Disclosure of Invention
The invention aims to provide a method for determining high-efficiency oil extraction temperature and pressure parameters of underground in-situ pyrolysis of organic rock, which can prevent a shaft from being blocked and is convenient for extraction of pyrolysis products.
In order to achieve the purpose, the invention provides a method for determining temperature and pressure parameters of high-efficiency oil extraction by underground in-situ pyrolysis of organic rock, which comprises the following steps:
Sampling an organic matter-rich rock stratum in an in-situ pyrolysis zone to obtain a representative pyrolysis sample, and carrying out a simulation experiment which is the same as underground pyrolysis conditions by an indoor experimental device to accurately obtain pyrolysis products of each reaction stage in the experimental process;
Step two, according to pyrolysis products of each reaction stage, establishing a fluid P-T phase diagram of each reaction stage, judging fluid phase characteristics under different temperature and pressure conditions through the P-T phase diagram, and identifying fluid phase by combining with underground temperature and pressure conditions;
Determining saturation pressures of different reaction stages through a P-T phase diagram, and calculating the viscosity of the fluid in the pit by combining the underground temperature and pressure by using a viscosity calculation model;
Establishing a change trend model of the phase state, the saturation pressure and the viscosity of the fluid in the extraction well along with the pyrolysis process, establishing a change model of the pyrolysis conversion rate along with the pyrolysis process, and determining the wellhead temperature and the wellhead pressure of efficient extraction in the corresponding stage by taking the fluid saturation pressure as a standard;
And fifthly, judging the pyrolysis conversion rate according to the characteristic parameters of the wellhead products, and judging the corresponding temperature and pressure parameters of the wellhead through the model established in the fourth step based on the pyrolysis conversion rate.
Further, the fluid P-T phase diagram is established by PR state equation.
Further, in the third step, the viscosity of the fluid in the well is calculated by a CS viscosity model, and the calculation formula is as follows:
In the above formula, mumix and muo are respectively the viscosity of the mixture and the reference substance, pa.s, p, T are respectively the pressure Pa and the temperature K of the mixture, Tcmix and To are respectively the critical temperature K of the mixture and the reference substance, pcmix and po are respectively the critical pressure Pa of the mixture and the reference substance, MWmix and MWo are respectively the molecular weights g/mol of the mixture and the reference substance, amix and ao are respectively the coupling coefficients of the mixture and the reference substance, To is the temperature of the reference substance, K and po is the pressure Pa of the reference substance.
The method has the advantages that the method utilizes an indoor simulation experiment to establish a P-T phase diagram and a viscosity change model of pyrolysis product fluid, and further obtains saturation pressure of the underground fluid under different temperature conditions, so that the efficient extraction temperature and pressure parameters of pyrolysis products in different pyrolysis stages are calculated reversely, and based on the parameters, the method combines with underground in-situ pyrolysis reaction process monitoring, so that the optimal oil and gas extraction temperature and pressure conditions are judged, the blockage of a shaft is avoided, the efficient extraction temperature and pressure parameters of underground in-situ pyrolysis oil and gas resources are regulated in real time, and the adjustment of the flow and pressure of injection heat transfer fluid is combined, so that the efficient extraction of the oil and gas fluid produced by the underground in-situ pyrolysis of the organic rock is realized.
The invention will now be described in detail with reference to the drawings and examples.
Detailed Description
The following detailed description, structural features and functions of the present invention are provided with reference to the accompanying drawings and examples in order to further illustrate the technical means and effects of the present invention to achieve the predetermined objects.
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In the description of the present invention, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "aligned," "overlapping," "bottom," "inner," "outer," and the like indicate orientations or positional relationships based on the orientation or positional relationships shown in the drawings, merely to facilitate description of the present invention and simplify the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operate in a specific orientation, and therefore should not be construed as limiting the present invention.
The terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature, and in the description of the invention, unless otherwise indicated, the meaning of "a plurality" is two or more.
The invention provides a method for determining temperature and pressure parameters of high-efficiency oil extraction by underground in-situ pyrolysis of organic rock, which comprises the following steps:
Sampling an organic matter-rich rock stratum in an in-situ pyrolysis zone to obtain a representative pyrolysis sample, and carrying out a simulation experiment which is the same as underground pyrolysis conditions by an indoor experimental device to accurately obtain pyrolysis products of each reaction stage in the experimental process;
Step two, according to pyrolysis products of each reaction stage, establishing a fluid P-T phase diagram of each reaction stage, judging fluid phase characteristics under different temperature and pressure conditions through the P-T phase diagram as shown in fig. 1, and identifying fluid phase by combining with underground temperature and pressure conditions;
determining the saturation pressure of different reaction stages through a P-T phase diagram after determining the phase state of the fluid in the well, and calculating the viscosity of the fluid in the well by combining the temperature and the pressure in the well through a viscosity calculation model;
As shown in FIG. 2, the liquid phase region is a single liquid phase under the temperature and pressure conditions of the region corresponding to the partial region above the bubble point line pressure and the gas phase region is a single gas phase under the temperature and pressure conditions of the region corresponding to the partial region above the dew point line pressure and the gas phase region is a temperature and pressure region within the whole bubble point line and dew point line connection, and the liquid phase is a gas-liquid phase. The bubble point line is the temperature and pressure point connection line when the gas phase appears in the liquid phase region, the dew point line is the temperature and pressure point connection line when the liquid phase appears in the gas phase region, the critical point C is the switching point of the bubble point line and the dew point line, and 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 is condensed, and the maximum condensation pressure Pmax is the maximum pressure point when the fluid is condensed.
Establishing a change trend model of the phase state, the saturation pressure and the viscosity of the fluid in the extraction well along with the pyrolysis process, establishing a change model of the pyrolysis conversion rate along with the pyrolysis process, and determining the wellhead temperature and the wellhead pressure of efficient extraction in the corresponding stage by taking the fluid saturation pressure as a standard;
And fifthly, judging the pyrolysis conversion rate according to the characteristic parameters of the wellhead products, and judging the corresponding temperature and pressure parameters of the wellhead through the model established in the fourth step based on the pyrolysis conversion rate.
Example 1
This example uses oil-rich coal as an example:
The method comprises the steps of firstly, obtaining a rich coal sample of a target coal seam through drilling construction, then carrying out a simulation experiment which is the same as underground pyrolysis conditions by using an indoor experimental device, wherein the indoor experimental device is an organic matter-rich rock stratum in-situ pyrolysis high-temperature simulation experimental device ZL2021220444725, developing a comprehensive system thermal simulation experiment based on a simulation experimental scheme designed in ZL2021220444725, and accurately obtaining pyrolysis products of each reaction stage in the experimental process.
And secondly, establishing a fluid P-T phase diagram of each reaction stage according to pyrolysis products of each reaction stage, judging fluid phase characteristics under different temperature and pressure conditions through the P-T phase diagram, and identifying the fluid phase as a single gas phase, a gas-liquid phase or a single liquid phase by combining the downhole temperature and pressure conditions.
The calculation of the fluid P-T phase diagram curve is completed through PR state equation:
Wherein R is the molar gas constant, 8.314J/(mol.K), T is the temperature, K, Vm is the molar volume, a is the constant related to the intermolecular forces, b is the constant related to the molecular sphere size, both under critical conditions:
Wherein Tc is critical temperature, K, Pc is critical pressure, pa;
Whereas the generalized expression a (T) for the temperature-related parameter is given by:
a(T)=a(Tc)α(T)
Wherein:
Wherein:
m=0.3746+1.5423ω-0.2699ω2
Here ω is the eccentricity factor, dimensionless.
According to the calculation, fluid saturation pressure under different temperature conditions can be obtained, and a P-T phase diagram can be obtained, so that fluid phase characteristics and volume coefficients under different temperature and pressure conditions can be accurately judged, and further corresponding fluid density can be obtained.
And thirdly, determining the saturation pressure of different reaction stages through a P-T phase diagram after determining the phase state of the fluid in the well, and calculating the viscosity of the fluid in the well through a CS viscosity model.
Further, the CS viscosity model is:
Wherein mumix and muo are the viscosity of the mixture and the reference substance, pa.s, p, T are the pressure Pa and the temperature K of the mixture, Tcmix and Tco are the critical temperature K of the mixture and the reference substance, pcmix and pco are the critical pressure Pa of the mixture and the reference substance, MWmix and MWo are the molecular weights g/mol of the mixture and the reference substance, amix and ao are the coupling coefficients of the mixture and the reference substance, To is the temperature of the reference substance, K and po is the pressure Pa of the reference substance.
And fourthly, based on the temperature-pressure gradient of the fluid in the extraction well from the bottom of the well to the top of the well (the temperature from the bottom of the well to the top of the well is gradually reduced), according to the principle, based on the temperature-change gradient, the high-efficiency extraction pressure is determined by the fluid saturation pressure corresponding to the lowest temperature, a change trend model of the phase state, the saturation pressure and the viscosity of the fluid in the extraction well along with the pyrolysis process is established, a change model of the pyrolysis conversion rate along with the pyrolysis process is established, and the top of the well temperature and the top of the high-efficiency extraction at the corresponding stage are determined by taking the fluid saturation pressure as a standard. Generally, the method is divided into two cases, wherein ① is used for fluid critical temperature being higher than stratum temperature in a certain reaction period, when the conversion rate is 20%, the fluid critical temperature is 350 ℃, the corresponding critical pressure is 8MPa, the fluid saturation pressure is selected when the fluid temperature is the actual stratum temperature according to the actual stratum condition, the exploitation well temperature is 150 ℃ according to the actual underground in-situ pyrolysis condition, and the corresponding saturation pressure is selected to be high-efficiency extraction pressure when the fluid P-T phase diagram is based on the fluid P-T phase diagram. ② When the critical temperature of the fluid is lower than the stratum temperature in a certain reaction period and the conversion rate reaches 70%, the critical temperature of the fluid is 100 ℃, the corresponding critical pressure is 15MPa, the temperature of a production well is 150 ℃ in combination with the actual stratum condition, the corresponding saturated pressure is selected to be the high-efficiency extraction pressure when the temperature is 150 ℃ based on the PT phase diagram of the fluid, and if the maximum condensation temperature of the PT phase diagram is lower than 150 ℃, the high-efficiency extraction pressure can be controlled according to the actual engineering condition without specific control and the production well flow rate is controlled according to the energy utilization rate maximization principle.
And fifthly, judging the pyrolysis conversion rate according to the characteristic parameters of wellhead products, wherein the pyrolysis conversion rate is judged by a monitoring and evaluating method ZL202111001610X for the in-situ pyrolysis reaction degree of the oil-rich coal, and the pyrolysis reaction degree is judged by five models established in the fourth step to judge the corresponding temperature and pressure parameters of the wellhead.
For example, assuming that when the in-situ pyrolysis conversion rate reaches 50% based on the thermal simulation experiment, the viscosity of the fluid to be efficiently extracted is 0.25mp·s, and the corresponding density is 0.45g/cm3, the corresponding temperature is determined to be 50 ℃ and the pressure is determined to be 6MPa by the model diagrams obtained in the second step and the fourth step, and the wellhead temperature and pressure control in the aspect of the extraction well is required to be not lower than the temperature and pressure conditions.
The foregoing is a further detailed description of the invention in connection with the preferred embodiments, and it is not intended that the invention be limited to the specific embodiments described. It will be apparent to those skilled in the art that several simple deductions or substitutions may be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.