The Configuration of a Multi-Node Deep-Well Observation and Hoisting System and the Design of Its Hoisting/Lowering Process

Abstract

Existing deep-well multi-node observation instrument hoisting and lowering systems suffer from poor compartment coupling adaptability, fuzzy anti-jamming judgment criteria, non-standard operation procedures, and lack of classified hoisting control strategies, which easily cause compartment jamming. Aiming at the above research gaps, this study proposes a standardized full-process hoisting/lowering technology tailored for deep-well multi-node observation instruments. This paper first summarizes and classifies mainstream instrument compartment coupling and hoisting schemes and quantitatively compares their application boundaries, operational risks and applicable borehole conditions. Then it optimizes the integral system layout, compartment installation mode and unified standardized operating workflow for downhole instrument deployment. Furthermore, the downhole jamming mechanism and rapid identification means of instrument compartments are clarified. Classified collaborative control strategies are also established to match different hoisting/lowering working conditions. The research results fill the gap in standardized anti-jamming operation specification for deep-well multi-node instrument deployment and can effectively reduce downhole fault handling time and observation operation interruption frequency, providing feasible technical support for the safe and efficient deployment of downhole observation equipment.

1. Introduction

During the seismogenic process, the electrical properties of underground media often change, accompanied by variations in geoelectric currents and natural electric fields [1]. Monitoring these changes helps to identify possible pre-seismic anomalies and to examine their relationships with earthquake occurrence, thereby providing useful information for seismic prediction research [2,3]. To capture such geological activity parameters, sensors are commonly deployed several kilometers below the surface, with the acquired data transmitted upward for subsequent analysis [4,5,6]. Because deep geological processes and their associated parameters vary markedly with depth, multiple sensors are integrated within a single instrument compartment. A series of these compartments are then arranged at different depths to form a deep-well multi-node observation system [7,8].

The deployment configuration of multi-node observation instruments in deep wells is illustrated in Figure 1. Instrument compartment nodes are arranged at different depths and connected by tubes or cables. Within the SAFOD (San Andreas Fault Observatory at Depth) project in the United States, all instruments were enclosed in sealed compartments to prevent direct contact with downhole fluids [9]. These compartments were mounted outside thickened tubes and coupled to the casing through distributed bow springs [10]. A similar approach was adopted in the CCSD (China Continental Scientific Drilling) project of China. The instruments were also housed in sealed compartments, which were threaded to drill pipes to form a “drill pipe–instrument” string and then suspended from a downhole hanger [11]. The weight of the drill pipes was partly balanced by the hanger and the buoyancy of the downhole fluid. Under gravity, the drill pipes underwent deformation, allowing each instrument compartment to contact and couple with the casing wall [12]. Cable-based deployment has also been used in several projects. In the German KTB (Kontinentales Tiefborhprogramm der Bundesrepublik) project, instrument compartments were lowered by cable in 1996 [7,13]. In 2005, Japanese researchers adopted a similar method to install long-term comprehensive geophysical observation instruments at a depth of 1030 m [14,15]. In these two projects, the instruments were arranged in a multi-node observation configuration. In 2015, researchers in Turkey fixed four instrument compartments and optical fibers to a transmission pipeline at specified intervals. Steel straps were used for cable clamping, and the recommended spacing for strap installation was 10–15 m [16]. However, the deepest instrument compartment in this project was located only 300 m underground, so it does not fall within the scope of deep-well observation.

At present, studies that specifically examine and systematically summarize hoisting and lowering technologies for multi-node deep-well observation systems remain limited. This paper reviews the connection methods and wall-coupling modes of instrument compartments, compares their advantages and limitations, and clarifies the conditions under which each scheme is most applicable.

Based on the commonly used connection configurations of instrument compartments, a multi-node hoisting/lowering system suitable for a deep well in northeastern China was designed; both rigid and hybrid connection schemes were developed. Meanwhile the installation methods for the components of the instrument string were then designed, and the corresponding hoisting and lowering procedures were established. The causes of downhole jamming involving node instrument compartments are also analyzed, and practical release methods are proposed. Furthermore, an adaptive neural-network-based control strategy for the multi-node hoisting/lowering process is introduced, together with a multi-winch coordinated control scheme tailored to actual well-site conditions. The results provide a useful reference for the field deployment and retrieval of multi-node observation instruments in deep wells.

2. Design of Multi-Node Observation System

2.1. Connection Scheme for Instrument Compartments

As shown in Figure 2, multi-node instrument compartments can generally be connected in three ways: flexible, rigid, and hybrid connections. In the flexible configuration, the observation instruments are linked by armored cables, and a counterweight is installed at the bottom to maintain cable tension under gravity, as illustrated in Figure 2a. In the rigid configuration, the instruments are connected by drill pipes or thickened tubing; coiled tubing may also be used in certain applications, as shown Figure 2b. The hybrid configuration combines these two approaches: the upper instrument compartments are connected by drill pipes, while the lower compartments are linked by armored cables, with a counterweight arranged at the bottom, as shown in Figure 2c. The main advantages and limitations of the three connection methods are summarized in

Table 1. Comparison of instrument compartment connection methods.

Connection Method	Advantages	Disadvantages	Operability	Applicable Conditions
Flexible coupling	Fast deployment and easy operation	The cables are prone to tangling	Easy	The well has only slight deviation and a relatively shallow depth
Rigid wired	Precise instrument positioning	Slow lowering speed	Difficult	Large-diameter deep well
Hybrid junction	Fast deployment speed with precise instrument positioning	Low deployment speed; cables are prone to entanglement	Moderate	Large-diameter deep wells with slight inclination

.

2.2. Coupling Method Between the Instrument Compartment and Casing

To ensure that the sensors inside the instrument compartment can accurately capture formation-related signals, the compartment must be brought into close contact with the casing wall. The main coupling methods include pusher cylinder coupling, support-pipe deformation coupling, spring coupling, and permanent cemented coupling, as illustrated in Figure 3. In the pusher cylinder coupling mode, once the instrument compartment reaches the target depth, a ground-based control system actuates the mechanical arm inside the compartment. The arm extends until it contacts the casing, and the resulting reaction force drives the compartment toward the opposite side, pressing it against the casing wall to achieve coupling, as illustrated in Figure 3a. In the support-pipe deformation coupling mode, a hanger is installed in the well, while the lower end of the tube rests on the hanger or the well bottom. Under its own weight and elastic deformation, the tube bends within the wellbore, causing the instrument compartment to contact and couple with the casing wall. In the bow-spring coupling mode, bow springs are mounted on the instrument compartment, and a counterweight is attached to the lowest instrument. After the instrument string reaches the predetermined position, the spring force pushes the compartment against the casing wall, thereby achieving coupling, as illustrated in Figure 3b. Mechanical or hydraulic packers may also be used to couple the instrument compartment with the casing wall, as illustrated in Figure 3c. In the permanent cemented coupling mode, cement is injected into the wellbore after the instrument compartment reaches the designated depth. Once the cement solidifies, the compartment becomes firmly coupled to the casing wall, as illustrated in Figure 3d. The advantages and disadvantages of these coupling methods are summarized in

Table 2. Comparison of coupling methods between instrument compartment and casing.

Coupling Method	Advantages	Disadvantages	Coupling Performance	Applicable Conditions
Push cylinder coupling	Flexible control with strong coupling performance	Susceptible to damage under high-temperature and high-pressure conditions	Strong	Low-temperature well conditions
Tube deformation coupling	Simple and easy to operate	Requires installation of a hanger	Medium	A downhole suspension device is installed
Spring coupling	Easy to install with effective coupling performance	Prone to jamming	Medium	Small well deviation
Permanent fixed coupling	High reliability	Instrument compartment cannot be retrieved	Very strong	Permanent monitoring wells

.

3. Design of Multi-Node Instrument Compartment Hoisting/Lowering System

This study develops a hoisting and lowering system and operating procedure for multi-node observation instrument compartments in a deep well in northeastern China. The observation scheme requires instrument nodes to be installed at depths of 1500 m and 3000 m, while the optical cable must extend to at least 4500 m. This study is based solely on the aforementioned observation nodes and cable depth as examples and can be modified according to different observational requirements and wellbore structures.

3.1. Design of Hoisting/Lowering Scheme for Instrument Compartments

The lowering sequence for a rigidly connected multi-node instrument compartment system is illustrated in Figure 4. First, the hanger and tube are assembled on the drill floor, and the end of the armored optical cable is secured to the hanger. The traveling block is then used to lower the tube, as shown in Figure 4a. During this stage, additional tubes are connected continuously, while the pipes and armored optical cable are fastened together with clamps. When the hanger reaches a depth of 1.6 km, the first instrument compartment is installed, as shown in Figure 4b. After installation, the tube is lowered further, as illustrated in Figure 4c. Once the hanger reaches 3.1 km, the second instrument compartment is installed, as shown in Figure 4d. The lowering operation then continues until the second instrument compartment reaches its designated depth, as presented in Figure 4e. Throughout the entire lowering process, changes in hook load should be closely monitored to identify potential abnormalities during hoisting and lowering operations. The process of hoisting is exactly the reverse of the above-mentioned procedure.

The lowering sequence for a hybrid-connected multi-node instrument compartment system is illustrated in Figure 5. First, the counterweight is connected to the armored optical cable on the operating platform of the drilling tower. After assembly, the ground winch provides the driving force for cable deployment, as shown in Figure 5a. During lowering, the deployment depth should be monitored continuously. When the armored optical cable reaches a depth of 1.6 km, the first instrument compartment and the tube are installed, as shown in Figure 5b. The tube, optical cable, and electric cable are then lowered together, as presented in Figure 5c. When the armored optical cable reaches a depth of 3.1 km, the second instrument compartment is installed, as shown in Figure 5d. After installation, lowering continues until the second compartment reaches its designated position, as shown in Figure 5e. Throughout the operation, changes in hook load should be closely observed to identify possible abnormalities in the hoisting and lowering process. The hoisting procedure follows the reverse sequence of the lowering operation described above.

3.2. Composition of the Hoisting/Lowering System and Installation of Instrument Compartments

The hoisting/lowering system for multi-node deep-well instrument compartments consists of a surface facilities system and a downhole system. The surface facilities system is configured as follows:

A guide pulley is mounted on the second platform of the drilling tower to redirect the cable and guide it from the winch toward the lower operating platform. At the wellhead, personnel manually guide the cable into the borehole. The installation arrangement of the guide pulley is shown in Figure 6. To monitor the operating condition of the cable in real time, the guide pulley should be equipped with tension sensors capable of recording cable-tension variations continuously.

The electric winches for the different cables are arranged on the ground at a straight-line distance of no less than 35 m from the base of the drilling tower, to avoid interference with operations on the cable catwalk and to prevent affecting other equipment. High-capacity, high-traction hydraulic or electric winches should be adopted. These winches are equipped with accurate cable deployment mechanisms and depth-measurement systems. The drum capacity must satisfy the required depth, and constant-tension control should be incorporated to maintain a stable lowering speed and controllable cable tension. For operational convenience, all cable winches may be designed with the same overall dimensions, differing only in the amount of cable wound on each drum.

Deep-well monitoring instruments may include sensors for natural gamma radiation, temperature, pressure, in situ stress, magnetic fields, and electric fields. These sensors are modularly assembled and integrated into instrument compartments. Threaded mechanical connections are adopted between individual instruments and the tubes. Because each instrument compartment may require one or two cables for power supply and signal transmission, reliable sealing and stable communication at the cable–compartment interfaces are essential under high-temperature and high-pressure downhole conditions. The instrument string mainly consists of tubes, pipe connectors, centralizers, instrument compartments, cable clamps, various cables, and optical fibers. To reduce friction and compression between the cables and the inner walls of the instrument compartments and casing, cable grooves are machined on the outer surface of each compartment. Centralizers are installed at both the upper and lower ends of the compartment. Their outer diameter is slightly larger than that of the compartment, which helps limit direct contact between the compartment body and the casing wall. Cable clamps are used to secure the cables to the tubes, thereby preventing excessive swinging during deployment and reducing the downward tensile load carried by the cables. Each clamp consists of two semicircular rings fastened by socket-head screws. Several grooves are arranged on the inner surface of the rings, allowing the cables to pass through and remain firmly fixed.

The instrument string is composed of the instrument compartment, centralizer, clamp, tubing joint, optical cable and cable. The composition of the instrument string is shown in Figure 7. The installation diagram of the instrument compartment is shown in Figure 8. In the figure, the orange lines represent armored optical fibers, while the blue lines denote the power supply and communication cables for the instrument compartment. Centralizers are installed at both ends of the compartment to prevent direct contact with the wellbore and reduce the risk of sensor damage. The centralizers are connected to the tubes through cable protectors, and all components are joined using matched male and female connectors. Before lowering, the tubes, centralizers, and instrument compartment are assembled on the drilling platform.

To reduce operating time and improve efficiency during lowering, three cable protectors and three tubes may be preassembled in advance and placed on the first-level operating platform of the drilling tower, as shown in Figure 6. During deployment, the preassembled tubes are lifted to the wellhead by hook, and workers complete the connection using a drill pipe wrench. Once the connection is secured, the tubes are lowered further. This procedure is generally similar to the conventional connection and running process of drill pipes. The main difference is that tube joints must be installed between adjacent tubes, and cable clamps are required at both ends of each tube joint to secure the cables. During lowering, the number of tubes run into the well should be recorded accurately so that the downhole position of each instrument compartment can be determined.

4. Causes of Instrument Compartment Jamming and Methods for Unjamming

Because the outer diameter of the instruments compartment is close to the inner diameter of the casing, contact between the two becomes much more likely. This problem is especially pronounced when the casing condition is poor, where scraping, friction, or even jamming may occur between the instrument compartment and the casing wall [17,18].

4.1. Causes of Instrument Compartment Jamming

Long-term exposure to formation stress and uneven loading can cause the downhole casing to deform or distort, weakening its structural integrity and increasing the likelihood of the instrument compartment sticking during lowering. In general, three main factors may lead to entrapment of the instrument compartment within the casing: casing diameter reduction, casing bending, and the piston effect, as illustrated in Figure 9.

Casing diameter reduction refers to a local decrease in the inner diameter of the casing, which narrows the available passage in the wellbore. When an instrument compartment passes through such a section, its outer surface may contact or rub against the casing wall, potentially causing rigid mechanical jamming and preventing smooth lowering. Casing bending occurs when the casing axis deviates from its original alignment and forms a curved section. As the relatively rigid instrument compartment moves through this area, continuous contact and friction with the casing wall increases the running resistance and may eventually lead to jamming [19]. These two forms of jamming are both associated with casing deformation or structural damage. The piston effect, by contrast, is mainly caused by the small clearance between the outer diameter of the instrument compartment and the inner diameter of the casing. As the compartment moves axially within the casing, it compresses the well fluid in a piston-like manner, generating a pressure difference between its upper and lower ends and thereby resisting further movement. For instance, during the deployment of the L4 instrument compartment in the CCSD project main well in 2011, jamming and cable entanglement occurred because of its relatively large outer diameter, insufficient self-weight, and excessive lowering speed. Overall, casing diameter reduction and casing bending mainly result in mechanical sticking, whereas the piston effect produces hydraulic resistance caused by fluid-pressure imbalance. In practice, these mechanisms may occur simultaneously or reinforce one another, greatly increasing the risk of downhole operational failure.

4.2. Methods for Preventing Instrument Compartment Jamming

(1)

Optimize the structure of instrument compartment

An ideal instrument compartment should be as short and slender as possible to improve its passability in the casing. In practice, however, the overall compartment size is largely constrained by the dimensions of the enclosed sensors. With appropriate optimization of the sensor layout, tapered upper and lower ends can be adopted to reduce fluid resistance during lowering. In addition, grooves may be machined on the outer surface of the compartment for two purposes: to accommodate the cables and reduce friction against the casing, and to provide flow paths for the wellbore fluid during descent, thereby limiting the pressure difference between the upper and lower ends of the compartment.

(2)

Run an instrument compartment pre-lowering test

After the dimensions of the instruments compartment were determined, a steel dummy compartment was fabricated with the same outer diameter, length, and overall geometry as the actual compartment but without any internal instruments. The dummy compartment was then lowered into the well in strict accordance with the planned installation and deployment procedure and retrieved after reaching the target depth. Throughout the operation, hook-load variations were continuously recorded to evaluate whether interference or obstruction occurred between the compartment and the inner casing wall, locate potential sticking sections, and provide reference data for the subsequent deployment of the actual instrument compartment.

(3)

Install guide shoe at the bottom of the tube

A guide shoe may be installed at the lower end of the tube. During lowering, contact between the instrument compartment, tubing, and wellbore wall can generate friction and additional running resistance. A powered guide shoe fitted with a rotating turbine, spiral ribs, or blade-like structures can help disturb and remove deposits or residual cement from the inner casing surface, thereby reducing lowering resistance and improving deployment efficiency. However, operation of such a guide shoe requires an additional power source. The use of a downhole motor would therefore increase the technical complexity of the lowering system to some extent.

4.3. Solutions for Instrument Compartment Jamming

(1)

Reduced lowering speed

During lowering, a marked decrease in the drill tower hook load may indicate increased running resistance or the onset of obstruction. In this case, the lowering speed of the tube should first be reduced. If jamming occurs, the tube should be slowly pulled back by a short distance, held in place for a period, and then lowered again. If the obstruction remains, the retraction-and-lowering process may be repeated several times until the instrument compartment passes through the restricted section smoothly.

(2)

Sudden-release hoisting

To improve downhole passability, the instrument string may first be hoisted to an appropriate height so that sufficient gravitational potential energy is accumulated. It is then released and lowered rapidly, converting the stored potential energy into kinetic energy. This short-duration impact can help the instrument assembly overcome localized high friction and pass through restricted casing sections, thereby facilitating continued lowering of the tube.

(3)

Rotating the tube

Rotating the tube can alter its downhole orientation and help relieve localized contact or jamming. Torque is transmitted along the tubing string, and the compartment is rotated to the desired angle, the top drive should be lowered and released gradually while closely monitoring changes in hook load. If the resistance does not decrease, the tubing string may be lifted slightly, then rotated again and lowered slowly. This operation requires careful coordination with the top drive throughout the process.

(4)

Applying down pressure to tube

When the instruments compartment encounters resistance in a specific well section, operators may reduce the hook load to apply a controlled downward force and help the compartment pass through the restricted area. However, the applied force must be carefully limited. Excessive downward pressure may cause the tubing string to lose stability or buckle inside the casing, turning a temporary obstruction into permanent jamming and making further deployment more difficult. In practice, the allowable downward force is usually determined on site based on operational experience and the need to maintain tubing stability; meanwhile systematic theoretical studies on this issue remain relatively limited.

(5)

Running a wellbore expander

If the above jamming-relief measures fail to allow continued lowering of the instrument string, poor casing condition is likely to be the main cause. The blockage depth should first be recorded accurately. The instrument string and tubing are then retrieved, after which a wellbore expander is run into the casing. Through local reaming, correction of deformed sections, and grinding of internal obstructions, the narrowed or irregular casing section can be improved, thereby eliminating the mechanical cause of jamming.

5. Control Strategy for Instrument Compartment Hoisting/Lowering

The neural-network-based adaptive control scheme for multi-node deep-well hoisting and lowering operations makes use of the nonlinear mapping and self-learning capabilities of neural networks. During operation, real-time data such as lowering speed and hook load are continuously collected. Based on model training and online adjustment, the system dynamically regulates the hoisting and lowering speed, enabling early identification of potential blockage risks and timely mitigation during deployment [20,21].

5.1. Adaptive Control for the Hoisting/Lowering of the Instrument Compartment

The instrument compartment may become jammed during hoisting/lowering, but the data reflecting downhole jamming on the surface often exhibits a delay. This significantly affects both the safety of the downhole instrument compartment and the efficiency of the hoisting/lowering operation. Therefore, it is necessary to develop a jamming prediction algorithm to continuously assess the risk of jamming during tripping operations. Currently, there is no existing algorithm specifically designed for predicting sticking during the tripping of deep-well multi-node observation instrument chambers; thus, algorithms used in predicting drilling stick events can be referenced [22].

To enable accurate and real-time identification of sticking events during deep-well operations, an LSTM (Long Short-Term Memory) neural network model was developed using hook-load data and the string-friction results obtained in the previous section [23,24]. The model uses hook-load fluctuations, abrupt changes in friction, and variations in axial force as input features. Historical data from normal operations and representative sticking events are adopted as training samples, allowing the model to learn operating patterns and distinguish abnormal states autonomously [25]. The model outputs a binary judgment. When the real-time load or friction data exhibit features associated with sticking, such as sudden mutations, abnormal increases, or persistent fluctuations, the model outputs 1, indicating that a sticking event has occurred. Otherwise, it outputs 0, indicating that the system remains in a normal operating state and that the current operation can continue. The control scheme is shown in Figure 10.

5.2. Coordinated Control of Multiple Surface Winches

In the CCSD project, multiple cables are tied to the drill pipe, but no motor is installed on the cable winch; instead, the tension in the cable drives the rotation of the winch drum. In the scheme, the tension in the cable is time-varying, especially during the initial lowering stage when a sudden change in cable tension occurs, significantly affecting the cable’s safety and causing unnecessary pulling on the downhole equipment. In summary, it is best to maintain stable tension in all cables during the hoisting/lowering of the instrument compartments. Therefore, the cable speed and rate of descent must be synchronized with the lowering speed of the instrument compartments, requiring a coordinated control algorithm to ensure that the winches on the ground operate in synchronization with the velocity of instrument compartments.

To address the above issues, a cooperative control algorithm is proposed in this paper. The coordinated control system for multiple surface winches adopts a speed feedforward–tension feedback strategy [26]. It takes the hoisting and lowering speed of the tubing string as the primary reference, while coordinating the deployment speeds of the other cables. Cable tension is monitored in real time and fed back to adjust the rotational speed of each winch, thereby enabling synchronized operation and continuous monitoring of both running depth and cable tension. During tubing descent, all cables remain attached to the tubing string. Their tension therefore varies not only with lowering depth but also with the descent speed of the tubing. For this reason, it is essential to keep the relatively lowering speeds of all cables consistent with that of the tubing string. Building on conventional tension-stability control, this method introduces speed feedforward compensation and forms an integrated speed feedforward–tension feedback control scheme, as shown in Figure 11. This strategy can support fully automated operation with minimal manual intervention, which helps reduce onsite workload. Its main limitations are the need for a relatively dense sensor network and more-sophisticated control algorithms.

6. Conclusions

This paper systematically studies the hoisting and lowering operation technology of deep-well multi-node observation instrument compartments, focusing on overall system layout, standardized operation workflow, downhole jamming failure mechanism and intelligent collaborative control strategy. This study systematically sorts out the structural composition of the special hoisting system, the whole deployment procedure of instrument strings, the dominant inducements of downhole compartment jamming, as well as matched prevention and emergency disposal schemes. Targeted classified control strategies are further formulated, which can effectively reduce downhole safety risks and operation downtime, providing a theoretical basis and operable field implementation specifications for the safe, high-efficiency and low-failure deployment of deep-well multi-node observation equipment.

(1)

The overall structural layout and matching configuration of the multi-node instrument hoisting system are proposed. This study compares multiple connection modes of instrument compartments and contact coupling forms between instrument assemblies and casings. Oriented to the actual geological and wellbore parameters of a deep well in Northeast China, a dedicated hoisting and lowering scheme is determined, together with standardized step-by-step operation procedures. Field application shows that the formulated process can shorten single-trip instrument deployment time and avoid misoperation caused by irregular field operation habits.

(2)

The main inducements for instrument compartment jamming are quantitatively analyzed, among which casing shrinkage, casing bending deformation and piston hydrodynamic effect account for the highest proportion of downhole stuck accidents. Clear targeted preventive measures are put forward: optimizing the outer contour structure and rounding transition of instrument compartments to reduce friction and clamping probability; limiting the continuous lowering speed within a safe range of 0.5–1.2 m/min; conducting casing caliper inspection before instrument running to avoid severely deformed well sections; arranging centralized parking correction at fixed well-depth intervals. When jamming occurs, emergency disposal methods including repeated small-stroke tripping and tension-limited lifting are adopted, which can improve the one-time success rate.

(3)

An LSTM-based adaptive early-warning control method for hoisting and lowering operations is constructed. Relying on real-time hook load monitoring data, the proposed model can predict potential stuck risks in advance and dynamically adjust the running speed to avoid overload stuck faults. Combined with the multi-winch synchronous control strategy adopting speed feedforward and tension feedback, the speed synchronization error of multiple winches is controlled within ±2%, which greatly improves the operation safety and automatic control level of deep-well multi-node instrument tripping operations.