CN111610212B - Scanning electron microscope sample positioning device and method for oil and gas reservoir transformation experiment - Google Patents

Abstract

The invention relates to a scanning electron microscope sample positioning device and method for oil and gas reservoir transformation experiments. The sample positioning device includes a sample stage base, connecting bolts and a positioning sample stage. The sample stage base is used for direct connection with the scanning electron microscope. The positioning sample table is used to carry the rock samples to be tested; multiple positioning reference points are arranged on the top of the cylindrical positioning sample table, through which the oil and gas reservoir before and after the reconstruction experiment can be accurately and quickly positioned. The observation point optimizes the experimental operation steps, and realizes the rapid analysis and comparison of the microscopic morphology of the sample before and after the reservoir stimulation experiment, which is convenient for accurately evaluating the effectiveness of the reservoir stimulation.

Description

Scanning electron microscope sample positioning device and method for oil and gas reservoir stimulation experiments

technical field

The invention relates to the technical field of oil and gas reservoir transformation experiments, in particular to a scanning electron microscope sample positioning device and method in oil and gas reservoir transformation experiments.

Background technique

Scanning electron microscopy (scanning electron microscope for short) analysis technology is a test and analysis technology used to study the microscopic morphology, composition and other characteristics of micro-nano scale, which is widely used in materials science, biology, medicine, geology and other fields. Reservoir stimulation technology is the transformation of oil and natural gas reservoirs by acidification, water injection, fracturing and other processes. It is an important method and means to improve oil and gas recovery and production capacity in the process of oil and gas field development. In the process of reservoir stimulation evaluation, in order to find out the sensitivity of different minerals (quartz, feldspar, clay minerals, etc.) The same mineral or the same point in the same sample before and after the reservoir stimulation experiment is positioned and observed, so as to microscopically characterize the changes and differences in mineral characteristics before and after the experiment, and thus evaluate the effectiveness of reservoir stimulation.

However, since the scanning electron microscope is usually used to study the microscopic morphology, composition and other characteristics of the micro-nano scale, and the mineral particles in the rock sample are small, it needs to be magnified hundreds to thousands of times or even tens of thousands of times under the scanning electron microscope. The existing technology of positioning and searching for samples in scanning electron microscopy is often to judge the position of samples according to the microscopic characteristics observed in the field of view during a single experiment. The positions of the samples in the two experiments must be strictly consistent, otherwise, slight deviations on the macroscopic level will lead to huge differences on the microscopic level, as the so-called "Missing a small difference, the difference is a thousand miles", which greatly increases the difference between the samples before and after the experiment. The difficulty of positioning has resulted in the time-consuming and labor-intensive work of comparing the positioning before and after the reservoir stimulation experiment in the scanning electron microscope. In addition, more importantly, when the microscopic morphology of minerals changes before and after the reservoir stimulation experiment, it will not be possible to judge whether the observation point before and after the experiment is the same point, so that the effectiveness of reservoir stimulation cannot be evaluated.

In addition, during the research process of feldspar dissolution simulation experiments on the formation mechanism of oil and gas sandstone reservoirs, and calcite and dolomite dissolution simulation experiments on the formation mechanism of carbonatite reservoirs, in order to evaluate the experimental results more accurately, it is necessary to analyze the same Minerals (feldspar, calcite, dolomite, etc.) were compared, observed and analyzed before and after the experiment. Therefore, a device and method that can be used to accurately and quickly locate and compare the same mineral or the same point in the same sample before and after the oil and gas reservoir stimulation experiment using scanning electron microscopy needs to be solved urgently.

Contents of the invention

The purpose of the present invention is to address the deficiencies of the prior art, to provide a scanning electron microscope sample positioning device and method for oil and gas reservoir transformation experiments, which can realize the same mineral or the same point in the same sample before and after the reservoir transformation experiment Perform precise and fast positioning.

The technical scheme adopted by the present invention to achieve the above object is: the scanning electron microscope sample positioning device for oil and gas reservoir transformation experiments of the present invention includes: a sample stage base, a positioning sample stage, and connecting bolts connected with the sample stage base and the positioning sample stage ;

The base of the sample stage is used as the base for positioning the sample stage, the bottom of which is connected with the scanning electron microscope, and the top is connected with the positioning sample stage by bolts, and a radial base alignment mark and a circumferential base are arranged from the center to the edge of the top surface Alignment markings, screw holes are provided in the center of the top surface, wherein the radial base alignment markings are set radially from the screw holes in the center of the top surface, and the radial base alignment markings are aligned with the circumferential base marking vertical;

The base of the sample stage and the positioning sample stage are fixedly connected by connecting bolts, which are used to fix the positioning sample stage on the base of the sample stage, and the connection and separation of the positioning sample stage and the base of the sample stage can be realized by rotation;

The positioning sample stage is cylindrical, and its top surface is three positioning reference point marks (A, B, C) distributed on the top surface of the cylinder wall, and the side is eight hollow columns evenly distributed, and each hollow column There is a bolt for fixing the sample on the upper and lower sides, and a sample stage positioning marking line on the bottom. The bottom surface is eight evenly distributed fan-shaped hollows, and the center is a screw hole;

The positioning sample table adopts a hollow cylindrical shape, which can fix and protect the rock samples, and prevent the impact on the rock reservoirs (such as micro-cracks, etc.) Finally, the sample is looser than before, and the positioning sample stage can play the role of fixing and protecting, truly preserving the original state of the transformation experiment, and improving the objectivity and effectiveness of reservoir evaluation;

The setting position of the circumferential base alignment mark on the radial base alignment mark is the outer radius of the cylindrical positioning sample stage. When the positioning sample stage is closely attached to the sample frame, the cylindrical cylindrical The side edge of the positioning sample stage is just aligned with the alignment mark line of the circumferential base. When the cylindrical positioning sample stage is not aligned with the alignment mark line of the circumferential base, it means that there is a gap between the positioning sample stage and the sample frame. If there is a deviation in the connection, remind the staff to check the connection method and correct the installation relationship;

The three positioning reference points (A, B, C) are evenly distributed on the top surface of the cylinder wall. In another embodiment, the number of positioning reference points can be increased, which can increase the accuracy of positioning, and can also give preference to observation The nearest reference point of point P is used as the scanning electron microscope field of view to find the direction, and it is more accurate and fast to locate the observation point before and after the oil and gas reservoir stimulation experiment;

The scanning electron microscope sample positioning method for oil and gas reservoir transformation experiment of the present invention comprises the following steps:

Step ①: put the standard plunger rock sample used in the reservoir stimulation experiment from the upper port of the positioning sample stage, make the top surface of the sample roughly parallel to the top surface of the positioning sample stage, fix the sample with the sample fixing bolt, and make the sample There is no relative displacement with the positioning sample stage;

Step ②: Connect the positioning sample stage and the base of the sample stage with connecting bolts; complete the loading of the sample before the reservoir transformation experiment, and put it into the scanning electron microscope to analyze the microstructure of the sample before the reservoir transformation experiment;

Step ③: Read and record the coordinates of the positioning reference points (A, B, C) on the top surface of the positioning sample stage under the scanning electron microscope as ((x _A , y _A ), (x _B , y _B ), (x _C , y _C )), read and record the coordinates (x _P , y _P ) of the observation point (P); use the scanning electron microscope to analyze the microscopic morphology of the sample before the reservoir stimulation experiment, and read and record the coordinates of each analysis point in turn coordinate;

Step ④: Unscrew the positioning sample stage to separate the positioning sample stage from the base of the sample stage and the connecting bolts; put the rock sample together with the positioning sample stage into the reservoir transformation experiment device, and keep There is no relative displacement between the rock sample and the positioning sample stage, and the reservoir reconstruction experiment is carried out;

Step ⑤: Take out the sample and the positioning sample stage after the reservoir modification experiment, repeat the above step ②; complete the loading of the sample after the reservoir modification experiment, put it into the scanning electron microscope for microscopic analysis of reservoir modification evaluation;

Step ⑥: Read and record the coordinates of the positioning reference points (A, B, C) on the top surface of the positioning sample stage under the scanning electron microscope as ((x' _A , y' _A ), (x' _B , y' _B ), (x' _C , y' _C )), the coordinates ((x _A , y _A ), (x _B , y _B ), (x _C , y _C )) and the P coordinates of the point to be observed (x _P , y _P ), and the new coordinates of the positioning reference points (A, B, C) on the top surface of the sample stage after the reservoir stimulation experiment ((x' _A , y' _A ), (x' _B , y' _B ), (x' _C , y' _C )), find the coordinates of the point P to be observed after the reservoir stimulation experiment (x' _P , y' B ) ' _P ) is:

Step ⑦: Input the coordinates of the point P to be observed (x' _P , y' _P ), then the point P to be observed after the reservoir transformation experiment can be found, and combined with stable minerals (such as quartz, etc.) for correction, the reservoir is completed by scanning electron microscopy Analysis of the microscopic morphology of the sample after the transformation experiment;

In the step ②, it is also included to read the initial angle α between the positioning sample stage and the sample stage base through the base alignment marking line on the sample stage base and/or the sample stage positioning marking line of the positioning sample stage ;

In the step ⑤, it is also included to read the angle α' between the positioning sample stage and the base of the sample stage again. By comparing the angle α' and α, the approximate position of the observation point can be preliminarily judged, and the observation point can be improved. positioning efficiency;

Of course, for convenience, in another embodiment, four quadrant areas can also be divided on the base of the sample stage, and the quadrant area to be observed is judged by the angle relationship;

In another embodiment, the top periphery of the sample stand and/or the bottom periphery of the side of the positioning sample stage are also provided with an angle measurement scale, by reading the alignment marks of the radial base before and after the experiment in the position The angle value on the sample stage and/or the angle value of the sample stage positioning marking line on the positioning sample stage on the sample stage can accurately position the position between the sample stage and the positioning sample stage. The relative position when rotating the connection, and then quickly determine the observation area before and after the experiment, accurately locate the same point, and greatly improve work efficiency;

In another embodiment, a limiting block is also arranged on the connecting bolt, and the limiting block can divide the bolt into two sections, the upper section is connected with the positioning sample stage, and the lower section is connected with the base of the sample stage , the limit block respectively limits the length of the connection between the connecting bolt and the positioning sample stage and the sample stage base, so as to ensure the alignment mark of the radial base and the positioning mark of the sample stage before and after the experiment. The positional relationship further improves the efficiency of determining the observation area;

The length of the above-mentioned connecting bolts is preferably 1/2-4/5 of the depth of the threaded holes embedded in the sample stand and the positioning sample stand;

The connection between the base of the sample stage and the positioning sample stage can be fixedly connected by connection methods such as clamping, nesting, and clamping, in addition to the connection by the connecting bolt;

The beneficial effect of the present invention is: the present invention is simple in structure, and is easy to operate, adopts the structure of sample table base, connecting bolt and positioning sample table, and the rock core sample is held and connected conveniently, and the periphery of sample table base top surface and/or positioning sample Angle scale values are arranged on the bottom periphery of the side of the stage, by reading the angle value of the radial base alignment mark on the positioning sample stage before and after the experiment and/or the position of the sample stage positioning marking on the sample stage on the sample stage Angle value, and then can accurately locate the positional relationship between the sample rack and the positioning sample stage, help to preliminarily determine the observation area before and after the experiment, accurately locate the same point, and greatly improve work efficiency; through the sample stage base and the positioning sample stage set The angle value of the marked line can be read, and the preliminary positioning of the observation point can be made according to the relationship between the front and rear angles;

The present invention limits the length of connection between the connecting bolt and the positioning sample stage and the sample stage by setting the limit block, thereby ensuring the positional relationship between the radial base alignment marking line and the sample stage positioning marking line before and after the experiment, and further optimizing the experimental operation steps. Improved efficiency in determining observation areas;

The positioning sample table of the present invention adopts a hollow structure, and a plurality of sample fixing bolts are arranged on the hollow column on the side, and the rock core sample is fixed by the sample fixing bolts to prevent the movement of the sample and the positioning sample table; There are multiple reference points on the top surface of the sample table, read and record the coordinates of the reference points before and after the reservoir transformation, and calculate the coordinates of the observation points after the reservoir transformation through the coordinate parameters, so as to realize the use of scanning electron microscope to study the oil and gas reservoir transformation before and after the experiment. Accurate and fast positioning and comparative observation of the same mineral or the same point in the same sample to evaluate the effectiveness of reservoir stimulation;

The present invention also combines stable minerals (such as quartz, etc.) for correction, further improves the accuracy of positioning, and uses scanning electron microscopy to complete the analysis of the microscopic appearance of samples after the reservoir reformation experiment; Put the sample stage into the reservoir reforming experimental device together, and keep the rock sample and the positioning sample stage without relative displacement, and carry out the reservoir reforming experiment; it also protects the core sample and prevents human activities from affecting the core, especially the reservoir reforming Finally, the rock samples are relatively loose. Using this structure and method not only protects the samples, but also improves the accuracy of the reservoir stimulation experiment, which is conducive to more objective evaluation of the effectiveness of reservoir stimulation;

The present invention can be used, but not limited to, to use the scanning electron microscope to accurately and quickly locate and compare the same mineral or the same point in the same sample before and after the oil and gas reservoir reconstruction experiment. Experiments of positioning and comparative observation at the same point before and after can be used, such as feldspar dissolution simulation experiments in the study of the formation mechanism of oil and gas sandstone reservoirs, and comparison experiments of before and after corrosion of metals such as steel.

Description of drawings

Fig. 1 is the overall composition diagram of the device of the present invention;

Figure 2 is a diagram of loading the sample to be tested into the positioning sample table;

Figure 3 Connection and positioning sample stage and sample pedestal diagram;

Figure 4 is the finished product after loading the sample to be tested;

Fig. 5 The top view of the positioning sample stage and the schematic diagram of the positioning reference point;

Figure 6 is an overall structural diagram of another embodiment of the device of the present invention;

Fig. 7 is a schematic structural diagram of connecting bolts.

Reference signs: 1. Sample stage base; 1.1. Radial base alignment mark; 1.2. Screw hole; 1.3 Circumferential base alignment mark; 2. Connecting bolt; 2.1 Limiting block; 3. Positioning sample stage; 3.1 Sample 3.2. Bolts for fixing samples; 3.3. Reference point for top surface positioning.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

As shown in Figure 1, the scanning electron microscope sample positioning device used for oil and gas reservoir transformation experiments of the present invention includes: a sample stage base 1, a positioning sample stage 3, and a connecting bolt 2 connected to the sample stage base 1 and the positioning sample stage 3;

The sample stage base 1 is used as a base for positioning the sample stage 3, and its bottom is connected to the scanning electron microscope, and the bolt 2 is used to connect with the positioning sample stage 3 on it, and a radial base alignment marking line is provided from the center to the edge of its top surface 1.1 and the circumferential base alignment marking line 1.3, a screw hole 1.2 is provided in the center of the top surface, wherein the radial base alignment marking line 1.1 is set radially from the screw hole 1.2 in the center of the top surface, and the radial base alignment The marking line 1.1 is perpendicular to the circumferential base alignment marking line 1.3;

The sample stage base 1 and the positioning sample stage 3 are fixedly connected by connecting bolts 2, which are used to fix the positioning sample stage 3 on the sample stage base 1, and the connection between the positioning sample stage 3 and the sample stage base 1 can be realized by rotation and separation;

The positioning sample stage 3 is cylindrical, and its top surface is three top surface positioning reference points 3.3 (A, B, C) distributed on the top surface of the cylinder wall, and the side is eight hollow columns evenly distributed. A hollow column is respectively distributed with a bolt 3.2 for fixing the sample, and there is a sample stage positioning marking line 3.1 at the bottom, and the bottom surface is eight fan-shaped hollows evenly distributed, and the center is a screw hole;

The positioning sample table 3 adopts a hollow cylindrical shape, which can fix and protect the rock samples, and prevent the influence (such as micro-cracks, etc.) on the rock reservoirs during the human operation process, especially when the rock samples have undergone reservoir transformation. After the experiment, the sample is looser than before, and the positioning sample stage 3 can play the role of fixing and protecting, truly preserving the original state of the transformation experiment, and improving the objectivity and effectiveness of reservoir evaluation;

The setting position of the circumferential base alignment marking line 1.3 on the radial base alignment marking line 1.1 is the outer radius of the cylindrical positioning sample stage 3, when the positioning sample stage 3 is closely attached to the sample stage frame 1 , the side edge of the cylindrical positioning sample stage 3 is just aligned with the alignment mark 1.3 of the circumferential base. When the cylindrical positioning sample stage 3 is not aligned with the alignment mark 1.3 of the circumferential base, it means If there is a deviation in the connection between the positioning sample stage 3 and the sample stage 1, remind the staff to check the connection method and correct the installation relationship;

The three top surface positioning reference points 3.3 (A, B, C) are evenly distributed on the top surface of the cylinder wall. In another embodiment, the number of top surface positioning reference points 3.3 can be increased, which can increase the positioning accuracy, It is also possible to preferentially select the top surface positioning reference point 3.3 closest to the observation point P as the scanning electron microscope field of view to find the direction, and it is more accurate and fast to locate the observation point before and after the oil and gas reservoir reconstruction experiment;

As shown in Figures 2, 3, 4, and 5, the scanning electron microscope sample positioning method for oil and gas reservoir transformation experiments of the present invention comprises the following steps:

Step ①: put the standard plunger rock sample used in the reservoir reconstruction experiment from the upper port of the positioning sample table 3, make the top surface of the sample roughly parallel to the top surface of the positioning sample table 3, and fix the sample with the sample fixing bolt 3.2 , so that there is no relative displacement between the sample and the positioning sample stage 3;

Step ②: Connect the positioning sample stage 3 and the sample stage base 1 with the connecting bolt 2; complete the loading of the sample before the reservoir modification experiment, put it into the scanning electron microscope to analyze the microstructure of the sample before the reservoir modification experiment;

Step ③: Read and record the coordinates of positioning reference point 3.3 (A, B, C) on the top surface of the positioning sample stage under the scanning electron microscope as ((x _A , y _A ), (x _B , y _B ), (x _C , y _C )), read and record the observation point (P) coordinates (x _P , y _P ); use scanning electron microscope to analyze the microscopic morphology of the sample before the reservoir stimulation experiment, and read and record each analysis point in turn coordinate of;

Step ④: Unscrew the positioning sample table 3 to separate the positioning sample table 3 from the sample table base 1 and the connecting bolt 2; put the rock sample together with the positioning sample table 3 into the reservoir transformation experiment In the device, and keep the rock sample and the positioning sample table 3 without relative displacement, carry out the reservoir reconstruction experiment;

Step ⑤: Take out the sample and the positioning sample stage after the reservoir modification experiment, repeat the above step ②; complete the loading of the sample after the reservoir modification experiment, put it into the scanning electron microscope for microscopic analysis of reservoir modification evaluation;

Step ⑥: Read and record the coordinates of the positioning reference point 3.3 (A, B, C) on the top surface of the positioning sample stage 3 under the scanning electron microscope as ((x' _A , y' _A ), (x' _B , y' _B ), (x' _C , y' _C )), using the coordinates ((x _A , y _A ), ( x _B , y _B ), (x _C , y _C )) and the P coordinates of the point to be observed (x _P , y _P ), and the positioning reference point 3.3 (A, B, C ) new coordinates ((x' _A , y' _A ), (x' _B , y' _B ), (x' _C , y' _C )) to obtain the coordinates of the point P to be observed after the reservoir stimulation experiment (x' _P , y' _P ) is:

Step ⑦: Input the coordinates of the point P to be observed (x' _P , y' _P ), then the point P to be observed after the reservoir transformation experiment can be found, and combined with stable minerals (such as quartz, etc.) for correction, the reservoir is completed by scanning electron microscopy Analysis of the microscopic morphology of the sample after the transformation experiment;

In the step ②, it is also included to read the positioning sample stage 3 and the sample stage base through the base alignment marking line 1.1 on the sample stage base 1 and/or the sample stage positioning marking line 3.1 of the positioning sample stage 3 1 The initial angle α of the relative relationship;

In the step ⑤, it also includes reading the angle α' between the positioning sample stage 3 and the sample stage base 1 again. By comparing the angle α' and α, the approximate position of the observation point can be preliminarily judged, and the observation point can be improved. The efficiency of positioning, for example, in a certain experiment, the initial angle α is 10°, and the angle α' after the reservoir stimulation experiment is 170°, then the staff can judge that the observation point P is at the initial position after the reservoir stimulation experiment the opposite direction; of course, for convenience, in another embodiment, four quadrant areas can also be divided on the sample stage base 1, and the quadrant area to be observed is judged by the angle relationship;

As shown in Figure 6, in another embodiment, the top periphery of the sample stage base 1 and/or the bottom periphery of the side of the positioning sample stage 3 are also provided with an angle measurement scale, by reading the radial direction before and after the experiment. The angle value of the base alignment marking line 1.1 on the positioning sample stage 3 and/or the angle value of the sample stage positioning marking line 3.1 on the positioning sample stage 3 on the sample stage base 1 can be accurately Locate the relative position of the sample stage base 1 and the positioning sample stage 3 when they are connected in rotation, and then quickly determine the observation area before and after the experiment, accurately locate the same point, and greatly improve work efficiency;

As shown in Figure 7, in another embodiment, a limit block 2.1 is also provided on the connecting bolt 2, and the limit block 2.1 can divide the bolt 2 into two sections, and the upper section and the positioning sample stage 3 connection, the lower section is connected with the base of the sample stage 1, and the limit block 2.1 respectively limits the length of the connection between the connecting bolt 2 and the positioning sample stage 3 and the base of the sample stage 1, thereby ensuring the The positional relationship between the radial base alignment marking line 1.1 and the sample stage positioning marking line 3.1 further improves the efficiency of determining the observation area;

The length of the above-mentioned connecting bolt 2 is preferably 1/2-4/5 of the depth of the threaded hole embedded in the sample stage base 1 and the positioning sample stage 3;

The connection between the sample stage base 1 and the positioning sample stage 3 can be fixedly connected by connection methods such as clamping, nesting, and clamping in addition to the connection by the connecting bolt 2;

The device and method of the present invention can be used for similar experiments that require a scanning electron microscope to locate and compare the same point before and after the experiment, such as the feldspar dissolution simulation experiment in the study of the formation mechanism of oil and gas sandstone reservoirs, before and after the corrosion of metals such as steel Positioning comparison experiments, etc.

The above-mentioned embodiments are only to illustrate the technical concept and characteristics of the present invention, and its purpose is to enable those of ordinary skill in the art to understand the content of the present invention and implement it accordingly, and cannot limit the protection scope of the present invention. All equivalent changes or modifications made according to the essence of the present invention shall fall within the protection scope of the present invention.

Claims (7)

1. A scanning electron microscope sample positioning device for oil and gas reservoir transformation experiments, characterized in that: the sample positioning device comprises a sample stage base (1), connecting bolts (2) and positioning sample stage (3), wherein said The bottom of the sample stage base (1) is directly connected to the scanning electron microscope, and the top is fixedly connected to the positioning sample stage (3) through the connecting bolt (2); the positioning sample stage (3) is cylindrical, and The bottom edge of the side wall of the positioning sample stage (3) is provided with a sample stage positioning marking (3.1), and a radial base alignment marking (1.1) is provided on the top surface of the sample stage base (1). The relative position of the radial base alignment mark (1.1) and the sample stage positioning mark (3.1) of the positioning sample stage (3) can preliminarily judge the position of the test point, and the side of the positioning sample stage (3) A plurality of sample fixing bolts (3.2) are arranged on the wall, and the rock test sample can be fixed in the positioning sample stage by adjusting the tightness of the sample fixing bolts (3.2). On the top of the cylindrical cylindrical positioning sample stage (3) A plurality of top surface positioning reference points (3.3) are provided, and the observation points before and after the oil and gas reservoir transformation experiment can be accurately positioned through the multiple top surface positioning reference points (3.3), and the sample microscopic morphology analysis and comparison are carried out; A circumferential base alignment mark (1.3) is also arranged on the top surface of the sample stage base (1), and the circumferential base alignment mark (1.3) is perpendicular to the radial base alignment mark (1.1); the sample stage base The top circumferential direction of (1) and the bottom circumferential direction of the side wall of the positioning sample stage (3) are also arranged with angular scale values, through the radial base alignment mark (1.1) on the sample stage base (1) and the The sample stage positioning marking (3.1) of the positioning sample stage (3) reads the rotation angle between the positioning sample stage (3) and the sample stage base (1), which is convenient for the preliminary judgment of the position of the observation point; The side of the positioning sample stage (3) is eight evenly distributed hollow columns, and a sample fixing bolt (3.2) is respectively distributed up and down each of the hollow columns; the bottom surface of the positioning sample stage (3) is eight There are two evenly distributed fan-shaped hollows, and the central position is a threaded hole (1.2) for connecting with the connecting bolt (2). 2. The scanning electron microscope sample positioning device for oil and gas reservoir transformation experiments according to claim 1, characterized in that: both ends of the connecting bolt (2) are provided with external threads, and the base of the sample table (1) Both the top center of the positioning sample stage (3) and the bottom center of the positioning sample stage (3) are provided with threaded holes (1.2), and the connection and separation of the positioning sample stage (3) and the sample stage base (1) can be realized by rotation. 3. The scanning electron microscope sample positioning device for oil and gas reservoir reconstruction experiment according to claim 1, characterized in that: the preliminary positioning of the observation point is carried out by recording the angle values twice before and after. 4. A positioning method adopting the scanning electron microscope sample positioning device for oil and gas reservoir transformation experiments described in any one of claims 1-3, it is characterized in that: the positioning method comprises the following steps: Step 1.: the reservoir The standard plunger rock sample used for the transformation experiment is put into from the upper port of the positioning sample stage (3), so that the top surface of the sample is roughly parallel to the top surface of the positioning sample stage (3), and the sample fixing bolt (3.2 ) fix the sample so that there is no relative displacement between the sample and the positioning sample stage (3); Step ②: Connect the positioning sample stage (3) and the sample stage base (1) with the connecting bolt (2), complete the loading of the sample before the reservoir transformation experiment, and put it into the scanning electron microscope for the microcosmic analysis of the sample before the reservoir transformation experiment. Structural analysis; step ③: read and record the coordinates of positioning reference points A, B, and C on the top surface of the positioning sample stage under the scanning electron microscope as (x _A , y _A ), (x _B , y _B ), (x _C , y _C ), read and record the coordinates of the point P to be observed as (x _P , y _P ), use a scanning electron microscope to analyze the microscopic morphology of the sample before the reservoir stimulation experiment, and read and record the coordinates of each analysis point in turn coordinate; Step ④: Unscrew the positioning sample stage (3), separate the positioning sample stage (3) from the sample stage base (1) and the connecting bolts (2), and place the rock sample together with the positioning sample stage (3) ) together into the reservoir reformation experiment device, and keep the rock sample and the positioning sample platform without relative displacement, and carry out the reservoir reformation experiment; Step ⑤: Take out the sample and the positioning sample stage after the reservoir modification experiment, repeat the above step ②, complete the loading of the sample after the reservoir modification experiment, put it into the scanning electron microscope for microscopic analysis of reservoir modification evaluation; Step ⑥: Read and record the coordinates of the positioning reference points A, B, and C on the top surface of the positioning sample stage (3) under the scanning electron microscope as (x' _A , y' _A ), (x' _B , y' _B ), (x' _C , y' _C ), using the coordinates (x A , y A ), (x _B , y _B ), (x _B , y _B ) and ( x _C , y _C ) and the coordinates of the point P to be observed (x _P , y _P ), and the new coordinates (x' _A , y' _A ), (x' _B , y' _B ), (x' _C , y' _C ) to obtain the coordinates (x' _P , y' _P ) of the point P to be observed after the reservoir stimulation experiment is: x _p '＝[(y _C '-y _A ')(x' _B ² -x _B ² +x _A ² -x' _A ² +2x _P (x _B -x _A )+y' _B ² -y _B ² +y _A ² -y' _A ² +2y _P (y _B -y _A )) -(y _B '-y _A ')(x' _C ² -x _C ² +x _A ² -x' _A ² +2x _P (x _C -x _A )+y' _C ² -y _C ² +y _A ² -y' _A ² +2y _P (y _C -y _A ))]/2((x' _B -x' _A )(y' _C -y' _A )-(x' _C -x' _A )( y' _B -y' _A )), y _p '＝[(x _C '-x _A ')(x' _B ² -x _B ² +x _A ² -x' _A ² +2x _P (x _B -x _A )+y' _B ² -y _B ² +y _A ² -y' _A ² +2y _P (y _B -y _A ))-(x _B '-x _A ')(x' _C ² -x _C ² +x _A ² -x' _A ² + 2x _P (x _C -x _A )+y' _C ² -y _C ² +y _A ² -y' _A ² +2y _P (y _C -y _A ))]/2((y' _B -y' _A )(x' _C -x' _A )-(y' _C -y' _A )(x' _B -x' _A )); Step ⑦: Input the coordinates (x' _P , y' _P ) of the point P to be observed, that is, the point P to be observed after the reservoir transformation experiment can be accurately located, and the sample after the reservoir transformation experiment is completed by using a scanning electron microscope Microscopic morphology analysis. 5. The positioning method according to claim 4, characterized in that: in step ②, it also includes aligning the marking line (1.1) and the positioning sample stage (3) through the radial base on the sample stage base (1) The sample stage positioning marking (3.1) reads the initial angle α between the positioning sample stage (3) and the sample stage base (1); in the step ⑤, it also includes reading the positioning sample stage ( 3) By comparing the included angle α' with the base of the sample stage (1), the approximate position of the observation point can be preliminarily judged by comparing the included angle α' with α. 6. The positioning method according to claim 4, characterized in that: four quadrant areas can be further divided on the base of the sample stage (1), and the quadrant area where the point to be observed is located is judged by the angle relationship. 7. The positioning method according to claim 4, characterized in that: in said step ⑦, correction is also included in combination with stable minerals, wherein said stable minerals include quartz.

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