A method for determining the initial porosity of mixed sedimentary rocks

Abstract

This invention relates to the field of oil and gas exploration technology research, specifically to a method for determining the initial porosity of mixed sedimentary rocks. The method includes the following steps: establishing a classical porosity model for the mixed sedimentary rock reservoir to obtain the initial porosity formula for terrigenous clastic sediments; determining the effective storage of snail-like biocavities in the mixed sedimentary rock reservoir through simulation experiments, thereby obtaining the initial porosity of bioclastic sediments in the mixed sedimentary rock; and combining the initial porosity of terrigenous clastic sediments and the initial porosity of bioclastic sediments to obtain the initial porosity of the mixed sedimentary rock. Compared with existing methods, the calculation method of this invention includes biocavity porosity, and particularly, comprehensively considers the influence of terrigenous clastic sediments and bioclastic sediments during deposition, effectively increasing the accuracy of the initial porosity calculation for mixed sedimentary rocks.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas exploration technology, and relates to the field of porosity technology research, specifically a method for determining the initial porosity of mixed sedimentary rocks. Background Technology

[0002] After sediment deposition, under the influence of factors such as temperature, pressure, and formation water, the originally loose sediments become hard rocks. Sediment porosity is the starting point for studying the porosity evolution of mixed sedimentary rocks. Previous studies on initial porosity have focused on sandstone, with the most comprehensive research being that of Beard and Weyl. They mixed sand of known grain sizes to prepare mixtures with different sorting coefficients and measured the average porosity of different types of sand bodies. Assuming that sand in nature is randomly deposited, they established the relationship between porosity and the sorting coefficient So under moist surface conditions: Φ = 20.91 + 22.90 / So. The sorting coefficient is defined using Krask. The reservoir space at the beginning of sandstone reservoir deposition is only the intergranular pores. However, mixed sedimentary rocks have diverse reservoir space types. At the beginning of deposition, the sediments contain both terrigenous clastics and bioclastics. Among the bioclastics, the biocavity pores can directly provide reservoir space. The higher the bioclastic content, the higher the proportion of biocavity pores, which provides more reservoir space and the better the physical properties of the mixed sedimentary rock reservoir. However, the commonly used formula for calculating initial porosity does not include the porosity of biocavity pores. Therefore, the original empirical formula for calculating the initial porosity of reservoirs is not applicable to mixed sedimentary rock reservoirs.

[0003] Therefore, it is necessary to construct a simple, effective and applicable method for calculating the initial porosity of mixed sedimentary rocks in the study area, so as to quickly determine the initial porosity of mixed sedimentary rocks. Summary of the Invention

[0004] Based on the problems existing in the prior art, this invention proposes a method for determining the initial porosity of mixed sedimentary rocks. It combines the porosity of biological cavity pores with commonly used formulas for calculating the initial porosity of reservoirs to obtain a calculation formula applicable to the original porosity of mixed sedimentary rocks in the study area. This method enables rapid determination of the initial porosity of mixed sedimentary rocks, fully considers both terrigenous and biological debris, and improves the accuracy of calculating the initial porosity of mixed sedimentary rocks.

[0005] The technical solution of the present invention is as follows:

[0006] A method for determining the initial porosity of mixed sedimentary rocks includes the following steps:

[0007] (1) For mixed sedimentary reservoirs, a classical porosity model is established to obtain the initial porosity of terrigenous clastic rocks;

[0008] (2) The effective storage of snail body cavity pores in mixed sedimentary rock reservoirs was determined by simulation experiments, and the initial porosity of bioclastic debris in mixed sedimentary rocks was obtained.

[0009] (3) The initial porosity of terrigenous clastic rocks and the initial porosity of bioclastic rocks are combined to obtain the initial porosity of mixed sedimentary rocks.

[0010] Based on the above scheme, the method for obtaining the initial porosity of the mixed sedimentary rock in step (3) is as follows:

[0011] Φ 初始 =Φ 陆源 +Φ 生物 (16)

[0012] Where: Φ 陆源 Φ represents the initial porosity of terrigenous debris. 生物 The initial porosity of the pores in the body cavity.

[0013] Based on the above scheme, the step (1) of establishing a classical porosity model and obtaining the initial porosity of terrigenous clastic material specifically includes:

[0014] Establish a classical porosity model, in which medium-diameter particles are arranged in a square or rhomboid pattern;

[0015] The initial porosity is determined when the particle deposition mode is a cubic arrangement;

[0016] The initial porosity is determined when the particle deposition mode is a rhombic arrangement;

[0017] By studying the grain size characteristics of terrigenous clastic particles, the initial porosity of terrigenous clastic particles in mixed sedimentary rocks was obtained.

[0018] Based on the above scheme, the method for obtaining the initial porosity of terrigenous clastic rocks in mixed sedimentary rocks is as follows:

[0019] Φ 陆源 =20.91+22.90 / S o (10)

[0020] In the formula, S o Φ is the Trask sorting coefficient. 陆源 The initial porosity of terrigenous debris.

[0021] Based on the above scheme, the method for obtaining the initial porosity of bioclastic rocks in step (2) is as follows:

[0022] Snails were used as experimental samples;

[0023] The volume of the pores in the body cavity of snails can be determined using a formula method.

[0024] The volume percentage of pores in the body cavities of snails and the volume percentage of pores not filled with sediments were obtained through simulation experiments, and the initial porosity of bioclastic debris in mixed sedimentary rocks was obtained.

[0025] Based on the above scheme, the method for obtaining the initial porosity of bioclastics in mixed sedimentary rocks is as follows:

[0026]

[0027] In the formula, A1 is the snail content in bioclastic sediments, a1 and b1 are the radii of the body cavity pores, r is the logarithmic spiral, θ is the rotation angle, and V 螺总 P is the total volume of the screw. 储集孔 for Φ 生物 The initial porosity of the pores in the body cavity.

[0028] Compared with existing technologies, the method of this invention studies the volume and porosity of biological cavities through physical simulation experiments, formula calculations, and physical experiments. It combines the porosity of biological cavities with commonly used formulas for calculating initial reservoir porosity, ultimately obtaining a formula applicable to the calculation of the initial porosity of mixed sedimentary rocks in the study area. Specifically, the calculation method of this invention studies the cavities that directly provide reservoir space in the bioclastic aspect, obtaining a formula for calculating the volume of snail cavities. Then, through simulation experiments, the effective reservoir portion of the cavities is determined, resulting in a formula applicable to calculating the initial porosity of the bioclastic portion in mixed sedimentary rocks. Combining the calculation formulas for terrigenous and bioclastic materials yields a formula for calculating the initial porosity of mixed sedimentary rocks. Furthermore, this model has clear physical meaning, a simple structure, and comprehensively considers influencing factors, thus improving calculation accuracy. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the sediment particle stacking method and stress condition shown in Example 2 of the present invention (equal diameter particles arranged in a square);

[0030] Figure 2 This is a schematic diagram of the sediment particle stacking method and stress condition shown in Example 2 of the present invention (equal diameter particles arranged in a rhomboid shape);

[0031] Figure 3 This is a schematic diagram of the sediment particle stacking method and stress condition shown in Example 2 of the present invention (particles with a particle size of R1 are arranged in a square);

[0032] Figure 4 This is a calculation diagram of the rhomboid arrangement of particles with a particle size of R1 shown in Example 2 of the present invention;

[0033] Figure 5 This is a schematic diagram of the sediment particle stacking mode and stress condition shown in Example 2 of the present invention (particles with a diameter of R1 are arranged in a rhomboid shape);

[0034] Figure 6This is a calculation diagram of the rhomboid arrangement of particles with a particle size of R1 shown in Example 2 of the present invention;

[0035] Figure 7 This is a partial sample of 18 types of biological cavity pores shown in Example 3 of the present invention;

[0036] Figure 8 This is a schematic diagram showing the relationship between the volume of the green snail cavity and the total volume in the experimental method of Example 3 of the present invention;

[0037] Figure 9 This is a schematic diagram showing the proportion of body cavities of different snails in the experimental method illustrated in Example 3 of the present invention;

[0038] Figure 10 This is a schematic diagram of the logarithmic spiral plane in the formula method shown in Embodiment 3 of the present invention;

[0039] Figure 11 This is a schematic diagram of the three-dimensional logarithmic spiral curve in the formula method shown in Embodiment 3 of the present invention;

[0040] Figure 12 This is a comparison diagram of the volume of the body cavity orifice obtained by the experimental method and the formula method as shown in Example 3 of the present invention;

[0041] Figure 13 This is a diagram illustrating the tectonic experimental mixed sedimentary model of the present invention as shown in Example 3.

[0042] Figure 14 This is a diagram showing the relationship between the volume of the snail body cavity and the effective porosity in Example 3 of the present invention. Detailed Implementation

[0043] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not constitute any limitation thereof.

[0044] Example 1

[0045] This embodiment provides a method for determining the initial porosity of mixed sedimentary rocks, which is carried out according to the following steps:

[0046] (1) For mixed sedimentary reservoirs, a classical porosity model is established to obtain the initial porosity formula of terrigenous clastic rocks, as shown in the following formula:

[0047] Φ 陆源 =20.91+22.90 / S o (10)

[0048] In the formula, S o Φ is the Trask sorting coefficient. 陆源 Initial porosity of terrigenous debris;

[0049] (2) The effective storage capacity of snail body cavity pores in mixed sedimentary rock reservoirs was determined through simulation experiments, and the initial porosity of bioclastic debris in mixed sedimentary rocks was obtained, as shown in the following formula:

[0050]

[0051] In the formula, A1 is the snail content in bioclastic sediments, a1 and b1 are the radii of the body cavity pores, r is the logarithmic spiral, θ is the rotation angle, and V 螺总 P is the total volume of the screw. 储集孔 for Φ 生物 Initial porosity of the pores in the body cavity;

[0052] (3) The initial porosity of the mixed sedimentary rocks is obtained by combining the initial porosity of terrigenous clastic rocks and bioclastic rocks, as shown in the following formula:

[0053] Φ 初始 =Φ 陆源 +Φ 生物 (16)

[0054]

[0055] As a specific implementation plan, the specific implementation process of step (1) is as follows: First, a classical porosity model is established, in which the medium-diameter particles are arranged in a square or rhomboid pattern; second, the initial porosity is calculated when the particle deposition mode is cubic and when the particle deposition mode is rhomboid; finally, the initial porosity of the terrigenous clastic particles in the mixed sedimentary rocks of the study area is obtained by studying the particle size characteristics of the terrigenous clastic particles in the study area.

[0056] As a specific implementation plan, the specific implementation process of step (2) is as follows: First, select experimental samples, choosing 18 species of coelomic snails that are similar in appearance to modern Ganges snails; second, calculate the coelomic pore volume using experimental methods, and find that the species of snail has the largest influence on the proportion of the coelomic pore volume; next, calculate the coelomic pore volume using formula methods, and obtain the formula for the coelomic pore volume of snails as follows:

[0057]

[0058] Thread curve r = ae bθ To determine the values ​​of a and b, when θ = 0, the value of a is equal to the starting point r. To improve the accuracy of r, a vernier caliper is used for measurement. Once the value of a is determined, any value of θ can be chosen, and r can be measured accordingly. Substituting these values ​​into the thread curve formula will determine the value of b. For the same type of screw, the values ​​of a and b are the same, resulting in the same thread curve. For different types of screws, the thread curve differs depending on the values ​​of a and b. For example, the thread curve of a green screw is r = 0.1e.0.1θ The spiral curve of the whelk is elliptical, with r = 0.12e. 0.12θ The spiral curve of the small snail is elliptical, with r = 0.1e. 0.07θ a1 and b1 are the pore radius values. The diameter has been obtained in the previous experiment. Take half of the diameter length and substitute the value into formula (15) to obtain the volume of the biological cavity pore. The results of the formula method and the experimental method are compared to verify the accuracy and applicability of the formula method. Finally, the effective storage part of the cavity pore is obtained by simulation experiments, etc., and the initial porosity formula applicable to calculating the bioclastic part in mixed rocks is obtained.

[0059] As a specific implementation plan, the specific implementation process of step (3) is as follows: Based on the above study on the initial porosity of sedimentary terrigenous clastic particles and bioclastic particles, it is believed that the initial porosity of terrigenous clastic particles is still selected from the M. Scherer empirical formula Φ. 初始 =20.91+22.90 / S o Regarding bioclastics, research was conducted on the body cavity pores that directly provide storage space, resulting in a formula for calculating the volume of body cavity pores in snails. Furthermore, through simulation experiments, the effective storage portion of the body cavity pores was determined, leading to a formula applicable to calculating the initial porosity of bioclastic components in mixed sedimentary rocks. Combining the initial porosity of terrigenous and bioclastic materials, a formula for calculating the initial porosity of mixed sedimentary rocks was obtained, as follows:

[0060] Φ 初始 =Φ 陆源 +Φ 生物 (16)

[0061]

[0062] In the formula, S o Trask sorting factor, A1 is the snail content in bioclastic sediment (ostracods are not reflected in the formula because in the initial stage, the organism dies, the shells open and are filled by sediment, and cannot provide storage space), a1 and b1 are the pore radius values, r is the logarithmic spiral, θ is the rotation angle, and V 螺总 P is the total volume of the screw. 储集孔 for

[0063]

[0064] The method in Embodiment 1 of this invention is illustrated below, using the Bohai Bay Depression as the research area.

[0065] Example 2

[0066] Based on the method of Example 1, this example provides a method for calculating the initial porosity of terrigenous clastic rocks in the study area, including the following steps:

[0067] (1) Establishing a classical porosity model:

[0068] Assuming that all terrigenous detrital particles are approximately spherical, in a lake environment, a water film exists at the particle contact points, and fluid can flow freely in the interparticle pores. In the classical porosity model, medium-diameter particles are arranged in a square or rhomboid pattern, such as... Figure 1 As shown, in a square arrangement, the combined effects of the particles' own weight, the buoyancy of the water, and the supporting force and pressure from surrounding particles maintain a dynamic equilibrium among the sediment particles; for example... Figure 2 As shown, in a rhomboid arrangement, the sediment particles are subjected to increased forces from the surrounding particles, and under the combined action, the sediment particles are also in a dynamic equilibrium state.

[0069] (2) The formula for calculating the initial porosity of terrigenous clastic rocks in the mixed sedimentary rocks of the study area is derived.

[0070] (a) When the particle deposition pattern is cubic, the initial porosity is calculated.

[0071] Assuming the sediment is composed of particles with a diameter of R1, such as Figure 3 As shown, the initial porosity is calculated when the particle deposition mode is a cubic arrangement.

[0072] When the particle radius is R1, such as Figure 4 As shown, the distance between the centers is 2R1, and the volume of the cube is V. 正 for:

[0073] V 正 =(2R1) 3 (1)

[0074] The volume of the granular part consists of 8 sub-particles V 粒 The volume is:

[0075]

[0076] interparticle volume V 间 for:

[0077] V 间 =V 正 -V 粒 (3)

[0078] The porosity Φ in this arrangement pattern is:

[0079] Φ=V 间 / V 正 (4)

[0080] The porosity was calculated to be 47.64% when the particles were arranged in a cubic pattern and deposited using formulas (1, 2, 3, 4).

[0081] (b) When the particle deposition pattern is rhombic arrangement, the initial porosity is calculated.

[0082] like Figure 5-6 As shown, let the side length of the rhombus be m, ∠BAD=∠BAH=θ, BY is perpendicular to plane ADHG, BX and BZ are perpendicular to AD and AH respectively, BX=BZ=msinθ, AZ=AX=mcosθ, AZ is perpendicular to plane ZBY, then AZ is perpendicular to ZY, therefore:

[0083]

[0084] S ADGH =m 2 sinθ (7)

[0085]

[0086] In the formula, V 菱形 Let S be the volume of the rhombus. ADGH Let y be the area of ​​plane ADHG, AY be the length from vertex A to Y, BY be the length from vertex B to Y, AB be the length from vertex A to B, and AY be the length from vertex A to Y.

[0087] The distance between the centers of the circles is 2R1, so the side length of the rhombus is m = 2R1, and the volume of a single particle is... Therefore, the porosity of the rhombus is:

[0088]

[0089] After deriving and calculating using formulas (5), (6), (7), (8), and (9), it was found that... The porosity is independent of the particle size and varies with the value of θ. When θ is 60°, the porosity has a minimum value of 25.95%. Combined with the fact that the porosity is 47.64% when the cube is arranged above, the initial porosity range in particles of equal size is 25.95% to 47.64%.

[0090] (c) Formula for calculating the initial porosity of terrigenous clastic rocks in the study area

[0091] The actual situation of clastic particles deposited in reservoirs is more complex. Through the study of the grain size characteristics of terrigenous clastic particles in the study area, the clastic particles as a whole have an unequal grain size sandy structure. Clastic particles of different sizes are mixed and deposited. Evaluation indexes are established by the characteristics of grain size distribution curves.

[0092] The commonly used formula is the empirical formula (10) proposed by M. Scherer (1988) for calculating the initial porosity of the reservoir:

[0093] Φ初始 =20.91+22.90 / S o (10)

[0094] S o =P 25 / P 75 (11)

[0095] In the formula, S o P is the Trask sorting coefficient. 25 and P 75 The particle size values ​​(mm) at 25% and 75% of the particle size accumulation curve are shown below. S was obtained using image particle size analysis software. o The value of is substituted into formula (10) to obtain the initial porosity at that depth.

[0096] Φ 初始 The value of .

[0097] Based on the above research on the porosity of equal-sized particles and considering the actual characteristics of clastic particle size, it is believed that the empirical formula of M. Scherer (1988) is more suitable. That is, the formula for calculating the initial porosity of terrigenous clastics in the mixed sedimentary rocks of the study area is Φ 初始 =20.91+22.90 / S o .

[0098] Example 3

[0099] Based on the calculation method of Example 1, this example provides a method for calculating the initial porosity of biological debris. Specifically, it includes a method for calculating the porosity of body cavity pores. By simulating sediment burial conditions through experiments (water injection method), formula method, and structural physics experiments, the volume ratio of body cavity pores in snails and the volume ratio of body cavity pores not filled by sediments are investigated, and the porosity of body cavity pores is obtained.

[0100] Based on core photographs and thin sections of casts from the study area, it is believed that two species of organisms, snails and ostracods, were present in the study area during the depositional period, with snails being more abundant than ostracods. Previous studies on paleontological fossils in the study area suggest that the genus *Gangesia* held an absolute numerical advantage (Pan Wenjing, 2020). Influenced by lake wave action, snails and ostracods accumulated along the shoreline. Exposed to the surface due to a lack of suitable living conditions, these organisms gradually died, their internal soft tissues decomposed, leaving only the exoskeleton. The preservation of the coelomic pores of organisms is related to the size, structure, and mineral composition of the organisms. In the study area, snails range in height from 0.5 to 20.0 mm, and their calcareous shells have strong compressive strength. Their unique and complex enclosed shell structure can reduce the infilling of other sediments. Ostracods are half small, ranging in length from 0.4 to 2.0 mm, and have a relatively simple structure, mainly composed of two shell lobes. After the organism dies, the two shells open, and the coelomic pores are easily filled. Only under atmospheric water dissolution and subsequent organic acid dissolution can they provide reservoir space. Therefore, it is believed that only the coelomic pores of snails in the study area have a reservoir function. The coelomic pores of snails can directly provide reservoir space and greatly improve reservoir properties.

[0101] (1) Selection of experimental samples

[0102] Based on the types of snails in the study area, it is believed that modern *Viviparus chinensis* structurally corresponds to the *Gangesiana* genus in the sedimentary area. To obtain a suitable formula for calculating the pore volume of snail cavities and improve accuracy, 18 species, totaling 180 individuals, of modern snails with similar appearance to *Gangesiana* were selected. Figure 7 As shown, the types of snails are a – Red Snail; b – Ancient Snail; c – Green Snail; d – Field Snail; e – White Jade Snail; f – Spotted Snail; g – Flower Snail; h – Zebra Snail; i – Small Onion Snail; j – Gray Flat Snail; k – Torch Snail; l – Striped Spotted Snail; m – Small Field Snail; n – Cat's Eye Snail; o – Cone Snail; p – Fragrant Snail; q – Red Mouth Snail; r – Spiny Snail.

[0103] (2) Experimental method for determining the volume of body cavity orifices

[0104] (a) Experimental equipment

[0105] Select graduated cylinders with specifications of 100ml, 20ml, 50ml and 10ml, beakers of 1000ml and 500ml, 5ml syringe, 3ml dropper (accurate to 0.05ml), infusion tubing, a certain amount of water and ruler, and other experimental equipment.

[0106] (b) Experimental Principles and Procedures

[0107] The volume of the coelomic pore was determined by injecting water into the pore using a combination of a 5ml syringe, a syringe tubing, and a 3ml dropper. The pore was then placed in a graduated cylinder or beaker containing a predetermined volume of water, and the change in liquid level was recorded. The portion showing the change in liquid level was then slowly removed using a 5ml syringe and a 3ml dropper; this volume represents the snail's total volume. Total volume - coelomic pore volume = shell volume; coelomic pore volume percentage = coelomic pore volume / total volume, as shown in Table 1.

[0108] Table 1. Data on the percentage of body cavity volume in some snails obtained using experimental methods.

[0109]

[0110]

[0111]

[0112] The pore volume of the body cavity was determined for the same species of snail. Taking the green snail as an example, experimental data shows that the pore volume of the green snail accounts for 57.39% to 70.59% of the total volume, as shown in Table 2, with an average proportion of 64.32%. When the volume of the green snail is smaller, the measured proportion of the body cavity will also be smaller. This error may be related to the size of the tail end of the body cavity in snails. The proportion of the body cavity does not vary significantly for the same species of snail. Figure 8 As shown, there is a linear positive correlation between the volume of the coelomic pores and the total volume, and the proportion of coelomic pore volume varies significantly among different snail species, such as... Figure 9 As shown, the proportion of body cavity pores in 18 snail species ranged from 36.07% to 88.89%. Among them, the proportion of body cavity volume in *Sinocyclocheilus rubrifolius* and *Sinocyclocheilus spp.* was relatively small, with average values ​​of 36.32% and 36.57%, respectively, while the proportion of body cavity volume in *Viburnum chinense* and *Sinocyclocheilus zebratus* was relatively large, with average values ​​of 83.0% and 85.12%, respectively. Therefore, the species of snail is the most significant factor affecting the proportion of body cavity pore volume.

[0113] Table 2 Experimental data on the volume ratio of the pores of the green snail body.

[0114]

[0115] (3) Formula method for determining the volume of body cavity orifices

[0116] Based on the thread curve characteristics of the snail samples, a multi-faceted comparative study was conducted, such as... Figure 10 As shown, the logarithmic spiral equation is chosen as r = ae bθ To find the equation on the plane; such as Figure 11 As shown, establish a three-dimensional coordinate system. A point m in space rotates around the Z-axis with an angular velocity w on a spiral surface, while simultaneously rising with a linear velocity v in the positive direction parallel to the Z-axis. The trajectory of this point m is a spiral.

[0117] Let the coordinates of M be (0,0,0) at time t = 0. Then the coordinates of M at time t are (X, Y, Z), where X = vt × cos(wt), Y = vt × sin(wt), and Z = vt.

[0118] Let wt = θ, then the parametric equation of the helix is: X = cosθae bθ Y = sinθae bθ Z = r = ae bθ， In the formula, θ is the rotation angle; the length is calculated using calculus, taking a infinitesimal element ds, the arc length formula is as follows:

[0119]

[0120] Let X = cosθae bθ Y = sinθae bθ Z = r = ae bθ Substituting into the formula, we obtain the formula for the arc length:

[0121] In the formula, r represents a logarithmic spiral.

[0122] The cross-section of the cavity pore of the experimental snail sample is approximately elliptical (a circle is a special type of ellipse), and the formula for an ellipse is as follows:

[0123]

[0124] In the formula, a is the length of the major semi-axis and b is the length of the minor semi-axis.

[0125] Let the area of ​​the ellipse be πa1b1, where a1 is the length of the major semi-axis and b1 is the length of the minor semi-axis. Let the area of ​​the circle be πr. 2 The circle exists only when a1 = b1, therefore the base area of ​​the screw opening cross-section is πa1b1. Since the calculated arc lengths are all the outermost arc lengths, we can calculate the volume arc length S. 1 / 2 It should be half the length of the outermost arc. The formula for the actual arc length is as follows:

[0126]

[0127] Based on formulas (3), (4), and (5) and the basic characteristics such as the volume of a cone, the volume formula for the cavity of a spiral is considered to be:

[0128]

[0129] Thread curve r = ae bθTo determine the values ​​of a and b, when θ = 0, the value of a is equal to the starting point r. To improve the accuracy of r, a vernier caliper is used for measurement. Once the value of a is determined, any value of θ can be chosen, and r can be measured accordingly. Substituting these values ​​into the thread curve formula will determine the value of b. For the same type of screw, the values ​​of a and b are the same, resulting in the same thread curve. For different types of screws, the thread curve differs depending on the values ​​of a and b. For example, the thread curve of a green screw is r = 0.1e. 0.1θ The spiral curve of the whelk is elliptical, with r = 0.12e. 0.12θ The spiral curve of the small snail is elliptical, with r = 0.1e. 0.07θ a1 and b1 are the pore radius values. The diameter has been obtained in the previous experiment. Take half of the diameter length and substitute the values ​​into formula (15) to obtain the pore volume of the organism, as shown in Table 3.

[0130] Table 3. Data on the pore volume of different snails using the formula method.

[0131]

[0132]

[0133]

[0134]

[0135] (4) Comparison of results between formula method and experimental method

[0136] By comparing two methods for determining the volume of the body cavity pores, the experimental method and the formula method yielded small errors in obtaining the volume of the body cavity pores of organisms, with an error range of 1.32% to 10.04%, which is within a reasonable range. Taking each type of snail (number 1) as an example, ... Figure 12 As shown, the volume ratio of the biological cavity obtained by the experimental method and the formula method is roughly the same, which not only proves the rationality of the two methods for calculating the volume, but also further illustrates the accuracy and applicability of the formula method.

[0137] (5) Initial porosity of biological cavities

[0138] During the initial deposition and burial process of snails, some sediment enters the body cavity pores, leaving the unfilled portion as storage space. Understanding the sedimentary environment of the study area, such as... Figure 13As shown, the sedimentary environment at that time was simulated. Relying on the "structural physics simulation experimental equipment" independently developed and designed by the Shandong Provincial Key Laboratory of Geology and Reservoirs of China University of Petroleum (East China), fine sand, medium sand and silt-grade detrital particles were mixed with snail organisms under moist conditions (wave washing) and subjected to multiple lateral and longitudinal tectonic movements. The experiment then obtained the volume of sediment filling the cavities under burial conditions. The volume of the remaining unfilled cavities is the effective storage space. The total snail volume = snail cavity pore volume + snail shell volume, the proportion of cavity pores = snail cavity pore volume / total snail volume, and the porosity = unfilled cavity pore volume / snail cavity pore volume, as shown in Table 4.

[0139] Table 4. Data on the percentage of storage space in some body cavity pores during physical simulation experiments.

[0140]

[0141]

[0142]

[0143]

[0144] The experimental results show that different species of snails, under the same burial conditions, have different volumes of unfilled coelom pores. The proportion of volume providing storage space in the coelom pores, i.e., the porosity, ranges from 46.27% to 90.00%. Even within the same species of snail, there are slight differences in coelom pore porosity during burial, mainly reflected in the size of the coelom pores. Larger pores have larger openings and are relatively easier to fill, while smaller pores have smaller openings and are relatively more difficult to fill. Figure 14 As shown, taking the whelk as an example, it can be seen that there is a negative correlation between the volume of the body cavity pores and the effective porosity.

[0145] The effective storage capacity of snail body cavities in mixed sedimentary rock reservoirs was determined through simulation experiments, and the initial porosity of bioclastic debris in the mixed sedimentary rocks was obtained, as shown in the following formula:

[0146]

[0147] In the formula, A1 is the snail content in bioclastic sediments, a1 and b1 are the radii of the body cavity pores, r is the logarithmic spiral, θ is the rotation angle, and V 螺总 P is the total volume of the screw. 储集孔 for Φ 生物 The initial porosity of the pores in the body cavity.

[0148] Example 4

[0149] Based on the calculation method of Example 1, this example provides a method for determining the initial porosity of mixed sedimentary rocks. Specifically, in Examples 2 and 3, through the study of the initial porosity of terrigenous clastic particles and bioclastic particles in sediments, it is believed that the initial porosity of terrigenous clastic particles still uses the M. Scherer empirical formula Φ. 初始 =20.91+22.90 / S o In the area of ​​bioclastics, research was conducted on the body cavity pores that directly provide storage space, resulting in a formula for calculating the volume of body cavity pores in snails. Furthermore, through simulation experiments, the effective storage portion of the body cavity pores was determined, yielding an initial porosity Φ suitable for calculating the bioclastic portion in mixed sedimentary rocks. 初始 The formula combines the calculation formulas for terrigenous clastic rocks and bioclastic rocks to obtain a formula for calculating the initial porosity of mixed sedimentary rocks.

[0150] Φ 初始 =Φ 陆源 +Φ 生物 (16)

[0151]

[0152] In the formula, S o Trask sorting factor, A1 is the snail content in bioclastic sediment (ostracods are not reflected in the formula because in the initial stage, the organism dies, the shells open and are filled by sediment, and cannot provide storage space), a1 and b1 are the pore radius values, r is the logarithmic spiral, θ is the rotation angle, and V 螺总 P is the total volume of the screw. 储集孔 for

[0153] Φ 陆源 Φ represents the initial porosity of terrigenous debris. 生物 The initial porosity of the pores in the body cavity.

[0154] Using the method of this embodiment, the volume and porosity of biological cavities are studied through physical simulation experiments, formula calculations, and physical experiments. The porosity of biological cavities is combined with commonly used formulas for calculating the initial porosity of reservoirs, and finally a formula for calculating the original porosity of mixed sedimentary rocks in the study area is obtained, which has broad application value.

[0155] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method of determining initial porosity of a mixtite, characterized by, The method comprises the following steps: (1) establishing a classical porosity model for the mixed rock reservoir to obtain an initial porosity formula of terrigenous clastic particles; (2) determining the effective reservoir of the spiral body cavity pores in the mixed rock reservoir through simulation experiments, and then obtaining the initial porosity of bioclasts in the mixed rock; (3) combining the initial porosity of terrigenous clastic particles and the initial porosity of bioclasts to obtain the initial porosity of the mixed rock; The method for obtaining the initial porosity of the mixed rock in step (3) is: Φinitial = Φland + Φbio (16) where: 陆源 Φland is the initial porosity of the terrigenous clastics, 生物 Φbio is the initial porosity of the organism cavities; The step of establishing the classical porosity model and obtaining the initial porosity of terrigenous clastic particles in step (1) specifically comprises: establishing a classical porosity model, and the classical porosity model is a square or rhombic arrangement of medium-diameter particles; calculating the initial porosity when the particle deposition mode is a cubic arrangement; calculating the initial porosity when the particle deposition mode is a rhombic arrangement; obtaining the initial porosity of terrigenous clastic particles in the mixed rock through research on the particle size characteristics of terrigenous clastic particles; The method for obtaining the initial porosity of bioclasts in the mixed rock is: In the formula, A1 is the content of the spiral in the bioclast in the deposit, a1 and b1 are the values of the body cavity orifice radius, r is the logarithmic spiral, θ is the rotation angle, V 螺总 is the total volume of the spiral, P 储集孔 is the Φ 生物 is the initial porosity of the organism cavity hole.

2. The method of determining initial porosity of a mixture rock according to claim 1, wherein, The method for obtaining the initial porosity of terrigenous clastic particles in the mixed rock is: Φ 陆源 = 20.91 + 22.90 / S o (10) where S o is the Trask sorting coefficient, Φ 陆源 is the initial porosity of terrigenous clastics.

3. The method of determining initial porosity of a mixture rock according to claim 1, wherein, The method for obtaining the initial porosity of bioclasts in the mixed rock in step (2) is: selecting a spiral as the experimental sample; calculating the volume of the spiral body cavity pores through a formula method; obtaining the volume proportion of the spiral body cavity pores and the volume proportion of the body cavity pores not filled with sediments through simulation experiments, and obtaining a formula suitable for the initial porosity of bioclasts in the mixed rock.

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