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This document specifies the method for determining the temperature at which natural gas hydrates form using differential scanning calorimetry (DSC). It includes specific requirements regarding principles, apparatus, materials, operating procedures, data processing, and precision. This document is applicable to measuring the hydrate formation temperature of methane gas in both pure water and saline systems. For hydrate formation temperatures in systems beyond the scope of this document, precision requirements are not specified.
This document establishes a standardized method for determining the natural gas hydrate formation temperature, i.e., the phase equilibrium temperature, using Differential Scanning Calorimetry (DSC). The primary purpose are: 1) To establish a unified procedure, providing global stakeholders with a clear and reproducible testing methodology encompassing sample preparation, instrumentation, testing protocols, and data analysis; 2) To achieve micro-scale, rapid, and precise measurements, leveraging the advantages of DSC, minimal sample requirement, fast testing speed, and high accuracy, thereby complementing the ongoing development of ISO DIS 23335 (Natural gas — Upstream area — Determination of hydrate equilibrium temperature); 3) To provide critical data, delivering reliable thermodynamic foundation data for flow assurance design and hydrate inhibitor selection in the oil and gas industry. The justification for developing this document is as follows: In numerous countries and regions worldwide, the low-temperature and high-pressure conditions inherent to long-distance pipelines readily initiate hydrate blockages. Such blockages not only reduce transportation efficiency but also pose significant safety risks. The hydrate formation temperature, or hydrate phase equilibrium temperature, is crucial for defining inhibitor injection conditions, mitigating blockage risks, and ensuring continuous production. Consequently, the accurate determination of the hydrate formation temperature is of paramount importance for both hydrate science and industrial applications. The fundamental principle of DSC involves measuring the heat flow difference between a hydrate sample and a reference material under programmed temperature control. When the hydrate decomposes endothermically during heating, this heat flow difference changes, and the phase transition temperature is determined by identifying characteristic points of the resulting endothermic peak. This method offers several significant advantages: Firstly, it has a broad application scope and is widely used in materials science, chemical biology, and other fields. For instance, research institutions such as the China Geological Survey and the National University of Singapore utilize DSC to study the thermodynamic properties of hydrates. Secondly, the technology is highly mature. After years of development, DSC has become an established thermal analysis technique. Internationally, relevant ISO standards (e.g., the ISO 11357 series) exist in fields like plastics, covering DSC measurements of properties such as the glass transition temperature. Thirdly, it provides high-precision quantitative analysis and exhibits strong sample adaptability. Given that hydrate testing requires low-temperature and high-pressure environments, DSC necessitates only a small sample amount for testing, yielding high-precision results. It is well-suited for the thermodynamic analysis of multi-component systems like natural gas hydrates. Currently, ISO DIS 23335 has successfully passed the DIS ballot stage with an "Approved" outcome. This standard primarily employs the constant-volume method principle within PVT analysis, determining the hydrate phase equilibrium point by plotting experimental data, and offers excellent engineering applicability and data reliability. The DSC-based method for determining the hydrate formation temperature proposed in this document represents a micro-scale and highly efficient detection technique. It will complement ISO DIS 23335, significantly reduce testing thresholds and time costs, facilitate the acquisition of uniformly recognized analytical data by global stakeholders, support the implementation of international collaborative projects on hydrate blockage prevention and control and the efficient development of oil and gas resources, and promote the innovative application of hydrate technology in fields such as flow assurance and new energy.
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