Hydrate Formation And Inhibition In Gas Or Gas Condensate Streams
Authors: Robinson D.B. 
Published: March 2010

Experimental data on hydrate formation in the presence of methanol solutions is presented for pure methane, pure carbon dioxide, a binary mixture of methane and carbon dioxide and a seven-component mixture of typical hydrocarbons and non-hydrocarbons. Data are also given on hydrate formation for methane in the presence of ethylene glycol solutions.

The state-of-the-art in the ability to predict incipient hydrate formation in typical industrial systems is illustrated through the use of the EQUI-PHASE ™ HYDRATE program.

Several typical applications of current interest involving hydrate formation in handling gases and gas condensates are described.

Introduction

Hydration is a process whereby a lattice or cage-like structure of water molecules is stablilized by the presence of anyone or more possible hydrate formers. The water molecules forming the latrice are known as host molecules and the hydrate formers are known as guest molecules.

Since 1930, the phenomenon of hydrate formation has played an important role in the development of the oil and gas industry. This is because of the tendency of hydrates to form in transportation and processing equipment thereby plugging pipelines, valves, distillation column trays and other associated equipment. In recent years there has been a renewed interest in gathering data on the pressures and temperatures where hydrates will form from different gas mixtures, in determining the degree to which the gas must be dried to prevent hydrate formation, or in calculating the amount of inhibitors required to prevent hydrate formation at operating conditions. As new resources of natural gas or gas-condensates are found offshore in deep cold water or on-shore in colder climates, the occasions when hydrate inhibition may be required will increase. Methanol or glycols are commonly used to inhibit hydrate formation either continuously or on an interim basis.

Hydrate formation can often play an important role in the design of a tertiary recovery program for a reservoir using hydrocarbon or carbon dioxide flooding. In order to prevent hydrate formation in the injection solvents, one must make an economic decision based on whether to install a water removal unit or to inject a hydrate inhibitor. Improved hydrate predictive methods can aid in determining the better choice.

In this study new experimental data on hydrate forming conditions for selected simple and complex mixtures in the presence of methanol and I or ethylene glycol up to 50 wt % in the aqueous phase are presented. The data for simple systems can be used to improve correlations, and data for complex systems can be used to test them.

Data Determination

Experimental data have been obtained on hydrate formation in the presence of methanol and ethylene glycol solutions for selected pure components, binary pairs and multicomponent systems. The temperature range covered by these studies has been from about −50 °C to 30 °C and pressures have normally been up to about 20.7 MPa.

Experimental Method

The experimental measurements were carried out in two sets of experimental equipment. The first was the conventional variable volume windowed pressure cell type and the second was a constant volume, full-view sapphire equilibrium cell mounted in a cryostat.