Neutron porosity scale well

Abstract

The invention relates to the technical field of oil well logging, in particular to a neutron porosity scale well which comprises a well body made of natural rock, and a plurality of small artificial holes are evenly drilled in the well body. According to the method, manual drilling is conducted on the natural rock well body, the hole diameter and porosity can be controlled, the porosity uniformity and overall stability of the scale well can be effectively improved by reasonably designing the size of the well body, the layout and arrangement mode of small holes and the like, the porosity within a certain value range is constructed, the multi-porosity calibration requirement of a laboratory is met, and the calibration efficiency is improved. The structure is stable and processing is easy.

Description

Technical Field

[0001] This application relates to the technical field of oil logging, and particularly relates to a neutron porosity calibration well. Background Art

[0002] Neutron porosity calibration wells play an important role in the fields of oil exploration and geological research. Their main function is to provide a calibration environment for neutron logging instruments, thereby ensuring the accuracy of logging data. In recent years, with the continuous progress of oil and gas resource development technologies, the accuracy requirements for porosity measurement by neutron logging instruments have been increasing day by day, which has further promoted the development of neutron porosity calibration well technology. Neutron porosity calibration wells can simulate the formation environment and provide stable calibration conditions for logging instruments, which is of great importance for improving the reliability of logging data and plays an irreplaceable role in fields such as oil exploration, geological surveys, and mineral resource development. To meet the needs of different application scenarios, the technical requirements for neutron porosity calibration wells in the industry are also constantly increasing, especially in terms of porosity range, structural stability, and processing convenience. Currently, the common methods for constructing neutron porosity calibration wells in the industry mainly include the natural rock block method, the stacking method, the rock block method, and the water well method. The natural rock block method directly uses natural rocks (such as limestone, sandstone, dolomite, etc.) as the main body of the calibration well; the stacking method forms a composite structure by stacking rock particles or mixing sand and gravel; the rock block method is composed of multiple layers of rock plates stacked together; the water well method is a special structure based on a pure water environment. These methods all aim to simulate the formation porosity through different construction methods, so as to provide a calibration basis for neutron logging instruments. However, the above methods have many defects in practical applications. The natural rock block method is limited by the porosity range of natural rocks themselves (usually 0.1 p.u.), and it is difficult to meet the needs of multi-porosity calibration in the laboratory; the structure formed by the stacking method is loose, the porosity range that can be simulated is limited (13 - 40 p.u.), and its long-term stability is poor; the rock block method is difficult to prepare large-sized rock plates, the construction is complex, and problems such as fragmentation and sliding are likely to occur during long-term use; the water well method is only applicable to a single high-porosity environment (100 p.u.), and its application scenario is very limited. Therefore, how to construct a neutron porosity calibration well with a wide porosity range, stable structure, and easy processing has become an urgent technical problem to be solved. Summary of the Invention

[0003] In order to solve the problems existing in the construction methods of existing neutron porosity calibration well groups, this application provides a new neutron porosity calibration well.

[0004] The neutron porosity calibration well provided by this application adopts the following technical solution: A neutron porosity calibration well includes a well body composed of natural rock, and a plurality of artificial small holes are uniformly drilled on the well body.

[0005] By adopting the above - mentioned solution, artificial drilling can be carried out on the natural rock - block wellbore to control the aperture and porosity. By reasonably designing the size of the wellbore, the layout and arrangement of small holes, etc., the porosity uniformity and overall stability of the calibration well can be effectively improved, constructing a porosity within a certain value range to meet the calibration requirements of multi - porosity in the laboratory, with a stable structure and easy to process.

[0006] As a further improvement of the above - mentioned technical solution, the wellbore includes a plurality of rock single - blocks, and the rock single - blocks are overlapped and fixedly connected to each other.

[0007] By adopting the above - mentioned solution, the wellbore is divided into a plurality of rock single - blocks, which is convenient for processing and assembly, and can also better ensure the accuracy, perpendicularity and position accuracy of artificial small holes, etc.

[0008] As a further improvement of the above - mentioned technical solution, the outer contour of the wellbore is a cylinder or a regular polyhedron.

[0009] By adopting the above - mentioned solution, a specific - shaped outer form can make the wellbore easy to process, have a suitable weight, and be conducive to on - site hoisting.

[0010] As a further improvement of the above - mentioned technical solution, the artificial small holes are arranged along the axial direction of the wellbore.

[0011] By adopting the above - mentioned solution, the artificial small holes are arranged along the axial direction of the wellbore to ensure consistency with the pore direction of the natural rock itself.

[0012] As a further improvement of the above - mentioned technical solution, the radial thickness of the wellbore is T, T≥650mm; the axial height is H, 1.5≤H≤1.7m.

[0013] As a further improvement of the above - mentioned solution, the diameter of the artificial small hole is d, 20mm≤d≤30mm.

[0014] As a further improvement of the above - mentioned technical solution, in the cross - section of the wellbore, the artificial small holes are evenly distributed in the form of multiple minimum units, and the artificial small holes in each minimum unit are arranged in the form of a regular polygon or concentric circles.

[0015] By adopting the above - mentioned solution, the layout of artificial small holes in a specific - shaped close - packed manner maximizes the circumferential uniformity and radial uniformity, and the calibration well can maintain the uniformity of pore distribution within any angular range.

[0016] As a further improvement of the above - mentioned technical solution, the distance between the artificial small hole and the wellbore of the wellbore is not less than 10mm, and the distance between the artificial small hole and the outer wall of the wellbore is not less than 10mm.

[0017] By adopting the above scheme, it is avoided that the artificial small holes coincide with the wellbore or the edge of the outer wall of the wellbore, resulting in notch holes for the artificial small holes, and it is ensured that the artificial small holes are complete holes.

[0018] In summary, the present application includes at least one of the following beneficial technical effects: 1. By uniformly drilling artificial small holes in natural rock blocks, a neutron porosity calibration well with a wide porosity range (5 - 50 p.u.), stable structure and easy processing is constructed. This calibration well can meet the requirements of neutron instrument calibration in the laboratory environment.

[0019] 2. By reasonably designing the size and outer contour of the well body, the processing difficulty and cost of the calibration well are effectively controlled, and the long-term stability is also improved.

[0020] 3. By adopting the layout of artificial small holes in a hexagonal close-packed manner, the calibration well can maintain the uniformity of pore distribution within any angular range, thereby improving the reliability of logging data. Description of the Drawings

[0021] Figure 1 is the top view of the neutron porosity calibration well of the embodiment of the present application.

[0022] Figure 2 is Figure 1 the enlarged view of part A in

[0023] Figure 3 is the three-dimensional view of the neutron porosity calibration well of the embodiment of the present application.

[0024] Description of the reference numerals: 1. Well body; 2. Artificial small hole; 3. Single rock block; 4. Wellbore. Detailed Embodiments

[0025] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the attached Figures 1 to 3 , and the described embodiments are only possible technical implementations of the present invention, not all possible implementations. Those skilled in the art can fully combine the embodiments of the present invention to obtain other embodiments without creative labor, and these embodiments are also within the protection scope of the present invention. Aiming at the problems of narrow porosity range, poor structural stability, and large processing difficulty existing in the existing neutron porosity calibration wells, the present application mainly adopts the following scheme to achieve the effect of constructing a neutron porosity calibration well with a wide porosity range, stable structure and easy processing by uniformly drilling small holes in natural rock blocks. The following is a further detailed description of the present application.

[0026] An embodiment of the present application discloses a neutron porosity calibration well. As the name implies, neutron porosity logging is used to measure the formation porosity. Therefore, a standard porosity calibration well is to simulate various different porosities through various methods.

[0027] As Figure 1 and Figure 3 As shown, the neutron porosity calibration well of this embodiment includes a wellbore 1 composed of natural rock blocks, and a plurality of artificial small holes 2 are uniformly drilled on the wellbore 1. Natural rock itself has certain pores. Generally, it is considered that the natural pores of pure limestone and granite are 0.1 p.u. However, due to the relatively small inherent porosity of natural rock, it cannot meet the laboratory multi-porosity calibration requirements. In this embodiment, by artificially creating some pores, a standard well with various different pores can be formed. The artificial small holes 2 are arranged along the axial direction of the wellbore to ensure that they are consistent with the pore direction of the natural rock itself. It should be noted that on the premise that the existing process can be satisfied, it is required that the drilled holes be as small as possible to make the pores of the calibration well as uniform as possible. The holes are drilled in a dense pattern, and the aperture of the small holes in the same calibration well is unified.

[0028] Artificial drilling can control the aperture and porosity. By reasonably designing the size of the wellbore, the layout and arrangement of the small holes, etc., the porosity uniformity and overall stability of the calibration well can be effectively improved, a certain range of porosities can be constructed to meet the laboratory multi-porosity calibration requirements, and the structure is stable and easy to process. While the traditional rock block method requires the preparation of large-sized thin rock plates, and the porosity simulation is realized by stacking layer by layer. This stacking method has poor structural stability (seismic performance, long-term stability performance, etc.). The artificial drilling of this embodiment has obvious advantages in processing cost compared with the stacking method and the rock block method.

[0029] (1) The structural design of the neutron porosity calibration well is specifically reflected in several aspects such as the radial thickness design of the calibration well, the axial height design of the calibration well, the outer contour design of the calibration well, and the layered design.

[0030] (1) Radial thickness design of the calibration well: The radial thickness of the wellbore 1 is T, and it is required to satisfy T≥650mm (the thinnest part of the special-shaped contour meets this size) to meet the condition of simulating the "uniform infinite large" formation. Through numerical simulation (such as MCNP) and empirical value verification, the radial thickness of the calibration well, 650mm is the comprehensive embodiment of numerical simulation and empirical values. Generally, the neutron detection depth does not exceed 600mm.

[0031] (2)Axial height design of the calibration well: The axial height of the well body 1 is H. Since the source distances of various compensated neutron instruments are different, according to experience, it is generally appropriate to take a height of 1.5 - 1.7 m (i.e., 1.5 ≤ H ≤ 1.7 m). The specific value needs to be adjusted according to the different source distances of various compensated neutron instruments. For example, for an instrument with a larger source distance, the well body height can take the upper limit value of 1.7 m; for an instrument with a smaller source distance, the well body height can take the lower limit value of 1.5 m.

[0032] (3)Shape contour design of the calibration well: Common shape contours include circular, square (regular quadrilateral), chamfered square (or regular octagon), regular hexagon, etc.; under the same design parameters, the circular shape has the advantage of the smallest weight (for example, taking the overall limestone module with a 200 mm wellbore, 650 mm formation thickness, 1.5 m height, and a density of 2.7 g / cm 3 as an example, the weight of the well body with a circular contour is 7030 kg, while the weight of the well body with a square contour is 8985 kg), but its circular outer contour is not convenient for processing and is not conducive to on-site hoisting; regular polygons (such as chamfered square or regular octagon) achieve a better balance between weight and processing convenience. Therefore, regular polygons are preferably used as the shape contour of the well body. The more sides the regular polygon has, the closer it is to a circle, but the processing difficulty also increases accordingly. The chamfered square (or regular octagon) is better than the regular hexagon, and finally the square. In this embodiment, the chamfered square (i.e., regular octagon) contour is preferably used.

[0033] (4)Laminated design: Limited by the overall technological level of the existing stone processing industry, it is difficult to drill a series of artificial small holes on a 1.5 - 1.7 m high integral natural rock block. Therefore, the well body 1 is generally divided into 3 - 4 sections in the height direction for processing, that is, the well body is divided into multiple rock single blocks 3. Generally, the height h of a single rock single block is about 400 mm, which is convenient for processing and assembly, and can also better ensure the accuracy, perpendicularity, and position accuracy of the artificial small holes, etc. After the segmented processing of the rock single blocks 3, they are formed into a complete neutron calibration well by bonding. The depth of the artificial small holes 2 penetrates the entire rock single block 3 to ensure the formation of a continuous pore structure after stacking. The bonding material can be epoxy resin or other high-strength adhesives to ensure the connection strength without affecting the overall performance of the well body. The connection surfaces between adjacent rock single blocks need to be polished to improve the tightness and flatness of the connection.

[0034] In the structural design of this calibration well, the well body formed by stacking multiple rock blocks, combined with uniformly drilled artificial small holes, can effectively improve the porosity uniformity and overall stability of the calibration well. At the same time, the reasonably designed well body size and outer contour can reduce the processing difficulty and cost on the premise of ensuring structural stability. For example, the well body with a chamfered square contour weighs only about 80% of the well body with a regular quadrilateral contour, significantly reducing the transportation and hoisting difficulties.

[0035] (2) Porosity design of neutron calibration well Calibrating the compensated neutron logging tool means establishing the response relationship between the long and short source distance count ratio (SHR) of the tool and the porosity value (φ). The two are positively correlated (non-linearly positively correlated). Generally, at least 5 - 6 points are selected for testing in the range of 0.1 - 100 p.u. It is known that the porosity of natural rock blocks is about 0.1 p.u., and the porosity of water wells is 100 p.u. To facilitate the establishment of the multiple response relationship between the long and short source distance count ratio (SHR) and the porosity value (φ), referring to the porosity value design of existing standard calibration wells, it is preferably established: neutron standard wells of 50 p.u., 35 p.u., and 20 p.u. The manufactured neutron calibration wells have a wide porosity range (5 - 50 p.u.), which can meet the calibration requirements of neutron instruments in the laboratory environment.

[0036] (3) Structural design of artificial small holes (1) Setting the diameter of artificial small holes: From the perspective of improving the porosity uniformity of the neutron calibration well, to ensure the circumferential uniformity (the porosity distribution is uniform within any angular range) and radial uniformity (the porosity distribution is uniform in any area from the inside to the outside) of the neutron calibration well, a series of artificial small holes 2 drilled on the well body 1 should have a small enough diameter (the smaller the diameter of the small holes, the more uniform the distribution, and the better the circumferential and radial uniformity); from the perspective of processing technology, too small a diameter of the small holes also means higher processing difficulty. Considering the existing stone drilling processing methods and the existing process level, the diameter d of the artificial small holes is designed to be 20 - 30 mm (20 mm ≤ d ≤ 30 mm), and preferably 30 mm in this embodiment to achieve better porosity uniformity on the premise of ensuring processing feasibility. The shape of the artificial small holes 2 is cylindrical, and the hole wall is smooth without obvious burrs or cracks.

[0037] (2) Setting the close-packed arrangement of artificial small holes: In this embodiment, to further improve the uniformity of the porosity distribution, within the cross-section of the well body 1, the artificial small holes 2 are evenly distributed in the form of multiple minimum units, and each artificial small hole 2 within the minimum unit is arranged in the form of a regular polygon or concentric circles.

[0038] The optional schemes for the minimum unit close-packed small holes in a plane are: hexagonal (honeycomb) close packing, concentric circle close packing, and square close packing. Square close packing: The radial uniformity is average (the arrangement of small holes is more uneven closer to the wellbore 4), and the circumferential uniformity is poor. Concentric circle close packing: The circumferential uniformity is excellent, and the radial uniformity is poor; Hexagonal close packing: The radial uniformity is excellent, and the circumferential uniformity is average. As Figure 2 shown, in this embodiment, the arrangement of the artificial small holes 2 on the well body 1 is preferably arranged in a hexagonal close-packed manner, that is, with the wellbore 4 as the center, hexagonal close-packed small holes are made in the plane. Taking the example of drilling 30mm artificial small holes on the well body, for example, when the target porosity is 35 p.u., the side length L of the hexagon is about 48.29mm; when the target porosity is 50 p.u., the side length L of the hexagon is about 40.40mm; when the target porosity is 20 p.u., the side length L of the hexagon is about 63.88mm. In addition, the arrangement of the artificial small holes also needs to meet the distance requirements from the wellbore and the outer wall of the well, that is, the distance between the artificial small hole and the wellbore is not less than 10mm, and the distance between the artificial small hole and the outer wall of the well body is not less than 10mm, so as to avoid the adverse impact of the pore structure on the strength of the well body.

[0039] In this embodiment, by uniformly drilling artificial small holes on the natural rock block, a neutron porosity calibration well with a wide porosity range (5 - 50 p.u.), stable structure and easy to process is constructed. This calibration well can meet the needs of neutron instrument calibration in the laboratory environment, and its porosity range can reach 5 - 50 p.u., which is significantly better than the existing methods. By adopting the layout of artificial small holes in a hexagonal close-packed manner, the calibration well can maintain the uniformity of pore distribution within any angular range, thereby improving the reliability of logging data. In addition, by reasonably designing the size and outer contour of the well body, the processing difficulty and cost of the calibration well are effectively controlled, and the long-term stability is also improved. This embodiment provides an efficient, economical and reliable scheme for constructing a neutron porosity calibration well, providing important support for the development of neutron logging technology.

[0040] In this embodiment, taking the manufacture of a neutron calibration well with a porosity of 35 p.u. as an example, the drilling scheme and each parameter are as follows: Porosity 35 p.u.

[0041] Wellbore diameter: 200mm.

[0042] Lithology: Limestone.

[0043] Well body height: 1600mm.

[0044] Well body stratification: 1600mm / 400mm = 4 layers.

[0045] Drilling diameter: 30mm.

[0046] Artificial small hole arrangement method: hexagonal dense arrangement, with the side length of the hexagon being approximately 48.29 mm.

[0047] Drilling plan: Make a hexagonal close-packed artificial small hole in the plane with the wellbore as the center. If the artificial small hole overlaps with the wellbore or the outer wall of the well, or the distance between the edge of the artificial small hole and the wellbore or the well wall is less than 10 mm, this artificial small hole is not processed.

[0048] The above are all preferred embodiments of the present application. The protection scope of the present application is not limited thereby. Therefore, all equivalent changes made according to the structure, shape, and principle of the present application should be covered within the protection scope of the present application.

Claims

1. A neutron porosity calibration well, characterized in that: The invention comprises a well body (1) formed of natural rock, wherein a plurality of artificial small holes (2) are evenly drilled on the well body (1).

2. The neutron porosity calibration well according to claim 1, characterized in that: The well body (1) comprises a plurality of rock monoliths (3), wherein the rock monoliths (3) are mutually superimposed and fixedly connected.

3. The neutron porosity calibration well according to claim 1, characterized in that: The outer contour of the well body (1) is a cylinder or a regular polygon.

4. The neutron porosity calibration well according to claim 3, characterized in that: The artificial small hole (2) is arranged along the axial direction of the well body.

5. The neutron porosity calibration well according to any one of claims 1 to 4, characterized in that: The radial thickness of the well body (1) is T, T≥650 mm; the axial height is H, 1.5≤H≤1.7 m.

6. The neutron porosity calibration well according to any one of claims 1 to 4, characterized in that: The diameter of the artificial small hole (2) is d, 20 mm ≤ d ≤ 30 mm.

7. The neutron porosity calibration well according to any one of claims 1 to 4, characterized in that: In the cross section of the well body (1), the artificial small holes (2) are evenly distributed in the form of a plurality of minimum units, and each artificial small hole (2) in the minimum unit is arranged in the form of a regular polygon or concentric circles.

8. The neutron porosity calibration well according to any one of claims 1 to 4, characterized in that: The distance between the artificial small hole (2) and the wellbore (4) of the well body (1) is not less than 10 mm, and the distance between the artificial small hole (2) and the outer wall of the well body (1) is not less than 10 mm.

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