The application of hole cleaning devices can effectively solve the hole cleaning problem during the drilling of horizontal wells. Improving the hole cleaning performance is directly related to subsequent drilling time and cost. In this paper, the solid–liquid two-phase hydrodynamic characteristics under the action of the V-shaped hole cleaning device for drilling horizontal wells were studied experimentally and numerically. The decay law of spiral flow induced by the V-shaped hole cleaning device was obtained numerically using the commercial CFD code “Fluent” by changing the blade rotational speed, blade helix angle, and consistency coefficient of drilling fluid. The helix angle will cause the flow direction of local fluid to deflect. The swirl intensity of spiral flow increases significantly with an increase in rotational speed. The hole cleaning performance was better when the helix angle was from about 10 to 20 degrees. Increasing the fluid consistency coefficient will rapidly make the spiral flow decay, resulting in a shorter effective action distance and a worse hole cleaning effect. The simulation results were validated against the experimental results of the flow loop. Both experimental and simulation results showed that the hole cleaning performance was improved by using the V-shaped hole cleaning device. The very good agreement achieved between the results has presented an opportunity to study the hole cleaning effect of a hole cleaning device in unsteady state conditions. The results will provide theoretical guidance for efficient hole cleaning using V-shaped hole cleaning devices for horizontal well drilling.

In the longstanding development of hydrate-bearing sediment (HBS) reservoirs, slow and permanent deformation of the formation will occur under the influence of stress, which endangers the safety of hydrate development projects. This paper takes hydrate-bearing sandy sediment (HBSS) as the research object and conducts triaxial compression creep tests at different saturation degrees (20%, 30%, and 40%). The results show that the hydrate-containing sandy sediments have strong creep characteristics, and accelerated creep phenomenon will occur under the long-term action of high stress. The longstanding destructive power of the specimen progressively raises with the increase in hydrate saturation, but the difference in the triaxial strength of the specimen progressively increases. This indicates that the damage to the hydrate structure during long-term loading is the main factor causing the strength decrease. Further, a new nonlinear creep constitutive model was developed by using the nonlinear Burgers model in series with the fractional-order viscoplastic body model, which can well describe the creep properties of HBSS at different saturation levels.

During drilling operations, drilling fluids undergo heat exchange with hydrate-bearing formations. The intrusion of drilling fluids affects hydrate stability, leading to variations in stress fields around a wellbore and complex scenarios such as borehole collapse, significantly hindering the efficient development of natural gas hydrate resources. This study establishes a thermo-hydro-mech model for hydrate-bearing inclined wells based on linear thermoelastic porous media theory and an appropriately high inhibitive drilling fluid temperature. This research reveals that drilling should follow directions of minimum horizontal stress or perpendicular to maximum horizontal stress during drilling operations to control wellbore stability. Hydrate decomposition due to factors like drilling fluid pressure and temperature can rapidly reduce the strength of low-saturation formations, significantly increasing the risk of wellbore instability. Therefore, selecting appropriate highly inhibitive and low-temperature drilling fluids during drilling operations helps control hydrate decomposition and reduce fluid intrusion, thereby mitigating risks associated with wellbore instability.

The decomposition of hydrate during hydrate mining can reduce the strength of the formation and induce engineering geological disasters. Clarifying the decomposition characteristics of geological hydrate during hydrate mining is of great significance for preventing marine geological disasters. This study comprehensively examines the effects of various extraction conditions, including production pressure, hydrate saturation, and permeability, on methane hydrate decomposition during depressurization-based extraction. Key findings show that reduced production pressure significantly increases gas and water production rates due to an enhanced pressure differential, albeit at the cost of potential geomechanical instability. Variations in hydrate saturation reveal that lower-saturation reservoirs initially exhibit higher production due to faster pressure propagation and greater porosity, whereas high-saturation layers may sustain production in the later stages. Permeability changes impact pressure diffusion and heat transfer within the formation; higher permeability leads to faster initial production but causes rapid energy depletion, requiring supplementary energy inputs to maintain production. These findings provide essential insights for optimizing methane hydrate extraction, ensuring high productivity while mitigating formation stability risks.

When acoustic waves propagate through hydrate samples, they carry extensive information related to their physical and mechanical properties. These details are comprehensively reflected in acoustic parameters such as velocity, attenuation coefficient, waveform, frequency, spectrum, and amplitude variations. Based on these parameters, it is possible to invert the physical and mechanical indicators and microstructural characteristics of hydrate samples, thereby addressing a series of issues in hydrate development engineering. This study first provides an overview of the current applications and prospects of acoustic testing in hydrate development. Subsequently, it systematically elaborates on the progress in research on acoustic testing systems for hydrate samples, including the principles of acoustic testing, ship-borne hydrate core acoustic detection systems, laboratory hydrate sample acoustic testing systems, and resonance column experimental systems. Based on this foundation, this study further discusses the development trends and challenges of acoustic testing equipment for hydrate-bearing sediments.

In natural gas hydrate exploitation, the large amount of sand production directly or indirectly leads to the low efficiency of hydrate exploitation and even the termination of exploitation. A spiral-cyclone coupling separator was used to achieve the separation of mud and sand. In this study, based on the actual size of the spiral-cyclone separator for natural gas hydrate, an experimental prototype of the spiral-cyclone separator suitable for indoor experiments was processed, and an indoor experimental system was built. A pressure loss experiment on the hydrate separation device was carried out, and the results proved the correctness of the numerical simulation model of the spiral-swirl separator and the calculation results. The influence of the inlet flow rate of the separator on the separation effect was studied. It was found that with an increase in the flow rate, the mud/sand separation area began to move up, and the mud/sand settlement area at the bottom appeared to have different degrees of mud/sand accumulation. The indoor experimental results and numerical simulation results show that the separation efficiency increases with the flow rate increase in the range of 5–25 m³/h. This study can provide theoretical guidance for the indoor experimental verification of downhole in situ separators.