Methanol has been used to prevent hydrate formation in industrial handling of hydrate forming mixtures containing water for many decades. Ethanol is also used for the same purpose in countries that have easy access to low price ethanol, like for instance Brasil. Common to these small alcohols is that they also have surfactant properties that will promote hydrate formation, but when added to water in sufficient amounts, the hydrate prevention characteristics will dominate. These alcohols will primarily prevent heterogeneous hydrate formation on the interface between water and a separate hydrate phase. The effect of "alcohol" on both of these routes to hydrate formation are investigated and compared to experimental data. In particular we also investigate the effects of these small alcohols on Gibbs free energy for the hydrate formed on the new, shifted, stability conditions. Gibbs free energy is generally higher than hydrate formed from pure water. Enthalpies of hydrate formation are also higher for hydrate formed from water containing alcohols. These are negative numbers, so in absolute values released formation enthalpy is lower. The presence of these alcohols in water will also prevent homogeneous hydrate formation from dissolved hydrate formers in water. Glycols have more important roles in other routes to hydrate nucleation. Heterogeneous hydrate nucleation towards mineral surfaces is feasible in different ways. Polar hydrate formers like H2S and CO2 can adsorb directly on rust, and as discussed here, are able to form hydrate from adsorbed state on rust surface. Non-polar hydrocarbons like, for instance methane might get trapped in structured water and then nucleate to hydrate. Some research on this is published and further research is in progress. Glycols have very strong attraction to rust and corresponding chemical potentials for adsorbed glycols on rust are favourable enough to facilitate phase transition from glycols dissolved in water over to adsorption. Injection of glycol in gas processing plants has been used by industry for many years and in many cases it might even be economically and technically feasible compared to expensive drying units. Exceptions are situations that will lead to water/glycol freezing. But even in multiphase transport of hydrocarbons with various water cuts, mixtures of alcohols might be a technically efficient solution in which the small alcohols may be very efficient as discussed above and glycols may go through adsorption phase transition from water solution over to glycol film on rust and prevent hydrate nucleation towards rust surface. This possible strategy requires more theoretical work as well as experimental investigation. On the basis of thermodynamic analysis and calculations of hydrate formation from different routes, it is argued that real natural and industrial systems are unable to reach thermodynamic equilibrium. It is therefore a need for a consistent thermodynamic platform with a uniform reference system for all phases. We propose and demonstrate a residual thermodynamic model system for all phases.
Strengthening exploration and development of oil and gas is crucial for mitigating China's reliance on oil and gas supply from foreign countries and ensuring national energy security. Since the 11th Five-Year period, fundamental research on the deep-water area of the northern South China Sea has been strengthened, along with the acceleration of technological innovation and increase in exploration investment. As a result, a series of major exploration discoveries were found. This paper presents five major learnings regarding the theories of exploration geology and two achievements in the innovation of exploration technology. It also discusses the new challenges and coping strategies for oil and gas exploration in deep-water areas, and prospects the exploration potentials of three major exploration fields—medium-deep layers, buried hills, and lithologic traps—in the deep-water area of the northern South China Sea. Our research shows that the detachment of the continental margin in the deep-water area of northern South China Sea controls the formation of large sags in the Pearl River Estuary Basin and the Qiongdongnan Basin. Three sets of large-scale source rocks were developed from lacustrine, terrestrial-marine transitional, and marine sedimentary facies. High yet variable subsurface temperature controls the rapid hydrocarbon generation from the source rocks in the sags. In addition, three different hydrocarbon accumulation modes were established: accumulation mode of large axial canyon channel in the deep-water area of the Qiongdongnan Basin, late natural gas accumulation mode of deep-water fan in the deep-water area of Baiyun Sag, and differential hydrocarbon accumulation mode jointly controlled by fault and ridge. Meanwhile, the broadband seismic acquisition and processing technology for three-dimensional source triggering and plow-like cable receiving was independently developed. Guided by several geological theories and innovative technologies, a series of large- and medium-sized gas fields represented by "Deep Sea No. 1" (LS 17-2) were discovered, which are of great significance to ensuring the energy supply of the Guangdong-Hong Kong-Macao Greater Bay Area, facilitating the green development of energy in the Hainan Free Trade Zone (Port), and promoting the increase of oil and gas reserves and production in China.
A self-developed large-scale 3D platform with a maximal volume of 1695 L and pressure of 30 MPa was employed to investigate the production behavior of hydrate-bearing sediment using depressurization and thermal stimulation technology. Moreover, a novel method involving the joint development of hydrate-bearing sediments and shallow gas was first carried out based on the established apparatus. Experimental results show that the temperature in the reactor exhibits a decreasing trend as a whole with the continuous heat adsorption of hydrate dissociation due to slow heat transfer in the large-scale device. Heat transfer is the main factor controlling the gas production rate in the whole process of depressurization. The temperature of the reactor almost approaches the equilibrium point corresponding to the internal pressure, and the hydrate keeps dissociating near the phase equilibrium curve. Meanwhile, local overpressure is first observed during depressurization, indicating that dissociated gas from hydrate cannot be fully released while some are trapped in the deposits. In addition, thermal stimulation may not be applicable for field-scale marine natural gas hydrate development owing to the large heat loss in the pipelines and the low heat transfer in the sediments. Investigation of the joint development of hydrate-bearing deposits and shallow gas indicates that hydrate hardly dissociates initially at the large production rate of shallow gas and starts to decompose gradually with the decreased value, showing strong interlayer interaction between hydrate layers and shallow gas. Therefore, it is necessary to reasonably allocate the production rate of different reservoirs at different depths to achieve the most economical development during the coproduction of multigas. Compared with that in small-scale experiments, the production behavior in the large-scale experimental apparatus is closer to field-scale development. Moreover, the first large-scale experimental investigation on the joint development of hydrate-bearing sediments and shallow gas provides novel insight for efficiently developing natural gas hydrate reservoirs.
Marine gas hydrate is a potential alternative energy. As the 173rd new mineral species, it can be qualitatively divided into diagenetic and non-diagenetic types. Because of its few drilling and production cases, high sampling cost, and great difficulty in heat preservation and pressure preservation technology, the in situ test of reservoir physical properties and the quantitative classification and evaluation of resource grade are not clear, and the relationship between resource-grade division and development-mode response is not clear. Therefore, in this paper, to solve this problem and technical difficulties, in combination with the actual hydrate sampling core data in the South China Sea, using the indoor hydrate acoustoelectric testing device, the physical parameters, such as acoustic wave, resistivity, saturation, permeability, partial stress and strain of hydrate deposits with different composition and saturation, were measured. An entropy weight comprehensive evaluation model for the sensitivity of physical parameters of natural gas hydrate is established on the basis of the decomposed hierarchy process. The order of sensitivity of hydrate parameters from high to low is stress, partial stress, decomposed gas, longitudinal wave, resistivity, permeability, and shear wave. In this paper, the evaluation method of physical parameters of marine natural gas hydrate and the five-grade classification standard of natural gas hydrate are established according to the law of parameter variation and the results of sensitivity analysis. Finally, the Liwan hydrate reservoir in the northern South China Sea is taken as a case study and defined as non-diagenetic grade II, which belongs to argillaceous shallow sedimentary hydrate with high saturation and high methane content without complete trap structure. This study provides an important technical method and theoretical guidance for the evaluation and classification of marine gas hydrate resources and the optimization of corresponding suitable development methods in the future.
With the development of economy and society, the consumption of fossil energy is gradually increasing. In order to solve the current energy dilemma, Natural gas hydrate (NGH) is considered as an ideal alternative energy. At the same time, solid fluidization exploitation is an ideal method. However, in the process of that, sand and hydrate ore bodies enter the closed pipeline together, which will block the pipeline and increase the difficulty of exploitation. Therefore, the pre-separation of sand by hydrocyclone plays an important role in solid fluidization exploitation. In this study, the numerical simulation method was used to study the internal flow field characteristics of the hydrocyclone, and the effects of different flow rate, different flow ratio, different sand content and different particle diameter on the phase distribution were investigated. The results show that: at the same axial position, the increase of flow rate and sand content makes the sand phase more distributed at the edge of the flow field. Under the same working conditions, the sand gradually migrates to the center of the flow field with the increase of the axial distance. By calculation, it is obtained that under the optimum working condition of the flow rate is 4.83m3/h, the flow ratio is 20%, the sand content is 20%, and sand diameter is 80μm, the maximum Es is 22.1% and the minimum is 86.1%. Finally, a comprehensive analysis of the hydrocyclone in this study shows that this hydrocyclone is only applicable to rough pre-separation of sand in the process of solid fluidization exploitation. Through the study of the internal flow field characteristics and phase distribution law of the hydrocyclone, this study provides a reference for the practical engineering application of sand phase pre-separation in the solid fluidization exploitation of NGH.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)