A fixed-point injection fracturing structure and process in a heterogeneous thick oil layer

Abstract

The present application relates to the technical field of oilfield fracturing, and particularly relates to a non-uniform thick oil layer fixed-point jetting fracturing structure and process, which comprises a connecting pipe, a jetting pipe, a first mounting pipe, a second mounting pipe and a positioner. The jetting pipe is connected to the lower end of the connecting pipe, a plurality of jetting holes are formed in the jetting pipe, and the first mounting pipe is connected to the outside of the connecting pipe. The second mounting pipe is slidably arranged in the first mounting pipe, and the upper end of the second mounting pipe is provided with a hollow area. The positioner is arranged on the second mounting pipe. When the hydraulic pressure in the jetting pipe increases and pushes the second mounting pipe to move downward relative to the first mounting pipe, the fracturing fluid is jetted out from the jetting hole corresponding to the hollow area. The connecting pipe can drive the jetting pipe to move up and down relative to the first mounting pipe, so that the jetting holes at different positions correspond to the hollow areas respectively, and the needs of longitudinal non-uniform and layered reconstruction of the non-uniform thick oil layer are met, and the service life is prolonged.

Description

Technical Field

[0001] This invention relates to the field of oilfield fracturing technology, and in particular to a fixed-point injection fracturing structure and process for heterogeneous thick oil reservoirs. Background Technology

[0002] The main development formations in the old blocks of the oilfield are heterogeneous thick oil-bearing layers. These layers are characterized by large vertical thickness, complex lithology, frequent internal interlayers, and significant permeability differences, resulting in extremely high reservoir heterogeneity. After water injection development, the high-permeability zones of the oil-bearing layers exhibit severe water channeling and high levels of water flooding, while the low-permeability enrichment areas have abundant remaining oil reserves, scattered in a fragmented manner. These areas represent the core potential regions for stable and increased production in the old oilfield.

[0003] However, constrained by the strong heterogeneity of reservoirs, conventional general fracturing and overall layered fracturing techniques have significant limitations in adaptability, making it difficult to fully adapt to the complex reservoir characteristics of thick oil-bearing layers. The fundamental reason is that the fracture initiation location is uncertain during traditional fracturing operations, and the extension direction is easily influenced by differences in physical properties, deviating from expectations. This objectively leads to repeated stimulation and ineffective fracturing of high-permeability layers, while low-permeability oil-rich layers are often not effectively utilized. This results in a severe imbalance in the vertical utilization of oil layers, with the fracturing production enhancement effect deteriorating year by year, and limited increases in single-well productivity, becoming a key technical bottleneck restricting the improvement of recovery rates in old oilfields. Summary of the Invention

[0004] Therefore, it is necessary to provide a fixed-point injection fracturing structure and process for heterogeneous thick oil reservoirs to address the technical problem that current fracturing processes cannot adapt to the complex reservoir characteristics of thick oil reservoirs.

[0005] The above objectives are achieved through the following technical solutions:

[0006] A targeted injection fracturing structure for heterogeneous thick oil reservoirs includes a connecting pipe, an injection pipe, a first mounting pipe, a second mounting pipe, and a locator. The connecting pipe extends vertically and is used to be lowered into the casing. The injection pipe is connected to the lower end of the connecting pipe and communicates with the interior of the connecting pipe. Multiple injection holes are spaced vertically on the injection pipe for injecting fracturing fluid into the inner wall of the casing. The first mounting pipe is threaded to the outside of the connecting pipe. The second mounting pipe is slidably disposed vertically inside the lower end of the first mounting pipe, and the injection pipe passes through the second mounting pipe. Inside the tube, the upper end of the second mounting tube has a hollowed-out area; the locator is set on the second mounting tube and is used to position the second mounting tube to correspond to the target oil layer; in the initial state, the hollowed-out area is blocked by the lower end of the first mounting tube; when the hydraulic pressure inside the injection tube increases and pushes the second mounting tube to move downward relative to the first mounting tube, the hollowed-out area extends from the lower end of the first mounting tube, so that fracturing fluid is ejected from the injection hole corresponding to the hollowed-out area; the connecting tube can drive the injection tube to move up and down relative to the first mounting tube so that the injection holes at different positions can correspond to the hollowed-out areas respectively.

[0007] Furthermore, the upper end of the second mounting tube is provided with multiple baffles evenly distributed around its circumference. The baffles extend in the vertical direction, and the position between two adjacent baffles forms the hollow area.

[0008] Furthermore, a first retaining sleeve is coaxially provided on the outside of the first mounting tube, and a second retaining sleeve is coaxially provided on the outside of the second mounting tube. The outer circumferential surfaces of the first retaining sleeve and the second retaining sleeve form a sealing fit with the inner wall of the casing, thereby accumulating the fracturing fluid ejected from the injection hole.

[0009] Furthermore, both the first and second retaining sleeves are conical sleeves, and the large end of the first retaining sleeve corresponds vertically to the large end of the second retaining sleeve.

[0010] Furthermore, the injection hole is a conical hole, the axis of which is perpendicular to the axis of the connecting pipe, and the small end of the conical hole is positioned away from the axis of the injection pipe.

[0011] Furthermore, the upper outer circumferential surface of the connecting pipe is provided with a wedge-shaped block extending radially therefrom, and the wedge-shaped block has an inclined surface that is radially inclined relative to the connecting pipe; the inner wall of the first mounting pipe is provided with a slot extending radially therefrom, and an elastic block is provided in the slot, and the inclined surface and the elastic block slide together to allow the elastic block to retract into the slot.

[0012] Furthermore, a U-shaped spring is provided in the slot, the U-shaped spring can extend and retract radially along the first mounting tube, and the elastic block is connected to the U-shaped spring.

[0013] Furthermore, the first stop sleeve, the second stop sleeve, and the elastic block are all made of rubber material.

[0014] Furthermore, the lower end of the first mounting tube is provided with an inner retaining ring, and the upper end of the second mounting tube is provided with an outer retaining ring. A compression spring that can extend and retract in the vertical direction is provided between the inner retaining ring and the outer retaining ring. The compression spring is used to reset the second mounting tube upward.

[0015] Furthermore, a first stabilizer is also fitted onto the first mounting tube, the first stabilizer being located above the first stop sleeve, and a second stabilizer is also fitted onto the second mounting tube, the second stabilizer being located below the second stop sleeve.

[0016] Furthermore, the upper end of the connecting pipe is also provided with a slip connector, which has multiple slips evenly distributed around the circumference of the connecting pipe. The slips can open radially along the connecting pipe and engage with the inner wall of the sleeve to anchor the connecting pipe inside the sleeve.

[0017] Furthermore, the lower end of the second mounting tube is also provided with a straightening guide head, which is located below the locator and is used to straighten and guide the movement of the second mounting tube.

[0018] Furthermore, the positioner has a clamp that is detachably and fixedly installed at the lower end of the second mounting tube.

[0019] A targeted jet fracturing process within a heterogeneous thick oil reservoir, employing the aforementioned targeted jet fracturing structure within a heterogeneous thick oil reservoir, includes the following steps:

[0020] S1. Determine the target well and target interval based on reservoir parameters;

[0021] S2. The fixed-point injection fracturing structure in the heterogeneous thick oil layer is lowered into the well to a predetermined depth, and the lowering depth is detected by the positioner;

[0022] S3. Pump fracturing fluid into the connecting pipe, thereby increasing the hydraulic pressure inside the injection pipe and pushing the second mounting pipe downward relative to the first mounting pipe, so that the hollowed-out area extends out from the lower end of the first mounting pipe, and then the fracturing fluid is ejected through the injection hole corresponding to the hollowed-out area. The injection hole generates a high-speed jet at the preset injection point in the thick oil layer. Based on Bernoulli's principle, a local low-pressure area is formed around the injection point, inducing the fracture to start at the preset position.

[0023] Furthermore, the targeted jet fracturing process within heterogeneous thick oil reservoirs also includes the following steps:

[0024] S4. When it is necessary to switch the spray holes in different positions, the ground column is rotated to drive the connecting pipe to rotate a set number of times, so that the connecting pipe drives the spray pipe to move up and down relative to the first mounting pipe, so that the spray holes in different positions correspond to the positions of the hollow area respectively.

[0025] S5. Repeat step S3 to complete the targeted injection fracturing operation of the new target oil layer.

[0026] The beneficial effects of this invention are:

[0027] The present invention provides a fixed-point injection fracturing structure and process for heterogeneous thick oil layers. First, the well depth can be precisely controlled by the locator, thereby enabling fracturing operations to be carried out on the target oil layer, which is suitable for the needs of longitudinal non-uniformity and stratified modification of heterogeneous thick oil layers. Furthermore, by rotating the connecting pipe, the injection holes at different positions can correspond to the hollowed-out area to achieve injection, thereby avoiding frequent replacement of the entire tubing string due to wear of the injection holes and extending its service life.

[0028] Secondly, the first and second baffles can prevent fracturing fluid from spreading to other oil layers, thereby improving the efficiency of fracturing operations. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall structure of a fixed-point injection fracturing structure in a heterogeneous thick oil layer according to an embodiment of the present invention.

[0030] Figure 2 This is an exploded view of a fixed-point injection fracturing structure within a heterogeneous thick oil layer according to an embodiment of the present invention;

[0031] Figure 3 This is a side view of a fixed-point injection fracturing structure in a heterogeneous thick oil layer according to an embodiment of the present invention;

[0032] Figure 4 for Figure 3 Sectional view of AA;

[0033] Figure 5 for Figure 4 Another state diagram;

[0034] Figure 6 for Figure 3 BB section view;

[0035] Figure 7 This is a schematic diagram of the tubing string inside the casing in a fixed-point injection fracturing process within a heterogeneous thick oil layer, as provided in an embodiment of the present invention.

[0036] in:

[0037] 101. First mounting tube; 102. Connecting tube; 103. Injection tube; 1031. Injection hole; 104. Vault connector; 105. First centralizer; 106. First retaining sleeve; 107. Second retaining sleeve; 108. Second centralizer; 109. Positioner; 110. Centralizer guide head; 111. Second mounting tube; 112. Wedge block; 113. Elastic block; 114. Sleeve. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0039] The component designations used in this document, such as "first" and "second," are merely for distinguishing the described objects and do not have any sequential or technical meaning. The terms "connection" and "linkage" used in this invention, unless otherwise specified, include both direct and indirect connections (linkages). It should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention.

[0040] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0041] like Figures 1 to 6As shown, an embodiment of the present invention provides a fixed-point injection fracturing structure for heterogeneous thick oil layers, comprising a connecting pipe 102, an injection pipe 103, a first mounting pipe 101, a second mounting pipe 111, and a locator 109; the axis of the connecting pipe 102 extends vertically and is used to be lowered into the casing 114 downhole; the injection pipe 103 is connected to the lower end of the connecting pipe 102 and communicates with the interior of the connecting pipe 102, and the injection pipe 103 has a plurality of injection holes 1031 arranged at intervals in the vertical direction, the injection holes 1031 being used to inject fracturing fluid into the inner wall of the casing 114; the first mounting pipe 101 is threaded to the outside of the connecting pipe 102; the second mounting pipe 111 is slidably disposed inside the lower end of the first mounting pipe 101 in the vertical direction. The injection pipe 103 is inserted inside the second mounting pipe 111, and the upper end of the second mounting pipe 111 has a hollow area. The locator 109 is disposed on the second mounting pipe 111 and is used to position the second mounting pipe 111 to correspond to the target oil layer. In the initial state, the hollow area is blocked by the lower end of the first mounting pipe 101. When the hydraulic pressure inside the injection pipe 103 increases and pushes the second mounting pipe 111 to move downward relative to the first mounting pipe 101, the hollow area extends out from the lower end of the first mounting pipe 101, so that fracturing fluid is ejected from the injection hole 1031 corresponding to the hollow area. The connecting pipe 102 can drive the injection pipe 103 to move up and down relative to the first mounting pipe 101 so that the injection holes 1031 at different positions can correspond to the hollow areas respectively.

[0042] Specifically, the lower end of the injection pipe 103 is threadedly connected to the connecting pipe 102, facilitating the disassembly and replacement of the injection pipe 103. The injection pipe 103 is made of tungsten alloy material to improve structural strength and avoid fatigue damage. After being lowered into the downhole casing 114, the relative positions of the injection pipe 103 and the connecting pipe 102 remain fixed, and the relative positions of the first mounting pipe 101 and the inner wall of the casing 114 also remain fixed, allowing the connecting pipe 102 and the injection pipe 103 to slide vertically and rotate circumferentially relative to the first mounting pipe 101. This fixed-point injection fracturing structure within a heterogeneous thick oil layer is a section of the tubing string.

[0043] The non-homogeneous thick oil layer fixed-point injection fracturing structure of the present invention can accurately control the well depth through the positioner 109, thereby carrying out fracturing operations on the target oil layer, adapting to the needs of longitudinal non-uniformity and stratified modification of non-homogeneous thick oil layers; and by rotating the connecting pipe 102, the injection holes 1031 at different positions can be aligned with the hollow area to achieve injection, avoiding frequent replacement of the entire tubing string due to wear of the injection holes 1031, and extending the service life.

[0044] Furthermore, the upper end of the second mounting tube 111 is provided with multiple baffles evenly distributed around its circumference. These baffles extend vertically, and the space between adjacent baffles forms the hollow area. The baffle structure is simple, easy to manufacture, and possesses a certain structural strength. Specifically, the number of baffles is set to approximately four to eight.

[0045] Furthermore, a first retaining sleeve 106 is coaxially provided on the outside of the first mounting pipe 101, and a second retaining sleeve 107 is coaxially provided on the outside of the second mounting pipe 111. The outer circumferential surfaces of both the first retaining sleeve 106 and the second retaining sleeve 107 form a sealing fit with the inner wall of the casing 114, thereby concentrating the fracturing fluid ejected from the injection hole 1031. The first retaining sleeve 106 and the second retaining sleeve 107 can prevent the fracturing fluid from diffusing into other oil layers, thereby improving the efficiency of fracturing operations.

[0046] Furthermore, both the first stop sleeve 106 and the second stop sleeve 107 are conical sleeves, and the large end of the first stop sleeve 106 corresponds vertically to the large end of the second stop sleeve 107. The conical sleeve structure can achieve local pressurization, increase the jet velocity, and enhance the rock-breaking ability.

[0047] Furthermore, the injection hole 1031 is a conical hole, the axis of which is perpendicular to the axis of the connecting pipe 102, and the small end of the conical hole is positioned away from the axis of the injection pipe 103. This increases the jet velocity of the injection hole 1031, enhancing its rock-breaking and fracture-creating capabilities. At least two sets of injection holes 1031 are provided circumferentially around the injection pipe 103, thereby improving injection efficiency.

[0048] Furthermore, the upper outer circumferential surface of the connecting pipe 102 is provided with a wedge-shaped block 112 extending radially therefrom, the wedge-shaped block 112 having an inclined surface that is radially inclined relative to the connecting pipe 102; the inner wall of the first mounting pipe 101 is provided with a groove extending radially therefrom, the groove containing an elastic block 113, the inclined surface slidingly engaging with the elastic block 113 to allow the elastic block 113 to retract into the groove. This allows the wedge-shaped block 112 to pass over the elastic block 113, thereby facilitating the rotation of the connecting pipe 102 relative to the first mounting pipe 101 a set number of turns. Additionally, the circumferential blocking engagement of the wedge-shaped block 112 and the elastic block 113 allows for determination of whether the injection hole 1031 corresponds to the hollowed-out area. Figure 6 As shown, the wedge block 112 and the elastic block 113 engage in a stop-fitting manner in the circumferential direction of the connecting pipe 102. When the connecting pipe 102 rotates counterclockwise relative to the first mounting pipe 101 ( Figure 6(Looking at the paper from the center) After rotating a set number of turns, since there is no stop structure in front along the direction of rotation, the wedge block 112 may continue to rotate at a certain angle, which can easily cause the injection hole 1031 to misalign with the hollowed-out area. At this time, simply rotate the connecting tube 102 360° in the opposite direction. When the wedge block 112 on the connecting tube 102 and the elastic block 113 are aligned again... Figure 6 After the circumferential stop engagement state is reached, the injection hole 1031 and the hollow area are re-aligned. Subsequently, even if the reverse rotation continues, the two will only rotate synchronously in the opposite direction, and the injection hole 1031 and the hollow area will not be misaligned.

[0049] Furthermore, a U-shaped spring is provided in the slot, which can extend and retract radially along the first mounting tube 101, and the elastic block 113 is connected to the U-shaped spring. The U-shaped spring has uniform force distribution and strong fatigue resistance, which can ensure the long-term stable positioning and avoidance of the elastic block 113, and is suitable for downhole operation conditions.

[0050] Furthermore, the first retaining sleeve 106, the second retaining sleeve 107, and the elastic block 113 are all made of rubber material. Rubber material has good elasticity and fit, excellent sealing performance, can adapt to the deformation of the sleeve 114, and at the same time protect the inner wall of the sleeve 114 from scratches.

[0051] Furthermore, the lower end of the first mounting tube 101 is provided with an inner retaining ring, and the upper end of the second mounting tube 111 is provided with an outer retaining ring. A compression spring that can extend and retract in the vertical direction is provided between the inner and outer retaining rings. The compression spring is used to reset the second mounting tube 111 upwards. After the pressure of the fracturing fluid disappears, the compression spring will push the second mounting tube 111 upwards to reset, so that the hollowed-out area is once again blocked by the lower end of the first mounting tube 101, preventing impurities such as sand particles from entering the hollowed-out area.

[0052] Furthermore, a first stabilizer 105 is fitted onto the first mounting tube 101, located above the first retaining sleeve 106. A second stabilizer 108 is fitted onto the second mounting tube 111, located below the second retaining sleeve 107. The first stabilizer 105 and the second stabilizer 108 ensure that the first mounting tube 101 and the second mounting tube 111 are centered within the sleeve 114, ensuring a uniform distance between the spray hole 1031 and the inner wall of the sleeve 114, resulting in consistent spraying. Both the first stabilizer 105 and the second stabilizer 108 employ an elastic slotted spring stabilizer structure. Both the first stabilizer 105 and the second stabilizer 108 include multiple circumferentially distributed stabilizer blocks. A spring connects the stabilizer blocks to the outer circumferential surface of the first mounting tube 101 or the outer circumferential surface of the second mounting tube 111. The spring can extend and retract radially along the spray tube 103, ensuring a stable effect.

[0053] Furthermore, the upper end of the connecting pipe 102 is also provided with a slip connector 104. The slip connector 104 is provided with multiple slips evenly distributed around the circumference of the connecting pipe 102. The slips can open radially along the connecting pipe 102 and engage with the inner wall of the casing 114 to anchor the connecting pipe 102 within the casing 114. In this way, during fracturing operations, the slip connector 104 can lock the downhole depth of the targeted injection fracturing structure within the heterogeneous thick oil layer, preventing movement or displacement during the operation and ensuring targeted fracturing.

[0054] Furthermore, the lower end of the second installation pipe 111 is also provided with a straightening guide head 110. The straightening guide head 110 is located below the positioner 109 and is used to straighten and guide the movement of the second installation pipe 111, ensuring the sliding coaxiality of the fixed-point injection fracturing structure in the heterogeneous thick oil layer, avoiding eccentric jamming and wear, and improving the reliability of downhole movement.

[0055] Furthermore, the locator 109 has a clamp, which is detachably and fixedly installed at the lower end of the second mounting pipe 111, thus facilitating on-site assembly and disassembly.

[0056] Based on the above embodiments, the usage principle and working process of the embodiments of the present invention are as follows:

[0057] First, the tubing string equipped with the fixed-point injection fracturing structure within the heterogeneous thick oil layer is lowered into the casing 114. During the downhole process, the first centralizer 105 and the second centralizer 108 elastically abut against the inner wall of the casing 114, keeping the tubing string centered within the casing 114. The centralizing guide head 110 at the lower end of the second installation pipe 111 guides the tubing string smoothly through steps, diameter reductions, and other sections within the casing 114. Simultaneously, the locator 109, installed on the second installation pipe 111, monitors the downhole depth of the tubing string in real time. When the locator 109 detects that the tubing string has reached the preset target oil layer depth, it stops descending and, through the slips on the slip connector 104, engages with the inner wall of the casing 114, anchoring the connecting pipe 102 within the casing 114.

[0058] In the initial state, such as Figure 4 As shown, the lower end of the first mounting tube 101 blocks the hollow area at the upper end of the second mounting tube 111, and all the injection holes 1031 on the injection tube 103 are blocked by the inner wall of the second mounting tube 111, preventing the fracturing fluid from being ejected. At the same time, the wedge-shaped block 112 at the upper end of the connecting tube 102 and the elastic block 113 in the groove on the inner wall of the first mounting tube 101 engage in a circumferential blocking engagement.

[0059] When fracturing operations are required at the target oil reservoir, high-pressure fracturing fluid is pumped from the ground into the connecting pipe 102. The fracturing fluid then enters the injection pipe 103 through the connecting pipe 102. Because the injection orifice 1031 is blocked, the hydraulic pressure inside the injection pipe 103 rises rapidly. This increased hydraulic pressure acts on the second mounting pipe 111, such as... Figure 5 As shown, the second mounting tube 111 overcomes the elastic force of the compression spring and slides downward, causing the hollowed-out area to extend from the lower end of the first mounting tube 101. The injection hole 1031 is exposed to the annular space of the casing 114 through the hollowed-out area. High-pressure fracturing fluid is ejected at high speed from the injection hole 1031 through the hollowed-out area. At this time, the injection hole 1031 corresponding to the hollowed-out area is in the injection state. Subsequently, the fracturing fluid impacts the rock to form an initial fracture; at the same time, based on Bernoulli's principle, the high-speed jet forms a local low-pressure area around the injection point, inducing the fracture to initiate and propagate in a predetermined position. During the injection process, the first retainer 106 and the second retainer 107 are both sealed to the inner wall of the casing 114 to prevent the fracturing fluid from diffusing into non-target oil layers.

[0060] When switching injection orifices 1031, first stop pumping fracturing fluid into the connecting pipe 102, allowing the second mounting pipe 111 to return to its original position under the action of the compression spring, thus re-covering the hollowed-out area. Then, rotate the connecting pipe 102 a set number of turns via the ground tubing string. The rotation and up-and-down movement of the connecting pipe 102 relative to the first mounting pipe 101 can drive the injection pipe 103 to move up and down, moving the injection orifices 1031 at different positions to the corresponding hollowed-out areas. During rotation, the inclined surface of the wedge block 112 slides into the elastic block 113, causing the elastic block 113 to retract into its slot and then extend again. The operator senses the number of rotations through the periodic changes in ground torque. Finally, rotate in the opposite direction one full turn (360°), causing the wedge block 112 and the elastic block 113 to circumferentially stop and engage again. At this point, the injection orifice 1031 corresponds to the hollowed-out area, and fracturing fluid can be pumped in again for a new round of injection operations.

[0061] After all target oil layers have been modified, the second installation pipe 111 automatically returns to its original position under the action of the compression spring, thus blocking the hollow area again and stopping the spraying.

[0062] This invention also provides a targeted jet fracturing process within a heterogeneous thick oil reservoir, employing the aforementioned targeted jet fracturing structure within a heterogeneous thick oil reservoir, and comprising the following steps:

[0063] S1. Determine the target well and target interval based on reservoir parameters;

[0064] S2. The fixed-point injection fracturing structure in the heterogeneous thick oil layer is lowered into the well to a predetermined depth, and the lowering depth is detected by the positioner 109;

[0065] S3. Pump fracturing fluid into the connecting pipe 102, thereby increasing the hydraulic pressure inside the injection pipe 103 and pushing the second mounting pipe 111 downward relative to the first mounting pipe 101, so that the hollow area extends out from the lower end of the first mounting pipe 101, and then the fracturing fluid is ejected through the injection hole 1031 corresponding to the hollow area. The injection hole 1031 generates a high-speed jet at the preset injection point in the thick oil layer, and based on Bernoulli's principle, a local low-pressure area is formed around the injection point, inducing the fracture to start at the preset position.

[0066] Furthermore, the targeted jet fracturing process within heterogeneous thick oil reservoirs also includes the following steps:

[0067] S4. When it is necessary to switch the spray holes 1031 at different positions, the ground column is rotated to drive the connecting pipe 102 to rotate a set number of times, so that the connecting pipe 102 drives the spray pipe 103 to move up and down relative to the first mounting pipe 101, so that the spray holes 1031 at different positions correspond to the positions of the hollow area respectively.

[0068] S5. Repeat step S3 to complete the targeted injection fracturing operation of the new target oil layer.

[0069] Furthermore, step S1 also includes:

[0070] 1. Well and Layer Selection Methods

[0071] Due to casing damage risk, water injection in the Sa I group ceased in 2010. It has been under flexible production for several years. The selected section has an unexploited sandstone thickness of 11.2m and an effective thickness of 7.0m. Based on previous tracer monitoring charts, the remaining recoverable reserves are predicted to be 201,000 tons, accounting for 39.2% of the unexploited recoverable reserves. The focus is on wells with an average sandstone thickness of over 40m, an effective thickness of over 20m, an initial oil saturation of over 50%, high recoverable reserves, low cumulative oil production, and considerable remaining recoverable reserves.

[0072] In response to the development characteristics of the Sa I Formation oil layer, the following measures were taken: First, continuously developed thick oil layers were preferred, with the remaining oil concentrated at the top of each rhythmic segment. Priority was given to tapping the remaining oil at the top to achieve precise development of the thick oil layers. Second, concentrated thin and poorly developed layers were preferred, with the remaining oil evenly distributed. Layers with an effective thickness of more than 0.5m and an oil saturation of more than 40% were selected.

[0073] 2. Energy replenishment methods

[0074] Based on the inverse relationship between sublayer permeability and initial and cumulative oil recovery intensity, it is analyzed that layers with low permeability have low recovery rates before fracturing, while layers with high permeability have high recovery rates before fracturing. The injection ratio of replenishing fluid is designed for different recovery rates. The control volume of each sublayer is calculated by combining the sand body strike, effective reservoir thickness, and porosity.

[0075] Permeability ≥ 400mD: High recovery rate, designed liquid volume based on 35% of control volume;

[0076] 200mD≤permeability<400mD: High recovery rate, design liquid volume based on 30% of control volume;

[0077] Permeability < 200mD: Low recovery rate, designed liquid volume based on 20% of the control volume.

[0078] 3. Tubing design method

[0079] For wells with thick oil layers or alternating thin and thick layers (with thin interlayers <0.4m), coiled tubing hydraulic jet fracturing strings are preferred, such as... Figure 7 As shown, a 2.5-inch continuous tubing is used to carry a φ118mm injection and fracturing integrated tubing string to achieve targeted stimulation of wells with casing inner diameters of φ121mm and φ124mm.

[0080] For wells with alternating thin and thick layers (thinner layers > 0.4m), two fracturing techniques were used: coiled tubing with double-sealed single clamp and hydraulic jetting tubing, both requiring two tubing runs. However, to improve operational efficiency and reduce costs, an integrated tubing string combining double-sealed single clamp and hydraulic jetting was developed, enabling the entire fracturing operation to be completed in a single tubing run. Specific parameters are shown in Table 1.

[0081] Table 1. Parameters of the tubing string

[0082] Well logging evaluation method: Install a pressure gauge at the top, middle and bottom of the nozzle. First, verify the changes in bottom hole pressure at different stages through stepped flow rate testing to determine the optimal perforation flow rate. Second, monitor the changes in bottom hole pressure during construction in two types of thick oil layers: those with physical interlayers and those with homogeneity, to evaluate the hydraulic jet sealing capability.

[0083] 4. In conjunction with water-blocking technology

[0084] This invention targets fracturing and production enhancement measures in the pure oil zone of the Sa I Group. To accurately ensure the stimulation effect of the target layer and avoid interference from lower water layers and subsequent water breakthrough, a mechanical water shut-off process is adopted to seal and isolate all layers below the Sa I Group. This achieves complete isolation of the lower layers, ensuring that the effect of fracturing after commissioning is only the production of fluid and oil from the pure oil layer of the Sa I Group. On the one hand, this facilitates effect tracking and process analysis, and on the other hand, it avoids inter-layer interference, effectively improves the fracturing effect of a single well, and delays the subsequent increase in water cut.

[0085] Example 1 of the fixed-point injection fracturing process in heterogeneous thick oil reservoirs of the present invention

[0086] Targeted jet fracturing of well L4-1312:

[0087] 1. Well and Layer Selection: This well is located in Block 2 of the North North Block. It was put into production in April 1992. Before fracturing, it produced 82 tons of fluid and 1.6 tons of oil per day, with a combined water cut of 98.1%, and a cumulative oil production of 51,900 tons. This time, a targeted jet fracturing test was carried out on the densely developed thick oil layer in the Sa I Group. The small layers with remaining oil enrichment were selected, and the potential was finely tapped by using thin interlayers for shielding.

[0088] 2. Process Design: This well has 25 sub-layers perforated. This time, the Sa I group oil layer is selected for targeted jet fracturing. The coiled tubing hydraulic jet fracturing string is selected, and the jetting and fracturing integrated string is adopted to realize the targeted stimulation of this well. Among them, the Sa I 1 (1) to Sa I 4+5 (3) oil layers mainly develop sheet sand, with a sandstone thickness of 12.5m and an effective thickness of 7.5m. There are 2 water wells connected to it. Based on the thickness of the sub-layers, the difference in permeability and the development of the interlayers, 6 points for targeted potential tapping are selected. The depths of the fracturing jet points are: 1082.1m, 1078.9m, 1076.4m, 1072.2m, 1063.2m and 1061.4m respectively.

[0089] 3. Tubing String Design: This well uses coiled tubing for fracturing. The overall tooling, from top to bottom, consists of: slip connector 104, double-acting release mechanism, flow meter, adapter, centralizer, spray gun, filter, hydraulic anchor (SLM116A), tubing sub, dead-end adapter, flow meter, locator 109, and centralizer guide head 110. The locator 109 precisely corrects the tubing string's insertion depth, ensuring accurate tool setting. The hydraulic anchor provides tubing string anchoring, preventing upward movement and displacement during fracturing operations. The flow meter monitors the flow rate in real time, the filter ensures the cleanliness of the incoming fluid, and the centralizer and centralizer guide head 110 ensure the tubing string is centered and smoothly lowered. The spray gun serves as the fracturing channel, enabling directional fracturing of the S1 group. The double-acting release mechanism allows for safe release and retrieval of the tubing string later, ensuring safety during the initial fracturing operation and subsequent work.

[0090] 4. On-site implementation and production results: During the fracturing operation of well L4-1312, the fixed-point injection fracturing process was adopted. The overall pressure fluctuation was stable, and no sand blockage or sand burial occurred. The operation proceeded normally. In the initial stage after commissioning, the fluid production was 34t / d and the oil production was 13.2t / d. The effective period of the stage was 230 days, and the cumulative increase in oil production during the stage was 2252t. The input-output ratio of the stage was 1:6.0.

[0091] In summary, the targeted injection fracturing technology for heterogeneous thick oil reservoirs of this invention achieves the following advantages: First, it improves the accuracy of fracturing: relying on targeted injection and Bernoulli's principle, it enables precise perforation and fracture creation within thick oil reservoirs without the constraints of interlayers, effectively avoiding high-permeability water-flooded sections, targeting and transforming remaining oil-rich areas, and avoiding ineffective fracturing and repeated stimulation. Second, it improves the balance of reservoir utilization: precisely controlling the longitudinal extension of fractures reduces the impact of intra-layer heterogeneity, interlayer obstruction, and inter-layer interference, significantly improving the longitudinal utilization of thick oil reservoirs and fully tapping the potential of scattered remaining oil. Third, it enhances the production increase effect of single wells: high fracturing fluid utilization and good fracture creation effect can effectively activate low-permeability and difficult-to-utilize reserves, significantly improving single-well production capacity and production increase, and providing stable and lasting fracturing effects. Fourth, it enhances process adaptability: applicable to heterogeneous thick oil reservoirs with different permeabilities and rhythmic characteristics, it can be flexibly adapted to multi-segment, thin and poor-quality layers, and continuous thick oil reservoirs, with simple construction string and strong process controllability.

[0092] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0093] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A fixed-point injection fracturing structure for heterogeneous thick oil reservoirs, characterized in that, include: A connecting pipe, the axis of which extends in the vertical direction, is used to be lowered into the casing in the well. The injection pipe is connected to the lower end of the connecting pipe and communicates with the interior of the connecting pipe. The injection pipe has multiple injection holes arranged at intervals in the vertical direction. The injection holes are used to inject fracturing fluid into the inner wall of the casing. The first mounting tube is threaded to the outside of the connecting tube; The second mounting tube is slidably disposed inside the lower end of the first mounting tube in the vertical direction, the spray tube passes through the interior of the second mounting tube, and the upper end of the second mounting tube is provided with a hollow area. A locator, which is disposed on the second mounting pipe, is used to locate the position of the second mounting pipe so as to correspond to the target oil layer; In the initial state, the hollowed-out area is blocked by the lower end of the first mounting tube; when the hydraulic pressure inside the injection tube increases and pushes the second mounting tube to move downward relative to the first mounting tube, the hollowed-out area extends out from the lower end of the first mounting tube, so that fracturing fluid is sprayed out from the injection hole corresponding to the hollowed-out area; the connecting tube can drive the injection tube to move up and down relative to the first mounting tube so that the injection holes at different positions can correspond to the hollowed-out area respectively.

2. The fixed-point injection fracturing structure within a heterogeneous thick oil layer according to claim 1, characterized in that, The upper end of the second mounting tube is provided with multiple baffles evenly distributed around its circumference. The baffles extend in the vertical direction, and the position between two adjacent baffles forms the hollow area.

3. The fixed-point injection fracturing structure within a heterogeneous thick oil layer according to claim 2, characterized in that, The first mounting tube is coaxially fitted with a first retaining sleeve on its outside, and the second mounting tube is coaxially fitted with a second retaining sleeve on its outside. The outer circumferential surfaces of the first retaining sleeve and the second retaining sleeve form a sealing fit with the inner wall of the casing, thereby accumulating the fracturing fluid ejected from the injection hole.

4. The fixed-point injection fracturing structure within a heterogeneous thick oil layer according to claim 3, characterized in that, Both the first and second retaining sleeves are conical sleeves, and the large end of the first retaining sleeve corresponds vertically to the large end of the second retaining sleeve.

5. The fixed-point injection fracturing structure within a heterogeneous thick oil layer according to claim 1, characterized in that, The injection hole is a conical hole, the axis of which is perpendicular to the axis of the connecting pipe, and the small end of the conical hole is set away from the axis of the injection pipe.

6. The targeted injection fracturing structure within a heterogeneous thick oil reservoir according to claim 3, characterized in that, The upper outer circumferential surface of the connecting tube is provided with a wedge-shaped block extending radially therefrom, and the wedge-shaped block has an inclined surface that is radially inclined relative to the connecting tube; the inner wall of the first mounting tube is provided with a slot extending radially therefrom, and an elastic block is provided in the slot, and the inclined surface and the elastic block slide together to allow the elastic block to retract into the slot.

7. The targeted injection fracturing structure within a heterogeneous thick oil reservoir according to claim 6, characterized in that, The slot is equipped with a U-shaped spring, which can extend and retract radially along the first mounting tube, and the elastic block is connected to the U-shaped spring.

8. The targeted injection fracturing structure within a heterogeneous thick oil reservoir according to claim 7, characterized in that, The first stop sleeve, the second stop sleeve, and the elastic block are all made of rubber material.

9. The fixed-point injection fracturing structure within a heterogeneous thick oil layer according to claim 1, characterized in that, The lower end of the first mounting tube is provided with an inner retaining ring, and the upper end of the second mounting tube is provided with an outer retaining ring. A compression spring that can extend and retract in the vertical direction is provided between the inner retaining ring and the outer retaining ring. The compression spring is used to reset the second mounting tube upward.

10. The targeted injection fracturing structure within a heterogeneous thick oil layer according to claim 3, characterized in that, The first mounting tube is also fitted with a first stabilizer, which is located above the first stop sleeve. The second mounting tube is also fitted with a second stabilizer, which is located below the second stop sleeve.

11. The fixed-point injection fracturing structure within a heterogeneous thick oil layer according to claim 1, characterized in that, The upper end of the connecting pipe is also provided with a slip connector. The slip connector has multiple slips evenly distributed around the circumference of the connecting pipe. The slips can open radially along the connecting pipe and engage with the inner wall of the sleeve to anchor the connecting pipe inside the sleeve.

12. The fixed-point injection fracturing structure within a heterogeneous thick oil layer according to claim 1, characterized in that, The lower end of the second mounting tube is also provided with a straightening guide head, which is located below the locator and is used to straighten and guide the movement of the second mounting tube.

13. The targeted injection fracturing structure within a heterogeneous thick oil reservoir according to claim 1, characterized in that, The locator has a clamp, which is detachably and fixedly installed at the lower end of the second mounting tube.

14. A targeted jet fracturing process within a heterogeneous thick oil reservoir, employing the targeted jet fracturing structure within a heterogeneous thick oil reservoir as described in any one of claims 1 to 13, characterized in that, Includes the following steps: S1. Determine the target well and target interval based on reservoir parameters; S2. The fixed-point injection fracturing structure in the heterogeneous thick oil layer is lowered into the well to a predetermined depth, and the lowering depth is detected by the positioner; S3. Pump fracturing fluid into the connecting pipe, thereby increasing the hydraulic pressure inside the injection pipe and pushing the second mounting pipe downward relative to the first mounting pipe, so that the hollowed-out area extends out from the lower end of the first mounting pipe, and then the fracturing fluid is ejected through the injection hole corresponding to the hollowed-out area. The injection hole generates a high-speed jet at the preset injection point in the thick oil layer. Based on Bernoulli's principle, a local low-pressure area is formed around the injection point, inducing the fracture to start at the preset position.

15. The targeted injection fracturing process within a heterogeneous thick oil reservoir according to claim 14, characterized in that, It also includes the following steps: S4. When it is necessary to switch the spray holes in different positions, the ground column is rotated to drive the connecting pipe to rotate a set number of times, so that the connecting pipe drives the spray pipe to move up and down relative to the first mounting pipe, so that the spray holes in different positions correspond to the positions of the hollow area respectively. S5. Repeat step S3 to complete the targeted injection fracturing operation of the new target oil layer.

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