Hydrate Risk Assessment and Restart-Procedure Optimization of an Offshore Well Using a Transient Hydrate Prediction Model

Abstract

A produced-hydrocarbon stream from a wellhead encounters formation of solid gas-hydrate deposits, which plug flowlines and which are one of the most challenging problems in deep subsea facilities. This paper describes a gas-hydrate model for oil-dominated systems, which can be used for the design and optimization of facilities focusing on the prevention, management, and remediation of hydrates in flowlines. Using a typical geometry and fluid properties of an offshore well from the Caratinga field located in the Campos basin in Brazil, the gas-hydrate model is applied to study the hydrate-plugging risk at three different periods of the well life. Additionally, the gas-hydrate model is applied to study the performance of the injection of ethanol as a thermodynamic hydrate inhibitor in steady-state flow and transient shut-in/restart operations. The application of the transient gas-hydrate model proved to be useful in determining the optimal ethanol concentration that minimized the hydrate-plugging risk.

Experimental Measurement and Modeling of the Solubility of Methane in Methanol and Ethanol

“…This is of particular importance in the modern petroleum industry where there is a move toward the use of greener, less toxic chemicals. It is also of interest to petroleum companies operating in South America where an abundance of ethanol makes its use far more economically viable than other inhibitors. − …”

Wax deposition process: mechanisms, affecting factors and mitigation methods

“…The composition of crude oil comprises a mixture of molecules of different natures: there are light molecules like methane that are responsible for solid hydrate formation at high pressure and low temperature and heavy molecules such as long linear alkanes and isoparaffins that tend to change phase at low temperature in the phase of both macro and microcrystalline solids. There is also a transition towards more polar compounds due to the appearance of aromatic compounds and the presence of heteroatoms (oxygen, sulphur and nitrogen) in the fractions known as resins and asphaltenes [31][32][33][34] mentioned in their literature review that the amount of deposited wax is impacted by the concentration of paraffin, light ends, and nucleating or inhibiting materials in the crude oil.…”

“…n Kp τ γ = where τ is the shear stress (N/m²) and γ is the shear rate of the fluid (1/s). 37 The other three mechanisms-Brownian diffusion, gravity settling and shear dispersion-are considered, according to the work of researchers, [28][29][30][31][32][33][34][35] as secondary mechanisms that can contribute to the wax deposition and identifying which mechanism plays the primary role in wax deposition stated that the Brownian diffusion of wax particles is not likely to be valid because the wall temperature is lower than the oil bulk temperature, resulting in more precipitated wax particles at the wall than in the bulk oil. Consequently, the impact of Brownian diffusion is to transport these precipitated particles from the wall toward the bulk oil, instead of moving them toward the wall and deposit 42 noted that gravity settling is also believed to be insignificant as there has not been a study claiming that wax deposits are generally thicker at the bottom than the top of the pipe wall in single-phase oil flow conditions.…”

Hydrate rheology of water-in-oil emulsions with cyclopentane

“…Adaptando esse mecanismo a um sistema multifásico óleo dominante, Sloan et al 8 propôs as seguintes etapas para a formação de um bloqueio de hidrato em um duto:  Dispersão de gotículas de água no óleo  Formação de uma "casca" (shell) de hidrato na interface com as gotículas  Aglomeração de partículas de hidrato  Plugueamento do duto…”