Method and system for preparing plunger rock samples for simulating shallow undiagenerated and uncemented reservoirs

Abstract

The present invention belongs to the technical field of petroleum exploration and development, and relates to a method and system for preparing a plunger rock sample for simulating a shallow undiagenerated and uncemented reservoir, and the steps are: obtaining characteristic parameters and distribution range of a target layer, formulating a plunger rock sample preparation plan, mixing mineral particles according to the design requirements, adding distilled water to moisten and fully mix, filling the mixture into a mold for compression molding and then drying at low temperature, taking out and cutting and polishing the initial rock sample, using a combination of "gauze + copper ring cap + heat shrink film" to reinforce the initial rock sample, drying the initial rock sample at low temperature for a second time until it is completely dry, measuring the rock physical response of the rock sample, and screening the plunger rock sample that meets the target layer's porosity and permeability characteristics and has a good appearance and a set pressure bearing strength. The plunger rock sample preparation method and system for simulating a shallow undiagenerated and uncemented reservoir of the present invention are easy to operate, highly repeatable, and low in production cost, and can be used to simulate the rock physical properties of shallow offshore ultra-fine-grained sediments, undiagenerated and uncemented reservoirs, and ultra-high porosity and permeability characteristics.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum exploration and development, relates to rock physics experimental technology, and specifically relates to a method and system for preparing a plunger rock sample for simulating a shallow undiagenerated and uncemented reservoir. Background Art

[0002] The shallow undiagenetic reservoirs on the seabed have loose structures and loose mineral particles. The rocks are in an undiagenetic and unconsolidated state, making it difficult to coring and preserve the cores. There are few natural cores that can be formed and pressurized to support rock physics experiments, which restricts and limits the exploration and development of shallow undiagenetic reservoirs at sea. Therefore, using artificial cores instead of natural cores for indoor experimental research is an inevitable choice and an important technical approach to simulate the rock physical response of shallow undiagenetic and unconsolidated reservoirs.

[0003] At present, artificial cores mainly include cemented cores and loose cores. Cemented cores are used to simulate medium-low porosity and permeability reservoirs with high diagenesis and strong cementation (such as tight sandstone, carbonate rock, shale, etc.). The production methods of cemented cores mainly include quartz sand epoxy resin cementation, quartz sand or glass ball filling, and quartz sand aluminum phosphate sintering (for example, Liang Wanlin. Research on artificial core preparation technology. Petroleum Instruments, 2008, 22(2): 72-74, 77; Pi Yanfu. Types and applications of special artificial cores. Science, Technology and Engineering, 2010, 10(31): 1671-1815; Santos KL, Figueiredo DJJ, Macedo LD, et al. A new way to construct synthetic porousfractured medium. Journal of Petroleum Science and Engineering, 2017, 156). Loose cores are mainly used to simulate weakly cemented loose rocks (such as loose sandstone, seafloor hydrate cores, etc.). By adding an appropriate amount of cementing agent and combining quartz sand of different particle sizes, artificial rock samples with medium and high porosity and permeability can be prepared (for example, Jiang Zhibin, Tang Hongming, Xie Xiaoyong, et al. Experimental study on the preparation method of loose sandstone simulation rock samples. Journal of Southwest Petroleum University, 2007, 29(11): 32-34; Han Xuehui, Yang Long, Hou Qingyu, et al. A new method for preparing artificial rock samples of dispersed mud-cemented loose sandstone. Progress in Geophysics, 2013, 28(06): 2944-2949; Xiong Yu, Wang Shuai, Geng Zhanli, et al. New technology for preparing artificial cores of weakly cemented high-permeability loose sandstone. Progress in Geophysics, 2015, 30(03): 1474-1479). However, the shallow layers of 0-500 m on the seafloor are mostly undiagenetic and uncemented strata (such as the Lingshui block in the Qiongdongnan Basin). The conventional diagenetic cemented artificial core production method cannot meet the requirements of the ultra-high porosity and permeability characteristics of shallow offshore layers, and the loose artificial core preparation method that relies on the bonding effect of the cementing agent cannot effectively simulate the undiagenetic and uncemented shallow ultra-fine-grained sedimentary strata on the seafloor (such as the ultra-fine-grained muddy and silty natural gas reservoir in the Lingshui block in the Qiongdongnan Basin). In addition, the destructive effect of the core holder confining pressure or axial pressure on the rock sample needs to be considered during the rock physics experiment, especially the undiagenetic loose rock samples are very susceptible to the influence of confining pressure or axial pressure, which can damage the core, resulting in poor experimental repeatability and unreliable measurement results.

[0004] In order to solve the problem of fragility during core testing, the invention patent with publication number CN106546466A discloses a skeleton conductive mixed mud sandstone artificial rock sample and a pressing molding method. The core is wrapped with a PPR hard tube, the core and the inner wall of the tube are glued together, and brass end caps with multiple 3mm diameter holes are drilled at both ends to achieve the production and molding of artificial samples, which are used to simulate the formation conditions of skeleton conductive mixed mud sandstone experimental core samples. The invention patent with publication number CN115824734A discloses an artificial core device that can simulate the compaction of loose sandstone and its production method. The rubber sleeve is filled with core powder, and the two ends are covered with screens and gaskets to obtain an artificial core that can simulate the compaction of loose sandstone. The above methods have the following shortcomings: (1) The external wrapping material is generally thick, which increases the actual volume of the core, resulting in the artificial core being larger than the size of the core holder and unable to be placed in it; (2) The production process is cumbersome and the core experiment is not repeatable enough, so they are not suitable for simulating shallow undiagenerated and uncemented reservoirs.

[0005] In summary, due to the difficulty in obtaining rock samples from shallow undiagenesized and uncemented reservoirs at sea and the lack of systematic supporting rock physics experiments, there is an urgent need to develop a method for preparing plunger artificial rock samples that can be used to simulate shallow undiagenesized and uncemented reservoirs, so as to provide basic data support for logging parameter modeling and saturation interpretation and evaluation of shallow undiagenesized and uncemented reservoirs such as those on the seabed. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a method and system for preparing a plunger rock sample for simulating a shallow undiagenerated and uncemented reservoir. The prepared plunger rock sample can effectively simulate the extremely high porosity and permeability rock physical properties of shallow undiagenerated and uncemented extremely fine-grained sediments in the offshore layer, is not easy to break in the subsequent experimental process, has good core integrity, high experimental measurement repeatability, is easy to operate, and has low rock sample production cost.

[0007] In a first aspect, the present invention provides a method for preparing a plunger rock sample for simulating a shallow undiagenerated and uncemented reservoir, the steps of which are as follows:

[0008] S1. Obtaining the rock physical characteristic parameters and distribution range of the target layer;

[0009] S2. Formulate a plunger rock sample preparation plan based on rock physical characteristic parameters and distribution range;

[0010] S3. Weigh a set mass of mineral particles according to the preparation plan, mix the mineral particles evenly according to the relative content ratio of the actual formation minerals, then add a set mass of distilled water, and stir thoroughly to make the mineral particles and the distilled water evenly mixed;

[0011] S4, filling the obtained uniform mixture into a cylindrical core mold, and pressing the mixture under a set pressure for a predetermined time;

[0012] S5, drying the mixture and the core mold at low temperature until the mixture reaches a set water content range, and taking out the initial rock sample from the core mold;

[0013] S6, cutting the initial rock sample to the length required for the experiment, and grinding the surface of the cut initial rock sample to make the surface smooth and flat;

[0014] S7, using gauze, hollow ring cap and heat shrink film to reinforce the initial rock sample after grinding;

[0015] S8, performing secondary low-temperature drying on the reinforced initial rock sample until the initial rock sample is completely dry;

[0016] S9, measuring the rock physical characteristic parameters of the plunger rock sample, selecting the plunger rock sample that meets the target reservoir porosity and permeability characteristics, has an intact appearance, and has a set pressure bearing strength, and repeating steps S3 to S9 until the rock sample preparation plan is met.

[0017] In some embodiments, in step S1, the lithological physical characteristic parameters and distribution ranges include formation water mineralization, reservoir lithology, clay mineral components and content distribution ranges, non-clay mineral components and content distribution ranges, particle size distribution ranges, porosity, permeability and bulk density physical property parameter distribution ranges.

[0018] In some embodiments, in step S3, the mass of the distilled water is 15-25% of the total mass of the mineral particles, so that the mixture is completely soaked but no excess flowable water floats on the surface of the mixture.

[0019] In some embodiments, in step S4, the pressing pressure does not exceed 2.5 MPa, and the pressing time is 2-4 hours.

[0020] In some embodiments, in step S5, the water content refers to the percentage of the mass of distilled water to the total mass of the mixture, and the water content is set to 30-50%. The water content is determined by weighing method, and the determination method is: record the mass of minerals and the mass of distilled water added to the core mold, record the mass of the current state after the mixture is pressed, and calculate the water content using formula (1), which is expressed as:

[0021] (1)

[0022] In the formula, is the water content, The amount of mineral added to the core mold, is the mass of distilled water added to the core mold, It is the mass of the pressed mixture after the first drying.

[0023] In some embodiments, in step S6, the specific method of surface grinding of the initial rock sample after cutting is: use 1000-2000 mesh sandpaper to grind the surface of the initial rock sample, grind the uneven parts of the surface, make the surface smooth and flat, the two end surfaces are parallel, the parallel angle error does not exceed 0.05°, and the two end surfaces of the rock sample are perpendicular to the lithology axis, and the vertical angle error does not exceed 0.25°.

[0024] In some embodiments, in step S7, the specific method of using the gauze, the hollow ring cap and the heat shrink film to reinforce the initial rock sample after the grinding process is:

[0025] A permeable gauze is added to each end of the polished initial rock sample, a hollow ring cap is added to the gauze, and the gauze, the hollow ring cap and the end face of the initial rock sample are closely fitted, and then the side of the initial rock sample is wrapped with a heat shrink film, and the initial rock sample is heated to make the heat shrink film completely fit the entire side of the initial rock sample without bubbles or gaps;

[0026] Alternatively, a permeable gauze is added to both ends of the polished initial rock sample, the side of the initial rock sample is wrapped with a heat shrink film, the initial rock sample is heated so that the heat shrink film completely fits the entire side of the initial rock sample without bubbles or gaps, and then a hollow ring cap is added to the gauze, and the gauze, the hollow ring cap and the end face of the initial rock sample are closely fitted;

[0027] Alternatively, wrap the polished side of the initial rock sample with a heat shrink film, heat the initial rock sample, make the heat shrink film completely fit the entire side of the initial rock sample without bubbles or gaps, then add a piece of permeable gauze to each end of the initial rock sample, add a hollow ring cap to the gauze, and make the gauze, hollow ring cap and the end face of the initial rock sample fit tightly.

[0028] In some embodiments, the mesh aperture is larger than the median particle size of the initial rock sample mineral particles, the mesh size is less than or equal to the end face size of the initial rock sample, and the mesh thickness does not exceed 0.5 mm; the outer ring size of the hollow ring cap is the same as the end face size of the initial rock sample, the inner ring size of the hollow ring cap is smaller than the mesh size, the outer ring diameter of the hollow ring cap or the circumscribed circle diameter of the outer ring is the inner ring diameter of the hollow ring cap or the circumscribed circle diameter of the inner ring plus twice the thickness of the hollow ring cap; the length of the heat shrink film is not less than 1.5 times the length of the initial rock sample.

[0029] In some embodiments, step S8 also includes the following steps: checking whether the reinforced initial rock sample is completely wrapped in the heat shrink film, whether the gauze and the hollow ring cap are firmly fixed on the initial rock sample, and when at least one of the heat shrink film is damaged, the gauze is loose, and the hollow ring cap is misplaced, the reinforced initial rock sample is adjusted and repaired.

[0030] In a second aspect, the present invention provides a plunger rock sample preparation system for simulating a shallow undiagenetic and uncemented reservoir, which is used to implement the plunger rock sample preparation method for simulating a shallow undiagenetic and uncemented reservoir described in the first aspect of the present invention, comprising:

[0031] A data acquisition module is used to obtain the rock physical characteristic parameters and distribution range of the target layer;

[0032] The plan formulation module formulates the plunger rock sample preparation plan based on the rock physical characteristic parameters and distribution range;

[0033] A weighing device for weighing mineral particles and distilled water;

[0034] a mixing container for mixing the mineral particles and the distilled water to obtain a mixture;

[0035] A cylindrical core mold for placing the mixture;

[0036] A hydraulic device for pressing the mixture in the core mold;

[0037] A drying device, used for drying the mixture to obtain an initial rock sample, and performing low-temperature drying on the reinforced initial rock sample to obtain a plunger rock sample;

[0038] A cutting device for cutting the initial rock sample;

[0039] A grinding device, used for grinding the initial rock sample after cutting;

[0040] A fitting device, used for fitting the gauze, the hollow ring cap and the end surface of the polished initial rock sample tightly to reinforce the initial rock sample;

[0041] A heating device is used to heat the initial rock sample covered with the heat shrink film so that the heat shrink film completely covers the entire side of the initial rock sample;

[0042] A measuring device for measuring the rock physical characteristic parameters of the plunger rock sample;

[0043] The screening module is used to screen the plug rock samples that meet the porosity and permeability characteristics of the target reservoir, have a good appearance, and have a set pressure bearing strength.

[0044] Compared with the prior art, the advantages and positive effects of the present invention are:

[0045] (1) The method and system for preparing a plunger rock sample for simulating a shallow undiagenetic and uncemented reservoir provided by the present invention do not add any binder (e.g., resin binder, aluminum phosphate binder, composite binder, etc.), and can prepare an uncemented standard plunger rock sample with ultra-high porosity and permeability. The method and system are easy to operate, highly repeatable, and low in production cost. The prepared plunger rock sample can be used to simulate the physical properties of shallow offshore ultra-fine-grained sediments, undiagenetic and uncemented reservoirs, and rock with ultra-high porosity and permeability characteristics.

[0046] (2) The method and system for preparing a plunger rock sample for simulating a shallow undiagenerated and uncemented reservoir provided by the present invention utilizes a method of infiltration with an aqueous solution and multiple low-temperature drying steps, so that the pore size can be flexibly adjusted and the rock sample is not easily broken.

[0047] (3) The method and system for preparing plunger rock samples for simulating shallow undiagenerated and uncemented reservoirs provided by the present invention use a combination of "gauze + hollow ring cap + heat shrink film" to reinforce the plunger rock sample, ensuring that the confining pressure or axial pressure of the core holder during the experiment will not cause damage to the rock sample, and the rock sample has good integrity and high experimental measurement repeatability. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A flow chart of a method for preparing a plunger rock sample for simulating a shallow undiagenerated and uncemented reservoir according to an embodiment of the present invention;

[0049] Figure 2 This is a structural block diagram of a plunger rock sample preparation system for simulating a shallow undiagenerated and uncemented reservoir according to an embodiment of the present invention;

[0050] Figure 3 This is a schematic diagram of the main lithology of the target layer in an embodiment of the present invention;

[0051] Figure 4 This is a schematic diagram of the main mineral components of the target layer of an embodiment of the present invention;

[0052] Figure 5 This is a schematic diagram of the particle size distribution of the target layer in an embodiment of the present invention;

[0053] Figure 6 This is a schematic diagram of porosity distribution of the target layer according to an embodiment of the present invention;

[0054] Figure 7 The design diagram of the cylindrical initial rock sample after reinforcement according to the embodiment of the present invention;

[0055] Figure 8 This is a design diagram of a permeable gauze and a hollow ring cap according to an embodiment of the present invention;

[0056] Fig. 9 This is a physical picture of the cylindrical initial rock sample after reinforcement according to an embodiment of the present invention;

[0057] Fig.10 This is a real picture of the permeable round yarn mesh according to an embodiment of the present invention;

[0058] Fig.11 This is a real picture of a hollow ring cap in an embodiment of the present invention;

[0059] Fig.12 This is a physical picture of the plunger rock sample of an embodiment of the present invention;

[0060] Fig.13 This is a graph showing the measurement results of the plug rock sample porosity and permeability experiment according to an embodiment of the present invention;

[0061] Fig.14 This is a comparison chart of the plunger rock sample density measurement value and the actual formation logging value according to an embodiment of the present invention.

[0062] In the figure, 1. data acquisition module, 2. program formulation module, 3. weighing device, 4. mixing container, 5. cylindrical core mold, 6. hydraulic device, 7. drying device, 8. cutting device, 9. grinding device, 10. bonding device, 11. heating device, 12. measuring device, 13. screening module, 14. plunger rock sample, 15. gauze, and 16. hollow ring cap. DETAILED DESCRIPTION

[0063] The present invention will be described in detail below by way of exemplary embodiments in conjunction with the accompanying drawings. However, it should be understood that, without further description, elements, structures and features in one embodiment may also be beneficially combined in other embodiments.

[0064] The present invention provides a method and system for preparing a plunger rock sample for simulating a shallow unlithified and uncemented reservoir. The mineral particles are mixed in the required proportion according to the design, distilled water is added for wetting, and after being fully mixed again, they are taken out after being pressed into shape, and dried at low temperature for multiple times. A permeable gauze and a hollow ring cap are used to fit tightly to the end face of the rock sample, and the side of the rock sample is wrapped with a heat shrink film. The produced unlithified and uncemented artificial rock core can be used to simulate the rock physical properties of shallow offshore ultra-fine-grained sediments, unlithified and uncemented reservoirs, and ultra-high porosity and permeability characteristics, while ensuring that the confining pressure or axial pressure of the core holder during the experiment will not cause damage to the core. The core has good integrity, which improves the measurement and calculation accuracy of such cores. The following is a detailed description of the above-mentioned method and system for preparing a plunger rock sample for simulating a shallow unlithified and uncemented reservoir in conjunction with the accompanying drawings.

[0065] See also Figure 1 The first embodiment of the present invention provides a method for preparing a plunger rock sample for simulating a shallow undiagenerated and uncemented reservoir, the steps of which are as follows:

[0066] S1. Obtain the target layer rock physical characteristic parameters and distribution range.

[0067] Specifically, the characteristic parameters and distribution ranges include formation water salinity, reservoir lithology, clay mineral components and content distribution ranges, non-clay mineral components and content distribution ranges, particle size distribution ranges, porosity, permeability and bulk density physical property parameter distribution ranges.

[0068] S2. Formulate a plunger rock sample preparation plan based on rock physical characteristic parameters and distribution range.

[0069] Specifically, in the plunger rock sample preparation plan, the formation water mineralization is consistent with the actual reservoir formation water mineralization, which is obtained through water data analysis. The reservoir clay mineral components and content distribution range, non-clay mineral components and content distribution range and particle size distribution range are obtained through logging data, analytical test data, and petrological analysis experiments of crushed samples. Determine the main mineral components and their contents, and cover the distribution range of the main mineral contents according to the proportion of each mineral component (for example: quartz: illite: kaolin: chlorite = 80:10:5:5), determine the particle size distribution range, screen minerals of different particle sizes, and ensure that they are consistent with the median particle size or the particle size distribution range (for example: diameter>2mm: diameter 0.5-2mm: diameter 0.25-0.5mm: diameter 0.0625-0.25mm: diameter 0.0039-0.0625mm: diameter <0.0039mm=0:0:0:7.89:69.51:22.6). The formation porosity, permeability and volume density distribution range of the target layer are calculated through the logging curve (for example: porosity distribution range 15.1-45.5%, permeability distribution range 2.36-1256.11mD, volume density distribution range 1.65-2.13g / cm3).

[0070] S3. According to the preparation plan, a set mass of mineral particles is weighed, and the mineral particles are evenly mixed according to the relative content ratio of the actual formation minerals. Then, a set mass of distilled water is added, and the mixture is fully stirred to make the mineral particles and the distilled water evenly mixed to obtain a mixture.

[0071] Specifically, the mass of distilled water is 15-25% of the total mass of the mineral particles, so that the mixture is completely soaked but no excess flowable water floats on the surface of the mixture. It should be noted that the mass of the mineral particles is determined according to actual needs, and the total mass of the mineral particles can be calculated by multiplying 80% of the volume of the core mold cavity by the skeleton density.

[0072] S4, filling the obtained mixture into a cylindrical core mold, and pressing the mixture under a set pressure for a predetermined time.

[0073] Specifically, a hydraulic press is used to perform pressure pressing at a constant pressure. It should be noted that the pressing pressure and time can affect the porosity and permeability of the artificial rock sample; for the ultra-high porosity and permeability plunger rock sample simulating the shallow undiagenerated and uncemented reservoir, the pressing pressure does not exceed 2.5MPa, and the pressing time is 2-4 hours.

[0074] S5. Dry the mixture and the core mold at low temperature until the mixture reaches the set water content range, and remove the initial rock sample from the core mold. The purpose of low temperature drying is to avoid cracking of the rock sample and changes in minerals and organic matter. Drying the mixture until it reaches the set water content range is to facilitate the removal of the initial rock sample from the core mold.

[0075] Specifically, the water content is the percentage of the mass of distilled water to the total mass of the mixture, and the water content is set to 30-50%. The water content is determined by weighing method, and the determination method is: record the mass of minerals and distilled water added to the core mold, record the current state mass after the mixture is pressed, and calculate the water content using formula (1), which is expressed as:

[0076] (1)

[0077] In the formula, is the water content, The amount of mineral added to the core mold, is the mass of distilled water added to the core mold, It is the mass of the pressed mixture after the first drying.

[0078] It should be noted that in order to smoothly remove the rock sample from the core mold and prevent the rock sample from falling off during the subsequent rock sample reinforcement process, the rock sample needs to have a certain water content. The presence of water can also adhere to mineral particles, but does not affect the mineral properties. The water content of the rock sample needs to be maintained at, but not limited to, 30-50%.

[0079] S6. Cut the initial rock sample to the length required for the experiment, and grind the surface of the cut initial rock sample to make the surface smooth and flat.

[0080] Specifically, the specific method for grinding the surface of the initial rock sample after cutting is: use 1000-2000 mesh sandpaper to grind the surface of the initial rock sample, grind the uneven parts of the surface, make the surface smooth and flat, the two end faces are parallel, the parallel angle error does not exceed 0.05°, the two end faces of the rock sample are perpendicular to the lithology axis, and the vertical angle error does not exceed 0.25°. In some embodiments, when the rock sample is a cylindrical rock sample, the diameter of the rock sample is 25 mm, and the diameter length error of the rock sample does not exceed 0.5 mm.

[0081] S7. Use gauze, hollow ring caps and heat shrink film to reinforce the initial rock sample after grinding.

[0082] Specifically, in some embodiments, the specific method of using the gauze, hollow ring cap and heat shrink film to reinforce the polished initial rock sample is: add a permeable gauze to each end of the polished initial rock sample, add a hollow ring cap to the gauze, and make the gauze and the hollow ring cap fit closely with the end face of the initial rock sample, then wrap the side of the initial rock sample with a heat shrink film, heat the initial rock sample, and make the heat shrink film completely fit the entire side of the initial rock sample without bubbles or gaps. Then cut off the excess heat shrink film on both sides of the rock sample.

[0083] Specifically, in some embodiments, the specific method of using the gauze, hollow ring cap and heat shrink film to reinforce the polished initial rock sample is: add a piece of permeable gauze to both ends of the polished initial rock sample, wrap the side of the initial rock sample with heat shrink film, heat the initial rock sample, make the heat shrink film completely fit the entire side of the initial rock sample without bubbles or gaps, then add the hollow ring cap to the gauze, and make the gauze, the hollow ring cap and the end face of the initial rock sample fit tightly. Then cut off the excess heat shrink film on both sides of the rock sample.

[0084] Specifically, in some embodiments, the specific method of using the gauze, hollow ring cap and heat shrink film to reinforce the polished initial rock sample is: wrap the side of the polished initial rock sample with the heat shrink film, heat the initial rock sample, make the heat shrink film completely fit the entire side of the initial rock sample without bubbles or gaps, then add a piece of permeable gauze to both ends of the initial rock sample, add the hollow ring cap on the gauze, and make the gauze, the hollow ring cap and the end face of the initial rock sample fit tightly. Then cut off the excess heat shrink film on both sides of the rock sample.

[0085] It should be noted that the above reinforcement method can be used to reinforce rock samples of different sizes, such as round and square cross-section rock samples, as long as matching permeable gauze and hollow ring caps are selected. Since the order of gauze, hollow ring cap, and heat shrink film in the above reinforcement method is different, different orders require the selection of hollow ring caps with different inner ring sizes.

[0086] Specifically, in some embodiments, the mesh aperture is larger than the median particle size of the initial rock sample mineral particles, the mesh size is less than or equal to the end face size of the initial rock sample, and the mesh thickness does not exceed 0.5 mm. For example: when the initial rock sample is cylindrical, the mesh is circular, and the mesh diameter is less than or equal to the end face diameter of the initial rock sample. It should be noted that the mesh diameter should not be less than 2 mm of the end face diameter of the initial rock sample. Usually, the cylindrical initial rock sample has a diameter of 25 mm, the mesh diameter is 25 mm, and the mesh thickness is 0.1 mm.

[0087] Specifically, in some embodiments, the outer ring size of the hollow ring cap is the same as the end face size of the initial rock sample, the inner ring size of the hollow ring cap is smaller than the mesh size, and the outer ring diameter or the circumscribed circle diameter of the hollow ring cap is the inner ring diameter or the circumscribed circle diameter of the hollow ring cap plus twice the thickness of the hollow ring cap, so that the fluid can pass freely through the rock sample.

[0088] Specifically, in some embodiments, the length of the heat shrink film is not less than 1.5 times the length of the initial rock sample.

[0089] Specifically, in some embodiments, the heat shrinkable film is a tubular PVC heat shrinkable film, and the diameter of the heat shrinkable film is no more than twice the diameter of the rock sample (the cross section of the rock sample is circular).

[0090] Specifically, in some embodiments, a heat gun is used to heat the heat shrink film, the heating temperature does not exceed 100°C, and the air outlet is not less than 4 cm away from the heat shrink film. It should be noted that the higher the temperature of the heat source, the farther away from the heat shrink film is needed to prevent the heat shrink film from being damaged due to excessive shrinkage.

[0091] Specifically, in some embodiments, after reinforcing the initial rock sample, check whether the initial rock sample is completely wrapped in the heat shrink film, and whether the gauze and the hollow ring cap are firmly fixed on the initial rock sample. When at least one of the heat shrink film is damaged, the gauze is loose, and the hollow ring cap is misplaced, adjustments and repairs are performed. When adjustments and repairs are not possible, the initial rock sample is reinforced again to ensure the reinforcement effect.

[0092] The rock samples are reinforced with the combined reinforcement scheme of “heat shrink film + gauze + copper ring cap”, which can ensure that the confining pressure or axial pressure of the core holder during the experiment will not cause damage to the rock samples, and the integrity of the rock samples is good, and the subsequent experimental measurements are highly repeatable.

[0093] S8. The reinforced initial rock sample is subjected to secondary low-temperature drying until the initial rock sample is completely dried to obtain a plunger rock sample.

[0094] Specifically, in some embodiments, the reinforced rock sample is placed in a dry, ventilated open space with a temperature not exceeding 30°C to allow the core to air dry naturally; or an oven is used with the drying time set to 8 hours and the temperature set to 50°C to allow the rock sample to dry completely.

[0095] Specifically, in some embodiments, the side of the rock sample is wrapped again with a heat shrink film to further reinforce the side of the rock sample. The method of wrapping the rock sample again with a heat shrink film is the same as step S7, which will not be repeated here.

[0096] It should be noted that the initial rock sample after reinforcement is dried at a low temperature of less than 60°C to prevent the high temperature from destroying the properties of the mineral components and damaging the heat shrink film, effectively protecting the heat shrink film. In addition, the initial rock sample is infiltrated with an aqueous solution and then dried at low temperature twice. The purpose of the two low-temperature dryings is to allow the water in the core to evaporate slowly, flexibly adjust the porosity of the artificial rock sample, and prevent the core from being damaged during the core reinforcement process.

[0097] S9, measuring the rock physical characteristic parameters of the plunger rock sample, selecting the plunger rock sample that meets the porosity and permeability characteristics of the target reservoir, has a good appearance and has a set pressure bearing strength, and repeating steps S3 to S9 until the rock sample preparation plan is met.

[0098] Specifically, when measuring the characteristic parameters of the plunger rock sample, the volume, mass, bulk density, porosity and permeability of the plunger rock sample are measured. The specific measurement method is based on the National Standard of the People's Republic of China "Core Analysis Method" GB / T29172-2012. It should be noted that all measurement results need to subtract the volume and mass of the gauze, hollow ring cap, and heat shrink film.

[0099] The method and system for preparing a plunger rock sample for simulating a shallow undiagenetic and uncemented reservoir of the present invention are easy to operate, highly repeatable, and low in production cost. Without adding any binder (such as resin binder, aluminum phosphate binder, and composite binder), the preparation of an uncemented standard plunger rock sample with ultra-high porosity and permeability can be achieved, and can be used to simulate the physical properties of shallow offshore ultra-fine-grained sediments, undiagenetic and uncemented reservoirs, and rock with ultra-high porosity and permeability characteristics.

[0100] The second embodiment of the present invention provides a plunger rock sample preparation system for simulating a shallow undiagenetic and uncemented reservoir, which is used to implement the plunger rock sample preparation method for simulating a shallow undiagenetic and uncemented reservoir described in the first aspect of the present invention, comprising:

[0101] Data acquisition module 1, used to obtain the target layer formation rock physical characteristic parameters and distribution range;

[0102] Plan formulation module 2, formulates the plunger rock sample preparation plan based on the rock physical characteristic parameters and distribution range;

[0103] A weighing device 3, used for weighing mineral particles and distilled water;

[0104] A mixing container 4, used for mixing the mineral particles and distilled water to obtain a mixture;

[0105] A cylindrical core mold 5 for placing the mixture;

[0106] A hydraulic device 6 for pressing the mixture in the core mold;

[0107] A drying device 7, used for drying the mixture to obtain an initial rock sample, and performing low-temperature drying on the reinforced initial rock sample to obtain a plunger rock sample 14;

[0108] A cutting device 8, for cutting the initial rock sample;

[0109] A grinding device 9, used for grinding the initial rock sample after cutting;

[0110] The fitting device 10 is used to fit the gauze 15 and the hollow ring cap 16 tightly to the end surface of the polished initial rock sample to reinforce the initial rock sample;

[0111] A heating device 11 heats the initial rock sample covered with the heat shrink film so that the heat shrink film completely covers the entire side of the initial rock sample;

[0112] A measuring device 12 for measuring rock physical characteristic parameters of the plunger rock sample 14;

[0113] The screening module 13 is used to screen the plug rock samples 14 that meet the porosity and permeability characteristics of the target reservoir, have a good appearance, and have a set pressure bearing strength.

[0114] Specifically, in some embodiments, the weighing device is an electronic balance. The hydraulic device is a hydraulic press. The drying device is an oven. The cutting device is a cutting machine. The grinding device is 1000-2000 mesh sandpaper. The heating device is a hot air gun. The measuring device uses an existing characteristic parameter measuring device.

[0115] The above-mentioned plunger rock sample preparation system for simulating shallow unaugmented and uncemented reservoirs in the embodiment of the present invention can achieve the preparation of unaugmented standard plunger rock samples with ultra-high porosity and permeability without adding any binder (such as resin binder, aluminum phosphate binder and composite binder), and can be used to simulate the physical properties of shallow offshore ultra-fine-grained sediments, unaugmented and uncemented reservoirs, and ultra-high porosity and permeability characteristics.

[0116] In order to verify the effectiveness of the plunger rock sample preparation method and system for simulating shallow undiagenerated and uncemented reservoirs described in the above embodiments of the present invention, the following specific embodiments are used for description.

[0117] Example: Take the preparation of artificial rock samples of shallow undenabed and uncemented rock in the northern seabed of the South China Sea as an example. The preparation steps are:

[0118] S1. Collect rock chip data from the shallow target area in the northern South China Sea. Based on the characteristics of the shallow undiagenetic and uncemented, extremely fine-grained sediments in the South China Sea, carry out mineral XRD, clay analysis, and cast thin-section petrology experimental measurements. Figure 3 , it is clear that the main lithology of the target reservoir is siltstone, fine sandstone and muddy sandstone. Figure 4 The non-clay mineral content is 60-90%, mainly quartz and feldspar, and the clay mineral content is 10-40%, mainly illite / montmorillonite mixed layer, illite, kaolinite and chlorite. Figure 5 The median particle size is mainly concentrated in the range of 0.0078-0.0310 mm. By converting it into different mesh sizes, the mesh size combination of quartz sand can be determined. Figure 6 The porosity is mainly distributed in the range of 15-40%, and the permeability is mainly distributed in the range of 10-2000mD.

[0119] S2. Based on the above analysis results, the quartz sand particle size is designed to be 80-2000 mesh, the illite, kaolin, and chlorite particle sizes are all 2000 mesh, the porosity range is 20-40%, the permeability range is 10-3000mD, and the plunger rock sample preparation scheme with 5 kinds of mud content (0%, 10%, 20%, 30%, 40%) is designed. As shown in Tables 1-3, Table 1 is the plunger rock sample preparation scheme with different mud contents, Table 2 is the plunger rock sample particle size and proportion design scheme, and Table 3 is the density of different mineral particles.

[0120] Table 1

[0121]

[0122] Table 2

[0123]

[0124] Table 3

[0125]

[0126] Taking the preparation scheme with 20% mud content as an example, the mineral components are mainly quartz; clay is mainly kaolin, chlorite, and illite. In addition to being used as a material, clay can also be used as a clay binder to a certain extent. Use an electronic balance to weigh quartz sand 80 mesh 10g, 150 mesh 10g, 200 mesh 15g, 400 mesh 15g, 600 mesh 10g, 1000 mesh 10g, 1500 mesh 5g, 2000 mesh 5g; illite 2000 mesh 10g, kaolin 2000 mesh 5g, chlorite 2000 mesh 5g.

[0127] S3. Mix the weighed minerals thoroughly, add 20g of distilled water to the mixture to moisten it, and stir the mixture again to make it completely moist but without any excess flowable water floating on the surface of the mixture.

[0128] S4. Fill the mixture into a cylindrical core mold with a diameter of 25 mm and press it with a hydraulic press at a pressure of 2 MPa for 2.5 hours. During this period, some pores are filled due to the pressure, so pay attention to the pressure change and maintain constant pressure.

[0129] S5. Put the pressed mixture and the core mold into the oven. To ensure that the water content of the mixture is 30-50%, the drying time is set to 4 hours and the temperature is set to 40°C. After the time is up, the oven is turned off and the artificial rock sample that has not been completely dried is taken out from the mold. Specifically, the pressed mixture and the core mold are taken out together and put into a constant temperature drying oven. The drying time is set to 4 hours and the temperature is set to 40°C. The drying oven will first increase the temperature inside the oven from room temperature to 40°C, and then count down for 4 hours. After the time is up, the oven stops running. Wait for 30 minutes before taking out the initial rock sample and the core mold. Open the core mold, take out the initial rock sample that has not been completely dried from the core mold, weigh the mass of the initial rock sample at this time, and calculate the current water content of the initial rock sample according to formula (1), and keep the water content of the initial rock sample at 30-50%.

[0130] S6. Use 2000-grit sandpaper to grind the surface of the initial rock sample (i.e., the initial rock sample with a water saturation of 30-50%) that has not been completely dried, so that its surface (side and two end faces) is smooth and flat. It is mainly to grind away the pores existing at the joint of the mold and the excess parts of the rock sample protruding during the pressing process. At the same time, grind or cut the uneven parts of the end faces on both sides so that the two end faces are parallel, and the parallel angle error does not exceed 0.05°, so that the two end faces of the rock sample are perpendicular to the lithological axis, the angle between the two is 90°, and the vertical angle error does not exceed 0.25°. The purpose is to avoid the mesh 15 and the hollow ring cap 16 not fitting with the end face of the rock sample when adding them later, affecting the subsequent experimental measurement and increasing the error. Finally, a cylindrical rock sample with a diameter of 25mm±0.5mm and a length of 41-72mm is obtained.

[0131] S7. Add a permeable mesh 15 with a pore size of about 400 mesh, a diameter of 25mm, and a thickness of 0.1mm to each end of the polished rock sample. The mesh 15 should evenly cover the sample end surface to ensure that both sides of the rock sample are completely covered. Then add a copper hollow ring cap with an inner diameter of 25mm to the mesh 15 (the outer diameter of the hollow ring cap is 25mm, the outer diameter of the outer circle is 25.4mm, the inner diameter is 21mm, and the cap height is 4mm. For details, see Figures 7 to 11 ), and make the gauze 15 and the hollow ring cap fit tightly with the end face of the rock sample. Cover the rock sample with a cylindrical PVC heat shrink film about twice the height of the rock sample, and make the core of the rock be located in the middle of the heat shrink film. Use a hot air gun to set the temperature to 100°C, with the air outlet about 5 cm away from the heat shrink film, and heat the surface of the heat shrink film so that the heat shrink film tightly wraps the side of the rock sample, ensuring that the heat shrink film completely fits the side of the sample without bubbles or gaps. Then cut off the excess heat shrink film on both sides of the rock sample.

[0132] Specifically, first check whether the rock sample is completely wrapped in the heat shrink film, and whether the gauze 15 and the copper hollow ring cap are firmly fixed on the rock sample. If any problems are found, such as damage to the heat shrink film, loose gauze or misalignment of the copper hollow ring cap, adjustments and repairs should be made in time.

[0133] It should be noted that the mass and volume of each piece of gauze 15, each copper hollow ring cap, and each heat shrink film wrapping the rock sample must be recorded, so that the data obtained in the subsequent parameter calculation only reflects the characteristics of the rock sample, making the data more real and reliable.

[0134] S8. Place the reinforced rock sample in a dry, ventilated open space with a temperature not exceeding 30°C to allow the rock sample to dry naturally, or use an oven with the drying time set to 8 hours and the temperature set to 50°C to allow the rock sample to dry completely. Use heat shrink film to wrap the side of the rock sample again to further reinforce the rock sample.

[0135] S9, measure the volume, mass, bulk density, porosity and permeability of the plunger rock sample 14, screen out the plunger rock sample 14 that meets the porosity and permeability characteristics of the target reservoir and has a good appearance and a set pressure bearing strength, and repeat the above S3-S9 until the plunger rock sample preparation plan formulated in step S2 is met.

[0136] Specifically, a certain number of unformed and uncemented plug rock samples 14 are prepared. According to the national standard GB / T 29172-2012 of the People's Republic of China on "core analysis method", the volume, mass, porosity, permeability, bulk density and other parameters reflecting the physical properties of the core are measured, and compared with the experimental design requirements. If they meet the requirements, the preparation is completed, and if not, it needs to be re-prepared ( Fig.12 A batch of finished plug rock samples that meet the requirements are shown in the figure). The porosity and permeability characteristics can be adjusted by adjusting the pressing pressure and pressing time. The volume and mass of the gauze 15, the hollow ring cap 16, and the heat shrink film need to be subtracted from the measurement results.

[0137] The results of the plunger rock sample experiment test of the physical characteristics of ultra-high porosity and permeability rock of shallow offshore undiagenerated and unconsolidated ultra-fine-grained sediments prepared according to the above steps are as follows: Fig.13 , Fig.14 As shown in the figure, a total of 125 rock samples with different shale contents were prepared, with porosity ranging from 20-43%, permeability ranging from 10-3000mD, and dry sample bulk density ranging from 1.50-1.87g / cm 3 The volume density of saturated samples ranges from 1.87 to 2.10 g / cm 3 The results show that the lithology porosity and permeability distribution range of 120 blocks are within the design range, the volume density distribution range is within the design range, and the overall production success rate is over 96%.

[0138] The above embodiments are used to explain the present invention rather than to limit the present invention. Any modification and change made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a plunger rock sample simulating a shallow undiagenerated and uncemented reservoir, characterized in that: The steps are: S1. Obtaining the rock physical characteristic parameters and distribution range of the target layer; S2. Formulate a plunger rock sample preparation plan based on rock physical characteristic parameters and distribution range; S3. Weigh a set mass of mineral particles according to the preparation plan, mix the mineral particles evenly according to the relative content ratio of the actual formation minerals, then add a set mass of distilled water, and stir thoroughly to make the mineral particles and the distilled water evenly mixed to obtain a mixture; S4, filling the obtained mixture into a cylindrical core mold, and pressing the mixture under a set pressure for a predetermined time; S5, drying the mixture and the core mold at low temperature until the mixture reaches a set water content range, and taking out the initial rock sample from the core mold; S6, cutting the initial rock sample to the length required for the experiment, and grinding the surface of the cut initial rock sample to make the surface smooth and flat; S7, using gauze, hollow ring cap and heat shrink film to reinforce the initial rock sample after grinding; S8, performing secondary low-temperature drying on the reinforced initial rock sample until the initial rock sample is completely dried to obtain a plunger rock sample; S9, measuring the rock physical characteristic parameters of the plunger rock sample, selecting the plunger rock sample that meets the target reservoir porosity and permeability characteristics, has an intact appearance, and has a set pressure bearing strength, and repeating steps S3 to S9 until the rock sample preparation plan is met.

2. The method for preparing a plunger rock sample for simulating a shallow undiagenerated and uncemented reservoir as claimed in claim 1, characterized in that: In step S1, the lithological physical characteristic parameters and distribution ranges include formation water salinity, reservoir lithology, clay mineral components and content distribution ranges, non-clay mineral components and content distribution ranges, particle size distribution ranges, porosity, permeability and bulk density physical property parameter distribution ranges.

3. The method for preparing a plunger rock sample for simulating a shallow undiagenerated and uncemented reservoir as claimed in claim 1, characterized in that: In step S3, the mass of the distilled water is 15-25% of the total mass of the mineral particles, so that the mixture is completely wetted but no excess flowable water floats on the surface of the mixture.

4. The method for preparing a plunger rock sample for simulating a shallow undiagenerated and uncemented reservoir as claimed in claim 1, characterized in that: In step S4, the pressing pressure does not exceed 2.5 MPa, and the pressing time is 2-4 hours.

5. The method for preparing a plunger rock sample for simulating a shallow undiagenerated and uncemented reservoir as claimed in claim 1, characterized in that: In step S5, the water content refers to the percentage of the mass of distilled water to the total mass of the mixture, and the water content is set to 30-50%. The water content is determined by weighing method, and the determination method is: record the mass of minerals and the mass of distilled water added to the core mold, record the mass of the current state after the mixture is pressed, and calculate the water content using formula (1), which is expressed as: （1） In the formula, is the water content, The amount of mineral added to the core mold, is the mass of distilled water added to the core mold, It is the mass of the pressed mixture after the first drying.

6. The method for preparing a plunger rock sample for simulating a shallow undiagenerated and uncemented reservoir as claimed in claim 1, characterized in that: In step S6, the specific method for surface grinding of the initial rock sample after cutting is: use 1000-2000 mesh sandpaper to grind the surface of the initial rock sample, grind the uneven parts of the surface, make the surface smooth and flat, the two end surfaces are parallel, the parallel angle error does not exceed 0.05°, and the two end surfaces of the rock sample are perpendicular to the lithology axis, and the vertical angle error does not exceed 0.25°.

7. The method for preparing a plunger rock sample for simulating a shallow undiagenerated and uncemented reservoir as claimed in claim 1, characterized in that: In step S7, the specific method of using the gauze, the hollow ring cap and the heat shrink film to reinforce the polished initial rock sample is as follows: a piece of permeable gauze is added to both ends of the polished initial rock sample, a hollow ring cap is added to the gauze, and the gauze, the hollow ring cap and the end face of the initial rock sample are closely fitted, and then the side of the initial rock sample is wrapped with a heat shrink film, and the initial rock sample is heated so that the heat shrink film is completely fitted to the entire side of the initial rock sample without bubbles or gaps; Alternatively, a permeable gauze is added to both ends of the polished initial rock sample, the side of the initial rock sample is wrapped with a heat shrink film, the initial rock sample is heated so that the heat shrink film completely fits the entire side of the initial rock sample without bubbles or gaps, and then a hollow ring cap is added to the gauze, and the gauze, the hollow ring cap and the end face of the initial rock sample are closely fitted; Alternatively, wrap the polished side of the initial rock sample with a heat shrink film, heat the initial rock sample, make the heat shrink film completely fit the entire side of the initial rock sample without bubbles or gaps, then add a piece of permeable gauze to each end of the initial rock sample, add a hollow ring cap to the gauze, and make the gauze, hollow ring cap and the end face of the initial rock sample fit tightly.

8. The method for preparing a plunger rock sample for simulating a shallow undiagenerated and uncemented reservoir as claimed in claim 7, characterized in that: The mesh aperture is larger than the median particle size of the initial rock sample mineral particles, the mesh size is less than or equal to the end face size of the initial rock sample, and the mesh thickness does not exceed 0.5mm; the outer ring size of the hollow ring cap is the same as the end face size of the initial rock sample, the inner ring size of the hollow ring cap is smaller than the mesh size, the outer ring diameter of the hollow ring cap or the outer ring circumscribed circle diameter is the inner ring diameter of the hollow ring cap or the inner ring circumscribed circle diameter plus twice the thickness of the hollow ring cap; the length of the heat shrink film is not less than 1.5 times the length of the initial rock sample.

9. The method for preparing a plunger rock sample for simulating a shallow undiagenerated and uncemented reservoir as claimed in claim 7, characterized in that: In step S8, the following steps are also included: checking whether the reinforced initial rock sample is completely wrapped in the heat shrink film, whether the gauze and the hollow ring cap are firmly fixed on the initial rock sample, and when at least one of the heat shrink film is damaged, the gauze is loose, and the hollow ring cap is misplaced, the reinforced initial rock sample is adjusted and repaired.

10. A plunger rock sample preparation system for simulating a shallow undiagenerated and uncemented reservoir, used to implement the plunger rock sample preparation method for simulating a shallow undiagenerated and uncemented reservoir as claimed in any one of claims 1 to 9, characterized in that: include: A data acquisition module is used to obtain the physical characteristic parameters and distribution range of the target layer rock; The plan formulation module formulates the plunger rock sample preparation plan based on the rock physical characteristic parameters and distribution range; A weighing device for weighing mineral particles and distilled water; a mixing container for mixing the mineral particles and distilled water to obtain a mixture; A cylindrical core mold for placing the mixture; A hydraulic device for pressing the mixture in the core mold; A drying device, used for drying the mixture to obtain an initial rock sample, and performing low-temperature drying on the reinforced initial rock sample to obtain a plunger rock sample; A cutting device for cutting the initial rock sample; A grinding device, used for grinding the initial rock sample after cutting; A fitting device, used for fitting the gauze, the hollow ring cap and the end surface of the polished initial rock sample tightly to reinforce the initial rock sample; A heating device is used to heat the initial rock sample covered with the heat shrink film so that the heat shrink film completely covers the entire side of the initial rock sample; A measuring device for measuring the rock physical characteristic parameters of the plunger rock sample; The screening module is used to screen the plug rock samples that meet the porosity and permeability characteristics of the target reservoir, have a good appearance, and have a set pressure bearing strength.

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