product fluid and a viscosity change model, thereby obtaining the saturation pressure of the downhole fluid under different temperature conditions, thereby inversely calculating the efficient extraction temperature and pressure parameters of the pyrolysis products at different pyrolysis stages. Based on this, combined with underground in-situ pyrolysis reaction process monitoring, the optimal oil and gas extraction temperature and pressure conditions are determined to avoid wellbore blockage, and the efficient extraction temperature and pressure parameters of underground in-situ pyrolysis oil and gas resources are regulated in real time. Combined with the adjustment of the flow rate and pressure of the injected heat-carrying fluid, efficient extraction of oil and gas fluid produced by underground in-situ pyrolysis of organic-rich rocks is achieved.

[0016] The present invention is described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a determination diagram of temperature and pressure parameters for efficient oil extraction by underground in-situ pyrolysis of organic-rich rocks.

[0018] Figure 2 It is composed of various parts of the PT phase diagram. DETAILED DESCRIPTION

[0019] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined purpose, the specific implementation methods, structural features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and embodiments.

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] In the description of the present invention, it is necessary to understand that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "aligned", "overlap", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0022] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features; in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0023] The present invention provides a method for determining temperature and pressure parameters of underground in-situ pyrolysis of organic-rich rocks for efficient oil extraction, comprising the following steps:

[0024] Step 1: Sampling the organic-rich rock layer in the in-situ pyrolysis area to obtain representative pyrolysis samples; conducting a simulation experiment with the same underground pyrolysis conditions through an indoor experimental device, and accurately obtaining the pyrolysis products of each reaction stage during the experiment;

[0025] Step 2: According to the pyrolysis products of each reaction stage, establish the fluid PT phase diagram of each reaction stage, such as Figure 1As shown, the PT phase diagram is used to determine the phase characteristics of the fluid under different temperature and pressure conditions, and the fluid phase is identified in combination with the downhole temperature and pressure conditions;

[0026] Step 3: After determining the phase state of the downhole fluid, determine the saturation pressure at different reaction stages through the PT phase diagram, and use the viscosity calculation model combined with the downhole temperature and pressure to calculate the viscosity of the fluid downhole;

[0027] like Figure 2 It is composed of various parts of the PT phase diagram. The liquid phase area is between the left side of the critical point C and the temperature and pressure conditions of the area above the bubble point line pressure. The fluid phase is a single liquid phase; the gas phase area is between the right side of the critical point C and the temperature and pressure conditions of the area above the dew point line pressure. The fluid phase is a single gas phase; the two-phase area is the temperature and pressure area within the entire bubble point line and the dew point line connection line. The fluid phase is gas-liquid two-phase. The bubble point line is the temperature and pressure point connection line when the gas phase appears in the liquid phase area, and the dew point line is the temperature and pressure point connection line when the liquid phase appears in the gas phase area. The critical point C is the conversion point of the bubble point line and the dew point line. The fluid near the critical point is between the gas phase and the liquid phase. The maximum condensation temperature Tmax is the maximum temperature point when the fluid undergoes condensation, and the maximum condensation pressure Pmax is the maximum pressure point when the fluid undergoes condensation.

[0028] Step 4: Establish a model for the change trend of the phase state, saturation pressure, and viscosity of the fluid in the extraction well as the pyrolysis process, establish a model for the change of the pyrolysis conversion rate as the pyrolysis process, and determine the wellhead temperature and pressure of efficient extraction at the corresponding stage based on the fluid saturation pressure;

[0029] Step 5: Determine the pyrolysis conversion rate according to the characteristic parameters of the wellhead products, and determine the corresponding temperature and pressure parameters of the wellhead based on the pyrolysis conversion rate through the model established in step 4.

[0030] Example 1

[0031] This embodiment takes oil-rich coal as an example:

[0032] The first step is to obtain oil-rich coal samples from the target coal seam through drilling construction, and then use the indoor experimental device to conduct a simulation experiment with the same underground pyrolysis conditions. The indoor experimental device is an in-situ pyrolysis high-temperature simulation experimental device for organic-rich rock formations ZL2021220444725. Based on the simulation experimental scheme designed in ZL2021220444725, a comprehensive and systematic thermal simulation experiment is carried out to accurately obtain the pyrolysis products of each reaction stage during the experiment.

[0033] The second step is to establish the fluid PT phase diagram of each reaction stage based on the pyrolysis products of each reaction stage, determine the phase characteristics of the fluid under different temperature and pressure conditions through the PT phase diagram, and identify the fluid phase as a single gas phase, gas-liquid two-phase or a single liquid phase in combination with the downhole temperature and pressure conditions.

[0034] The calculation of the fluid PT phase diagram curve is completed through the PR state equation, which is:

[0035]

[0036] Where R is the molar gas constant, 8.314 J / (mol·K); T is the temperature, K; V m is the molar volume, a is a constant related to the intermolecular force, and b is a constant related to the size of the molecular sphere. Under critical conditions, the two are:

[0037]

[0038]

[0039] Where T c is the critical temperature, K; P c is the critical pressure, Pa;

[0040] The generalized expression for the temperature-dependent parameter a(T) is given by:

[0041] a(T)=a(Tc)α(T)

[0042] in:

[0043]

[0044] in:

[0045] m=0.3746+1.5423ω-0.2699ω 2

[0046] Here ω is the eccentricity factor and is dimensionless.

[0047] According to the above calculations, the saturated pressure of the fluid under different temperature conditions can be obtained, and the PT phase diagram can be obtained, based on which the phase characteristics and volume coefficient of the fluid under different temperature and pressure conditions can be accurately determined, and then the corresponding fluid density can be obtained.

[0048] The third step is to determine the phase state of the downhole fluid, determine the saturation pressure at different reaction stages through the PT phase diagram, and calculate the viscosity of the fluid downhole through the CS viscosity model.

[0049] Furthermore, the CS viscosity model is:

[0050]

[0051] where μ mix and μ o are the viscosities of the mixture and the reference substance, Pa·s; p, T are the pressure Pa and temperature K of the mixture, respectively; T cmix and T co are the critical temperatures of the mixture and the reference substance, K; p cmix and p co are the critical pressures of the mixture and the reference, Pa; MW mix and MW o are the molecular weights of the mixture and the reference substance, g / mol; a mix and a o are the coupling coefficients of the mixture and the reference substance; T o is the temperature of the reference substance, K; p o is the pressure of the reference substance, Pa.

[0052] The fourth step is to establish a model of the change trend of the phase state, saturation pressure, and viscosity of the fluid in the extraction well with the pyrolysis process based on the temperature and pressure gradient of the fluid temperature from the bottom of the well to the wellhead (the temperature from the bottom of the well to the wellhead is gradually reduced. According to this principle, based on the temperature change gradient, the fluid saturation pressure corresponding to the lowest temperature is required to determine the efficient extraction pressure). Establish a model of the change of the pyrolysis conversion rate with the pyrolysis process, and determine the wellhead temperature and pressure of the efficient extraction in the corresponding stage based on the fluid saturation pressure. Generally, there are two situations: ① When the critical temperature of the fluid is greater than the formation temperature: in a certain reaction period, when the conversion rate is 20%, the critical temperature of the fluid is 350℃, and the corresponding critical pressure is 8MPa. Combined with the actual conditions of the formation, the fluid saturation pressure when the fluid temperature is the actual formation temperature is selected. According to the actual underground in-situ pyrolysis conditions, the temperature of the extraction well is 150℃. Based on the fluid PT phase diagram at this time, the saturation pressure corresponding to the temperature of 150℃ is selected as the efficient extraction pressure. ② When the critical temperature of the fluid is lower than the formation temperature: in a certain reaction period, when the conversion rate reaches 70%, the critical temperature of the fluid is 100°C, and the corresponding critical pressure is 15MPa. Combined with the actual formation conditions, the temperature of the production well is 150°C. Based on the PT phase diagram of the fluid at this time, the saturation pressure corresponding to the temperature of 150°C is selected as the efficient extraction pressure. If the maximum condensation temperature of the PT phase diagram is lower than 150°C at this time, the efficient extraction pressure can be based on the actual engineering conditions without specific control. According to the principle of maximizing energy utilization, the flow rate of the production well can be controlled.

[0053] The fifth step is to determine the pyrolysis conversion rate based on the characteristic parameters of the wellhead products. The pyrolysis conversion rate is determined by an in-situ pyrolysis reaction degree monitoring and evaluation method for oil-rich coal ZL202111001610X. The pyrolysis reaction degree is determined by the five models established in the fourth step to determine the corresponding temperature and pressure parameters of the wellhead.

[0054] For example, assuming that based on the thermal simulation experiment, when the in-situ pyrolysis conversion rate reaches 50%, the viscosity of the fluid for efficient extraction is 0.25 MP·s and the corresponding density is 0.45 g / cm3. Then, through the model diagrams obtained in the second and fourth steps above, it is determined that the corresponding temperature is 50°C and the pressure is 6 MPa. In this case, the wellhead temperature and pressure of the extraction well must be controlled to be no lower than the above temperature and pressure conditions.

[0055] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A method for determining temperature and pressure parameters for efficient oil extraction by underground in-situ pyrolysis of organic-rich rocks, characterized by: The steps include: Step 1: Sampling the organic-rich rock layer in the in-situ pyrolysis area to obtain representative pyrolysis samples; conducting a simulation experiment with the same underground pyrolysis conditions through an indoor experimental device, and accurately obtaining the pyrolysis products of each reaction stage during the experiment; Step 2: According to the pyrolysis products of each reaction stage, a PT phase diagram of the fluid at each reaction stage is established, and the phase characteristics of the fluid under different temperature and pressure conditions are determined by the PT phase diagram, and the fluid phase is identified in combination with the downhole temperature and pressure conditions; Step 3: After determining the phase state of the downhole fluid, determine the saturation pressure at different reaction stages through the PT phase diagram, and use the viscosity calculation model combined with the downhole temperature and pressure to calculate the viscosity of the fluid downhole; Step 4: Establish a model for the change trend of the phase state, saturation pressure, and viscosity of the fluid in the extraction well as the pyrolysis process, establish a model for the change of the pyrolysis conversion rate as the pyrolysis process, and determine the wellhead temperature and pressure of efficient extraction at the corresponding stage based on the fluid saturation pressure; Step 5: Determine the pyrolysis conversion rate according to the characteristic parameters of the wellhead products, and determine the corresponding temperature and pressure parameters of the wellhead based on the pyrolysis conversion rate through the model established in step 4.

2. The method for determining temperature and pressure parameters for efficient oil extraction by underground in-situ pyrolysis of organic-rich rocks according to claim 1, characterized in that: The fluid PT phase diagram is established by the PR state equation.

3. The method for determining temperature and pressure parameters for efficient oil extraction by underground in-situ pyrolysis of organic-rich rocks according to claim 1, characterized in that: In step 3, the viscosity of the fluid in the well is calculated by the CS viscosity model, and the calculation formula is: In the above formula, μ mix and μ o are the viscosities of the mixture and the reference substance, Pa·s; p, T are the pressure Pa and temperature K of the mixture, respectively; T cmix and T co are the critical temperatures of the mixture and the reference substance, K; p cmix and p co are the critical pressures of the mixture and the reference, Pa; MW mix and MW o are the molecular weights of the mixture and the reference substance, g / mol; a mix and a o are the coupling coefficients of the mixture and the reference substance; T o is the temperature of the reference substance, K; p o is the pressure of the reference substance, Pa.

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