CN114151070A - Crude oil cracking gas reservoir fluid ancient pressure recovery method - Google Patents
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- 239000010779 crude oil Substances 0.000 title claims abstract description 168
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- 238000000197 pyrolysis Methods 0.000 claims abstract description 6
- 239000004215 Carbon black (E152) Substances 0.000 claims description 19
- 229930195733 hydrocarbon Natural products 0.000 claims description 19
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Abstract
The invention provides a crude oil pyrolysis gas reservoir fluid paleo-pressure recovery method, wherein the paleo-pressure recovery method comprises the following steps: determining the hydrostatic pressure, the formation temperature and the natural gas compression factor of a gas reservoir when the crude oil is completely cracked; measuring the volume coefficient, density, asphalt density and cracking rate of crude oil; and calculating the fluid pressure of the gas reservoir according to the real gas state equation to finish the recovery of the fluid paleo-pressure of the crude oil cracking gas reservoir. The ancient pressure recovery method provided by the invention can be used for quantitatively calculating the highest pressure of the gas reservoir after the crude oil cracking is finished, volume parameters are not needed in the calculation process, the reliability and the accuracy of the calculation result are improved, and the practicability is higher.
Description
Technical Field
The invention relates to the technical field of oil and gas reservoir dynamics, in particular to a fluid paleo-pressure recovery method for a crude oil pyrolysis gas reservoir.
Background
The reservoir formation dynamics is a comprehensive subject for researching the formation, evolution and migration processes and aggregation rules of oil and gas in sedimentary basins by comprehensively utilizing geology, geophysical, geochemical means and computer simulation technology and analyzing chemical dynamics, hydrodynamics and kinematics processes of energy field evolution and control thereof in basin evolution history and under a transportation grid. The foundation of the research of the burial dynamics is basin evolution history and a fluid conductance framework, and the core of the research is the chemical dynamics and the fluid dynamics process of the evolution of an energy field (comprising a temperature field, a pressure field and a stress field) and the control of the evolution. In recent years, due to the development of deep and multidisciplinary combined research of oil and gas exploration, the accumulation dynamics makes important progress in various aspects such as a fluid transportation system, basin energy field evolution and fluid flow pattern, an oil and gas accumulation mechanism, filling history analysis and the like.
The formation fluid pressure is the result of the comprehensive actions of deposition evolution, tectonic movement, hydrodynamic force, water-rock interaction and the like, and is one of the indispensable parameters in the aspects of reservoir formation dynamics such as reservoir formation process, hydrocarbon source rock evolution, reservoir stratum evolution and the like. Formation pressure can be obtained by drilling rod test nowadays, but the ancient fluid pressure is difficult to obtain, because of the irreversible characteristic of geological process, so that it is difficult to recover geological process. At present, there are many methods available for recovering ancient fluid pressure, for example, ancient pressure is determined according to the equilibrium relationship between the uniform temperature of the fluid inclusion and the fluid components (fluid inclusion method for short); the method is based on physical-chemical mechanism of pressure generation, and can be used for performing one-dimensional single well pressure evolution reconstruction, and performing two-dimensional section and even three-dimensional pressure history simulation analysis.
The ancient pressure recovery by using the fluid inclusion is limited by a sample sampling position, an inclusion capturing temperature and a capturing period, and only the ancient pressure change within a uniform temperature change range can be simulated to obtain the uniform pressure or the minimum capturing pressure during fluid filling, and the overpressure limit value generated by crude oil cracking lacks more inclusion evidences, so that the overpressure generated by crude oil cracking is difficult to determine. The acoustic time difference method calculates the ancient fluid pressure in the mudstone, and cannot calculate the fluid pressure in the reservoir; is not suitable for non-mudstone strata and other abnormal pressure forming mechanisms except under compaction. Although the basin simulation method can reflect the ancient pressure and the evolution process thereof from the region, the mathematical model adopted by basin simulation software is a simplification of the complex geological condition, the parameters are various, the uncertain factors are too many, and the result and the actual geological condition often have great errors.
Disclosure of Invention
In order to solve the above problems, the present invention provides an ancient pressure recovery method for a crude oil cracking gas reservoir fluid, which can quantitatively calculate the highest pressure of the gas reservoir after the crude oil cracking is completed by using a real gas state equation, and has no need of volume parameters in the calculation process, so that the reliability and accuracy of the calculation result are improved, and the ancient pressure recovery method has strong practicability.
In order to achieve the above object, the present invention provides a method for recovering paleo-pressure of a crude oil pyrolysis gas reservoir fluid, wherein the method comprises:
determining the hydrostatic pressure, the formation temperature and the natural gas compression factor of a gas reservoir when crude oil is completely cracked;
measuring the volume coefficient, density, asphalt density and cracking rate of crude oil;
and step three, calculating the fluid pressure of the gas reservoir according to the real gas state equation, and completing the recovery of the fluid paleo-pressure of the crude oil cracking gas reservoir.
In particular embodiments of the invention, "formation crude oil" refers to crude oil produced from hydrocarbon source rock of a gas reservoir, or crude oil produced from hydrocarbon source rock of the same type as the hydrocarbon source rock of the gas reservoir under the conditions of the gas reservoir formation, i.e., undegassed crude oil; "crude oil" (or: surface degassed crude oil) refers to crude oil obtained after surface degassing of the formation crude oil.
According to the specific embodiment of the invention, in the step one, the hydrostatic pressure and the formation temperature are obtained through basin simulation software simulation. In some embodiments, hydrostatic pressure and formation temperature may be obtained by basin simulation software simulating the burial history, the geothermal history, the hydrocarbon production history of a single well; specifically, the corresponding burial depth and the formation temperature in the middle of the gas reservoir can be read through a gas generation history curve given by basin simulation software, and then the hydrostatic pressure is calculated according to the read burial depth. The basin simulation software may be PetroMod1D or the like.
In step one, the natural gas compressibility factor is typically read on a gas compressibility factor chart based on the hydrostatic pressure and formation temperature, according to embodiments of the present invention. In some embodiments, the major component of the natural gas is methane, and the natural gas compression factor is typically a methane compression factor.
According to an embodiment of the present invention, in the second step, the crude oil volume coefficient is also called the crude oil subsurface volume coefficient, and is defined as the ratio of the volume of crude oil in the subsurface (i.e. the volume of crude oil in the formation) to the volume of crude oil degassed at the surface (i.e. the volume of crude oil).
According to an embodiment of the present invention, in the second step, the crude oil volume coefficient may be calculated according to the formation temperature, the volume ratio of dissolved gas and oil in the formation crude oil, the relative density of the surface degassed crude oil and the relative density of the separated gas, for example, according to a standard empirical formula.
The volume ratio of solution gas to crude oil in the formation crude oil, the relative density of the surface degassed crude oil, and the relative density of the separated gas as described above may be experimentally measured according to specific embodiments of the present invention. For example, step two of the above ancient pressure recovery method may further comprise placing the formation crude oil on the surface, standing, degassing, weighing the volume and mass of the crude oil before and after degassing, and calculating the volume ratio of dissolved gas and oil in the formation crude oil, the relative density of the surface degassed crude oil, and the relative density of the separated gas.
According to an embodiment of the present invention, in step two, the crude oil volume coefficient is calculated according to the following formula:
Bo＝0.972+1.1213×10-2F1.175，
wherein Bo is the volume coefficient of the crude oil; rs is the volume ratio of dissolved gas to oil in crude oil of the stratum; ro is ground threshingRelative density of gas and crude oil, dimensionless quantity; rg is the relative density of the separated gas (taking the air density as 1 kg/m)3) No dimensional quantity; t is the formation temperature in K.
According to a particular embodiment of the invention, in step two, the crude oil density is measured at surface conditions, for example at 20 ℃, at 0.101MPa surface conditions. In some embodiments, when crude oil in a gas reservoir to be restored to paleo-pressure is cracked and cannot be sampled, formation crude oil generated by hydrocarbon source rocks of the same type as the hydrocarbon source rocks in the gas reservoir can be selected as a sample, and the crude oil density under the surface condition is measured.
According to the specific embodiment of the invention, in the second step, the asphalt density and the crude oil cracking rate are obtained by hydrocarbon generation simulation experiments. In some embodiments, the hydrocarbon generation simulation experiment may include heating (typically controlled at 800 ℃) crude oil to full cracking, weighing the mass and volume of the crude oil before and after heating, and calculating the crude oil cracking rate and bitumen density (bitumen is the residue remaining after full cracking of crude oil, i.e., the density of the residue after thermal cracking).
According to an embodiment of the present invention, the crude oil cracking rate is calculated by the following formula: xm＝(m1-m2)/m1Wherein X ismM is the cracking rate of crude oil1Mass m before heating of crude oil2The quality of the crude oil after heating and cracking.
In an embodiment of the present invention, the cracking rate of the crude oil may be calculated as a range, because the cracking rate measured by selecting different samples is different due to the type, maturity and composition of the crude oil.
According to a specific embodiment of the present invention, in step three, the real gas state equation is PVgZnRT, where P is the fluid pressure of the gas reservoir in Pa; vgIs the volume of natural gas in the gas reservoir, and is expressed in m3(ii) a Z is a natural gas compression factor; n is the amount of substances of the natural gas of the gas reservoir, and the unit is mol; r is a molar gas constant which can be 8.3145; t is the formation temperatureThe bit is K.
According to a specific embodiment of the present invention, the calculation formula of the amount of substance of the gas reservoir natural gas may include:
n＝Xm×ρo×V/(M×Bo)，
wherein n is the amount of the substance in the natural gas of the gas reservoir, M is the molar mass (generally the relative molecular mass of methane) of the natural gas, and X ismV is the total reservoir space of the gas reservoir (i.e. the sum of the natural gas volume and the asphalt volume of the gas reservoir) in m, which is the cracking rate of crude oil3；ρoIs the crude oil density in g/m3；BoIs the volume factor of crude oil. This formula can be derived by the following derivation:
(1) calculating the mass of the natural gas of the gas reservoir: according to the principle of mass conservation, the mass of the natural gas of the gas reservoir is equal to the cracking mass of the crude oil, and the method comprises the following steps:
m＝Xm×mo＝Xm×ρo×V/Bo，
wherein m is the mass of natural gas and XmM is the cracking rate of crude oiloThe unit is g of crude oil reserves of the ancient oil reservoirs; rhooIs the crude oil density in g/m3(ii) a V is the total reservoir space of the gas reservoir in m3；BoIs the volume coefficient of crude oil;
(2) substituting the natural gas mass M calculation formula in the step (1) into n ═ M/M (n is the amount of natural gas substances in the gas reservoir, and M is the molar mass of the natural gas), so as to obtain: n-M/M-Xm×ρo×V/(M×Bo)。
According to a specific embodiment of the present invention, the volume of the gas reservoir natural gas can be calculated according to the following formula:
Vg＝V[1-(1-Xm)×ρo/(ρb×Bo)]，
wherein, VgIs the volume of natural gas in the gas reservoir, and is expressed in m3(ii) a V is the total reservoir space of the gas reservoir in m3；XmThe cracking rate of crude oil; rhooIs the crude oil density in g/m3；ρbTo be leachedGreen density in g/m3；BoIs the volume factor of crude oil.
Volume V of the above gas reservoirgThe calculation formula (c) can be obtained by the following derivation process:
volume V of asphaltb(i.e., the reservoir space occupied by bitumen) is: vb＝mb/ρbWherein the mass m of the asphaltb＝(1-Xm)×moAnd crude oil mass mo＝ρo×V/BoSubstituting into a calculation formula of the volume of the asphalt to obtain: vb＝(1-Xm)×ρo×V/(ρb×Bo) (ii) a Thus, volume V of natural gasgThe calculation formula of (2) is as follows: vg＝V-Vb＝V[1-(1-Xm)×ρo/(ρb×Bo)]。
According to a specific embodiment of the present invention, in step three, the calculation formula of the gas reservoir fluid pressure may be:
wherein, P is the fluid pressure of the gas reservoir and has the unit of Pa; z is a natural gas compression factor; r is a molar gas constant; t is the formation temperature in K; xmThe cracking rate of crude oil; rhooIs the crude oil density in g/m3；ρbIs the density of asphalt in g/m3；BoIs the volume coefficient of crude oil; m is the molar mass of natural gas and has the unit of g/mol.
According to a specific embodiment of the present invention, the above-mentioned ancient pressure recovery method may comprise the following processes:
1. and simulating the burying history, the geothermal history and the hydrocarbon generation history of the single well by using basin simulation software. According to the gas generation history curve, judging the time when the natural gas stops generating, namely the geological time when the crude oil is completely cracked into the natural gas, reading the corresponding burial depth and the formation temperature T (unit is K) in the middle of the gas reservoir in the address period, and calculating the hydrostatic pressure according to the burial depth;
2. reading a natural gas compression factor Z on a methane compression factor chart according to the formation temperature and the hydrostatic pressure obtained in the step 1;
3. placing a certain amount of formation crude oil on the ground, standing and degassing, weighing the volume and mass of the crude oil before and after degassing, calculating the volume ratio Rs of dissolved gas and oil, the relative density Ro of the ground degassed crude oil and the relative density Rg of separated gas, and then calculating the volume coefficient B of the crude oil according to the following formulao：
Bo＝0.972+1.1213×10-2F1.175，
4. Selecting crude oil generated by hydrocarbon source rocks of the same type as the hydrocarbon source rocks of the gas reservoir, and measuring the density rho of the crude oil under the ground standard conditiono(unit is g/m)3)；
5. According to the experimental procedure of hydrocarbon generation thermal simulation, crude oil is heated (preferably at 800 ℃) until the crude oil is completely cracked, and the mass m of the crude oil before heating is weighed1Mass m after heating2，Xm＝(m1-m2)/m1Calculating the crude oil cracking rate XmAnd measuring the density rho of the asphaltb(unit is g/m)3)；
6. Calculating the amount n of the substances of the natural gas of the gas reservoir, wherein the calculation formula is as follows:
n＝m/M＝(Xm×ρo×V)/(M×Bo)，
wherein M is the mass of the natural gas in the gas reservoir, and M is the relative molecular mass of the natural gas and has the unit of g/mol; v is the total reservoir space of the gas reservoir in m3；BoThe volume coefficient of the crude oil measured in the step 3; rhooThe crude oil density measured in step 4 is in g/m3；XmThe crude oil cracking rate calculated for step 5.
7. Calculating the volume V of natural gas in a gas reservoirg(unit is m)3) The calculation formula is as follows:
Vg＝V[1-(1-Xm)×ρo/(ρb×Bo)]；
wherein V is the total storage space of the gas reservoir and the unit is m3；BoThe volume coefficient of the crude oil measured in the step 3; rhooThe crude oil density measured in step 4 is in g/m3；XmThe crude oil cracking rate calculated for step 5; rhobThe density of the asphalt measured in step 5 is given in g/m3。
8. According to the real gas state equation PVgZnRT, the amount n of the substance of the gas reservoir natural gas in the step 6 and the volume V of the gas reservoir natural gas in the step 7 are calculatedgSubstituting, calculating gas reservoir fluid pressure:
wherein, P is the pressure of gas reservoir fluid and the unit is Pa; r is a molar gas constant.
The invention has the beneficial effects that:
the method for recovering the fluid paleo-pressure of the crude oil cracking gas reservoir is a method for calculating the highest fluid pressure of the crude oil cracking gas reservoir of the carbonate rock reservoir in a reasonable and quantitative mode, overcomes the limitations and the defects of the conventional paleo-pressure recovery technology of the oil-gas-containing basin, can quantitatively calculate the highest pressure of the crude oil cracking-finished gas reservoir without volume parameters according to experimental parameters (such as oil density, asphalt density, crude oil volume coefficient, natural gas compression factor, crude oil cracking rate and the like), improves the reliability and the accuracy of a calculation result, and has stronger practicability.
Drawings
Fig. 1 is a work flow diagram of the ancient pressure recovery method of example 1.
FIG. 2 is a gas production history curve for a single well of the gas reservoir of example 1.
Detailed Description
The technical solutions of the present invention will be described in detail below in order to clearly understand the technical features, objects, and advantages of the present invention, but the present invention is not limited to the practical scope of the present invention.
Example 1
The present embodiment provides a method for recovering ancient pressure of a crude oil pyrolysis gas reservoir fluid, and fig. 1 is a work flow chart of the ancient pressure recovery method of the present embodiment. The ancient pressure recovery method is applied to the process of grinding the stream block of the Miao group of the Longwang temple in the air field of the four-Sichuan basin and the Yue and acquiring the fluid pressure of the air reservoir, and specifically comprises the following steps:
1. obtaining the burial depth, the hydrostatic pressure and the formation temperature of the ancient gas reservoir:
the burial history, the geothermal history and the hydrocarbon production history of a single well were simulated using PetroMod1D basin simulation software. FIG. 2 is a gas production history curve for a single well. According to the figure 2, the moment when the natural gas stops generating, namely the geological period when the crude oil is completely cracked, is judged, the corresponding burial depth of the middle part of the gas reservoir in the geological period is 7000m, the corresponding formation temperature is 473K (200 ℃), and the hydrostatic pressure is calculated to be 68.6MPa according to the burial depth.
2. Reading a natural gas compression factor:
for a crude oil pyrolysis gas reservoir, the main component of natural gas is methane, and the methane compressibility factor is read in a methane compressibility factor chart to be 1.6 according to the hydrostatic pressure and formation temperature obtained in step 1.
3. Obtaining the volume coefficient of crude oil:
taking out a certain quantity of crude oil from stratum, and immediately measuring its mass ma1And volume Va1Then standing the crude oil for a period of time, separating the natural gas dissolved in the crude oil, and measuring the mass m of the degassed crude oila2And volume Va2Volume of separated natural gas is Va3Density of air is ρa：
Calculating the volume ratio Rs ═ V of dissolved gas and oil in crude oil of stratuma3/Va2；
Ground degassed crude oil relative density Ro ═ ma2/(ρa×Va2)；
Separated gas relative density Rg ═ m (m)a1-ma2)/(ρa×Va3)；
The crude oil volume coefficient was calculated according to the following formula:
Bo＝0.972+1.1213×10-2F1.175，
wherein, BoIs the volume coefficient of crude oil, and Rs is the volume ratio of dissolved gas to oil in the crude oil in the stratum; ro is the relative density of the ground degassed crude oil, and is a dimensionless quantity; rg is the relative density of the separated gas and has no dimensional quantity; t is the formation temperature in K; finally calculating to obtain BoIs 1.243.
4. Determination of crude oil density at surface conditions:
selecting formation crude oil generated by hydrocarbon source rocks with the same type as the hydrocarbon source rocks of the gas reservoir, and measuring the density rho of the degassed crude oil under the ground standard conditions (20 ℃, 0.101MPa)oIs 8.575X 105g/m3。
5. Measuring the mass and density of the asphalt, and calculating the cracking rate of the crude oil:
weighing mass m according to the steps of hydrocarbon generation thermal simulation experiment1Injecting the weighed crude oil into a gold tube by using a glass injector, heating the crude oil in the gold tube to 800 ℃ until the crude oil is completely cracked, weighing the mass m of the cracked crude oil2The mass of the asphalt is calculated, and the density of the cracked crude oil is calculated, namely the density of the asphalt;
calculating the cracking rate X of the crude oil according to the measurement result of the hydrocarbon generation thermal simulation experimentm＝(m1-m2)/m1Obtaining XmIs 0.4-0.5.
6. Calculating the amount of the substances of the natural gas of the gas reservoir, and the specific process comprises the following steps:
according to the principle of conservation of mass, the mass of natural gas in a gas reservoir is equal to the cracking mass of crude oil, i.e. the mass of natural gas in a gas reservoir
m＝Xm×mo＝Xm×ρo×V/Bo，
Wherein m is the mass of the natural gas of the gas reservoir,the unit is g; xmThe cracking rate of crude oil; m isoThe unit is g and is the total mass of the crude oil; rhooIs the crude oil density in g/m3(ii) a V is the total reservoir space of the gas reservoir and is expressed in m3；BoIs the volume factor of crude oil.
Substituting the calculation formula of the mass m of the gas reservoir natural gas into the calculation formula of the mass of the gas reservoir natural gas:
n＝m/M＝(Xm×ρo×V)/(M×Bo)，
wherein m is the mass of the natural gas in the gas reservoir, and the unit is g; m is the natural gas molar mass (in this example, the relative molecular mass of methane) in g/mol; xmThe cracking rate of crude oil; m isoIs the crude oil mass in g; v is the total reservoir space of the gas reservoir and is expressed in m3；BoIs the volume factor of crude oil.
7. The volume of the natural gas (namely the total storage space of the gas reservoir) of the gas reservoir is calculated by the following specific process:
according to the mass m of the asphaltb＝(1-Xm)×moCalculating the storage space V occupied by the asphaltb：
Vb＝mb/ρb＝(1-Xm)×mo/ρb，
M is to beo＝ρo×V/BoSubstituting, then the above formula is:
Vb＝mb/ρb＝(1-Xm)×ρo×V/(ρb×Bo)，
thus, the volume of the gas reservoir natural gas is Vg＝V-Vb＝V[1-(1-Xm)×ρo/(ρb×Bo)]，
Wherein, VgIs the volume of natural gas in the gas reservoir, and is expressed in m3(ii) a V is the total reservoir space of the gas reservoir and is expressed in m3；XmThe cracking rate of crude oil; rhooIs the crude oil density in g/m3。
8. And calculating the fluid pressure of the gas reservoir according to a real gas state equation:
substituting the calculation formula of the amount of the substances of the gas reservoir natural gas in the step 6 and the calculation formula of the volume of the gas reservoir natural gas in the step 7 into a real gas state equation PV of the gas reservoir natural gasgZnRT to yield:
wherein, P is the pressure of gas reservoir fluid and the unit is Pa; z is a methane compression factor; t is the formation temperature in K; xmThe cracking rate of crude oil; r is the molar gas constant, value 8.3145; rhooIs the crude oil density in g/m3；ρbIs the density of asphalt in g/m3(ii) a M is the relative molecular mass of methane and the unit is g/mol; bo is the crude oil volume coefficient.
The values read, measured and calculated in steps 1-7 are summarized in table 1.
TABLE 1
| Z | R | T(K) | Xm | Bo | M | ρo(g/m3) | ρb(g/m3) |
| 1.6 | 8.3145 | 473 | 0.4-0.5 | 1.243 | 16 | 8.575×105 | 1.9×106 |
From the data in table 1, the gas reservoir fluid pressure P is calculated to be 138.75MPa (corresponding to X)m0.4), P165.74 MPa (corresponding to X)m0.5), namely the ancient pressure value of the Longwanggao group grinding section is 138.75-165.74 MPa.
The ancient pressure of the same block is restored by using a basin simulation means, and the obtained ancient pressure value of the block is 125-130MPa, which is relatively close to the ancient pressure value restored by adopting the method provided by the embodiment.
The embodiment proves that the ancient pressure recovery method provided by the invention can quantitatively calculate the highest pressure of the gas reservoir after the crude oil cracking is finished, and the calculation result of the method has reliability, accuracy and stronger practicability and is easy to popularize.
Claims (15)
1. A crude oil pyrolysis gas reservoir fluid paleo-pressure recovery method, wherein the paleo-pressure recovery method comprises:
determining the hydrostatic pressure, the formation temperature and the natural gas compression factor of a gas reservoir when crude oil is completely cracked;
measuring the volume coefficient, density, asphalt density and cracking rate of crude oil;
and step three, calculating the fluid pressure of the gas reservoir according to the real gas state equation, and completing the recovery of the fluid paleo-pressure of the crude oil cracking gas reservoir.
2. The ancient pressure recovery method of claim 1, wherein, in step one, the hydrostatic pressure and the formation temperature are obtained by basin simulation software.
3. The ancient pressure recovery method according to claim 1 or 2, wherein, in step one, the natural gas compressibility factor is read on a gas compressibility factor chart according to the hydrostatic pressure and formation temperature.
4. The ancient pressure recovery method of claim 1, wherein, in step two, the crude oil volume factor is calculated from the formation temperature, the volume ratio of dissolved gas and oil in the formation crude oil, the relative density of the surface degassed crude oil, and the relative density of the separated gas.
5. The ancient pressure recovery method according to claim 1 or 4, wherein the second step further comprises the operations of:
placing the formation crude oil on the ground, standing and degassing, weighing the volume and the mass of the crude oil before and after degassing, and calculating the volume ratio of dissolved gas and oil in the formation crude oil, the relative density of the ground degassed crude oil and the relative density of separated gas.
6. The ancient pressure recovery method according to any one of claims 1 and 4-5, wherein, in the second step, the crude oil volume coefficient is calculated according to the following formula:
Bo＝0.972+1.1213×10-2F1.175，
wherein Bo is the volume coefficient of crude oil, and Rs is the volume ratio of dissolved gas to oil in the crude oil of the stratum; ro is the relative density of the ground degassed crude oil, and is a dimensionless quantity; rg is the relative density of the separated gas and has no dimensional quantity; t is the formation temperature in K.
7. The ancient pressure recovery method of claim 1, wherein, in step two, the crude oil density is measured at surface conditions in g/m3(ii) a Preferably, the ground conditions are 20 ℃ and 0.101 MPa.
8. The ancient pressure recovery method of claim 1, wherein, in step two, the bitumen density and crude oil cracking rate are obtained by hydrocarbon generation simulation experiments.
9. The ancient pressure recovery method according to claim 1 or 8, wherein step two comprises the following operations:
heating crude oil to be completely cracked, weighing the mass and the volume of the crude oil before and after heating, and calculating the cracking rate of the crude oil and the density of the asphalt.
10. The ancient pressure recovery method of claim 9, wherein the crude oil was heated to a temperature of 800 ℃.
11. The ancient pressure recovery method according to any one of claims 1 and 8-10, wherein in the second step, the calculation formula of the crude oil cracking rate comprises:
Xm＝(m1-m2)/m1，
wherein, XmM is the cracking rate of crude oil1Mass m before heating of crude oil2Is the heated quality of the crude oil.
12. The ancient pressure recovery method of claim 1, wherein, in step three, the real gas state equation comprises:
PVg＝ZnRT，
wherein, P is the pressure of gas reservoir fluid and the unit is Pa; vgIs the volume of natural gas in the gas reservoir, and is expressed in m3(ii) a Z is a natural gas compression factor; n is the amount of substances of the natural gas of the gas reservoir, and the unit is mol; r is a molar gas constant; t is the formation temperature in K.
13. The ancient pressure recovery method of claim 12, wherein the formula for calculating the amount of matter of the gas reservoir natural gas comprises:
n＝Xm×ρo×V/(M×Bo)，
wherein n is the amount of substances of the natural gas of the gas reservoir, and the unit is mol; xmThe cracking rate of crude oil; v is the total reservoir space volume of the gas reservoir in m3；ρoIs the crude oil density in g/m3(ii) a M is the molar mass of natural gas and the unit is g/mol; b isoIs the volume factor of crude oil.
14. The ancient pressure recovery method according to claim 12 or 13, wherein the volume calculation formula of the gas reservoir natural gas comprises:
Vg＝V[1-(1-Xm)×ρo/(ρb×Bo)]，
wherein, VgIs the volume of natural gas in the gas reservoir, and is expressed in m3(ii) a V is the total reservoir space volume of the gas reservoir in m3；XmThe cracking rate of crude oil; rhooIs the crude oil density in g/m3；ρbIs the density of asphalt in g/m3；BoIs the volume factor of crude oil.
15. The ancient pressure recovery method according to any one of claims 1, 12-14, wherein, in step three, the gas reservoir fluid pressure is calculated by the formula:
wherein, P is the pressure of gas reservoir fluid and the unit is Pa; z is a natural gas compression factor; r is a molar gas constant; t is the formation temperature in K; xmThe cracking rate of crude oil; rhooIs the crude oil density in g/m3；ρbIs the density of the asphalt in g-m3；BoIs the volume coefficient of crude oil; m is the natural gas molar mass and the unit is g/mol.
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