Method for identifying and predicting water invasion zone of loose sandstone gas reservoir

Abstract

The application discloses a method for identifying and predicting water invasion zones in loose sandstone gas reservoirs, and is implemented according to the following steps: step 1, establishing a reservoir geological model and positioning water invasion dominant zones; step 2, analyzing water sources of water wells and diagnosing water invasion horizons in combination with the water invasion dominant zones; and step 3, establishing a percolation model based on the diagnosed water invasion horizons, then rechecking the water invasion zones and predicting water invasion zone expansion dynamics. The application aims to accurately identify water invasion zones in gas reservoirs, thereby improving the success rate and yield of development of the gas reservoirs.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of natural gas development, and particularly relates to a method for identifying and predicting water invasion zones of loose sandstone gas reservoirs. BACKGROUND

[0002] Loose sandstone gas reservoir is an important unconventional natural gas resource and an important part of oil and gas resources in China. The exploitation of water-invasion loose sandstone gas reservoir will be accompanied by the infiltration and accumulation of edge water along the water invasion zone into the gas reservoir, resulting in the decrease of gas reservoir pressure and the decrease of gas permeability, and further significantly affecting the recovery and production of gas. The water invasion problem has always been a difficulty in the effective development of this type of gas reservoir. The location and range of the water invasion zone have a great influence on the reasonable layout and recovery of the gas reservoir, therefore, the positioning, identification and prediction of the water invasion zone of the loose sandstone gas reservoir are important technical problems in exploration and development.

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

[0004] (1) Physical exploration method. Physical exploration method includes seismic exploration and well logging technology. Seismic exploration determines the underground structure and mineral type by analyzing the speed and amplitude of seismic wave propagation in underground rock layers. In water-invasion loose sandstone gas reservoir, seismic exploration technology can determine the existence and location of water invasion zone by analyzing the reflection and refraction of seismic wave in water invasion zone; well logging technology determines the physical properties of the rock around the well wall by analyzing the formation information in the well hole, and determines the underground structure and mineral type. In water-invasion loose sandstone gas reservoir, well logging technology can determine the existence and location of water invasion zone by measuring parameters such as resistivity, natural gamma radiation, neutron, density, etc.

[0005] (2) Geological exploration method: Geological exploration method includes core analysis, geological profile and geological model technology. Core analysis determines the physical properties and mineral types of underground rock layers by testing the physical, chemical and microstructure of core samples. In water-invasion loose sandstone gas reservoir, core analysis technology can determine the existence and location of water invasion zone by analyzing information such as mineral composition, pore structure and rock mechanical properties; geological profile technology identifies the location and range of water invasion zone by drawing geological profile map perpendicular to the surface. Geological model technology predicts the location and range of water invasion zone by collecting geological data and using computer simulation method to establish three-dimensional geological model.

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

[0007] Although the above methods can identify water invasion zone to some extent, there are still some limitations. For example, core analysis can only obtain local information and cannot obtain global information; the interpretation of rock physical properties in well logging analysis has errors, and the inversion result of numerical simulation method is greatly affected by the geological model. 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

[0008] The purpose of the present application is to provide a method for identifying and predicting water invasion zone in unconsolidated sandstone gas reservoir, aiming to accurately identify water invasion zone in gas reservoir, thereby improving the success rate and yield of development of such gas reservoir.

[0009] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: a method for identifying and predicting water invasion zone in unconsolidated sandstone gas reservoir, which is implemented according to the following steps:

[0010] Step 1, establish a reservoir geological model to locate the water invasion dominant zone;

[0011] Step 2, analyze the water source of water wells and diagnose the water invasion horizon in combination with the water invasion dominant zone;

[0012] Step 3, establish a seepage model based on the diagnosed water invasion horizon, and then review the water invasion zone and predict the water invasion zone expansion dynamics.

[0013] As a preferred technical scheme of the present application, in the step 1, the establishment of the reservoir geological model is implemented according to the following steps:

[0014] Step 1.1, analyze the seismic interpretation results to obtain the overall geological structure and rock property information, and determine whether there is a fault;

[0015] Step 1.2, if it is determined in step 1.1 that there is a fault, analyze the well logging interpretation results and obtain the spatial distribution of rock properties and stratigraphic structure characteristics in combination with the well trajectory;

[0016] Step 1.3, based on the spatial distribution of rock properties and stratigraphic structure characteristics obtained in step 1.2, a three-dimensional quantitative geological model is established based on the small layer and plane grid scheme, and a plane scatter interpolation algorithm is used.

[0017] As a preferred technical scheme of the present application, in the step 1, the positioning of the water invasion advantage zone specifically comprises:

[0018] Step 1.4, a water phase permeability distribution field is drawn, that is, a water invasion advantage zone background map, and the water invasion advantage zone is located in a high water phase permeability zone.

[0019] As a preferred technical scheme of the present application, in the step 2, the water source of the water well is analyzed, the water invasion zone is diagnosed in combination with the water invasion advantage zone, and the following steps are specifically implemented:

[0020] Step 2.1, based on the water invasion process and form, the water source type of the watered gas well is judged;

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

[0022] Step 2.3, for the edge water invasion well, the water invasion zone is implemented in combination with the range of the near well water invasion advantage zone;

[0023] Step 2.4, for the watered layer of the water invasion well, the average value KWA of the water phase permeability in the range of the water invasion advantage zone is counted;

[0024] Step 2.5, the overall water invasion form of the small layer is sketched in combination with the watered time, well position and layer position.

[0025] As a preferred technical scheme of the present application, in the step 3, the seepage flow model is established based on the diagnosed water invasion zone, and then the water invasion zone is reviewed, the water invasion zone expansion dynamic is predicted, and the following steps are specifically implemented:

[0026] Step 3.1, based on the water invasion zone implemented in step 2.3, the seepage flow model is established by integrating the fluid model, the well model and the production history data;

[0027] Step 3.2, the seepage flow model is adjusted in view of the special seepage flow mechanism of the water invasion loose sandstone gas reservoir;

[0028] Step 3.3, the watered history fitting is performed for the edge water invasion well by using the seepage flow model adjusted in step 3.2;

[0029] Step 3.4, the water invasion zone expansion history process and the current distribution situation in the region not controlled by the water invasion well are analyzed according to the fitting result;

[0030] Step 3.5, the future expansion process of the water invasion zone is predicted according to the result obtained in step 3.4, and the remaining gas enrichment area is analyzed to provide a geological basis for tapping;

[0031] Step 3.6, adjustment and tapping measures are formulated to stabilize gas and control water, and the optimization scheme is compared through the production index.

[0032] The beneficial effects of this invention are as follows: The method for identifying and predicting water-transgressed zones in loose sandstone gas reservoirs firstly identifies the dominant water-transgression zone based on static data, focusing on the distribution range of the water-transgression zone and improving the accuracy and efficiency of identification. Secondly, it fully utilizes the technical advantages of numerical simulation methods, focusing on the overall water-transgressed gas reservoir, thus overcoming the limitations of diagnosing water-transgression zones based on limited well points. This allows the method to simulate water transgression processes not only within the dominant water-transgression zone but also within non-dominant zones. Furthermore, the historical fitting process of the numerical simulation serves to verify the distribution of the dominant water-transgression zone established based on geological understanding and the water source obtained from gas reservoir engineering analysis. The combination of geology, engineering, and numerical simulation, along with the mutual verification between theoretical calculations and field monitoring, provides a reliable basis for the identification and prediction of water-transgressed zones in water-transgressed loose sandstone gas reservoirs. This invention has undergone rigorous field implementation verification, and the results are accurate and reliable. Attached Figure Description

[0033] Figure 1 This is a schematic diagram illustrating the working principle of the method for identifying and predicting water intrusion zones in loose sandstone gas reservoirs according to the present invention. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

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

[0036] Example 1

[0037] like Figure 1 As shown, the method for identifying and predicting water intrusion zones in loose sandstone gas reservoirs of the present invention is implemented according to the following steps:

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

[0039] Step 2: Analyze the water source of the well and diagnose the water-invaded strata by combining the dominant water-invaded zone;

[0040] Step 3: Based on the diagnosed water-entrapment layers, establish a seepage model, then verify the water-entrapment zone and predict its expansion dynamics.

[0041] The method for identifying and predicting water-intrusion zones in loose sandstone gas reservoirs of this invention aims to accurately identify water-intrusion zones in gas reservoirs, thereby improving the success rate and production of such gas reservoirs. By identifying water-intrusion zones, the current gas-bearing range and effective reservoir layers can be determined more accurately, thus avoiding ineffective layers in well pattern adjustments and production stabilization and enhancement measures during the later stages of development, and providing a more accurate basis for the development and production of such gas reservoirs.

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

[0043] The application scope of the method for identifying and predicting water invasion zones in loose sandstone gas reservoirs mainly involves water invasion problems and reservoir evaluation of loose sandstone gas reservoirs, which can provide scientific basis and technical support for the exploration and development of such gas reservoirs. Specifically, it includes: 1) Water invasion problem in exploration and development of loose sandstone gas reservoirs: It can help professionals determine the distribution of water invasion zones, boundary position, 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 water invasion risk in the gas reservoir, and take corresponding preventive measures in advance. 2) Reservoir evaluation: Through comprehensive analysis of the petrological characteristics, pore structure and physical property characteristics of loose sandstone reservoirs, the position and water invasion degree of water invasion zones in loose sandstone reservoirs can be determined, which can provide scientific basis and technical support for reservoir evaluation. 3) Water invasion gas reservoir: The method is mainly aimed at loose sandstone gas reservoirs, and can also be used for water invasion problems in tight gas reservoirs, shale gas reservoirs and other reservoirs.

[0044] Through the method for identifying and predicting water invasion zones in loose sandstone gas reservoirs, the water invasion zones in the gas reservoir can be accurately identified and predicted, avoiding the development of invalid layers and resource waste, and improving the success rate and efficiency of the exploration and development of such gas reservoirs. At the same time, as more and more oil and gas reservoirs will face water invasion problems, this method will get more and more attention and promotion. Specifically, it includes: 1) Providing scientific basis and technical support for oil and gas exploration and development: The method can accurately identify water invasion zones, determine the boundary and effective reservoir of gas reservoirs, 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 research and analysis of the petrological characteristics of the reservoir, the oil and gas bearing capacity and development prospect of the reservoir can be more accurately judged, which provides an important reference for oil and gas reservoir evaluation. 3) Providing technical support for optimization of oil and gas engineering: Through the research and analysis of water invasion problems in the development process of gas reservoirs, corresponding development plan and technical measures can be formulated to improve the efficiency and economic benefit of gas reservoir development.

[0045] Example 2

[0046] As Figure 1 shown, different from example 1, in the method for identifying and predicting water invasion zones in loose sandstone gas reservoirs of the application, in step 1: analyzing the water source of water wells, combining with water invasion advantage zone to diagnose water invasion layer, specifically according to:

[0047] Step 1.1. Analyzing the seismic interpretation results to obtain the overall geological structure and rock property information, and determining whether there is a fault;

[0048] Step 1.2. If it is determined in step 1.1 that there is a fault, analyzing the well logging interpretation results and combining the well trajectory to obtain the spatial distribution of rock properties and formation structure characteristics;

[0049] Step 1.3. Based on the spatial distribution of rock properties and formation structure characteristics obtained in step 1.2, using a plane scatter interpolation algorithm, a three-dimensional quantitative geological model is established based on the sublayer and plane grid scheme;

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

[0051] Example 3

[0052] As Figure 1 shown, different from example 1, in the identification and prediction method of the water invasion zone of the loose sandstone gas reservoir of the application, in step 2: analyzing the water source of the water well, combining the water invasion dominant zone to diagnose the water invasion horizon, which is implemented according to the following steps:

[0053] Step 2.1. Based on the water invasion process and shape, determine the water source type of the gas well water;

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

[0055] 1) Intraformational water: water production immediately after production, low water fluctuation, resulting in moderate production decline;

[0056] 2) Non-dominant zone edge water invasion: water production is the latest, water production is followed by a sharp increase in water, which is prone to water flooding and shutdown;

[0057] 3) Overall edge water advance along the dominant direction: water production is relatively late, and the water production is gradually increased after the water production, which is significantly reduced;

[0058] 4) Edge water advance along a narrow interval of the dominant zone: water production is relatively early, water fluctuation is high, and production is greatly reduced;

[0059] 5) Edge water channeling along the dominant channel: water production is the earliest, water fluctuation is medium or disappears, and only small production is reduced.

[0060] Step 2.2. Identify the main water source of the gas well;

[0061] The main water source of the gas well is identified according to the following process;

[0062] 1) Gas production trend change cause type:

[0063] ① Stable: no liquid accumulation;

[0064] ② Decreasing fluctuations: Fluid accumulation in the wellbore or insufficient formation supply;

[0065] ③ Slow decrease: Reduced production capacity due to near-well formation water production may be caused by water accumulation within the formation or edge water intrusion.

[0066] ④ A sharp drop followed by a large outflow of water and a subsequent recovery in production: the accumulated water within the layer is drained;

[0067] 2) Types of causes for changes in water output trends:

[0068] ① Water is produced immediately upon commissioning - water in the near-well zone;

[0069] ② After commissioning, water volume changes were analyzed according to the following pattern to determine the water intrusion patterns:

[0070] A: Water volume gradually increases and then decreases: a. If the water volume and gas volume change trends are consistent, it is judged to be intra-layer water; b. If the gas volume is stable, it is judged to be intra-layer water breaking through and gradually drying up; c. If there is a water invasion dominance zone, it is judged to be edge water intrusion into the dominance zone, followed by water-sensitive blockage; d. If there is a water invasion dominance zone and adjacent wells are put into production, the water volume decreases to dispersed water from adjacent wells.

[0071] B: Rapid increase in water volume until the gas well stops flowing: a. The edge water advances simultaneously from multiple directions within the dominant zone until the gas well is flooded; b. The gas well production section is adjacent to the edge water, and large-scale water intrusion occurs until the gas well production section is flooded.

[0072] C: Water volume gradually increases and then remains stable: a. Water in the formation at the far well converges and then forms a continuous supply to the well's production section; b. Edge water rushes along the dominant zone, but the water intrusion energy is offset by the resistance along the way, and the water intrusion volume remains stable.

[0073] Step 2.3: For wells with water intrusion at the edge, determine the water intrusion strata by combining the range of the dominant water intrusion zone near the well.

[0074] Step 2.4: For the water-bearing strata of the water-bearing well, calculate the average water phase permeability KWA within the water-bearing dominant zone.

[0075] Step 2.5: Combine the water outflow time, well location, and stratigraphic position to delineate the overall water intrusion morphology of the sub-layer.

[0076] Example 4

[0077] like Figure 1As shown, unlike Example 1, in the method for identifying and predicting the water invasion zone of the loose sand gas reservoir of the present application, in Step 3: a percolation model is established based on the diagnosed water invasion zone, and then the water invasion zone is reviewed, and the expansion dynamics of the water invasion zone is predicted, which is implemented according to the following steps: Step 3.1, on the basis of the water invasion zone settled in Step 2.3, the percolation model is established by incorporating the fluid model, the well model and the production history data;

[0078] Step 3.2, according to the special percolation mechanism of the water invasion loose sand gas reservoir, the percolation model is adjusted as follows: 1) determine the range of the dominant zone where water invasion may occur in the percolation model: the area higher than KWA of the second step (4); 2) after the edge water invades, the argillaceous in the water invasion zone will be dissolved and the permeability will be increased. Referring to the relevant core experiment data and the research results of digital core microscopic pore network flow simulation, the permeability increase ratio under the grid scale of the numerical model is usually 5-10, and the formation plane direction conductivity in the dominant zone where water invasion may occur determined by 1) above is modified; 3) according to the regional formation water potential energy data, the directional edge water of the percolation model is set by analyzing the water body;

[0079] Step 3.3, the percolation model adjusted in Step 3.2 is used to perform water production history matching for the edge water invasion well, and the main adjusted parameters include: 1) gas-water relative permeability curve: global water production matching is the adjustment target; 2) the ratio of the plane conductivity in the water invasion dominant zone; 3) the water invasion intensity of the analyzed edge water body;

[0080] Step 3.4, according to the fitting results, the water invasion zone expansion history process and the current distribution in the area not controlled by the water invasion well are analyzed;

[0081] Step 3.5, according to the results obtained in Step 3.4, the future expansion process of the water invasion zone is predicted, and the remaining gas enrichment area is analyzed to provide geological basis for tapping potential;

[0082] Step 3.6, with the goal of stabilizing gas and controlling water, adjustment and tapping measures are developed, and the optimization scheme is compared through production indicators.

[0083] Therefore, compared with the prior art, the identification and prediction method of the water invasion zone of the unconsolidated sandstone gas reservoir of the present application firstly identifies the water invasion advantage 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, the technical advantages of the numerical simulation method are fully utilized, and the whole water invasion gas reservoir is focused on, which makes up for the one-sidedness of the water invasion zone diagnosis based on limited well points, so that the method can not only simulate the water invasion process in the water invasion advantage zone, but also simulate the water invasion process in the non-water invasion advantage zone; and the history matching process of numerical simulation plays a testing role on the distribution of the water invasion advantage zone based on geological understanding and the water source obtained by gas reservoir engineering analysis. The combination of geology, engineering and numerical simulation, the mutual verification of theoretical calculation and field monitoring, and the reliable basis provided for the identification and prediction of the water invasion zone of the water invasion unconsolidated sandstone gas reservoir are provided. The present application has been strictly verified in the field, and the results are accurate and reliable.

[0084] The foregoing description shows and describes several preferred embodiments of the invention, but it is to be understood that the invention is not limited to the foregoing description, should not be seen as excluding other embodiments, and can be used in various other combinations, modifications and environments, and can be modified within the scope of the inventive concept described herein by the above teaching or related technical or knowledge. Any modification and change made by those skilled in the art without departing from the spirit and scope of the invention shall be within the protection scope of the claims of the invention.

Claims

1. A method for identifying and predicting water invasion zones in unconsolidated sand gas reservoirs, characterized in that, Specifically, the following steps are implemented: Step 1, establish a reservoir geological model, locate the water invasion advantage zone; Step 2, analyze the water source of the water well, and diagnose the water invasion horizon in combination with the water invasion advantage zone; Step 3, establish a seepage model based on the diagnosed water invasion horizon, and then review the water invasion zone and predict the expansion dynamics of the water invasion zone; In the step 1, the locating of the water invasion advantage zone is specifically: Step 1.4, draw a water phase permeability distribution field, that is, a water invasion advantage zone background map, and the water invasion advantage zone is located in the high permeability area of the water phase; In the step 2, the water source of the water well is analyzed, and the water invasion horizon 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 well, combined with the near well water invasion advantage zone range, the water invasion horizon is implemented; Step 2.4, for the water invasion well, the average value KWA of the water phase permeability in the water invasion advantage zone range of the water invasion horizon is calculated; Step 2.5, combined with the water time, well location and horizon, the overall water invasion morphology of the layer is sketched; In the step 3, the seepage model is established based on the diagnosed water invasion horizon, and then the water invasion zone is reviewed and the expansion dynamics of the water invasion zone is predicted, which is specifically implemented according to the following steps: Step 3.1, based on the water invasion horizon implemented in step 2.3, the fluid model, well model and production history data are integrated to establish a seepage model; Step 3.2, for the special seepage mechanism of the water invasion loose sandstone gas reservoir, the seepage model is adjusted as follows: 1) determine the advantage zone range where water invasion may occur in the seepage model: the area higher than KWA in step 2.4; 2) after the edge water invasion, the argillaceous in the water invasion zone will be dissolved to increase the permeability; referring to the relevant core experiment data and the research results of digital core micro pore network flow simulation, the formation plane direction conductivity in the above-mentioned advantage zone range where water invasion may occur is modified; 3) according to the regional formation water potential energy data, the directional edge water of the seepage model is set by analyzing the water body; Step 3.3, the seepage model adjusted in step 3.2 is used to focus on the water production history fitting of the edge water invasion well; Step 3.4, according to the fitting result, the water invasion zone expansion history process and the current distribution in the area not controlled by the water invasion well are analyzed; Step 3.5, according to the result obtained in step 3.4, the future expansion process of the water invasion zone is predicted, and the remaining gas enrichment area is analyzed to provide geological basis for tapping potential; Step 3.6, aiming at stabilizing gas and controlling water, adjustment and tapping measures are developed, and the optimization scheme is compared through production index; 2. The method for identifying and predicting water invasion zones in unconsolidated sand gas reservoirs according to claim 1, wherein, In the step 1, the establishment of the reservoir geological model is specifically implemented according to the following steps: Step 1.1, analyze the seismic interpretation results to obtain the overall geological structure and rock property information, and determine whether there is a fault; Step 1.2, if it is determined that there is a fault in step 1.1, analyze the logging interpretation results, and obtain the spatial distribution of rock properties and formation structure characteristics in combination with the well trajectory; Step 1.3, based on the spatial distribution of rock properties and formation characteristics obtained in step 1.2, a three-dimensional quantitative geologic model is established using a plane scatter interpolation algorithm based on the sublayer and plane grid scheme.

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