【Ten Years of Great Development in Chemical Engineering Equipment】The 2,316-meter Yangtze River crossing section of the Yizheng-Changling crude oil pipeline project, Jiujiang, from 1975 to 2004

The preparation work for the drilling site of the Jiujiang Yangtze River Crossing Project began at the end of 2004, involving tasks such as site drainage, dredging, backfilling, site grading, and the installation and calibration of equipment; by early February 2005, the conditions were ready to start drilling. The construction of the optical cable sleeves was carried out first; drilling commenced on February 4, 2005, and was completed on March 8, taking 33 days. During this period, there was a challenge related to the difficulty of guiding the long-distance guide holes upward on the side where they were being extracted from the ground. Drilling of the main bore began on March 15; the guide hole was completed on March 31, the pre-reaming operation was finished on May 7, and retraction was completed on May 14. During the reaming process, difficulties such as drill pipe unseating and ineffective transmission of torque from the drilling rig arose. To address the numerous technical challenges associated with the Jiujiang Yangtze River crossing project, the following technologies and processes were improved on-site during implementation: ① The installation process for the direction-control signal wires was improved. Comparative tests were conducted in advance on the tensile strength and elongation rates of various domestic and imported signal wires; those with higher insulation strength and better wear resistance were selected. Additionally, the density of wire clamps used was increased appropriately, and the installation process for heat-shrink sleeves used for wiring was refined. These measures ensured accurate transmission of direction-control signals and effectively addressed the risk of these wires being broken by high-pressure mud. ② The casing installation process was improved by directly using the drilling rig to install a single-layer large casing with a diameter of φ377 mm up to the rock layer; the total length of the casing installed was 130 m. This approach ensured proper preparation for the timely replacement of drilling tools inside the hole, and it also effectively solved the problem of difficulty in keeping the long guiding hole from rising on the side facing the surface. ③ The mud formula takes full account of the challenges associated with passing through the 1780m rock layer, enhancing the mud’s debris-carrying capacity to ensure the cleanliness of the borehole. ④ The drilling process in soft strata on the extraction side of ultra-long-distance guide holes was improved by adjusting the mud pressure and employing a high-side thrusting method throughout the process, thereby solving the problem of the drilling tools sinking automatically due to their heavy weight and the vibrations generated by the mud motors. ⑤ The retrieval drill pipe docking technique was employed to solve the problem of re-docking the drill pipe after it became disengaged, and successful retrieval and docking of the drill pipe was achieved at a distance of 252 m from the drilling rig and at a depth of 36.8 m. ⑥ The drilling process for large-diameter reaming over long distances in rocky formations has been improved; for reaming at the second stage and above, 6 5/8″ high-strength drill pipes are used, which ensures effective transmission of torque from the drilling rig. At the same time, drilling parameters are strictly controlled, allowing the drill bits to remain unchanged during each reaming operation and thus reducing the risks associated with penetration work.

Construction Challenges and Countermeasures 2.1 There is no established experience available domestically or internationally for crossing rock over extremely long distances; the first challenges we face are related to the techniques needed to control the direction of movement. ⑴ The crossing distance is extremely long; the horizontal length of the Yangtze River crossing in Jiujiang is 2316.03 meters, which requires high precision in direction control. However, the terrain conditions make it possible to maintain accurate direction control only over a land distance of less than 500 meters. On the large areas of water, since it is not possible to set up ground-based beacon systems, direction control must be carried out using the geomagnetic azimuth on a \"blurry\" basis. To this end, before starting drilling, the geomagnetic azimuth relative to the center line of crossing is accurately determined using a signal rod and a total station, and the left-right deviation of the drill bit while crossing the river is controlled based on this value. ⑵ Due to the characteristics of the rock strata, the use of a mud motor is necessary during the drilling of guide holes, which increases the distance between the drill bit and the signal rod by 14 meters. This entire distance constitutes a blind area where direction control is not possible. It is precisely this blind area that greatly increases the difficulty of maintaining accurate direction control. Any minor error in direction control cannot be corrected effectively during the drilling through the rock strata, and such errors can have catastrophic consequences for the eventual retraction of the pipeline. Two main measures were taken on site. The first was to use two non-magnetic drill collars when connecting the drilling tools during the drilling of guide holes, in order to eliminate the magnetic interference generated by the mud motor (a magnet) and the long sequence of drill pipes that followed on the signal rod ； Secondly, when drilling through rock sections, increase the frequency of signal measurement – taking a reading every 1–3 meters of drilling – to ensure that the trajectory of the guide hole meets the requirements of the design curve. Ultimately, the guide hole was successfully excavated, with a lateral deviation of 0 from the designed position and a longitudinal deviation of 1.5 m.

In horizontal directional drilling, mud control is a key technical issue in the drilling process. Due to geological conditions, we encountered three challenges related to mud control. ⑴ The strata characteristics along the Yangtze River in Jiujiang are such that the middle section consists of rock layers, while the sides are made up of softer strata. When passing through these softer strata, it is necessary for the mud to have good wall-stabilizing properties in order to prevent mud loss and hole collapse ； Moreover, when passing through rock layers, the mud needs to have strong capabilities for suspending and carrying drill cuttings in order to keep the borehole clean, which imposes high requirements on the properties of the mud. Based on the changes in the stratigraphic conditions along the Jiujiang Yangtze River crossing site, a composite mud formulation technique is employed. Special bentonite designed for directional drilling is mixed with fresh water at a weight ratio of 8–10% to produce the base mud; various mud additives are then added at a rate of 2–4‰ of the base mud’s weight. The main mud additives used include wall stabilizers, loss control agents, debris removers, and lubricants, all of which ensure that the mud properties meet the requirements of the strata being crossed. The requirements for adjusting the properties of the mud during construction are as follows: ① In sections passing through ordinary soft soil layers: control the mud’s water loss to prevent hole collapse, and increase the amount of wall-stabilizing agents ； ②Rock passing section: To ensure the removal of cuttings and the cleanliness of the borehole, it is necessary to increase the dosage of cutting fluid and lubricant in a timely manner, maintain good rheological properties of the mud, and at the same time enhance its lubricating capacity in order to reduce friction between the drilling tools and the formation. ⑵ At each stage of rock formation penetration construction, the amount of mud required is dozens of times that needed for penetrating soft formations; in fact, it is necessary to produce 100 cubic meters of suitable mud within 1 hour, which places considerable demands on the timely supply of large quantities of high-performance mud. To this end, on-site, 3 sets of mud mixing and feeding systems were installed; the length of the circulation pipelines was increased to prolong the curing and mixing time of bentonite and additives ； On the other hand, to further ensure a timely supply of large volumes of mud for crossing long distances and rock layers, a mud purification and recycling system has been installed on site, allowing the mud to be reused. This reduces the need to keep large amounts of mud on site and also minimizes environmental pollution. ⑶ During the use of a mud motor to drill guide holes, in order to ensure its service life and minimize the need to replace it, high requirements are also placed on the sand content in the mud. The key to controlling the sand content in the mud lies in the recovered mud; a three-stage filtration method is employed on-site. First, a preliminary coarse screening is carried out at the pit where the mud is recovered, using a screen with a mesh size of 50–60 mesh ； Then secondary screening is carried out in the mud recovery tank, with a screen mesh size of around 100 mesh ； Finally, the slurry undergoes three stages of fine screening through the screen located beneath the cyclone separator (sludge remover); the mesh size of the screen is selected to be 200 mesh or higher, depending on the volume of slurry to be processed. The sand content in the mud that eventually reaches the mud motor is kept below 1%, and a sand content meter is used on-site to measure it every hour.

The crossing of long-distance rock layers has posed unprecedented challenges to drilling processes and construction techniques; the drill operator and the drilling procedures have encountered two major difficulties. ⑴ The Yangtze River crossing in Jiujiang involves a combination of soft and hard strata, and the transition from soft strata to rock layers, as well as from soft rocks to hard rocks, requires advanced crossing techniques. A slight mistake in judgment, or even a delay in making a judgment, can render all previous efforts futile. The construction method adopted is as follows: first, reduce the drilling speed and the drilling thrust (or pull), as well as lower the rotation speed of the drill rig. Once the drill bit (or reamer) has penetrated 1–1.5 meters into the hard stratum, then increase the drilling thrust (or pull) and adjust the rotation speed of the drill rig, in order to prevent the drilling path from deviating from the intended target due to excessive speed. ⑵ Crossing a rock layer that is 2316 meters long requires overcoming the challenge of high drill torque, especially during the stage of large-diameter pre-drilling; this imposes high demands on the capabilities of the drill rig, the drilling tools used for expansion, as well as the construction techniques employed. The following measures were taken on site: ① For the Jiujiang Yangtze River crossing project, a super-large horizontal directional drilling rig of the DD-1100 type manufactured by American company Ogee was used. This rig has a maximum torque of 132 KN.m and a maximum pushing and pulling force of 500 tons; it fully met the construction requirements throughout the project. ② The main drilling tools in the pre-reaming stage are reamers and centering devices. Generally, for short-distance rock penetration, a maximum diameter for the reamer of 1.2 times the diameter of the penetration tube is sufficient; however, for long-distance penetrations, it must be taken into account that the drill cuttings within the borehole cannot be removed completely, so a diameter of 1.5 times the penetration tube diameter should be chosen to reduce the risk associated with pulling the pipeline back. The reaming step size should be determined based on the hardness of the rock and the capacity of the drilling rig; generally, 4–6″ is appropriate. If the grade difference is too small, on the one hand, the overall efficiency is low and it is not economical; on the other hand, it increases the risk of tool jamming ； A large grade difference requires high torque from the drilling rig, which in turn increases the risk of drill sticking. The center locator, also known as an aligner, serves to keep the reamer in alignment, ensuring that it moves as closely as possible along the original hole trajectory. This helps to distribute the chips in a uniform manner where they come into contact with the reamer bits, thereby reducing the reaming torque. The diameter of the center locator should be 1 1/2 to 2″ smaller than the diameter of the previous stage of reamers. For the Yangtze River crossing in Jiujiang, three stages of reaming are employed. For the first stage of pre-reaming, an 18″ rock reamer is used; for the second stage, the drilling tool combination consists of a 16″ center locator plus a 24″ rock reamer, while for the third stage, the combination uses a 22″ center locator plus a 28″ rock reamer. ③ The main technical parameters for controlling the reaming operation of rock formations are the thrust and pull force applied by the drilling rig to the reamer (pull force during reverse reaming, thrust force during forward reaming), also known as drilling pressure, rotational speed, and the volume of mud pumped during reaming. An important principle that should be followed in the reaming of rock layers is that the harder the rock to be broken, the greater the drilling pressure required, and the lower the desired drilling speed ； At the same drilling speed on the same drill rig, reamers of different diameters produce varying reaming effects; the larger the diameter of the reamer, the greater the linear velocity at its outer edge, and the more severe the wear. During the reaming of rock layers, the main functions of mud are to cool the reamer and carry away the drill cuttings. The actual pumping volume of mud should be determined by calculating the amount of drill cuttings generated at each stage of reaming along with the mud’s capacity to carry those cuttings; it generally should not be less than 1 m3/min.

　At 23:16 on May 14, 2005, at the Yangtze River crossing site for the Jiujiang section of the Yichang Crude Oil Pipeline operated by Sinopec Pipeline Company, accompanied by the roar of machinery and driven by a horizontal directional drill, a pipeline with a diameter of 457 millimeters and a length of 2,316 meters was pushed out of the ground on the south bank of the Yangtze River. This marked the successful completion of the Yangtze River crossing for this pipeline section; it also set world records for both the length of the river crossing and the length of the rock layer that had to be penetrated (the previous record was 2,308 meters, set in 2002 by CNPC Pipeline Company for its crude oil pipeline crossing beneath the Qiantang River). 　　The Yichang Crude Oil Pipeline, constructed under the organization of Sinopec Pipeline Company, is a key project approved by Sinopec. With a total length of 976 kilometers, it spans five provinces – Jiangsu, Anhui, Jiangxi, Hubei, and Hunan – and connects five major refining and chemical enterprises owned by Sinopec in the middle and lower reaches of the Yangtze River. Among these, there are 3 crossings of the Yangtze River; as per the design, two crossings will be made using horizontal directional drilling while one will be accomplished through tunneling with a shield machine. These represent the key construction control points for the construction of the Yichang-Cangzhou crude oil pipeline. Therefore, the success of the Yangtze River crossing will directly affect the timely completion and commissioning of the Yichang-Crude Oil Pipeline. 　　Sinopec Pipeline Company’s Crossing Branch, which is responsible for this construction project to cross the Yangtze River, is a seasoned and experienced team with a track record of achievements in this field in China. Prior to this, it has successfully used horizontal directional drilling technology to cross the Yangtze River 8 times and seas 3 times. This is the 9th time it has crossed the Yangtze River, and its crossing distance as well as the length of the rock layers involved are not recorded in any international crossing records. Therefore, this is not only a test of the performance of existing equipment, but also a test of the crossing technology and courage required to cross the branch offices. On February 10, 2005, after successfully crossing the Yangtze River at the Jihonghu section of the branch route, they headed east immediately, setting up camp along the Yangtze River at the Jiujiang section in order to challenge for a new world record. With the careful organization by the pipeline company and the project management team, the branch company was well-prepared in terms of technology and equipment, and the construction measures were properly arranged. After completing the crossing of the 121-mm diameter optical fiber cable pipeline across the Yangtze River at the same location on March 8, drilling resumed on March 15 to carry out the crossing of a 2,316-meter-long crude oil pipeline, including 1,780 meters of crossing through rock layers, and the task was ultimately completed successfully. 　　It is reported that the successful crossing of the Yangtze River at the Honghu section and the Jiujiang section has removed two major obstacles to the construction of the Yichang pipeline, laying a solid foundation for achieving the production targets set by Sinopec on schedule.

A roundup of Sinopec Pipeline Company’s directional drilling projects across the Yangtze River:
1. Yijin crude oil pipeline, ф406 – February 26 – March 12, 2002
2. Yonghuuning crude oil pipeline, ф508 – March 26 – May 31, 2002
3. Optical cable pipeline, ф121 – March 26 – March 31, 2002
4. Jinyang material pipeline, ф273 – August 25 – September 2, 2002
5. Jinyang material pipeline, ф159 – September 18 – September 23, 2002
6. Honghu-Yichang optical cable, ф121 – November 1 – December 21, 2004
7. Honghu-Yichang pipeline, ф406 – January 7 – February 10, 2005
8. Jiujiang-Yichang optical cable, ф121 – February 4 – March 8, 2005
9. Jiujiang-Yichang pipeline, ф457 – March 15 – May 14, 2005

The directional drilling project with the largest pipe diameter is the Ganjiang River directional drilling project for the Nanchang–Shanghai branch of the West-East Gas Pipeline II; its pipe diameter is 1219 millimeters, and the drilling length is 1351 meters. This project was completed in February 2012； The longest pipeline crossing project is the Yangtze River directional drilling crossing project for the Jiangdu-Rudong gas pipeline, with a crossing length of 3,302 meters and a pipe diameter of 711 millimeters; it was completed in May 2013.

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