Recognition and prediction method for water invasion zone of loose sandstone gas reservoir

Abstract

The invention discloses an identification and prediction method for a loose sandstone gas reservoir water invasion zone, and the method specifically comprises the following steps: 1, building a reservoir geologic model, and positioning a water invasion dominant zone; 2, analyzing a well water source, and diagnosing a water invasion layer by combining a water invasion dominant zone; and step 3, establishing a seepage model on the basis of the diagnosed water invasion horizon, then rechecking the water invasion zone, and predicting the expansion dynamic state of the water invasion zone. The method aims to accurately identify the water invasion zone in the gas reservoir, so that the success rate and the yield of gas reservoir development are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of natural gas development, and in particular relates to a method for identifying and predicting a water invasion zone in a loose sandstone gas reservoir. Background Art

[0002] Unconsolidated sandstone gas reservoirs are an important unconventional natural gas resource and an important component of my country's oil and gas resources. The exploitation of water-invaded unconsolidated sandstone gas reservoirs will be accompanied by the infiltration and accumulation of edge water along the water invasion zone into the gas reservoir, resulting in a decrease in gas reservoir pressure and a decrease in gas permeability, which in turn significantly affects gas recovery and production. The water invasion problem has always been a difficulty that restricts the effective development of this type of gas reservoir. The location and range of the water invasion zone have a great impact on the reasonable layout and recovery rate of gas reservoir development. Therefore, the positioning, identification, and prediction of the water invasion zone of unconsolidated sandstone gas reservoirs are important technical problems in exploration and development.

[0003] The modern petroleum industry has developed a variety of technologies to identify water invasion zones in water-invaded loose sandstone gas reservoirs. Among them, the most commonly used technologies include physical exploration, geological exploration and numerical simulation.

[0004] (1) Physical exploration methods. Physical exploration methods include seismic exploration and well logging technology. Seismic exploration determines underground structures and mineral deposit types by the speed and amplitude of seismic waves propagating in underground rock formations. In water-invaded loose sandstone gas reservoirs, seismic exploration technology can determine the existence and location of the water-invaded zone by analyzing the reflection and refraction of seismic waves in the water-invaded zone; well logging technology determines the physical properties of the rocks around the well wall and the underground structures and mineral deposit types by analyzing the stratigraphic information in the wellbore. In water-invaded loose sandstone gas reservoirs, well logging technology can determine the existence and location of the water-invaded zone by measuring parameters such as resistivity, natural gamma radiation, neutrons, and density.

[0005] (2) Geological exploration methods: Geological exploration methods include core analysis, geological profiles and geological models. Core analysis determines the physical properties and mineral types of underground rock formations by conducting physical, chemical and microstructural tests on core samples. In water-invaded loose sandstone gas reservoirs, core analysis technology can determine the existence and location of water invasion zones by analyzing information such as mineral composition, pore structure and rock mechanical properties; geological profile technology identifies the location and range of water invasion zones by drawing geological profiles perpendicular to the surface. Geological model technology collects geological data and uses computer simulation methods to establish a three-dimensional geological model to predict the location and range of water invasion zones.

[0006] (3) Numerical simulation method. The numerical simulation method simulates the migration process of underground gas and water through mathematical models to predict the location and range of the water invasion zone. The numerical simulation method needs to accurately describe the physical properties of the underground medium and the laws of fluid migration, so it requires a large amount of physical experiments and geological exploration data as input. At the same time, the numerical simulation method also requires high-performance computers for calculation, so it has the characteristics of high computational complexity and high computational cost.

[0007] Although the above methods can identify water invasion zones to a certain extent, they still have some limitations. For example, core analysis can only obtain local information, not global information; logging analysis has errors in the interpretation of rock properties, and the inversion results of numerical simulation methods are greatly affected by geological models. Therefore, in order to improve the accuracy and precision of water invasion zone identification, it is necessary to combine multiple technical means for research. Summary of the invention

[0008] The purpose of the present invention is to provide a method for identifying and predicting water invasion zones in loose sandstone gas reservoirs, aiming to accurately identify water invasion zones in gas reservoirs, thereby improving the success rate and output of the development of such gas reservoirs.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is: a method for identifying and predicting water invasion zones in loose sandstone gas reservoirs, which is specifically implemented according to the following steps:

[0010] Step 1: Establish a reservoir geological model and locate the water invasion dominant zone;

[0011] Step 2: Analyze the water source of the well and diagnose the water invasion layer in combination with the water invasion advantage zone;

[0012] Step 3: Establish a seepage model based on the diagnosed water invasion layer, then review the water invasion zone and predict the expansion dynamics of the water invasion zone.

[0013] As a preferred technical solution of the present invention, in step 1, establishing a reservoir geological model is specifically implemented according to the following steps:

[0014] Step 1.1: Analyze the seismic interpretation results to obtain the overall geological structure and rock physical property information to determine whether there are faults;

[0015] Step 1.2: If the fault is determined to exist in step 1.1, the logging interpretation results are analyzed and combined with the wellbore trajectory to obtain the spatial distribution of rock physical properties and stratigraphic structural characteristics;

[0016] Step 1.3, according to the spatial distribution of rock physical properties and stratigraphic structural characteristics obtained in step 1.2, a three-dimensional quantitative geological model is established based on the small layer and plane grid scheme using a plane scattered point interpolation algorithm.

[0017] As a preferred technical solution of the present invention, in step 1, locating the water intrusion advantage zone is specifically as follows:

[0018] Step 1.4, draw the water phase permeability distribution field, that is, the background map of the water invasion dominant zone. The water invasion dominant zone is located in the water phase high permeability area.

[0019] As a preferred technical solution of the present invention, in step 2, the water source of the well is analyzed, and the water invasion layer is diagnosed in combination with the water invasion dominant zone, which is specifically implemented according to the following steps:

[0020] Step 2.1, based on the water invasion process and morphology, determine the water source type of the gas well water;

[0021] Step 2.2, identify the main water source of the gas well;

[0022] Step 2.3, for the edge water invasion wells, determine the water invasion layer in combination with the range of the near-well water invasion advantage zone;

[0023] Step 2.4, for the water-producing layer of the water-invasion well, calculate the average value KWA of the water phase permeability within the water-invasion dominant zone;

[0024] Step 2.5, based on the water discharge time, well location, and layer position, outline the overall water invasion morphology of the small layer.

[0025] As a preferred technical solution of the present invention, in step 3, a seepage model is established based on the diagnosed water invasion layer, and then the water invasion zone is reviewed to predict the expansion dynamics of the water invasion zone, which is specifically implemented in the following steps:

[0026] Step 3.1, based on the water invasion layer determined in step 2.3, the fluid model, well model and production history data are incorporated to establish a seepage model;

[0027] Step 3.2, adjusting the seepage model according to the special seepage mechanism of water-invaded loose sandstone gas reservoirs;

[0028] Step 3.3, using the seepage model adjusted in step 3.2 to focus on the edge water intrusion wells to perform water output history fitting;

[0029] Step 3.4, based on the fitting results, analyze the historical process and current distribution of the water invasion zone in the area without water invasion well control;

[0030] Step 3.5, predict the future expansion process of the water invasion zone based on the results obtained in step 3.4, and analyze the remaining gas enrichment area to provide a geological basis for potential tapping;

[0031] Step 3.6, with the goal of stabilizing air and controlling water, formulate adjustment and potential-exploring measures, and optimize the plan through comparison of production indicators.

[0032] The beneficial effects of the present invention are as follows: the method for identifying and predicting the water invasion zone of the loose sandstone gas reservoir of the present invention first identifies the water invasion dominant zone based on static data, focuses on the distribution range of the water invasion zone, and improves the identification accuracy and work efficiency of the water invasion zone; secondly, it makes full use of the technical advantages of the numerical simulation method, focuses on the overall water invasion gas reservoir, and makes up for the one-sidedness of diagnosing the water invasion zone based on limited well points, so that the method can not only simulate the water invasion process in the water invasion dominant zone, but also simulate the water invasion process in the non-water invasion dominant zone; and the historical fitting process of the numerical simulation plays a role in testing the distribution of the water invasion dominant zone established based on geological knowledge and the water source obtained by the gas reservoir engineering analysis. The combination of geology, engineering and numerical modeling, and the mutual verification of theoretical calculations and mine monitoring provide a reliable basis for the identification and prediction of the water invasion zone of the water-invaded loose sandstone gas reservoir. The present invention has been strictly verified in the mine implementation, and the results are accurate and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a working principle diagram of the method for identifying and predicting the water invasion zone of the loose sandstone gas reservoir of the present invention. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with the accompanying drawings, tables and specific embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0035] The present invention is further described below by way of examples, but is not limited to the following embodiments.

[0036] Example 1

[0037] like Figure 1 As shown, the method for identifying and predicting the water invasion zone of the loose sandstone gas reservoir of the present invention is specifically implemented according to the following steps:

[0038] Step 1: Establish a reservoir geological model and locate the water invasion dominant zone;

[0039] Step 2: Analyze the water source of the well and diagnose the water invasion layer in combination with the water invasion advantage zone;

[0040] Step 3: Establish a seepage model based on the diagnosed water invasion layer, then review the water invasion zone and predict the expansion dynamics of the water invasion zone.

[0041] The method for identifying and predicting the water invasion zone of the loose sandstone gas reservoir of the present invention aims to accurately identify the water invasion zone in the gas reservoir, thereby improving the success rate and production of the development of such gas reservoirs. Through the identification of the water invasion zone, the current gas-bearing range and effective reservoir can be more accurately determined, thereby avoiding the invalid layers of the well pattern adjustment and the stable and increased production measures in the middle and late stages of development, and providing a more accurate basis for the development and production of such gas reservoirs.

[0042] After practical application verification in multiple loose sandstone gas reservoirs, this method has high accuracy and reliability in identifying the location and range of water invasion zones, and effectively solves the water invasion problem in loose sandstone gas reservoirs. This method is not only suitable for the identification of water invasion zones in single wells, but also for the comprehensive analysis of water invasion zones in the entire gas reservoir. At the same time, this method has the advantages of simple data source, low cost, and easy operation.

[0043] The scope of application of the method for identifying and predicting the water invasion zone of the loose sandstone gas reservoir of the present invention mainly involves the water invasion problem and reservoir evaluation of the loose sandstone gas reservoir, which can provide a scientific basis and technical support for the exploration and development of this type of gas reservoir. Specifically including: 1) Water invasion problem in the exploration and development of loose sandstone gas reservoirs: It can help professionals determine the distribution of water invasion zones, boundary positions, water invasion degree and other information of gas reservoirs, and provide scientific basis and technical support for oil and gas development. At the same time, the method can also be used to predict the possible water invasion risks in gas reservoirs and take corresponding preventive measures in advance. 2) Reservoir evaluation: Through a comprehensive analysis of the petrological characteristics, pore structure and physical properties of loose sandstone reservoirs, the location and degree of water invasion of water invasion zones in loose sandstone reservoirs can be determined, providing a scientific basis and technical support for reservoir evaluation. 3) Water invasion gas reservoirs: This method is mainly aimed at loose sandstone gas reservoirs, and can also be used for water invasion problems of tight gas reservoirs, shale gas reservoirs, etc.

[0044] Through the identification and prediction method of the water invasion zone of the loose sandstone gas reservoir of the present invention, the accurate identification and prediction of the water invasion zone in the gas reservoir can be achieved, the development of invalid layers and waste of resources can be avoided, and the success rate and efficiency of the exploration and development of such gas reservoirs can be improved. At the same time, as more and more oil and gas reservoirs will face the problem of water invasion, this method will receive more extensive attention and promotion. Specifically including: 1) Providing scientific basis and technical support for oil and gas exploration and development: This method can accurately identify the water invasion zone, determine the boundary and effective reservoir of the gas reservoir, avoid the development of invalid layers, and improve the efficiency and success rate of exploration and development. 2) Providing scientific basis and technical support for oil and gas reservoir evaluation: Through the study and analysis of the petrological characteristics of the reservoir, the oil and gas performance and development prospects of the reservoir can be more accurately judged, providing an important reference for the evaluation of oil and gas reservoirs. 3) Providing technical support for the optimization of oil and gas engineering: Through the study and analysis of the water invasion problem in the process of gas reservoir development, corresponding development plans and technical measures can be formulated to improve the efficiency and economic benefits of gas reservoir development.

[0045] Example 2

[0046] like Figure 1 As shown, different from Example 1, in the method for identifying and predicting the water invasion zone of the loose sandstone gas reservoir of the present invention, in step 1: analyzing the water source of the water well, and diagnosing the water invasion layer in combination with the water invasion dominant zone, specifically according to:

[0047] Step 1.1: Analyze the seismic interpretation results to obtain the overall geological structure and rock physical property information to determine whether there are faults;

[0048] Step 1.2: If the fault is determined to exist in step 1.1, the logging interpretation results are analyzed and combined with the wellbore trajectory to obtain the spatial distribution of rock physical properties and stratigraphic structural characteristics;

[0049] Step 1.3, according to the spatial distribution of rock physical properties and stratigraphic structural characteristics obtained in step 1.2, a three-dimensional quantitative geological model is established based on a small layer and plane grid scheme using a plane scattered point interpolation algorithm;

[0050] Step 1.4, draw the water phase permeability distribution field (i.e., the water invasion dominant zone background map), and the water invasion dominant zone is located in the water phase high permeability area.

[0051] Example 3

[0052] like Figure 1 As shown, different from Example 1, in the method for identifying and predicting the water invasion zone of the loose sandstone gas reservoir of the present invention, in step 2: analyzing the water source of the well, and diagnosing the water invasion layer in combination with the water invasion dominant zone, the specific implementation is as follows:

[0053] Step 2.1, based on the water invasion process and morphology, determine the water source type of the gas well water;

[0054] The water source types and corresponding production characteristics of gas well water include the following types:

[0055] 1) Intralayer water: water is produced as soon as it is put into production, and the water volume fluctuates at low values, resulting in moderate production reduction;

[0056] 2) Water intrusion at the edge of the non-dominant zone: The water comes out the latest, and the water volume increases sharply after the water comes out, which can easily lead to flooding;

[0057] 3) Overall water advancement along the dominant position: water discharge is late, and the water volume gradually increases after discharge, which significantly reduces production;

[0058] 4) Edge water advance along the narrow interval of the dominant zone: water discharge is early, water volume fluctuates to high values, and production is greatly reduced;

[0059] 5) Edge water intrusion along the dominant channel: water is discharged earliest, the water volume fluctuates to the median or disappears, and only a small reduction in production occurs.

[0060] Step 2.2, identify the main water source of the gas well;

[0061] Follow the process below to identify the primary water source for a gas well;

[0062] 1) Causes of changes in gas production trends:

[0063] ①Stable: no effusion;

[0064] ② Fluctuation decrease: wellbore fluid accumulation or insufficient formation supply;

[0065] ③ Slow decline: Water production in the formation near the wellbore reduces production capacity, which may be caused by water accumulation in the formation or water intrusion from the edge;

[0066] ④ Rapid decline, and the production is restored after a large amount of water discharge: the water in the layer is discharged;

[0067] 2) Causes of water output trend changes:

[0068] ① Water is produced as soon as it is put into production - water in the near-wellbore layer;

[0069] ② After the water volume is put into operation, according to the change law, the water intrusion form is analyzed according to the following model:

[0070] A: Water volume increases gradually and then decreases: a. If the water volume and gas volume change trends are consistent, it is judged to be water in the layer; b. If the gas volume is stable, it is judged that the water body in the layer has broken through and gradually dried up; c. If there is a water invasion zone, it is judged that water from the edge of the zone has entered, and then the water sensitive is blocked; d. If there is a water invasion zone and the adjacent well is put into production, the water volume decreases to dispersed water in the adjacent well.

[0071] B: The water volume increases rapidly until the gas well stops lying: a. The edge water advances in multiple directions in the dominant zone at the same time until the gas well is flooded; b. The gas well production section is close to the edge water, and large-scale water invasion occurs until the gas well production section is flooded;

[0072] C: The water volume gradually increases and then remains stable: a. The water in the layer far from the well converges and then forms a continuous supply to the production section of the well; b. The edge water advances along the dominant zone, but the water invasion energy is offset by the resistance along the way, and the water invasion volume remains stable.

[0073] Step 2.3, for the edge water invasion wells, determine the water invasion layer in combination with the range of the near-well water invasion advantage zone;

[0074] Step 2.4, for the water-producing layer of the water-invasion well, calculate the average value KWA of the water phase permeability within the water-invasion dominant zone;

[0075] Step 2.5, based on the water discharge time, well location, and layer position, outline the overall water invasion morphology of the small layer.

[0076] Example 4

[0077] like Figure 1As shown, different from Example 1, in the method for identifying and predicting the water invasion zone of the loose sandstone gas reservoir of the present invention, in step 3: a seepage model is established based on the diagnosed water invasion layer, and then the water invasion zone is reviewed to predict the expansion dynamics of the water invasion zone, which is specifically implemented according to the following steps: step 3.1, based on the water invasion layer determined in step 2.3, the fluid model, well model and production history data are incorporated to establish a seepage model;

[0078] Step 3.2, in view of the special seepage mechanism of water-invaded loose sandstone gas reservoirs, the seepage model is adjusted as follows: 1) Determine the range of the dominant zone where water intrusion may occur in the seepage model: the area higher than the KWA in the second step (4); 2) After the edge water invades, it will dissolve the mud in the water intrusion zone, thereby increasing the permeability. Referring to the relevant core experimental data and the research results of digital core micro-pore network flow simulation, the permeability increase ratio at the digital model grid scale is usually 5 to 10, and the stratum plane directional conductivity within the dominant zone where water intrusion may occur determined by 1) is modified; 3) According to the regional formation water potential energy data, the directional edge water of the seepage model is set by using the analytical water body method;

[0079] Step 3.3, using the seepage model adjusted in step 3.2 to focus on the water history fitting of the edge water invasion wells, the main adjusted parameters include: 1) gas-water relative permeability curve: taking the global water fitting as the adjustment target; 2) the multiple ratio of the plane conductivity in the water invasion dominant zone; 3) analyzing the water invasion intensity of the edge water body;

[0080] Step 3.4, based on the fitting results, analyze the historical process and current distribution of the water invasion zone in the area without water invasion well control;

[0081] Step 3.5, predict the future expansion process of the water invasion zone based on the results obtained in step 3.4, and analyze the remaining gas enrichment area to provide a geological basis for potential tapping;

[0082] Step 3.6, with the goal of stabilizing air and controlling water, formulate adjustment and potential-exploring measures, and optimize the plan through comparison of production indicators.

[0083] Therefore, compared with the prior art, the method for identifying and predicting the water invasion zone of the loose sandstone gas reservoir of the present invention first identifies the water invasion dominant zone based on static data, focuses on the distribution range of the water invasion zone, and improves the identification accuracy and work efficiency of the water invasion zone; secondly, it makes full use of the technical advantages of the numerical simulation method, focuses on the overall water invasion gas reservoir, and makes up for the one-sidedness of diagnosing the water invasion zone based on limited well points, so that the method can not only simulate the water invasion process in the water invasion dominant zone, but also simulate the water invasion process in the non-water invasion dominant zone; and the historical fitting process of the numerical simulation plays a role in testing the distribution of the water invasion dominant zone established based on geological knowledge and the water source obtained by the gas reservoir engineering analysis. The combination of geology, engineering and numerical modeling, and the mutual verification of theoretical calculations and mine monitoring provide a reliable basis for the identification and prediction of the water invasion zone of the water-invaded loose sandstone gas reservoir. The present invention has been strictly verified in the mine implementation, and the results are accurate and reliable.

[0084] The above description shows and describes several preferred embodiments of the invention, but as mentioned above, it should be understood that the invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the invention concept described herein through the above teachings or the technology or knowledge of the relevant field. Changes and modifications made by those skilled in the art should be within the scope of protection of the claims attached to the invention without departing from the spirit and scope of the invention.

Claims

1. A method for identifying and predicting water invasion zones in loose sandstone gas reservoirs, characterized in that: Follow the steps below to implement it: Step 1: Establish a reservoir geological model and locate the water invasion dominant zone; Step 2: Analyze the water source of the well and diagnose the water invasion layer in combination with the water invasion advantage zone; Step 3: Establish a seepage model based on the diagnosed water invasion layer, then review the water invasion zone and predict the expansion dynamics of the water invasion zone.

2. The method for identifying and predicting water invasion zones in loose sandstone gas reservoirs according to claim 1, characterized in that: In step 1, the reservoir geological model is established by specifically following the steps below: Step 1.1: Analyze the seismic interpretation results to obtain the overall geological structure and rock physical property information to determine whether there are faults; Step 1.2: If the fault is determined to exist in step 1.1, the logging interpretation results are analyzed and combined with the wellbore trajectory to obtain the spatial distribution of rock physical properties and stratigraphic structural characteristics; Step 1.3, according to the spatial distribution of rock physical properties and stratigraphic structural characteristics obtained in step 1.2, a three-dimensional quantitative geological model is established based on the small layer and plane grid scheme using a plane scattered point interpolation algorithm.

3. The method for identifying and predicting water invasion zones in loose sandstone gas reservoirs according to claim 2, characterized in that: In step 1, locating the water intrusion advantage zone is specifically as follows: Step 1.4, draw the water phase permeability distribution field, that is, the background map of the water invasion dominant zone. The water invasion dominant zone is located in the water phase high permeability area.

4. The method for identifying and predicting water invasion zones in loose sandstone gas reservoirs according to claim 3 is characterized in that: In step 2, the water source of the well is analyzed, and the water invasion layer is diagnosed in combination with the water invasion advantage zone, which is specifically implemented according to the following steps: Step 2.1, based on the water invasion process and morphology, determine the water source type of the gas well water; Step 2.2, identify the main water source of the gas well; Step 2.3, for the edge water invasion wells, determine the water invasion layer in combination with the range of the near-well water invasion advantage zone; Step 2.4, for the water-producing layer of the water-invasion well, calculate the average value KWA of the water phase permeability within the water-invasion dominant zone; Step 2.5, based on the water discharge time, well location, and layer position, outline the overall water invasion morphology of the small layer.

5. The method for identifying and predicting water invasion zones in loose sandstone gas reservoirs according to claim 4, characterized in that: In step 3, a seepage model is established based on the diagnosed water invasion layer, and then the water invasion zone is reviewed to predict the expansion dynamics of the water invasion zone, which is specifically implemented in the following steps: Step 3.1, based on the water invasion layer determined in step 2.3, the fluid model, well model and production history data are incorporated to establish a seepage model; Step 3.2, adjusting the seepage model according to the special seepage mechanism of water-invaded loose sandstone gas reservoirs; Step 3.3, using the seepage model adjusted in step 3.2 to focus on the edge water intrusion wells to perform water output history fitting; Step 3.4, based on the fitting results, analyze the historical process and current distribution of the water invasion zone in the area without water invasion well control; Step 3.5, predict the future expansion process of the water invasion zone based on the results obtained in step 3.4, and analyze the remaining gas enrichment area to provide a geological basis for potential tapping; Step 3.6, with the goal of stabilizing air and controlling water, formulate adjustment and potential-exploring measures, and optimize the plan through comparison of production indicators.

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