2.1

Project overview

The directional drilling crossing project studied in this research is located in the north-eastern region of China. The entry angle of the directional drilling crossing river is 10°, while the exit angle is 7°. The crossing is conducted in a curved manner, with a curvature radius reaching 1500 times the outer diameter of the pipeline. The pipeline used has a size of φ611 mm×11.1 mm. The length of the crossing through the river is 1280 m. The construction process during the crossing is illustrated in Table 1.

Table 1.

Directional drilling crossing construction process.

2.2

Pre-construction preparation stage

During the pre-construction preparation stage, activities primarily include surveying and staking, site leveling, on-site equipment assembly, mud preparation, and drill rig trial drilling. These tasks aim to provide necessary site and material conditions for subsequent construction operations.

(1) Surveying and staking

According to design requirements and terrain conditions, we determine the starting and ending points of the drilling crossing, as well as the path and depth of the borehole. A surveying plan based on the drilling requirements and on-site conditions is developed. The measurement methods and select appropriate instruments and equipment are determined. We conduct on-site surveys along the designated drilling path, including using surveying instruments to measure and record ground terrain and underground pipelines. We set markers at key locations such as the starting point, ending point, and turning points of the drilling path to indicate the position and direction of the borehole³. Surveying instruments such as transits and rangefinders are utilized to accurately stake out the drilling positions and directions. Necessary adjustments and corrections are made based on survey results to ensure alignment with design requirements.

(2) Site leveling

During the site leveling process, excavation is conducted for mud pits and drill rig anchors. In this project, the dimensions of the mud pits and anchor pits are as shown in Figure 1. Sufficient slope should be left during excavation of anchor pits and mud pits.

Figure 1.

Dimensions of mud pits and anchor pits.

After the excavation of the anchor pit is completed, the anchor box needs to be placed into the anchor pit. Concrete is poured between the anchor box and the anchor pit. Once the concrete has fully cured, the drill rig is anchored to the anchor box. The structure of the drill rig anchor in this project is as shown in Figure 2.

Figure 2.

Structure diagram of drill rig anchor.

After anchoring the drill rig, it is necessary to arrange the entry and exit points of the site reasonably. The layout of the entry point and exit point for this project is shown in Figures 3 and 4, respectively.

Figure 3.

Layout diagram of entry point site.

Figure 4.

Layout diagram of entry and exit point site.

(3) Assembling Equipment

After arranging the site properly and cleaning the construction foundation to ensure it is flat and sturdy, providing a solid foundation for the installation of the drill rig. Following the assembly instructions and construction drawings of the drill rig, assemble the drill rig, including installing drill bits, drill columns, hydraulic systems, control systems, and other components. Weconnect supporting pipelines such as water inlet and drainage pipes according to construction needs to ensure the water source and drainage required for the drill rig’s normal operation.

(4) System Debugging

We determine the starting point, ending point, and path of the borehole according to design requirements and terrain conditions. We select a certain number of control points along the drilling path for measurement and control of the borehole direction. The materials and equipment required for the coils are prepared, including wires, insulation materials, brackets, etc., according to measurement requirements. Suitable positions and directions are selected for laying coils based on the drilling path and control point locations to ensure effective measurement and control. The laid coils are checked to ensure their connection and fixing are in good condition without any looseness or breakage⁴. We debug and test the measurement instruments to ensure their normal operation and accurate measurement. Conditions for real-time monitoring and control of the borehole direction are prepared.

(5) Mud preparation

We determine a suitable mud formula based on geological conditions, drilling purposes, pipeline requirements, and other factors. Mud formulas typically include base liquids, suspending agents, thickeners, pH regulators, etc. The required raw materials and chemicals are prepared according to the mud formula to ensure the quality of raw materials meets the requirements and ensure the stability and effectiveness of the mud during construction. We add various raw materials to the mixing tank according to the formula ratio and mix the mud thoroughly using mixing equipment to ensure uniform distribution of all components and achieve the required concentration and performance requirements.

(6) Drill rig trial drilling

The borehole position and direction and select appropriate trial drilling points are comfired according to design requirements and geological conditions.We inspect and prepare the drilling tools, drill bits, mud, auxiliary equipment, etc., required for trial drilling. The required drilling tools on the drill rig are installed, including drill bits, drill columns, drill rods, etc., ensuring a firm connection to prevent breakage or detachment during trial drilling. Drilling parameters are adjusted according to geological conditions and design requirements, including rotation speed, feed speed, mud flow rate, mud density, etc., to ensure smooth trial drilling and protection of the stratum. We start the drill rig and begin trial drilling, gradually adjusting drilling parameters according to design requirements and geological conditions to ensure smooth trial drilling⁵. We monitor the operation status of the drill rig and the progress of drilling in real-time, promptly identifying and resolving any potential problems.

2.3

Directional drilling operations stage

2.4

Final closure stage

The equipment, machinery, and tools used for drilling operations are evacuated from the construction site. Cranes, trailers, or other transportation tools are used to transport the equipment away from the construction site, ensuring safety during transportation. The construction site is cleaned, including removing debris, waste, and residues from the site. Temporary facilities, fences, and signs around the construction site are dismantled and cleaned⁷. The surface of the construction site is repaired and restored by filling and leveling the soil to its original condition. Grass, trees, and other vegetation are planted to restore the original landscape. Soil protection and fixation measures are strengthened to prevent soil erosion and loss of soil and water.

3.1

Prefabrication technology

Outside the construction site, prefabricate the pipeline, including determining the length, diameter, and material of the pipeline, and manufacturing and assembling the pipeline in a factory or other location. The length of the prefabricated pipeline is usually customized according to actual needs to fit specific drilling projects. Appropriate joint systems are designed to facilitate easy connection of prefabricated pipelines during drilling. These joints should be quickly installable and removable while ensuring the sealing and structural integrity of the pipeline. Suitable transportation plans are arranged to transport prefabricated pipelines to the drilling construction site, considering the dimensions, weight, and transportation routes of the pipelines to ensure a safe and efficient transportation process⁸. On the drilling construction site, prefabricated pipelines segment by segment is installed into the borehole, requiring precise operation and docking to ensure smooth installation and proper positioning and orientation of prefabricated pipelines. After the installation of prefabricated pipelines, we carry out the connection work between the pipelines, including the joint systems between pipeline sections, to ensure firm and sealed connections. After completing the installation and connection of prefabricated pipelines, we conduct testing and acceptance of the pipelines, including checking and testing the sealing, strength, and stability of the pipelines to ensure compliance with design and construction requirements.

3.2

Pipeline welding and mud treatment

In directional drilling for long-distance pipelines, pipeline welding and mud treatment are crucial. For pipeline welding, high-quality welding materials and equipment are needed to ensure the quality and strength of welded joints. Appropriate welding processes are adopted, including gas shielded welding, arc welding, etc., to ensure stable and reliable welding processes. We strict quality control and testing of welded joints, including weld seam inspection, ultrasonic testing, etc., to ensure welding quality meets standards and requirements. For mud treatment, we select suitable mud formulas and adjust mud parameters such as density and viscosity according to geological conditions and pipeline requirements. Efficient mud treatment equipment is used, including agitators, centrifuges, filters, etc., to ensure mud stability and cleanliness. We regularly monitor and adjust the mud, promptly handling impurities and pollutants in the mud to maintain its performance and effectiveness. Measures are taken to reduce pollutant emissions during mud treatment, including recycling mud and treating wastewater, to protect the construction site and surrounding environment and prevent mud from polluting soil and water sources, reducing environmental impact.