A blending-screening design method for packing sand control gravel size design

Abstract

The present application belongs to the technical field of oil and gas development engineering, and particularly relates to a blending-screening design method for size design of filling type sand control gravel. The present application uses limited commercially available filling material particle size specifications, and through blending of two particle size specifications of filling materials or screening of a single particle size specification of filling materials, can achieve reasonable gravel-formation sand particle size matching when carrying out sand control design of formation sand gravel filling in an effective range of arbitrary particle size medium. The present application solves the problem of matching design "dead angle" of commercially available specifications of filling materials for different particle sizes of formation sand, and influences the sand control effect. Finally, the present application improves the sand blocking efficiency while maintaining a high flow capacity, reduces the risk of fine sand penetration and production capacity loss, and realizes synchronous improvement of sand control effect and production capacity maintenance.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas development engineering technology, specifically relating to a blending-screening design method for gravel size design in filling sand control. It is applicable to gravel filling sand control in loose sandstone reservoirs. Based on the formation sand particle size characteristic data, it designs a blend of gravel or ceramsite of various particle sizes to achieve reasonable particle size matching and efficient sand control. Background Technology

[0002] Gravel packing is one of the dominant sand control technologies widely used in loose sandstone oil and gas reservoirs. It involves filling near-wellbore reservoir sand production gaps or wellbore / casing annulus with solid packing material (natural quartz sand or artificial ceramic aggregate) to block formation sand during production while maintaining a certain flow capacity. In gravel packing sand control, the particle size selection of the packing material is a key parameter determining the sand-blocking effect and production capacity. To ensure a stable bridging structure between the formation sand and the gravel layer, achieving efficient sand blocking without severe blockage, the ratio of the median particle size of the packing material to the median particle size of the formation sand (referred to as the gravel-sand ratio) should be controlled within a reasonable range (e.g., the Saucier method recommends a reasonable gravel-sand ratio of 5-6). Currently, the available particle size specifications for solid filler materials on the market are very limited. The four main particle sizes available in large quantities are: 16-30 mesh (corresponding to 0.58-1.19 mm), 20-40 mesh (0.42-0.84 mm), 30-50 mesh (0.3-0.6 mm), and 40-70 mesh (0.21-0.42 mm). Due to the relatively low actual market demand for other particle sizes, there is virtually no large-scale supply.

[0003] However, the grain size distribution of formation sands in oil and gas reservoirs varies extremely widely under different conditions, ranging from a few micrometers of fine sand to hundreds of micrometers of coarse sandstone. Faced with such diverse formation sand conditions, engineers can only select the closest grain size specification from the four fixed specifications mentioned above, based on the principle of proximity. With limited grain size specifications, the large range of formation sand grain sizes makes it difficult to achieve a reasonable match between the median grain size of the designed backfill material and the median grain size of the formation sand. This results in insufficient sand control, inability to block fine formation sand, or low permeability of gravel layers leading to production losses.

[0004] Taking the commonly used Saucier gravel size design method as an example, it requires that the median particle size of the backfill material be 5 to 6 times the median particle size of the formation sand it blocks. Based on this principle, the corresponding median particle size ranges of formation sand for commonly used backfill material sizes of 0.21-0.42mm, 0.3-0.58mm, 0.42-0.84mm, and 0.58-1.19mm are shown in Table 1.

[0005] Table 1. Commonly Used Backfill Material Specifications and Matching Median Sand Grain Size Range for Covering Formations

[0006] Among them, the median particle size needs to be obtained by actual sieve analysis. For relatively uniform gravel products, the average particle size is selected here.

[0007] Analysis of Table 1 reveals that within the total coverage range of 0.053-0.177 mm for the four particle sizes, existing backfill materials can reasonably cover 61% of the formation sand particle size range, while failing to cover 39% of the range. If smaller or larger formation sand particles are considered, such as those less than 0.053 mm and greater than 0.177 mm, the percentage of areas that existing backfill materials cannot cover will be even greater. This means that within the widely distributed median particle size range of formation sand, there are at least 39% of cases where there are "dead zones" requiring proper matching. In other words, using currently available backfill material sizes for sand control design will result in at least 39% of cases failing to achieve a reasonable mix ratio, thus affecting the sand control effect.

[0008] Therefore, there is an urgent need for a design method that can achieve precise matching of any target particle size through multi-particle blending within the existing commercially available particle size range, so as to fundamentally solve this long-standing problem that has plagued the sand control engineering industry.

[0009] In summary, the following key issues still exist in the design of gravel packing for sand control in loose sandstone oil and gas reservoirs: (1) Currently, in the field of sand control, the commonly used backfill materials (quartz sand and ceramsite) have four main particle sizes: 16~30 mesh (0.58-1.19mm), 20~40 mesh (0.42-0.84mm), 30~50 mesh (0.3-0.58mm), and 40~70 mesh (0.21-0.42mm). The range of available backfill material particle sizes is very limited, making it difficult to meet the sand control needs of formation sands with different particle sizes.

[0010] (2) The distribution range of formation sand particle size and median value in oil and gas fields is very wide, ranging from a few micrometers to several hundred micrometers. Based on the ratio of the median value of formation sand to the median value of backfill material particle size of 5 to 6 times and the principle of selecting the nearest, the particle size of backfill material selected from the above four commonly used backfill materials often fails to meet the reasonable particle size ratio, resulting in poor sand control effect or serious blockage, which restricts the sand control production effect.

[0011] (3) There is an urgent need for an effective solution that can achieve precise matching of any particle size of formation sand under the condition of available backfill material particle size in the market, so as to achieve the dual purpose of efficient sand retention and high flow production. Summary of the Invention

[0012] This invention aims to provide a blending-screening design method for the size design of gravel used in sand control backfilling. It seeks to achieve a reasonable gravel-to-formation sand particle size ratio in sand control designs using a limited range of commercially available backfill material particle sizes. This is achieved through blending two particle size specifications or screening a single particle size specification of backfill material, ensuring that the design can be tailored to any median particle size within the effective range. This solves the problem of a "dead zone" in matching commercially available backfill materials with different particle sizes of formation sand, which affects sand control effectiveness. Ultimately, it improves sand control efficiency while maintaining high seepage capacity, reducing the risk of fine sand penetration and production capacity loss, thus achieving a simultaneous improvement in sand control effectiveness and production capacity retention.

[0013] The technical problem to be solved by this invention is achieved by the following technical solution: a blending-sieving design method for the size design of fill-type sand and gravel, comprising the following steps: S1. Establish the coverage area of ​​the filling material. By selecting various commercially available backfill materials with different particle size ranges, and based on the ratio between the median particle size of the selected backfill material and the median particle size of the target formation sand, and the median particle size of the selected backfill material, the range of median particle size of the formation sand that the selected commercially available backfill material can cover is obtained; once the ratio is determined, those skilled in the art can calculate the limit of the median range using existing methods. S2. Based on the median particle size of the formation sand, determine whether to use a dual-size blending or single-size sieving method. By comparing the median grain size of the target formation sand with the range of median grain size of the selected backfill material, the design mode is determined, including three modes: direct application of a single type of backfill material, blending of two types of backfill materials, and screening of a single type of backfill material. When the median sand particle size of the target formation is within the coverage range corresponding to a certain specification of backfill material, the backfill material of that specification is directly used for sand control design, i.e., the direct application mode of a single specification of backfill material. When the median particle size of the target formation sand is located in the matching blank interval between the coverage areas of two adjacent specifications of backfill materials, a dual-specification backfill material mixing mode is adopted, and the target particle size is obtained by adjusting the mixing ratio of the two specifications of backfill materials. When the median particle size of the target formation sand is less than the lower limit of the coverage range of the finest backfill material or greater than the upper limit of the coverage range of the coarsest backfill material, a single-size backfill material screening mode is adopted. By screening the standard-size backfill material that is closest to the target requirement, the particle size of the backfill material that meets the design requirements is obtained. S3. Based on the selected design mode, determine the mixing ratio of the two specifications of backfill material or the screening ratio of a single specification of backfill material. Based on the proportioning relationship determined in step S1 and the two selected specifications of filling materials, calculate the optimal mixing ratio of different specifications of filling materials; or calculate the sieving ratio based on the selected single specification of filling material. This ensures that the error between the median particle size of the blended or screened backfill material and the median particle size of the target formation sand is less than the preset value; it achieves precise approximation of the target design particle size for backfill materials of limited specifications, providing a quantitative basis for on-site mixing; S4. The actual filling material is obtained by uniformly mixing according to the mixing or sieving ratio. According to the mixing or sieving ratio determined in step S3, the backfill materials of different specifications are uniformly mixed and verified by particle size testing (common particle size testing instruments such as vibrating screens or particle size analyzers can be used) to verify whether the particle size of the backfill materials after mixing meets the design requirements. After meeting the target particle size conditions, it is applied to gravel backfill sand control construction, so that the formed backfill layer establishes a reasonable particle size matching relationship and a stable bridging structure with the formation sand, and achieves the unity of efficient sand blocking and high flow capacity production.

[0014] Preferably, in step S1 of this invention: The particle size ranges corresponding to the commonly used commercially available backfill material sizes Ga, Gb, Gc, and Gd are as follows: Ga: 40~70 mesh (0.21-0.42mm); Gb: 30~50 mesh (0.3-0.58mm); Gc: 20~40 mesh (0.42-0.84mm); Gd: 16~30 mesh (0.58-1.19mm). The reasonable ratio range between the median particle size of the backfill material and the median particle size of the formation sand is set as follows: (1) In the formula, d 50g The median particle size of the target filling material, in mm; d 50 R represents the median grain size of the formation sand, in mm. min To determine the lower limit of a reasonable gravel-sand mix ratio, a dimensionless value is typically taken as 5; R max The upper limit of a reasonable gravel-sand ratio is dimensionless and is usually taken as 6; For any specification of backfill material, the median range of formation sand grain size that can be reasonably matched can be determined by the following formula: (2) (3) In the formula, d i50min The lower limit of the median grain size of the formation sand corresponding to the i-th specification of backfill material, in mm; d i50max The upper limit of the median grain size of the formation sand corresponding to the i-th specification of backfill material, in mm; d 50i Let be the median particle size of the i-th specification of filling material, in mm; in this invention, i is a, b, c, d; According to formulas (2) and (3), the median range of sand grain size in the Ga-grade filling material covering the formation is calculated as (d a50min d a50max The median range of sand grain size in the overburden formation for Gb specification filling materials is (d b50min d b50max The median range of sand grain size in the overburden formation covered by Gc specification filling material is (d c50mi n, d c50max The median range of sand grain size in the overburden formation covered by Gd specification filling material is (d d50min d d50max ); Further, the formation sand cover intervals corresponding to the four specifications of backfill materials were arranged according to particle size to obtain the complete cover relationship, as shown in Table 2; Table 2 is based on the proportion range (R) min R max The calculated median range of formation sand grain size

[0015] Based on the above method, the entire range of the median grain size of formation sand is represented as: (0, d) a50min )-(d a50min d a50max )-(d a50max d b50min )-(d b50min d b50max )-(d b50max d c50min )-(d c50min d c50max )-(d c50max d d50mi n)-(d d50min d d50max )-(>d d50max Using the above method, a coverage correspondence between commercially available standard specification backfill materials and the median particle size of formation sand can be established, thereby identifying the range of formation sands that a single specification backfill material can reasonably match and the particle size matching gaps between different specifications. This provides a basis for selecting a single specification design, a dual specification blending design, or a screening design mode in the subsequent step S2.

[0016] The advantages of obtaining the range of median formation sand grain sizes covered by four commercially available backfill material specifications, based on the ratio between the median of the selected backfill material and the median of the formation sand grain size, are as follows: It transforms the traditional design approach of directly selecting backfill material specifications based on formation sand grain size into one that reverses the process by establishing a formation sand grain size coverage range based on existing commercially available backfill material specifications. This achieves a quantitative correspondence between standard backfill material specifications and the applicable formation sand range. This method can intuitively identify the applicable boundaries of different backfill material specifications and the grain size matching gaps between adjacent specifications, providing a clear basis for subsequent single-specification design, dual-specification blending design, or sieving design.

[0017] Preferably, in step S2 of the present invention, Based on the median formation sand particle size coverage range corresponding to the four specifications of filling materials (Ga, Gb, Gc, and Gd) established in step S1, the median formation sand particle size d 50 By comparing with different cover zones, the applicable gravel size design pattern is determined. Based on the position of the median sand grain size of the target formation in different cover zones, the infill material size design patterns can be divided into three categories: (1) Direct application mode of single specification filling material When the median sand particle size of the target formation meets the following conditions, it indicates that the sand particle size of the target formation is within the effective coverage range of a certain size of gravel, and the corresponding size of gravel can be directly used for sand control design, i.e., the single-size backfill material can be directly applied: (4) (2) Mixing mode of dual-specification filling materials When the median grain size of the target formation sand exceeds the coverage range of all commercially available gravel sizes, i.e., when either of the following two conditions is met, it indicates that the grain size of the target formation sand is within the matching gap between the two sizes of backfill materials, and neither single size of backfill material can meet the preset gravel-sand ratio requirements. In this case, a dual-size backfill material blending mode is adopted (see Appendix). Figure 2 ), and in subsequent steps, calculate the optimal blending ratio of the two specifications of filling materials: (5) (6) (7) (3) Screening mode for single-specification filling materials When the median particle size of the target formation sand exceeds the coverage range of all commercially available gravel sizes, i.e., when either of the following two conditions is met, it indicates that the existing standard-sized gravel cannot meet the design requirements. In this case, a single-size filling material screening mode is adopted. By screening the standard-sized gravel that is closest to the target particle size requirement, the gravel particle size that meets the design requirements is obtained: (8) (9) Using the above discrimination method, the optimal gravel size design path can be quickly determined based on the median sand particle size of the target formation, realizing the automatic selection of gravel size design methods under different formation conditions, and providing a basis for subsequent blending ratio calculation or screening parameter design.

[0018] The advantages and characteristics of the gravel size design model based on the median grain size of formation sand are as follows: By establishing a correspondence between the target formation sand grain size and the coverage range of commercially available gravel specifications, a standardized selection of gravel size design paths is achieved. This method can automatically identify areas where existing standard gravel specifications can be directly applied, areas with gaps in matching specifications, and areas exceeding the coverage range. It then employs targeted design methods such as direct application, blending, or screening to avoid the problem of relying on experience for grain size selection in traditional design processes. This improves the rationality and adaptability of gravel size design and provides a clear basis for subsequent blending and screening designs.

[0019] Preferably, in step S3 of this invention, based on the design mode determined in step S2, the mixing ratio or sieve particle size limit that meets the target formation sand particle size requirements is calculated using either a dual-specification backfill material blending design or a single-specification backfill material sieving design. When the median grain size of the target formation sand is located between two adjacent gravel sizes, and a dual-size backfill material blending model is used: the median grain size d of the target backfill material is calculated based on the preset gravel-sand ratio. 50g Then, based on the median particle size d of the two selected filling materials... 50A and d 50B A weighted relationship based on particle size median was established, and the optimal blending ratio of the two filling materials was calculated. Let the median particle size of the finer-gauge filling material be d. 50A The median particle size of coarser-sized filler material is d. 50B The corresponding mass percentages are X A and X B Then the following condition is met: (10) In the formula, X A This refers to the mass percentage of finer-sized filling materials, dimensionless; X B This represents the mass percentage of coarser-sized backfill material, dimensionless. The most commonly used method in the industry for gravel-sand ratio is the Saucier method, where the median gravel size is selected as 5-6 times the median formation sand size. The preset gravel-sand ratio can be flexibly selected; for example, if the sand-retaining performance of the backfill layer is emphasized, the selected ratio can be decreased; if the flow performance of the backfill layer is emphasized, the selected ratio can be appropriately increased. Based on the principle of weighted average of particle size, a calculation model for the median particle size of the blended filling material is established: (11) In the formula, d 50A The median particle size of finer-gauge filler material is expressed in μm; d 50B This represents the median particle size of coarser filler material, in μm. The mass ratio of the two filling materials is obtained by solving the simultaneous equations: (12) (13) Further calculate the actual usage of each specification of filling material based on the total designed filling volume M: (14) (15) In the formula, M A For finer-gauge filler material usage, kg; M B M represents the amount of coarser grade backfill material used, in kg; M represents the total designed backfill material usage, in kg. When the median particle size of the target formation sand exceeds the coverage range of all standard-sized gravel, and a single-size backfill material sieving mode is used: the cumulative particle size distribution function of the target gravel is set as P(d) (generally obtained by a formation sand particle size analyzer, a commonly used detection method in the industry), which represents the cumulative mass percentage of gravel particles with a particle size less than or equal to d. Based on the median particle size of the target gravel d... 50g Calculate the sieve retention ratio using the particle size distribution curve of the selected standard-sized gravel: (16) In the formula, η is the sieve retention ratio, %; P(d) 50g The percentage (%) represents the cumulative mass percentage of the target gravel size in the original gravel size distribution curve, expressed as %. A single-size backfill material sieving mode is used, under which only Ga and Gd gravel can be selected. If Ga is selected, the median target gravel size d... 50g That is, 0.315mm. If Gd is selected, its median particle size is 0.885mm. In this invention, the original gravel is a commercially available filling material with different particle size ranges, and gravel is used as the filling material. Subsequently, the proportion of coarse or fine particles to be removed is determined based on the cumulative gravel size distribution function, and the retention ratio is controlled to ensure that the median gravel size after screening gradually approaches the target median gravel size d. 50gFinally, a filling material that meets the design requirements is obtained. By adjusting the sieve cutoff particle size and sieve retention ratio, the error between the median particle size of the sieved gravel and the median particle size of the target gravel is made to meet the design requirements. The criterion for judging the optimal blending ratio of the two filling materials is that the median particle size of the blended filling material is basically the same as that of the target filling material. The blending ratio obtained by this method has a median particle size that is basically exactly the median particle size d50g of the target gravel, which can be considered as the optimal ratio. The advantages and characteristics of determining the blending ratio of two types of backfill materials or the sieving ratio of a single type of backfill material based on the selected design mode are as follows: Given the limited available gravel sizes and the wide distribution of formation sand particle sizes, the matching problem between the target particle size and the standard gravel size is transformed into a blending ratio design or sieving ratio design problem, achieving continuous control over the target gravel particle size. Specifically, for target particle sizes located within the coverage range of adjacent sizes, the required particle size is obtained by calculating the optimal blending ratio of the two backfill materials; for target particle sizes exceeding the coverage range of the standard sizes, the particle size of existing gravel sizes is adjusted by calculating the sieving retention ratio, further expanding its applicability. This method can achieve precise design of any target particle size without customizing new particle size specifications, improving the accuracy and adaptability of gravel size design, and providing a guarantee for the subsequent formation of a reasonable gravel-sand ratio and a stable bridging structure.

[0020] Preferably, in step S4 of this invention: Based on the blending ratio of dual-specification backfill materials or the screening ratio of single-specification backfill materials determined in step S3, the corresponding specifications of gravel are mixed or screened to obtain the target gravel material. When using the dual-specification backfill material blending mode, the two specifications of backfill materials are weighed according to the calculated mass ratio and uniformly mixed using a mechanical mixing device, a continuous conveying mixing device, or an on-site sand mixing device. When using the single-specification backfill material screening mode, the original gravel is screened according to the calculated screening retention ratio to retain the particle components that meet the design requirements, thereby obtaining the target particle size gravel material.

[0021] After blending or sieving, the resulting gravel material is subjected to particle size analysis to obtain its particle size distribution curve and median particle size d. 50m and the median particle size of the design target d 50g Comparative verification was conducted. The design requirements were considered met when the following equation was satisfied: (17) In the formula, d 50m The measured median particle size of the mixed filling material is given in μm; δ is the allowable error coefficient, which is recommended to be 10%.

[0022] Once the test results meet the requirements, the blended filling material will be applied to sand control operations such as gravel filling or extrusion filling of the screen pipe. This filling material will fill the annulus, the outside of the screen pipe, and the near-wellbore void area, forming a sand control layer with a reasonable particle size distribution, effectively intercepting and supporting formation sand (see appendix). Figure 3 ).

[0023] The characteristics and advantages of the above-mentioned method for mixing and applying backfill materials are as follows: it transforms the aforementioned theoretical design results into a directly implementable field application scheme; it achieves precise acquisition of the target gravel particle size through mixing or sieving; and it verifies the design results through particle size analysis to ensure that the final gravel particle size is consistent with the design target. This method is simple to operate and convenient to implement, making full use of existing standard-sized gravel resources, achieving precise matching of gravel particle sizes under different formation sand conditions, which is conducive to forming a stable and dense sand-control bridging structure, improving sand-blocking effect and production capacity retention, and ensuring the long-term stability of sand-control construction effects.

[0024] Preferably, in step S4 of this invention, δ is 10%.

[0025] In a preferred embodiment of the present invention, in step S1, the median particle size of the target formation sand is obtained by analyzing the sand particle size using a laser particle size analyzer or a vibrating screen.

[0026] Preferably, in step S1 of this invention, the ratio of the median particle size of the selected backfill material to the median particle size of the formation sand is based on the 5-6 times principle of the Saucier method or other ratios. According to the 5-6 times principle of the Saucier method or other ratios, the reasonable range of median particle sizes of the formation sand is calculated based on the median particle sizes of the four backfill materials (Ga, Gb, Gc, and Gd). The Saucier method is based on the mechanism of complete sand retention, at which point the effective permeability of the gravel backfill zone can be considered maximum. Furthermore, this method is simple and easy to implement, making it very suitable for field backfilling operations. Other ratios can be considered as simply different values; if more emphasis is placed on the sand retention performance of the backfill layer, the selected ratio can be decreased; if more emphasis is placed on the flow performance of the backfill layer, the selected ratio can be appropriately increased.

[0027] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention provides a method for constructing gravel size coverage range based on the gravel-formation sand particle size ratio. By establishing the correspondence between commercially available standard-sized gravel and the range of suitable formation sand particle sizes, it achieves quantitative characterization of the applicable range of different-sized gravel and the blank range of particle size matching. This method transforms the traditional experience-based gravel selection process into a discrimination design process based on coverage range, improving the scientificity, standardization, and applicability of gravel size design.

[0028] (2) This invention provides a gravel size design method that combines the blending of two-specification backfill materials with the screening of a single-specification backfill material. When the target formation sand particle size is between the coverage range of adjacent gravel sizes, the target gravel particle size is obtained by calculating the optimal blending ratio; when the target formation sand particle size exceeds the coverage range of standard-specification gravel, the particle size of the standard-specification gravel is adjusted by calculating the screening ratio, thereby realizing the continuous design of the target particle size under limited gravel size conditions. This breaks through the problem that traditional sand control design is limited by standard gravel size, and can meet the sand control requirements under different reservoir conditions without developing new gravel sizes.

[0029] (3) The target gravel material obtained by using the design of this invention can form a more reasonable ratio with the median particle size of the formation sand, so as to achieve a precise match between the gravel size and the characteristics of the formation sand. At the same time, the particle size composition of the gravel after blending or screening is more in line with the design requirements, which is conducive to forming a stable and dense bridging structure at the interface between the formation sand and the gravel layer. While improving the sand blocking efficiency, it maintains a high seepage capacity, reduces the risk of fine sand penetration and production capacity loss, and achieves a simultaneous improvement in sand control effect and production capacity retention capacity. Attached Figure Description

[0030] Figure 1 Flowchart of the blending-screening design method for the size design of gravel for backfilling; Figure 2 Schematic diagram illustrating the principle of matching target particle size with standard specifications; Figure 3 A diagram illustrating the matching effect of formation sand and backfill material; Figure 4 Let be the cumulative grain size distribution function for Ga gravel. Detailed Implementation

[0031] The invention will be described in more detail below with reference to examples.

[0032] Example 1 This paper takes the gravel packing sand control design of Well P in a loose sandstone reservoir as an example. The formation sand grain size analysis results show that the median grain size is 0.135 mm (laser particle size analyzers or vibrating screens are commonly used for formation sand grain size analysis). The Saucier method is adopted as the principle for the gravel-to-formation sand grain size ratio, i.e., R... min =5、R max =6. Available gravel on-site includes: Ga: 40~70 mesh (0.21-0.42mm); Gb: 30~50 mesh (0.30-0.58mm); Gc: 20~40 mesh (0.42-0.84mm); Gd: 16~30 mesh (0.58-1.19mm). The corresponding median gravel sizes are: d 50a =0.315mm; d 50b=0.44mm; d 50c =0.63mm; d 50d =0.885mm. According to Figure 1 The steps shown illustrate the blending-screening design method for the size design of gravel used in filling systems: (1) Establish gravel-covered areas The median coverage range of formation sand grain size corresponding to the four types of gravel was calculated using the method described in step S1. The calculation results are shown in Table 3. Table 3 shows the median range of formation sand grain size calculated according to the ratio range (5, 6).

[0033] This results in the following range of median grain size in the formation sand: (0, 0.053 mm) - (0.053 mm, 0.063 mm) - (0.063 mm, 0.073 mm) - (0.073 mm, 0.088 mm) - (0.088 mm, 0.105 mm) - (0.105 mm, 0.126 mm) - (0.126 mm, 0.147 mm) - (0.147 mm, 0.177 mm) - (>0.177 mm).

[0034] (2) Determine the gravel size design pattern Due to the median sand grain size d in well P 50 =0.135mm, which satisfies:

[0035] Located between the Gc and Gd coverage areas, it belongs to the specification matching blank area. Therefore, a dual-specification filling material blending mode should be adopted, and two specifications of filling materials, 20~40 mesh and 16~30 mesh, should be selected for blending.

[0036] (3) Calculate the blending ratio Using the Saucier method, R=5.5 was selected, and the target median gravel size was calculated based on the median gravel-sand mix ratio R=5.5:

[0037] Let X be the mass percentage of 20-40 mesh filling material. A The mass percentage of 16-30 mesh filling material is X. B Based on the weighted relationship of particle size median and the fact that the sum of the mass percentages is 1, we obtain:

[0038]

[0039] Solving the system of equations simultaneously yields:

[0040]

[0041] That is, the mass percentage of 20-40 mesh filling material is 55.9%, and the mass percentage of 16-30 mesh filling material is 44.1%.

[0042] (4) On-site mixing and construction The total design material usage for well P is 12t. Therefore, the usage of 20-40 mesh filling material is 12 × 0.559 = 6.71t, and the usage of 16-30 mesh filling material is 12 × 0.441 = 5.29t. A continuous sand mixing device was used on-site for uniform mixing. Sampling and sieving revealed a median particle size of 0.738mm for the mixed filling material, which has an error of 0.61% compared to the design target median particle size of 0.7425mm, meeting the design requirements (the error between the median particle size of the mixed filling material and the median particle size of the target formation sand should be less than 10%).

[0043] Subsequently, conventional screen-tube gravel packing technology was used for construction, with mixed packing materials used to fill the annulus outside the screen tube and the near-wellbore area. After well P was put into production, it was continuously monitored for 12 months. No significant sand production occurred at the wellhead, and the production pressure differential remained stable. This verified that the method of the present invention can achieve the target particle size design using gravel of limited specifications and obtain good sand control and production capacity maintenance effects.

[0044] Example 2 This paper takes the gravel packing sand control design of Well M in a loose sandstone reservoir as an example. The formation sand grain size analysis results show that the median grain size is 0.046 mm. The Saucier method is used as the principle for the gravel-to-formation sand grain size ratio, i.e., R... min =5、R max =6. Available gravel on-site includes: Ga: 40~70 mesh (0.21-0.42mm); Gb: 30~50 mesh (0.30-0.58mm); Gc: 20~40 mesh (0.42-0.84mm); Gd: 16~30 mesh (0.58-1.19mm). The corresponding median gravel sizes are: d 50a =0.315mm; d 50b =0.44mm; d 50c =0.63mm; d 50d =0.885mm. According to Figure 1 The steps shown illustrate the blending-screening design method for the size design of gravel used in filling systems: (1) Establish gravel-covered areas The median coverage range of formation sand grain size corresponding to the four gravel sizes was calculated using the method described in step S1. The calculation results are shown in Table 4. Table 4 shows the median range of formation sand grain size calculated according to the mix ratio range (5, 6).

[0045] This results in the following range of median grain size in the formation sand: (0, 0.053 mm) - (0.053 mm, 0.063 mm) - (0.063 mm, 0.073 mm) - (0.073 mm, 0.088 mm) - (0.088 mm, 0.105 mm) - (0.105 mm, 0.126 mm) - (0.126 mm, 0.147 mm) - (0.147 mm, 0.177 mm) - (>0.177 mm).

[0046] (2) Determine the gravel size design pattern Due to the median sand grain size d in well M 50 =0.046mm, which satisfies:

[0047] Since the median particle size of well M is smaller than the coverage range of Ga, and exceeds the coverage range of all standard gravel specifications, a single-specification filling material screening mode is adopted, and 40~70 mesh filling materials are selected for screening.

[0048] (3) Calculate the sieve retention ratio Using the Saucier method, R=5.5 was selected, and the target median gravel size was calculated based on the median gravel-sand mix ratio R=5.5:

[0049] Next, obtain the cumulative grain size distribution function of the target gravel, that is, the cumulative grain size distribution function of Ga gravel, such as... Figure 4 As shown.

[0050] As can be seen from the figure, the screening retention ratio η is the cumulative mass percentage of gravel particles with a diameter less than or equal to 0.253 mm, which is 16%. In subsequent screening, 84% of the larger-diameter gravel in Ga is screened out, so that the median gravel diameter after screening gradually approaches the target median gravel diameter of 0.253 mm, and finally the filling material that meets the design requirements is obtained.

[0051] (4) On-site construction Particle size analysis was performed on the filling material determined for well M. The median particle size of the mixed filling material was measured to be 0.247 mm, which is 2.37% lower than the design target median particle size of 0.253 mm (the error between the median particle size of the sieved filling material and the median particle size of the target formation sand is required to be less than 10%), thus meeting the design requirements.

[0052] Subsequently, conventional screen-tube gravel filling technology was used for construction, with mixed filling materials used to fill the annulus outside the screen tube and the near-wellbore area. After well M was put into production, it was continuously monitored for 12 months. No significant sand production occurred at the wellhead, and the production remained stable. This verified that the method of the present invention can achieve the target particle size design using gravel screening of limited specifications and obtain good sand-blocking and flow performance of the filling layer.

Claims

1. A blending-sieving design method for the size design of gravel used in filling systems, characterized in that, Includes the following steps: S1. Establish the coverage area of ​​the filling material. Select a variety of commercially available backfill materials with different particle size ranges. Based on the ratio between the median particle size of the selected backfill material and the median particle size of the target formation sand, and the median particle size of the selected backfill material, obtain the range of median particle size of the formation sand that the selected commercially available backfill material can cover. S2. Based on the median particle size of the formation sand, determine whether to use a dual-size blending or single-size sieving method. By comparing the median grain size of the target formation sand with the range of median grain size of the selected backfill material, the design mode is determined, including three modes: direct application of a single type of backfill material, blending of two types of backfill materials, and screening of a single type of backfill material. When the median sand particle size of the target formation is within the coverage range corresponding to a certain specification of backfill material, the backfill material of that specification is directly used for sand control design, i.e., the direct application mode of a single specification of backfill material. When the median particle size of the target formation sand is located in the matching blank interval between the coverage areas of two adjacent specifications of backfill materials, a dual-specification backfill material mixing mode is adopted, and the target particle size is obtained by adjusting the mixing ratio of the two specifications of backfill materials. When the median particle size of the target formation sand is less than the lower limit of the coverage range of the finest backfill material or greater than the upper limit of the coverage range of the coarsest backfill material, a single-size backfill material screening mode is adopted. By screening the standard-size backfill material that is closest to the target requirement, the particle size of the backfill material that meets the design requirements is obtained. S3. Based on the selected design mode, determine the mixing ratio of the two specifications of backfill material or the screening ratio of a single specification of backfill material. Based on the proportioning relationship determined in step S1 and the two selected specifications of filling materials, calculate the optimal mixing ratio of different specifications of filling materials; or calculate the sieving ratio based on the selected single specification of filling material. The error between the median particle size of the mixed or screened backfill material and the median particle size of the target formation sand should be less than a preset value. S4. The actual filling material is obtained by uniformly mixing according to the mixing or sieving ratio. According to the mixing or sieving ratio determined in step S3, the filling materials of different specifications are uniformly mixed, and the particle size of the mixed filling materials is verified by particle size detection to see if the particle size meets the design requirements. After meeting the target particle size conditions, it is applied to gravel filling sand prevention construction.

2. The blending-sieving design method for the size design of fill-type sand and gravel as described in claim 1, characterized in that, In step S1: The particle size ranges corresponding to the size specifications Ga, Gb, Gc, and Gd of commercially available filling materials are as follows: Ga: 40~70 mesh; Gb: 30~50 mesh; Gc: 20~40 mesh; Gd: 16~30 mesh. The reasonable ratio range between the median particle size of the backfill material and the median particle size of the formation sand is set as follows: （1） In the formula, d 50g The median particle size of the target filling material, in mm; d 50 R represents the median grain size of the formation sand, in mm. min The lower limit of a reasonable gravel-sand mix ratio is dimensionless; R max The upper limit of a reasonable gravel-sand mix ratio is dimensionless. For any specification of backfill material, the reasonable matching range of the median grain size of the formation sand is determined by the following formula: （2） （3） In the formula, d i50min The lower limit of the median grain size of the formation sand corresponding to the i-th specification of backfill material, in mm; d i50max The upper limit of the median grain size of the formation sand corresponding to the i-th specification of backfill material, in mm; d 50i Let be the median particle size of the i-th specification of filler material, in mm; According to formulas (2) and (3), the median range of sand grain size in the Ga-grade filling material covering the formation is calculated as (d a50min d a50max The median range of sand grain size in the overburden formation for Gb specification filling materials is (d b50min d b50max The median range of sand grain size in the overburden formation covered by Gc specification filling material is (d c50mi n, d c50max The median range of sand grain size in the overburden formation covered by Gd specification filling material is (d d50min d d50max ); Furthermore, the formation sand cover intervals corresponding to the four sizes of gravel were arranged according to grain size to obtain a complete cover relationship; Based on the above method, the entire range of the median grain size of formation sand is represented as: (0, d) a50min )-(d a50min d a50max )-(d a50max d b50min )-(d b50min d b50max )-(d b50max d c50min )-(d c50min d c50max )-(d c50max d d50mi n)-(d d50min d d50max )-(>d d50max ).

3. The blending-sieving design method for the size design of fill-type sand and gravel as described in claim 2, characterized in that, In step S2: Based on the median formation sand particle size coverage range corresponding to the four specifications of filling materials (Ga, Gb, Gc, and Gd) established in step S1, the median formation sand particle size d 50 Compared with different cover zones, based on the position of the median sand grain size of the target formation in different cover zones, the design patterns for infill material size are divided into three categories: (1) Direct application mode of single specification filling material When the median sand particle size of the target formation meets the following conditions, it indicates that the sand particle size of the target formation is within the effective coverage range of a certain size of gravel, and the corresponding size of gravel can be directly used for sand control design, i.e., the single-size backfill material can be directly applied: （4） (2) Mixing mode of dual-specification filling materials When the median grain size of the target formation sand exceeds the coverage range of all commercially available gravel sizes, i.e., when either of the following two conditions is met, it indicates that the grain size of the target formation sand is in the matching gap between the two sizes of backfill materials, and neither single size of backfill material can meet the preset gravel-sand ratio requirements. In this case, a dual-size backfill material blending mode is adopted, and the optimal blending ratio of the two sizes of backfill materials is calculated in subsequent steps: （5） （6） （7） (3) Screening mode for single-specification filling materials When the median particle size of the target formation sand exceeds the coverage range of all commercially available gravel sizes, i.e., when either of the following two conditions is met, it indicates that the existing standard-sized gravel cannot meet the design requirements. In this case, a single-size filling material screening mode is adopted. By screening the standard-sized gravel that is closest to the target particle size requirement, the gravel particle size that meets the design requirements is obtained: （8） （9） Using the above discrimination method, the optimal gravel size design path is determined based on the median sand grain size of the target formation.

4. The blending-sieving design method for the size design of fill-type sand and gravel as described in claim 3, characterized in that, In step S3, based on the design mode determined in step S2, the blending ratio or sieve size limit that meets the target formation sand particle size requirement is calculated using either the dual-specification backfill material blending design or the single-specification backfill material sieving design. When using a dual-size backfill material blending mode, the median particle size d of the target backfill material is calculated based on the preset gravel-sand ratio. 50g Let the median particle size of the finer-gauge filler be d. 50A The median particle size of coarser-sized filler material is d. 50B The corresponding mass percentages are X A and X B Then the following condition is met: （10） In the formula, X A This refers to the mass percentage of finer-sized filling materials, dimensionless; X B This represents the mass percentage of coarser grade filling material, and is dimensionless. Based on the principle of weighted average of particle size, a calculation model for the median particle size of the blended filling material is established: （11） In the formula, d 50A The median particle size of finer-gauge filler material is expressed in μm; d 50B This represents the median particle size of coarser filler material, in μm. The mass ratio of the two filling materials is obtained by solving the simultaneous equations: （12） （13） Further calculate the actual usage of each specification of filling material based on the total designed filling volume M: （14） （15） In the formula, M A For finer-gauge filler material usage, kg; M B M represents the amount of coarser grade backfill material used, in kg; M represents the total designed backfill material usage, in kg. When using a single-size backfill material screening mode, the original cumulative gravel particle size distribution function is set as P(d), which represents the cumulative mass percentage of gravel particles with a diameter less than or equal to d; based on the target gravel particle size median d... 50g Calculate the sieve retention ratio using the particle size distribution curve of the selected standard-sized gravel: （16） In the formula, η is the sieve retention ratio, %; P(d) 50g () represents the cumulative mass percentage corresponding to the target gravel size in the original gravel size distribution curve, %; The proportion of coarse or fine particles to be screened out is determined based on the original gravel particle size distribution curve.

5. The blending-sieving design method for the size design of fill-type sand and gravel as described in claim 4, characterized in that, In step S4: Based on the blending ratio of dual-specification backfill material or the sieving ratio of single-specification backfill material determined in step S3, after blending or sieving, the resulting gravel material is subjected to particle size analysis to obtain its particle size distribution curve and median particle size d. 50m and the median particle size of the design target d 50g A comparative verification was conducted, and the design requirements were considered met when the following formula was satisfied: （17） In the formula, d 50m δ represents the median measured particle size of the mixed filling material, in μm; δ is the allowable error coefficient.

6. The blending-sieving design method for the size design of fill-type sand and gravel as described in claim 5, characterized in that, In step S4: δ is 10%.

7. The blending-sieving design method for the size design of fill-type sand and gravel as described in claim 1, characterized in that, In step S1, the median particle size of the target formation sand is obtained by analyzing the sand particle size using a laser particle size analyzer or a vibrating screen.

8. The blending-sieving design method for the size design of fill-type sand and gravel as described in claim 1, characterized in that, In step S1, the ratio of the median size of the selected filling material to the median size of the formation sand is based on the principle of 5 to 6 times according to the Saucier method.

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