Diversion capacity determination method and proppant pack ratio determination method
Patent Information
- Application Number
- CN202411911529.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-24
- Publication Date
- 2026-11-03
- Estimated Expiration
- 2044-12-24
AI Technical Summary
Existing technologies have low accuracy in measuring fracture conductivity, making it impossible to accurately determine the optimal packing ratio of microparticle proppant, which affects the fracturing operation results.
By selecting core samples that have been cracked into first and second parts, proppant is laid on the cracked surfaces to form core samples to be tested. The permeability and crack aperture are determined by fluid seepage experiments, the conductivity is calculated, and the optimal proppant packing ratio is finally determined.
It improves the accuracy of measuring fracture conductivity, ensures a more accurate optimal packing ratio of microparticle size proppant, effectively guides fracturing operations, and significantly increases production.
Smart Images
Figure CN120558789B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of oil and gas development technology, specifically to a method for determining flow capacity and a method for determining proppant bulk ratio. Background Technology
[0002] The exploration and development of unconventional oil and gas reservoirs plays an increasingly important role in the global energy landscape. However, unconventional oil and gas reservoirs typically have low natural production capacity, and most require production enhancement measures to reach industrial production levels. Among these measures, fracture-network volumetric stimulation is a key method for the efficient production of unconventional reservoirs such as shale oil, shale gas, and tight oil. During fracture-network volumetric stimulation, secondary fractures and microfractures are often generated. Standard-sized proppant cannot effectively support these secondary and microfractures, making them prone to closure. This results in a situation where initial production increases after fracture-network volumetric stimulation are good, but long-term stable production capacity is poor.
[0003] To address the undersupport issue of secondary and microfractures, the use of microparticle proppant has been proposed. Because of their sufficiently small size, microparticle proppant can effectively support fractures with small openings. Determining the optimal microparticle proppant packing ratio (i.e., the optimal packing ratio) for achieving optimal fracture conductivity can effectively guide fracturing operations.
[0004] However, the methods provided in the prior art have low accuracy in measuring the conductivity of cracks, which makes it impossible to accurately obtain the optimal packing ratio of microparticle proppant. Summary of the Invention
[0005] The purpose of this invention is to overcome the problem that the accuracy of measuring the conductivity of cracks in the prior art is low, which leads to the inability to accurately obtain the optimal packing ratio of microparticle-sized proppant, and to provide a method for determining conductivity and a method for determining proppant packing ratio.
[0006] To achieve the above objectives, a first aspect of the present invention provides a method for determining flow guiding capacity, comprising:
[0007] Select a core sample that has been cracked into a first part and a second part. Lay proppant on the cracked surfaces of the first part and the second part. The mass of proppant laid on the cracked surface of the first part is based on the area of the cracked surface of the first part, the preset proppant bulk ratio, and the true density of the proppant. The mass of proppant laid on the cracked surface of the second part is based on the area of the cracked surface of the second part, the preset proppant bulk ratio, and the true density of the proppant.
[0008] The cracked surface of the first part and the cracked surface of the second part are merged to form the core to be tested, and the target crack is formed between the cracked surface of the first part and the cracked surface of the second part.
[0009] A fluid seepage experiment was conducted on the core sample to be tested, and the permeability of the core sample and the first aperture of the target fracture were determined based on the fluid seepage experiment.
[0010] The conductivity of the target fracture is calculated based on the permeability and the first opening.
[0011] In this embodiment of the application, the crack between the first part and the second part is formed when the core is located in the strata.
[0012] In the embodiments of this application, the particle size of the proppant is less than 150 μm.
[0013] In this embodiment of the application, before applying the proppant to the cracked surfaces of the first portion and the second portion, the method further includes:
[0014] The proppant is selected based on preset requirements, including: the sorting coefficient of the proppant is less than 1.2, and the breakage rate of the proppant is less than 10% under 4000psi conditions.
[0015] The application of proppant on the cracked surfaces of the first and second portions includes:
[0016] A proppant conforming to the preset requirements is laid on the cracked surfaces of the first part and the second part.
[0017] In this embodiment, the mass of the proppant laid on the cracked surface of the first portion is determined based on the following formula:
[0018]
[0019] Where, m p The mass of the proppant laid on the cracked surface of the first part, in kg; ρ pt The true density of the proppant is expressed in kg / m³. 3 a is the length of the cracked surface of the first part, in meters; b is the width of the cracked surface of the first part, in meters; d is the particle size of the proppant, in meters; Rp is the preset proppant packing ratio.
[0020] In this embodiment, the mass of the proppant laid on the cracked surface of the second portion is determined based on the following formula:
[0021]
[0022] Where, m p The mass of the proppant laid on the cracked surface of the second part, in kg; ρ pt The true density of the proppant is expressed in kg / m³. 3 a is the length of the cracked surface in the second part, in meters; b is the width of the cracked surface in the second part, in meters; d is the particle size of the proppant, in meters; R p This is the preset proppant packing ratio.
[0023] In this embodiment of the application, the method further includes:
[0024] An antistatic brush is used to apply a proppant to the cracked surfaces of the first part and the second part.
[0025] In this embodiment of the application, after applying proppant to the cracked surfaces of the first portion and the second portion, the method further includes:
[0026] The proppant placement effect is verified based on a preset method, which includes: randomly selecting multiple areas in each cracked surface to observe the proppant placement.
[0027] If there is no overlap of proppant particles in any of the multiple regions, the proppant laid on the cracked surface will not be adjusted; if there is overlap of proppant particles in any of the multiple regions, the proppant laid on the cracked surface will be adjusted.
[0028] In this embodiment of the application, the step of conducting a fluid seepage experiment on the core sample to be tested and determining the permeability of the core sample based on the fluid seepage experiment includes:
[0029] Saturate the target crack with fluid;
[0030] A pressure difference is established between the upstream and downstream ends of the core sample to be tested, and fluid seeps into the core sample based on the pressure difference.
[0031] The permeability of the core sample is determined based on the pressure at the upstream and downstream ends of the core sample during the seepage process.
[0032] In this embodiment of the application, the step of conducting a fluid seepage experiment on the core sample to be tested, and determining the first aperture of the target fracture based on the fluid seepage experiment, includes:
[0033] Saturate the target crack with fluid;
[0034] A pressure difference is established between the upstream and downstream ends of the core sample to be tested, and fluid seeps into the core sample based on the pressure difference.
[0035] During the seepage process, the perimeter of the cross section at the upstream or downstream end of the core sample is monitored. Based on the reduction in the perimeter of the cross section and the compression of the core sample, the first opening of the target fracture is determined.
[0036] In this embodiment of the application, determining the first aperture of the target fracture based on the reduction in the perimeter of the cross-section and the compression of the core sample includes:
[0037] The reduction in the aperture of the target fracture is determined based on the reduction in the perimeter of the cross section and the compression of the core sample.
[0038] The first opening of the target crack is determined based on the reduction in the opening of the target crack and the initial opening.
[0039] In this embodiment, the reduction in the aperture of the target crack is determined based on the following formula:
[0040] L3 = (L1 - L2) × 50%;
[0041] Where L3 is the reduction in the opening of the target crack, in meters; L1 is the reduction in the perimeter of the cross section, in meters; and L2 is the compression of the core sample, in meters.
[0042] In this embodiment of the application, calculating the conductivity of the target fracture based on the permeability and the first aperture includes:
[0043] The conductivity of the target fracture is calculated based on the product of the permeability and the first aperture.
[0044] A second aspect of this application provides a method for determining the proppant bulk ratio, comprising:
[0045] The flow capacity obtained by the first method for determining flow capacity is taken as the flow capacity corresponding to the preset proppant bulk ratio.
[0046] Set multiple other proppant packing ratios, and determine the flowability corresponding to each of the multiple other proppant packing ratios based on the flowability determination method of the first aspect;
[0047] The optimal flow-guiding capacity is determined from the various flow-guiding capacities, and the proppant packing ratio corresponding to the optimal flow-guiding capacity is taken as the optimal proppant packing ratio.
[0048] In this embodiment of the application, determining the optimal flow-conducting capacity from among the various flow-conducting capacities and using the proppant packing ratio corresponding to the optimal flow-conducting capacity as the optimal proppant packing ratio includes:
[0049] A flowability curve is plotted with the proppant bulk ratio on the x-axis and the flowability on the y-axis. The flowability curve has a maximum value, and the maximum value is located at the inflection point of the curve.
[0050] The proppant packing ratio corresponding to the maximum value is taken as the optimal proppant packing ratio.
[0051] The above technical solution includes: selecting a core sample that has been fractured into a first part and a second part; laying proppant on the fracture surfaces of the first part and the second part, wherein the mass of the proppant laid on the fracture surface of the first part is obtained based on the area of the fracture surface of the first part, a preset proppant bulk ratio, and the true density of the proppant; the mass of the proppant laid on the fracture surface of the second part is obtained based on the area of the fracture surface of the second part, a preset proppant bulk ratio, and the true density of the proppant; merging the fracture surfaces of the first part and the second part relative to each other to form a core sample to be tested, forming a target fracture between the fracture surfaces of the first part and the second part; conducting a fluid seepage experiment on the core sample to be tested, determining the permeability of the core sample to be tested and the first aperture of the target fracture based on the fluid seepage experiment; and calculating the conductivity of the target fracture based on the permeability and the first aperture. Based on the solution provided in the embodiments of this application, the accuracy of measuring fracture conductivity can be improved, thereby making the optimal packing ratio of the microparticle size proppant more accurate and effectively guiding fracturing operations.
[0052] Other features and advantages of the embodiments of this application will be described in detail in the following detailed description section. Attached Figure Description
[0053] The accompanying drawings are provided to further illustrate the embodiments of this application and form part of the specification. They are used together with the following detailed description to explain the embodiments of this application, but do not constitute a limitation on the embodiments of this application. In the drawings:
[0054] Figure 1 The illustration shows a flowchart of a method for determining flow capacity according to an embodiment of this application;
[0055] Figure 2 This illustration schematically shows a method for measuring the size of a core crack surface according to an embodiment of this application;
[0056] Figure 3This illustration schematically shows a theoretical model of a single-layer proppant layer according to an embodiment of this application;
[0057] Figure 4 The illustration shows a flowchart of a method for determining the proppant bulk ratio according to an embodiment of this application;
[0058] Figure 5 The diagram schematically illustrates a proppant layup diagram with a bulk ratio according to an embodiment of this application;
[0059] Figure 6 The diagram schematically illustrates a proppant layup with another bulk ratio according to an embodiment of this application;
[0060] Figure 7 A permeability curve is schematically shown according to an embodiment of this application;
[0061] Figure 8 A crack aperture curve according to an embodiment of this application is illustrated schematically;
[0062] Figure 9 A flow-guiding capacity curve according to an embodiment of this application is illustrated schematically. Detailed Implementation
[0063] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for illustration and explanation of the embodiments of this application.
[0064] This is not intended to limit the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.
[0065] It should be noted that if the embodiments of this application involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.
[0066] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.
[0067] As described in the background section, the exploration and development of unconventional oil and gas reservoirs plays an increasingly important role in the global energy landscape. However, unconventional oil and gas reservoirs typically have low natural production capacity, and most require production enhancement measures to reach industrial production levels. Among these measures, fracture-network volumetric stimulation (FMS) is a key method for the efficient production of unconventional reservoirs such as shale oil, shale gas, and tight oil. During FMS, secondary fractures and microfractures are often generated. Proppants of conventional sizes cannot penetrate these secondary and microfractures, thus failing to provide effective support. This leads to the easy closure of these fractures and microfractures, resulting in good initial production increases but poor long-term stable production, or poor initial and long-term production. To address the problem of under-support of secondary and microfractures, the use of microparticle-sized proppant has been proposed. Because microparticle-sized proppant is small enough, it can penetrate fractures with smaller openings for effective support. Determining the optimal microparticle-sized proppant packing ratio (i.e., the optimal packing ratio of microparticle-sized proppant) for achieving optimal conductivity can effectively guide...
[0068] Fracturing operations. However, in existing testing methods, many have attempted to use conventional fracture conductivity testers to measure the change in proppant conductivity under different particle size proppant concentrations. However, experimental results often show that "fracture conductivity increases with increasing particle size proppant concentration," failing to determine an optimal conductivity point. This is inconsistent with theoretical understanding and field observations. The reason is that conventional fracture conductivity testing methods have significant errors in proppant selection and placement, permeability testing, and proppant fracture width testing. In other words, existing technologies have low accuracy in measuring fracture conductivity, and may even fail to determine the optimal conductivity, thus making it impossible to accurately obtain the optimal particle size proppant packing ratio.
[0069] To address this, one embodiment of this application provides a method for determining the conductivity of a crack, which can be used to measure the conductivity of the crack. For example... Figure 1 As shown, the method for determining the flow capacity may include the following steps:
[0070] Step 101: Select the core that has been cracked into a first part and a second part, and lay proppant on the cracked surfaces of the first part and the second part.
[0071] Preferably, the core is a core that has naturally split into a first part and a second part, that is, the crack between the first part and the second part is formed when the core is located in the strata.
[0072] The proppant is specifically a microparticle proppant with a particle size ranging from tens to hundreds of micrometers. More preferably, the particle size of the microparticle proppant corresponds to that of commonly used microparticle proppants, and is less than 150 μm. For simplicity, subsequent descriptions of the proppant can be understood as referring to microparticle proppants.
[0073] In specific implementation, before applying proppant to the cracked surfaces of the first and second parts, the proppant can be selected based on preset requirements. Applying proppant to the cracked surfaces of the first and second parts then includes applying proppant that meets the preset requirements. These preset requirements may include: a proppant sorting coefficient of less than 1.2, and a proppant breakage rate of less than 10% under 4000 psi conditions.
[0074] Considering that proppant has better flow conductivity when laid in a single layer, therefore the first part
[0075] The proppant applied to the cracked surface and the cracked surface of the second part is preferably applied in a single layer. To ensure that the proppant is applied in as single a layer as possible on the cracked surface, before applying the proppant to the cracked surfaces of the first part and the second part, the proppant bulk ratio determination method provided in this application embodiment may further include: determining the mass of the proppant applied to the cracked surface of the first part based on the area of the cracked surface of the first part, a preset proppant bulk ratio, and the true density of the proppant; and determining the mass of the proppant applied to the cracked surface of the second part based on the area of the cracked surface of the second part, the preset proppant bulk ratio, and the true density of the proppant.
[0076] Specifically, the mass of the proppant laid on the cracked surface of the first part can be calculated based on the following formula (1):
[0077]
[0078] In the above formula (1), m p The mass of the proppant laid on the cracked surface of the first part, in kg; ρ ptThe true density of the proppant is expressed in kg / m³. 3 a is the length of the cracked surface in the first part, in meters; b is the width of the cracked surface in the first part, in meters; d is the particle size of the proppant, in meters; R p The preset proppant packing ratio is given; l represents the distance between proppant particles, in meters (m). The length and width of the cracked surface can be measured as follows: Figure 2 As shown.
[0079] The mass of the proppant laid on the cracked surface of the second part can also be calculated based on the above formula (1), the difference being: m p The mass of the proppant laid on the cracked surface of the second part, a is the length of the cracked surface of the second part, and b is the width of the cracked surface of the second part.
[0080] Among them, the theoretical model for single-layer proppant placement can be as follows: Figure 3 As shown.
[0081] To ensure the proppant can disperse quickly and be laid in a single layer and evenly on the cracked surface as much as possible, in practical applications, an antistatic brush can be used to lay the proppant on the cracked surfaces of the first and second parts.
[0082] After applying proppant to the cracked surfaces of the first and second parts, the proppant application effect can be verified based on a preset method, which includes: in each
[0083] Multiple areas are randomly selected from the cracked surface to observe the proppant distribution. If there is no overlap of proppant particles in any of the multiple areas, it is considered that the proppant has been distributed in a single layer and uniformly, and no adjustment is made to the proppant distribution on the cracked surface. If there is overlap of proppant particles in any of the multiple areas, it is considered that the proppant has not been distributed in a single layer and uniformly, and the proppant distribution on the cracked surface is adjusted, such as by continuing to brush the cracked surface with an antistatic brush to further disperse the proppant particles.
[0084] In practice, for example, five areas can be randomly selected from a cracked surface, and a 30X magnifying glass can be used to observe whether the proppant particles overlap.
[0085] Step 102: Combine the cracked surface of the first part with the cracked surface of the second part to form the core to be tested, and form a target crack between the cracked surface of the first part and the cracked surface of the second part.
[0086] It is understood that proppant is distributed in the target crack.
[0087] Step 103: Conduct a fluid seepage experiment on the core sample to be tested, and determine the permeability of the core sample and the first opening of the target fracture based on the fluid seepage experiment.
[0088] In practical implementation, the transient pulse method can be used, and the GCTS high-temperature, high-pressure, rapid triaxial rock testing system can be employed to conduct fluid seepage experiments on the core sample. The process of conducting fluid seepage experiments on the core sample and determining its permeability based on these experiments can specifically include steps one, two, and three:
[0089] Step 1: Saturate the target crack with fluid.
[0090] The fluid can be a gas or a liquid.
[0091] In practice, the target crack can be saturated with gas or liquid at a certain pressure.
[0092] Step 2: Establish a pressure difference between the upstream and downstream ends of the core sample to be tested, and based on the pressure difference, fluid seeps into the core sample to be tested.
[0093] In practice, a target confining pressure can be applied to the core sample. After the pressure of the core sample stabilizes, the pressure difference between the upstream and downstream ends of the core sample can be established by reducing the pressure at the downstream end. The target confining pressure can be selected based on the actual formation pressure.
[0094] Step 3: Determine the permeability of the core sample based on the pressure at the upstream and downstream ends during the seepage process.
[0095] The permeability of the core sample to be tested can be understood as the permeability of the core sample to be tested under the target confining pressure.
[0096] As fluid seepage proceeds in the core sample, the pressure at the upstream end of the core sample continuously decreases, while the pressure at the downstream end of the core sample continuously increases, and gradually tends to reach equilibrium.
[0097] In practice, the pressure at the upstream and downstream ends of the core sample can be monitored during fluid seepage. Then, a functional relationship between the average pressure at the upstream and downstream ends and time can be established to calculate the permeability of the core sample.
[0098] During fluid seepage, if the pressure difference between the upstream and downstream ends of the core sample changes slowly, the confining pressure can be changed when the pressure difference changes by a certain value (generally by 0.1 MPa). This allows for the measurement of permeability under multiple effective stresses in a single pulse, and the pressure at which the upstream and downstream ends of the core sample reach equilibrium can be recorded. If the pressure difference between the upstream and downstream ends of the core sample changes rapidly, only one set of confining pressures can be measured permeability per pulse. Therefore, after measuring one set of confining pressures, a pressure relief operation needs to be performed at the downstream end of the core sample to ensure that the initial pressure difference between the upstream and downstream ends of the core sample is consistent when measuring different confining pressures. The pressure at which the upstream and downstream ends of the core sample reach equilibrium, recorded in the previous set, is used as the downstream pressure for the next set of tests.
[0099] A fluid seepage experiment is conducted on the core sample to be tested, and the aperture of the target fracture is determined based on the fluid seepage experiment. Specifically, this may include steps i, ii, and iii:
[0100] Step i, saturate the target crack with fluid.
[0101] The fluid can be a gas or a liquid. In specific implementations, the target crack can be saturated with a gas or liquid at a certain pressure.
[0102] Step ii: A pressure difference is established between the upstream and downstream ends of the core sample to be tested, and fluid seeps into the core sample based on the pressure difference.
[0103] In practice, a target confining pressure can be applied to the core sample. After the pressure of the core sample stabilizes, the pressure difference between the upstream and downstream ends of the core sample can be established by reducing the pressure at the downstream end. The target confining pressure can be selected based on the actual formation pressure.
[0104] Step iii: During the seepage process, monitor the cross-sectional perimeter of the upstream or downstream end of the core sample to be tested, and determine the first opening of the target fracture based on the reduction in the cross-sectional perimeter and the compression of the core sample to be tested.
[0105] In this embodiment of the application, determining the first aperture of the target fracture based on the reduction in the perimeter of the cross-section and the compression of the core sample can specifically include steps ① and ②:
[0106] Step ①: Determine the reduction in the opening of the target fracture based on the reduction in the perimeter of the cross section and the compression of the core sample.
[0107] The compression of the core sample can be defined as the compression of the core sample under the target confining pressure, i.e., the compression of the cross-sectional perimeter of the core sample under the target confining pressure. In practical applications, a crack-free core sample can be used as a control core sample, and the compression of the cross-sectional perimeter of the control core sample is measured under the target confining pressure. This compression is then used to determine the compression of the cross-sectional perimeter of the core sample under the target confining pressure.
[0108] The reduction in cross-sectional perimeter during seepage is due to two factors: firstly, the reduction in the target fracture aperture leads to a decrease in cross-sectional perimeter; secondly, the compression of the core sample itself leads to a decrease in cross-sectional perimeter. Therefore, the reduction in the target fracture aperture can be determined based on the following formula (2):
[0109] L3 = (L1 - L2) × 50% (2);
[0110] In the above formula (2), L3 is the reduction in the opening of the target crack, in meters; L1 is the reduction in the perimeter of the cross section, in meters; and L2 is the compression of the core sample, in meters.
[0111] In specific experiments, a displacement sensor can be installed around the core to record the displacement of the core perimeter, thereby obtaining the reduction in cross-sectional perimeter and the compression of the interface perimeter.
[0112] Step ②: Determine the first opening of the target crack based on the reduction in the opening of the target crack and the initial opening of the target crack.
[0113] Wherein, the first opening of the target crack can be the target crack under the target confining pressure.
[0114] Opening degree.
[0115] In practice, the first opening of the target crack can be obtained by subtracting the reduction in opening from the initial opening.
[0116] It should be understood that, in specific experiments, the permeability of the core sample and the first opening of the target fracture can be determined based on the same fluid seepage experiment.
[0117] Step 104: Calculate the flow conduction capacity of the target fracture based on the permeability and the first opening.
[0118] In this embodiment of the application, the flow conduction capacity of the target fracture can be calculated based on the product of the permeability and the first aperture.
[0119] It is understood that the method for determining the conductivity provided in this application includes: selecting a core sample that has been fractured into a first part and a second part; laying proppant on the fracture surfaces of the first part and the second part, wherein the mass of the proppant laid on the fracture surface of the first part is obtained based on the area of the fracture surface of the first part, a preset proppant bulk ratio, and the true density of the proppant; the mass of the proppant laid on the fracture surface of the second part is obtained based on the area of the fracture surface of the second part, a preset proppant bulk ratio, and the true density of the proppant; merging the fracture surfaces of the first part and the second part relative to each other to form a core sample to be tested, forming a target fracture between the fracture surfaces of the first part and the second part; conducting a fluid seepage experiment on the core sample to be tested, determining the permeability of the core sample to be tested and the first aperture of the target fracture based on the fluid seepage experiment; and calculating the conductivity of the target fracture based on the permeability and the first aperture. Based on the solution provided in the embodiments of this application, the accuracy of measuring fracture conductivity can be improved, thereby making the optimal packing ratio of the microparticle size proppant more accurate and effectively guiding fracturing operations.
[0120] Based on the flow conductivity determination method provided in the above embodiments of this application, this application also provides a proppant packing ratio determination method, which can be used to determine the packing ratio corresponding to the optimal flow conductivity of the crack, that is, it can be used to determine the optimal packing ratio of the microparticle size proppant. Figure 4 As shown, the
[0121] The method for determining the proppant bulk ratio may include the following steps:
[0122] Step 105: The flow capacity obtained by the flow capacity determination method is taken as the flow capacity corresponding to the preset proppant packing ratio.
[0123] That is, the flow capacity obtained by the flow capacity determination method provided in the above embodiments of this application is used as the flow capacity corresponding to the preset proppant packing ratio.
[0124] Step 106: Set multiple other proppant packing ratios, and determine the flowability corresponding to each of the multiple other proppant packing ratios based on the above flowability determination method.
[0125] It is understandable that in specific experiments, multiple different proppant packing ratios can be preset, and then multiple cores that have been cracked into two parts can be taken, with each core corresponding to a proppant packing ratio. Then, the conductivity corresponding to each proppant packing ratio can be obtained according to the above-mentioned method for determining conductivity.
[0126] Step 107: Determine the optimal flow-conducting capacity from among the various flow-conducting capacities, and take the proppant packing ratio corresponding to the optimal flow-conducting capacity as the optimal proppant packing ratio.
[0127] In practice, this may include steps I and II:
[0128] Step I: Plot a flowability curve with the proppant bulk ratio as the x-axis and the flowability as the y-axis. The flowability curve has a maximum value, and the maximum value is located at the inflection point of the curve.
[0129] That is, based on the correspondence between each flow conductivity and each proppant packing ratio, a flow conductivity curve is plotted in a coordinate system with the proppant packing ratio as the horizontal axis and the flow conductivity as the vertical axis.
[0130] In this embodiment of the application, the flow-conducting capacity curve has a maximum value, and the maximum value is at the inflection point of the curve, indicating that the preset multiple proppant stacking ratios are reasonable. If the flow-conducting capacity curve does not have a maximum value or the maximum value is not at the inflection point of the curve, it indicates that the preset multiple proppant stacking ratios are unreasonable, and more proppant stacking ratios need to be set to conduct the above-mentioned flow-conducting capacity test.
[0131] Step II: The proppant packing ratio corresponding to the maximum value is taken as the optimal proppant packing ratio.
[0132] In practical implementation, a permeability curve can be plotted with the proppant bulk ratio as the abscissa and permeability as the ordinate, wherein the permeability curve has a maximum value, and the maximum value is located at the inflection point of the curve; and a crack curve can be plotted with the proppant bulk ratio as the abscissa and the first aperture of the target crack as the ordinate.
[0133] The crack aperture curve has a maximum value, which is located at the inflection point of the curve. The optimal proppant packing ratio is further determined by combining the maximum value of the permeability curve and the maximum value of the crack aperture curve.
[0134] In practical applications, the flow-guiding capacity determination method and the proppant packing ratio determination method provided in the embodiments of this application can be implemented for different confining pressures to obtain the optimal proppant packing ratio corresponding to each confining pressure.
[0135] It is understood that, based on the proppant packing ratio determination method provided in the above embodiments of this application, the optimal packing ratio of microparticle-sized proppant can be determined, thereby effectively guiding fracturing operations.
[0136] It has been found that, based on the optimal proppant packing ratio determined in this application, microproppant fracturing design can achieve a 3-6 times increase in production after fracturing of unconventional reservoirs. Compared with wells that do not adopt the optimal proppant packing ratio design, the production of a single well can be increased by an additional 20%-30% under the same production pressure differential, and the potential damage to the fracture conductivity caused by microparticles can be avoided.
[0137] The solutions provided in the above embodiments of this application will be described below with specific examples. It should be understood that the following examples are merely specific implementation methods and do not imply an improper limitation of the solutions in this application.
[0138] Taking a shale core from a Chinese oilfield as an example, its basic parameters are: elastic modulus 10 GPa, Poisson's ratio 0.13, and clay mineral content 35%. A naturally fractured core was selected, and the length and width of the fracture surface were measured. The results were 24.06 mm and 20.74 mm, respectively, with a fracture surface area of 499.004 mm². 2 The scheme provided in the above embodiments of this application was implemented using 140-200 mesh quartz sand taken from Chifeng, Inner Mongolia, China as a proppant.
[0139] Before the experiment, the proppant was sampled and tested. The results showed that the sorting coefficient was 1.11 and the breakage rate of the proppant was 8.2% under 4000psi conditions, which met the requirements.
[0140] The true density of the quartz sand was measured to be 2.64 g / cm³. 3 Five proppant packing ratios were preset: 0, 0.25, 0.50, 0.75, and 1.0. The layup masses corresponding to the five proppant packing ratios were calculated using the formula (1) above: 0 g, 0.0097 g, 0.0386 g, 0.0869 g, and 0.1545 g, respectively.
[0141] Due to manual operation errors, the actual proppant bulk ratios during weighing and application on cracked surfaces were 0, 0.28, 0.4, 0.55, and 1.0, corresponding to 0%, 28%, 40%, 55%, and 100%, respectively. The application of a proppant bulk ratio of 0.55 is shown below. Figure 5 As shown, the proppant stacking ratio of 1.0 is as follows: Figure 6 As shown.
[0142] During the actual testing process, it was found that the optimal proppant packing ratio was between 0.25 and 0.50. Therefore, the subsequent seepage test with a proppant packing ratio of 0.75 was cancelled, and a subsequent seepage test with a proppant packing ratio of 0.4 was conducted.
[0143] Fluid seepage experiments were conducted using the transient method with high-pressure pulses. The permeability and fracture width (i.e., fracture aperture) corresponding to different proppant bulk ratios were measured at two closure pressures (confining pressures) of 21 MPa and 28 MPa. The resulting permeability curves can be plotted as follows: Figure 7 As shown, the optimal proppant packing ratio is 0.4. The resulting crack aperture curve can be plotted as follows: Figure 8 As shown, the optimal packing ratio of the proppant is 0.4.
[0144] The conductivity corresponding to various proppant bulk ratios under confining pressures of 21 MPa and 28 MPa was calculated based on permeability and fracture aperture. The resulting conductivity curves can be plotted as follows: Figure 9 As shown, the optimal packing ratio of the proppant is 0.4.
[0145] Therefore, 0.4 will be used as the optimal packing ratio for the micro-supported fracturing design of this block to obtain the optimal proppant concentration, which will be used to guide on-site construction.
[0146] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.
[0147] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.
Claims
1. A method for determining flow guiding capacity, characterized in that, The method includes: Select a core sample that has been cracked into a first part and a second part. Lay proppant on the cracked surfaces of the first part and the second part. The mass of proppant laid on the cracked surface of the first part is based on the area of the cracked surface of the first part, the preset proppant bulk ratio, and the true density of the proppant. The mass of proppant laid on the cracked surface of the second part is based on the area of the cracked surface of the second part, the preset proppant bulk ratio, and the true density of the proppant. The cracked surface of the first part and the cracked surface of the second part are merged to form the core to be tested, and a target crack is formed between the cracked surface of the first part and the cracked surface of the second part. A fluid seepage experiment was conducted on the core sample to be tested, and the permeability of the core sample and the first aperture of the target fracture were determined based on the fluid seepage experiment. The conductivity of the target fracture is calculated based on the permeability and the first opening. The mass of the proppant laid on the cracked surface of the first part is determined based on the following formula: ； in, The mass of the proppant laid on the cracked surface of the first part is expressed in kg. The true density of the proppant is expressed in kg / m³. 3 ; The length of the cracked surface in the first part, in meters; The width of the crack surface in the first part, in meters; The particle size of the proppant is expressed in meters (m). The preset proppant packing ratio; The mass of the proppant laid on the cracked surface of the second part is determined based on the following formula: ； in, The mass of the proppant laid on the cracked surface of the second part is expressed in kg. The true density of the proppant is expressed in kg / m³. 3 ; The length of the crack surface in the second part is in meters (m). The width of the crack surface in the second part, in meters; The particle size of the proppant is expressed in meters (m). The preset proppant packing ratio; The determination of the first aperture of the target crack based on the fluid seepage experiment includes: The reduction in the opening of the target fracture is determined based on the reduction in the cross-sectional perimeter of the upstream or downstream end of the core sample and the compression of the core sample. The first opening of the target crack is determined based on the reduction in the opening of the target crack and the initial opening.
2. The method for determining flow guiding capacity according to claim 1, characterized in that, The crack between the first part and the second part was formed when the core was located in the strata.
3. The method for determining flow guiding capacity according to claim 1, characterized in that, The particle size of the proppant is less than 150 μm.
4. The method for determining flow guiding capacity according to claim 3, characterized in that, Before applying the proppant to the cracked surfaces of the first and second portions, the method further includes: The proppant is selected based on preset requirements, including: the proppant sorting coefficient is less than 1.2, and the proppant breakage rate is less than 10% under 4000psi conditions.
5. The method for determining flow guiding capacity according to claim 1, characterized in that, The method further includes: An antistatic brush is used to apply a proppant to the cracked surfaces of the first part and the second part.
6. The method for determining flow guiding capacity according to claim 1, characterized in that, After applying proppant to the cracked surfaces of the first and second portions, the method further includes: The proppant placement effect is verified based on a preset method, which includes: randomly selecting multiple areas in each cracked surface to observe the proppant placement. If there is no overlap of proppant particles in any of the multiple regions, the proppant laid on the cracked surface will not be adjusted; if there is overlap of proppant particles in any of the multiple regions, the proppant laid on the cracked surface will be adjusted.
7. The method for determining flow guiding capacity according to claim 1, characterized in that, The step of conducting a fluid seepage experiment on the core sample and determining the permeability of the core sample based on the fluid seepage experiment includes: Saturate the target crack with fluid; A pressure difference is established between the upstream and downstream ends of the core sample to be tested, and fluid seeps into the core sample based on the pressure difference. The permeability of the core sample is determined based on the pressure at the upstream and downstream ends of the core sample during the seepage process.
8. The method for determining flow guiding capacity according to claim 1, characterized in that, The reduction in the cross-sectional perimeter of the upstream or downstream end of the core sample is obtained through the following process: Saturate the target crack with fluid; A pressure difference is established between the upstream and downstream ends of the core sample to be tested, and fluid seeps into the core sample based on the pressure difference. During the seepage process, the perimeter of the cross section at the upstream or downstream end of the core sample is monitored to obtain the reduction in the perimeter of the cross section.
9. The method for determining flow guiding capacity according to claim 1, characterized in that, The reduction in the aperture of the target crack is determined based on the following formula: L3 = (L1 - L2) × 50%; Where L3 is the reduction in the aperture of the target crack, in meters; L1 is the reduction in the perimeter of the cross section, in meters; and L2 is the compression of the core sample, in meters.
10. The method for determining flow guiding capacity according to claim 1, characterized in that, The step of calculating the conductivity of the target fracture based on the permeability and the first aperture includes: The conductivity of the target fracture is calculated based on the product of the permeability and the first aperture.
11. A method for determining the proppant packing ratio, characterized in that, include: The flow capacity obtained by the flow capacity determination method described in claim 1 is taken as the flow capacity corresponding to the preset proppant bulk ratio. Set multiple other proppant packing ratios, and determine the flowability corresponding to each of the multiple other proppant packing ratios based on the flowability determination method described in claim 1; The optimal flow-guiding capacity is determined from the various flow-guiding capacities, and the proppant packing ratio corresponding to the optimal flow-guiding capacity is taken as the optimal proppant packing ratio.
12. The method for determining the proppant packing ratio according to claim 11, characterized in that, The step of determining the optimal flow-conducting capacity from among the various flow-conducting capacities, and taking the proppant packing ratio corresponding to the optimal flow-conducting capacity as the optimal proppant packing ratio, includes: A flowability curve is plotted with the proppant bulk ratio on the x-axis and the flowability on the y-axis. The flowability curve has a maximum value, and the maximum value is located at the inflection point of the curve. The proppant packing ratio corresponding to the maximum value is taken as the optimal proppant packing ratio.