As an unconventional clean resource with huge reserves and a wide distribution, natural gas hydrates (NGHs) have good application prospects. However, due to limited understanding and available production technology for NGHs, there is still a large gap between current production tests and commercial exploitation. A breakthrough in reservoir stimulation technologies is key to realizing the industrialization of NGHs in the future. Through a comprehensive summary of hydrate production test cases in Japan and China, this paper highlights the difficulties in the transformation of weakly-consolidated reservoirs. By systematically reviewing the theory and technology of hydrate reservoir transformation and engineering applications, this paper elucidates in detail the technical principles and mechanisms of several available stimulation technologies for weakly-consolidated reservoirs, and assesses the feasibility of their application to increase the production of NGHs. Existing problems and challenges are summarized and future prospects are discussed. Finally, suggestions are put forward for research and development of transformation technology for weakly-consolidated NGHs reservoirs in the future.

Offshore deepwater cementing generally faces more challenges than onshore cementing. Shallow formations in deepwater wells often exhibit low structural strength, high porosity, and are prone to shallow gas influx and hydrate ... | Find, read and cite all the research you need on Tech Science Press

As a controllable power generation method requiring no energy storage, Ocean Thermal Energy Conversion (OTEC) technology demonstrates characteristics of abundant reserves, low pollution, and round-the-clock stable operation. The free-standing cold-water pipe (CWP) in the system withstands various complex loads during operation, posing potential failure risks. To reveal the deformation and stress mechanisms of OTEC CWPs, this study first analyzes wave particle velocity and acceleration to determine wave loads at different water depths. Based on the Euler-Bernoulli beam model, a quasi-static load calculation model for OTEC CWPs was established. The governing equations were discretized using the finite difference method, and matrix equations were solved to analyze bending deformation, bending moments, and surface stresses at discrete points along the pipe. Results indicate that water depths within 50 m represent a critical zone where wave particle velocity, acceleration, and wave loads exhibit significant variations in harmonic patterns, while beyond 50 m depth wave loads decrease linearly. Ocean currents and surface wind-driven currents substantially influence the CWP’s lateral displacement. Considering the effect of clump weights, the maximum lateral displacement occurs at 600–800 m below sea level. Utilizing large-wall-thickness high-strength pipes at the top section significantly enhances the structural safety of the CWP system.

Ocean Thermal Energy Conversion (OTEC) is characterized by its abundant reserves and pollution-free nature, enabling stable power generation around the clock. Since the power output of an OTEC system is significantly influenced by the energy available from cold and warm seawater, the accurate evaluation of the outlet temperature of the cold-water pipe (CWP) is crucial. To analyze the heat transfer performance of the CWP, this paper investigates the temperature field of the OTEC CWP and employs numerical simulation methods to conduct finite element analysis of the temperature field under different discharge conditions. The results indicate that during the pumping of deep-sea cold water through the CWP, heat is absorbed from the warmer upper seawater layers. When the pumping discharge rate is higher, the shorter fluid residence time due to higher flow velocity results in a lower outlet temperature. Compared to steel CWPs, high-density polyethylene (HDPE) is more suitable for OTEC systems due to its lower thermal conductivity and density.

Ocean Thermal Energy Conversion (OTEC) is a promising renewable energy technology for remote islands, offshore platforms, and maritime infrastructure, yet its commercialization is constrained by low cycle efficiency, high auxiliary energy demand, and the engineering challenges associated with large-scale seawater transport. This study presents the integration and experimental evaluation of a 20 kW class containerized OTEC prototype using R134a in a closed Rankine cycle. The working fluid circulates within the power-generation module, while warm surface seawater supplies the evaporator and cold deep seawater is pumped through an insulated intake pipe to the container-mounted condenser. The prototype integrates a radial-inflow turbine, stainless-steel heat exchangers, circulation pumps, and a programmable logic controller-based control system. Land-based commissioning tests, conducted at initial warm-to-cold-water temperature differences of approximately 20–25 °C, produced a peak electrical output of 11 kW in one run and approximately 5 kW for 11 min in another. Sea trials in the South China Sea recorded a peak electrical output of 16.4 kW and a cumulative power-generation duration of 4 h 47 min across separate runs. These results document the integration and short-duration operation of the prototype under offshore conditions and identify priorities for improved control and longer-duration testing.

Natural gas hydrate is an important emerging strategic resource, but low permeability makes the horizontal well length a key factor limiting productivity. A prediction model for friction torque of deepwater riserless drilling strings was established, and the segmented friction coefficient of hydrate horizontal wells was inverted and applied to the Shenhu hydrate reservoir. The results show that the main limiting factor for the extreme extension length of natural gas hydrate horizontal wells is the mechanical extreme extension length. The main affecting factor of the mechanical extreme extension length is the running limit of the screen pipe. The friction coefficient is the most significant factor affecting the mechanical extreme extension of horizontal wells, with the friction coefficient inside the casing in the high-build-rate section being the largest. The research identifies the primary factors governing the limit extension during horizontal well construction. The findings provide theoretical guidance for reservoir selection, well site determination, and wellbore configuration optimization in hydrate development. Ultimately, this contributes to maximizing single-well productivity and advancing the commercialization of hydrate resources.