During the development of natural gas hydrates, it is important to ensure the stability of the reservoir. The hydrate reservoirs in the South China Sea are clayey silt sediments, which are prone to sand production and collapse during hydrate dissociation. This study innovatively proposes the idea of consolidation-acidizing for NGH reservoir modification. Based on the core parameters of well A drilling in the Shenhu Sea area of the South China Sea, NGH sediment skeleton samples were artificially prepared. Core sensitivity testing indicates that the NGH reservoir has the potential for acidizing modification. After using tetraethyl orthosilicate to solidify the sample, it was found that Young’s modulus of the sample increased by 58.8%, and the compressive strength increased by 54.78%. Although the porosity decreased by 39.33%, the pores were not completely blocked. After the acidizing experiment, the permeability of the consolidated sample was 2.88 mD, and the porosity increased by 10.63%; The permeability of the unconsolidated sample was 1.86 mD, and the porosity decreased by 10.73%. The CT scan images also showed that the pores of the sample after consolidation-acidizing developed uniformly without significant deformation; The unconsolidated sample undergoes severe deformation and sand production after acidizing. This study demonstrates that the consolidation-acidizing modification method is feasible in clayey silt hydrate reservoirs.

During the drilling of highly deviated and horizontal wells, a pump shutdown causes drill cuttings to settle and form a cuttings bed in the annulus. This study investigated the incipient motion law of the particles on the cuttings bed surface when the drilling fluid starts circulating again. This work could help field engineers to determine a reasonable incipient pump displacement to improve hole-cleaning efficiency. In this study, the effects of the well inclination angle, cuttings size, and different cuttings densities on the critical velocity of particle motion are analyzed experimentally, using a large-scale flow loop. Next, based on a stress analysis of the particles on the cutting bed surface and on the boundary layer flow around the particles, an analytical formula for the surface shear force of the drilling fluid on particles is derived and a critical velocity model for incipient motion is established. Verification is then carried out and combined with the experimental results. This study has important implications for the design of drilling operations and for the management of cuttings transport in oil and gas wells. It can guide the setting and prediction of pump discharge to improve hole-cleaning efficiency.

Marine gas hydrates are recognized as a promising offshore energy resource. Self-heat fluid injection is an innovative thermal-enhanced gas recovery technique for hydrate exploitation engineering. This study numerically investigates hydrate saturation during the self-heating reagent injection process in a sub-sea hydrate reservoir, decoupled from gas production interference. This process employs two consecutive stages: reactive chemical flow stage followed by non-reactive flow stage. The simulation output parameters encompass reservoir temperature, fluid saturation, thermal conductivity, and heat flow rate. The base case demonstrates that fluid injection elevates reservoir temperature from 13.0 °C to 29.3 °C and reduces hydrate saturation from 0.40 to 0.21 through coupled heat–mass transfer mechanisms during the reactive flow stage. In the consequent non-reactive flow stage, hydrate saturation decreases to zero. Sensitivity analysis reveals that initial permeability variation governs the hydrate saturation and temperature during the non-reactive phase. The permeability range of less than 15 mD is the optimal threshold preventing hydrate reformation during fluid injection. 55–70 mD permeability triggers severe secondary hydrate generation, which decreases the fluid application feasibility. Fluid flooding demonstrates superior hydrate dissociation efficacy compared to in situ thermal stimulation. This study develops a novel simulation approach to characterize marine hydrate saturation dynamics.