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Directional drilling technology is one of the most advanced drilling technologies in the global oil exploration and development field today. It relies on special downhole tools, measurement instruments, and process technologies to effectively control the wellbore trajectory, guiding the drill bit to reach the predetermined underground target along a specific direction. This technology breaks the limitation of vertical wells, which "can only develop resources directly below the wellhead". By adopting directional drilling technology, oil and gas resources restricted by surface or underground conditions can be developed economically and effectively, significantly increasing oil and gas production and reducing drilling costs. In essence, a directional well is a drilling method that guides the wellbore to reach the target formation along a pre-designed deviation angle and azimuth. There are three main types of its well profiles: (1) Two-section type: Vertical section + build-up section; (2) Three-section type: Vertical section + build-up section + tangent section; (3) Five-section type: Upper vertical section + build-up section + tangent section + drop-off section + lower vertical section A horizontal well is a type of directional well. Conventional oil wells penetrate the oil reservoir vertically or at a shallow angle, resulting in a short wellbore section passing through the reservoir. In contrast, after drilling vertically or at an angle to reach the oil reservoir, the wellbore of a horizontal well is turned to a near-horizontal direction to remain parallel to the oil reservoir, allowing long-distance drilling within the reservoir until completion. Equipped with high-strength heavy-weight drill pipes (HWDP) for horizontal sections and wear-resistant PDC (Polycrystalline Diamond Compact) bits, the length of the reservoir-penetrating section can range from hundreds of meters to over 2,000 meters. This not only reduces the flow resistance of fluids entering the well but also increases production capacity several times compared to conventional vertical or deviated wells, facilitating enhanced oil recovery. Ⅰ. Application Scenarios 1. Overcoming Surface/Underground Obstacles Surface obstacles: When there are buildings, railways, lakes, or ecological protection zones above the reservoir, directional wells can be drilled outside these obstacles to reach the reservoir at an angle (e.g., development of oil and gas reservoirs around cities). Underground obstacles: When bypassing hazardous geological features such as underground caves, salt domes, and faults, shock-resistant and collapse-proof drill collars and high-pressure blowout preventers (BOP) are used in coordination to avoid drilling accidents like pipe sticking and blowouts. 2. Enhancing Production Capacity of Unconventional Oil and Gas Reservoirs Unconventional reservoirs such as shale gas and tight oil have "extremely low permeability". Vertical wells can only access a small area of the reservoir, leading to limited production capacity. However, horizontal wells traverse the reservoir horizontally over a distance of several hundred meters, increasing the contact area with the reservoir by dozens of times. The daily gas production of a single horizontal well can be 5 to 10 times that of a vertical well, making it a core technology for unconventional oil and gas development. 3. Reducing Development Costs Offshore oil and gas fields: Drilling a cluster of wells from a single offshore platform is far less costly than building a separate platform for each target, resulting in a 30% to 50% reduction in development costs. Mature oil fields: Through "sidETracking" of directional wells (drilling branches from the wellbore of an old well to develop remaining oil reservoirs in the surrounding area), there is no need to drill new vertical wells, significantly reducing investment. Ⅱ. Advantages and Disadvantages Compared with Vertical Wells Advantages 1.Strong resource coverage capability: It can develop offset reservoirs and scattered reservoirs that are inaccessible to vertical wells, improving the production efficiency of oil and gas reservoirs. 2.High single-well production capacity: Horizontal wells, in particular, greatly increase the contact area between the wellbore and the reservoir, offering significant advantages in the development of unconventional oil and gas reservoirs. 3.Superior cost-effectiveness: Cluster wells and multi-lateral wells, supported by integrated drilling rigs and matched drilling equipment (such as top drives and mud pumps), reduce surface occupation and platform construction costs, making them suitable for offshore and intensive development scenarios. Disadvantages 1.High technical complexity: It requires professional directional drillers, rotary steerable systems (RSS), and MWD (Measurement While Drilling) equipment, resulting in a much higher technical threshold than vertical wells. 2.High costs: The investment in a single directional well is usually 20% to 50% higher than that of a vertical well of the same depth (due to increased costs of tools, equipment, and labor). 3.High risks: The complex trajectory leads to high circulating resistance of drilling fluid and increased difficulty in wellbore stability, resulting in a higher incidence of accidents such as pipe sticking and wellbore collapse compared to vertical wells. 4.Long construction cycle: Frequent trajectory adjustments and data measurements are required, leading to a 30% to 60% longer construction cycle than vertical wells of the same depth. Ⅲ. Conclusion In summary, directional drilling represents a milestone in the evolution of oil drilling from simple vertical development to complex and precise development. Currently, in global oil and gas resource development, the application proportion of directional wells has exceeded that of vertical wells, making it one of the core technologies for ensuring oil and gas supply.