**Feasibility Analysis of Pipeline Directional Drilling Technology**
Pipeline directional drilling is technically feasible, provided that a stable tunnel can be formed underground to allow the pipeline to be smoothly pulled back. Alternatively, if the soil becomes fluid, the pipeline can follow these fluids and be dragged back with external force. However, ideal fluid conditions across the entire crossing section are rare. Localized obstructions may damage the pipeline’s anti-corrosion coating, making it essential to create a stable tunnel before pulling the pipe and inject suitable drilling mud into it.
If the tunnel remains clear during the pulling process, the maximum stress on the pipeline, drill pipes, and the rig equipment will stay within acceptable limits, confirming the feasibility of directional drilling. That said, there is no universal standard to determine whether directional drilling is suitable for a given project. It largely depends on the technical capabilities and experience of the construction team.
To simplify the analysis, one can compare the current project’s parameters with those of previous similar projects. The key factors include the geological formation, the length of the crossing, and the diameter of the pipeline. These elements significantly influence the success of directional drilling.
The most challenging formations for crossing are those with high gravel content or extremely hard and strong rock. Gravel-heavy strata are difficult to drill through due to poor stability, which may lead to partial collapse after hole formation. Additionally, the gravel may not be effectively removed by the drilling mud, causing blockages during the pipeline pullback. Similarly, highly resistant rocks slow down drilling and reaming processes, increase tool wear, and make directional control more difficult.
On the other hand, soft and easily broken rock, such as loose gravel, can also cause instability. Table 1 illustrates the relationship between formation conditions and crossing feasibility.
Pipeline crossings often involve complex geological conditions where different strata are present in various sections. While optimization design may pass through less favorable layers, the actual feasibility depends on the length, continuity, and integrity of the stratum along the crossing path. Changing the sequence of strata can drastically alter the crossing conditions. Moreover, the understanding of the subsurface is based on core analysis, which is conducted intermittently. During actual drilling, unexpected formations may be encountered, requiring thorough preparation and risk assessment.
The length of the crossing and the diameter of the pipeline are primarily limited by the capacity of the drilling rig and tools. As the crossing length increases, the flexibility of the drill pipe decreases, and the ability to control the drill bit’s direction diminishes, making it harder to follow the designed path.
To pull back the finished pipeline, the borehole must be expanded to 1.2 to 1.5 times the pipe’s diameter. For large-diameter pipelines, this requires significant reaming torque, especially in hard strata, which may exceed the strength of the drill pipe. In sandy or gravelly strata, larger tunnels are more prone to instability and landslides, further limiting the feasibility of large-diameter crossings. Table 2 lists the maximum recorded lengths and diameters of completed directional drilling projects, which can serve as a reference when assessing feasibility.
This article is reproduced from Bazhou Lutong Engineering Co., Ltd.: http://
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