CN111912960B - Quantitative evaluation method and system for kerogen free oil in shale - Google Patents
Quantitative evaluation method and system for kerogen free oil in shale Download PDFInfo
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Abstract
The invention relates to a quantitative evaluation method and system for kerogen free oil in shale. Loading each kerogen molecular model into a slit-type pore formed by a graphene lamellar structure by establishing different types of kerogen molecular models, and performing energy minimization treatment, relaxation treatment and simulated annealing processes to obtain the slit-type pore of the kerogen; loading shale oil molecules to a kerogen slit-type pore to obtain an initial model; evaluating the force fields of the shale oil molecules and the kerogen molecules in the model to obtain kerogen and shale oil density results, and drawing kerogen and shale oil density curves; obtaining the free oil quantification of the kerogen according to the curve; determining the free oil quantification of the kerogen in unit area and the specific surface area of the kerogen; and determining the free oil quantification of the kerogen in different evolution stages according to the free oil quantification of the kerogen in unit area and the specific surface area of the kerogen. The method can improve the accuracy of the quantitative evaluation of the kerogen free oil.
Description
Technical Field
The invention relates to the field of quantitative evaluation of free kerogen oil in shale, in particular to a method and a system for quantitative evaluation of free kerogen oil in shale.
Background
Effective exploration and development of shale oil and shale fracture reservoirs in China show that shale has the potential of serving as an oil reservoir, but whether oil can flow effectively and how much oil can flow in the shale is related to pore throat size, structure, distribution and connectivity of the shale, liquid-solid interaction and occurrence states and mechanisms (such as adsorption, dissociation, dissolution and the like) of the oil in the reservoir, and the liquid-solid interaction is further related to composition, type and physical properties (such as viscosity and density) of the shale oil.
Preliminary evaluation shows that the shale oil resources in China are very rich, the geological resource amount can reach 320 hundred million barrels (3450 hundred million barrels in total) and the shale oil resources are ranked the third place in 41 countries all over the world. At present, a batch of geological resources of 5 multiplied by 10 are found in three-fold series extension groups of Erdos basin, two-fold series reed grass ditch groups of pseudo-Ozel basin and Qing section areas of Songliao basin in China 8 Ton to 10X 10 8 Reserves between tons. There are also many important findings in the gray matter shale in the Bohai Bay region and the Sichuan basin. Compared with North American marine shale oil, china's lake shale oil is heavier, has high wax content, and has higher polar components (colloid and asphaltene) than North American shale oil. These heavy components have strong interactions with the kerogen in shale and the extensively developed nanopores in minerals, making lake-facies shale oil more adsorptive in shale reservoirs and difficult to develop efficiently. Therefore, these polar components that lead to errors in estimates of recoverable resources should be considered in the evaluation of shale oil resources.
Since the beginning of molecular dynamics methods, the theory, technology and application fields of the molecular dynamics methods are greatly expanded, and the molecular dynamics methods can be applied to balanced and unbalanced systems. Due to the complexity of kerogen, researchers have generally used graphene, a two-dimensional carbon material, instead of kerogen, in molecular dynamics simulation studies of the interaction of shale oil on the surface of kerogen. However, kerogen elements and functional groups are complex in composition, research on shale oil adsorption by replacing kerogen with graphene, a two-dimensional simple carbon material, is not feasible, and a shale oil adsorption system simulated by molecular dynamics is too small (the simulation system is usually smaller than 20nm, and the pore diameter of a shale reservoir larger than 20nm accounts for a large part), so that the shale oil adsorption system is difficult to apply to geological conditions of shale oil swelling and adsorption. The occurrence state of shale oil in shale, the proportion of different occurrence states (dissolution, swelling, adsorption and dissociation), the occurrence pore size and the interconversion condition, namely the shale oil occurrence mechanism are closely related to the shale oil flowability. Because the water content in shale is low, and the oil solubility in water is extremely low, the dissolved shale oil can be ignored in shale oil occurrence research. The swollen shale oil exists in an organic matrix, shale oil molecules are surrounded by kerogen molecules, and the swollen shale oil is difficult to flow. The adsorbed petroleum is adsorbed on the surface of organic matter and mineral particles in a 'solid-like state', and the flowability is inferior. The free shale oil is not adsorbed by kerogen and mineral particles and flows most easily. The shale oil resource which is abundant in quantity and exists in a free state in the shale is a key scientific problem to be solved for shale oil geological research, and whether the shale oil resource can be effectively explored and developed.
Disclosure of Invention
The invention aims to provide a method and a system for quantitatively evaluating free kerogen oil in shale, which can improve the accuracy of evaluating the free kerogen oil.
In order to achieve the purpose, the invention provides the following scheme:
a quantitative evaluation method for kerogen free oil in shale comprises the following steps:
establishing different types of kerogen molecular models, and loading each kerogen molecular model into a slit-type pore formed by a graphene lamellar structure to obtain an initial model;
performing energy minimization treatment and relaxation treatment on each initial model to obtain a compacted kerogen aggregate model;
simulating an annealing process of the compacted kerogen aggregate model to obtain slit-shaped kerogen pores;
loading shale oil molecules to the slit-type pores of the kerogen to obtain an initial swelling and adsorption model of the shale oil in the kerogen;
evaluating the swelling of the shale oil in the kerogen and the force field for adsorbing the shale oil molecules and the kerogen molecules in the initial model to obtain the density results of the kerogen and the shale oil;
drawing a kerogen and shale oil density curve according to the kerogen and shale oil density result;
determining the swelling oil quantity of the kerogen in unit mass according to the kerogen and shale oil density curve;
determining the specific surface area of the kerogen according to the swelling oil quantity of the kerogen per unit mass;
determining the amount of oil adsorbed by the kerogen in unit area according to the kerogen and shale oil density curve;
determining the amount of the kerogen adsorbed oil in different evolution stages according to the free oil quantification of the kerogen in unit area and the specific surface area of the kerogen;
determining the volume of the kerogen adsorption oil phase according to the amount of the kerogen adsorption oil;
determining the shale oil density according to the kerogen and shale oil density curve;
and determining the amount of the organic pore free oil according to the specific surface area of the kerogen, the volume of the kerogen-adsorbed oil phase and the shale oil density.
Optionally, the energy minimization and relaxation treatment of each initial model is performed to obtain a compacted kerogen aggregate model, and the method specifically includes:
and performing energy minimization treatment and 200ps relaxation treatment on the initial model by using Gromacs software under the temperature and pressure conditions of 75 ℃ and 20MPa to obtain a compacted kerogen aggregate model.
Optionally, the compacted kerogen aggregate model is subjected to simulated annealing process to obtain kerogen slit-type pores, and the method specifically includes:
performing 200ps relaxation heating on the compacted kerogen aggregate model;
and (3) carrying out 2ns simulation, temperature reduction and pressurization treatment on the kerogen aggregate model subjected to relaxation heating by utilizing NPT ensemble under the temperature and pressure conditions of 800 ℃ and normal pressure to obtain kerogen slit-type pores.
Optionally, the determining the swelling oil amount of the kerogen in unit mass according to the kerogen and shale oil density curve specifically includes:
adopting a formula according to the kerogen and shale oil density curve
Obtaining the swelling oil quantity of kerogen;
wherein Q is oil The amount of swelling oil of kerogen; l is o1 The initial position of the intersection of the kerogen density curve and the shale oil density curve is shown; l is o2 The cut-off position of the intersection of the kerogen density curve and the shale oil density curve is defined; s model Is the cross-sectional area of the kerogen-shale oil swelling and adsorbing model; rho oil Is a shale oil density curve;
obtaining the quality of kerogen;
and determining the swelling oil quantity of the kerogen in unit mass according to the swelling oil quantity of the kerogen and the mass of the kerogen.
Optionally, determining the amount of oil adsorbed by kerogen in unit area according to the kerogen and shale oil density curve specifically includes:
adopting a formula according to the kerogen and shale oil density curve
And
obtaining the oil adsorption amount of the left side wall surface and the oil adsorption amount of the right side wall surface of the kerogen;
adding the oil adsorption amount of the left side wall surface of the kerogen and the oil adsorption amount of the right side wall surface to obtain the kerogen adsorption oil quantification;
wherein m is a1 The amount of oil adsorbed on the left side wall surface of the kerogen is shown; l is 1 The left side position where the kerogen density curve and the shale oil density curve are intersected is taken as a reference position; l is 2 The left side position of the junction of the shale oil density curve adsorption area and the free area; m is a unit of a2 The adsorbed oil amount of the right side wall surface of the kerogen is shown; l is 3 The position of the right side of the junction of the shale oil density curve adsorption area and the free area is shown; l is a radical of an alcohol 4 The right side position where the kerogen density curve and the shale oil density curve are intersected is shown; s. the model Is the cross-sectional area of the kerogen-shale oil swelling and adsorbing model; ρ is a unit of a gradient oil Is a shale oil density curve;
obtaining the left side sectional area and the right side sectional area of the kerogen model;
adding the left side sectional area and the right side sectional area to obtain the sum of the kerogen model sectional areas;
and dividing the amount of the kerogen adsorbed oil by the sum of the cross sections of the kerogen models to obtain the amount of free kerogen oil in unit area.
Optionally, the determining the specific surface area of the kerogen by the swelling oil amount of the kerogen in unit mass specifically includes:
adopting a formula according to the swelling oil quantity of the kerogen in unit mass
wherein,
is the specific surface area of kerogen, Q v Amount of swollen kerogen per unit mass, V gh Volume of organic pores, V, due to formation of oil and gas by kerogen f Volume corresponding to the convertible part of kerogen, F t To conversion, V s The volume corresponding to the non-convertible fraction of kerogen.
Optionally, the determining the amount of the kerogen adsorbed oil in different evolution stages according to the free oil quantification of the kerogen in the unit area and the specific surface area of the kerogen specifically comprises:
and multiplying the kerogen adsorption oil quantity in unit area by the specific surface area of the kerogen to obtain the kerogen adsorption oil quantity in different evolution stages.
Optionally, determining the volume of the kerogen-adsorbed oil phase according to the amount of the kerogen-adsorbed oil specifically includes:
obtaining shale oil adsorption phase density;
and determining the volume of the kerogen-adsorbed oil phase according to the amount of the kerogen-adsorbed oil and the density of the shale oil-adsorbed phase.
Optionally, the determining the amount of organic pore free oil according to the specific surface area of kerogen, the volume of the kerogen-adsorbed oil phase and the shale oil density specifically comprises:
adopting a formula according to the specific surface area of the kerogen, the volume of the kerogen adsorption oil phase and the shale oil density
Determining the amount of free oil in organic pores;
wherein,
is the specific surface area of kerogen, V ad Adsorption of the oil phase volume, rho, for kerogen oil Is shale oil density, Q free The amount of free oil in the organic pores.
A system for quantitatively evaluating kerogen free oil in shale comprises:
the first initial model building module is used for building different types of kerogen molecular models, and loading each kerogen molecular model into a slit-type pore formed by a graphene lamellar structure to obtain an initial model;
the compaction module is used for performing energy minimization treatment and relaxation treatment on each initial model to obtain a compacted kerogen aggregate model;
the annealing module is used for simulating an annealing process of the compacted kerogen aggregate model to obtain kerogen slit-type pores;
the second initial model building module is used for loading shale oil molecules to the kerogen slit-shaped pores to obtain a swelling and adsorption initial model of the shale oil in the kerogen;
the evaluation module is used for evaluating the swelling of the shale oil in the kerogen and the force field for adsorbing the shale oil molecules and the kerogen molecules in the initial model to obtain the density results of the kerogen and the shale oil;
the oil density curve drawing module is used for drawing kerogen and shale oil density curves according to the kerogen and shale oil density results;
the device comprises a swelling oil quantity determining module for the kerogen of unit mass, a swelling oil quantity determining module for the kerogen of unit mass and a swelling oil quantity determining module for the kerogen of unit mass according to the density curve of the kerogen and the shale oil;
the kerogen specific surface area determining module is used for determining the kerogen specific surface area according to the swelling oil quantity of the kerogen in unit mass;
the device comprises a unit area kerogen adsorbed oil quantity determining module, a unit area kerogen adsorbed oil quantity determining module and a control module, wherein the unit area kerogen adsorbed oil quantity determining module is used for determining the unit area kerogen adsorbed oil quantity according to the kerogen and shale oil density curve;
the kerogen adsorbed oil quantity determining module is used for determining the kerogen adsorbed oil quantities in different evolution stages according to the free oil quantification of the kerogen in unit area and the specific surface area of the kerogen;
the kerogen adsorbed oil phase volume determining module is used for determining the kerogen adsorbed oil phase volume according to the kerogen adsorbed oil quantity;
the shale oil density determining module is used for determining the shale oil density according to the kerogen and shale oil density curve;
and the free oil quantity determination module is used for determining the organic pore free oil quantity according to the specific surface area of the kerogen, the volume of the kerogen adsorption oil phase and the shale oil density.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the method uses the real kerogen model to overcome the problems existing in the process of researching the adsorption between the kerogen and the shale oil by simply using the graphene to replace the kerogen in the prior art: because the graphene is a two-dimensional carbon material, the surface of the graphene is very smooth, and the difference between the surface structure of the graphene and kerogen molecules is large; and shale oil molecules cannot penetrate through the graphene material to enter the lamellar structure of the graphene material, so that the swelling phenomenon cannot be generated, and the structure is not consistent with the real kerogen structure. The pretreatment of the kerogen collection model overcomes the problem of incomplete compaction of the kerogen collection: incomplete compaction of the kerogen aggregates can result in "large pores" within the kerogen aggregate model, making the density of the kerogen aggregate model lower than that of the kerogen sample.
The processing process of the swelling oil mass of the kerogen in unit mass and the adsorption oil mass of the kerogen in unit area overcomes the problem that the molecular dynamics simulation system is too small to be applied to the geological condition of shale oil adsorption: the shale oil-kerogen system simulated by molecular dynamics is too small, the pore diameter of the simulated system is usually less than 20nm, the pore diameter of the shale reservoir layer with the pore diameter of more than 20nm accounts for a large part, and the swelling ratio parameter of kerogen is calculated by calculating the swelling oil mass of kerogen in unit mass and combining the actual geological parameter-swelling coefficient reduction parameter; the oil absorption amount of the kerogen is calculated by calculating the oil absorption amount of the kerogen in unit area and combining an actual geological parameter-the specific surface area of the kerogen, so that the accuracy of the result is greatly improved.
The quantitative evaluation of the free oil amount of kerogen in different evolution stages provides important parameters for evaluation of shale oil mobility, and can improve the accuracy of evaluation of shale oil mobility.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a flow chart of the quantitative evaluation method of kerogen free oil in shale of the invention;
FIG. 2 is a schematic diagram of an initial model for swelling and adsorption of shale oil in different types of kerogen according to the present invention;
FIG. 3 is a graph of the density of type I kerogen and shale oils according to the invention;
FIG. 4 shows the parameters along with R required for quantitative calculation of I type kerogen adsorbed oil o (ii) an evolutionary graph of the changes;
FIG. 5 is a graph showing the evolution trend of the amount of oil adsorbed by type I kerogen according to Ro in the present invention;
FIG. 6 shows the parameters with R required for quantitative calculation of type I kerogen free oil in accordance with the present invention o (ii) an evolutionary graph of the changes;
fig. 7 is a structural diagram of a system for quantitatively evaluating kerogen free oil in shale according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In order to make the aforementioned objects, features and advantages of the present invention more comprehensible, the present invention is described in detail with reference to the accompanying drawings and the detailed description thereof.
FIG. 1 is a flow chart of the quantitative evaluation method of kerogen free oil in shale. As shown in fig. 1, a method for quantitatively evaluating kerogen free oil in shale comprises the following steps:
step 101: and (3) establishing different types of kerogen molecular models, and loading each kerogen molecular model into a slit-type pore formed by the graphene lamellar structure to obtain an initial model.
The model of the kerogen molecules of type I, type II and type III is established by using the Avogadro software, as a preferred embodiment, only the kerogen molecule model of type II is selected for illustration, specifically, 100 kerogen molecules of type II are loaded into a slit-type pore composed of a graphene lamellar structure (the size of the graphene lamellar structure is about 7.38nm × 7.67nm × 0.85 nm) by using the Packmol software.
Step 102: performing energy minimization treatment and relaxation treatment on each initial model to obtain a compacted kerogen aggregate model, which specifically comprises the following steps:
and carrying out energy minimization treatment and 200ps relaxation treatment on the initial model by utilizing Gromacs software under the temperature and pressure conditions of 75 ℃ and 20MPa by using an NPT (non-uniform pressure) ensemble to obtain a compacted kerogen aggregate model.
Step 103: and simulating an annealing process of the compacted kerogen aggregate model to obtain a kerogen slit-type pore, which specifically comprises the following steps:
and (3) carrying out 200ps relaxation heating on the compacted kerogen aggregate model.
And (3) carrying out 2ns simulation, temperature reduction and pressurization treatment on the kerogen aggregate model subjected to relaxation heating by utilizing NPT (nitrogen-phosphorus-contained T) ensemble under the temperature and pressure conditions of 800 ℃ and normal pressure to obtain the slit-shaped kerogen pores.
Step 104: and (3) loading shale oil molecules into the slit-type pores of the kerogen to obtain an initial swelling and adsorption model of the shale oil in the kerogen.
And (3) loading shale oil molecules into the slit-shaped kerogen pores obtained in the step 103 by using Packmol software to obtain an initial swelling and adsorption model of kerogen internal shale oil, wherein FIG. 2 is a schematic diagram of the initial swelling and adsorption model of different types of kerogen internal shale oil, as shown in FIG. 2, kerogen wall models after a simulated annealing process are arranged on two sides of the model, and a shale oil model is arranged in the middle of the model.
Step 105: and (3) evaluating the swelling of the kerogen internal shale oil and the force field for adsorbing the shale oil molecules and the kerogen molecules in the initial model to obtain the density results of the kerogen and the shale oil.
Assigning the force fields of the shale oil molecules and the kerogen molecules in the swelling and adsorption initial model of the kerogen shale oil obtained in the step 104 by using a Charmm 36/Cgonff force field, using a Lorentz-Bertholt mixing rule for the interaction force of the shale oil molecules and the kerogen molecules, using a Particle-Mesh-Ewald model (PME) for an electrostatic force model, taking the Van der Waals radius as 1.4nm, using Gromacs software to simulate an NPT ensemble on the model after assigning the force fields, wherein the simulation temperature is 75 ℃, the pressure is 20MPa, the simulation time is 200ns, drawing a kerogen and shale oil density curve graph (step 106), and FIG. 3 is a type I kerogen and shale oil density curve graph of the invention.
Step 106: and drawing a kerogen and shale oil density curve according to the kerogen and shale oil density result.
Step 107: determining the swelling oil mass of the kerogen in unit mass according to the kerogen and shale oil density curve, and specifically comprises the following steps:
adopting a formula according to the kerogen and shale oil density curve
The amount of the kerogen swollen oil was obtained.
Wherein Q is oil The swelling oil amount of kerogen is given in g; l is o1 The initial position of the intersection of the kerogen density curve and the shale oil density curve is represented by nm; l is a radical of an alcohol o2 The cutoff position of the intersection of the kerogen density curve and the shale oil density curve is represented by nm; s model Is the cross-sectional area of the kerogen-shale oil swelling and adsorbing model, and the unit is m 2 ；ρ oil Is shale oil density curve with unit of kg/m 3 (ρ oil ，L o1 ，L o2 May be read from the density curve of shale oil).
And obtaining the quality of the kerogen.
And determining the swelling oil quantity of the kerogen in unit mass according to the swelling oil quantity of the kerogen and the mass of the kerogen. Specifically, the swelling oil amount Q of the kerogen in unit mass is obtained by dividing the swelling oil amount of the kerogen by the mass of the kerogen w The amount of swelling oil in kerogen I and kerogen III was 161.04mg/g TOC, and the initial swelling factor Q was obtained in a dimensionless manner v0 Is 1.161.
Step 108: determining the specific surface area of the kerogen according to the swelling oil quantity of the kerogen in unit mass, and specifically comprises the following steps:
adopting a formula according to the swelling oil quantity of the kerogen in unit mass
wherein,
is the specific surface area of kerogen, Q v Amount of swelling oil per unit mass of kerogen, V gh Volume of organic pores, V, due to formation of oil and gas by kerogen f Volume corresponding to the convertible part of kerogen, F t To conversion, V s The volume corresponding to the non-convertible part of the kerogen.
Specifically, the process for determining the specific surface area of kerogen is as follows:
dividing the shale micropores (< 10 nm), the small holes (10 nm-50 nm), the medium holes (50 nm-150 nm) and the large holes (150 nm-1000 nm, 1000 nm-10000 nm) according to logarithmic coordinates, averagely dividing each section into 10 parts, and counting the nth section (D) n-1 ～D n ) The surface area of the organic pores in the pore diameter, the organic pore surface area SK can be obtained by the sum of the n sections of specific surface area:
in the formula, n is the sectional statistical number of the pore diameters of the shale, and n =50 is dimensionless; SK n Is the nth segment (D) n-1 ～D n ) Surface area of cheese root pores within the pore diameter, in m 2 。
Let the nth segment (D) n-1 ～D n ) The pores of the organic matter in the pore diameter are all D n Spherical pore composition of (2), then SK n Can be derived from the following formula:
in the formula (II b), NK n Is the nth segment (D) n-1 ～D n ) The number of organic matter pores in the pore diameter is dimensionless;
is a single diameter of D n In m of the surface area of the spherical pores 2 (ii) a RK is a kerogen pore surface roughness coefficient which is taken according to the kerogen pore surface roughness coefficient of a Ha16 shale oil sample, and RK =1.2176.
n-th stage (D) n-1 ～D n ) Number NK of organic pores in pore diameter n Can be composed of the nth segment (D) n-1 ～D n ) Organic matter pore volume VK in pore diameter n Divided by a single diameter of D n Volume of spherical pores
To obtain:
in the formula,
1g of original organic carbon corresponds to the pore volume of kerogen in m 3 ；Pk n Is the nth segment (D) n-1 ～D n ) The proportion of the pore diameter on the pore diameter distribution of the scanning electron microscope is dimensionless.
N-th stage (D) n-1 ～D n ) Ratio of pore size Pk in nuclear magnetic resonance pore size distribution n Can be derived from the following formula:
in the formula, P SEM The aperture distribution proportion is based on the scanning electron microscope experiment and has no dimension.
The kerogen pore volume is increased along with the increase of kerogen hydrocarbon generation, but a part of pores are reduced due to swelling effect, the compaction effect of stratum on rock also can cause the reduction of organic pores, and the organic pore volume corresponding to 1g of original organic carbon is combined with the three factors
In the formula, V gh Is the organic pore volume generated by oil gas generated by kerogen, and has unit of cm 3 /g TOC；V sw Is the swelling volume of kerogen in cm 3 /TOC；V os Volume of dead carbon produced for oil cracking to gas in cm 3 /g TOC；V comp Is a compaction factor, dimensionless.
Organic pore volume V due to oil gas generated by kerogen gh Can be obtained by the following formula:
V gh ＝V f ·F t
in the formula, V f Is the volume corresponding to the convertible part of kerogen, and has unit of cm 3 /g TOC；F t For conversion, there is no dimension. Volume V corresponding to convertible part of kerogen f The volume of original kerogen corresponding to 1g of organic carbon
And volume V corresponding to the non-convertible part of the kerogen s So that:
V s ＝m s /ρ s
m s ＝1-HI 0 ·0.083/100
in the formula, HI 0 Is the original hydrogen index in mg/g TOC (750 mg/g TOC); 0.083 is the conversion coefficient of carbon in hydrogen index, dimensionless;
is the density of the unripe kerogen in g/cm 3 ；ρ s Is the density of the non-convertible fraction of kerogen in g/cm 3 . Referring to the type I kerogen density profiles from the hummus (1995) at the unripe and overtured stages,
and rho s Are respectively 1.25g/cm 3 And 1.35g/cm 3 。
Organic pore volume
Swelling capacity with kerogen Q v And organic pore volume V generated by oil gas generated by kerogen gh The following steps are involved:
in the formula, Q v For the type I kerogen swell ratio, pass the initial swell ratio parameter Q in step 4 v0 Multiplied by the swelling ratio reduction parameter, dimensionless.
Calculating to obtain the organic pore volume and the kerogen specific surface area along with R o Is shown. FIG. 4 shows the parameters along with R required for quantitative calculation of I type kerogen adsorbed oil o Evolution of the changes. As can be seen in FIG. 4, with R o (the reflectivity of the vitrinite can reflect the maturity of organic matters), the organic pore volume and the kerogen specific surface area both show the trend of increasing first and then decreasing, but the trend of the kerogen specific surface area decreasing is slower than the trend of the organic pore volume decreasing due to the increase of the proportion of small holes and medium holes in organic pores in a high evolution stage.
Step 109: determining the amount of the kerogen adsorbed oil in unit area according to the kerogen and shale oil density curve, and specifically comprises the following steps:
adopting a formula according to the kerogen and shale oil density curve
And
the amount of oil adsorbed on the left side wall surface and the amount of oil adsorbed on the right side wall surface of kerogen were obtained.
And adding the oil adsorption amount of the left side wall surface of the kerogen and the oil adsorption amount of the right side wall surface to obtain the quantitative kerogen adsorption oil.
Wherein m is a1 The unit is g, which is the oil amount absorbed by the left side wall surface of the kerogen; l is 1 The position (left side) where the kerogen density curve intersects the shale oil density curve is in nm; l is 2 The boundary position (left side) of the shale oil density curve adsorption area and the dissociation area is shown as the unit of nm; m is a2 G is the adsorbed oil mass on the right wall surface of the kerogen; l is 3 The unit is nm, which is the boundary position (right side) of the shale oil density curve adsorption area and the dissociation area; l is a radical of an alcohol 4 The position where the kerogen density curve intersects the shale oil density curve (right side) is in nm; s model Is the cross-sectional area of the kerogen-shale oil swelling and adsorbing model, and the unit is m 2 ；ρ oil Is shale oil density curve with unit of kg/m 3 (ρ oil ，L 1 ，L 2 ，L 3 ，L 4 Read from the density curve of shale oil).
And acquiring the left side sectional area and the right side sectional area of the kerogen model.
And adding the left side sectional area and the right side sectional area to obtain the sum of the kerogen model sectional areas.
And dividing the amount of the kerogen adsorbed oil by the sum of the cross sections of the kerogen models to obtain the amount of free kerogen oil in unit area. According to the above formula, the sum of the amounts of oil (m) adsorbed on the kerogen walls on the left and right sides a1 +m a2 ) Divided by the sum of the cross-sectional areas of the kerogen models on both sides (2. S) model ) The mass can obtain the amount Q of the kerogen absorbed by the unit area a The unit area of the absorbed oil of the I type kerogen is 1.149mg/m 2 。
Step 110: determining the amount of the kerogen adsorbed oil in different evolution stages according to the free oil quantification of the kerogen in unit area and the specific surface area of the kerogen, and specifically comprises the following steps:
and multiplying the kerogen adsorption oil quantity in unit area by the specific surface area of the kerogen to obtain the kerogen adsorption oil quantity in different evolution stages.
Kerogen absorbed oil quantity is along with R o Is increasing and then decreasing, although with R o The formation temperature is increased, but the adsorption quantity per unit area caused by the temperature is changed little, the trend of kerogen oil adsorption quantity is consistent with the trend of kerogen specific surface area, and the kerogen oil adsorption quantity is mainly controlled by the kerogen specific surface area. FIG. 5 is a graph showing the evolution trend of the amount of oil adsorbed by type I kerogen according to Ro in the present invention.
Step 111: determining the volume of the kerogen-adsorbed oil phase according to the amount of the kerogen-adsorbed oil, and specifically comprising the following steps:
and obtaining the shale oil adsorption phase density. Specifically, the shale oil adsorption phase density is obtained through molecular dynamics simulation.
And determining the volume of the kerogen-adsorbed oil phase according to the amount of the kerogen-adsorbed oil and the density of the shale oil-adsorbed phase.
Step 112: determining the shale oil density according to the kerogen and shale oil density curve; specifically, the shale oil density is obtained by weighting the change of the proportion of each component oil generated according to hydrocarbon generation dynamics along with the Ro and the density of each component oil.
Step 113: and determining the amount of the organic pore free oil according to the specific surface area of the kerogen, the volume of the kerogen-adsorbed oil phase and the shale oil density.
In organic pores, shale oil exists mainly in two occurrence states of an adsorption state and a free state, and the volume of an adsorption phase of the shale oil is deducted to obtain the volume of a free phase of the shale oil.
As a preferred embodiment, step 113 specifically includes:
according to the specific surface area of the kerogen, the volume of the kerogen-adsorbed oil phase and the shale oil densityUsing a formula
The amount of organic pore free oil was determined.
Wherein,
is the specific surface area of kerogen, V ad The volume of the oil phase adsorbed by the kerogen is cm 3 /g TOC；ρ oil Is shale oil density in g/cm 3 ；Q free Is the free oil mass of the organic pores. Wherein, V ad ＝Q ad /ρ ad ，Q ad The amount of oil absorbed by kerogen is mg/g TOC; ρ is a unit of a gradient ad The kerogen adsorbs the volume of oil phase in cm 3 /g TOC。
Dividing the obtained kerogen adsorption capacity by shale oil adsorption phase density obtained by molecular dynamics simulation to obtain kerogen adsorption oil phase volume, combining organic pore volume to obtain organic pore free oil phase volume, multiplying by shale oil density to finally obtain organic pore free oil mass along with R o Is being developed. FIG. 6 shows the parameters with R required for quantitative calculation of type I kerogen free oil in accordance with the present invention o Evolution of the changes. As can be seen in FIG. 6, the amount of organic pore free oil is dependent on R o The increase of (2) shows a trend of increasing first and then decreasing, and the maximum organic pore free oil amount is 91.37mg/g TOC which is 2.24 times of the maximum kerogen adsorbed oil amount of 40.82mg/g TOC. In the organic pores in type I kerogen, shale oil predominates in the free state.
The real kerogen model is used in the steps 101-104 of the invention, so that the problems existing in the process of researching the adsorption between the kerogen and the shale oil by simply using the graphene to replace the kerogen in the prior art are solved: since the graphene is a two-dimensional carbon material, the surface of the graphene is very smooth, and the difference between the surface structure of the graphene and kerogen molecules is large; and shale oil molecules cannot penetrate through the graphene material to enter the lamellar structure of the graphene material, so that the swelling phenomenon cannot be generated, and the structure is not consistent with the real kerogen structure. The pretreatment of the kerogen collection model overcomes the problem of incomplete compaction of the kerogen collection: incomplete compaction of the kerogen aggregates can result in "large pores" within the kerogen aggregate model, making the density of the kerogen aggregate model lower than that of the kerogen sample.
The processing procedures of the swelling oil quantity of the kerogen in unit mass and the adsorption oil quantity of the kerogen in unit area in the steps 105 to 112 overcome the problem that the molecular dynamics simulation system is too small to be applied to the geological condition of shale oil adsorption: the shale oil-kerogen system simulated by molecular dynamics is too small, the pore diameter of the simulated system is usually less than 20nm, the pore diameter of the shale reservoir larger than 20nm accounts for a large part, and the kerogen swelling ratio parameter is calculated by calculating the swelling oil mass of the kerogen in unit mass and combining an actual geological parameter-swelling coefficient reduction parameter; the amount of the kerogen-adsorbed oil is calculated by calculating the amount of the kerogen-adsorbed oil in unit area and combining an actual geological parameter-the specific surface area of the kerogen, so that the accuracy of the result is greatly improved.
Step 113 is used for quantitatively evaluating the free oil amount of kerogen in different evolution stages, so that important parameters are provided for evaluating the mobility of shale oil, and the accuracy of evaluating the mobility of shale oil can be improved.
The invention also provides a system for quantitatively evaluating the free oil of the kerogen in the shale. FIG. 7 is a structural diagram of a system for quantitatively evaluating kerogen free oil in shale according to the present invention. As shown in fig. 7, a system for quantitatively evaluating free oil in kerogen in shale comprises:
the first initial model establishing module 201 is used for establishing different types of kerogen molecular models, and loading each kerogen molecular model into a slit-type pore formed by a graphene sheet layer structure to obtain an initial model.
And the compacting module 202 is used for performing energy minimization treatment and relaxation treatment on each initial model to obtain a compacted kerogen aggregate model.
And the annealing module 203 is used for simulating an annealing process of the compacted kerogen aggregate model to obtain kerogen slit-type pores.
The second initial model establishing module 204 is configured to load shale oil molecules into the kerogen slit-type pores to obtain an initial model of swelling and adsorption of the shale oil in the kerogen.
And the assignment module 205 is configured to assign force fields of the swelling of the shale oil in the kerogen and the adsorption of the shale oil molecules in the initial model to obtain density results of the kerogen and the shale oil.
And the oil density curve drawing module 206 is used for drawing a kerogen and shale oil density curve according to the kerogen and shale oil density result.
And the swelling oil quantity per unit mass determination module 207 is used for determining the swelling oil quantity per unit mass of the kerogen according to the density curve of the kerogen and the shale oil.
And a kerogen specific surface area determination module 208 for determining the kerogen specific surface area through the unit mass of the kerogen swelling oil quantity.
And the kerogen absorption oil quantity determining module 209 for determining the kerogen absorption oil quantity of the unit area according to the kerogen and shale oil density curve.
And the kerogen adsorbed oil quantity determining module 210 is used for determining the kerogen adsorbed oil quantity in different evolution stages according to the free oil quantity of the kerogen in unit area and the specific surface area of the kerogen.
And the kerogen adsorbed oil phase volume determining module 211 is used for determining the kerogen adsorbed oil phase volume according to the kerogen adsorbed oil quantity.
And the shale oil density determining module 212 is used for determining the shale oil density according to the kerogen and shale oil density curve.
And a free oil quantity determining module 213, configured to determine the organic pore free oil quantity according to the kerogen specific surface area, the kerogen adsorbed oil phase volume, and the shale oil density.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the foregoing, the description is not to be taken in a limiting sense.
Claims (6)
1. A quantitative evaluation method for kerogen free oil in shale is characterized by comprising the following steps:
establishing different types of kerogen molecular models, and loading each kerogen molecular model into a slit-type pore formed by a graphene lamellar structure to obtain an initial model;
performing energy minimization treatment and relaxation treatment on each initial model to obtain a compacted kerogen aggregate model, which specifically comprises the following steps:
utilizing Gromacs software to perform NPT ensemble on the initial model under the temperature and pressure conditions of 75 ℃ and 20MPa, and performing energy minimization treatment and 200ps relaxation treatment to obtain a compacted kerogen aggregate model;
and simulating an annealing process of the compacted kerogen aggregate model to obtain a kerogen slit-type pore, which specifically comprises the following steps:
performing 200ps relaxation heating on the compacted kerogen aggregate model;
carrying out 2ns simulation, temperature reduction and pressurization treatment on the kerogen aggregate model subjected to relaxation heating by utilizing NPT (nitrogen-phosphorus-zinc-tin) ensemble under the temperature and pressure conditions of 800 ℃ and normal pressure to obtain slit-shaped kerogen pores;
loading shale oil molecules to the slit-shaped kerogen pores to obtain an initial swelling and adsorption model of the shale oil in the kerogen, which specifically comprises the following steps:
loading shale oil molecules into the kerogen slit-type pores by using Packmol software to obtain an initial swelling and adsorption model of the kerogen internal shale oil;
evaluating the swelling of the shale oil in the kerogen and the force field for adsorbing the shale oil molecules and the kerogen molecules in the initial model to obtain the density results of the kerogen and the shale oil;
drawing a kerogen and shale oil density curve according to the kerogen and shale oil density result, which specifically comprises the following steps:
assigning a force field of a Charmm 36/Cgonff force field for swelling and adsorbing shale oil molecules and kerogen molecules in the initial model of the kerogen internal shale oil, using a Lorentz-Bertholt mixing rule for the interaction force of the shale oil molecules and the kerogen molecules, using a Particle-Mesh-Ewald model for an electrostatic force model, taking the Van der Waals radius as 1.4nm, using Gromacs software to simulate an NPT ensemble for the model after assigning the force field, wherein the simulation temperature is 75 ℃, the pressure is 20MPa, the simulation time is 200ns, and drawing a kerogen and kerogen oil density curve chart;
determining the swelling oil mass of the kerogen in unit mass according to the density curve of the kerogen and the shale oil, and specifically comprising the following steps:
adopting a formula according to the kerogen and shale oil density curve
Obtaining the swelling oil quantity of kerogen;
wherein Q is oil The swelling oil amount of kerogen is expressed in g; l is o1 The initial position of the intersection of the kerogen density curve and the shale oil density curve is represented by nm; l is a radical of an alcohol o2 The cutoff position of the intersection of the kerogen density curve and the shale oil density curve is shown in nm; s model Is the cross-sectional area of the kerogen-shale oil swelling and adsorbing model, and the unit is m 2 ；ρ oil Is a shale oil density curve with the unit of kg/m 3 ；
Obtaining the quality of kerogen;
determining the swelling oil amount of the kerogen in unit mass according to the swelling oil amount of the kerogen and the mass of the kerogen;
determining the specific surface area of the kerogen according to the swelling oil quantity of the kerogen per unit mass;
determining the amount of the kerogen adsorbed oil in unit area according to the kerogen and shale oil density curve, and specifically comprises the following steps:
adopting a formula according to the kerogen and shale oil density curve
And
obtaining the oil adsorption amount of the left side wall surface and the oil adsorption amount of the right side wall surface of the kerogen;
adding the oil adsorption amount of the left side wall surface of the kerogen and the oil adsorption amount of the right side wall surface to obtain the kerogen adsorption oil quantification;
wherein m is a1 The unit is g, which is the oil amount absorbed by the left side wall surface of the kerogen; l is a radical of an alcohol 1 The left side of the intersection position of the kerogen density curve and the shale oil density curve is shown in nm; l is a radical of an alcohol 2 The unit is nm, which is the left side of the junction position of the shale oil density curve adsorption area and the dissociation area; m is a unit of a2 G is the adsorbed oil mass on the right wall surface of the kerogen; l is a radical of an alcohol 3 The unit is nm, and the right side of the boundary position of the shale oil density curve adsorption area and the dissociation area; l is 4 The right side of the intersection position of the kerogen density curve and the shale oil density curve is shown, and the unit is nm; s. the model Is the cross-sectional area of the kerogen-shale oil swelling and adsorbing model, and the unit is m 2 ；ρ oil Is a shale oil density curve with the unit of kg/m 3 ；
Obtaining the left side sectional area and the right side sectional area of the kerogen model;
adding the left side sectional area and the right side sectional area to obtain the sum of the kerogen model sectional areas;
dividing the amount of the kerogen adsorbed oil by the sum of the cross sections of the kerogen models to obtain the amount of free kerogen oil in unit area;
determining the amount of the kerogen adsorbed oil in different evolution stages according to the free oil quantification of the kerogen in unit area and the specific surface area of the kerogen;
determining the volume of the kerogen adsorption oil phase according to the kerogen adsorption oil quantity;
determining the shale oil density according to the kerogen and shale oil density curve;
and determining the amount of the organic pore free oil according to the specific surface area of the kerogen, the volume of the kerogen-adsorbed oil phase and the shale oil density.
2. The method for quantitatively evaluating the kerogen free oil in the shale as claimed in claim 1, wherein the determination of the specific surface area of the kerogen through the unit mass of the swollen oil amount of the kerogen specifically comprises the following steps:
adopting a formula according to the swelling oil quantity of the kerogen in unit mass
Determining the specific surface area of kerogen;
wherein,
is the specific surface area of kerogen, Q v Amount of swelling oil per unit mass of kerogen, V gh Volume of organic pores, V, due to formation of oil and gas by kerogen f Volume corresponding to the convertible part of kerogen, F t To conversion, V s The volume corresponding to the non-convertible fraction of kerogen.
3. The method for quantitatively evaluating the kerogen free oil in the shale as claimed in claim 1, wherein the determining the amount of the kerogen-adsorbed oil in different evolution stages according to the free oil per unit area and the specific surface area of the kerogen specifically comprises:
and multiplying the kerogen adsorption oil quantity in unit area by the specific surface area of the kerogen to obtain the kerogen adsorption oil quantity in different evolution stages.
4. The method for quantitatively evaluating the kerogen free oil in the shale according to the claim 1, wherein the determining the kerogen-adsorbed oil phase volume according to the kerogen-adsorbed oil quantity specifically comprises:
obtaining shale oil adsorption phase density;
and determining the volume of the kerogen-adsorbed oil phase according to the amount of the kerogen-adsorbed oil and the density of the shale oil-adsorbed phase.
5. The method for quantitatively evaluating the kerogen free oil in the shale according to claim 1, wherein the determining the organic pore free oil quantity according to the specific kerogen surface area, the kerogen adsorbed oil phase volume and the shale oil density specifically comprises:
adopting a formula according to the specific surface area of the kerogen, the volume of the kerogen adsorption oil phase and the shale oil density
Determining the amount of organic pore free oil;
wherein,
is the specific surface area of kerogen, V ad Adsorption of the oil phase volume, p, for kerogen oil Is shale oil density, Q free The amount of free oil in the organic pores.
6. A system for quantitatively evaluating free oil of kerogen in shale is characterized by comprising:
the first initial model building module is used for building different types of kerogen molecular models, and loading each kerogen molecular model into a slit-shaped pore formed by a graphene lamellar structure to obtain an initial model;
the compaction module is used for performing energy minimization treatment and relaxation treatment on each initial model to obtain a compacted kerogen aggregate model, and specifically comprises the following steps:
utilizing Gromacs software to carry out NPT ensemble treatment and 200ps relaxation treatment on the initial model under the temperature and pressure conditions of 75 ℃ and 20MPa to obtain a compacted kerogen aggregate model;
the annealing module is used for simulating an annealing process of the compacted kerogen aggregate model to obtain kerogen slit-type pores, and specifically comprises the following steps:
performing 200ps relaxation heating on the compacted kerogen aggregate model;
carrying out 2ns simulation, temperature reduction and pressurization treatment on the kerogen aggregate model subjected to relaxation heating by utilizing NPT (nitrogen-phosphorus-zinc-tin) ensemble under the temperature and pressure conditions of 800 ℃ and normal pressure to obtain slit-shaped kerogen pores;
the second initial model building module is used for loading shale oil molecules to the kerogen slit-type pores to obtain a swelling and adsorption initial model of the shale oil in the kerogen, and specifically comprises the following steps:
loading shale oil molecules into the kerogen slit-type pores by using Packmol software to obtain an initial swelling and adsorption model of the kerogen internal shale oil;
the evaluation module is used for evaluating the swelling of the shale oil in the kerogen and the force field for adsorbing the shale oil molecules and the kerogen molecules in the initial model to obtain the density results of the kerogen and the shale oil;
the oil density curve drawing module is used for drawing a kerogen and shale oil density curve according to the kerogen and shale oil density result, and specifically comprises the following steps:
assigning values to a force field of swelling and adsorbing shale oil molecules and kerogen molecules in an initial model of the kerogen shale oil by using a Charmm 36/Cgonff force field, assigning an interaction force of the shale oil molecules and the kerogen molecules by using a Lorentz-Bertholt mixing rule, using a Particle-Mesh-Ewald model as an electrostatic force model, taking a Van der Waals radius as 1.4nm, simulating an NPT (non-point transient) ensemble by using Gromacs software on the model after assigning the force field, wherein the simulation temperature is 75 ℃, the pressure is 20MPa, the simulation time is 200ns, and drawing density graphs of the kerogen and the kerogen;
the determination module of the swelling oil quantity of the kerogen in unit mass is used for determining the swelling oil quantity of the kerogen in unit mass according to the density curve of the kerogen and the shale oil, and specifically comprises the following steps:
according to whatThe kerogen and shale oil density curve adopts a formula
Obtaining the swelling oil quantity of kerogen;
wherein Qoil is the swelling oil quantity of kerogen, and the unit is g; lo1 is the initial position of intersection of the kerogen density curve and the shale oil density curve, and the unit is nm; lo2 is the cut-off position of the intersection of the density curve of the kerogen and the density curve of the shale oil, and the unit is nm; smodel is the cross-sectional area of a kerogen-shale oil swelling and adsorbing model, and the unit is m2; rhooil is a shale oil density curve with the unit of kg/m3;
obtaining the quality of kerogen;
determining the amount of the swollen oil of the kerogen in unit mass according to the amount of the swollen oil of the kerogen and the mass of the kerogen;
the kerogen specific surface area determining module is used for determining the kerogen specific surface area according to the swelling oil quantity of the kerogen in unit mass;
the module for determining the amount of the kerogen adsorbed oil in unit area is used for determining the amount of the kerogen adsorbed oil in unit area according to the kerogen and shale oil density curve, and specifically comprises the following steps:
adopting a formula according to the kerogen and shale oil density curve
And
obtaining the oil adsorption amount of the left side wall surface and the oil adsorption amount of the right side wall surface of the kerogen;
adding the oil adsorption amount of the left side wall surface of the kerogen and the oil adsorption amount of the right side wall surface to obtain the kerogen adsorption oil quantification;
wherein, ma1 is the adsorbed oil mass of the left side wall surface of the kerogen, and the unit is g; l1 is the left side of the intersection position of the kerogen density curve and the shale oil density curve, and the unit is nm; l2 is the left side of the boundary position of the shale oil density curve adsorption area and the free area, and the unit is nm; ma2 is the amount of oil adsorbed on the right wall surface of kerogen, g; l3 is the right side of the boundary position of the shale oil density curve adsorption area and the dissociation area, and the unit is nm; l4 is the right side of the intersection position of the kerogen density curve and the shale oil density curve, and the unit is nm; smodel is the cross-sectional area of the kerogen-shale oil swelling and adsorbing model, and the unit is m2; rhooil is a shale oil density curve with the unit of kg/m3;
acquiring the left side sectional area and the right side sectional area of the kerogen model;
adding the left side sectional area and the right side sectional area to obtain the sum of the kerogen model sectional areas;
dividing the amount of the kerogen adsorbed oil by the sum of the cross sections of the kerogen models to obtain the amount of free kerogen oil in unit area;
the kerogen adsorbed oil quantity determining module is used for determining the kerogen adsorbed oil quantity in different evolution stages according to the free oil quantity of the kerogen in unit area and the specific surface area of the kerogen;
the kerogen adsorption oil phase volume determining module is used for determining the kerogen adsorption oil phase volume according to the kerogen adsorption oil quantity;
the shale oil density determining module is used for determining the shale oil density according to the kerogen and shale oil density curve;
and the free oil quantity determining module is used for determining the free oil quantity of the organic pores according to the specific surface area of the kerogen, the volume of the kerogen-adsorbed oil phase and the shale oil density.
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