Design method of exploration well, well bore structure and construction method of horizontal well

Abstract

The invention relates to the field of oil and gas development, in particular to a design method of an exploration well, a well bore structure and a construction method of a horizontal well, the design method designs the well bore structure of the exploration well according to a well track of the horizontal well, and the well bore structure of the exploration well is composed of a vertical well section and an inclined well section; when a horizontal well is developed, a drilled section of an exploration well can be fully utilized, the drilling difficulty of a target reservoir of the horizontal well is reduced, the drilling efficiency is improved, and the drilling cost is saved; according to the well body structure, the design of a well track is optimized, a horizontal well can be developed more easily through the inclined well section, and the drilling footage during horizontal well drilling is shortened; according to the construction method of the horizontal well, the well track of the horizontal well and the well track of the inclined well section are partially overlapped, the transverse distance between the well bottom of the exploration well and the target spot of the development horizontal well is shortened, the geological prediction precision is improved, and landing of the horizontal well is better facilitated.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas development, and in particular to a design method for an exploration well, a wellbore structure and a horizontal well construction method. Background Art

[0002] Oil and gas production needs to go through the exploration, evaluation and development stages. Exploration wells 100 need to take into account the tasks of logging and data acquisition. They often need to drill through the target reservoir and obtain detailed geological parameters of the target reservoir to provide detailed geological data for future development well construction. Horizontal wells are the main well type for shale gas exploration and development. In order to quickly convert from exploration wells 100 to development horizontal wells, it is generally necessary to backfill and side-drill development horizontal wells on the basis of exploration vertical wells.

[0003] However, when the existing vertical exploration wells are converted to horizontal development wells, a lot of footage is wasted. Taking the Longmaxi Formation in southern Sichuan as an example, the technical casing is lowered to the top of the Shiniulan Formation, and the open hole section of the exploration vertical well is about 1,000 meters long. After logging, about 800 meters of footage needs to be backfilled. When developing horizontal wells, there are problems such as less utilization of the drilled well section, more footage is wasted, longer cement plugs are used for backfilling the well section, and greater difficulty in side drilling new wells in vertical wells. Especially for exploration vertical wells with deeper technical casing, later development horizontal wells need to be side drilled through windows in the technical casing, and the process is relatively complicated.

[0004] Therefore, there is an urgent need for a technical solution to solve the technical problems of converting current vertical exploration wells into horizontal wells, such as insufficient utilization of drilled sections, high footage waste, long cement plugs used for backfilling sections, and difficulty in side-drilling new wellbores in vertical wells. Summary of the Invention

[0005] The purpose of the present invention is to provide a design method for an exploration well, a wellbore structure and a construction method for a horizontal well in response to the technical problems that exist when converting a current vertical exploration well to a horizontal well, such as insufficient utilization of the drilled well section, a large amount of footage wasted, a long cement plug used for backfilling the well section and great difficulty in sidetracking a new wellbore in the vertical well.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: A method for designing an exploration well comprises the following steps: S1. Obtain the target reservoir location; S2. Design a horizontal well suitable for the target reservoir based on the target reservoir location and determine the horizontal wellbore trajectory orientation; S3. Designing an inclined well section of the exploration well based on the horizontal wellbore trajectory orientation, wherein the inclined well section penetrates the target reservoir, and the horizontal wellbore trajectory at least partially passes through the inclined well section; S4. Designing a vertical well section of the exploration well according to the position of the inclined well section, wherein the vertical well section smoothly transitions with the inclined well section; Based on the three pressure profiles and formation complexity, S5 optimizes the isolation layer position and well depth of each drill bit in the vertical well section and optimizes the wellbore structure of the exploration well.

[0007] The invention provides a method for designing an exploration well. The method obtains data of the drilling area, obtains the position of the target reservoir through analysis, and designs the horizontal wellbore trajectory at the target reservoir in priority. According to the horizontal wellbore trajectory, the inclined well section of the exploration well is designed, so that the horizontal wellbore trajectory partially passes through the inclined well section and enters the target reservoir from the side wall of the inclined well section, and the wellbore trajectory of the inclined well section coincides with the wellbore trajectory of the horizontal well; according to the position of the inclined well section, a vertical well section with a smooth transition to the inclined well section is designed, so that the vertical well section is located at the top of the inclined well section, the vertical well section is connected to the inclined well section, and the wellbore structure of the vertical well is the same as that of the exploration vertical well; according to the three pressure profiles and the complexity of the formation, the isolation layer position and well section depth of each drill bit of the vertical well section are optimized, so that the maximum insertion depth of the technical casing can be as deep as the inclined well section; under the conditions of formation pore pressure, formation The vertical well section and the inclined well section are designed based on the fracture pressure and the formation collapse pressure, thereby ensuring the rationality of the wellbore trajectory; this design method reversely designs the inclined well section and the vertical well section of the exploration well from the wellbore trajectory of the horizontal well, so that when the exploration well is subsequently converted to a horizontal well for development, the horizontal well construction can make full use of the drilled well section of the exploration well and reduce the footage of the exploration well being scrapped; setting the inclined well section in the exploration well reduces the difficulty of drilling the target reservoir of the horizontal well, reduces the drilling footage of the target reservoir during horizontal well development, and improves the drilling efficiency of the horizontal well; during horizontal well development, the lateral distance between the bottom of the exploration well and the development target point is shortened, the geological prediction accuracy is improved, and it is more conducive to the landing of the horizontal well; it avoids the casing window when the technical casing is lowered to a deep depth, saves the pipe cost, saves the cement plug backfill cost, and reduces the overall cost of the whole well.

[0008] The isolation layer position and well section depth of each drill bit in the vertical well section are determined by the three pressure profiles of the formation combined with the complexity of the formation. During the vertical well drilling process, multiple drillings are required to ensure the stability of the wellbore structure.

[0009] As a preferred embodiment of the present invention, in S1, the target reservoir position is obtained based on drilling data, and the data of the drilling area include drilling situation data of the adjacent area, geological data of the drilling area, and geostress data of the drilling area. Through the drilling situation of adjacent wells or adjacent areas, the complex situations that each drilled layer will encounter can be analyzed. When designing the wellbore structure of the exploration well, the risks in the drilling process can be avoided, and the safety of exploration well drilling construction and horizontal well drilling construction can be ensured; the geological data of the drilling area and the geostress data of the drilling area can provide designers with data for well design, so that the designed well can be smoothly constructed; the drilling situation data of the adjacent area mainly collects the complex situations encountered during the drilling process.

[0010] As a preferred embodiment of the present invention, in S1, the geostress data of the drilling area includes the direction of the maximum horizontal principal stress, and in S2, the horizontal wellbore trajectory is perpendicular to the direction of the maximum horizontal principal stress, or the angle between the horizontal wellbore trajectory and the direction of the maximum horizontal principal stress is greater than or equal to 60 degrees. A horizontal wellbore trajectory designed perpendicular to the direction of the maximum horizontal principal stress, or with an angle between the horizontal wellbore trajectory and the direction of the maximum horizontal principal stress greater than or equal to 60 degrees, is less likely to cause formation collapse during drilling, thereby ensuring the stability of the horizontal wellbore trajectory. This improves the effectiveness of hydraulic fracturing during hydraulic fracturing and accelerates oil and gas recovery.

[0011] As a preferred embodiment of the present invention, the horizontal wellbore trajectory includes a straight well section, a first inclination-increasing section, a steady inclination section, a second inclination-increasing section, and a horizontal section. The straight well section coincides with the vertical well section trajectory, the first inclination-increasing section coincides with the inclined well section trajectory, the steady inclination section passes through the side wall of the inclined well section, and the second inclination-increasing section and the horizontal section pass through the target reservoir. The trajectory of the straight well section coincides with the trajectory of the vertical well section, and the trajectory of the first inclination-increasing section coincides with the trajectory of the inclined well section. When the horizontal well is developed, the horizontal wellbore trajectory enters the inclined well section along the bottom of the vertical well section and is obliquely drilled into the target reservoir from the side wall of the inclined well section, thereby reducing the difficulty of the horizontal well entering the target reservoir and improving the directional drilling efficiency of the horizontal well. When the horizontal well is developed, the inclined well section trajectory can be overlapped with the wellbore trajectory of part of the horizontal well, and the inclined well section can be used to reduce the drilling footage of the target reservoir.

[0012] As a preferred embodiment of the present invention, the inclination angle of the stabilizing section is 35 to 55 degrees, and the length of the stabilizing section is greater than or equal to 30 meters. Controlling the inclination angle of the stabilizing section to 35 to 55 degrees ensures the utilization of the inclined well section, enabling the stabilizing section of the horizontal well to enter the target reservoir from the sidewall of the inclined well section. The length of the stabilizing section is greater than or equal to 30 meters, leaving sufficient length for smooth steering of the drill bit and reservoir casing, ensuring smooth drilling of the drill bit and smooth running of the reservoir casing.

[0013] As a preferred embodiment of the present invention, in S5, the isolation layer and well depth for each drill bit are determined based on the principle of maintaining the highest drilling fluid density in the openhole section without losing the upper formation and isolating complex formations. This ensures that the technical casing can be lowered to the upper middle portion of the inclined wellbore section. The maximum running depth of the technical casing is sufficient to reach the upper middle portion of the inclined wellbore section, optimizing the wellbore structure in the vertical wellbore section, reducing the development cost of the exploration well, and improving the drilling efficiency of the exploration well.

[0014] As a preferred embodiment of the present invention, the inclined well section is provided with a logging pocket for stabilizing inclination drilling, and the logging pocket is located below the target reservoir. The logging pocket is a well section reserved at the bottom of the inclined well section after continued drilling of the inclined well section. The logging pocket can reduce the difficulty of directional drilling. The logging pocket is provided below the target reservoir to facilitate logging operations and the acquisition of complete logging data. During cementing, the cement slurry fills the inclined well section, ensuring that the horizontal well is not affected by the drilled wellbore during development. The stabilizing inclination section of the horizontal well is directionally constructed along the inclined well section of the exploration well, overlapping the stabilizing inclination section by approximately 30 meters, facilitating directional drilling of the horizontal well.

[0015] A wellbore structure of an exploration well is designed using the above-mentioned design method for an exploration well, comprising a vertical well section and an inclined well section. The vertical well section is provided with a technical casing, and the technical casing is connected to the inclined well section.

[0016] The wellbore structure of an exploration well of the present invention is designed according to the wellbore trajectory of a horizontal well. The wellbore structure consists of a vertical well section and an inclined well section. The vertical well section is vertically arranged. By setting the inclined well section, when developing a horizontal well, the footage of the exploration well that is scrapped is reduced by utilizing the inclined well section. The horizontal well is developed from the inclined well section, which reduces the drilling difficulty of the horizontal well and improves the drilling efficiency of the horizontal well. The inclined well section is not isolated by a technical casing, which can avoid windowing operations on the technical casing during horizontal well development, thereby saving pipe costs. By setting the inclined well section, the lateral distance between the bottom of the exploration well and the target point of the development horizontal well is shortened, thereby improving the accuracy of geological prediction.

[0017] As a preferred embodiment of the present invention, the vertical well section is provided with a surface casing, and the technical casing can be lowered from the surface casing to the inclined well section. The maximum lowering depth of the technical casing can extend to the top of the inclined well section. When conducting horizontal well development, the horizontal wellbore trajectory enters the inclined well section from the bottom of the technical casing and eventually penetrates into the target reservoir from the sidewall of the inclined well section. Part of the wellbore in the inclined well section can serve as the horizontal wellbore trajectory. After the horizontal well is drilled, part of the inclined wellbore can be used to arrange the oil layer casing. The drill bit of the horizontal well is drilled obliquely from the sidewall of the inclined well section, which reduces the drilling difficulty of the target reservoir of the horizontal well, improves the directional drilling efficiency of the horizontal well, and reduces the drilling footage of the target reservoir.

[0018] A method for constructing a horizontal well, including the above-mentioned wellbore structure of an exploration well, comprises the following steps: Step 1: Conduct exploration well logging operations; Step 2: Optimize horizontal well trajectory: Horizontal well trajectory based on logging data; Step 3: Backfill cementing: Backfill the inclined well section with cement plugs and wait for the cement plugs to solidify; Step 4: Drilling the horizontal well: Drilling operations are carried out according to the optimized horizontal wellbore trajectory; Step 5: Lower the casing into the oil layer.

[0019] A horizontal well construction method of the present invention shortens the lateral distance between the bottom of the exploration well and the target point of the development horizontal well by carrying out horizontal well development on the exploration well body structure of the present invention, improves the geological prediction accuracy, and is more conducive to the landing of the horizontal well; fully utilizes the inclined well section, reduces the drilling difficulty of the horizontal well target reservoir, improves the development efficiency of the horizontal well, reduces the use of backfill materials, and saves backfill costs.

[0020] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. A method for designing an exploration well of the present invention obtains data on the drilling area, obtains the position of the target reservoir through analysis, and preferentially designs the horizontal wellbore trajectory at the target reservoir. According to the horizontal wellbore trajectory, an inclined well section of the exploration well is designed, so that the horizontal wellbore trajectory partially passes through the inclined well section and enters the target reservoir from the side wall of the inclined well section, and the wellbore trajectory of the inclined well section coincides with the wellbore trajectory of the horizontal well; according to the position of the inclined well section, a vertical well section with a smooth transition to the inclined well section is designed, so that the vertical well section is located at the top of the inclined well section, the vertical well section is connected to the inclined well section, and the wellbore structure of the vertical well is the same as that of the exploration vertical well; according to the three pressure profiles and the complexity of the formation, the isolation layer position and well section depth of each drill bit of the vertical well section are optimized, so that the maximum insertion depth of the technical casing can be as deep as the inclined well section; under the conditions of formation pore pressure, formation The vertical well section and the inclined well section are designed based on the formation fracture pressure and formation collapse pressure, thereby ensuring the rationality of the wellbore trajectory; this design method reversely designs the inclined well section and the vertical well section of the exploration well from the wellbore trajectory of the horizontal well, so that when the exploration well is subsequently converted to horizontal well development, the horizontal well construction can make full use of the drilled well section of the exploration well and reduce the footage scrapped of the exploration well; setting the inclined well section in the exploration well reduces the difficulty of drilling the target reservoir of the horizontal well, reduces the drilling footage of the target reservoir during horizontal well development, and improves the drilling efficiency of the horizontal well; during horizontal well development, the lateral distance between the bottom of the exploration well and the development target point is shortened, the geological prediction accuracy is improved, and it is more conducive to the landing of the horizontal well; it avoids the casing window when the technical casing is lowered to a deep depth, saves the pipe cost, saves the cement plug backfill cost, and reduces the comprehensive cost of the whole well.

[0021] 2. The wellbore structure of an exploration well of the present invention is designed according to the wellbore trajectory of a horizontal well. The wellbore structure consists of a vertical well section and an inclined well section. The vertical well section is arranged vertically. By setting the inclined well section, when developing a horizontal well, the footage of the exploration well that is scrapped is reduced by utilizing the inclined well section. The horizontal well is developed from the inclined well section, which reduces the drilling difficulty of the horizontal well and improves the drilling efficiency of the horizontal well. The inclined well section does not use technical casing for isolation, which can avoid windowing operations on the technical casing during horizontal well development, thereby saving pipe costs. By setting the inclined well section, the lateral distance between the bottom of the exploration well and the target point of the development horizontal well is shortened, thereby improving the accuracy of geological prediction.

[0022] 3. A horizontal well construction method of the present invention shortens the lateral distance between the bottom of the exploration well and the target point of the development horizontal well by developing the horizontal well on the exploration well body structure of the present invention, improves the geological prediction accuracy, and is more conducive to the landing of the horizontal well; fully utilizes the inclined well section, reduces the drilling difficulty of the horizontal well target reservoir, improves the development efficiency of the horizontal well, reduces the use of backfill materials, and saves backfill costs.

[0023] 4. The design method of an exploration well of the present invention is easy to implement. By designing the exploration well to consist of an inclined well section and a vertical well section, the wellbore structure of the exploration well is optimized, so that the inclined well section of the exploration well can adapt to the development of horizontal wells, reducing the development difficulty of horizontal wells, improving the development efficiency of horizontal wells, reducing the consumption of backfill materials during horizontal well development, avoiding window opening operations on technical casings, and reducing the construction cost of horizontal well development. It has good economic value and practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the existing exploration well structure; Figure 2 is a schematic structural diagram of the horizontal wellbore trajectory of Example 1; Figure 3 This is a schematic diagram of a design process of an exploration well in Example 1; Figure 4 It is a schematic diagram of the structure of an exploration well; Figure 5 This is a flow chart of a horizontal well construction method of Example 3.

[0025] icon: 1-vertical well section, 2-inclined well section, 3-horizontal wellbore trajectory, 4-ground, 11-technical casing, 12-surface casing, 31-vertical well section, 32-first inclination section, 33-stable inclination section, 34-second inclination section, 35-horizontal section, 100-exploration well. DETAILED DESCRIPTION

[0026] The present invention will be described in detail below with reference to the accompanying drawings.

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] Example 1 like Figures 1-4 A method for designing an exploration well is shown, comprising the following steps: S1. Obtain the location of the target reservoir: Determine the location of the target reservoir based on the data of the drilling area; collect drilling data, geological data and ground stress data of the adjacent area. Designers can obtain sufficient drilling references through the drilling data of the adjacent area. When designing the wellbore structure, they can avoid some problems encountered in the drilling operation through the wellbore design, making the wellbore structure more reasonable and the drilling operation more efficient; the location distribution of the target reservoir can be analyzed through the geological data of the drilling area, providing data support for the design of the horizontal wellbore trajectory 3; the ground stress data of the drilling area can be used to plan the horizontal wellbore trajectory 3 more reasonably, further reducing the risks of collapse, well leakage, and pipe sticking during the horizontal well drilling process; focus on collecting data such as pressure bearing capacity, faults, cracks, oil, gas and water displays in the drilling conditions of the adjacent area.

[0029] S2. Design horizontal wells: Design a horizontal well suitable for the target reservoir based on the location of the target reservoir; design and optimize the horizontal wellbore trajectory 3 suitable for the target reservoir by obtaining drilling data from the adjacent area, geological data from the drilling area, and stress data from the drilling area, determine the position and orientation of the horizontal well entering the target reservoir, and select the optimal position to design the horizontal wellbore trajectory 3.

[0030] S3. Design the inclined well section 2 of the exploration well: Based on the horizontal wellbore trajectory 3 and azimuth, design the inclined well section 2 of the exploration well. The horizontal wellbore trajectory 3 partially passes through the inclined well section 2, and the inclined well section 2 drills through the target reservoir. The inclined well section 2 is designed by the horizontal wellbore trajectory 3 entering the target reservoir. The horizontal wellbore trajectory 3 partially passes through the inclined well section 2. The horizontal wellbore trajectory 3 can utilize the inclined well section 2 to shorten the drilling footage of the horizontal wellbore trajectory 3. The horizontal wellbore trajectory 3 is drilled from the side wall of the inclined well section 2, which reduces the drilling difficulty and improves the drilling efficiency. The setting of the inclined well section 2 shortens the lateral distance between the bottom of the exploration well and the development target (i.e., in the horizontal direction, the farthest distance from the starting point of the horizontal section 35 of the horizontal well to the inner wall of the exploration well), thereby improving the accuracy of geological prediction.

[0031] S4. Design the vertical well section 1 of the exploration well: Design the vertical well section 1 based on the position of the inclined well section 2, with a smooth transition between the vertical well section 1 and the inclined well section 2. The smooth transition between the vertical well section 1 and the inclined well section 2 facilitates the smooth development of the horizontal well, reduces friction during horizontal well drilling, tripping, and logging, and improves drilling operation efficiency.

[0032] S5. Optimizing the Wellbore Structure of the Exploration Well: Based on the three pressure profiles and formation complexity, the isolation layer position and well depth of each drill bit in vertical well section 1 were optimized. This optimization resulted in more reasonable isolation layer position and well depth design for each drill bit, improving drilling efficiency and reducing drilling costs. In-situ stress data was used to optimize the wellbore structure of inclined well section 2.

[0033] Specifically, the horizontal wellbore trajectory 3 is perpendicular to the direction of the horizontal maximum principal stress. When the horizontal wellbore trajectory 3 is set perpendicular to the direction of the horizontal maximum principal stress, a complex fracture network is more easily formed in the formation after volume fracturing, which can improve the effect of fracturing transformation and accelerate the oil and gas collection speed.

[0034] Specifically, a five-segment profile of "straight, increasing, stable, and flat" is adopted to design the wellbore trajectory of the horizontal well. The horizontal wellbore trajectory 3 includes a straight well section 31, a first increasing inclination section 32, a stable inclination section 33, a second increasing inclination section 34, and a horizontal section 35. The trajectory of the straight well section 31 coincides with the trajectory of the vertical well section 1, the trajectory of the first increasing inclination section 32 partially coincides with the trajectory of the inclined well section 2, the stable inclination section 33 completely coincides with the trajectory of the inclined well section 2, the length of the inclined well section 2 is greater than that of the stable inclination section 33, and the second increasing inclination section 34 and the horizontal section 35 pass through the target reservoir; the trajectory of the straight well section 31 coincides with the trajectory of the vertical well section 1. The trajectories overlap, the trajectory of the first increasing inclination section 32 overlaps with the trajectory of the inclined well section 2, and the stabilizing inclination section 33 overlaps with the trajectory of the inclined well section 2; when developing a horizontal well, the horizontal wellbore trajectory 3 enters the inclined well section 2 from the bottom of the vertical well section 1 and is obliquely drilled into the target reservoir from the side wall of the inclined well section 2, which reduces the difficulty of the horizontal well entering the target reservoir and improves the directional drilling efficiency of the horizontal well; when developing a horizontal well, the wellbore trajectory of the inclined well section 2 is overlapped with the wellbore trajectory 3 of part of the horizontal well, and the inclined well section 2 is used to reduce the drilling footage of the target reservoir, thereby reducing the drilling cost.

[0035] Specifically, the well inclination angle of the stabilizing section 33 is 45 degrees, and the length of the stabilizing section 33 is 40m; the well inclination angle of the stabilizing section 33 is 35 degrees to 55 degrees, preferably 45 degrees, so that the turning angle of the vertical section to the stabilizing section 33 is the same as the turning angle of the stabilizing section 33 to the horizontal section 35, which is convenient for the steering of the drill bit, drilling tools and oil layer casing; the length of the stabilizing section 33 needs to be greater than or equal to 30m, and sufficient length is reserved to enable the drill bit to be converted from the vertical direction to the horizontal direction; the stabilizing section 33 serves as a transition section from the vertical section to the horizontal section 35, and the well inclination angle set should not be too large. An excessively large well inclination angle will increase the difficulty of drilling the exploration well, and will encounter excessive resistance when drilling, logging, and lowering the oil layer casing.

[0036] Specifically, the isolation layer and well depth for each drill bit are determined based on the principle that the highest drilling fluid density in the openhole section does not leak out the upper formation and isolates complex formations. Based on the principle that the highest drilling fluid density in the openhole section does not leak out the formation at the upper casing shoe and the complex casing isolation formation, the formation is segmented to divide the isolation layer for each drilling run. Depth intervals are set between adjacent well sections. The three-pressure profile changes within the depth intervals are minimal, allowing the drill bits in adjacent runs to drill within the depth intervals, providing room for dynamic optimization of the drill bit's drilling process. The wellbore structure of vertical well section 1 is optimized, and the technical casing 11 is connected to the middle and upper part of the inclined well section 2. Technical casing 11 meets the conditions for reaching the inclined well section 2.

[0037] Specifically, inclined well section 2 is designed to stabilize inclination drilling and reduce the difficulty of directional drilling. A logging pocket is reserved, located below the target reservoir. After the drill bit penetrates the target reservoir along the wellbore trajectory of inclined well section 2, stable inclination drilling continues along the wellbore trajectory of inclined well section 2. The drilling section beyond the target reservoir serves as the logging pocket. The logging pocket is primarily used to allow logging instruments to penetrate deeper during logging operations, allowing for complete and accurate geological data of the target reservoir. During cementing, the cement plug completely fills the logging pocket.

[0038] A method for designing an exploration well of the present invention determines a horizontal wellbore trajectory 3 based on various geological data, designs the exploration well based on the horizontal wellbore trajectory 3 and the orientation, so that the exploration well has a vertical well section 1 and an inclined well section 2, so that the inclined well section 2 can be more convenient for horizontal well development; the vertical well section 1 adopts three pressure profiles and is optimized in combination with the complex formation conditions, so that the technical casing 11 can not only isolate the complex layer above the target reservoir, but also avoid opening windows on the technical casing 11 during horizontal well development, thereby optimizing the process of horizontal well development, accelerating the efficiency of horizontal well development, and saving costs.

[0039] The invention provides a method for designing an exploration well. The method obtains data of the drilling area, obtains the position of the target reservoir through analysis, and designs the horizontal wellbore trajectory at the target reservoir in priority. According to the horizontal wellbore trajectory, the inclined well section of the exploration well is designed, so that the horizontal wellbore trajectory partially passes through the inclined well section and enters the target reservoir from the side wall of the inclined well section, and the wellbore trajectory of the inclined well section coincides with the wellbore trajectory of the horizontal well; according to the position of the inclined well section, a vertical well section with a smooth transition to the inclined well section is designed, so that the vertical well section is located at the top of the inclined well section, the vertical well section is connected to the inclined well section, and the wellbore structure of the vertical well is the same as that of the exploration vertical well; according to the three pressure profiles and the complexity of the formation, the isolation layer position and well section depth of each drill bit of the vertical well section are optimized, so that the maximum insertion depth of the technical casing can be as deep as the inclined well section; under the conditions of formation pore pressure, formation The vertical well section and the inclined well section are designed based on the fracture pressure and the formation collapse pressure, thereby ensuring the rationality of the wellbore trajectory; this design method reversely designs the inclined well section and the vertical well section of the exploration well from the wellbore trajectory of the horizontal well, so that when the exploration well is subsequently converted to a horizontal well for development, the horizontal well construction can make full use of the drilled well section of the exploration well and reduce the footage of the exploration well being scrapped; setting the inclined well section in the exploration well reduces the difficulty of drilling the target reservoir of the horizontal well, reduces the drilling footage of the target reservoir during horizontal well development, and improves the drilling efficiency of the horizontal well; during horizontal well development, the lateral distance between the bottom of the exploration well and the development target point is shortened, the geological prediction accuracy is improved, and it is more conducive to the landing of the horizontal well; it avoids the casing window when the technical casing is lowered to a deep depth, saves the pipe cost, saves the cement plug backfill cost, and reduces the overall cost of the whole well.

[0040] Example 2 like Figure 4 The wellbore structure of an exploration well shown is designed using the design method of an exploration well in Example 1, and includes a vertical well section 1 and an inclined well section 2. The vertical well section 1 is provided with a technical casing 11, and the technical casing 11 is connected to the inclined well section 2.

[0041] Specifically, a surface casing 12 is provided in the vertical well section 1, and the technical casing 11 extends from the surface casing 12, with a maximum insertion depth of the middle and upper part of the inclined well section 2. When developing a horizontal well, the wellbore trajectory of the horizontal well enters the inclined well section 2 from the bottom of the technical casing 11, and finally penetrates into the target reservoir from the side wall of the inclined well section 2. Part of the wellbore of the inclined well section 2 can be used as the horizontal wellbore trajectory 3. After the horizontal well drilling is completed, part of the inclined wellbore can be used to arrange the oil layer casing. The drill bit of the horizontal well is drilled obliquely from the side wall of the inclined well section 2, which reduces the drilling difficulty of the target reservoir of the horizontal well, improves the directional drilling efficiency of the horizontal well, and reduces the drilling footage of the target reservoir.

[0042] The wellbore structure of an exploration well of the present invention is designed according to the horizontal wellbore trajectory 3. The wellbore structure consists of a vertical well section 1 and an inclined well section 2. The vertical well section 1 is vertically arranged, and the oil layer casing can be lowered into the vertical well section from the surface. By setting the inclined well section 2, when developing the horizontal well, the footage of the exploration well that is scrapped is reduced by utilizing the inclined well section 2. The horizontal well is developed from the inclined well section, which reduces the drilling difficulty of the horizontal well and improves the drilling efficiency of the horizontal well. The inclined well section 2 is not isolated by the technical casing 11, which can avoid the windowing operation of the technical casing 11 during the horizontal well development, thereby saving the cost of pipes. By setting the inclined well section 2, the lateral distance between the bottom of the exploration well and the target point of the development horizontal well is shortened, thereby improving the accuracy of geological prediction.

[0043] Example 3 like Figure 5 The horizontal well construction method shown includes a wellbore structure of an exploration well in Example 2, comprising the following steps: Step 1: Conduct exploration well logging operations and analyze the oil and gas content of the target reservoir; Step 2: Optimize horizontal well trajectory: Optimize horizontal well trajectory based on logging data3; Step 3: Backfill cementing: Backfill the inclined well section 2 with cement plugs so that the elevation difference between the top of the cement plug and the horizontal section 35 is about 30m; and wait for the cement plug to solidify; Step 4: Drilling the horizontal well: Based on the optimal target of the horizontal wellbore trajectory 3 determined by well logging, the drilling operation is carried out according to the optimized horizontal wellbore trajectory 3; Step 5: Lower the casing into the oil layer.

[0044] A horizontal well construction method of the present invention shortens the lateral distance between the bottom of the exploration well and the target point of the development horizontal well by carrying out horizontal well development on the exploration well body structure of the present invention, improves the geological prediction accuracy, and is more conducive to the landing of the horizontal well; fully utilizes the inclined well section 2, reduces the drilling difficulty of the horizontal well target reservoir, improves the development efficiency of the horizontal well, reduces the use of backfill materials, and saves backfill costs.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements 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 method for designing an exploration well, characterized in that: The following steps are involved: S1. Obtain the target reservoir location; S2. Design a horizontal well suitable for the target reservoir based on the target reservoir location and determine the horizontal wellbore trajectory orientation; S3. Designing an inclined well section of the exploration well based on the horizontal wellbore trajectory orientation, wherein the inclined well section penetrates the target reservoir, and the horizontal wellbore trajectory at least partially passes through the inclined well section; S4. Designing a vertical well section of the exploration well according to the position of the inclined well section, wherein the vertical well section smoothly transitions with the inclined well section; Based on the three pressure profiles and formation complexity, S5 optimizes the isolation layer position and well depth of each drill bit in the vertical well section and optimizes the wellbore structure of the exploration well.

2. The method for designing an exploration well according to claim 1, wherein: In S1, the target reservoir position is obtained based on drilling data, and the data of the drilling area includes drilling situation data of adjacent areas, geological data of the drilling area, and ground stress data of the drilling area.

3. The method for designing an exploration well according to claim 2, wherein: In S1, the geostress data of the drilling area includes the horizontal maximum principal stress direction, and in S2, the azimuth of the horizontal wellbore trajectory is perpendicular to the horizontal maximum principal stress direction, or the angle between the azimuth of the horizontal wellbore trajectory and the horizontal maximum principal stress direction is greater than or equal to 60 degrees.

4. The method for designing an exploration well according to claim 3, wherein: The horizontal wellbore trajectory includes a vertical well section, a first inclination-increasing section, a stable inclination section, a second inclination-increasing section and a horizontal section. The vertical well section coincides with the vertical well section trajectory, the first inclination-increasing section coincides with the inclined well section trajectory, the stable inclination section passes through the side wall of the inclined well section, and the second inclination-increasing section and the horizontal section pass through the target reservoir.

5. The method for designing an exploration well according to claim 4, wherein: The well inclination angle of the stable inclination section is 35 degrees to 55 degrees, and the length of the stable inclination section is greater than or equal to 30m.

6. A method for designing an exploration well according to any one of claims 1 to 5, characterized in that: In S5, the isolation layer and well section depth of each drill bit were determined according to the principle of not losing the upper formation at the highest drilling fluid density in the open hole section and isolating the complex layer section, and ensuring that the technical casing could be lowered to the middle and upper part of the inclined well section.

7. The method for designing an exploration well according to any one of claims 1 to 5, characterized in that: The inclined well section is provided with a logging pocket for stabilizing the inclination drilling of the well, and the logging pocket is located below the target reservoir.

8. A wellbore structure of an exploration well, designed using the design method of an exploration well according to any one of claims 1 to 7, characterized in that: It comprises a vertical well section and an inclined well section. The vertical well section is provided with a technical casing, and the technical casing is communicated with the inclined well section.

9. The wellbore structure of an exploration well according to claim 8, characterized in that: The vertical well section is provided with a surface casing, and the technical casing can be lowered from the surface casing to the inclined well section.

10. A method for constructing a horizontal well, comprising the wellbore structure of an exploration well according to any one of claims 8 to 9, comprising the following steps: Step 1: Conduct exploration well logging operations; Step 2: Optimize horizontal well trajectory: Optimize the horizontal well trajectory based on logging data; Step 3: Backfill cementing: Backfill the inclined well section with cement plugs and wait for the cement plugs to solidify; Step 4: Drilling the horizontal well: Drilling operations are carried out according to the optimized horizontal wellbore trajectory; Step 5: Lower the casing into the oil layer.

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