Method for accurately obtaining physical property parameters of a core

Abstract

This invention discloses an accurate method for calculating the physical properties of rock cores, belonging to the field of petroleum exploration and development. When the porosity of the rock core is large, its expansion and contraction are strong. Under test conditions, it expands or contracts with changes in external pressure, leading to inaccurate acoustic transit time measurements and consequently inaccurate physical properties of shale. This invention provides a method for characterizing porosity and offers different physical property measurement methods for shale with different porosity sizes, thus greatly improving the accuracy of shale physical property measurement values.

Description

Technical Field

[0001] This invention relates to the field of petroleum exploration and development, and in particular to a method for obtaining the physical properties of rock cores. Background Technology

[0002] In oilfield exploration and development, oil content is a crucial basis for assessing oilfield resource assets. However, accurately determining oil content is difficult, and oil saturation is an important and commonly used parameter for estimating oil content. Current technologies typically use methods such as closed coring and oil-based mud coring to directly obtain oil saturation data under formation conditions. However, these methods cannot be applied to all oilfields, especially for some foreign oilfields controlled by my country. Due to economic and environmental factors, these methods have not been widely adopted, and estimations are usually only possible through relevant parameters.

[0003] Taking saturation as an example, Archie's formula uses a combination of porosity and resistivity to obtain the saturation value, and it is currently the most widely used saturation model. Its porosity is usually obtained using a simple and easy-to-implement method combining resistivity and acoustic measurements. However, the porosity of sedimentary clastic rocks is related to pressure. Under pressure, this includes not only plastic deformation caused by the arrangement of clay and sandstone particles (which is irreversible), but also elastic compression. When core samples are taken from the formation to the surface during drilling, the porosity of the core sample increases due to pressure release and elastic expansion. During subsequent pressurization measurements, the core expands or contracts with changing pressure, and the density of the gas changes, significantly affecting the acoustic propagation speed and leading to inaccurate acoustic transit time measurements. This deviation becomes more pronounced with increasing porosity. When the core porosity reaches a certain range, it is no longer suitable to obtain core porosity using a combination of acoustic parameters. Similar problems exist in the measurement of other core physical properties. Summary of the Invention

[0004] One of the main technical problems addressed by this invention is the lack of existing methods for measuring the physical properties of rock cores based on differences in core porosity. This invention provides a method for accurately measuring the physical properties of rock cores.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] (1) Embed the multi-functional integrated sensor into the corresponding layer of the model during model making;

[0007] (2) After the model is completed, basic data collection is carried out on the unexperimented model to obtain core acoustic time difference data;

[0008] (3) The resistivity of each layer of the model was collected in real time during the experiment;

[0009] (4) Calculate the core porosity based on the core acoustic transit time data;

[0010] (5) Characterize the pore structure of the core;

[0011] (6) Select different methods for measuring the physical properties of cores for different core porosities.

[0012] Characterizing the pore structure of rock cores specifically includes the following steps:

[0013] 1) Select representative rock samples and drill to obtain cores. The cores should be 50 mm long and 20 mm in diameter.

[0014] 2) Scan the cross-section of the core sample to obtain two-dimensional grayscale images of each cross-section;

[0015] 3) After filtering, the two-dimensional grayscale image is binarized, denoised, and optimized. Then, the three-dimensional digital core is reconstructed and reconstructed by layer-by-layer stacking.

[0016] 4) Based on the principle of topology, the three-dimensional digital core is simplified topologically to extract a mathematical network model of the pores in the three-dimensional core. In this model, pores in the pore network are designated as nodes, and channels in the pore network are designated as edges in the topological network.

[0017] 5) The arithmetic mean of the degrees of all nodes is calculated to characterize the three-dimensional pore network structure of the core.

[0018] Different logging methods are selected for different core porosities, and the specific steps include the following:

[0019] When the arithmetic mean of the degrees of all nodes is greater than 6, resistivity is used to measure the physical properties of the core.

[0020] When the arithmetic mean of the degrees of all nodes is not greater than 6, the physical parameters of the core are measured by a combination of acoustic and resistivity measurements.

[0021] Preferably, scanning of the core cross-section is achieved using nano-CT or micro-CT.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] When the core porosity is large, the core has strong expansion and contraction properties. Under test conditions, it expands or contracts with changes in external pressure, which changes the density of the gas and significantly affects the propagation speed of sound waves, resulting in inaccurate sound wave transit time. However, the liquid volume remains constant, and the liquid phase volume does not change with the magnitude of external pressure. Therefore, the electrolyte concentration fluctuates less, and the measured resistivity is accurate.

[0024] The applicant uses the degree to characterize the development of the pore network inside the core. A higher degree value indicates a more developed pore structure and greater porosity. Each increase of 1 in degree corresponds to a significant increase in pore development, theoretically reaching up to a doubling, and consequently, higher expansion and contraction. Through extensive parallel experiments, a threshold of 6 was determined. When the degree is greater than 6, it indicates a complex network structure within the core, indicating higher porosity. In this case, resistivity alone provides a more accurate porosity reading. Conversely, when the degree is no greater than 6, the impact on acoustic wave detection results is minimal, and acoustic resistivity combined with other measurements yields more accurate porosity data. Attached Figure Description

[0025] The schematic diagram of the experimental setup for the verification experiment in this embodiment is shown in the attached figure.

[0026] Figure 1 This is a schematic diagram of the measurement of the physical parameters of the rock core. Figure 2 This is a diagram of a software data processing and acquisition system.

[0027] Reference numerals: 1. Multifunctional integrated sensor; 2. Data acquisition circuit; 3. Resistance acquisition converter; 4. Acoustic wave receiver; 5. Acoustic wave transmitter; 6. Software data processing and acquisition system.

[0028] The multifunctional integrated sensor includes resistance, longitudinal wave, and transverse wave sensors. The probe has a withstand voltage of 100MPa, a temperature resistance of 150°C, a longitudinal wave main frequency of 800kHz, a transverse wave main frequency of 600kHz, and an acoustic excitation voltage of 300-1000V. It employs a two-stage method to measure resistivity at a measurement frequency of 1kHz, with an insulation resistance greater than 100MΩ. Detailed Implementation

[0029] The specific steps in this embodiment include:

[0030] (1) Embed the multi-functional integrated sensor into the corresponding layer of the model during model making;

[0031] (2) After the model is completed, basic data collection is carried out on the unexperimented model to obtain core acoustic time difference data;

[0032] (3) The resistivity of each layer of the model was collected in real time during the experiment;

[0033] (4) Calculate the core porosity based on the core acoustic transit time data;

[0034] (5) Characterize the pore structure of the core;

[0035] (6) Select different methods for measuring the physical properties of cores for different core porosities.

[0036] Characterizing the pore structure of rock cores specifically includes the following steps:

[0037] 1) Select representative rock samples and drill to obtain cores. The cores should be 50 mm long and 20 mm in diameter.

[0038] 2) Scan the cross-section of the core sample to obtain two-dimensional grayscale images of each cross-section;

[0039] 3) After filtering, the two-dimensional grayscale image is binarized, denoised, and optimized. Then, the three-dimensional digital core is reconstructed and reconstructed by layer-by-layer stacking.

[0040] 4) Based on the principle of topology, the three-dimensional digital core is simplified topologically to extract a mathematical network model of the pores in the three-dimensional core. In this model, pores in the pore network are designated as nodes, and channels in the pore network are designated as edges in the topological network.

[0041] 5) The arithmetic mean of the degrees of all nodes is calculated to characterize the three-dimensional pore network structure of the core.

[0042] Preferably, the process of simplifying the digital core network based on topology theory is as follows: First, nodes with a degree of 2 or less are discarded, because the pore structure represented by these nodes has a relatively small effect on the seepage movement of fluid within the pores; second, for nodes with higher degrees, their flow performance is significantly affected by their structural stability, and therefore they are not considered. Finally, the arithmetic mean of the degrees is used to characterize the pore network of the core.

[0043] Different logging methods are selected for different core porosities, and the specific steps include the following:

[0044] When the arithmetic mean of the degrees of all nodes is greater than 6, resistivity is used to measure the physical properties of the core.

[0045] When the arithmetic mean of the degrees of all nodes is not greater than 6, the physical parameters of the core are measured by a combination of acoustic and resistivity measurements.

[0046] Preferably, scanning of the core cross-section is achieved using nano-CT or micro-CT.

Claims

1. A method for accurately calculating the physical properties of rock cores, characterized in that, Includes the following steps: (1) Embed the multi-functional integrated sensor into the corresponding layer of the model during model making; (2) After the model is completed, basic data collection is carried out on the unexperimented model to obtain core acoustic time difference data; (3) The resistivity of each layer of the model was collected in real time during the experiment; (4) Calculate the core porosity based on the core acoustic transit time data; (5) Characterize the pore structure of the core; (6) Select different methods for measuring the physical properties of cores for different core porosities; Characterizing the pore structure of rock cores specifically includes the following steps: 1) Select representative rock samples and drill to obtain rock cores. The length of the rock cores is 50 mm and the diameter is 20 mm. 2) Scan the cross-section of the core sample to obtain two-dimensional grayscale images of each cross-section; 3) After filtering, the two-dimensional grayscale image is binarized, denoised, and optimized. Then, the three-dimensional digital core is reconstructed and reconstructed by layer-by-layer stacking. 4) Based on the principle of topology, the three-dimensional digital core is simplified topologically to extract a mathematical network model of the pores in the three-dimensional core. In this model, pores in the pore network are designated as nodes, and channels in the pore network are designated as edges in the topological network. 5) The arithmetic mean of the degrees of all nodes is calculated to characterize the three-dimensional pore network structure of the core. Different logging methods are selected for different core porosities, and the specific steps include the following: When the arithmetic mean of the degrees of all nodes is greater than 6, resistivity is used to measure the physical properties of the core. When the arithmetic mean of the degrees of all nodes is not greater than 6, the physical parameters of the core are measured by a combination of acoustic and resistivity measurements.

2. The method for accurately calculating the physical properties of rock cores as described in claim 1, characterized in that, Scanning the cross-section of the rock core is achieved using nano-CT or micro-CT.

Images