A method for constructing a reservoir throat-pore model based on multi-information fusion

Abstract

The present invention relates to the technical field of oil exploitation, and specifically, to a method for constructing a reservoir throat-pore model based on multi-information fusion, which comprises the following steps: Step 1: Obtain two-dimensional characteristic parameters of pores of different genetic types; Step 2: Obtain pore volume and pore size distribution parameters controlled by throats of different levels; Step 3: Establish a matrix equation to calculate the genetic, pore size, and volume parameters of pores connected by throats of different levels; Step 4: Construct a multi-information model of throat-pore. The present invention can preferably obtain the characteristic parameters of different types of pores.

Description

Technical Field

[0001] The present invention relates to the technical field of oil extraction, and specifically, to a method for constructing a reservoir throat-pore model based on multi-information fusion. Background Art

[0002] With the deepening of unconventional oil and gas exploration and development, the research focus of clastic rock reservoirs has gradually shifted to low-porosity, low-permeability, and tight sandstones. Compared with conventional reservoirs, the primary porosity of tight sandstones has been greatly lost due to strong compaction and cementation, and secondary pores and various micropores have become important reservoir spaces, even exceeding the primary pores, and the pore structure is complex.

[0003] For a long time, the characterization of pores in tight sandstones and shales has the following characteristics: 1. The characterization focus is concentrated on the morphology and size of pores and throats; 2. The characterization methods include semi-quantitative (rock thin sections, scanning electron microscopy) and quantitative (high-pressure mercury injection, nuclear magnetic resonance, CT, nitrogen adsorption, etc.); 3. Different characterization methods often calculate the relevant parameters of pores and throats based on a single pore-throat model; 4. There is a lack of effective integration between different technical methods.

[0004] Currently, existing technologies often calculate and transform test data based on a single pore-throat model to obtain certain characteristics of pore throats. However, recent studies have shown that there are often different pore-throat models in reservoir pores; there is a lack of effective integration between different testing technologies. The thin-section electron microscopy obtains two-dimensional pore information, nuclear magnetic resonance obtains the pore radius distribution, and high-pressure mercury injection obtains the size of throats and the distribution of the connected pore volume. There is a lack of integration between different types of data. Summary of the Invention

[0005] The content of the present invention is to provide a method for constructing a reservoir throat-pore model based on multi-information fusion, which effectively fuses the pore and throat information obtained by different types of testing methods, and finally constructs a multi-information pore model including various characteristic parameters of pores and throats.

[0006] A method for constructing a reservoir throat-pore model based on multi-information fusion according to the present invention includes the following steps:

[0007] Step 1: Obtain two-dimensional characteristic parameters of pores of different genetic types;

[0008] Step 2: Obtain the pore volume and pore size distribution parameters controlled by throats of different levels;

[0009] Step 3: Establish a matrix equation to calculate the genetic origin, pore size, and volume parameters of pores connected by throats of different levels;

[0010] Step 4: Construct a multi-information model of throat-pores.

[0011] Preferably, in step 1, the specific steps are as follows:

[0012] 1.1) Conduct cast thin section and scanning electron microscope analyses to obtain two-dimensional pore images;

[0013] 1.2) Use Image J software to extract and characterize pores in the images to obtain two-dimensional key characteristic parameters of pores of different genetic types, including pore size, roundness, elongation ratio, and pore surface ratio;

[0014] 1.3) Calculate the contribution of different pores to porosity based on the pore surface ratios of pores of different genetic types obtained.

[0015] Preferably, in step 2, the specific steps are as follows:

[0016] 2.1) Select representative samples to conduct nuclear magnetic resonance analysis under saturated water conditions to obtain the distribution of the full pore radius;

[0017] 2.2) Conduct experiments under different centrifugation conditions, set sequentially increasing centrifugation speed conditions, and conduct multiple centrifugation experiments; after each centrifugation experiment, convert the centrifugation speed to the throat radius, and conduct nuclear magnetic resonance to obtain the pore volume and pore size distribution of the pores controlled by throats of different radii.

[0018] Preferably, in step 3, the specific steps are as follows:

[0019] 3.1) Assume that the pore seepage level is divided into 3 levels. According to the changes in different centrifugation T2 curves, the movable pore volume and pore size distribution of different seepage levels can be obtained;

[0020] 3.2) Comprehensively use thin sections, electron microscopes, and CT scan pore identification to obtain the pore volume and pore size distribution of pores of different genetic types; the pore volumes of different genetic types include intergranular pore volume, dissolution pore volume, and micropore volume;

[0021] 3.3) Assume that the total movable pore volume of seepage level i is V i (i = 1, 2, 3), where the intergranular pore volume, dissolution pore volume, and micropore volume of different seepage levels are V i-a 、V i-b 、V i-c , then:

[0022] V i =V i-a +V i-b +V i-c

[0023] At the same time, pores of the same type (such as intergranular pore V a ) are connected by throats of different levels. Therefore:

[0024] Va = V 1-a + V 2-a + V 3-a

[0025] Based on this, a matrix equation is established. With the pore throat parameters of thin sections, electron microscopy, and CT scans as constraints, iterative calculations are performed using MATLAB to obtain the optimal solutions of V i-a , V i-b , V i-c .

[0026] The present invention provides a method for constructing a throat - pore model for multi - information fusion of tight reservoirs, which can help clarify the internal connection and co - evolutionary process of reservoir connectivity and accumulation, reveal the internal reasons for the differences in the occurrence and flow of reservoir fluids, and overcome the limitation of the classical clastic rock pore evolution model that only studies pore types and porosity changes.

[0027] The technical solution of the present invention is mainly based on obtaining the characteristic parameters of different types of pores from thin sections, establishing an identification database of key characteristic parameters of pore types, and using mathematical methods of cross - validation and grid search to carry out iterative calculations of pore parameters at different NMR seepage levels. This method can overcome the problem of difficult information fusion of different testing means for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a flowchart of a method for constructing a reservoir throat - pore model based on multi - information fusion in an embodiment;

[0029] Figure 2 is a schematic diagram of a calculation model of the characteristic parameter matrix of pores at each seepage level in an embodiment;

[0030] Figure 3 is a schematic diagram of the characterization of the configuration characteristics and key parameters of different - level throat - pore in an embodiment;

[0031] Figure 4 is a schematic diagram of the "tree - like" distribution pattern of throat - pore in an embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] To further understand the content of the present invention, the present invention will be described in detail with reference to the drawings and embodiments. It should be understood that the embodiments are only for explaining the present invention and not for limiting it.

[0033] Embodiment

[0034] As Figure 1 shown, this embodiment provides a method for constructing a reservoir throat - pore model based on multi - information fusion, which includes the following steps:

[0035] Step 1: Obtain two - dimensional characteristic parameters of pores of different genetic types;

[0036] The specific steps are as follows:

[0037] 1.1) Conduct cast thin section and scanning electron microscope analyses to obtain two-dimensional pore images;

[0038] First, cut the core samples, take part of them for thin section and electron microscope observations, and use the remaining part for nuclear magnetic resonance and CT scans. Wash the oil from the samples and inject blue casting resin, then grind them into cast thin sections with a thickness of 0.04 mm, slightly thicker than the conventional thickness (0.03 mm) for subsequent argon ion polishing. Obtain the rock cast thin section images using a polarized light microscope. It is difficult to identify the pore parameters of micropores within components such as clay minerals through single polarized light observation of the thin sections. Therefore, the cast thin sections need to be thinned a second time using an ion thinning instrument, and the micropore parameters are observed using a field emission electron microscope. Fix the polished thin section on the sample stage with conductive glue, and coat a platinum film with a thickness of about 15 nm using an ion sputtering instrument.

[0039] 1.2) Use Image J software to extract and characterize the pores in the images, and obtain the two-dimensional key characteristic parameters of pores of different genetic types, including pore size, roundness, elongation ratio, and pore area ratio; this method has a large observation field of view and can obtain the pore parameters of relatively large and connected pores such as primary intergranular pores and dissolution pores.

[0040] 1.3) Calculate the contribution of different pores to the porosity according to the pore area ratios of pores of different genetic types obtained.

[0041] Step 2: Obtain the pore volume and pore size distribution parameters controlled by throats of different levels;

[0042] The specific steps are as follows:

[0043] 2.1) Select representative samples to conduct nuclear magnetic resonance analysis under saturated water conditions to obtain the distribution of the radii of all pores;

[0044] Select representative samples to conduct nuclear magnetic resonance analysis under saturated water conditions: Nuclear magnetic resonance is the best means to obtain the information of the radii of all pores in the samples without damage. By combining multiple centrifugations with nuclear magnetic resonance, the pore volume and pore size distribution of pores controlled by different throats can be obtained. Nuclear magnetic resonance mainly reflects the pore size distribution through the transverse relaxation time T2. Therefore, it is necessary to calibrate T2 and convert it into the pore size distribution. The specific steps are as follows:

[0045] Measure the T2 curves of the same sample under different centrifugal force conditions, and read the separation points of the different centrifugal T2 curves and the saturated water T2 curve. The separation point represents the minimum pore that the fluid can pass through under this centrifugal condition, that is, the throat. The T2 time corresponding to the separation point is the transverse relaxation time of the seepage throat.

[0046] 2.2) Conduct experiments under different centrifugation conditions, set gradually increasing centrifugation speed conditions, and conduct multiple centrifugation experiments; after each centrifugation experiment, convert the centrifugation speed to the throat radius, and conduct nuclear magnetic resonance to obtain the pore volume and pore size distribution of the pores controlled by throats with different radii.

[0047] Through multiple centrifugation experiments and nuclear magnetic resonance tests, the T2 relaxation time (T 2Throat ) corresponding to different throats can be obtained. By regression analysis, the T2 spectrum conversion coefficient C can be obtained to calculate the pore size distribution.

[0048] Step 3: Establish a matrix equation to calculate the origin, pore size, and volume parameters of the connected pores of different levels of throats;

[0049] In step one, the pore size, pore face ratio, and pore volume of pores of different origin types can be obtained; in step two, the volume and pore size distribution of pores controlled by different throats can be obtained. Now, the information from the first two steps still needs to be integrated to establish a pore-throat model including throats, pore origin, pore volume, and radius. The specific steps are as follows:

[0050] 3.1) Assume that the pore seepage level is divided into 3 levels. According to the changes in different centrifugation T2 curves, the movable pore volumes (V1, V2, V3) and pore size distributions (step two) of different seepage levels can be obtained;

[0051] 3.2) Comprehensively utilize thin sections, electron microscopes, and CT scan pore identification to obtain the pore volume and pore size distribution of pores of different origin types (step one); the pore volumes of different origin types include the intergranular pore volume V a , the dissolution pore volume V b , and the micropore volume V c ;

[0052] 3.3) Assume that the total movable pore volume of seepage level i (i = 1, 2, 3) is V i , where the intergranular pore, dissolution pore, and micropore volumes of different seepage levels are V i-a , V i-b , V i-c , respectively. Then:

[0053] V i = V i-a + V i-b + V i-c

[0054] At the same time, the same type of pores (such as intergranular pores V a ) are connected by throats of different levels. Therefore:

[0055] V a = V 1-a + V 2-a + V3-a

[0056] Based on this, a matrix equation is established. As Figure 2 shown, taking the pore throat parameters of thin sections, electron microscopy, and CT scans as constraint conditions, iterative calculations are performed using MATLAB to obtain the optimal solutions of V i-a , V i-b , V i-c .

[0057] Step 4: On the basis of the first three steps, construct a multi-information model of throat-pore, as Figure 3 and Figure 4 shown. On the basis of characterizing the features of throat and pore at all levels, summarize the configuration relationship and variation law of throat-pore in tight sandstone, and construct a multi-information model of throat-pore. Through the model, the characteristic parameters of different types of pores can be better obtained.

[0058] This embodiment provides a method for constructing a throat-pore model with multi-information fusion in tight reservoirs, which can help to clarify the internal connection and co-evolution process of reservoir connectivity and accumulation, reveal the internal reasons for the differences in fluid occurrence and flow in the reservoir, and overcome the limitation of the classical clastic rock pore evolution model that only studies pore types and porosity changes.

[0059] The technical solution of this embodiment is mainly based on obtaining the characteristic parameters of different types of pores from thin sections, establishing an identification database of key characteristic parameters of pore types, and using mathematical methods of cross-validation and grid search to carry out iterative calculations of pore parameters at different percolation levels of nuclear magnetic resonance. This method can overcome the problem of difficult information fusion of different testing means for a long time.

[0060] The above schematically describes the present invention and its embodiments. This description is not restrictive, and only one of the embodiments of the present invention is shown in the drawings. The actual structure is not limited to this. Therefore, if those of ordinary skill in the art are inspired by it and design similar structural modes and embodiments without creative efforts without departing from the purpose of the present invention, they shall fall within the protection scope of the present invention.

Claims

1. A method for constructing a reservoir throat-pore model based on multi-information fusion, characterized in that: It includes the following steps: Step 1: Obtain the two-dimensional characteristic parameters of pores of different genetic types; Step 2: Obtain the pore volume and pore size distribution parameters controlled by throats of different levels; Step 3: Establish a matrix equation to calculate the genetic, pore size, and volume parameters of connected pores of different levels of throats; In Step 3, the specific steps are as follows: 3.1) Assume that the pore seepage level is divided into 3 levels. According to the changes in different centrifugal T2 curves, the movable pore volume and pore size distribution of different seepage levels can be obtained; 3.2) Identify the pore volume and pore size distribution of different genetic types by comprehensively using thin sections, electron microscopy, and CT scan pore identification; the pore volume of different genetic types includes intergranular pores V a , dissolution pores V b and micropore volume V c ; 3.3) Let the total volume of movable pores at seepage level i be V i , where i = 1, 2, 3. The volumes of intergranular pores, dissolved pores, and micropores at different seepage levels are V i-a , V i-b , V i-c , respectively. Then: V i = V i-a + V i-b + V i-c At the same time, pores of the same type are connected by throats of different levels. Therefore: V a = V 1-a + V 2-a + V 3-a Based on this, a matrix equation is established. With the pore throat parameters of thin sections, electron microscopy, and CT scans as constraints, iterative calculations are performed using MATLAB to obtain the optimal solutions of V i-a , V i-b , V i-c ; Step 4: Construct a multi-information model of throat-pore.

2. The method for constructing a reservoir throat-pore model based on multi-information fusion according to claim 1, wherein: In Step 1, the specific steps are as follows: 1.1) Conduct cast thin section and scanning electron microscope analyses to obtain two-dimensional pore images; 1.2) Use Image J software to extract and characterize pores in the images, and obtain the two-dimensional key characteristic parameters of pores of different genetic types, including pore size, roundness, elongation ratio, and pore face ratio; 1.3) Calculate the contribution of different pores to porosity according to the pore face ratio of pores of different genetic types obtained.

3. A method for constructing a reservoir throat-pore model based on multi-information fusion according to claim 1, characterized in that: In Step 2, the specific steps are as follows: 2.1) Select representative samples to conduct nuclear magnetic resonance analysis under saturated water conditions to obtain the distribution of the full pore radius; 2.2) Conduct experiments under different centrifugal conditions, set sequentially increasing centrifugal speed conditions, and conduct multiple centrifugal experiments; after each centrifugal experiment, convert the centrifugal speed to the throat radius, and conduct nuclear magnetic resonance to obtain the pore volume and pore size distribution of pores controlled by throats of different radii.

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