A method for predicting the scale of a braided river sand body

Abstract

The present application belongs to the technical field of unconventional natural gas exploitation, and specifically provides a braided river sand body scale prediction method, which solves the problem of the braided river sand body in the existing research area, which is multi-layer superimposed, frequent river channel migration and thin sand body thickness, increases the difficulty of predicting the reservoir scale of seismic data, and urgently needs a new sandstone reservoir scale prediction method and means; according to the characteristics of the braided river and the actual gas field development, the present application screens out the relationship between the sand body thickness drilled by the block well and the corresponding well spacing and two parameters of the river channel swing angle, predicts the river channel sand body scale, perfects the sand body prediction method, establishes a set of braided river sand body scale prediction mode suitable for the whole basin, has good effect, is a good supplement to the seismic prediction of the sand body scale, and provides technical support for the deployment and effective exploitation of the natural gas well.

Description

Technical Field

[0001] This invention belongs to the field of unconventional natural gas extraction technology, specifically relating to a method for predicting the size of braided river sand bodies. Background Technology

[0002] Domestically and internationally, the prediction of braided river sand body size primarily relies on seismic data. For strata with a reservoir thickness greater than 20m, seismic data can provide relatively accurate predictions. However, for the loess plateau topography in the southern part of the basin, seismic data acquisition and analysis have consistently presented significant challenges. Due to the presence of a thick loess layer, the quality of seismic data is poor, and the accuracy and precision of sand body identification urgently need improvement. This is particularly true for the braided river sand bodies in the study area, characterized by multiple superimposed layers, frequent channel migration, and relatively thin sand body thickness (4-20m), which greatly increases the difficulty of predicting reservoir size using seismic data, necessitating new methods and techniques for predicting sandstone reservoir size.

[0003] Chinese patent document CN107203651A, published on September 26, 2017, discloses a method for dissecting the reservoir configuration of braided river tight sandstone gas reservoirs. This method establishes a braided river geological knowledge base; identifies the configuration units corresponding to five levels of interfaces; determines the boundaries of configuration units between wells; identifies four levels of braided river configuration units; uses well logging curve cyclic method, sedimentation layer development location identification method, and vertical microfacies change method of core bars and channels to determine the position of the core bar on the plane; applies well logging curves to determine the boundaries of three levels of configuration units within the core bar; identifies and describes the morphology and scale of core bar accretion bodies within the three levels of configuration unit boundaries; and, combined with physical property and gas-bearing analysis, quantitatively describes effective single sand bodies, thus forming a hierarchical description method for finely describing the configuration of braided river reservoirs. This document characterizes different levels of configuration units in strongly heterogeneous tight sandstone reservoirs, realizing the size and distribution of core bar configuration units, thereby effectively guiding the design of reasonable well networks and well types in gas fields and fine three-dimensional reservoir geological modeling. The well network and well type were optimized, improving the gas field recovery rate. However, this literature is applicable to braided river reservoir gas fields where the well network spacing is larger than that of oil wells, and is not applicable to the scale prediction of braided river sand bodies with thick loess layers, multiple superimposed layers, frequent river channel migration, and thin sand body thickness (4-20m) in the study area. Summary of the Invention

[0004] The purpose of this invention is to provide a method for predicting the size of braided river sand bodies. This method addresses the problem that existing technologies for predicting the size of braided river sand bodies in the study area, which are characterized by multiple superimposed layers, frequent river channel migration, and relatively thin sand body thickness (4-20m), increase the difficulty of predicting reservoir size using seismic data. Therefore, new methods and means for predicting the size of sandstone reservoirs are urgently needed.

[0005] Therefore, the present invention provides a method for predicting the size of braided river sand bodies, comprising the following steps:

[0006] 1) Select the existing well network of the gas field and establish a rectangular coordinate system; in the rectangular coordinate system, the horizontal distance between adjacent well points on the X-axis is the well spacing, and the vertical distance between adjacent wells on the Y-axis is the row spacing;

[0007] 2) Determine the sand body thickness encountered at each well point based on the logging data of each well point, and use the regression curve of the relationship between the sand body thickness encountered at each well point and the X-axis to obtain the relationship between the sand body thickness encountered by the block wells and the corresponding well distance.

[0008] 3) Determine the center position of each well channel based on the logging data and well logging data of each well point;

[0009] 4) Determine the river channel swing angle and establish a block river channel swing angle database;

[0010] 5) Correct the block channel swing angle database;

[0011] 6) Based on the maximum and minimum channel swing angles in the block channel swing angle database, predict the channel swing angle. After determining the range of selected gas field channel swing angles, predict the center position of each well row channel again. Combined with the relationship between the thickness of sand body encountered by well drilling in the block and the corresponding well spacing, predict the scale of channel sand body.

[0012] Preferably, after obtaining the relationship between the thickness of the sand body encountered by the block well and the corresponding well distance in step 2), the relationship between the thickness of the sand body encountered by the block well and the corresponding well distance is modified.

[0013] Preferably, the relationship between the thickness of the sand body encountered in the block well and the corresponding well distance is modified based on the abundance of drilling data in the block.

[0014] Preferably, the specific method for determining the channel swing angle and establishing a block channel swing angle database is as follows: after determining the positions of any two rows of main channels, the channel swing angle is determined by combining the relationship between the thickness of the sand body encountered by the block well drilling and the corresponding well spacing. The above method for determining one channel swing angle is repeated to obtain multiple channel swing angles, and a block channel swing angle database is established.

[0015] Preferably, the formula for calculating the channel swing angle is tgθ = well distance between two well points / row distance between two well points; θ is the channel swing angle.

[0016] Preferably, the method for correcting the block channel swing angle database is as follows: Substitute an actual channel swing angle into the block channel swing angle database, compare the actual channel swing angle with the maximum and minimum channel swing angles in the database, and when θ... 实 <θ min , then θ 实 Corrected to θ 实 =θ min When θmin <θ 实 <θ max If θ, then the database will not be corrected; when θ 实 >θ max , then θ 实 Corrected to θ 实 =θ max ;;θ 实 θ represents the actual river channel swing angle. max θ is the maximum channel swing angle. min This represents the minimum river channel swing angle.

[0017] Preferably, the method for determining a channel swing angle by using the relationship between the thickness of the sand body encountered by the block well and the corresponding well distance after the positions of any two rows of main channels are determined is as follows: take a sample point from each of the two rows of main channels, and determine a channel swing angle by the ratio of the well distance between the two sample points to the row distance between the two sample points.

[0018] The beneficial effects of this invention are:

[0019] 1. The braided river sand body size prediction method provided by this invention, based on the characteristics of braided rivers and the actual development of gas fields, predicts the size of river sand bodies by selecting two parameters: the relationship between the thickness of sand bodies encountered by wells in the block and the corresponding well spacing, and the river channel swing angle. This improves the sand body prediction method and establishes a braided river sand body size prediction method suitable for the entire basin. It has good results and is a good supplement to seismic sand body size prediction, providing technical support for the deployment and effective exploitation of natural gas wells.

[0020] 2. The braided river sand body size prediction method provided by this invention obtains the relationship between the thickness of the sand body encountered by a block well and the corresponding well distance. Based on the abundance of completed drilling data in the block, the relationship between the thickness of the sand body encountered by a block well and the corresponding well distance is corrected. Based on the abundance of sample points, the data carried by the samples re-regresses the existing relationship between the thickness of the sand body encountered by a block well and the corresponding well distance to obtain a more accurate relationship between the thickness of the sand body encountered by a block well and the corresponding well distance.

[0021] 3. The braided river sand body size prediction method provided by this invention can determine the location of the main channel of each well row based on the well logging data and well logging data of each well point. The accurate location of the main channel is of great significance for studying the channel swing and the characteristics of sand body deposition. Attached Figure Description

[0022] The present invention will now be described in further detail with reference to the accompanying drawings.

[0023] Figure 1 This is a schematic diagram of the current well network and well point distribution;

[0024] Figure 2It is a regression curve of the relationship between the thickness of the sand body encountered at each well point in the study area and the X-axis;

[0025] Figure 3 The graph shows that the error in the regression curve of the relationship between the thickness of the sand body encountered during drilling and the X-axis is increased due to the meandering of the river channel.

[0026] Figure 4 This is a flowchart for correcting the database of river channel swing angles in the corrected block;

[0027] Figure 5 This is a flowchart of a method for predicting the size of braided river sand bodies;

[0028] Figure 6 It is a diagram for calculating the river channel swing angle. Detailed Implementation

[0029] Example 1:

[0030] like Figure 5 As shown, a method for predicting the size of braided river sand bodies includes the following steps:

[0031] 1) Select the existing well pattern of the gas field and establish a rectangular coordinate system (see...). Figure 1 In the rectangular coordinate system, the horizontal distance between adjacent well points on the X-axis is the well spacing, and the vertical distance between adjacent wells on the Y-axis is the row spacing.

[0032] 2) Determine the sand body thickness encountered at each well point based on the logging data (see Table 1) (this determination method is well-known and will not be described in detail here). Using the regression curve of the sand body thickness encountered at each well point versus the X-axis, obtain the relationship between the sand body thickness encountered by the block wells and the corresponding well spacing. The actual drilling data for each well point includes drilling data, logging data, and well logging data. The relationship between the sand body thickness encountered by the block wells and the corresponding well spacing is y = f(x) (see Table 1). Figure 2 );

[0033] Table 1. Thickness of Sand Body Encountered at Each Well Drilling Point

[0034]

[0035]

[0036] 3) Determine the center location of each channel based on the logging data and well logging data of each well point; specifically, according to the well-known fact that the center location of the channel during the same depositional period has strong hydrodynamics and the largest sand body thickness; the shape of the logging electrical logging curve is "box-shaped"; at the same time, compared with the adjacent wells, it also has the characteristics of the largest sand body thickness and the best sand body continuity, which can be judged as the center location of the channel.

[0037] Well logging data includes well logging curves, the main curves used are deep and shallow lateral curves, natural gamma curves (GR), spontaneous potential curves, sonic transit time curves, compensated neutron curves, PE curves, etc., which can be used for stratigraphic correlation, stratigraphic division, simple analysis of reservoir properties, and determination of the thickness, lithology, and physical properties of the sand bodies encountered during drilling, etc.

[0038] Well logging data includes cuttings logging, which involves systematically observing and identifying the cuttings returned to the surface during drilling to determine lithology, mineral composition, structure, and hydrocarbon content.

[0039] Combining well logging data and well logging data can comprehensively determine the location of the sand body encountered during drilling. For example, the electrical characteristics of the sand body in the main channel are "box-shaped", with large thickness, coarse rock grain size, high quartz content, good rock grain sorting, good physical properties and gas content, reflecting strong hydrodynamic characteristics during the deposition period.

[0040] The criteria for determining the channel center location are as follows: When logging shows a sand body vertical thickness greater than 8m, cuttings logging shows a quartz content greater than 80%, and rock particle sorting is good (uniform particle size with a certain particle size exceeding 90% indicates good sorting); and the electrical parameters of this sand body on the logging curves meet the following requirements: natural gamma curve value below 50 API, PE curve value below 2.4 bar / electron, sonic transit time greater than 210 μs / m, deep double lateral resistivity greater than 80 Ω·m, and the sand body is most developed compared to adjacent wells (i.e., located in the main channel, with the thickest sand body, best rock particle sorting, and a "box-shaped" logging curve compared to adjacent wells), this location is the channel center. Accurately locating the channel center is crucial for studying channel undulation and sand body depositional characteristics.

[0041] 4) Determine the river channel swing angle and establish a block river channel swing angle database;

[0042] 5) Correct the block channel swing angle database;

[0043] See Figure 6 When the calculated channel swing angle of the newly completed well (row B) and row A is within the value of the known channel swing angle database, it proves that the channel swing angle represented by the row of wells matches the predicted channel swing angle, that is, the channel prediction is accurate. Otherwise, the channel swing angle value must be included in the channel swing angle database; thus, the correction and improvement of the database are completed.

[0044] 6) Based on the maximum and minimum channel swing angles in the block channel swing angle database, predict the channel swing angle. After determining the range of selected gas field channel swing angles, predict the center position of each well row channel again. Combined with the relationship between the thickness of sand body encountered by well drilling in the block and the corresponding well spacing, predict the scale of channel sand body.

[0045] This invention provides a method for predicting the size of braided river sand bodies. Based on the characteristics of braided rivers and the actual development of gas fields, it predicts the size of river sand bodies by selecting two parameters: the relationship between the thickness of sand bodies encountered by wells in a block and the corresponding well spacing, and the river channel oscillation angle. This improves the sand body prediction method and establishes a set of methods suitable for predicting the size of braided river sand bodies throughout the entire basin. It has shown good results and is a good supplement to seismic sand body size prediction, providing technical support for the deployment and effective exploitation of natural gas wells. This method has been applied in the Sulige gas field for one year with excellent results. Based on the prediction of sand body size in the gas field, the average sandstone reservoir encounter rate in the horizontal sections of horizontal wells in the gas field increased from 78.2% to 85.3%, effectively improving the gas field development efficiency.

[0046] Example 2:

[0047] Based on Example 1, after obtaining the relationship between the thickness of the sand body encountered by the block well and the corresponding well distance in step 2), the relationship between the thickness of the sand body encountered by the block well and the corresponding well distance is modified.

[0048] During the deposition of braided rivers, the river channel oscillates, which increases the error of the regression curve of the relationship between the thickness of the sand body encountered by each well point and the X-axis. The accuracy is improved by correcting the relationship between the thickness of the sand body encountered by the block wells and the corresponding well spacing.

[0049] Preferably, the relationship between the thickness of the sand body encountered in the block well and the corresponding well distance is modified based on the abundance of drilling data in the block.

[0050] Figure 3 (a) is the regression curve of the relationship between sand body thickness and well spacing for well groups A and B due to the swaying of the main channel, which changed from the original y=-1E-05x 2 +0.0235x + 3.6727 becomes y = -1E-05x 2 +0.0282x-3.3818. If the regression curve of the relationship between sand body thickness and well spacing is not corrected ( Figure 3 (b) will result in significant errors. Therefore, as the drilling data for the block becomes more abundant and comprehensive, it is essential to correct the regression curve of the relationship between sand body thickness and well spacing.

[0051] After obtaining the relationship between the thickness of the sand body encountered by the block well and the corresponding well distance, the relationship is corrected based on the abundance of drilling data in the block. Based on the abundance of sample points, the data carried by the samples are used to re-regress the existing relationship between the thickness of the sand body encountered by the block well and the corresponding well distance to obtain a more accurate relationship.

[0052] Preferably, the specific method for determining the channel swing angle and establishing a block channel swing angle database is as follows: after determining the positions of any two rows of main channels, the channel swing angle is determined by combining the relationship between the thickness of the sand body encountered by the block well drilling and the corresponding well spacing. The above method for determining one channel swing angle is repeated to obtain multiple channel swing angles, and a block channel swing angle database is established.

[0053] Preferably, the method for determining a channel swing angle after determining the positions of any two rows of main channels, using the relationship between the thickness of the sand body encountered by the block well and the corresponding well spacing, is as follows: Take one sample point from each of the two rows of main channels, and determine a channel swing angle by the ratio of the well spacing between the two sample points to the row spacing between the two sample points. (See...) Figure 6 )

[0054] The formula for calculating the river channel swing angle is tgθ = well distance between two well points / row distance between two well points; θ is the river channel swing angle.

[0055] This calculation method is simple.

[0056] Preferably, the method for correcting the block channel swing angle database is as follows: Substitute an actual channel swing angle into the block channel swing angle database, compare the actual channel swing angle with the maximum and minimum channel swing angles in the database, and when θ... 实 <θ min , then θ 实 Corrected to θ 实 =θ min When θ min <θ 实 <θ max If θ, then the database will not be corrected; when θ 实 >θ max , then θ 实 Corrected to θ 实 =θ max ;;θ 实 θ represents the actual river channel swing angle. max θ is the maximum channel swing angle. min Minimum channel swing angle (see) Figure 4 ). Figure 4 and Figure 5 In the above, Y is always Yes, meaning the condition is met or satisfied, and N is always No, meaning the condition is not met or not satisfied.

[0057] This method utilizes continuously enriched sample point data. Based on the original river channel swing angle θ, if the new actual river channel swing angle θ conforms to the range of the original river channel swing angle θ database, then there is no need to correct the river channel swing angle database. Otherwise, correcting the river channel swing angle database can improve the river channel swing angle and make the understanding of the river channel swing area more accurate.

[0058] The above examples are merely illustrative of the present invention and do not constitute a limitation on the scope of protection of the present invention. All designs that are the same as or similar to the present invention are within the scope of protection of the present invention.

Claims

1. A method for predicting the size of braided river sand bodies, characterized in that: Includes the following steps: 1) Select the existing well network of the gas field and establish a rectangular coordinate system; in the rectangular coordinate system, the horizontal distance between adjacent well points on the X-axis is the well spacing, and the vertical distance between adjacent wells on the Y-axis is the row spacing; 2) Determine the sand body thickness encountered at each well point based on the logging data. Utilize the regression curve of the sand body thickness encountered at each well point versus the X-axis to obtain the relationship between the sand body thickness encountered by wells in the block and the corresponding well spacing. After obtaining the relationship between the sand body thickness encountered by wells in the block and the corresponding well spacing in step 2), the relationship is corrected. Based on the abundance of completed drilling data in the block, the relationship between the sand body thickness encountered by wells in the block and the corresponding well spacing is further corrected. 3) Determine the center location of each well channel based on the logging and well logging data at each well point; 4) Determine the channel swing angle and establish a block channel swing angle database; The specific method for determining the channel swing angle and establishing a block channel swing angle database is as follows: After the positions of any two rows of main channels are determined, a channel swing angle is determined by using the relationship between the thickness of the sand body encountered by the block well and the corresponding well spacing. The above method for determining a channel swing angle is repeated to obtain multiple channel swing angles, and a block channel swing angle database is established. 5) Correct the database of river channel swing angles in the blocks; 6) Based on the maximum and minimum channel swing angles in the block channel swing angle database, predict the channel swing angle. After determining the range of selected gas field channel swing angles, predict the center position of each well row channel again. Combined with the relationship between the thickness of the sand body encountered by the block well and the corresponding well spacing, predict the scale of the channel sand body. The formula for calculating the channel swing angle is tgθ = well spacing between two well points / row spacing between two well points; θ is the channel swing angle.

2. The method for predicting the size of braided river sand bodies as described in claim 1, characterized in that: The method for correcting the block river channel swing angle database is as follows: Substitute an actual river channel swing angle into the block river channel swing angle database, and compare this actual river channel swing angle with the maximum and minimum river channel swing angles in the database: when θ 实 <θ min , then θ 实 Corrected to θ 实 =θ min When θ min <θ 实 <θ max If θ is not corrected, the database will not be modified; when θ is not corrected, the database will not be modified. 实 >θ max , then θ 实 Corrected to θ 实 = θ max ;θ 实 θ represents the actual river channel swing angle. max θ is the maximum channel swing angle. min This represents the minimum river channel swing angle.

3. The method for predicting the size of braided river sand bodies as described in claim 1, characterized in that: The method for determining a channel swing angle by using the relationship between the thickness of the sand body encountered by the block well and the corresponding well spacing after the positions of any two rows of main channels are determined is as follows: take a sample point from each of the two rows of main channels, and determine a channel swing angle by the ratio of the well spacing of the two sample points to the row spacing of the two sample points.

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