Hydrate Formation and Decomposition Regularities in Offshore Gas Reservoir Production Pipelines

Abstract

In recent years, the exploitation and utilization of offshore oil and gas resources have attracted more attention. In offshore gas reservoir production, wellbore temperature and pressure change continuously when water-bearing natural gas flows upward. The wellbore temperature is also affected by the low-temperature sea water. The combination of temperatures and pressures controlled by the upward flow, and cooling from the surrounding seawater frequently leads to the conditions of temperature and pressure for hydrate formation. This can lead to pipeline blockage and other safety accidents. In this study, we utilize mathematical models of hydrate phase equilibrium, wellbore temperature, wellbore pressure to study hydrate formation and decomposition in offshore gas reservoir production. Numerical solution algorithms are developed and numerical solutions are validated. The sensitivity influence of different parameters on the regions and regularities of hydrate formation and decomposition in wellbores are obtained through numerical simulations. It is found that increased daily gas production, water content, or geothermal gradient in offshore gas reservoir production pipelines results in less hydrate formation in the wellbores. Accordingly, the risk of wellbore blockage decreases and production safety is maintained. Decreased tubing head pressure or seawater depth results in similar effects. The result of this study establishes a set of prediction methods for hydrate formation and decomposition that can be used in the development of guidelines for safe construction design.

Status of Natural Gas Hydrate Flow Assurance Research in China: A Review

“…293,295,296 The method was subsequently applied to long-distance, natural gas transmission pipelines to evaluate the risk of hydrate blockage and conduct a sensitivity analysis of the temperature, flow, and dew point of natural gas. 297−300 In addition, Wei et al 301 established a set of prediction methods for hydrate formation and decomposition in wellbores.…”

“…Liu and co-workers , proposed an evaluation model for the degree of wellbore hydrate plugging, which could calculate the amount and location of hydrate formation and the degree of blockage characterized by the thickness of the sedimentary layer in the wellbore. Sensitivity analysis of natural gas production, inhibitor concentration, water content, and shut-in time in gas wells was carried out to facilitate hydrate prevention and provide control measures. ,, The method was subsequently applied to long-distance, natural gas transmission pipelines to evaluate the risk of hydrate blockage and conduct a sensitivity analysis of the temperature, flow, and dew point of natural gas. − In addition, Wei et al established a set of prediction methods for hydrate formation and decomposition in wellbores.…”

Relative Pressure Drop Model for Hydrate Formation and Transportability in Flowlines in High Water Cut Systems

“…The ϕ max is equal to 0.74, which represents highly poly-dispersed systems, (-) [21,22]. In the present work, the coefficient of multiple determinations (R 2 is in the range of 0 to 1) is used to determine the fit between the experimental and the developed model data. If the coefficient of multiple determinations approaches 1, then there is a good agreement between the experimental and regressed data (Figure 2).…”

“…at low temperature and high pressure [1]. In flow assurance, gas hydrate is a major concern, becoming a potential risk (plug) to subsea pipelines [2]. To prevent plugging, several chemical strategies are applied to subsea flowlines, such as using thermodynamic inhibitors (THIs) or low dosage hydrate inhibitors (LDHIs), such as kinetic hydrate inhibitors (KHIs) or anti-agglomerants (AAs).…”

Development of a high-thermal-storage composite material embedded with PCM microcapsules and analysis of its unsteady heat transfer process

“…Offshore oil and gas fields have been extensively explored in recent years. Subsea oil and gas are primarily transported via subsea pipelines, which are playing an increasingly vital role [3][4][5][6]. In the development of deep-sea natural gas resources, the low-temperature and high-pressure conditions encountered in deepwater environments can easily cause the formation and deposition of natural gas hydrates (NGHs), which can lead to pipeline flow problems and equipment damage [7,8].…”