Separate layer fracturing method and system suitable for sand page complex lithologic section

Abstract

The invention belongs to the technical field of shale oil gas and tight gas exploration and development, and particularly discloses a separate layer fracturing method suitable for a sand page complex lithologic section, which comprises the following steps: S1, identifying a reservoir section; s2, underground casing perforation construction is carried out; s3, lithology is judged; s4, fracturing construction is carried out, and staged fracturing is carried out on the reservoir section according to the lithology category judged in the step S3; s5, the longitudinal upper sand page thin interbed section and the thick-layer sandstone interlayer shale of the reservoir section exist at the same time or the sand page thin interbed section and the thick-layer shale interlayer sandstone section exist at the same time; and the two reservoir sections are segmented by using a segmented bridge plug. A separate-layer fracturing system suitable for a lithologic section with a complicated sand page comprises an identification module, a perforation construction module, a judgment module, a crack construction module, a construction module for a section with shale sandwiched by thick-layer sandstone or a section with sandstone sandwiched by thick-layer shale, and a tripping-in bridge plug subsection construction module. The method can solve the problem that at present, sufficient transformation is difficult to achieve on a reservoir with tight sandstone and shale reservoir alternately developed in the longitudinal direction.

Description

Technical Field

[0001] The present invention relates to the technical field of shale oil and gas and tight gas exploration and development, and in particular to a layered fracturing method and system suitable for sandstone complex lithology sections. Background Art

[0002] In recent years, China has increased its efforts in the exploration and development of shale oil and gas and tight gas. Xinjiang, Daqing, Changqing, Southwest and other oil and gas fields have made important breakthroughs in the field of shale oil and gas or tight gas. Shale reservoirs and tight sandstone reservoirs have poor physical properties. At the same time, the current status of shale oil and gas and tight gas exploration and development in major oil fields was investigated and found that shale reservoirs and tight sandstone reservoirs often overlap vertically, resulting in increased lithology complexity, which brings uncertainty to the effect of reservoir fracturing transformation.

[0003] Considering the differences between sandstone and shale reservoirs, the transformation purposes of shale reservoirs and tight sandstone reservoirs in China are different. Natural fractures are often developed inside shale reservoirs, and the transformation is mainly aimed at forming complex fracture networks and increasing the transformation volume; natural fractures in tight sandstone reservoirs are generally not developed or developed locally, so they are mainly transformed to form long fractures and increase the oil and gas contact area. At present, although the transformation purposes are different, both shale and tight sandstone reservoirs can be increased by using segmented multi-cluster fracturing technology. However, for reservoir sections where sandstone and shale are alternately superimposed vertically, it is difficult to fully transform the reservoir without formulating targeted transformation process measures. Therefore, a layered fracturing design method suitable for complex lithology sections of sandstone and shale was invented, which can fully transform complex lithology reservoir sections and increase reservoir transformation volume and drainage area. Summary of the invention

[0004] The present invention provides a layered fracturing method suitable for sandstone and shale complex lithology sections, aiming to solve the problem that it is difficult to fully transform the reservoirs with dense sandstone and shale reservoirs alternately developed in the vertical direction.

[0005] The present invention is implemented by the following technical scheme: a layered fracturing method suitable for a sand sheet with complex lithology, comprising the following steps:

[0006] S1, identifying the reservoir segment and determining the location and length of the reservoir segment;

[0007] S2, downhole casing perforation construction;

[0008] S3, determining the lithology, and adopting different fracturing methods according to different lithologies, wherein the reservoir section includes one of a thin interbedded sandstone section, a thick sandstone interbedded shale section, and a thick shale interbedded sandstone section, or the reservoir section includes a thin interbedded sandstone section and a thick sandstone interbedded shale section, or the reservoir section includes a thin interbedded sandstone section and a thick shale interbedded sandstone section;

[0009] S4, fracturing construction, performing staged fracturing on the reservoir section according to the lithology category determined in S3;

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

[0011] S41, when the reservoir section is a thin interlayer of sand sheets, a "slippery water + gelling fluid" reverse mixed fracturing process is adopted, wherein the slippery water and gelling fluid are mixed and injected to carry sand, and the gelling fluid is first injected to carry sand to press through the thin interlayer of sand sheets; then the slippery water is injected to carry sand, and after the slippery water completes the transport of the proppant, the gelling fluid is finally injected to complete the transport of the proppant;

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

[0013] If the fracture pressure of sandstone is less than that of shale, the order of injecting fracturing fluid is: slippery water, gelling fluid, knot temporary plugging agent, gelling fluid, slippery water;

[0014] If the fracture pressure of sandstone is greater than that of shale, the order of injecting fracturing fluid is: gelling fluid, slippery water, knot temporary plugging agent, slippery water, gelling fluid;

[0015] S5, in the vertical direction of the reservoir section, thin interbedded sand and shale sections and thick sandstone and shale sections exist simultaneously, or thin interbedded sand and shale sections and thick shale and sandstone sections exist simultaneously; then the two reservoir sections are segmented using segmented bridge plugs, and are transformed section by section from bottom to top, and steps S1-S4 are performed respectively.

[0016] Compared with the prior art, the present invention has the following advantages and beneficial effects: This scheme takes into account the differences between sandstone and shale reservoirs, makes a lithology judgment before transformation, and then adopts different fracturing methods according to different lithological characteristics, so that the reservoir section can be fully and effectively transformed.

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

[0018] With respect to step S41, in the technology adopted when the reservoir section is a thin interlayer of sand sheets, in the prior art, a mixed injection method is usually adopted when the reservoir section is a thin interlayer of sand sheets, that is, first injecting slippery water to carry sand, and then injecting bonding liquid to carry sand, while the reverse mixed pressure process in this scheme is to first inject bonding liquid to carry sand, and then inject slippery water to carry sand. In the present invention, slippery water and the bonding liquid can transport proppant, and the bonding liquid is first injected to carry sand, which is used to press through the thin interlayer of sand sheets and increase the upward extension of the fractures; then slippery water is injected to carry sand to reduce the damage of the liquid to the reservoir. After the slippery water completes the transportation of the proppant, the bonding liquid is finally injected to complete the transportation of the proppant to the farther end of the fracture with the high-viscosity bonding liquid.

[0019] The characteristics of the gelling fluid are high viscosity and low filtration loss. It has two characteristics: one is that it can penetrate the bedding vertically, and the other is that it has good sand carrying performance, which can transport sand to the farther end of the fracture and improve the conductivity of the distal fracture; the slick water has a lower viscosity, higher filtration loss, and weaker sand carrying capacity, and is not easy to transport sand to the far end of the fracture, but it is less harmful to the reservoir than the gelling fluid; therefore, the idea of ​​the present invention is to first use the gelling fluid to penetrate the bedding, lengthen the fracture horizontally and make it higher vertically, and then use the slick water to transport the proppant to fill the fracture (the use of slick water is considered to be less harmful to the formation), and finally inject the gelling fluid, the purpose is to reduce the formation damage while increasing the distance that the sand is transported in the fracture. The "sand" and "proppant" described in the present invention have the same meaning.

[0020] For step S42 of the present invention, when the reservoir section is a thick sandstone intercalated with shale section or a thick shale intercalated with sandstone section, the principle and benefits of the sequence of injecting the fracturing fluid are:

[0021] The low fracture pressure of sandstone means that the sandstone layer starts to fracture first. The sandstone layer is generally characterized by underdeveloped bedding, and does not require high-viscosity bonding fluid to penetrate the layers vertically during the fracture extension stage. Therefore, slippery water-carrying sand fracturing is first used to extend the fracture laterally, and then a small amount of high-viscosity bonding fluid is used to carry sand to the far end of the fracture. When the fracture of the sandstone layer is no longer extending, a temporary plugging knot is put in to force the shale layer to fracture. Since the bedding and natural fractures in the shale layer are relatively developed and the filtration loss is large, a higher viscosity bonding fluid is used to reduce the filtration loss and penetrate the shale bedding surface to extend the fracture vertically. Finally, slippery water-carrying sand fluid is injected to reduce reservoir damage and allow the fracture to extend laterally. The fracture pressure of shale is relatively low, which is the opposite of the above explanation.

[0022] Furthermore, in step S2, the perforation construction adopts a segmented construction method to form multiple segments of perforations, and the number of perforations in each segment is 48-54.

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

[0024] Furthermore, in step S2, a differentiated perforation structure is adopted within the segment, and the perforation cluster spacing of each segment is the same. This solution enables the dominant clusters (clusters with better physical properties and lower fracture pressure) within the segment to fracture quickly, thereby fully utilizing the dominant segment.

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

[0026] In this scheme, the volume change rate of each cluster of fractures in each fracturing section of the reservoir section is designed in advance to determine the timing of temporary plugging with knots. This can provide guidance for the timing of inserting knots, and can more accurately insert knots at the right time, which is conducive to better fracturing effects in the later stage.

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

[0028] Since the higher the fracture pressure of the rock formation, the more difficult it is to perform fracturing, this solution can reduce the fracture pressure of the rock formation and improve the flowback efficiency after fracturing by pre-injecting liquid CO2 in advance.

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

[0030] Slippery water and gel-linked fluid are used to transport 70 / 140 mesh, 40 / 70 mesh, and 30 / 50 mesh proppants.

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

[0032] Two liquids are considered for transporting proppants because they have different advantages and disadvantages. Slick water causes less damage to the reservoir, but it is not easy to transport the proppant to the far end of the fracture and cannot break through the lithologic bedding plane. Coating fluid causes greater damage to the reservoir, but it has a better effect on the vertical transformation of the shale layer. Therefore, two liquids are used.

[0033] Further, in step S41, firstly, the volume of the gelling fluid is equal to the length of the reservoir section × 15 cubic meters, and the sand is carried along with it, and finally, the volume of the slippery water is equal to the length of the reservoir section × 15 cubic meters, and the displacement is 16 to 18 cubic meters / minute.

[0034] This solution can achieve large-volume construction and improve construction efficiency.

[0035] Further, in step S42, slick water and gelling fluid are used to transport proppant, slick water is used to transport temporary plugging knots, proppant includes 70 / 140 mesh, 40 / 70, 30 / 50 mesh proppant, and the usage ratio of the three proppant is 4:4:2; the total volume of the injected proppant is the reservoir section length × 8 square meters, and the number of knots is 16 to 18;

[0036] If the fracture pressure of sandstone is lower than that of shale, firstly inject the slickwater sand-carrying fluid, then inject the cementing fluid sand-carrying fluid; then inject the knot temporary plugging agent to plug the artificial fracture holes; finally inject the cementing fluid sand-carrying fluid and the slickwater sand-carrying fluid in sequence, wherein the proppant ratios of 70 / 140 mesh, 40 / 70 mesh and 30 / 50 mesh delivered before and after the knot temporary plugging are all 4:4:2;

[0037] If the fracture pressure of sandstone is greater than that of shale, firstly, the sand-carrying fluid of cementing liquid and the sand-carrying fluid of slick water are injected in sequence, and then the temporary plugging agent of rope knot is put in to seal the artificial fracture holes formed, and finally the sand-carrying fluid of slick water and the sand-carrying fluid of cementing liquid are injected in sequence, wherein the ratio of 70 / 140 mesh, 40 / 70 mesh and 30 / 50 mesh proppant transported before and after temporary plugging of rope knot is 4:4:2.

[0038] Further, in step S42, if the fracture pressure of sandstone is less than the fracture pressure of shale, firstly, a slickwater sand-carrying fluid with a volume of 10 cubic meters of the reservoir length × 16 to 18 cubic meters per minute is injected, and then a gel-linked fluid sand-carrying fluid with a volume of 5 cubic meters of the reservoir length × 5 cubic meters is injected at the same displacement; then a knot temporary plugging agent is added to plug the formed artificial fracture holes; finally, a slickwater sand-carrying fluid with a volume of 5 cubic meters of the reservoir length × 10 cubic meters of the reservoir length × 16 to 18 cubic meters per minute is injected in sequence;

[0039] If the sandstone fracture pressure is greater than the shale fracture pressure, first, inject a volume of 5 cubic meters of reservoir length × 5 cubic meters of cementing fluid and a volume of 10 cubic meters of reservoir length × 10 cubic meters of slickwater sand-carrying fluid at a displacement of 16 to 18 cubic meters per minute, then add a knot temporary plugging agent to seal the artificial fracture holes formed, and finally inject a volume of 10 cubic meters of slickwater sand-carrying fluid and a volume of 5 cubic meters of reservoir length × 10 cubic meters of reservoir length × 5 cubic meters of cementing fluid sand-carrying fluid at a displacement of 16 to 18 cubic meters per minute.

[0040] Further, the rupture pressure in step S42 is calculated and determined by the following formula:

[0041] Pp=3σ h -σ H -P H +σ t ;

[0042] Where Pp represents the rock fracture pressure, σ h represents the minimum horizontal principal stress, σ H represents the maximum horizontal principal stress, P H represents the hydrostatic column pressure, σ t Represents the tensile strength of rock.

[0043] A layered fracturing system suitable for sand sheet complex lithology sections, comprising:

[0044] an identification module for determining the location and length of a reservoir segment;

[0045] Perforation construction module, used to perforate the downhole casing;

[0046] A judgment module is used to judge the lithology of the reservoir section;

[0047] Fracture construction module, used for staged fracturing of reservoir sections with different lithology types;

[0048] The crack construction module comprises:

[0049] The sand sheet thin interlayer section construction module is used to perform segmented fracturing construction on the sand sheet thin interlayer section;

[0050] A thick sandstone intercalated shale section or thick shale intercalated sandstone section construction module is used to perform staged fracturing construction on the thick sandstone intercalated shale section or thick shale intercalated sandstone section construction module;

[0051] The bridge plug segmented construction module is lowered to separate the thin interbedded sand-sheet section and the thick sandstone-shale section or the thin interbedded sand-sheet section and the thick shale-sandstone section, and then perform fracturing construction according to the thin interbedded sand-sheet section construction module and the thick sandstone-shale section or the thick shale-sandstone section construction module.

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

[0053] Under the condition of meeting the large displacement of 16 to 18 cubic meters per minute, the vertical sand sheet complex lithology reservoir section can be fully transformed. During the perforation construction process, the number of perforations may not meet the design requirements. The present invention uses a temporary plugging knot process to temporarily plug the wellbore pressure through knots, so that the designed perforations can be smoothly shot and the number of perforations can be increased to meet the design requirements. In this way, when the rock formation is subjected to fracturing construction in the later stage, the area of ​​the cracks generated by the extension can be increased, thereby achieving the purpose of increasing the reservoir transformation volume and the oil leakage area. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0055] Figure 1 It is a flowchart of a layered fracturing method and system embodiment applicable to a sand sheet complex lithology section of the present invention;

[0056] Figure 2 It is a design diagram of a layered fracturing method and system embodiment of the present invention applicable to a sand sheet complex lithology section, in which perforations are arranged in a differentiated manner;

[0057] Figure 3 The present invention is a schematic diagram of optimizing the timing of injecting temporary plugging agents in a layered fracturing method and system embodiment applicable to a sand sheet complex lithology section. DETAILED DESCRIPTION

[0058] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description 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 a sand sheet with complex lithology, comprising the following steps:

[0060] S1, using reservoir logging curve data, cuttings logging data, and core observation data to identify reservoir sections, and determine the location and length of the reservoir sections. This paper takes the Xu Si sandstone reservoir section and the Xu Wu sandstone interbedded reservoir section in the YQ102 well in actual production as an example. The vertical locations are 3430-3500m and 2928-3008m respectively, and the reservoir section lengths are 70m and 80m respectively;

[0061] S2, downhole casing perforation construction, the downhole casing is perforated by a tool with a cable. Since the reservoir section has a certain length, the perforation construction in this embodiment adopts a layered and clustered construction method to form multiple fractures in the longitudinal direction. In this embodiment, the number of perforations in each section is 48-54, which can ensure the later construction with a large displacement of 16-18 cubic meters per minute;

[0062] Combination Figure 2 As shown, in step S2 of this embodiment, a differentiated perforation structure is adopted within the segment, and the perforation cluster spacing of each segment is the same. The number of perforations in the cluster corresponding to the relatively high-quality reservoir is relatively small, and the number of perforations in the cluster corresponding to the relatively poor physical property reservoir is relatively large, with a total of 48 holes. In this way, the later construction can ensure the maximum utilization of the high-quality reservoir;

[0063] S3, determine the lithology, and use different fracturing methods according to different lithologies. The reservoir section includes one of the following: thin interbedded sand and shale sections, thick sandstone and shale sections, and thick shale and sandstone sections, or the reservoir section includes thin interbedded sand and shale sections and thick sandstone and shale sections, or the reservoir section includes thin interbedded sand and shale sections and thick shale and sandstone sections. In the vertical direction of Well YQ102, both "thin interbedded sand and shale" and "thick sandstone and shale" reservoir sections exist, with the bottom boundaries at 3500m and 3008m, respectively, and the lengths of the reservoir sections are 70m and 80m, respectively. Use different fracturing methods according to different lithologies. When there are two lithologies in the vertical direction, bridge plug segmented construction is used for transformation, and the transformation is carried out section by section from bottom to top, that is, the reservoir section in the lower layer is transformed first, and then the reservoir section in the upper layer is transformed.

[0064] S4, fracturing construction, according to the lithology category determined in S3, the reservoir section is subjected to staged fracturing; in this embodiment, 60 cubic meters of liquid carbon dioxide is injected into the reservoir section before the fracturing construction to reduce the fracture pressure of the reservoir, thereby reducing the difficulty of the subsequent fracturing construction and improving the flowback efficiency after fracturing;

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

[0066] S41, when the reservoir section is a thin interlayer of sand sheets, the "slippery water + gelling fluid" reverse mixed fracturing process is adopted. The prior art adopts a mixed injection process, that is, first injecting slippery water and carrying sand, and then injecting gelling fluid to carry sand. The reverse mixing process in this scheme refers to the mixed injection of slippery water and gelling fluid and carrying sand, and first injecting gelling fluid and carrying sand to press through the thin interlayer of sand sheets and increase the upward extension of the fractures; then injecting slippery water and carrying sand to reduce the damage of the liquid to the reservoir. After the slippery water completes the transportation of the proppant, the gelling fluid is finally injected. , the proppant is transported to the further end of the fracture by a high viscosity gelling fluid, and the proppant is transported by slick water and gelling fluid. The proppant includes 70 / 140 mesh, 40 / 70 mesh and 30 / 50 mesh proppant, and the usage ratio of the three proppant is 4:4:2. The total volume of the three proppant is the length of the reservoir section × 8 square meters. In this embodiment, the total volume of the three proppant is 640t. Specifically: In this embodiment, the three proppant are 70 / 140 mesh quartz sand, 40 / 70 mesh quartz sand and 30 / 50 mesh coated sand respectively;

[0067] First, a volume of 15 cubic meters of adhesive fluid and sand carrying is injected at a displacement of 16 to 18 cubic meters per minute, and finally a volume of 15 cubic meters of slippery water is injected at a displacement of 16 to 18 cubic meters per minute. Specifically: In this embodiment, 1200 cubic meters of adhesive fluid carrying sand is first injected at a displacement of 16 to 18 cubic meters per minute, and finally 1200 cubic meters of slippery water carrying sand is injected at a displacement of 16 to 18 cubic meters per minute;

[0068] S42, the reservoir section is a thick sandstone intercalated with shale or thick shale intercalated with sandstone. The "knot temporary plugging + layered transformation" fracturing process is adopted. First, the fracture pressure values ​​of sandstone and shale are determined according to the stress profile interpreted by well logging. The sequence of injecting fracturing fluid is further determined according to the fracture pressure.

[0069] In this embodiment, the burst pressure is determined by the following formula:

[0070] Pp=3σ h -σ H -P H +σ t ;

[0071] Where Pp represents the rock fracture pressure, unit: MPa, σ h Indicates the minimum horizontal principal stress, unit: MPa, σ H Indicates the maximum horizontal principal stress, unit: MPa, P H Indicates the hydrostatic column pressure MPa, σ t Indicates the tensile strength of rock, unit: MPa.

[0072] In step S42, slick water and gel-linked liquid are used to transport proppant, and slick water is used to transport temporary plugging knots. The proppant includes 70 / 140 mesh, 40 / 70 mesh, and 30 / 50 mesh proppant, and the proportion of the three proppant is 4:4:2; the total volume of the injected proppant is the reservoir section length × 8 square meters, and the number of knots is 16 to 18;

[0073] If the fracture pressure of sandstone is less than that of shale, the order of injecting fracturing fluid is: slippery water, gelling fluid, knot temporary plugging agent, gelling fluid, slippery water; specifically: first, inject slippery water sand-carrying fluid with a volume of reservoir length × 10 cubic meters at a displacement of 16 to 18 cubic meters / minute, then inject gelling fluid sand-carrying fluid with a volume of reservoir length × 5 cubic meters at the same displacement; then inject knot temporary plugging agent to seal the artificial fracture holes; finally, inject 16 to 18 cubic meters / minute to seal the artificial fracture holes; The displacement of 18 cubic meters per minute is used to inject slick water sand-carrying fluid with a volume of reservoir section length × 5 cubic meters and gel-linked fluid sand-carrying fluid with a volume of reservoir section length × 10 cubic meters. The proppant ratios of 70 / 140 mesh, 40 / 70 mesh, and 30 / 50 mesh delivered before and after temporary plugging with knots are all 4:4:2. As shown in Table 1, the order before temporary plugging is to use slick water first and then gel-linked fluid for delivery, and after temporary plugging, to use gel-linked fluid first and then slick water for delivery.

[0074] If the fracture pressure of sandstone is greater than that of shale, the order of injecting fracturing fluid is: gelling fluid, slippery water, knot temporary plugging agent, slippery water, gelling fluid; specifically: first, a gelling fluid carrying sand fluid with a volume of reservoir section length × 5 cubic meters and a slippery water carrying sand fluid with a volume of reservoir section length × 10 cubic meters are injected in sequence at a displacement of 16 to 18 cubic meters per minute, and then a knot temporary plugging agent is added to seal the formed artificial fracture holes, and finally, a slippery water carrying sand fluid with a volume of reservoir section length × 10 cubic meters and a gelling fluid carrying sand fluid with a volume of reservoir section length × 5 cubic meters are injected in sequence at a displacement of 16 to 18 cubic meters per minute, wherein the ratios of 70 / 140 mesh, 40 / 70 mesh, and 30 / 50 mesh proppants delivered before and after knot temporary plugging are all 4:4:2. As shown in Table 1, in this case, the order before temporary plugging is to use the glue-linked liquid for transportation first, and then use the slippery water for transportation. After temporary plugging, the slippery water is used first, and then the glue-linked liquid is used for transportation.

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

[0076] Specifically: first, 60 cubic meters of liquid carbon dioxide are injected at a displacement of 16 to 18 cubic meters per minute, and then 600 cubic meters of slippery water sand-carrying fluid is injected; then 340 cubic meters of adhesive liquid sand-carrying fluid is injected, and then the displacement is reduced to 4 to 8 cubic meters per minute and 18 temporary plugging knots are added, and 160 cubic meters of slippery water is sent to the bottom of the well to plug the perforation holes where artificial fractures are first formed (artificial fractures are fractures that are slowly formed when liquid is injected into the wellbore after perforation); finally, 370 cubic meters of adhesive liquid sand-carrying fluid and 630 cubic meters of slippery water sand-carrying fluid are injected in sequence at a displacement of 16 to 18 cubic meters per minute, and a total of 2160 cubic meters of liquid are injected, as shown in Table 1.

[0077] Table 1 Pumping program for shale intercalated sandstone (3430-3500 m)

[0078]

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

[0080] Perforation construction module, used to perforate the downhole casing;

[0081] A judgment module is used to judge the lithology of the reservoir section;

[0082] Fracture construction module, used for staged fracturing of reservoir sections with different lithology types;

[0083] The crack construction module includes:

[0084] The sand sheet thin interlayer section construction module is used to perform segmented fracturing construction on the sand sheet thin interlayer section;

[0085] A thick sandstone intercalated shale section or thick shale intercalated sandstone section construction module is used to perform staged fracturing construction on the thick sandstone intercalated shale section or thick shale intercalated sandstone section construction module;

[0086] The bridge plug segmented construction module is lowered to separate the thin interbedded sand-sheet section and the thick sandstone-shale section or the thin interbedded sand-sheet section and the thick shale-sandstone section, and then perform fracturing construction according to the thin interbedded sand-sheet section construction module and the thick sandstone-shale section or the thick shale-sandstone section construction module.

[0087] The difference between Example 2 and Example 1 is that: Figure 3 As shown, this is a diagram for optimizing the timing of temporary plugging agent injection, where series 1 represents: the volume change rate of the left wing crack; series 2 represents: the volume change rate of the right wing crack).

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

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

[0090] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method 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 in the scope of protection of the present invention.

Claims

1. A layered fracturing method suitable for sand sheet complex lithology sections, characterized in that: The following steps are involved: S1, identifying the reservoir segment and determining the location and length of the reservoir segment; S2, downhole casing perforation construction; S3, determining the lithology, and adopting different fracturing methods according to different lithologies, wherein the reservoir section includes one of a thin interbedded sandstone section, a thick sandstone interbedded shale section, and a thick shale interbedded sandstone section, or the reservoir section includes a thin interbedded sandstone section and a thick sandstone interbedded shale section, or the reservoir section includes a thin interbedded sandstone section and a thick shale interbedded sandstone section; S4, fracturing construction, performing staged fracturing on the reservoir section according to the lithology category determined in S3; In step S4, the following fracturing methods are respectively used for reservoir sections of different lithologies: S41, when the reservoir section is a thin interlayer of sand sheets, the "slippery water + gelling fluid" reverse mixed fracturing process is adopted, and the reverse mixed fracturing process refers to the mixed injection of slippery water and gelling fluid and the sand carrying, and the gelling fluid is first injected to carry sand to press through the thin interlayer of sand sheets; then the slippery water is injected to carry sand, and after the slippery water completes the transport of the proppant, the gelling fluid is finally injected to complete the transport of the proppant; S42, the reservoir section is a thick sandstone intercalated with shale or thick shale intercalated with sandstone. The "knot temporary plugging + layered transformation" fracturing process is adopted. First, the fracture pressure values ​​of sandstone and shale are determined according to the stress profile interpreted by well logging, and the injection sequence of fracturing fluid is further determined according to the fracture pressure. If the fracture pressure of sandstone is less than that of shale, the order of injecting fracturing fluid is: slippery water, gelling fluid, knot temporary plugging agent, gelling fluid, slippery water; If the fracture pressure of sandstone is greater than that of shale, the order of injecting fracturing fluid is: gelling fluid, slippery water, knot temporary plugging agent, slippery water, gelling fluid; S5, in the vertical direction of the reservoir section, thin interbedded sand and shale sections and thick sandstone and shale sections exist simultaneously, or thin interbedded sand and shale sections and thick shale and sandstone sections exist simultaneously; then the two reservoir sections are segmented using segmented bridge plugs, and are transformed section by section from bottom to top, and steps S1-S4 are performed respectively.

2. A layered fracturing method suitable for sand sheet complex lithology sections according to claim 1, characterized in that: The perforation construction in step S2 adopts a segmented construction method to form multiple segments of perforations, and the number of perforations in each segment is 48-54.

3. A layered fracturing method suitable for sand sheet complex lithology sections according to claim 2, characterized in that: In step S2, a differentiated perforation arrangement structure is adopted within the segment, and the perforation cluster spacing in each segment is the same.

4. A layered fracturing method suitable for sand sheet complex lithology sections according to claim 3, characterized in that: In step S2, the knot temporary plugging process is also used in conjunction with the perforation construction. During the construction, the knot temporary plugging timing is determined according to the volume change rate of each cluster of fractures in each fracturing section of the reservoir section.

5. A layered fracturing method suitable for sand sheet complex lithology sections according to any one of claims 1 to 4, characterized in that: Before the fracturing operation in step S3, liquid carbon dioxide is injected into the reservoir section.

6. A layered fracturing method suitable for sand sheet complex lithology sections according to any one of claims 1 to 4, characterized in that: In step S41, the proppant includes 70 / 140 mesh, 40 / 70 mesh and 30 / 50 mesh proppant, and the usage ratio of the three proppant is 4:4:2; Slippery water and gel-linked fluid were used to transport 70 / 140 mesh, 40 / 70 mesh, and 30 / 50 mesh proppants.

7. A layered fracturing method suitable for sand sheet complex lithology sections according to claim 6, characterized in that: In step S41, firstly, a volume of the cementing fluid and the sand-carrying fluid equal to the reservoir length × 15 cubic meters is injected at a displacement of 16 to 18 cubic meters per minute, and finally, a volume of the slippery water and the sand-carrying fluid equal to the reservoir length × 15 cubic meters is injected at a displacement of 16 to 18 cubic meters per minute.

8. A layered fracturing method suitable for sand sheet complex lithology sections according to any one of claims 1 to 4, characterized in that: In step S42, slick water and gel-linked liquid are used to transport proppant, and slick water is used to transport temporary plugging knots. The proppant includes 70 / 140 mesh, 40 / 70 mesh, and 30 / 50 mesh proppant, and the proportion of the three proppant is 4:4:2; the total volume of the injected proppant is the reservoir section length × 8 square meters, and the number of knots is 16 to 18; If the fracture pressure of sandstone is less than that of shale, first inject slickwater sand-carrying fluid, then inject gel-linked fluid sand-carrying fluid; Then, a knot temporary plugging agent is added to plug the artificial fracture holes; finally, a glue-linked sand-carrying liquid and a slippery water sand-carrying liquid are injected in sequence, wherein the ratio of the 70 / 140 mesh, 40 / 70 mesh and 30 / 50 mesh proppants delivered before and after the knot temporary plugging is 4:4:2; If the fracture pressure of sandstone is greater than that of shale, firstly, the sand-carrying fluid of cementing liquid and the sand-carrying fluid of slick water are injected in sequence, and then the temporary plugging agent of rope knot is put in to seal the artificial fracture holes formed, and finally the sand-carrying fluid of slick water and the sand-carrying fluid of cementing liquid are injected in sequence, wherein the ratio of 70 / 140 mesh, 40 / 70 mesh and 30 / 50 mesh proppant transported before and after temporary plugging of rope knot is 4:4:

2.

9. A layered fracturing method suitable for sand sheet complex lithology sections according to claim 8, characterized in that: In step S42, if the fracture pressure of sandstone is less than the fracture pressure of shale, firstly, a slickwater sand-carrying fluid having a volume of 10 cubic meters of the reservoir length × 16 to 18 cubic meters per minute is injected, and then a gel-linked fluid sand-carrying fluid having a volume of 5 cubic meters of the reservoir length × 16 to 18 cubic meters per minute is injected; Then, a knot temporary plugging agent is added to plug the artificial fracture holes; finally, a slickwater sand-carrying fluid with a volume of 5 cubic meters of reservoir length × 5 cubic meters and a gel-linked fluid sand-carrying fluid with a volume of 10 cubic meters of reservoir length × 16 to 18 cubic meters per minute are sequentially injected; If the sandstone fracture pressure is greater than the shale fracture pressure, first, inject a volume of 5 cubic meters of reservoir length × 5 cubic meters of cementing fluid and a volume of 10 cubic meters of reservoir length × 10 cubic meters of slickwater sand-carrying fluid at a displacement of 16 to 18 cubic meters per minute, then add a knot temporary plugging agent to seal the artificial fracture holes formed, and finally inject a volume of 10 cubic meters of slickwater sand-carrying fluid and a volume of 5 cubic meters of reservoir length × 10 cubic meters of reservoir length × 5 cubic meters of cementing fluid sand-carrying fluid at a displacement of 16 to 18 cubic meters per minute.

10. The layered fracturing method applicable to sand sheet complex lithology sections according to claim 1, characterized in that: The rupture pressure in step S42 is calculated and determined by the following formula: Pp=3σ h -s H -P H +s t ; Where Pp represents the rock fracture pressure, σ h represents the minimum horizontal principal stress, σ H represents the maximum horizontal principal stress, P H represents the hydrostatic column pressure, σ t Represents the tensile strength of rock.

11. A layered fracturing system suitable for sand sheet complex lithology sections, characterized in that: include: an identification module for determining the location and length of a reservoir segment; Perforation construction module, used to perforate the downhole casing; A judgment module is used to judge the lithology of the reservoir section; Fracture construction module, used for staged fracturing of reservoir sections with different lithology types; The crack construction module comprises: The sand sheet thin interlayer section construction module is used to perform segmented fracturing construction on the sand sheet thin interlayer section; A thick sandstone intercalated shale section or thick shale intercalated sandstone section construction module is used to perform staged fracturing construction on the thick sandstone intercalated shale section or thick shale intercalated sandstone section construction module; The bridge plug segmented construction module is lowered to separate the thin interbedded sand-sheet section and the thick sandstone-shale section or the thin interbedded sand-sheet section and the thick shale-sandstone section, and then perform fracturing construction according to the thin interbedded sand-sheet section construction module and the thick sandstone-shale section or the thick shale-sandstone section construction module.

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