A method and system for separate layer fracturing suitable for sand-shale complex lithology section

Abstract

The present application belongs to the technical field of shale oil and gas exploration and development, and specifically discloses a layered fracturing method suitable for sand-shale complex lithology section, which comprises the following steps: S1, identifying a reservoir section; S2, downhole casing perforation construction; S3, judging lithology; S4, fracturing construction, according to the lithology category judged in S3, performing staged fracturing on the reservoir section; S5, in the longitudinal direction of the reservoir section, sand-shale thin interbedded section and thick-layer sandstone interbedded shale exist simultaneously or sand-shale thin interbedded section and thick-layer shale interbedded sandstone section exist simultaneously; then, segmented bridge plugs are used between the two reservoir sections for staging. A layered fracturing system suitable for sand-shale complex lithology section comprises an identification module, a perforation construction module, a judging module, a fracture construction module, a thick-layer sandstone interbedded shale section or thick-layer shale interbedded sandstone section construction module, and a bridge plug staging construction module. The present application can solve the problem that the current vertically developed tight sandstone and shale reservoirs are difficult to be fully reformed.

Description

Technical Field

[0001] This invention relates to the field of shale oil and gas and tight gas exploration and development technology, specifically to a layered fracturing method and system applicable to complex lithological sections of sandstone and shale. Background Technology

[0002] In recent years, China has intensified its exploration and development efforts in shale oil and gas and tight gas. Oil and gas fields in Xinjiang, Daqing, Changqing, and Southwest China have all achieved significant breakthroughs in these areas. However, shale reservoirs and tight sandstone reservoirs have relatively poor physical properties. Furthermore, surveys of the current exploration and development status of shale oil and gas and tight gas in major oil fields reveal that shale reservoirs and tight sandstone reservoirs often exhibit overlapping development in the vertical direction, leading to increased lithological complexity and thus introducing uncertainty into the effectiveness of reservoir fracturing.

[0003] Considering the differences between sandstone and shale reservoirs, the objectives of stimulation for shale and tight sandstone reservoirs differ in China. Shale reservoirs often have naturally developed fractures, and stimulation aims to create complex fracture networks to increase the stimulated volume. Tight sandstone reservoirs generally have few or no naturally developed fractures, so stimulation primarily focuses on creating long fractures to increase the oil and gas contact area. Currently, despite the different objectives, both shale and tight sandstone reservoirs can achieve increased production using segmented multi-cluster fracturing technology. However, for vertically interbedded sandstone and shale reservoir sections, without specific stimulation techniques, it is difficult to achieve sufficient stimulation. Therefore, a layered fracturing design method suitable for complex lithological sections of sandstone and shale has been invented, which can achieve sufficient stimulation of complex lithological reservoir sections, increasing the stimulated volume and drainage area. Summary of the Invention

[0004] This invention provides a layered fracturing method suitable for complex sandstone and shale lithology sections, aiming to solve the current problem that reservoirs with alternating development of tight sandstone and shale reservoirs in the vertical direction are difficult to fully stimulate.

[0005] This invention is achieved through the following technical solution: a layered fracturing method suitable for complex lithological sections of sandstone and shale, comprising the following steps:

[0006] S1, Identify reservoir segments and determine their location and length;

[0007] S2, downhole casing perforation construction;

[0008] S3, determine the lithology, and adopt different fracturing methods according to different lithologies. The reservoir section includes one of the following: thin interbedded sandstone and shale section, thick sandstone interbedded with shale section, and thick shale interbedded with sandstone section; or the reservoir section includes thin interbedded sandstone and shale section and thick sandstone interbedded with shale section; or the reservoir section includes thin interbedded sandstone and shale section and thick shale interbedded with sandstone section.

[0009] S4, fracturing operation: Based on the lithology determined in S3, the reservoir section is fracturing in stages;

[0010] In step S4, the following fracturing methods are used for reservoir sections with different lithologies:

[0011] S41, when the reservoir section is a thin interbedded sand and shale layer, the "slickwater + crosslinking fluid" reverse mixing fracturing process is adopted. The reverse mixing fracturing process refers to the injection of slickwater and crosslinking fluid mixed together to carry sand. First, crosslinking fluid is injected to carry sand and is used to penetrate the thin interbedded sand and shale layer. Then, slickwater is injected to carry sand. After the slickwater completes the delivery of proppant, crosslinking fluid is finally injected to complete the delivery of proppant.

[0012] S42, the reservoir section is a thick sandstone interbedded with shale section or a thick shale interbedded with sandstone section. The fracturing process of "rope knot temporary plugging + layered stimulation" is adopted. First, the fracturing pressure values ​​of sandstone and shale are determined according to the stress profile interpreted by well logging. Then, the sequence of injecting fracturing fluid is further determined according to the fracturing pressure.

[0013] If the fracturing pressure of sandstone is less than that of shale, the order of injecting fracturing fluids is as follows: slickwater, crosslinking fluid, rope plugging agent, crosslinking fluid, slickwater;

[0014] If the fracturing pressure of sandstone is greater than that of shale, the order of injecting fracturing fluids is as follows: crosslinking fluid, slickwater, rope plugging agent, slickwater, crosslinking fluid;

[0015] S5. If, in the vertical direction of the reservoir section, thin interbedded sandstone and shale and thick sandstone interbedded with shale coexist, or thin interbedded sandstone and shale and thick shale interbedded with sandstone coexist, then the two reservoir sections are segmented using segmented bridge plugs, and the sections are modified from bottom to top, with steps S1-S4 executed respectively.

[0016] Compared with the prior art, the present invention has the following advantages and beneficial effects: the present invention takes into account the differences between sandstone and shale reservoirs, conducts lithology assessment before stimulation, and then adopts different fracturing methods according to different lithological characteristics, so as to fully and effectively stimulate the reservoir section.

[0017] In addition, this scheme adopts a segmented fracturing method for the reservoir section, which can fully transform the complex sand and shale lithology reservoir section in the vertical direction.

[0018] Regarding step S41, in the technology used when the reservoir segment is a thin interbedded sand and shale layer, the existing technology usually adopts a mixed injection method, that is, first injecting slickwater to carry sand, and then injecting crosslinking liquid to carry sand. However, the reverse mixed pressure process in this solution first injects crosslinking liquid to carry sand, and then injects slickwater to carry sand. In this invention, slickwater and the crosslinking liquid can transport proppant. First, the crosslinking liquid is injected to carry sand, which is used to pressure through the thin interbedded sand and shale layer and increase the upward extension of the fracture. Then, slickwater is injected to carry sand, which reduces the damage of the liquid to the reservoir. After the slickwater completes the transport of proppant, the crosslinking liquid is finally injected. The high viscosity crosslinking liquid completes the transport of proppant to the more distant part of the fracture.

[0019] Crosslinked liquids are characterized by high viscosity and low filtration loss, possessing two key advantages: firstly, they can penetrate bedding planes vertically; secondly, they have excellent sand-carrying capacity, transporting sand to more distant fractures and improving the conductivity of those fractures. Slickwater, on the other hand, has lower viscosity, higher filtration loss, and weaker sand-carrying capacity, making it less effective at transporting sand to distant fractures. However, it causes less damage to the reservoir than crosslinked liquids. Therefore, the approach of this invention is to first use crosslinked liquids to penetrate bedding planes, lengthening the fractures laterally and raising them vertically. Then, slickwater is used to deliver proppant to fill the created fractures (using slickwater because it causes less formation damage). Finally, crosslinked liquids are injected again. The aim is to increase the distance sand travels within the fractures while minimizing formation damage. In this invention, "sand" and "proppant" are synonymous.

[0020] Regarding step S42 of this invention, when the reservoir section is a thick sandstone interbedded with shale or a thick shale interbedded with sandstone, the principle and advantages of the sequence of injecting fracturing fluid are as follows:

[0021] The low fracturing pressure of sandstone indicates that the sandstone layer fracturing first. Sandstone layers are generally characterized by poor bedding, so high-viscosity crosslinking fluids are not needed to penetrate the layers vertically during the fracture extension stage. Therefore, slickwater fracturing is first used to carry sand and extend the fracture laterally. Then, a small amount of high-viscosity crosslinking fluid is used to carry sand to the far end of the fracture. When the sandstone layer fracture stops extending, temporary plugging knots are injected to force the shale layer to fracture. Since the bedding and natural fractures within the shale layer are relatively well-developed, the filtration is relatively large. Therefore, a high-viscosity crosslinking fluid is used to reduce filtration and penetrate the shale bedding planes, allowing the fracture to extend vertically. Finally, slickwater sand-carrying fluid is injected to reduce reservoir damage and allow the fracture to extend laterally. The fracturing pressure of shale is lower, which is the opposite of the above explanation.

[0022] Furthermore, in step S2, the perforation construction adopts a segmented construction method, forming multiple perforation segments, with each segment containing 48-54 perforations.

[0023] The number of perforations in this scheme can meet the requirements of large-volume fracturing operations of 16-18 cubic meters per minute, which can improve the efficiency of subsequent fracturing operations.

[0024] Furthermore, in step S2, a differentiated perforation structure is adopted within each segment, and the spacing between perforation clusters in each segment is the same. This scheme enables the dominant clusters (clusters with better physical properties and lower fracturing pressure) within a segment to initiate fracturing quickly, thereby making full use of the dominant segment.

[0025] Furthermore, in step S2, a rope knot temporary plugging process is also used to assist in the perforation construction. During the construction, the timing of the rope knot temporary plugging is determined based on the volume change rate of each cluster of fractures in each fracturing section of the reservoir.

[0026] In this scheme, the volume change rate of each cluster of fractures in each fracturing section of the reservoir is designed in advance to determine the timing of temporary plugging of the knots. This provides guidance for the timing of knot deployment, enabling more accurate deployment at the appropriate time, and facilitating better fracturing effects in the later stages.

[0027] Furthermore, liquid carbon dioxide is injected into the reservoir section before the fracturing operation in step S3.

[0028] The higher the fracturing pressure of the rock strata, the more difficult the fracturing becomes. However, in this scheme, by pre-injecting liquid CO2, the fracturing pressure of the rock strata can be reduced, and the post-fracturing flowback efficiency can be improved.

[0029] Furthermore, in step S41, the proppant includes 70 / 140 mesh, 40 / 70 mesh and 30 / 50 mesh proppants, and the usage ratio of the three proppants is 4:4:2;

[0030] Slippery water and crosslinking liquid are used to transport 70 / 140 mesh, 40 / 70 mesh, and 30 / 50 mesh proppant.

[0031] The purpose of using proppant with different particle sizes in this scheme is to match the conductivity of different locations in the formation and fracture. The proximal end of the fracture is close to the wellbore, where oil and gas will converge, so a larger conductivity is required, and the proppant used is larger in particle size (30 / 50 mesh). The distal end of the fracture does not require such a large conductivity as the proximal end, and only needs to match the permeability parameters of the formation matrix itself, so a smaller particle size proppant (70 / 140 mesh) can be used.

[0032] Two liquids were considered for transporting proppant because they have different advantages and disadvantages. Slippery water causes less damage to the reservoir, but it is not easy to transport proppant to the far end of the fracture and cannot break through the lithological bedding plane. Crosslinked liquid causes more damage to the reservoir, but it has a better effect on vertical modification of shale layers. Therefore, two liquids were used.

[0033] Furthermore, in step S41, firstly, a crosslinked liquid with a volume of reservoir section length × 15 cubic meters is injected at a discharge rate of 16-18 cubic meters per minute, carrying sand, and finally, slickwater with a volume of reservoir section length × 15 cubic meters is injected at a discharge rate of 16-18 cubic meters per minute.

[0034] This solution enables large-scale construction and improves construction efficiency.

[0035] Furthermore, in step S42, slickwater and crosslinking liquid are used to transport proppant. Slickwater is used to transport temporary plugging knots. The proppant includes 70 / 140 mesh, 40 / 70 mesh, and 30 / 50 mesh proppant, and the usage ratio of the three proppants is 4:4:2. The total volume of injected proppant is the reservoir section length × 8 cubic meters, and there are 16 to 18 knots.

[0036] If the sandstone fracturing pressure is less than that of shale, first inject slickwater carrying sand-carrying fluid, then inject crosslinking liquid carrying sand-carrying fluid; then inject rope knot temporary plugging agent to seal the artificial crack openings formed; finally, inject crosslinking liquid carrying sand-carrying fluid and slickwater carrying sand-carrying fluid in sequence, wherein the ratio of 70 / 140 mesh, 40 / 70 mesh and 30 / 50 mesh proppant transported before and after rope knot temporary plugging is 4:4:2;

[0037] If the sandstone fracturing pressure is greater than that of shale fracturing pressure, first inject crosslinked liquid carrying sand-carrying liquid and slickwater carrying sand-carrying liquid in sequence, then inject rope knot temporary plugging agent to seal the artificial crack openings formed, and finally inject slickwater carrying sand-carrying liquid and crosslinked liquid carrying sand-carrying liquid in sequence. The ratio of 70 / 140 mesh, 40 / 70 mesh, and 30 / 50 mesh proppant delivered before and after rope knot temporary plugging is 4:4:2.

[0038] Furthermore, in step S42, if the sandstone fracturing pressure is less than the shale fracturing pressure, firstly, a slickwater carrying sand fluid with a volume of reservoir section length × 10 cubic meters is injected at a discharge rate of 16-18 cubic meters / minute, followed by a crosslinked liquid carrying sand fluid with a volume of reservoir section length × 5 cubic meters at the same discharge rate; then, a rope knot temporary plugging agent is added to seal the artificial fracture pores formed; finally, a slickwater carrying sand fluid with a volume of reservoir section length × 5 cubic meters and a crosslinked liquid carrying sand fluid with a volume of reservoir section length × 10 cubic meters are injected sequentially at a discharge rate of 16-18 cubic meters / minute.

[0039] If the sandstone fracturing pressure is greater than that of the shale fracturing pressure, firstly, inject crosslinked fluid carrying sand and slickwater carrying sand at a rate of 16-18 cubic meters per minute, with a volume of 5 cubic meters of reservoir length and 10 cubic meters of reservoir length respectively. Then, inject rope-knotting agent to seal the artificial fracture pores formed. Finally, inject crosslinked fluid carrying sand and slickwater carrying sand at a rate of 10 cubic meters of reservoir length and 5 cubic meters of reservoir length respectively.

[0040] Furthermore, the rupture pressure mentioned in step S42 is calculated and determined using the following formula:

[0041] Pp=3σ h -σ H -P H +σ t ;

[0042] In the formula, Pp represents the rock fracture pressure, and σ h σ represents the minimum horizontal principal stress. H P represents the maximum horizontal principal stress. H σ represents the hydrostatic pressure. t This indicates the tensile strength of the rock.

[0043] A layered fracturing system suitable for complex lithological sections of sandstone and shale, comprising:

[0044] The identification module is used to determine the location and length of the reservoir segment;

[0045] The perforation construction module is used to perforate downhole casing;

[0046] The judgment module is used to determine the lithology of the reservoir section;

[0047] The fracture construction module is used for segmented hydraulic fracturing of reservoir sections with different lithologies.

[0048] The crack construction module includes:

[0049] The construction module for thin interlayered sand shale sections is used for segmented fracturing construction of thin interlayered sand shale sections.

[0050] Construction modules for thick sandstone interbedded with shale or thick shale interbedded with sandstone are used for segmented fracturing construction of thick sandstone interbedded with shale or thick shale interbedded with sandstone.

[0051] The bridge plug segment construction module is used to separate the thin interbedded sandstone and shale sections and the thick sandstone-shale interbedded sections, or the thin interbedded sandstone and shale interbedded sections and the thick shale-shale interbedded sections, and then carry out fracturing construction according to the construction modules for the thin interbedded sandstone and shale sections and the thick sandstone-shale interbedded sections, or the thick shale-shale interbedded sections.

[0052] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0053] Under the condition of a large discharge rate of 16-18 cubic meters per minute, it is possible to fully stimulate complex sand and shale reservoir sections in the vertical direction. Since the number of perforations may not meet the design requirements during the perforation construction process, this invention uses a temporary plugging rope knot process to temporarily plug the perforations and increase the wellbore pressure, which can make the designed perforations open smoothly, thereby increasing the number of perforations to meet the design requirements. This allows for a larger fracture area to be generated during subsequent fracturing operations, thereby increasing the reservoir stimulation volume and oil drainage area. Attached Figure Description

[0054] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0055] Figure 1 This is a flowchart illustrating an embodiment of a layered hydraulic fracturing method and system applicable to complex lithological sections of sandstone and shale according to the present invention.

[0056] Figure 2 This is a design diagram of a layered fracturing method and system embodiment applicable to complex lithological sections of sand and shale, with differentiated perforation layout;

[0057] Figure 3 This is a schematic diagram illustrating the optimization of the timing of temporary plugging agent injection in an embodiment of a layered fracturing method and system applicable to complex lithological sections of sand and shale according to the present invention. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0059] like Figure 1 As shown, this embodiment 1 provides a layered fracturing method suitable for complex lithological sections of sandstone and shale, including the following steps:

[0060] S1. Reservoir sections are identified using reservoir logging curve data, cuttings logging data, and core observation data, and their locations and lengths are determined. Taking the YQ102 well as an example, which has a vertically interbedded sandstone section and a sandstone section with alternating layers of sandstone and shale, the vertical locations are 3430–3500 m and 2928–3008 m, respectively, and the lengths of the reservoir sections are 70 m and 80 m, respectively.

[0061] S2, Downhole casing perforation construction, perforating the downhole casing with a cable-connected tool. Since the reservoir section has a certain length, the perforation construction in this embodiment adopts a layered and clustered construction method, forming multiple fractures in the longitudinal direction. In this embodiment, the number of perforations in each section is 48-54, which can ensure a large flow rate of 16-18 cubic meters / minute in the later stage.

[0062] Combination Figure 2 As shown, in this embodiment, step S2 adopts a segment-differentiated perforation structure. The perforation cluster spacing in each segment is the same. The number of perforations in clusters corresponding to relatively high-quality reservoirs is less, while the number of perforations in clusters corresponding to relatively poor-quality reservoirs is more. The total number of perforations is 48. This ensures that high-quality reservoirs can be utilized to the maximum extent during later construction.

[0063] S3. Lithology assessment: Different fracturing methods are employed based on different lithologies. The reservoir section includes one of the following: thin interbedded sandstone and shale, thick sandstone interbedded with shale, or thick shale interbedded with sandstone; or a combination of thin interbedded sandstone and shale and thick sandstone interbedded with shale; or a combination of thin interbedded sandstone and shale and thick shale interbedded with sandstone. In well YQ102, both thin interbedded sandstone and shale and thick sandstone interbedded with shale reservoir sections exist vertically, with bottom boundaries at 3500m and 3008m respectively, and lengths of 70m and 80m respectively. Different fracturing methods are employed based on different lithologies. When two lithologies exist vertically, bridge plug segmented fracturing is used, and fracturing proceeds segment by segment from bottom to top, i.e., the lower reservoir section is fracturing first, followed by the upper reservoir section.

[0064] S4, fracturing operation: Based on the lithology determined in S3, the reservoir section is fracturing in stages; in this embodiment, 60 cubic meters of liquid carbon dioxide is injected into the reservoir section before fracturing operation to reduce the fracturing pressure of the reservoir, which makes it easier to reduce the difficulty of subsequent fracturing operation and improve the flowback efficiency after fracturing.

[0065] In step S4, the following fracturing methods are used for reservoir sections with different lithologies:

[0066] S41, when the reservoir section is a thin interbedded sand and shale layer, a reverse mixing fracturing process of "slickwater + crosslinking fluid" is adopted. Existing technologies use a mixed injection process, i.e., slickwater is injected first to carry proppant, followed by crosslinking fluid to carry proppant. However, the reverse mixing process in this scheme refers to the injection of a mixture of slickwater and crosslinking fluid to carry proppant. First, crosslinking fluid is injected to carry proppant, used to penetrate the thin interbedded sand and shale layer and increase the upward extension of fractures. Then, slickwater is injected to carry proppant, reducing fluid damage to the reservoir. After the slickwater completes the proppant delivery, crosslinking fluid is injected last. High-viscosity crosslinking liquid is used to transport the proppant to the more distant part of the fracture. Slippery water and crosslinking liquid transport the proppant. The proppant includes 70 / 140 mesh, 40 / 70 mesh and 30 / 50 mesh proppant, and the usage ratio of the three proppants is 4:4:2. The total volume of the three proppants is the reservoir length × 8 cubic meters. In this embodiment, the total volume of the three proppants is 640t. Specifically, in this embodiment, the three proppants are 70 / 140 mesh quartz sand, 40 / 70 mesh quartz sand and 30 / 50 mesh coated sand.

[0067] First, a crosslinking fluid with a volume of 15 cubic meters per minute (reservoir length × 16-18 cubic meters per minute) is injected to carry sand. Finally, slickwater with a volume of 15 cubic meters per minute (reservoir length × 16-18 cubic meters per minute) is injected. Specifically, in this embodiment, 1200 cubic meters of crosslinking fluid carrying sand are injected first at a rate of 16-18 cubic meters per minute, and finally 1200 cubic meters of slickwater carrying sand are injected at a rate of 16-18 cubic meters per minute.

[0068] S42 is a reservoir section consisting of thick sandstone interbedded with shale or thick shale interbedded with sandstone. A "rope plugging + layered stimulation" fracturing technique is employed. First, the fracturing pressure values ​​of the sandstone and shale are determined based on the stress profile interpreted from well logging. Then, the injection sequence of fracturing fluids is determined according to the fracturing pressure levels.

[0069] In this embodiment, the rupture pressure is calculated and determined using the following formula:

[0070] Pp=3σ h -σ H -P H +σ t ;

[0071] In the formula, Pp represents the rock fracture pressure, in MPa, σ h Represents the minimum horizontal principal stress, in MPa, σ. H Represents the maximum horizontal principal stress, unit: MPa, P H σ represents the hydrostatic column pressure in MPa. t This indicates the tensile strength of rock, measured in MPa.

[0072] In step S42, proppant is delivered using slickwater and crosslinking liquid. Slickwater is used to deliver temporary plugging knots. The proppant includes 70 / 140 mesh, 40 / 70 mesh, and 30 / 50 mesh proppant, and the usage ratio of the three proppants is 4:4:2. The total volume of injected proppant is the reservoir section length × 8 cubic meters, and there are 16 to 18 knots.

[0073] If the sandstone fracturing pressure is less than that of shale, the order of injecting fracturing fluids is as follows: slickwater, crosslinked fluid, knotted temporary plugging agent, crosslinked fluid, slickwater; specifically: first, inject slickwater carrying sand at a flow rate of 16-18 cubic meters per minute, with a volume equal to the reservoir length × 10 cubic meters; then, inject crosslinked fluid carrying sand at the same flow rate, with a volume equal to the reservoir length × 5 cubic meters; next, inject knotted temporary plugging agent to seal the artificial fracture pores; finally, inject 16-... At a discharge rate of 18 cubic meters per minute, slickwater carrying liquid and crosslinked liquid carrying liquid with a volume of reservoir section length × 5 cubic meters were injected sequentially. The ratio of 70 / 140 mesh, 40 / 70 mesh, and 30 / 50 mesh proppant transported before and after temporary plugging was 4:4:2. As shown in Table 1, the order before plugging was slickwater first, followed by crosslinked liquid, and after plugging, crosslinked liquid was transported first, followed by slickwater.

[0074] If the sandstone fracturing pressure is greater than that of shale fracturing pressure, the order of injecting fracturing fluids is as follows: crosslinked fluid, slickwater, rope plugging agent, slickwater, crosslinked fluid; specifically: first, inject crosslinked fluid carrying sand and slickwater carrying sand at a flow rate of 16-18 cubic meters per minute, with a volume of 5 cubic meters of reservoir length × 10 cubic meters; then, inject rope plugging agent to seal the artificial fracture pores formed; finally, inject slickwater carrying sand and slickwater carrying sand at a flow rate of 10 cubic meters of reservoir length × 5 cubic meters; the ratio of 70 / 140 mesh, 40 / 70 mesh, and 30 / 50 mesh proppant delivered before and after rope plugging is 4:4:2. As shown in Table 1, in this case, the order before temporary blockage is to first use crosslinking liquid for transportation, and then use slickwater for transportation. After temporary blockage, the order is to first use slickwater for transportation, and then use crosslinking liquid for transportation.

[0075] In a specific embodiment: the average fracturing pressure of the sandstone in this section (50.5 MPa) is significantly lower than the fracturing pressure of the upper and lower shale layers (upper shale layer: 59.7 MPa, lower shale layer: 70.3 MPa), so the injection sequence of "slippery water + crosslinking fluid + rope knot temporary plugging agent + crosslinking fluid + slippery water" is adopted; slippery water and crosslinking fluid are also used to transport proppant in this step. The proppant includes 70 / 140 mesh, 40 / 70 mesh, and 30 / 50 mesh proppant, with 224t, 224t, and 112t respectively, in a ratio of 4:4:2, with a total of 560t, and 18 temporary plugging rope knots are used;

[0076] Specifically: First, inject 60 cubic meters of liquid carbon dioxide at a flow rate of 16-18 cubic meters per minute, followed by 600 cubic meters of slickwater carrying sand fluid; then inject 340 cubic meters of crosslinked liquid carrying sand fluid, and then reduce the flow rate to 4-8 cubic meters per minute and add 18 temporary plugging knots. Use 160 cubic meters of slickwater to send it to the bottom of the well to seal the perforation hole where artificial fractures were first formed (artificial fractures are fractures that slowly form after perforation when liquid is injected into the wellbore); finally, inject 370 cubic meters of crosslinked liquid carrying sand fluid and 630 cubic meters of slickwater carrying sand fluid at a flow rate of 16-18 cubic meters per minute, for a total injection of 2160 cubic meters of liquid, as shown in Table 1.

[0077] Table 1 Pumping Procedure for Shale Interbedded with Sandstone (3430–3500 m)

[0078]

[0079] This embodiment also discloses a layered fracturing system suitable for complex lithological sections of sand and shale, including: an identification module for determining the location and length of the reservoir section;

[0080] The perforation construction module is used to perforate downhole casing;

[0081] The judgment module is used to determine the lithology of the reservoir section;

[0082] The fracture construction module is used for segmented hydraulic fracturing of reservoir sections with different lithologies.

[0083] The crack construction module includes:

[0084] The construction module for thin interlayered sand shale sections is used for segmented fracturing construction of thin interlayered sand shale sections.

[0085] Construction modules for thick sandstone interbedded with shale or thick shale interbedded with sandstone are used for segmented fracturing construction of thick sandstone interbedded with shale or thick shale interbedded with sandstone.

[0086] The bridge plug segment construction module is used to separate the thin interbedded sandstone and shale sections and the thick sandstone-shale interbedded sections, or the thin interbedded sandstone and shale interbedded sections and the thick shale-shale interbedded sections, and then carry out fracturing construction according to the construction modules for the thin interbedded sandstone and shale sections and the thick sandstone-shale interbedded sections, or the thick shale-shale interbedded sections.

[0087] The difference between Example 2 and Example 1 is that: [The following text appears to be a continuation of the previous sentence and Figure 3 The diagram shown is an optimization chart for the timing of temporary plugging agent administration, where Series 1 represents the volume change rate of the left wing fracture and Series 2 represents the volume change rate of the right wing fracture.

[0088] In this embodiment, during the perforation construction in step S2, a rope knot temporary plugging process is also used to assist in the construction, so as to increase the degree of utilization of the reservoir by the fractures in the longitudinal direction. During construction, the timing of rope knot temporary plugging is determined based on the change rate of the volume change of each cluster of fractures in each fracturing section of the reservoir section with the fracturing time.

[0089] By designing the relationship between fracturing time and the volume change rate of each cluster of fractures in each fracturing section in advance according to the reservoir characteristics, when the volume change rate of the fractures gradually approaches the equilibrium state as the fracturing time increases, this can be regarded as the appropriate time to put in the rope plugging.

[0090] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A layered hydraulic fracturing method suitable for complex lithological sections of sandstone and shale, characterized in that, Includes the following steps: S1, Identify reservoir segments and determine their location and length; S2, downhole casing perforation construction; S3, determine the lithology, and adopt different fracturing methods according to different lithologies. The reservoir section includes one of the following: thin interbedded sandstone and shale section, thick sandstone interbedded with shale section, and thick shale interbedded with sandstone section; or the reservoir section includes thin interbedded sandstone and shale section and thick sandstone interbedded with shale section; or the reservoir section includes thin interbedded sandstone and shale section and thick shale interbedded with sandstone section. S4, fracturing operation: Based on the lithology determined in S3, the reservoir section is fracturing in stages; liquid carbon dioxide is injected into the reservoir section before fracturing operation; In step S4, the following fracturing methods are used for reservoir sections with different lithologies: S41, when the reservoir section is a thin interbedded sand and shale layer, a reverse mixing fracturing process of "slickwater + crosslinking fluid" is adopted. This reverse mixing fracturing process refers to the injection of a mixture of slickwater and crosslinking fluid to carry proppant. First, crosslinking fluid is injected to carry proppant, used to penetrate the thin interbedded sand and shale layers. Then, slickwater is injected to carry proppant. After the slickwater completes the proppant delivery, crosslinking fluid is finally injected to complete the proppant delivery. The proppant includes 70 / 140 mesh and 40 / 70 mesh. The three types of proppant are used in a ratio of 4:4:2, and 30 / 50 mesh proppant is used. Sliding water and crosslinking liquid are used to transport 70 / 140 mesh, 40 / 70 mesh, and 30 / 50 mesh proppant. In step S41, crosslinking liquid with a volume of reservoir length × 15 cubic meters is first injected at a rate of 16~18 cubic meters / minute, and sand-carrying liquid is injected at a rate of 16~18 cubic meters / minute, and sand-carrying liquid is injected at a rate of 16~18 cubic meters / minute. S42, the reservoir section is a thick sandstone interbedded with shale or a thick shale interbedded with sandstone. The fracturing process of "rope knot temporary plugging + layered stimulation" is adopted. First, the fracturing pressure values ​​of sandstone and shale are determined according to the stress profile interpreted by well logging. Then, the sequence of injecting fracturing fluid is further determined according to the fracturing pressure. If the fracturing pressure of sandstone is less than that of shale, the order of injecting fracturing fluids is as follows: slickwater, crosslinking fluid, rope plugging agent, crosslinking fluid, slickwater; If the fracturing pressure of sandstone is greater than that of shale, the order of injecting fracturing fluids is as follows: crosslinking fluid, slickwater, rope plugging agent, slickwater, crosslinking fluid; S5. If, in the vertical direction of the reservoir section, thin interbedded sandstone and shale and thick sandstone interbedded with shale coexist, or thin interbedded sandstone and shale and thick shale interbedded with sandstone coexist, then the two reservoir sections are segmented using segmented bridge plugs, and the sections are modified from bottom to top, with steps S1-S4 executed respectively.

2. The layered fracturing method applicable to complex lithological sections of sandstone and shale as described in claim 1, characterized in that, In step S2, the perforation construction adopts a segmented construction method, forming multiple perforation segments, with each segment containing 48-54 perforations.

3. The layered fracturing method applicable to complex lithological sections of sandstone and shale as described in claim 2, characterized in that, In step S2, a differentiated perforation structure is adopted within each segment, and the spacing between the perforation clusters in each segment is the same.

4. The layered fracturing method applicable to complex lithological sections of sandstone and shale as described in claim 3, characterized in that, In step S2, a rope knot temporary plugging technique is also used during perforation construction. The timing of rope knot temporary plugging is determined based on the volume change rate of each cluster of fractures in each fracturing section of the reservoir.

5. A layered fracturing method suitable for complex lithological sections of sandstone and shale according to any one of claims 1-4, characterized in that, In step S42, proppant is delivered using slickwater and crosslinking liquid. Slickwater delivers temporary plugging knots. The proppant includes 70 / 140 mesh, 40 / 70 mesh, and 30 / 50 mesh proppant, and the usage ratio of the three proppants is 4:4:

2. The total volume of injected proppant is the reservoir section length × 8 cubic meters, and there are 16 to 18 knots. If the sandstone fracturing pressure is less than that of shale, first inject slickwater carrying sand fluid, then inject crosslinking liquid carrying sand fluid. Then, a rope knot temporary plugging agent is added to seal the artificial cracks and holes formed; finally, crosslinking liquid and slickwater sand-carrying liquid are injected in sequence, wherein the ratio of 70 / 140 mesh, 40 / 70 mesh and 30 / 50 mesh proppant delivered before and after rope knot temporary plugging is 4:4:

2. If the sandstone fracturing pressure is greater than that of shale fracturing pressure, first inject crosslinked liquid carrying sand-carrying liquid and slickwater carrying sand-carrying liquid in sequence, then inject rope knot temporary plugging agent to seal the artificial crack openings formed, and finally inject slickwater carrying sand-carrying liquid and crosslinked liquid carrying sand-carrying liquid in sequence. The ratio of 70 / 140 mesh, 40 / 70 mesh, and 30 / 50 mesh proppant delivered before and after rope knot temporary plugging is 4:4:

2.

6. The layered fracturing method applicable to complex lithological sections of sandstone and shale as described in claim 5, characterized in that, In step S42, if the sandstone fracturing pressure is less than the shale fracturing pressure, first inject slickwater carrying sand fluid with a displacement of 16-18 cubic meters per minute, the volume of which is the length of the reservoir section × 10 cubic meters, and then inject crosslinked liquid carrying sand fluid with the same displacement, the volume of which is the length of the reservoir section × 5 cubic meters. Then, a rope knot temporary plugging agent is added to seal the artificial fracture openings formed; finally, slickwater carrying sand and crosslinking liquid carrying sand with a volume of 5 cubic meters of reservoir section length and 10 cubic meters of reservoir section length are injected sequentially at a discharge rate of 16-18 cubic meters / minute. If the sandstone fracturing pressure is greater than that of the shale fracturing pressure, firstly, inject crosslinked fluid carrying sand and slickwater carrying sand at a rate of 16-18 cubic meters per minute, with a volume of 5 cubic meters of reservoir length and 10 cubic meters of reservoir length respectively. Then, inject rope-knotting agent to seal the artificial fracture pores formed. Finally, inject crosslinked fluid carrying sand and slickwater carrying sand at a rate of 10 cubic meters of reservoir length and 5 cubic meters of reservoir length respectively.

7. The layered fracturing method applicable to complex lithological sections of sandstone and shale as described in claim 1, characterized in that, The rupture pressure mentioned in step S42 is determined by the following formula: ； In the formula Indicates rock fracture pressure, Indicates the minimum horizontal principal stress. Indicates the maximum horizontal principal stress. Indicates the hydrostatic pressure. This indicates the tensile strength of the rock.

8. A layered fracturing system suitable for complex lithological sections of sandstone and shale, the system being used to perform a layered fracturing method for complex lithological sections of sandstone and shale as described in any one of claims 1-7, characterized in that, include: The identification module is used to determine the location and length of the reservoir segment; The perforation construction module is used to perforate downhole casing; The judgment module is used to determine the lithology of the reservoir section; The fracture construction module is used for segmented hydraulic fracturing of reservoir sections with different lithologies. The crack construction module includes: The construction module for thin interlayered sand shale sections is used for segmented fracturing construction of thin interlayered sand shale sections. Construction modules for thick sandstone interbedded with shale or thick shale interbedded with sandstone are used for segmented fracturing construction of thick sandstone interbedded with shale or thick shale interbedded with sandstone. The bridge plug segment construction module is used to separate the thin interbedded sandstone and shale sections and the thick sandstone-shale interbedded sections, or the thin interbedded sandstone and shale interbedded sections and the thick shale-shale interbedded sections, and then carry out fracturing construction according to the construction modules for the thin interbedded sandstone and shale sections and the thick sandstone-shale interbedded sections, or the thick shale-shale interbedded sections.

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