A method for evaluating oiliness of a tight sandstone reservoir based on pore throat coordination degree

Abstract

This invention relates to the field of oil and gas engineering, and in particular to a method for evaluating the oil-bearing potential of tight sandstone reservoirs based on pore-throat coordination during exploration and development. The method for evaluating the oil-bearing potential of tight sandstone reservoirs based on pore-throat coordination is as follows: Obtain the throat-pore microstructure parameters of the target reservoir sample; obtain the critical throat diameter of the target reservoir sample; and, in conjunction with the pore microstructure parameters of the target reservoir sample, sequentially calculate the fluid passage probability and overall fluid passage probability for different throat diameters; based on the overall fluid passage probability, solve for the pore oil-bearing index with different coordination numbers, and then calculate the overall oil-bearing index, which characterizes the oil-bearing capacity of the overall pore region. This invention enables a novel method for evaluating the overall oil-bearing potential of different types of throat-pore combinations.

Description

Technical Field

[0001] This invention relates to the field of oil and gas engineering, and in particular to a method for evaluating the oil-bearing potential of tight sandstone reservoirs based on the degree of pore throat coordination during exploration and development. Background Technology

[0002] Oil-bearing capacity of reservoirs is a key factor influencing oil and gas resource potential assessment, geological sweet spot evaluation, and well pattern deployment. Researchers have conducted extensive testing and evaluation of reservoir oil-bearing capacity, and existing methods mainly include the following:

[0003] Patent application CN202311572092.6 discloses a method, system, equipment, and medium for evaluating the reservoir capacity of tight gas reservoirs. This method obtains the measured Young's modulus and effective porosity of each mineral component in standard rock samples of the tight gas reservoir to be tested, and then calculates the reservoir factor to achieve a comprehensive evaluation of the reservoir capacity. Patent application CN201911373290.3 discloses a method and apparatus for predicting oil and gas enrichment zones in tight sandstone. This method classifies completed wells in the work area into different types based on the thickness and / or daily production of the oil and gas-bearing sand bodies; for multiple seismic attributes, it determines the consistency rate of each seismic attribute with different types of completed wells in the work area; it performs multi-attribute weighted calculations on multiple seismic attributes to obtain the probability distribution parameters of oil and gas attributes in the work area; and based on the probability distribution parameters of oil and gas attributes in the work area, it predicts the oil and gas enrichment zones in the tight sandstone of the work area. Patent application CN202210502367.8 discloses an oil and gas enrichment evaluation method, device, storage medium and electronic equipment. The method generates an oil and gas charging adjustment model, an oil and gas preservation evaluation model and an oil and gas enrichment prediction model based on the fault activity period, reservoir formation period matching degree and fault source of the target fault zone, thereby realizing the evaluation of the oil and gas enrichment mode of the target fault zone.

[0004] A comparison with existing methods reveals that current research primarily relies on static, single-factor methods such as porosity testing of physical properties, geological and seismic modeling, and fault connectivity evaluation to assess hydrocarbon enrichment and oil-bearing potential within rock pores. However, these methods fail to address the essential factors influencing oil-bearing potential—the coordination degree of throats and pore microstructure—nor do they effectively evaluate the oil-bearing potential of rock micropores from the perspective of fluid flow capacity. Summary of the Invention

[0005] The present invention aims to address the above-mentioned problems by proposing a method for evaluating the oil-bearing potential of tight sandstone reservoirs based on the degree of pore-throat coordination.

[0006] The technical solution of this invention is as follows:

[0007] A method for evaluating the oil-bearing potential of tight sandstone reservoirs based on pore-throat coordination is as follows:

[0008] Obtain the throat-pore microstructure parameters of the target reservoir rock sample;

[0009] Obtain the critical throat diameter of the target reservoir rock sample, and calculate the fluid passage probability and overall fluid passage probability for different throat diameters in sequence, based on the pore microstructure parameters of the target reservoir rock sample.

[0010] The oil-bearing index of pores with different coordination numbers is solved based on the overall fluid flow probability, and then the overall oil-bearing index is calculated to characterize the oil-bearing capacity of the overall pore region.

[0011] The specific process of characterizing the oil-bearing capacity of the overall pore region by the overall oil content index is as follows: if 0.75 < overall oil content index ≤ 1, it is defined as oil content grade I; if 0.5 < overall oil content index ≤ 0.75, it is defined as oil content grade II; if 0.25 < overall oil content index ≤ 0.50, it is defined as oil content grade III; if 0 < overall oil content index ≤ 0.25, it is defined as oil content grade IV.

[0012] The throat-pore microstructure parameters include pore-throat attribute parameters and pore attribute parameters; the pore-throat attribute parameters include the diameter distribution of the pore throats and the number of pore throats at the corresponding diameters; the pore attribute parameters include the number of pores with different coordination numbers.

[0013] The specific calculation process for the probability of fluid passage through different throat diameters is as follows:

[0014] (1)

[0015] In the formula: For the first The specific value of the throat diameter, in micrometers; For the first The probability of fluid passing through a throat with a diameter is dimensionless; The critical throat diameter is in micrometers. It is an empirical constant, taking values ​​from 2 to 4, and is dimensionless.

[0016] The specific calculation process for the overall fluid flow probability is as follows:

[0017] (2)

[0018] In the formula: Let be the probability of the entire fluid passing through, which is dimensionless; For the first The number of larynxes corresponding to the diameter of each type of larynx; The total number of larynxes; The total number of different types of throat diameters.

[0019] The specific calculation process for the porosity oil content index with different coordination numbers is as follows:

[0020] (3)

[0021] In the formula: The coordination number is The pore oil content index is dimensionless.

[0022] The specific calculation process for the overall oil content index is as follows:

[0023] (4)

[0024] In the formula: This refers to the overall oil content index, which is dimensionless. For having The percentage of pores with coordination number %; The maximum coordination number is 1.

[0025] The critical throat diameter was determined by high-pressure mercury intrusion and removal experiment.

[0026] The pore throat attribute parameters were obtained through image analysis of the cast thin section.

[0027] The technical effects of this invention are as follows:

[0028] (1) For the first time, the analysis results of thin section images of core castings from the mine were combined to obtain key parameters affecting the microstructure of throat-pores in oil-bearing properties. A new method was proposed to first calculate the fluid flow capacity of a single throat and then calculate the oil-bearing index of pores with different coordination numbers, so as to realize the overall oil-bearing property evaluation of different types of throat-pore combinations.

[0029] (2) Based on the degree of coordination of the microstructure of the throat-pores that affect oil-bearing properties, the oil-bearing properties of the micropores of rocks are evaluated from the perspective of fluid flow capacity. Compared with the previous method of static testing of oil saturation through well logging, this method has been further improved and can provide a direct basis for evaluating the development capacity of oil fields. Attached Figure Description

[0030] Figure 1 A diagram showing the diameter and number of throats in a rock sample for testing.

[0031] Figure 2 This diagram shows the coordination number and porosity of a rock sample.

[0032] Figure 3 Thin section image of a test rock sample casting. Detailed Implementation

[0033] A method for evaluating the oil-bearing potential of tight sandstone reservoirs based on pore-throat coordination is as follows:

[0034] Step 1: Obtain the throat-pore microstructure parameters of the target reservoir rock sample; the throat-pore microstructure parameters include pore-throat attribute parameters and pore attribute parameters; the pore-throat attribute parameters include the diameter distribution of the pore throat and the number of pore throats at the corresponding diameter; the pore attribute parameters include the number of pores with different coordination numbers.

[0035] Step 2: Obtain the critical throat diameter of the target reservoir rock sample, and calculate the fluid passage probability of different throat diameters by combining the pore microstructure parameters of the target reservoir rock sample with formula (1); then calculate the overall fluid passage probability by formula (2).

[0036] Step 3: Solve the pore oil content index with different coordination numbers using formula (3), and then calculate the overall oil content index using formula (4). The overall oil content index characterizes the oil content capacity of the overall pore region: if 0.75 < overall oil content index ≤ 1, it is defined as oil content grade I; if 0.5 < overall oil content index ≤ 0.75, it is defined as oil content grade II; if 0.25 < overall oil content index ≤ 0.50, it is defined as oil content grade III; if 0 < overall oil content index ≤ 0.25, it is defined as oil content grade IV.

[0037] Specific experimental case: A typical tight sandstone reservoir sample from western China was selected as the application object for this example. Taking a downhole sample from the main development section of a vertical well as an example, the oil-bearing capacity was evaluated using the method provided in this application. Specifically:

[0038] A method for evaluating the oil-bearing potential of tight sandstone reservoirs based on pore-throat coordination is as follows:

[0039] Step 1: Obtain the throat-pore microstructure parameters of the target reservoir rock sample; the specific process is as follows:

[0040] 1.1 Pore throat attribute parameters: The diameter distribution of the pore throats and the number of pore throats at corresponding diameters were obtained through analysis of thin-section images of the cast body, as shown in Table 1 and... Figure 1 As shown:

[0041] Table 1. Throat Attribute Parameter Table

[0042] ;

[0043] 1.2 Pore Attribute Parameters: Combining pore throat attribute parameters, the number of pores with different coordination numbers is obtained, as shown in Table 2 and... Figure 2 As shown:

[0044] Table 2 Pore Property Parameters

[0045] ;

[0046] Step 2: Obtain the critical throat diameter of the target reservoir rock sample, and calculate the fluid passage probability and overall fluid passage probability for different throat diameters in sequence, based on the pore microstructure parameters of the target reservoir rock sample; the specific process is as follows:

[0047] 2.1 The critical throat diameter was determined to be 1.5 μm by high-pressure mercury intrusion and removal experiment, which represents the throat diameter that can overcome capillary forces;

[0048] 2.2 Taking empirical constants The throat diameter is set to 2, and for throat diameters less than 2.5 μm, the throat diameter is set to 1.25 μm. The fluid passage probabilities for different throat diameters are calculated using formula (1) and are shown in Table 3. Figure 1 As shown:

[0049] Table 3. Probability of fluid passage for different throat diameters

[0050] ;

[0051] 3. According to formula (2), the overall fluid passage probability is calculated to be 0.674;

[0052] Step 3: Based on the overall fluid flow probability, solve for the porosity oil-bearing index of different coordination numbers, and then calculate the overall oil-bearing index to characterize the oil-bearing capacity of the overall pore region; the specific process is as follows:

[0053] 3.1 Based on the seepage theory and coordination number, the oil content index of pores with different coordination numbers (excluding pores with a coordination number of 0) is obtained according to formula (3). The oil content index of pores with different coordination numbers is shown in Table 4. Figure 2 As shown:

[0054] Table 4 Pore Oil Content Index

[0055] ;

[0056] 3.2 According to formula (4), the overall oil content index is calculated to be 0.380, which is defined as Class III oil content.

[0057] The traditional method for evaluating the oil-bearing potential of tight sandstone reservoirs is to calculate the oil saturation of the target reservoir; the higher the oil saturation, the better the oil-bearing potential. Given that the oil saturation of the target reservoir sample is 40.2%, and similar reservoirs have oil saturation ranging from 30% to 60%, the following formula is used to evaluate the oil-bearing potential of tight sandstone reservoirs:

[0058] BI=(h m -h mmin ) / (h mmax -h mmin ) = 0.34;

[0059] In the formula: BI is the traditional calculation index for the overall oil content of tight sandstone reservoirs, which is dimensionless; h m The oil saturation of the reservoir is %; h mmin The lowest oil saturation for similar reservoirs, %; h mmax This represents the highest oil saturation of its kind, at %. BI is 0.34, and according to the oil content classification in this application, it is also classified as a Class III reservoir.

Claims

1. A method for evaluating oiliness of a tight sandstone reservoir based on coordination degree of pore throat, characterized in that, The method is as follows: Obtain the throat-pore microstructure parameters of the target reservoir rock sample; Obtain the critical throat diameter of the target reservoir rock sample, and calculate the fluid passage probability of each throat diameter and the overall fluid passage probability in sequence based on the pore microstructure parameters of the target reservoir rock sample. The specific calculation process for the fluid passage probability of each throat diameter is as follows: （1） In the formula: For the first Throat diameter, in micrometers; For the first The probability of fluid passing through a throat with a diameter is dimensionless; The critical throat diameter is in micrometers. This is an empirical constant, taking values ​​from 2 to 4, and is dimensionless. The specific calculation process for the overall fluid flow probability is as follows: （2） In the formula: Let be the probability of the entire fluid passing through, which is dimensionless; For the first The number of larynxes corresponding to the diameter of each type of larynx; The total number of larynxes; The total number of different types of larynx diameters; The overall oil content index is calculated by solving the pore oil content index with different coordination numbers based on the overall fluid flow probability, and then the overall oil content index is used to characterize the oil content capacity of the overall pore region. The specific calculation process for the pore oil content index with different coordination numbers is as follows: （3） In the formula: is the pore oil index, dimensionless, for which the coordination number is The specific calculation process for the overall oil content index is as follows: （4） In the formula: This refers to the overall oil content index, which is dimensionless. For having The percentage of pores with coordination number %; The maximum coordination number is 1.

2. The method for evaluating the oil-bearing capacity of tight sandstone reservoirs based on pore-throat coordination degree according to claim 1, characterized in that, The specific process of characterizing the oil-bearing capacity of the overall pore region by the overall oil content index is as follows: if 0.75 < overall oil content index ≤ 1, it is defined as oil content grade I; if 0.5 < overall oil content index ≤ 0.75, it is defined as oil content grade II; if 0.25 < overall oil content index ≤ 0.50, it is defined as oil content grade III; if 0 < overall oil content index ≤ 0.25, it is defined as oil content grade IV.

3. The method for evaluating the oil-bearing capacity of tight sandstone reservoirs based on pore-throat coordination degree according to claim 1, characterized in that, The throat-pore microstructure parameters include pore-throat attribute parameters and pore attribute parameters; the pore-throat attribute parameters include the diameter distribution of the pore throats and the number of pore throats at the corresponding diameters; the pore attribute parameters include the number of pores with different coordination numbers.

4. The method for evaluating the oil-bearing capacity of tight sandstone reservoirs based on pore-throat coordination degree according to claim 1, characterized in that, The critical throat diameter was determined by high-pressure mercury intrusion and removal experiment.

5. The method for evaluating oiliness of a tight sandstone reservoir based on pore throat coordination degree according to claim 3, characterized in that, The pore throat attribute parameters were obtained through image analysis of the cast thin section.

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