A proppant frac method with multistage effective proppant support

Abstract

The application relates to a proppant sanding method for effectively supporting multistage cracks, and relates to the technical field of oil and gas field stimulation and reconstruction, in particular to a proppant sanding method for effectively supporting multistage cracks, and relates to the field of proppant paving and distribution optimization methods in the technical field of fracturing construction, and more particularly to a proppant sanding method for effectively supporting multistage cracks, which comprises the following steps: obtaining the morphological characteristics of multistage cracks in a reservoir, and determining the crack width distribution characteristics and structural relationship of the cracks; building a proppant paving experimental device under corresponding crack conditions, carrying out a conventional particle size proppant paving experiment, optimizing the injection proportion and injection sequence, realizing the collaborative support of the main cracks and branch cracks through different injection modes, and obtaining an optimal injection scheme; on the basis of determining the optimal injection scheme, micro-proppant mixed injection is introduced; the application is suitable for the effective support of multistage cracks and the uniform distribution of proppants, and improves the flow conductivity of the cracks and the reservoir reconstruction effect.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field production enhancement and transformation technology, specifically to the field of proppant placement and distribution optimization methods in fracturing construction technology, and particularly to a proppant sand addition method for effective support of multi-stage fractures. Background Technology

[0002] As the exploration and development of unconventional oil and gas resources (such as shale gas and tight sandstone gas) continues to deepen, these reservoirs generally exhibit low porosity and low permeability, making economical extraction difficult to achieve solely through natural energy sources. Hydraulic fracturing, as a core method for enhancing the productivity of low-permeability reservoirs, has been widely applied in unconventional oil and gas development. During fracturing operations, a reasonable proppant-sanding process plays a crucial role in forming stable and continuous flow channels within the fractures, maintaining their long-term conductivity, and ultimately improving the fracturing production enhancement effect.

[0003] Currently, most existing fracturing processes use conventional proppant with a particle size ≥70 / 140 mesh. In the complex multi-level fracture network formed after fracturing in unconventional reservoirs, uneven proppant distribution and difficulty in supporting micro-fractures often occur (Zou Yushi, Shi Shanzhi, Zhang Shicheng, et al. Hydraulic fracture morphology and proppant distribution characteristics in thin interbedded shale oil reservoirs [J]. Petroleum Exploration and Development, 2022, 49(05):1025-1032.), weakening the fracturing effect. Especially when the aperture of multi-level fractures in the reservoir varies greatly and the extension direction is complex, traditional proppant addition methods cannot take into account the filling and support of fractures of different scales, resulting in a mismatch between the support capacity of the main fracture and the branch fracture, and limiting the conductivity of the fracture system.

[0004] Therefore, there is an urgent need for a proppant addition method that can adapt to the development characteristics of multi-level fractures, so as to achieve uniform distribution of proppant in multi-level fractures and effective support for micro-fractures, thereby improving the fracturing effect and post-fracturing production capacity of unconventional reservoirs. Summary of the Invention

[0005] To address the problem of poor support effect of multi-stage fractures during deep shale gas fracturing, this invention proposes a proppant sand addition method for effective support of multi-stage fractures. This method is suitable for effective support of multi-stage fractures and uniform distribution of proppant, aiming to improve the conductivity of fractures and the reservoir stimulation effect.

[0006] The present invention provides a proppant sand addition method for effective support of multi-level fractures, comprising the following steps: Step 1, obtaining the morphological characteristics of multi-level fractures in the reservoir and clarifying the fracture width distribution characteristics and structural relationship of each level of fracture;

[0007] Step 2: Based on the multi-level crack morphology characteristics obtained in Step 1, a proppant placement experimental device was built under the corresponding crack conditions. Conventional particle size proppant placement experiments were carried out to optimize the injection ratio and injection sequence. Through different injection modes, the main crack and branch cracks were supported in a coordinated manner to obtain the optimal injection scheme. Based on the determination of the optimal injection scheme, micro proppant mixed pump injection was introduced.

[0008] Step 3: Based on the true density, bulk density, dispersibility in fracturing fluids of different viscosities, influence on fracturing fluid viscosity, and static settling velocity of the microprop, conduct a basic performance evaluation of the microprop and select a microprop suitable for supporting microfractures in multi-stage fractures.

[0009] Step 4: Analyze the migration behavior and placement characteristics of conventional particle size proppant and micro proppant in multi-level fracture systems, evaluate the ability of micro proppant to migrate to the far end of the fracture and enter micro-cracks, assess the support effect and applicable scope of micro proppant, and obtain the single placement morphology of micro proppant.

[0010] Step 5: Based on the basic properties of the microproppant obtained in Step 3 and the single layup morphology obtained in Step 4, proppant layup experiments are carried out with microproppant and conventional particle size proppant at different mixing ratios. Through comparative analysis, the optimal mixing ratio that is conducive to the simultaneous and sufficient filling of the main crack and branch cracks is determined, so as to achieve overall efficient support for multi-level cracks.

[0011] Step 6: Combining the optimization results of the injection ratio and sequence of conventional particle size proppant obtained in Step 2, and the optimal mixing ratio of micro proppant and conventional particle size proppant obtained in Step 5, a proppant sand addition method suitable for effective support of multi-level cracks is constructed.

[0012] Preferably, the refueling mode in step two includes the following modes:

[0013] Single-size proppant injection mode: refers to the use of only one type of conventional proppant with a fixed particle size throughout the entire process, such as pumping only 70 / 140 mesh quartz sand or only 40 / 70 mesh ceramsite.

[0014] Different ratio injection mode: refers to the mode of injecting two or more conventional proppants with different particle sizes according to the design mass ratio and design sequence. For example, 70 / 140 mesh quartz sand and 40 / 70 mesh ceramsite are injected with tail-end ceramsite or middle-end ceramsite at a mass ratio of 8:2 or 6:4.

[0015] Tail-end proppant mode: This refers to the mode of first adding small-diameter proppant, such as 70 / 140 mesh quartz sand, and then adding large-diameter ceramsite, such as 40 / 70 mesh ceramsite, after the small-diameter proppant has been pumped in.

[0016] Medium-sized proppant mode: The three-stage injection mode is "small-diameter proppant – large-diameter proppant – small-diameter proppant".

[0017] Preferably, the morphological characteristics of multi-stage fractures in the reservoir in step one are obtained by numerical simulation of fracture propagation or large-scale hydraulic fracturing physical simulation experiments.

[0018] This invention is applicable to the effective support and uniform distribution of proppant in multi-level fractures, thereby improving the conductivity of fractures and the reservoir stimulation effect.

[0019] Compared with existing technologies, the advantages of this invention are as follows: Addressing the characteristics of multi-stage development and significant differences in fracture width in unconventional reservoirs after compression, this invention proposes a novel method for the synergistic addition of conventional proppant and microproppant. By optimizing the particle size distribution and injection sequence of conventional proppant, it achieves more uniform and sufficient distribution in both main and branch fractures. Furthermore, the introduction of microproppant in combination effectively reduces the settling rate of the proppant, enhances its long-distance migration capability, thereby improving the non-uniform distribution of proppant within multi-stage fractures and achieving effective support for micro-fractures, thus expanding the overall support volume of the fracture system. This method has been verified through experiments and field tests, demonstrating its ability to effectively improve single-well productivity and possessing broad application prospects. Attached Figure Description

[0020] Figure 1 Propionage distribution under different injection modes for conventional particle size proppant:

[0021] (a) Distribution diagram of proppant in the single 70 / 140 mesh quartz sand injection mode throughout the entire process;

[0022] (b) Distribution diagram of proppant in the tail-following proppant injection mode of 70 / 140 mesh quartz sand and 40 / 70 mesh ceramsite in an 8:2 ratio;

[0023] (c) Distribution diagram of proppant in the tail-following ceramsite injection mode of 70 / 140 mesh quartz sand and 40 / 70 mesh ceramsite in a 6:4 ratio;

[0024] (d) Distribution diagram of proppant in the top-mounted proppant injection mode of 70 / 140 mesh quartz sand, 40 / 70 mesh ceramsite, and 70 / 140 mesh quartz sand in a 4:3:3 ratio.

[0025] Figure 2 Micropropeptide sample.

[0026] Figure 3 Results of microproppant mixing and dispersing with liquids of different viscosities:

[0027] (a) The dispersion state of the micropropeptide in water;

[0028] (b) Dispersion state of microproppant in low-viscosity fracturing fluid;

[0029] (c) Dispersion state of microproppant in high-viscosity fracturing fluid.

[0030] Figure 4 Propionate distribution results under different mixing ratios of conventional and micropropionates:

[0031] (a) Distribution diagram of proppant added when 70 / 140 mesh quartz sand and micro-proppant are mixed in an 8:2 ratio;

[0032] (b) Distribution diagram of proppant added when 70 / 140 mesh quartz sand and micro-proppant are mixed in a 6:4 ratio;

[0033] (c) Distribution diagram of proppant added when 40 / 70 mesh ceramsite and micro proppant are mixed in a 6:4 ratio.

[0034] Figure 5 Construction curve of section 17 of well L-X1. Detailed Implementation

[0035] The present invention will be described below with reference to examples.

[0036] To verify the effectiveness of the proppant sand addition process optimization design method proposed in this invention, a systematic experimental study was conducted and field application was performed, combining the geological characteristics and fracture structure characteristics of the target reservoir in well L-X1. This invention provides a proppant sand addition method for effective support of multi-stage fractures, comprising the following steps:

[0037] (1) Determination of the morphological characteristics of multi-level cracks

[0038] Based on the on-site simulation data, the structural characteristics of the multi-level cracks were clarified, and the width of the main crack in the proppant laying experimental device was determined to be 6 mm, the width of the first-level branch crack was 3 mm, and the width of the second-level branch crack was 1 mm.

[0039] (2) Optimization of the proportion and sequence of conventional particle size proppant addition

[0040] Using 70 / 140 mesh quartz sand and 40 / 70 mesh ceramsite proppant, multiple experimental schemes were designed, including single-size proppant addition, proppant addition with different ratios, tail-end proppant addition, and mid-top proppant addition modes. Propant placement experiments were carried out in the experimental apparatus in step one to observe the distribution pattern of proppant in the main crack and primary and secondary branch cracks under each mode. The crack filling effect, proppant placement pattern, and sand ingress in the branch cracks were comprehensively evaluated. The tail-end proppant addition mode, which first adds 70 / 140 mesh quartz sand and then adds 40 / 70 mesh ceramsite, was determined to be the best mode. The ratio of 70 / 140 mesh quartz sand to 40 / 70 mesh ceramsite was 7:3. To further improve the filling effect of micro-cracks, micro-proppant was introduced.

[0041] (3) Selection and performance evaluation of micropropeptides

[0042] Micropropeptides with a particle size range of 200-400 mesh, prepared from silicate-based materials, are selected. They are solid powders with a true density of 2.0-2.8 g / cm³. 3 The bulk density is 1.0-1.3 g / cm³. 3 With a particle size approximately one-seventh that of conventional 70 / 140 mesh proppant, it is suitable for supporting micro-fractures in deep shale reservoirs.

[0043] Dispersibility tests showed that the micropropeptide could be uniformly dispersed in clear water, low-viscosity and medium-to-high-viscosity slickwater without clumping.

[0044] The viscosity test results of the mixture showed that the viscosity of the fracturing fluid did not increase significantly after the addition of micro proppant, thus ensuring good fluid transport performance.

[0045] Static settling test results show that the settling velocity of the microprop is about 0.8 cm / min, which is significantly lower than that of 70 / 140 mesh (6.5 cm / min) and 40 / 70 mesh (10.2 cm / min) proppant. It has good suspension performance, which is conducive to entering the far end of the crack with the liquid and achieving effective deep support.

[0046] (4) Analysis of the characteristics of proppant placement with single particle size

[0047] In low-viscosity slickwater at 2.5 mPa·s, proppant of 40 / 70 mesh, 70 / 140 mesh, 100 / 200 mesh and micro proppant were pumped in respectively to carry out proppant placement experiments. The results showed that the smaller the proppant particle size, the more its distribution in the main fracture changed from front-end accumulation to uniform spreading, and the difference in filling area between the front and rear ends of the fracture was significantly reduced, which verified the ability of micro proppant to be uniformly distributed in multi-level fractures.

[0048] (5) Optimization of the mixing ratio of micro proppant and conventional particle size proppant

[0049] Experiments were conducted on the application of mixed proppant at ratios of 8:2 and 6:4 for 70 / 140 mesh proppant and micro proppant, and at a ratio of 6:4 for 40 / 70 mesh proppant and micro proppant. The results showed that when 70 / 140 mesh proppant and micro proppant were mixed at a ratio of 8:2, the proppant application within the cracks was the smoothest, and the overall filling effect was the best. However, when micro proppant was mixed with 40 / 70 mesh ceramsite and pumped in, the proppant effect on branch cracks was poor. Therefore, it was determined that a mixture of 70 / 140 mesh proppant and micro proppant at a ratio of 8:2 should be used for pumping.

[0050] (6) Design and on-site implementation of proppant sand addition process

[0051] Based on the experimental results, the proppant injection mode was determined as follows: 70 / 140 mesh quartz sand and 40 / 70 mesh ceramsite were injected sequentially in a 7:3 ratio. Small-diameter proppant was first pumped in to improve the far-end support capacity, and large-diameter ceramsite was injected in the tail to strengthen the near-wellbore support strength. 70 / 140 mesh quartz sand and micro-proppant were mixed and pumped in an 8:2 ratio to improve the uniformity of proppant distribution and the degree of filling of micro-fractures.

[0052] Based on this, and considering the on-site geological conditions and construction risk characteristics of section 17 of well L-X1, a specific pumping procedure was designed. The well's designed discharge rate is 14 m³ / s. 3 The pumping proppant combination adopts the strategy of "medium-high viscosity joint formation (20~30 mPa·s) + low viscosity sand carrying throughout (3mPa·s) + high viscosity displacement (30 mPa·s)". The proppant combination uses 70 / 140 mesh quartz sand and 40 / 70 mesh ceramsite added sequentially in a 7:3 ratio. 70 / 140 mesh quartz sand and micro proppant are mixed and added in an 8:2 ratio. In the early stage, micro proppant and quartz sand are mixed and injected. In the middle, ceramsite is directly switched to follow up without displacement.

[0053] The well was successfully constructed, with an opening pressure of 48.5 MPa, a maximum construction pressure of 80.3 MPa, a general pressure of 72-78 MPa, and a maximum discharge of 14 m³. 3 / min, typical displacement 14 m 3 / min. Cumulative injection volume: 1058.79 m³ 3 Low-viscosity slickwater 695.79 m 3 (65.7%), medium-viscosity slickwater 363 m 3 A total of 110.13 tons of proppant was injected, including 61.24 tons of 70 / 140 mesh quartz sand, 38.89 tons of 40 / 70 mesh ceramsite, and 10 tons of micro-proppant.

[0054] See Figure 5 As shown, due to the effective support provided by the microproppant entering the submicro-cracks during the early stages of pumping, the pressure curve exhibits a clear upward trend. Adjustments were made using a slug-and-sand mixture method (Figures a1-a3). In the middle stage, a single 70 / 140 mesh proppant was injected, followed by a final injection of 40 / 70 mesh ceramsite to complete the construction. The highest sand concentration of the mixture of 70 / 140 mesh quartz sand and microproppant reached 160 kg / m³. 3 The highest sand concentration of a single 70 / 140 mesh quartz sand is 240 kg / m³. 3 The highest sand concentration of 40 / 70 mesh ceramsite is 160 kg / m³. 3 .

[0055] Under the 6.5mm nozzle system, the gas production rates for stages 15 and 16 are 6.77 m³ / s and 6.77 m³ / s, respectively. 3 / d and 6.71 m 3 / d, the gas production of the 17th stage is 10.7 m³ / d. 3 / d is 1.58 times and 1.59 times the gas production of adjacent sections. This indicates that the proppant-addition method for effectively supporting multi-stage fractures in this invention achieves effective proppant placement and uniform distribution, optimizes the support effect of multi-stage fractures, and improves the overall reservoir stimulation effect.

Claims

1. A method for proppant-sand addition to effectively support multi-level cracks, characterized in that, Includes the following steps: Step 1: Obtain the morphological characteristics of multi-level fractures in the reservoir and clarify the fracture width distribution characteristics and structural relationships of each level of fracture. Step 2: Based on the multi-level crack morphology characteristics obtained in Step 1, a proppant placement experimental device was built under the corresponding crack conditions. Conventional particle size proppant placement experiments were carried out to optimize the injection ratio and injection sequence. Through different injection modes, the main crack and branch cracks were supported in a coordinated manner to obtain the optimal injection scheme. Based on the determination of the optimal injection scheme, micro proppant mixed pump injection was introduced. Step 3: Based on the true density, bulk density, dispersibility in fracturing fluids of different viscosities, influence on fracturing fluid viscosity, and static settling velocity of the microprop, conduct a basic performance evaluation of the microprop and select a microprop suitable for supporting microfractures in multi-stage fractures. Step 4: Analyze the migration behavior and placement characteristics of conventional particle size proppant and micro proppant in multi-level fracture systems, evaluate the ability of micro proppant to migrate to the far end of the fracture and enter micro-cracks, assess the support effect and applicable scope of micro proppant, and obtain the single placement morphology of micro proppant. Step 5: Based on the basic properties of the microproppant obtained in Step 3 and the single layup morphology obtained in Step 4, proppant layup experiments are carried out with microproppant and conventional particle size proppant at different mixing ratios. Through comparative analysis, the optimal mixing ratio that is conducive to the simultaneous and sufficient filling of the main crack and branch cracks is determined, so as to achieve overall efficient support for multi-level cracks. Step 6: Combining the optimization results of the addition ratio and sequence of conventional particle size proppant obtained in Step 2 and the optimal mixing ratio of micro proppant and conventional particle size proppant obtained in Step 5, construct a proppant sand addition method suitable for effective support of multi-level cracks.

2. The proppant-addition sand method for effective support of multi-level cracks as described in claim 1, characterized in that, The refueling mode in step two includes the following modes: Single-particle-size injection mode: refers to the mode in which only one type of conventional proppant with a fixed particle size is used for pumping throughout the entire process; Different ratio injection mode: refers to the mode of injecting two or more conventional proppants with different particle sizes according to the designed mass ratio and design sequence; Tail-chasing ceramsite mode: refers to the mode of first adding small-diameter proppant, and then adding large-diameter ceramsite after the small-diameter proppant has been pumped in; The top-mounted ceramsite mode: a three-stage injection mode in which small-diameter proppant is added first, then large-diameter ceramsite is added, and finally small-diameter proppant is added.

3. The proppant-addition sand method for effective support of multi-level cracks as described in claim 1, characterized in that, In step one, the morphological characteristics of multi-stage fractures in the reservoir are obtained by numerical simulation of fracture propagation or physical simulation experiments of large-scale hydraulic fracturing.

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