An evaluation method for effective storage space of buried hill gas storage reservoirs

Abstract

The present invention belongs to the technical field of oil and gas exploration, and discloses an evaluation method for the effective storage space of buried hill gas storage reservoirs: observing and describing the development of fractures in the buried hill by using core samples to obtain main parameters; analyzing the development characteristics of fractures and dissolution pores under microscopic conditions, and clarifying the types of buried hill storage spaces and their internal genetic relationships; using core calibration logging, and combining with gas logging production data to divide the fracture system and matrix system of the single-well buried hill, and determining the logging response characteristics of the reservoir; using the calculation formula for the effective storage space, substituting the logging response characteristics and related parameters of the divided fracture system and effective matrix system, calculating the total pore volume of the reservoir and the pore volume of the ineffective reservoir, and determining the final effective storage space, which is the effective storage space for building a buried hill gas storage reservoir. In the present invention, the problem of calculating the ineffective storage space is deducted, the calculation accuracy is improved, and a basis is provided for subsequent reservoir capacity calculation and related research.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas exploration, relates to a technology for evaluating the gas storage space of an underground gas storage reservoir, and specifically relates to a method for evaluating the effective storage capacity of a buried-hill gas storage reservoir. Background Art

[0002] Underground gas storage (UGS) is a crucial link in the natural gas industry chain and has become a strategic infrastructure for ensuring a safe and stable gas supply. With the increasing proportion of natural gas in my country's energy consumption, UGS has become a key component in ensuring the safe supply of natural gas. Buried-hill oil and gas reservoirs are a popular target for exploration and development both domestically and internationally. Their large reserves and excellent sealing conditions make them attractive candidates for gas storage development.

[0003] Due to the complex and diverse lithology and lithofacies of buried-hill reservoirs, significant vertical and lateral variations, lithology identification is complex, and reservoir pore structure varies significantly. Existing methods for calculating the gas storage capacity of buried-hill gas storages fail to account for the loss of effective reservoir formation due to dissolution and filling. This leads to an overestimation of the effective gas storage capacity of buried-hill gas storages, and consequently, an overestimation of the storage capacity. Therefore, a method for evaluating the effective storage capacity of gas storages is urgently needed. Summary of the Invention

[0004] In order to better cope with the conversion of buried-hill oil and gas reservoirs into underground gas storage, it is necessary to establish an effective and applicable method for calculating the effective storage capacity of buried-hill reservoirs as soon as possible. Therefore, deducting the invalid storage space formed by weak dissolution from the final storage space is of great significance for the calculation of the storage capacity of buried-hill reservoirs and the subsequent deployment of injection and production wells.

[0005] The purpose of the present invention is to provide a method for solving the problem of accuracy in calculating the total reservoir space due to dissolution of a buried hill reservoir and a correction method for the calculation effect thereof.

[0006] To achieve the above-mentioned purpose, the present invention provides a method for predicting the effective storage space of buried-hill gas storage reservoirs based on well logging, gas logging, and lithofacies analysis theories, which mainly includes:

[0007] The purpose of the present invention can be achieved by the following steps:

[0008] Step 1: Use core observation to describe the development of buried-hill fractures and obtain key parameters such as the number of fractures, density, and aperture.

[0009] Step 2: Using cast thin sections, scanning electron microscopy, and other data, analyze the characteristics of fracture and dissolution pore development under microscopic conditions, and clarify the types of buried-hill reservoir spaces and their intrinsic genetic relationships;

[0010] Specifically, fractures serve as pathways for hydrothermal fluid migration within buried hills and play a crucial role in controlling the formation of dissolution pores. Dissolution creates secondary pores, such as intercrystalline pores and dissolution pores, which can easily form favorable reservoirs. Simultaneously, secondary minerals produced by alteration can fill reservoir spaces, forming ineffective reservoirs.

[0011] Step 3: Use core calibration logging and gas logging production data to divide the single well buried hill fracture system and matrix system to determine the reservoir logging response characteristics.

[0012] The matrix system is further divided into two categories: one is the effective matrix system and the other is the ineffective matrix system.

[0013] Based on the identification of alteration characteristics, the response characteristics of the invalid reservoir and effective reservoir of clay-induced alteration on conventional logging are further determined. The clay produced by alteration often contains a large amount of crystalline water, which fills the pores and cracks of the rock, resulting in an increase in neutron logging values, a decrease in density logging values, and a decrease in resistivity, showing good reservoir characteristics. However, the actual seepage characteristics are poor, indicating that it is a non-reservoir or a poor reservoir. Combined with the characteristics of the gas logging curve, the alteration characteristic curves are selected as the compensated neutron, deep lateral resistivity and total hydrocarbon curve shapes.

[0014] The specific parameters are as follows:

[0015] The compensation neutron is greater than 15% and the density is less than 2.8g / cm 3 , as the limit of the sensitive parameters of the logging curve of clay alteration characteristics, the sensitive parameters are used to establish the identification indicator factor between invalid reservoirs and effective reservoirs caused by alteration. When the index factor is greater than 10, it is an invalid reservoir, and when it is less than 10, it is an effective reservoir:

[0016] Φ=DEN*CNL*e

[0017] Where: CNL is compensated neutron logging, %; DEN is neutron density, g / cm 3 ; e is the difference of gas measurement curve.

[0018] Step 4: Using the effective reservoir space calculation formula shown below, the logging response characteristics and related parameters of the divided fracture system and effective matrix system are substituted to calculate the total pore volume of the reservoir and the pore volume of the ineffective reservoir, where the total pore volume is the sum of the fracture system and the matrix system.

[0019] Specific: V 有效 =A*(H 总 -H 无效 )*Φ e *S o

[0020] Where: V 有效 -Effective gas storage space, 10 6 m3 ; A - oil-bearing area, km 2 ; H 总 - total effective thickness of the reservoir, m; H ineffective reservoir thickness, m; Φe - porosity (fracture + matrix), decimal; So - oil saturation, decimal.

[0021] Step 5, determine that the final effective reservoir space is the effective reservoir space for building a gas storage in the buried hill.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] By carrying out the research on the calculation method of the reservoir space for reconstructing a gas storage in the buried hill oil and gas reservoir, the present invention deducts the problem of calculating the ineffective reservoir space, improves the calculation accuracy, and provides a basis for subsequent reservoir capacity calculation and related research. Specific embodiments

[0024] The present invention will be described in detail below through specific embodiments, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained from commercial channels.

[0025] Example 1

[0026] Taking the calculation of the effective pore volume of the buried hill reservoir in the MG block of a certain oilfield as an example:

[0027] First step, by observing the core of Well MG1-1, the macroscopic fracture characteristics are obtained, and its main parameters are as follows: the number of fracture groups is 2, the number of fractures is 16, the density is 26 fractures / m, the aperture is 0.2 - 0.5 mm, the dip angle is 30 - 90°, and the filling degree is semi-filled to unfilled.

[0028] Second step, according to the influence result of dissolution alteration on the reservoir, by using different core thin section analyses and other relevant data, it is analyzed that the main reservoir spaces in the buried hill are fractures and dissolution pores.

[0029] Among them, the dissolution pores are mainly distributed along the fractures, indicating that there is an inherent genetic connection between the two. The development degree of the fractures controls the distribution of the dissolution pores; the dissolution alteration characteristics show that the alteration plays an important controlling role in the formation of the buried hill reservoir. The alteration zone is mainly along the fracture strike and within the range of 10 - 50 m below the fracture zone.

[0030] In addition, the dissolution effect is mainly manifested as follows: the dissolution effect will produce secondary pores such as intergranular pores and dissolution pores, which are prone to form favorable reservoirs; conversely, the secondary minerals generated by the alteration will fill the reservoir pores and fractures, reducing the effectiveness of the reservoir pores. The dissolution pores are filled with a large amount of secondary minerals in the reservoir space, forming an ineffective reservoir.

[0031] The third step is to use core calibration logging and combine gas logging production data to divide the single well buried hill fracture system and matrix system and determine the reservoir logging response characteristics.

[0032] Matrix systems are further divided into two categories: effective and ineffective. The 4567.8-4579.3 m interval in Well MG1-1 shows increased neutron logging values, decreased density logging values, and decreased resistivity, exhibiting reservoir characteristics. However, after fracturing, the well produced 0.06 cubic meters of water per day, and the well test concluded it was dry with poor seepage characteristics, indicating a non-reservoir or poor reservoir.

[0033] Select characteristic sensitive logging curve to compensate neutrons and neutron density. Through research and analysis, the neutron density greater than 15% and the density less than 2.8g / cm 3 , the parameters are used to establish the identification indicator factor between invalid reservoirs and effective reservoirs caused by alteration. If the factor is greater than 17, it is an invalid reservoir.

[0034] In the fourth step, the total pore volume of the reservoir and the pore volume of the ineffective reservoir were calculated using the logging response characteristics of the divided effective reservoir and ineffective reservoir, which were 1550.7×10 6 m 3 and 254.8×10 6 m 3 The invalid storage space accounts for 16.43%. After deducting the invalid reservoir, the final gas storage space is 1295.9×10 6 m 3 .

[0035] Step 5: The final effective storage space of the MG block is 1295.9×10 6 m 3 .

[0036] The above-described embodiments are only preferred embodiments of the present invention, and are not intended to be all feasible embodiments of the present invention. Any obvious modifications made by a person skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A method for evaluating the effective storage capacity of a buried hill gas storage reservoir, characterized in that, It includes the following steps: Step 1: Observe and describe the development of buried hill fractures using cores to obtain main parameters; Step 2: Analyze the development characteristics of fractures and dissolution pores under microscopic conditions, and clarify the types of buried hill reservoir spaces and their internal genetic relationships; Step 3: Using core calibration logging, combined with gas logging production data, divide the single-well buried hill fracture system and matrix system, and determine the logging response characteristics of the reservoir; the matrix system is divided into two categories, one is the effective matrix system and the other is the ineffective matrix system; the specific parameters of the logging response characteristics of the reservoir are as follows: the compensated neutron is greater than 15%, and the density is less than 2.8 g / cm 3 , as the boundary of the sensitive parameter of the logging curve for the clay alteration feature, use the sensitive parameter to establish the identification indicator factor of the ineffective reservoir and the effective reservoir caused by alteration. When the exponential factor is greater than 10, it is an ineffective reservoir, and when it is less than 10, it is an effective reservoir: Φ = DEN * CNL * e, where: CNL is the compensated neutron logging, %; DEN is the neutron density, g / cm 3 ; e is the difference value of the gas logging curve; Step 4: Using the effective reservoir space calculation formula, input the logging response characteristics and related parameters of the divided fracture system and effective matrix system to calculate the total pore volume of the reservoir and the pore volume of the ineffective reservoir, where the total pore volume is the sum of the fracture system and the matrix system; the effective reservoir space calculation formula is: V 有效 =A * (H 总 -H 无效 ) * Φ e * S o , where: V 有效 - effective gas storage space, 10 6 m 3 ; A - oil-bearing area, km 2 ; H 总 -Total effective reservoir thickness, m; H ineffective reservoir thickness, m; Φe-porosity (fractures + matrix), decimal; So-oil saturation, decimal; Step 5: Determine that the final effective reservoir space is the effective reservoir space for building a buried hill reservoir.

2. The evaluation method for the effective storage capacity of buried hill gas storage reservoirs according to claim 1, wherein, The main parameters in Step 1 include the number of fractures, density, and aperture.

3. The evaluation method for the effective storage capacity of buried hill gas storage reservoirs according to claim 1, characterized in that The analysis method in Step 2 is to use casting thin sections, scanning electron microscopes and other data.

4. The evaluation method for the effective storage capacity of the buried hill gas storage reservoir according to claim 1, wherein In Step 2, the fractures are the internal hydrothermal migration channels of the buried hill, controlling the formation of dissolution pores.

5. The evaluation method for the effective storage capacity of buried hill gas storage reservoirs according to claim 1, characterized in that, In Step 2, the alteration is within the range of 10 - 50 m below the fracture zone.