CN108414311B - Preparation method of coal-series stratum-layer fracturing object model sample considering transition zone - Google Patents
Preparation method of coal-series stratum-layer fracturing object model sample considering transition zone Download PDFInfo
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Abstract
The invention relates to a preparation method of a coal-series layer-producing fracturing model sample with a transition zone considered, which comprises the following steps: uniformly mixing cement and quartz sand according to a certain proportion, adding water, stirring to form cement paste, and pouring the cement paste on the bottom layer of a sample mold to form a rock layer of a coal-series layer group; uniformly mixing cement, quartz sand and coal powder according to a certain proportion, adding water, stirring to form coal-containing slurry, preparing at least ten coal-containing slurries containing different proportions of coal powder, and pouring the coal-containing slurries into the middle layer of a sample mold layer by layer according to the sequence of the coal powder proportions from small to large, namely forming a transition zone of a coal-series production layer group; uniformly mixing cement, quartz sand and coal powder according to a certain proportion, adding water, stirring to form coal-containing slurry, pouring the coal-containing slurry on the top layer of a sample mold, and inserting a plurality of paraffin slices which are vertical to each other, so as to form the coal stratum of the coal-series production stratum. The physical model sample prepared by the method is infinitely close to a real coal-series produced layer group in mechanical property.
Description
Technical Field
The invention belongs to the technical field of rock sample preparation, and particularly relates to a preparation method of a coal-series stratum-producing fracturing model sample with a transition zone considered.
Background
The coal-rock series gas-bearing stratum is a gas-bearing stratum formed by overlapping a plurality of layers of unconventional reservoirs such as a coal bed, a compact sandstone layer and the like in the longitudinal direction, and has the characteristics of shallow buried depth, more gas-bearing strata, low resource abundance, poor permeability and the like, so that the benefit of singly exploiting a certain resource is poor, and therefore, the comprehensive exploration and development of the unconventional resource natural gas of the coal series is an important way for protecting natural gas resources and improving the development benefit. At present, the common development of coal-based multi-type gas reservoirs is highly concerned at home and abroad, and the precedent tests are carried out in regions such as the Surat basin in Australia, the Ordos basin in China and the like. In order to realize the combined development of two different gas producing layers, hydraulic fractures are required to be promoted to effectively communicate different gas producing layers in the longitudinal direction, and natural weak surfaces such as coal rock cleat and the like are communicated in a coal bed, so that the maximum seam network spreading is formed.
According to the deposit continuity law, the transition of different lithologies in the longitudinal direction is gradual and gradient, and the transition lithologies with certain thickness are called transition zones (or transition zones). To date, there have been few studies on the influence of rock mechanical properties in lithologic transition regions on hydraulic fracture propagation. The fracturing simulation test is an important means for recognizing the initiation and propagation behaviors of the coal-based multi-reservoir combined fracturing fracture, and how to prepare a suitable physical model test piece is the premise and the basis of the development of the test.
The invention patent with application publication number CN105334090A discloses a preparation method of a fracturing object model sample of a coal-containing productive layer group, wherein a coal rock thin plate and a rock thin plate are bonded together in a gluing mode to form the coal-containing productive layer group. But the method ignores the influence of transition zones between different lithologies, so that the physical model sample has great difference with an actual coal-series reservoir.
The invention patent with application publication number CN104034563A discloses a preparation method of an artificial core of joint shale, which adopts cement and quartz sand to simulate laminated shale, and simulates natural cracks in the shale by adding oatmeal and shredded paper. Because the directions and the sizes of the weak surfaces cannot be accurately controlled by adopting the oatmeal and the paper scraps, accurate simulation cannot be carried out on orthogonal weak surfaces, namely end cutting and surface cutting, existing in the coal bed.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a preparation method of a coal-series stratum-producing fracturing model sample with a transition zone considered, which comprises the following steps in sequence:
the method comprises the following steps: placing the sample mould on a horizontal plane; uniformly mixing cement and quartz sand according to a certain proportion, adding water into the mixture, and stirring to form cement paste; pouring the cement slurry on the bottom layer of the sample mold to form a rock layer of a coal-series layer group;
step two: uniformly mixing cement, quartz sand and coal powder according to a certain proportion, adding water into the mixture, and stirring to form coal-containing slurry; preparing at least ten coal-containing slurries containing coal dust in different proportions, and pouring the coal-containing slurries into the middle layer of the sample mold layer by layer according to the sequence of the coal dust proportions from small to large, so as to form a transition zone of a coal-series layer production group;
step three: uniformly mixing cement, quartz sand and coal powder according to a certain proportion, adding water into the mixture, and stirring to form coal-containing slurry; pouring the slurry containing the coal slime on the top layer of a sample mold, and inserting a plurality of paraffin slices which are vertical to each other into the slurry containing the coal slime to form a coal rock layer of a coal series production layer group;
step four: and standing, drying and forming to obtain the coal-series produced stratum fracturing physical model sample considering the transition zone.
Preferably, the cavity dimensions of the sample mold are 300mm × 300mm × 300mm or 400mm × 400mm × 400 mm. The physical model samples with two sizes respectively correspond to the existing 300mm true triaxial simulation fracturing test system and 400mm true triaxial simulation fracturing test system.
In any of the above schemes, preferably, the cement is composite portland cement, and the particle size of the quartz sand is 80-120 meshes. The composite portland cement has good compatibility and high cementing strength. The 80-100 mesh quartz sand can be fully and uniformly mixed with the composite Portland cement.
In any of the above schemes, preferably, in the first step, the volume ratio of the cement to the quartz sand in the cement paste is 1:1, and the mass of the added water is 15-25% of the total mass of the cement and the quartz sand.
In any of the above embodiments, preferably, the height of the grout poured in the sample mold is 50-100 mm.
In any of the above schemes, preferably, in the second step, ten parts of coal-containing slurry are prepared, wherein the volume ratios of cement, quartz sand and coal dust in the ten parts of coal-slurry are 1:1:0.05-0.15, 1:1:0.15-0.25, 1:1:0.25-0.45, 1:1:0.45-0.8, 1:1:0.8-1.3, 1:1:1.3-1.8, 1:1:1.8-2.6, 1:1:2.6-3.4, 1:1:3.4-3.9 and 1:1:3.9-4.25 respectively according to the sequence from small to large of the proportion of coal dust. A large number of tests prove that the coal content between the rock stratum and the coal stratum is gradually increased, the area is a transition zone, and when the cement, the quartz sand and the coal powder are proportioned, the formed transition zone is closest to or even the same as a real coal-series production layer group; in the ten layers of coal-containing slurry in the transition zone, the increasing range of the coal powder content is gradually changed from small to large and then from large to small, so that the unsmooth follow-up fracturing process caused by sudden increase or decrease of the variation range is avoided; when the cement, the quartz sand and the coal powder are mixed according to the proportion, the maximum seam net spreading can be obtained.
In any of the above schemes, preferably, the transition zone of the coal-series production layer group is more than ten layers of coal-containing slurry, wherein the volume ratio of cement, quartz sand and coal dust is 1:1: 4.25-4.45. A large number of tests prove that when the coal slurry containing the transition zone exceeds ten layers, the coal quality content is basically stable and cannot be changed greatly, and at the moment, when the cement, the quartz sand and the coal powder are proportioned, the maximum seam net spreading can be obtained.
In any of the above schemes, the mass of the water added into each part of the slurry containing coal slime is 10-20% of the total mass of the cement, the quartz sand and the coal dust in the slurry containing coal slime.
In any of the above embodiments, the mass of each coal-containing slurry in the transition zone of the coal-series production string is preferably equal.
In any scheme, preferably, the coal slime-containing slurry is poured into the transition zone of the coal-series layer group from bottom to top, and the coal slime-containing slurry is kept still for 3-5min after each layer is poured. A large number of tests prove that the slurry containing the coal slime can naturally permeate when each layer is stood for 3-5min after being poured, and the slurry containing the coal slime can not be mixed with the slurry containing the coal slime of the adjacent layer or generate an interface with the slurry containing the coal slime of the adjacent layer.
In any of the above schemes, preferably, in the third step, the volume ratio of the cement, the quartz sand and the coal dust in the slurry containing coal slime is 1:1:5, and the mass of the added water is 15-25% of the total mass of the cement, the quartz sand and the coal dust.
In any of the above schemes, preferably, the height of the slurry containing coal slime poured in the sample mold is 50-100 mm.
In any of the above solutions, it is preferable that the distance between every two adjacent parallel paraffin flakes is 5-10 mm.
In any of the above aspects, preferably, the thickness of the paraffin flake is 0.5 to 1 mm; the height of the paraffin wax thin sheet is equal to that of the coal stratum of the coal-series production stratum. The paraffin flakes must assume a vertically downward position in the coal formation. The melting point of the paraffin thin sheet is between 40 and 70 ℃, after the object model sample is fully dried, the paraffin thin sheet is melted when being heated to a certain temperature, and latticed cracks are formed in the object model sample so as to simulate the orthogonal face-cutting and end-cutting in the real coal rock.
In any of the above schemes, preferably, in step four, the drying is natural airing, and the continuous airing time is 1 to 3 days. The object model sample prepared by the method can be fully dried in a short time, and the interior of the object model sample can be fully dried.
The preparation method of the coal-based stratum-producing fracturing object model sample considering the transition zone has the advantages of simple operation, raw material saving and efficiency improvement, can be used for preparing the coal-containing cement sample with the coal-containing transition zone, can generate latticed cracks after treatment, and can accurately simulate the physical properties of the coal-containing stratum-producing stratum. The method simulates the gradual change characteristic of the coal quality content at the lithologic junction of the actual coal-containing layer by changing the proportion of the pulverized coal in the slurry, and simultaneously artificially produces latticed cracks after heating the sample by placing a fusible paraffin slice in the sample in advance so as to simulate the surface cutting and end cutting widely existing in the coal rock, so that the prepared physical model sample is infinitely close to the actual coal-containing layer in mechanical property.
Drawings
Fig. 1 is a schematic view of a model sample of a preferred embodiment of a method for preparing a fracture model sample of a coal-derived formation considering a transition zone according to the present invention.
The figures are labeled as follows: 1-rock layer of coal-series production stratum, 2-transition zone of coal-series production stratum, 3-coal-series production stratum and 4-paraffin slice.
Detailed Description
In order that the invention may be further understood, the invention will now be described in detail with reference to specific examples.
The first embodiment is as follows:
as shown in fig. 1, an embodiment of a method for preparing a coal-derived formation fracturing model sample considering a transition zone according to the present invention comprises the following steps in order:
the method comprises the following steps: placing the sample mould on a horizontal plane; uniformly mixing cement and quartz sand according to a certain proportion, adding water into the mixture, and stirring to form cement paste; pouring the cement slurry on the bottom layer of a sample mold to form a rock layer 1 of a coal-series layer group;
step two: uniformly mixing cement, quartz sand and coal powder according to a certain proportion, adding water into the mixture, and stirring to form coal-containing slurry; preparing ten coal-containing slurries containing coal dust in different proportions, and pouring the slurries into the middle layer of the sample mold layer by layer according to the sequence of the coal dust proportions from small to large to form a transition zone 2 of a coal-series layer production group;
step three: uniformly mixing cement, quartz sand and coal powder according to a certain proportion, adding water into the mixture, and stirring to form coal-containing slurry; pouring the slurry containing the coal slime on the top layer of a sample mould, and inserting a plurality of paraffin slices 4 which are vertical to each other into the slurry containing the coal slime to form a coal stratum 3 of a coal series production stratum group;
step four: and standing, drying and forming to obtain the coal-series produced stratum fracturing physical model sample considering the transition zone.
The cavity size of the sample mold is 300mm × 300mm × 300 mm. The cement is composite portland cement, and the granularity of the quartz sand is 80 meshes. The composite portland cement has good compatibility and high cementing strength. The 80-mesh quartz sand can be fully and uniformly mixed with the composite Portland cement.
In the first step, the volume ratio of cement to quartz sand in the cement paste is 1:1, and the mass of the added water is 15% of the total mass of the cement and the quartz sand. The height of the cement paste poured in the sample mould is 100 mm.
In the second step, ten parts of coal-containing slurry are prepared, wherein the volume ratios of cement, quartz sand and coal dust in the ten parts of coal-containing slurry are respectively 1:1:0.05, 1:1:0.15, 1:1:0.25, 1:1:0.45, 1:1:0.8, 1:1:1.3, 1:1:1.8, 1:1:2.6, 1:1:3.4 and 1:1:3.9 in the descending order of the proportion of the coal dust. A large number of tests prove that when the cement, the quartz sand and the pulverized coal are proportioned, the formed transition zone is very close to or even the same as a real coal-series produced layer group; in the ten layers of coal-containing slurry in the transition zone, the increasing range of the coal powder content is gradually changed from small to large and then from large to small, so that the unsmooth follow-up fracturing process caused by sudden increase or decrease of the variation range is avoided; when the cement, the quartz sand and the coal powder are mixed according to the proportion, the maximum seam net spreading can be obtained. The mass of water added into each part of slurry is 10 percent of the total mass of cement, quartz sand and coal powder in the slurry. And the mass of each coal-containing slurry in the transition zone of the coal-series layer production group is equal. And coal slurry is poured into the transition zone of the coal-series layer group from bottom to top, and standing for 3min after each layer is poured. A large number of tests prove that standing for 3min after each layer is poured can enable the coal slime-containing slurry of the layer to naturally permeate, and the slurry cannot be mixed with the coal slime-containing slurry of the adjacent layer or generate an interface with the coal slime-containing slurry of the adjacent layer.
In the third step, the volume ratio of cement, quartz sand and coal powder in the slurry containing coal slime is 1:1:5, and the mass of the added water is 15% of the total mass of the cement, the quartz sand and the coal powder. The height of the coal-containing slurry poured in the sample mold is 100 mm. The distance between every two adjacent parallel paraffin flakes is 10 mm. The thickness of the paraffin wax sheet is 0.5 mm; the height of the paraffin wax thin sheet is equal to that of the coal stratum of the coal-series production stratum. The melting point of the paraffin thin sheet is between 40 and 70 ℃, after the object model sample is fully dried, the paraffin thin sheet is melted when being heated to a certain temperature, and latticed cracks are formed in the object model sample so as to simulate the orthogonal face-cutting and end-cutting in the real coal rock.
And in the fourth step, the drying is natural airing, and the continuous airing time is 1 day. The phantom sample prepared by the method of this example was sufficiently dried in a short time, and the interior of the phantom sample was sufficiently dried.
The preparation method of the coal-based stratum pay fracturing model sample considering the transition zone has the advantages of being simple in operation, saving raw materials and improving efficiency, the coal-containing transition zone can be prepared by the method, the coal-containing cement sample with the coal-containing transition zone can generate latticed cracks after being processed, and the physical properties of the coal-containing stratum pay can be accurately simulated. The method simulates the gradual change characteristic of the coal quality content at the lithologic junction of the actual coal-containing layer by changing the proportion of the pulverized coal in the slurry, and simultaneously artificially produces latticed cracks after heating the sample by placing a fusible paraffin slice in the sample in advance so as to simulate the surface cutting and end cutting widely existing in the coal rock, so that the prepared physical model sample is infinitely close to the actual coal-containing layer in mechanical property.
Example two:
according to another embodiment of the preparation method of the coal-based layer formation fracturing model sample considering the transition zone, the specific steps, the preparation principle, the beneficial effects and the like are the same as those of the first embodiment, and the difference is that:
the granularity of the quartz sand is 120 meshes;
in the first step, the mass of the added water in the cement paste is 25% of the total mass of the cement and the quartz sand. The height of the cement paste poured in the sample die is 50 mm.
In the second step, the volume ratios of cement, quartz sand and coal dust in ten parts of the coal slurry are respectively 1:1:0.15, 1:1:0.25, 1:1:0.45, 1:1:0.8, 1:1:1.3, 1:1:1.8, 1:1:2.6, 1:1:3.4, 1:1:3.9 and 1:1:4.25 from small to large according to the proportion of the coal dust. The mass of water added into each part of slurry is 20% of the total mass of cement, quartz sand and coal powder in the slurry. And coal slurry is poured into the transition zone of the coal-series layer group from bottom to top, and standing for 5min after each layer is poured.
In the third step, the mass of the water added into the slurry containing the coal slime is 25 percent of the total mass of the cement, the quartz sand and the coal dust. The height of the coal-containing slurry poured in the sample mold is 50 mm. The distance between every two adjacent parallel paraffin thin slices is 5mm, and the thickness of each paraffin thin slice is 1 mm.
In the fourth step, the continuous airing time is 3 days.
Example three:
according to another embodiment of the preparation method of the coal-based layer formation fracturing model sample considering the transition zone, the specific steps, the preparation principle, the beneficial effects and the like are the same as those of the first embodiment, and the difference is that:
the granularity of the quartz sand is 100 meshes;
in the first step, the mass of the added water in the cement paste is 20% of the total mass of the cement and the quartz sand. The height of the cement paste poured in the sample die is 80 mm.
In the second step, the volume ratios of cement, quartz sand and coal dust in ten parts of the coal slurry are respectively 1:1:0.1, 1:1:0.2, 1:1:0.35, 1:1:0.6, 1:1:1.0, 1:1:1.5, 1:1:2.2, 1:1:3.0, 1:1:3.6 and 1:1:4.1 from small to large according to the proportion of the coal dust. The mass of water added into each part of the slurry containing coal slime is 15% of the total mass of cement, quartz sand and coal powder in the slurry containing coal slime. And coal slurry is poured into the transition zone of the coal-series layer group from bottom to top, and standing for 4min after each layer is poured.
In the third step, the mass of the water added into the slurry containing the coal slime is 20 percent of the total mass of the cement, the quartz sand and the coal dust. The height of the coal-containing slurry poured in the sample mold is 80 mm. The distance between every two adjacent parallel paraffin thin slices is 10mm, and the thickness of each paraffin thin slice is 0.5 mm.
In the fourth step, the continuous airing time is 2 days.
Example four:
according to another embodiment of the preparation method of the coal-based layer formation fracturing model sample considering the transition zone, the specific steps, the preparation principle, the beneficial effects and the like are the same as those of the first embodiment, and the difference is that:
in the first step, the mass of the added water in the cement paste is 18% of the total mass of the cement and the quartz sand. The height of the cement paste poured in the sample die is 90 mm.
In the second step, the volume ratios of cement, quartz sand and coal dust in ten parts of the coal slurry are respectively 1:1:0.08, 1:1:0.18, 1:1:0.3, 1:1:0.55, 1:1:0.9, 1:1:1.4, 1:1:2.0, 1:1:2.8, 1:1:3.5 and 1:1:4.0 in the sequence from small to large according to the proportion of the coal dust. The mass of water added into each part of the slurry containing coal slime is 13 percent of the total mass of cement, quartz sand and coal powder in the slurry containing coal slime.
In the third step, the mass of the water added into the slurry containing the coal slime is 18 percent of the total mass of the cement, the quartz sand and the coal dust. The height of the coal-containing slurry poured in the sample mold is 90 mm.
Example five:
according to another embodiment of the preparation method of the coal-based layer formation fracturing model sample considering the transition zone, the specific steps, the preparation principle, the beneficial effects and the like are the same as those of the first embodiment, and the difference is that:
in the first step, the mass of the added water in the cement paste is 22% of the total mass of the cement and the quartz sand. The height of the cement paste poured in the sample die is 70 mm.
In the second step, the volume ratios of cement, quartz sand and coal dust in ten parts of the coal slurry are respectively 1:1:0.12, 1:1:0.22, 1:1:0.4, 1:1:0.7, 1:1:1.15, 1:1:1.65, 1:1:2.4, 1:1:3.2, 1:1:3.75 and 1:1:4.2 from small to large according to the proportion of the coal dust. The mass of water added into each part of the slurry containing coal slime is 18 percent of the total mass of cement, quartz sand and coal powder in the slurry containing coal slime.
In the third step, the mass of the water added into the slurry containing the coal slime is 22 percent of the total mass of the cement, the quartz sand and the coal dust. The height of the coal-containing slurry poured in the sample mold is 70 mm.
Example six:
according to another embodiment of the preparation method of the coal-based layer formation fracturing model sample considering the transition zone, the specific steps, the preparation principle, the beneficial effects and the like are the same as those of the first embodiment, and the difference is that:
in the second step, eleven parts of coal-containing slurry are prepared, and the volume ratio of cement, quartz sand and coal powder in the eleventh part of coal-containing slurry is 1:1: 4.25. A large number of experiments prove that when the coal slurry in the transition zone exceeds ten layers, the coal quality content is basically stable and cannot be changed greatly, and at the moment, when the cement, the quartz sand and the coal powder are proportioned, the maximum seam net spreading can be obtained.
Example seven:
according to another embodiment of the preparation method of the coal-based layer formation fracturing model sample considering the transition zone, the specific steps, the preparation principle, the beneficial effects and the like are the same as those of the embodiment, and the difference is that:
and in the second step, twelve parts of coal-containing slurry are prepared, and the volume ratio of cement, quartz sand and coal dust in the tenth part of coal-containing slurry to the twelfth part of coal-containing slurry is 1:1: 4.45. A large number of experiments prove that when the coal slurry in the transition zone exceeds ten layers, the coal quality content is basically stable and cannot be changed greatly, and at the moment, when the cement, the quartz sand and the coal powder are proportioned, the maximum seam net spreading can be obtained.
Example eight:
according to another embodiment of the preparation method of the coal-based layer-producing fracturing model sample considering the transition zone, the specific steps, the preparation principle, the beneficial effects and the like are the same as those of the embodiment, and the difference is as follows:
and in the second step, thirteen parts of coal-containing slurry are prepared, and the volume ratios of cement, quartz sand and coal dust in the eleventh to thirteenth parts of coal-containing slurry are 1:1:4.45, 1:1:4.3 and 1:1:4.25 respectively. A large number of experiments prove that when the coal slurry in the transition zone exceeds ten layers, the coal quality content is basically stable and cannot be changed greatly, and at the moment, when the cement, the quartz sand and the coal powder are proportioned, the maximum seam net spreading can be obtained.
Example nine:
according to another embodiment of the preparation method of the coal-based layer formation fracturing model sample considering the transition zone, the specific steps, the preparation principle, the beneficial effects and the like are the same as those of the fourth embodiment, and the difference is that:
in the second step, fourteen parts of coal-containing slurry are prepared, and the volume ratios of cement, quartz sand and coal dust in the eleventh to fourteenth parts of coal-containing slurry are 1:1:4.3, 1:1:4.4, 1:1:4.25 and 1:1:4.45 respectively. A large number of experiments prove that when the coal slurry in the transition zone exceeds ten layers, the coal quality content is basically stable and cannot be changed greatly, and at the moment, when the cement, the quartz sand and the coal powder are proportioned, the maximum seam net spreading can be obtained.
Example ten:
according to another embodiment of the preparation method of the coal-series layer-producing fracturing model sample considering the transition zone, the specific steps, the preparation principle, the beneficial effects and the like are the same as those of the fifth embodiment, and the difference is that:
in the second step, fifteen parts of coal-containing slurry are prepared, and the volume ratios of cement, quartz sand and coal dust in the tenth part to the fifteenth part of the coal-containing slurry are 1:1:4.35, 1:1:4.45, 1:1:4.3 and 1:1:4.35 respectively. A large number of experiments prove that when the coal slurry in the transition zone exceeds ten layers, the coal quality content is basically stable and cannot be changed greatly, and at the moment, when the cement, the quartz sand and the coal powder are proportioned, the maximum seam net spreading can be obtained.
It will be understood by those skilled in the art that the method of making a coal-derived formation fracture model sample of the present invention, which takes into account the transition zone, includes any combination of the summary and detailed description of the invention in the above description and the portions shown in the drawings, is not to be construed as limiting the space and not describing every scheme made up of these combinations for the sake of brevity. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (15)
1. A preparation method of a coal-based stratum-producing fracturing model sample considering a transition zone comprises the following steps in sequence:
the method comprises the following steps: placing the sample mould on a horizontal plane; uniformly mixing cement and quartz sand according to a certain proportion, adding water into the mixture, and stirring to form cement paste; pouring the cement slurry on the bottom layer of the sample mold to form a rock layer of a coal-series layer group;
step two: uniformly mixing cement, quartz sand and coal powder according to a certain proportion, adding water into the mixture, and stirring to form coal-containing slurry; preparing at least ten coal-containing slurries containing coal dust in different proportions, and pouring the coal-containing slurries into the middle layer of the sample mold layer by layer according to the sequence of the coal dust proportions from small to large, so as to form a transition zone of a coal-series layer production group;
step three: uniformly mixing cement, quartz sand and coal powder according to a certain proportion, adding water into the mixture, and stirring to form coal-containing slurry; pouring the slurry containing the coal slime on the top layer of a sample mold, and inserting a plurality of paraffin slices which are vertical to each other into the slurry containing the coal slime to form a coal rock layer of a coal series production layer group;
step four: and standing, drying and forming to obtain the coal-series produced stratum fracturing physical model sample considering the transition zone.
2. The method for preparing the coal-based production group fracturing model sample considering the transition zone as claimed in claim 1, wherein: the cavity size of the sample mold is 300mm × 300mm × 300mm or 400mm × 400mm × 400 mm.
3. The method for preparing the coal-based production group fracturing model sample considering the transition zone as claimed in claim 1, wherein: the cement is composite portland cement, and the granularity of the quartz sand is 80-120 meshes.
4. The method for preparing the coal-based production group fracturing model sample considering the transition zone as claimed in claim 1, wherein: in the first step, the volume ratio of cement to quartz sand in the cement paste is 1:1, and the mass of the added water is 15-25% of the total mass of the cement and the quartz sand.
5. The method for preparing the coal-based production group fracturing model sample considering the transition zone as claimed in claim 4, wherein: the height of the cement paste poured in the sample mould is 50-100 mm.
6. The method for preparing the coal-based production group fracturing model sample considering the transition zone as claimed in claim 1, wherein: in the second step, ten parts of coal-containing slurry are prepared, wherein the volume ratio of cement, quartz sand and coal dust in the ten parts of coal-containing slurry is 1:1:0.05-0.15, 1:1:0.15-0.25, 1:1:0.25-0.45, 1:1:0.45-0.8, 1:1:0.8-1.3, 1:1:1.3-1.8, 1:1:1.8-2.6, 1:1:2.6-3.4, 1:1:3.4-3.9 and 1:1:3.9-4.25 respectively according to the sequence from small to large of the proportion of the coal dust.
7. The method for preparing the coal-based production group fracturing model sample considering the transition zone as claimed in claim 6, wherein: the transition zone of the coal-series layer production group exceeds ten layers of coal-containing slurry, wherein the volume ratio of cement to quartz sand to coal powder is 1:1: 4.25-4.45.
8. The method for preparing the coal-based production group fracturing model sample considering the transition zone as claimed in claim 7, wherein: and in the transition zone of the second step, the mass of the water added into each part of the slurry containing coal slime is 10-20% of the total mass of the cement, the quartz sand and the coal dust in the slurry containing coal slime.
9. The method for preparing the coal-based production group fracturing model sample considering the transition zone as claimed in claim 8, wherein: and the mass of each coal-containing slurry in the transition zone of the coal-series layer production group is equal.
10. The method for preparing the coal-based production formation fracturing model sample considering the transition zone as claimed in claim 9, wherein: and coal slurry is poured into the transition zone of the coal-series layer group from bottom to top, and standing for 3-5min after each layer is poured.
11. The method for preparing the coal-based production group fracturing model sample considering the transition zone as claimed in claim 1, wherein: in the third step, the volume ratio of the cement, the quartz sand and the coal dust in the slurry containing the coal slime is 1:1:5, and the mass of the added water is 15-25% of the total mass of the cement, the quartz sand and the coal dust.
12. The method for preparing the coal-based production formation fracturing model sample considering the transition zone as claimed in claim 11, wherein: and step three, pouring the coal-containing slurry in the coal rock layer in the sample mold to a height of 50-100 mm.
13. The method for preparing the coal-based production formation fracturing model sample considering the transition zone as claimed in claim 12, wherein: the distance between every two adjacent parallel paraffin slices is 5-10 mm.
14. The method for preparing a coal-derived formation fracturing model sample considering a transition zone as claimed in claim 13, wherein: the thickness of the paraffin wax sheet is 0.5-1 mm; the height of the paraffin wax thin sheet is equal to that of the coal stratum of the coal-series production stratum.
15. The method for preparing the coal-based production group fracturing model sample considering the transition zone as claimed in claim 1, wherein: and in the fourth step, the drying is natural airing, and the continuous airing time is 1-3 days.
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