PIPELINE TRANSPORT OF NATURAL GAS IN THE PRESENCE OF CONDENSATE, RESERVOIR WATER AND SUSPENDED HYDRATES

Objectif

The purpose of this project is to test dispersant additives selected amongst different classes of chemicals, in order to prevent the plugging of natural gas lines in the presence of hydrates, by limiting the growth and/or the coalescence of the crystals.
The benefit of these new additives is their ability to be used in very small amounts; indeed, their specific property is that they insert themselves at the water-hydrocarbons interface whereas the drawback of presently used solvents, such as methanol, is that lowering the hydrates formation temperature is directly linked with their concentration in the aqueous phase, which requires injection of solvent amounts comparable to the amount of water produced together with the hydrocarbons.
The project consists in studying the formation conditions of the hydrates and the effect of this formation on the evolution of flow parameters. These studies will be conducted in test loops with dry and condensate synthetic natural gas.
PHASE 1-ITEM 1.1
In order to determine the relative importance of various operating parameters on hydrates crystallization rate, the results describe the influence of turbulence, pressure and sub-cooling, as well as gas composition and presence of condensate.
Turbulence at the hydrocarbons-water interface in a reactor is controlled by the rotation rate of a mechanical stirrer between 200/1000 rpm.
For gas water systems, there is a strong influence of turbulence on the speed of hydrates formation when transition from a planar interface to foaming occurs. If condensate is present, emulsions are created at moderate stirring rates the results of which are poorly reproducible data.
Concerning pressure influence, it has been observed that for gas-water systems, it depends strongly on the sub-cooling level.
For condensate gas-water mixtures, there seems to be an influence of pressure on hydrate formation kinetics when the sub-cooling is at 2 kelvin.
The most important parameter for the rate of hydrates formation is sub-cooling. The obtained results indicate a strong increase of this rate above 3 kelvin. It has been observed visually that this is correlated to crystals agglomeration which occurs under these conditions.
Gas composition seems to have a relatively small effect on hydrates formation kinetics while the presence of condensate can induce a strong influence: in particular, the rate of formation in this last case can be multiplied by 8.
Having in view the building of a kinetic model, an experimental procedure has been established in order to separate the nucleation and the crystals growth step. This leads to highly reproducible rate of growth data as they are related to constant nuclei interfacial area. It is thus possible to fix all operating parameters except the one whose influence is to be determined.
As there are always solid particles existing in well streams, it has been observed experimentally and confirmed theoretically that their presence facilitates hydrate crystals formation.
PHASE 1-ITEM 1.2
The dispersant additives which have been selected and further tested are mainly surfactants, either commercially available or synthesized in our laboratories. Three preliminary screening methods have been used : stability of emulsions formed by condensate in presence of water as a function of water-oil ratio, viscosimetry and conductimetry measurements on these emulsions and finally determination of the temperature at which hydrate crystals agglomerate.
PHASE 2-ITEM 2.1
In order to operate the pilot loop under conditions leading to data which could be used to build reliable correlations and further models, the rheological laws which describe flow of solid suspensions in a liquid have been examined.
ITEM 2.2
Ultra-sonic probes have been tested as a way to measure crystals thickness on the wall of a pipe. It has been found, that under certain operating conditions, these tools could lead to such data which are further needed for modelling purposes.
This project comprises two phases :
Phase 1 : Laboratory testing
Phase 2 : Testing with a pilot scale loop and validation with a semi-industrial scale loop.
PHASE 1 will consist mainly in a "study of hydrate formation kinetics" in a first step, followed by the "selection of new classes of inhibitors".
The hydrate formation kinetics will be studied in a laboratory installation. This study will enable to analyse the various operating parameters : supercooling degree, water-oil ratio (WOR), composition of the gaseous hydrocarbon mixtures, gas-liquid ratio (GLR) and pressure influence.
Further, various inhibitors preventing the growth and/or coalescence of hydrates will be tested in a laboratory installation in order to select those able to prevent clogging of the flowlines and of the pipelines, even under conditions a priori favourable to the formation of crystals.
PHASE 2 will consist in "tests with a pilot scale loop" and further "validating these tests with a semi-industrial scaleloop".
The first tests will help to screen on a limited size loop the additives and materials previously selected and to adapt the semi-industrial installation to conditions typical of gas production wells.
The validation tests will be conducted on this last semi-industrial loop.
The additives screening tests will be performed on the pilot scale loop. This limited size installation will also help to test the sensitivity of the equipment functioning to the operating parameters, as well as to define the data necessary to be measured in view of interpretation and modelling work.
Finally, this pilot scale loop will help to define the hardware and software specifications for raw data acquisition and processing.
The validation of the above-described tests under semi-industrial conditions will be performed in pressure and temperature ranges, with gas and liquid phases velocities as well as water content close to those prevailing in actual gas field flowlines and pipelines. These validation tests will be used to determine the influence of the nature of the additives selected (control of crystal growth, of crystal shape, of hydrate coalescence, blocking of the gas-water interface) and to look for the optimal concentration of each inhibitor in order to determine the cost effectiveness of the process.

Programme(s)

ENG-HYDROCARB 2C - Programme (EEC) of support for technological development in the hydrocarbons sector, 1986-1989

Thème(s)

1.8 - PIPELINES

Appel à propositions

Data not available

Régime de financement

DEM - Demonstration contracts

Coordinateur

GERTH

Contribution de l’UE

Aucune donnée

Adresse

232 AV. NAPOLEON BONAPARTE
92500 Rueil Malmaison
France

Coût total